Magnetic recording medium

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance, a small surface resistivity and an excellent surface smoothness, and a filler contained in a magnetic recording layer constituting the magnetic recording medium.

With recent tendencies of miniaturization and weight reduction of video or audio magnetic recording and reproducing apparatuses as well as long-time recording by these apparatuses, magnetic recording media such as magnetic tapes or magnetic discs have been strongly required to have a high performance, namely high recording density, high durability, good electromagnetic performance or the like.

The magnetic recording media such as magnetic tapes or magnetic discs are contacted with a magnetic head upon recording and reproduction, so that a magnetic recording layer thereof tends to be abraded, resulting in contamination of the magnetic head as well as deterioration in recording and reproducing characteristics thereof. For this reason, it has been conventionally demanded to provide high-durability magnetic recording media having a high abrasion resistance.

Hitherto, in order to enhance an abrasion resistance of the magnetic recording layer of magnetic recording media, it has been attempted to incorporate various fillers such as alumina (Al

2

O

3

), hematite (α-Fe

2

O

3

) and dichromium trioxide (Cr

2

O

3

) into the magnetic recording layer.

For instance, as magnetic recording media using alumina (Al

2

O

3

), there have been proposed magnetic recording media in which α-Al

2

O

3

particles containing an amorphous phase are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 5-36059(1993)), magnetic recording media in which α-Al

2

O

3

particles having a specific crystal structure are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 7-244836(1995)) and the like; as magnetic recording media using hematite (α-Fe

2

O

3

), there have been proposed magnetic recording media in which granular α-Fe

2

O

3

particles are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 61-194628(1986)), magnetic recording media in which liquid hydrocarbon and α-Fe

2

O

3

particles are used (Japanese Patent Application Laid-Open (KOKAI) No. 54-70806(1979)) and the like; and as magnetic recording media using dichromium trioxide (Cr

2

O

3

), there have been proposed magnetic recording media in which acicular Cr

2

O

3

particles are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 62-112221(1987)) and the like.

Specifically, the magnetic recording medium described in Japanese Patent Application Laid-Open (KOKAI) No. 61-194628(1986) contains magnetic particles having a specific surface area of not less than about 28 m

2

/g and granular α-Fe

2

O

3

having an average particle diameter of about 0.05 to 1 μm. This magnetic recording medium is produced by dispersing a mixture composed of 300 parts by weight of Co-coated γ-Fe

2

O

3

, 38 parts by weight of vinyl chloride-vinyl acetate copolymer, 24 parts by weight of polyurethane resin, 7 parts by weight of stearic acid, one part by weight of silicone oil, a prescribed amount of granular α-Fe

2

O

3

having a predetermined particle size and 800 parts by weight of a mixed solvent containing methyl ethyl ketone and toluene in equal amounts, for 40 minutes using a ball mill to prepare a magnetic coating composition, and then coating a base film with the magnetic coating composition.

However, these fillers have respective inherent problems. Namely, it is known that alumina shows a poor dispersibility in binder resin. With increase in amount of alumina added, the obtained magnetic recording medium is considerably deteriorated in electromagnetic performance. Hematite particles exhibit a relatively good dispersibility in binder resin. However, in order to obtain magnetic recording media having a sufficient durability, it is required to add a considerably large amount of the hematite particles thereto, resulting in deteriorated filling percentage of magnetic particles and, therefore, poor electromagnetic performance. Further, the use of dichromium trioxide is unfavorable from environmental and hygienic viewpoints.

It is also known that when the amount of these fillers added to the magnetic layer is increased, resultant magnetic recording media are improved in durability, but deteriorated in dispersibility of magnetic particles in vehicle, thereby causing a considerable deterioration in electromagnetic performance thereof.

Accordingly, it has been strongly demanded to provide magnetic recording media containing such a filler which does not adversely affect the dispersibility of magnetic particles in vehicle even when the filler is added in an amount sufficient to impart a high durability thereto, thereby preventing the magnetic recording media from being deteriorated in electromagnetic performance thereof.

In current general-purpose video tape systems, the end position of such a magnetic tape is recognized by detecting a transparent leader tape provided at the tape end thereof using a sensor. However, with recent demands for high-density recording on magnetic recording media, the particle size of magnetic particles used therein becomes much finer, so that a magnetic recording layer containing such magnetic particles has a high light transmittance. As a result, there arises the risk of occurrence of errors upon detecting the end position of the magnetic tape. Therefore, it has been strongly required that a magnetic recording portion of the magnetic tape has a sufficiently high blackness, i.e., a low light transmittance.

Further, it has been endlessly demanded to further improve characteristics of magnetic recording media. Therefore, it is strongly required to provide magnetic recording media having not only the above-described characteristics but also a small surface resistivity, an improved running property and the like.

The reasons therefor are as follows. When the surface resistivity of magnetic recording media is large, the amount of electrostatic charge thereon is increased, so that cut chips of the magnetic recording media or dusts are adhered onto the surfaces of the magnetic recording media upon production and use thereof, thereby causing problems such as increase in drop-outs.

It is widely known that carbon black fine particles as a black filler are incorporated into a magnetic recording layer. Also, there have been proposed magnetic recording media in which black titanium (TiO) particles are used as a black filler (Japanese Patent Publication (KOKOKU) Nos. 62-21185(1987) and 62-22179(1987)), magnetic recording media in which graphite fluoride is used a black filler (Japanese Patent Application Laid-Open (KOKAI) No. 56-156930(1981)), or the like.

Also, hitherto, with the reduction in thicknesses of magnetic recording layer and non-magnetic base film of magnetic recording media, it has been variously attempted to impart good surface smoothness and large stiffness thereto by improving a substrate on which the magnetic recording layer is formed. For instance, there has been proposed a non-magnetic substrate composed of a non-magnetic base film and at least one undercoat layer formed on the non-magnetic base film. The undercoat layer is composed of a binder and non-magnetic particles dispersed in the binder, which contain iron as a main component, e.g., acicular hematite particles or acicular iron oxide hydroxide particles (hereinafter referred to merely as “non-magnetic undercoat layer”). Such a non-magnetic substrate is already put into practice (refer to Japanese Patent Publication (KOKOKU) No. 6-93297(1994), Japanese Patent Application Laid-Open (KOKAI) Nos. 62-159338(1987), 63-187418(1988), 4-167225(1992), 4-325915(1992), 5-73882(1993), 5-182177(1993), 5-347017(1993) and 6-60362(1994), or the like).

Thus, at present, it has been most strongly demanded to provide magnetic recording media having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance, a small surface resistivity and a good surface smoothness. However, such magnetic recording media capable of satisfying all of these requirements have not been obtained yet.

The above-described conventional magnetic recording media containing a filler such as alumina, hematite or dichromium trioxide, are considerably deteriorated in electromagnetic performance when the amount of the filler added thereto is increased in order to enhance the durability thereof. Therefore, the use of these fillers has failed to produce magnetic recording media capable of exhibiting both excellent durability and good electromagnetic performance.

When carbon black fine particles are used as a black filler, it is possible to obtain magnetic recording media having a low light transmittance due to excellent blackness of the carbon black fine particles added. However, since the carbon black fine particles inherently show a poor dispersibility in vehicle, the dispersibility of magnetic particles in vehicle is also deteriorated, thereby adversely affecting properties of the obtained magnetic recording media, e.g., deterioration in electromagnetic performance, durability or the like. In this regard, Japanese Patent Application Laid-Open (KOKAI) No. 4-139619(1992) describes that “When the binder resin and the magnetic particles are kneaded together to produce a coating material, if carbon black fine particles are added to the composition, there arises such a problem that the magnetic particles are deteriorated in orientation and filling property, as described below in Comparative Examples. Further, the carbon black particles are bulky particles having a bulk density of about 0.1 g/cm

3

, resulting in poor handling and processing properties thereof. Besides, the carbon black particles have problems concerning safety and hygiene such as carcinogenesis”.

Thus, it has been demanded to provide a black filler as an alternate material of the carbon black fine particles. However, the above-described conventional fillers cannot contribute to sufficient reduction in light transmittance of magnetic recording media as compared to the carbon black fine particles, since alumina, hematite and dichromium trioxide show white, red and green colors, respectively.

Further, the black titanium tends to be readily oxidized and, therefore, is insufficient in stability in air. The graphite fluoride tends to suffer from the deterioration in electromagnetic performance due to poor dispersibility in binder resin.

As a result of the present inventors' earnest studies for solving the above problems, it has been found that by using as a filler incorporated into a magnetic recording layer of a magnetic recording medium,

black composite hematite particles having an average diameter of 0.08 to 1.0 μm and comprising:

hematite particles as core particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles,

the obtained magnetic recording medium is free from deterioration in electromagnetic performance even when the back filler is added thereto in an amount sufficient to enhance the durability thereof; and has an excellent durability and a good electromagnetic performance; and can be suitably used for high density recording because the black composite hematite particles which exhibit a sufficient blackness and are capable of considerably reducing the amount of carbon black used in combination therewith, are used as a black filler. The present invention has been attained on the basis of this finding.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance due to high blackness of a filler used therein and a small surface resistivity by using such a black filler capable of inhibiting the electromagnetic performance of the magnetic recording medium from being deteriorated even when the filler is added thereto in an amount sufficient in order to enhance the durability thereof.

It is another object of the present invention to provide a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a smooth surface, a lower light transmittance and a smaller surface resistivity, by using such a black filler capable of suppressing the deterioration of electromagnetic performance of the magnetic recording medium even when the filler is added thereto in an amount sufficient in order to enhance the durability thereof.

To accomplish the aims, in a first aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film; and

a magnetic recording layer comprising a binder resin, magnetic particles, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm,

the said black composite hematite particles comprising:

hematite particles as core particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a second aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film; and

a magnetic recording layer comprising a binder resin, magnetic particles, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm,

the said black composite hematite particles comprising:

hematite particles as core particles, having a coat formed on at least a part of the surface of hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO

2

, based on the total weight of the hematite particles;

a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a third aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film; and

a magnetic recording layer comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm

the said black composite hematite particles comprising:

hematite particles as core particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a fourth aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film; and

a magnetic recording layer comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm

the said black composite hematite particles comprising:

hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO

2

, based on the total weight of the hematite particles;

a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a fifth aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film;

a non-magnetic undercoat layer formed on the non-magnetic base film; and

a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, magnetic particles and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm

the said black composite hematite particles comprising:

hematite particles as core particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a sixth aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film;

a non-magnetic undercoat layer formed on the non-magnetic base film; and

a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, magnetic particles, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm

the said black composite hematite particles comprising:

hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO

2

, based on the total weight of the hematite particles;

a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of said hematite particles.

In a seventh aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film;

a non-magnetic undercoat layer formed on the non-magnetic base film; and

a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm the said black composite hematite particles comprising:

hematite particles as core particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In an eighth aspect of the present invention, there is provided a magnetic recording medium comprising:

a non-magnetic base film;

a non-magnetic undercoat layer formed on the non-magnetic base film; and

a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 μm

the said black composite hematite particles comprising:

hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO

2

, based on the total weight of the hematite particles;

a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a ninth aspect of the present invention, there is provided a filler comprising black composite hematite particles having an average diameter of 0.08 to 1.0 μm and comprising:

hematite particles as core particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

In a tenth aspect of the present invention, there is provided a filler comprising black composite hematite particles having an average diameter of 0.08 to 1.0 μm and comprising:

hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO

2

, based on the total weight of the hematite particles;

a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:

(1) organosilane compounds obtained from an alkoxysilane compounds,

(2) polysiloxanes or modified polysiloxanes, and

(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and

a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is an electron micrograph (×20,000) showing a particle structure of black manganese-containing hematite particles used in Example 1.

FIG. 2

is an electron micrograph (×20,000) showing a particle structure of carbon black fine particles used in Example 1.

FIG. 3

is an electron micrograph (×20,000) showing a particle structure of black composite hematite particles obtained in Example 1.

FIG. 4

is an electron micrograph (×20,000) showing a particle structure of mixed particles composed of the black manganese-containing hematite particles and the carbon black fine particles, for comparison.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below.

First, the magnetic recording medium according to the present invention is explained.

In general, the magnetic recording medium (i) comprises a non-magnetic base film, and a magnetic recording layer formed on the non-magnetic base film and comprising a binder resin, magnetic particles and a filler; or (ii) comprises a non-magnetic base film, a non-magnetic undercoat layer formed on the non-magnetic base film and a magnetic recording layer formed on the non-magnetic undercoat layer and comprising a binder resin, magnetic particles and a filler.

In the magnetic recording medium according to the present invention, as a filler, there are used black composite hematite particles having an average diameter of 0.08 to 1.0 μm and comprising hematite particles as core particles which may be coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon; a coating layer formed on surface of the core particles and comprising an organosilicon compound; and a carbon black coat formed on the coating layer comprising the organosilicon compound.

As the core particles of the black composite hematite particles according to the present invention, there may be used hematite particles such as hematite particles or hematite particles containing manganese in an amount of 5 to 40% by weight based on the weight of the Mn-containing hematite particles. In the consideration of sufficient blackness of the black composite hematite particles, it is preferred that the Mn-containing hematite particles be used as the core particles.

The particle shape of the hematite particles as the core particles may include a granular shape such as a spherical shape, an irregular (anisotropic) shape, an octahedral shape, a hexahedral shape, a polyhedral shape or the like; an acicular shape such as a needle shape, a spindle shape, a rice ball shape or the like; and a plate shape, or the like.

The lower limit of the average particle size of the hematite particles as the core particles is usually 0.075 μm, preferably 0.085 μm, more preferably 0.095 μm, and the upper limit thereof is usually 0.95 μm, preferably 0.65 μm, more preferably 0.45 μm.

(i) In the case where the shape of the core particles is granular-shaped, the lower limit of the average particle diameter of the granular-shaped hematite particles is usually 0.075 μm, preferably 0.085 μm, more preferably 0.095 μm, and the upper limit thereof is usually 0.95 μm, preferably 0.65 μm, more preferably 0.45 μm.

(ii) In the case where the shape of the core particles is acicular-shaped, the lower limit of the average particle diameter (average major axis diameter) of the acicular-shaped hematite particles is usually 0.075 μm, preferably 0.085 μm, more preferably 0.095 μm, and the upper limit thereof is usually 0.95 μm, preferably 0.65 μm, more preferably 0.45 μm; and the lower limit-of the aspect ratio (average major axis diameter/average minor axis diameter) of the acicular-shaped hematite particles is usually 2:1, preferably 2.5:1, more preferably 3:1, and the upper limit thereof is usually 20:1, preferably 15:1, more preferably 10:1.

(iii) In the case where the shape of the core particles is plate-shaped, the lower limit of the average particle diameter (average plate surface diameter) of the plate-shaped hematite particles is usually 0.075 μm, preferably 0.085 μm, more preferably 0.095 μm, and the upper limit thereof is usually 0.95 μm, preferably 0.65 μm, more preferably 0.45 μm; and the lower limit of the plate ratio (average plate surface diameter/average thickness) of the plate-shaped hematite particles is usually 2:1, preferably 2.5:1, more preferably 3:1, and the upper limit thereof is usually 50:1, preferably 20:1, more preferably 10:1.

When the average particle size of the hematite particles is more than 0.95 μm, the obtained black composite hematite particles may be coarse particles, thereby causing the deterioration of the tinting strength, so that the light transmittance of the magnetic recording medium obtained may become high. On the other hand, when the average particle size is less than 0.075 μm, the intermolecular force between the particles may be increased due to the reduction in particle diameter, so that agglomeration of the particles tends to be caused. As a result, it may become difficult to uniformly coat the surface of the hematite particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer comprising the organosilicon compounds.

When the aspect ratio of the acicular-shaped hematite particles is more than 20:1, the particles may be entangled with each other in vehicle, so that it may become difficult to uniformly coat the surface of the acicular-shaped hematite particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer comprising the organosilicon compounds.

Further, in the case where the upper limit of the plate ratio of the plate-shaped hematite particles exceeds 50:1, the particles may tend to be stacked each other, and it also may become difficult to uniformly coat the surfaces of the plate-shaped hematite particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer composed of the organosilicon compounds.

The lower limit of the blackness of the Mn-containing hematite particles as core particles used in the present invention is usually 22 when represented by a L* value thereof, and the upper limit of the blackness thereof is usually 28, preferably 26 when represented by a L* value thereof. The lower limit of the blackness of the hematite particles as core particles used in the present invention is usually 22 when represented by a L* value thereof, and the upper limit of the blackness thereof is usually 38, preferably 36 when represented by a L* value thereof. When the L* value of the core particles exceeds the above-mentioned upper limit, the blackness thereof may become insufficient so that it is difficult to obtain black composite hematite particles having an excellent blackness.

The lower limit of the BET specific surface area of the hematite particles as core particles is usually 1.0 m

2

/g, preferably 2.0 m

2

/g, more preferably 2.5 m

2

/g, and the upper limit thereof is usually 200 m

2

/g, preferably 150 m

2

/g, more preferably 100 m

2

/g. When the BET specific surface area is less than 1.0 m

2

/g, the hematite particles as core particles may become coarse particles, or the sintering between the particles may be caused, so that the obtained black composite hematite particles also may become coarse particles and tend to be deteriorated in tinting strength and as a result, the light transmittance of the magnetic recording medium obtained may become high. On the other hand, when the BET specific surface area thereof is more than 200 m

2

/g, the intermolecular force between the particles may be increased due to the fineness thereof, so that it may become difficult to uniformly coat the surfaces of the hematite particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer composed of the organosilicon compounds.

As to the particle diameter distribution of the hematite particles used as core particles, the geometrical standard deviation value thereof is preferably not more than 1.8, more preferably not more than 1.7, still more preferably not more than 1.6. When the geometrical standard deviation value thereof is more than 1.8, coarse particles may be contained therein, so that the particles may be inhibited from being uniformly dispersed. As a result, it may also become difficult to uniformly coat the surfaces of the hematite particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer composed of the organosilicon compounds. The lower limit of the geometrical standard deviation value is 1.01 under the consideration of an industrial productivity.

In the hematite particles used as core particles of the present invention, the surfaces of the hematite particles as the core particles may be preliminarily coated with at least one compound selected from the group consisting of hydroxide of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon (hereinafter referred to as “hydroxides and/or oxides of aluminum and/or silicon coat”), if required. In this case, the dispersibility of the obtained black composite hematite particles in a vehicle may become improved as compared to those having no hydroxides and/or oxides of aluminum and/or silicon coat, so that a magnetic recording medium having more excellent durability and electromagnetic performance, can be obtained.

The amount of the hydroxides and/or oxides of aluminum and/or silicon coat is 0.01 to 50% by weight (calculated as Al, SiO

2

or a sum of Al and SiO

2

) based on the weight of the hematite particles as the core particles.

When the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is less than 0.01% by weight, the improvement of the dispersibility of the obtained black composite hematite particles in a vehicle cannot be achieved. On the other hand, when the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is more than 50% by weight, the obtained black composite hematite particles can exhibit a good dispersibility in a vehicle, but it is meaningless because the dispersibility cannot be further improved by using such an excess amount of the hydroxides and/or oxides of aluminum and/or silicon coat.

The hematite particles having the hydroxides and/or oxides of aluminum and/or silicon coat may be substantially identical in a particle size, a geometrical standard deviation of particle sizes, a BET specific surface area and a blackness (L* value), to those having no hydroxides and/or oxides of aluminum and/or silicon coat.

The coating layer formed on the surface of the core particle comprises at least one organosilicon compound selected from the group consisting of (1) organosilane compounds obtained from alkoxysilane compounds; (2) polysiloxanes or modified polysiloxanes selected from the group consisting of (2-A) polysiloxanes modified with at least one compound selected from the group consisting of polyethers, polyesters and epoxy compounds (hereinafter referred to merely as “modified polysiloxanes”), and (2-B) polysiloxanes whose molecular terminal is modified with at least one group selected from the group consisting of carboxylic acid groups, alcohol groups and a hydroxyl group (hereinafter referred to merely as “terminal-modified polysiloxanes”); and (3) fluoroalkyl organosilane compounds obtained from fluoroalkylsilane compounds.

The organosilane compounds (1) can be produced from alkoxysilane compounds represented by the formula (I):

R

1

a

SiX

4−a

(I)

wherein R

1

is C

6

H

5

—, (CH

3

)

2

CHCH

2

— or n-C

b

H

2b+1

— (wherein b is an integer of 1 to 18); X is CH

3

O— or C

2

H

5

O—; and a is an integer of 0 to 3.

The alkoxysilane compounds may be dried or heat-treated for producing the organosilane compounds (1), for example, at a temperature of usually 40 to 200° C., preferably 60 to 150° C. for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.

Specific examples of the alkoxysilane compounds may include methyl triethoxysilane, dimethyl diethoxysilane, phenyl triethyoxysilane, diphenyl diethoxysilane, methyl trimethoxysilane, dimethyl dimethoxysilane, phenyl trimethoxysilane, diphenyl dimethoxysilane, isobutyl trimethoxysilane, decyl trimethoxysilane or the like. Among these alkoxysilane compounds, in view of the desorption percentage and the adhering effect of carbon black, methyl triethoxysilane, phenyl triethyoxysilane, methyl trimethoxysilane, dimethyl dimethoxysilane and isobutyl trimethoxysilane are preferred, and methyl triethoxysilane and methyl trimethoxysilane are more preferred.

As the polysiloxanes (2), there may be used those compounds represented by the formula (II):

wherein R

2

is H— or CH

3

—, and d is an integer of 15 to 450.

Among these polysiloxanes, in view of the desorption percentage and the adhering effect of carbon black, polysiloxanes having methyl hydrogen siloxane units are preferred.

As the modified polysiloxanes (2-A), there may be used:

(a1) polysiloxanes modified with polyethers represented by the formula (III):

wherein R

3

is —(—CH

2

—)

h

—; R

4

is —(—CH

2

—)

i

—CH

3

; R

5

is —OH, —COOH, —CH═CH

2

, —CH(CH

3

)═CH

2

or —(—CH

2

—)

j

—CH

3

; R

6

is —(—CH

2

—)

k

—CH

3

; g and h are an integer of 1 to 15; i, j and k are an integer of 0 to 15; e is an integer of 1 to 50; and f is an integer of 1 to 300;

(a2) polysiloxanes modified with polyesters represented by the formula (IV):

wherein R

7

, R

8

and R

9

are (—CH

2

—)

q

— and may be the same or different; R

10

is —OH, —COOH, —CH═CH

2

, —CH(CH

3

)═CH

2

or —(—CH

2

—)

r

—CH

3

; R

11

is —(—CH

2

—)

s

—CH

3

; n and q are an integer of 1 to 15; r and s are an integer of 0 to 15; e′ is an integer of 1 to 50; and f′ is an integer of 1 to 300;

(a3) polysiloxanes modified with epoxy compounds represented by the formula (V):

wherein R

12

is —(—CH

2

—)

v

—; v is an integer of 1 to 15; t is an integer of 1 to 50; and u is an integer of 1 to 300; or a mixture thereof.

Among these modified polysiloxanes (2-A), in view of the desorption percentage and the adhering effect of carbon black, the polysiloxanes modified with the polyethers represented by the formula (III), are preferred.

As the terminal-modified polysiloxanes (2-B), there may be used those represented by the formula (VI):

wherein R

13

and R

14

are —OH, R

16

OH or R

17

COOH and may be the same or different; R

15

is —CH

3

or —C

6

H

5

; R

16

and R

17

are —(—CH

2

—)

y

—; wherein y is an integer of 1 to 15; w is an integer of 1 to 200; and x is an integer of 0 to 100.

Among these terminal-modified polysiloxanes, in view of the desorption percentage and the adhering effect of carbon black, the polysiloxanes whose terminals are modified with carboxylic acid groups are preferred.

The fluoroalkyl organosilane compounds (3) can be produced from fluoroalkylsilane compounds represented by the formula (VII):

CF

3

(CF

2

)

z

CH

2

CH

2

(R

18

)

′

SiX

4−a′

(VII)

wherein R

18

is CH

3

—, C

2

H

5

—, CH

3

O— or C

2

H

5

O—; X is CH

3

O— or C

2

H

5

O—; and z is an integer of 0 to 15; and a′ is an integer of 0 to 3.

The fluoroalkylsilane compounds may be dried or heat-treated for producing the fluoroalkyl organosilane compounds (3), for example, at a temperature of usually 40 to 200° C., preferably 60 to 150° C. for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.

Specific examples of the fluoroalkylsilane compounds may include trifluoropropyl trimethoxysilane, tridecafluorooctyl trimethoxysilane, heptadecafluorodecyl trimethoxysilane, heptadecafluorodecylmethyl dimethoxysilane, trifluoropropyl triethoxysilane, tridecafluorooctyl triethoxysilane, heptadecafluorodecyl triethoxysilane, heptadecafluorodecylmethyl diethoxysilane or the like. Among these fluoroalkylsilane compounds, in view of the desorption percentage and the adhering effect of carbon black, trifluoropropyl trimethoxysilane, tridecafluorooctyl trimethoxysilane and heptadecafluorodecyl trimethoxysilane are preferred, and trifluoropropyl trimethoxysilane and tridecafluorooctyl trimethoxysilane are more preferred.

The amount of the coating layer composed of the organosilicon compounds is usually 0.02 to 5.0% by weight, preferably 0.03 to 4.0% by weight, more preferably 0.05 to 3.0% by weight (calculated as Si) based on the weight of the hematite particles coated with the organosilicon compounds.

When amount of the coating layer composed of the organosilicon compounds is less than 0.02% by weight, it may become difficult to form the carbon black coat on the coating layer in such an amount enough to improve the blackness thereof. On the other hand, even when the coating amount of the organosilicon compounds is more than 5.0% by weight, a sufficient amount of carbon black can be coated on the coating layer. However, it is meaningless because the blackness cannot be further improved by using such an excess amount of the organosilicon compounds.

As the carbon black fine particles used in the present invention, there may be exemplified commercially available carbon blacks such as furnace black, channel black or the like. Specific examples of the commercially available carbon blacks usable in the present invention, may include #3050, #3150, #3250, #3750, #3950, MA100, MA7, #1000, #2400B, #30, MA77, MA8, #650, MA11, #50, #52, #45, #2200B, MA600, etc. (tradename, produced by MITSUBISHI CHEMICAL CORP.), SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H, SEAST 300, SEAST FM, etc. (tradename, produced by TOKAI CARBON CO., LTD.), Raven 1250, Raven 860, Raven 1000, Raven 1190 ULTRA, etc. (tradename, produced by COLOMBIAN CHEMICALS COMPANY), Ketchen black EC, Ketchen black EC60OJD, etc. (tradename, produced by KETCHEN INTERNATIONAL CO., LTD.), BLACK PEARLS-L, BLACK PEARLS 1000, BLACK PEARLS 4630, VULCAN XC72, REGAL 660, REGAL 400, etc. (tradename, produced by CABOT SPECIALTY CHEMICALS INK CO., LTD.), or the like.

Further, in the consideration of more uniform coat of carbon black to the coating layer comprising at least one organosilicon compound, the carbon black fine particles having a DBP oil absorption of not more than 180 ml/100 g is preferred. Especially, there may be exemplified #3050, #3150, #3250, MA100, MA7, #1000, #2400B, #30, MA77, MA8, #650, MA11, #50, #52, #45, #2200B, MA600 (tradename, produced by MITSUBISHI CHEMICAL CORP.), SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H, SEAST 300, SEAST FM (tradename, produced by TOKAI CARBON CO., LTD.), Raven 1250, Raven 860, Raven 1000, Raven 1190 ULTRA (tradename, produced by COLOMBIAN CHEMICALS COMPANY), BLACK PEARLS-L, BLACK PEARLS 1000, BLACK PEARLS 4630, REGAL 660, REGAL 400 (tradename, produced by CABOT SPECIALTY CHEMICALS INK CO., LTD.).

The lower limit of the average particle size of the carbon black fine particles used is usually 0.002 μm, preferably 0.005 μm, and the upper limit thereof is usually 0.05 μm, preferably 0.035 μm. When the average particle size of the carbon black fine particles used is less than 0.002 μm, the carbon black fine particles used are too fine to be well handled.

On the other hand, when the average particle size thereof is more than 0.05 μm, since the particle size of the carbon black fine particles used is much larger, it is necessary to apply a larger mechanical shear force for forming the uniform carbon black coat on the coating layer composed of the organosilicon compounds, thereby rendering the coating process industrially disadvantageous.

The amount of the carbon black formed is usually 1 to 30 parts by weight, preferably 3 to 25 parts by weight based on 100 parts by weight of the hematite particles as the core particles. When the amount of the carbon black coat formed is less than 1 part by weight, the blackness of the resultant black composite hematite particles may be unsatisfactory because of insufficient amount of the carbon black coat formed onto the coating layer. On the other hand, when the amount of the carbon black coat formed is more than 30 parts by weight, the carbon black may tend to be desorbed from the coating layer because of too much amount of the carbon black coat formed thereonto, though the obtained black composite hematite particles can show a sufficient blackness. As a result, since the desorbed carbon black may inhibit the black composite hematite particles from being homogeneously dispersed in vehicle, it may become difficult to obtain magnetic recording media which are excellent in both durability and electromagnetic performance.

The thickness of carbon black coat formed is preferably not more than 0.04 μm, more preferably not more than 0.03 μm, still more preferably not more than 0.02 μm. The lower limit thereof is more preferably 0.0001 μm.

The particle shape and particle size of the black composite hematite particles according to the present invention are considerably varied depending upon those of the hematite particles as core particles. The black composite hematite particles have a similar particle shape to that of the hematite particles as core particle, and a slightly larger particle size than that of the hematite particles as core particles.

The lower limit of the average particle size of the black composite hematite particles according to the present invention is usually 0.08 μm, preferably 0.09 μm, more preferably 0.1 μm, and the upper limit thereof is usually 1.0 μm, preferably 0.7 μm, more preferably 0.5 μm.

More specifically, when the granular-shaped hematite particles are used as core particles, the lower limit of the average particle diameter of the black composite hematite particles according to the present invention is usually 0.08 μm, preferably 0.09 μm, more preferably 0.1 μm, and the upper limit thereof is usually 1.0 μm, preferably 0.7 μm, more preferably 0.5 μm.

When the acicular-shaped hematite particles are used as core particles, the lower limit of the average particle diameter (average major axis diameter) of the black composite hematite particles according to the present invention is usually 0.08 μm, preferably 0.09 μm, more preferably 0.1 μm and the upper limit thereof is usually 1.0 μm, preferably 0.7 μm, more preferably 0.5 μm; and the lower limit of the aspect ratio (average major axis diameter/average minor axis diameter) of the black composite hematite particles according to the present invention, is usually 2:1, preferably 2.5:1, more preferably 3:1, and the upper limit thereof is usually 20:1, preferably 15:1, more preferably 10:1.

When the plate-shaped hematite particles are used as core particles, the lower limit of the average particle diameter (average plate surface diameter) of the black composite hematite particles according to the present invention is usually 0.08 μm, preferably 0.09 μm, more preferably 0.1 μm and the upper limit thereof is usually 1.0 μm, preferably 0.7 μm, more preferably 0.5 μm; and the lower limit of the plate ratio (average plate surface diameter/average thickness) of the black composite hematite particles according to the present invention, is usually 2:1, preferably 2.5:1, more preferably 3:1, and the upper limit thereof is usually 50:1, preferably 20:1, more preferably 10:1.

When the average particle size of the black composite hematite particles is less than 0.08 μm, the black composite hematite particles tends to be agglomerated by the increase of intermolecular force due to the reduction in particle size, thereby deteriorating the dispersibility in a vehicle upon production of the magnetic coating composition. As a result, the obtained magnetic recording media may suffer from deterioration in durability and electromagnetic performance. When the average particle diameter of the black composite hematite particles is more than 1.0 μm, the obtained black composite hematite particles may be coarse particles, and deteriorated in tinting strength, so that it may become difficult to reduce the light transmittance of the magnetic recording medium.

In case of the acicular-shaped black composite hematite particles, when the aspect ratio of the black composite hematite particles is more than 20.0:1, the black composite hematite particles may be entangled with each other in the binder resin, thereby deteriorating the dispersibility in a vehicle upon production of the magnetic coating composition. As a result, it may become difficult to obtain the magnetic recording media showing excellent durability and electromagnetic performance.

In case of the plate-shaped black composite hematite particles, when the plate ratio of the black composite hematite particles is more than 50.0:1, the black composite hematite particles may be stacked each other in the binder resin, thereby deteriorating the dispersibility in a vehicle upon production of the magnetic coating composition. As a result, it may become difficult to obtain the magnetic recording media showing excellent durability and electromagnetic performance.

As to the blackness of the black composite hematite particles according to the present invention, in the case the Mn-containing hematite particles are used as core particles, the upper limit of the blackness of the black composite hematite particles is usually 19.0, preferably 18.5 when represented by L* value. In the case the hematite particles are used as core particles, the upper limit of the blackness of the black composite hematite particles is usually 21.0, preferably 20.5 when represented by L* value.

When the L* value of the black composite hematite particles is more than the above-mentioned upper limit, the lightness of the obtained black composite hematite particles may become high, so that the black composite hematite particles having a sufficient blackness cannot be obtained and as a result, it may become difficult to reduce the light transmittance of the magnetic recording medium. The lower limit of the blackness thereof is preferably 15 when represented by L* value.

The percentage of desorption of carbon black from the black composite hematite particles according to the present invention, is preferably not more than 20%, more preferably not more than 10%. When the desorption percentage of the carbon black is more than 20%, the desorbed carbon black may tend to inhibit the black composite hematite particles from being uniformly dispersed in the binder resin upon production of the magnetic coating composition, so that it may become difficult to obtain magnetic recording media which are excellent in surface smoothness, durability and electromagnetic performance.

The BET specific surface area of the black composite hematite particles according to the present invention, is usually 1 to 200 m

2

/g, preferably 2 to 150 m

2

/g, more preferably 2.5 to 100 m

2

/g. When the BET specific surface area thereof is less than 1 m

2

/g, the obtained black composite hematite particles may be coarse and/or the sintering between the particles is caused, thereby deteriorating the tinting strength, so that it may become difficult to reduce the light transmittance of the magnetic recording medium. On the other hand, when the BET specific surface area is more than 200 m

2

/g, the black composite hematite particles tend to be agglomerated together by the increase in intermolecular force due to the reduction in particle diameter, thereby deteriorating the dispersibility in a binder resin upon production of the magnetic coating composition, so that the obtained magnetic recording media may suffer from deterioration in durability and electromagnetic performance.

The geometrical standard deviation value of the black composite hematite particles according to the present invention is preferably not more than 1.8. When the geometrical standard deviation value thereof is more than 1.8, the black composite hematite particles may contain a large amount of coarse particles, so that it may become difficult to disperse the particles in vehicle upon the production of a magnetic coating composition and, therefore, obtain magnetic recording media which are excellent in both durability and electromagnetic performance. In the consideration of the durability and electromagnetic performance of the obtained magnetic recording media, the geometrical standard deviation of diameters of the black composite hematite particles is preferably not more than 1.7, more preferably not more than 1.6. Further in the consideration of industrial productivity of the black composite hematite particles, the lower limit of the geometrical standard deviation of diameters thereof is 1.01.

The volume resistivity of the black composite hematite particles is preferably not more than 1×10

6

Ω·cm, more preferably 1×10

1

Ω·cm to 5×10

5

Ω·cm, still more preferably 1×10

1

Ω·cm to 1×10

5

Ω·cm. When the volume resistivity is more than 1×10

6

Ω·cm, it is difficult to reduce the surface resistivity value of the obtained magnetic recording media to a sufficiently low level.

As the non-magnetic base film, the following materials which are at present generally used for the production of a magnetic recording medium are usable as a raw material: a synthetic resin such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide and polyimide; foil and plate of a metal such as aluminum and stainless steel; and various kinds of paper. The thickness of the non-magnetic base film varies depending upon the material, but it is usually about 1.0 to 300 μm, preferably 2.0 to 200 μm.

In the case of a magnetic disc, polyethylene terephthalate is usually used as the non-magnetic base film. The thickness thereof is usually 50 to 300 μm, preferably 60 to 200 μm. In the case of a magnetic tape, when polyethylene terephthalate is used as the base film, the thickness thereof is usually 3 to 100 μm, preferably 4 to 20 μm. When polyethylene naphthalate is used, the thickness thereof is usually 3 to 50 μm, preferably 4 to 20 μm. When polyamide is used, the thickness thereof is usually 2 to 10 μm, preferably 3 to 7 μm.

As the magnetic particles used in the present invention, there may be exemplified magnetic iron oxide particles such as maghemite particles, magnetite particles and berthollide compound particles which are an intermediate oxide between maghemite and magnetite; particles obtained by incorporating any one or more different kinds of elements other than Fe, such as Co, Al, Ni, P, Zn, Si, B or the like in the said magnetic iron oxide particles; magnetic iron oxide particles obtained by coating the surface of the above-mentioned magnetic iron oxide particles or those containing different kinds of elements, with cobalt, both cobalt and iron or the like (hereinafter referred to merely as “magnetic cobalt-coated iron oxide particles”); magnetic metal particles containing iron as a main component; magnetic metal particles containing iron as a main component and elements other than Fe at least one selected from the group consisting of Co, Al, Ni, P, Si, Zn, B, Nd, La, Sm and Y. including magnetic iron-based alloy particles; magnetoplumbite-type ferrite particles such as plate-like ferrite particles containing-Ba, Sr or Ba-Sr; plate-like magnetoplumbite-type ferrite particles obtained by incorporating divalent metals or tetravalent metals (such as Co, Ni, Zn, Mg, Mn, Nb, Cu, Ti, Sn, Zr, Mo or the like) as a coercive force-reducing agent in the plate-like magnetoplumbite-type ferrite particles; or the like. With the consideration of the high-density recording, magnetic metal particles containing iron as a main component, magnetic cobalt-coated iron oxide particles and magnetic iron-based alloy particles containing elements other than Fe at least one selected from the group consisting of Co, Al, Ni, P, Si, Zn, B, Nd, La, Sm, Y or the like are preferable.

Especially, the magnetic metal particles containing iron as a main component comprising (i) iron and Al; (ii) iron, Co and Al, (iii) iron, Al and at least one rare-earth metal such as Nd, La and Y, or (iv) iron, Co, Al and at least one rare-earth metal such as Nd, La and Y is more preferable from the point of the durability of the magnetic recording medium. Further, the magnetic acicular metal particles containing iron as a main component comprising iron, Al and at least one rare-earth metal such as Nd, La and Y is still more preferable.

More specifically, the magnetic acicular metal particles containing iron as a main component may be exemplified as follows.

1) Magnetic acicular metal particles comprises iron; and cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles.

2) Magnetic acicular metal particles comprises iron; and aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles.

3) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; and aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles.

4) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Nd, La and Y of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

5) Magnetic acicular metal particles comprises iron;

aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Nd, La and Y of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

6) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Nd, La and Y of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

7) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Ni, P, Si, Zn, Ti, Cu and B of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

8) Magnetic acicular metal particles comprises iron; aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Ni, P, Si, Zn, Ti, Cu and B of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

9) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Ni, P, Si, Zn, Ti, Cu and B of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

10) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; at least one selected from the group consisting of Nd, La and Y of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Ni, P, Si, Zn, Ti, Cu and B of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

11) Magnetic acicular metal particles comprises iron; aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles; at least one selected from the group consisting of Nd, La and Y of ordinarily 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Ni, P, Si, Zn, Ti, Cu and B of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

12) Magnetic acicular metal particles comprises iron; cobalt of usually 0.05 to 40% by weight, preferably 1.0 to 35% by weight, more preferably 3 to 30% by weight (calculated as Co) based on the weight of the magnetic acicular metal particles; aluminum of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles; at least one selected from the group consisting of Nd, La and Y of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles; and at least one selected from the group consisting of Ni, P, Si, Zn, Ti, Cu and B of usually 0.05 to 10% by weight, preferably 0.1 to 7% by weight (calculated as the corresponding element) based on the weight of the magnetic acicular metal particles.

The iron content in the particles is the balance, and is preferably 50 to 99% by weight, more preferably 60 to 95% by weight (calculated as Fe) based on the weight of the magnetic particles containing iron as a main component.

From the consideration of the excellent durability of the magnetic recording medium, it is preferred to use as magnetic particles magnetic acicular metal particles containing iron as a main component, which contain aluminum of 0.05 to 10% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles containing iron as a main component, which are present within the particle.

It is more preferable to use as magnetic particles magnetic acicular metal particles containing iron as a main component containing Al in an amount of 0.05 to 10% by weight (calculated as Al) based on the weight of the magnetic acicular metal particles and a rare-earth metal such as Nd, La and Y in an amount of 0.05 to 10% by weight (calculated as element) based on the weight of the magnetic acicular metal particles. Especially, magnetic acicular metal particles containing iron as a main component containing Al and Nd therein are the even more preferable.

The magnetic particles may have not only an acicular shape but also a cubic shape, a plate-like shape or the like. Meanwhile, the term “acicular shape” used herein should be construed as including “needle shape”, “spindle shape”, “rice grain shape” and the like.

The magnetic particles have an average major axial diameter (an average particle diameter or average plate surface diameter) of usually 0.01 to 0.50 μm, preferably 0.03 to 0.30 μm; an average minor axial diameter (an average thickness) of usually 0.0007 to 0.17 μm, preferably 0.003 to 0.10 μm; and a geometrical standard deviation of major axial diameters of usually not more than 2.5, preferably 1.01 to 2.3.

When the magnetic particles have an acicular shape, the aspect ratio thereof is usually not less than 3:1, preferably not less than 5:1. In the consideration of good dispersibility of the particles in vehicle upon the production of a magnetic coating composition, the upper limit of the aspect ratio is usually 15:1, preferably 10:1.

When the magnetic particles have a plate shape, the plate ratio thereof is usually not less than 2:1, preferably not less than 3:1. In the consideration of good dispersibility of the particles in vehicle upon the production of a magnetic coating composition, the upper limit of the plate ratio is usually 20:1, preferably 15:1.

The magnetic particles have a BET specific surface area of usually not less than 15 m

2

/g, preferably not less than 20 m

2

/g. In the consideration of good dispersibility of the particles in vehicle upon the production of a magnetic coating composition, the upper limit of the BET specific surface area is preferably 100 m

2

/g, more preferably 80 m

2

/g. As to magnetic properties of the magnetic particles, in the case of acicular magnetic iron oxide particles or Co-coated acicular magnetic iron oxide particles, the coercive force value thereof is usually 250 to 1,700 Oe (19.9 to 135.3 kA/m), preferably 300 to 1,700 Oe (23.9 to 135.3 kA/m); and the saturation magnetization value thereof is usually 60 to 90 emu/g (60 to 90 Am

2

/kg), preferably 65 to 90 emu/g (65 to 90 Am

2

/kg).

In the case of acicular magnetic metal particles containing iron as a main component or acicular magnetic alloy particles containing iron as a main component, the coercive force value thereof is usually 800 to 3,500 Oe (63.7 to 278.5 kA/m), preferably 900 to 3,500 Oe (71.6 to 278.5 kA/m); and the saturation magnetization value thereof is usually 90 to 170 emu/g (90 to 170 Am

2

/kg), preferably 100 to 170 emu/g (100 to 170 Am

2

/kg).

In the case of plate-like magnetoplumbite-type ferrite particles, the coercive force value thereof is usually 500 to 4,000 Oe (39.8 to 318.3 kA/m), preferably 650 to 4,000 Oe (51.7 to 318.3 kA/m); and the saturation magnetization value thereof is usually 40 to 70 emu/g (40 to 70 Am

2

/kg), preferably 45 to 70 emu/g (45 to 70 Am

2

/kg).

As the binder resin used in the present invention, the following resins which are at present generally used for the production of a magnetic recording medium are usable: vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, urethane resin, styrene-butadiene copolymer, butadiene-acrylonitrile copolymer, polyvinyl butyral, cellulose derivative such as nitrocellulose, polyester resin, synthetic rubber resin such as polybutadiene, epoxy resin, polyamide resin, polyisocyanate, electron radiation curing acryl urethane resin and mixtures thereof. Each of these resin binders may contain a functional group such as —OH, —COOH, —SO

3

M, —OPO

2

M

2

and —NH

2

, wherein M represents H, Na or K. With the consideration of the dispersibility of the magnetic particles and the black composite hematite particles as a filler upon the production of the magnetic coating composition, a binder resin containing a functional group —COOH or —SO

3

M is preferable.

The thickness of the magnetic recording layer obtained by applying the magnetic coating composition on the surface of the non-magnetic base film and dried, is usually in the range of 0.01 to 5.0 μm. If the thickness is less than 0.01 μm, uniform coating may be difficult, so that unfavorable phenomenon such as unevenness on the coating surface may be observed. On the other hand, when the thickness exceeds 5.0 μm, it may be difficult to obtain desired electromagnetic performance due to an influence of diamagnetism. The preferable thickness is in the range of 0.05 to 1.0 μm.

The mixing ratio of the binder resin to the magnetic particles in the magnetic recording layer is usually 5 to 50 parts by weight, preferably 6 to 30 parts by weight based on 100 parts by weight of the magnetic particles.

When the content of the binder resin is more than 50 parts by weight, the content of the magnetic particles in the magnetic recording layer comparatively becomes too small, resulting in low filling percentage of the magnetic particles and further in deteriorated electromagnetic performance of the obtained magnetic recording media. When the content of the binder resin is less than 5 parts by weight, the blending ratio of the binder resin to the magnetic particles become too small, thereby failing to sufficiently disperse the magnetic particles in the magnetic coating composition, so that a coating film formed from such a magnetic coating composition tends to have an insufficient surface smoothness. Further, since the magnetic particles cannot be sufficiently bonded together through the binder resin, the obtained coating film tends to become brittle.

The blending ratio of the black composite hematite particles to the magnetic particles in the magnetic recording layer is usually 1 to 30 parts by weight, preferably 3 to 25 parts by weight based on 100 parts by weight of the magnetic particles.

When the content of the black composite hematite particles in the magnetic recording layer is as small as less than 1 part by weight, the obtained magnetic recording media may be insufficient in its durability, and it becomes difficult to sufficiently reduce the light transmittance and surface resistivity of the magnetic recording media. When the content of the black composite hematite particles is more than 30 parts by weight, the obtained magnetic recording media have a sufficient durability as well as low light transmittance and small surface resistivity. However, in this case, the amount of non-magnetic components in the magnetic recording layer becomes too large, thereby failing to produce magnetic recording media suitable for high-density recording.

It is possible to add an additive such as a lubricant, a polishing agent, an antistatic agent, etc. which are generally used for the production of a magnetic recording medium, to the magnetic recording layer. The mixing ratio of the additive to the binder resin is preferably 0.1 to 50 parts by weight based on 100 parts by weight of the binder resin.

The magnetic recording medium of the fifth to eighth aspects in the present invention, comprises a non-magnetic base film, a non-magnetic undercoat layer formed on the non-magnetic base film and a magnetic recording layer formed on the non-magnetic undercoat layer.

The thickness of the non-magnetic undercoat layer is preferably 0.2 to 10.0 μm. When the thickness of the non-magnetic undercoat layer is less than 0.2 μm, it may be difficult to improve the surface roughness of the non-magnetic substrate, and the stiffness of a coating film formed thereon tends to be unsatisfactory. In the consideration of reduction in total thickness of the magnetic recording medium as well as the stiffness of the coating film, the thickness of the non-magnetic undercoat layer is more preferably in the range of 0.5 to 5.0 μm.

As the binder resin, the same binder resin as that used for the production of the magnetic recording layer is usable.

The mixing ratio of the non-magnetic particles to the binder resin is usually 5 to 2000 parts by weight, preferably 100 to 1000 parts by weight based on 100 parts by weight of the binder resin.

When the content of the non-magnetic particles is as small as less than 5 parts by weight, such a non-magnetic undercoat layer in which the non-magnetic particles are uniformly and continuously dispersed may not be obtained upon coating, resulting in insufficient surface smoothness and insufficient stiffness of the non-magnetic substrate.

When the content of the non-magnetic particles is more than 2,000 parts by weight, the non-magnetic particles may not be sufficiently dispersed in a non-magnetic coating composition since the amount of the non-magnetic particles is too large as compared to that of the binder resin. As a result, when such a non-magnetic coating composition is coated onto the non-magnetic base film, it may become difficult to obtain a coating film having a sufficiently smooth surface. Further, since the non-magnetic particles may not be sufficiently bonded together through the binder resin, the obtained coating film tends to become brittle.

It is possible to add an additive such as a lubricant, a polishing agent, an antistatic agent, etc. which are generally used for the production of a magnetic recording medium, to the non-magnetic undercoating layer. The mixing ratio of the additive to the binder resin is preferably 0.1 to 50 parts by weight based on 100 parts by weight of the binder resin.

As the non-magnetic particles used in the non-magnetic undercoat layer of the present invention, there may be exemplified non-magnetic inorganic particles ordinarily used for forming a non-magnetic undercoat layer in conventional magnetic recording media. Specific examples of the non-magnetic particles may include hematite particles, iron oxide hydroxide particles, titanium oxide particles, zinc oxide particles, tin oxide particles, tungsten oxide particles, silicon dioxide particles, α-alumina particles, β-alumina particles, γ-alumina particles, chromium oxide particles, cerium oxide particles, silicon carbide particles, titanium carbide particles, silicon nitride particles, boron nitride particles, calcium carbonate particles, barium carbonate particles, magnesium carbonate particles, strontium carbonate particles, calcium sulfate particles, barium sulfate particles, molybdenum disulfide particles, barium titanate particles or the like. These non-magnetic particles may be used singly or in the form of a mixture of any two or more thereof. Among them, the use of hematite, iron oxide hydroxide, titanium oxide and the like is preferred.

In the present invention, in order to improve the dispersibility of the non-magnetic particles in vehicle upon the production of non-magnetic coating composition, the non-magnetic particles may be surface-treated with hydroxides of aluminum, oxides of aluminum, hydroxides of silicon, oxides of silicon or the like to form a coat made of any of these compounds on the surfaces thereof. Further, the non-magnetic particles may contain Al, Ti, Zr, Mn, Sn, Sb or the like inside thereof, if required, in order to improve various properties of the obtained magnetic recording media such as light transmittance, surface resistivity, mechanical strength, surface smoothness, durability or the like.

In the consideration of surface smoothness of the obtained non-magnetic undercoat layer, the non-magnetic particles preferably have an acicular shape. The term “acicular shape” used herein should be construed as including “needle shape”, “spindle shape”, “rice grain shape” or the like.

The non-magnetic particles have an average major axial diameter of usually 0.01 to 0.3 μm, preferably 0.015 to 0.25 μm, more preferably 0.02 to 0.2 μm, an aspect ratio of usually 2:1 to 20:1, preferably 3:1 to 15:1.

The magnetic recording medium according to the first aspect of the present invention in which the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler, has a coercive force value of usually 250 to 4,000 Oe (19.9 to 318.3 kA/m), preferably 300 to 4,000 Oe (23.9 to 318.3 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 160 to 300%, preferably 165 to 300%; a surface roughness Ra (of the coating film) of usually not more than 10.0 nm, preferably 2.0 to 9.5 nm, more preferably 2.0 to 9.0 nm; a Young's modulus (relative value to a commercially available video tape: and AV T-120 produced by Victor Company of Japan, Limited) of usually 122 to 160, preferably 124 to 160; a linear absorption (of the coating film) of usually 1.20 to 5.00 μm

−1

, preferably 1.30 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

10

Ω/cm

2

, preferably not more than 7.5×10

9

Ω/cm

2

, more preferably not more than 5.0×10

9

Ω/cm

2

.

The magnetic recording medium according to the second aspect of the present invention in which the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler, has a coercive force value of usually 250 to 4,000 Oe (19.9 to 318.3 kA/m), preferably 300 to 4,000 Oe (23.9 to 318.3 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 165 to 300%, preferably 170 to 300%; a surface roughness Ra (of the coating film) of usually not more than 9.5 nm, preferably 2.0 to 9.0 nm, more preferably 2.0 to 8.5 nm; a Young's modulus (relative value to a commercially available video tape: and AV T-120 produced by Victor Company of Japan, Limited) of usually 124 to 160, preferably 126 to 160; a linear absorption (of the coating film) of usually 1.20 to 5.00 μm

−1

, preferably 1.30 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

10

Ω/cm

2

, preferably not more than 7.5×10

9

Ω/cm

2

, more preferably not more than 5.0×10

9

Ω/cm

2

.

The magnetic recording medium according to the third aspect of the present invention in which the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler and magnetic metal particles containing iron as a main component or magnetic alloy particles containing iron as a main component are used as magnetic particles, has a coercive force value of usually 800 to 3,500 Oe (63.7 to 278.5 kA/m), preferably 900 to 3,500 Oe (71.6 to 278.5 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 185 to 300%, preferably 190 to 300%; a surface roughness Ra (of the coating film) of usually not more than 9.0 nm, preferably 2.0 to 8.5 nm, more preferably 2.0 to 8.0 nm; a Young's modulus (relative value to a commercially available video tape: and AV T-120 produced by Victor Company of Japan, Limited) of usually 122 to 160, preferably 124 to 160; a linear absorption (of the coating film) of usually 1.20 to 5.00 μm

−1

, preferably 1.30 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

10

Ω/cm

2

, preferably not more than 7.5×10

9

Ω/cm

2

, more preferably not more than 5.0×10

9

Ω/cm

2

.

The magnetic recording medium according to the fourth aspect of the present invention in which the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler and magnetic metal particles containing iron as a main component or magnetic alloy particles containing iron as a main component are used as magnetic particles, has a coercive force value of usually 800 to 3,500 Oe (63.7 to 278.5 kA/m), preferably 900 to 3,500 Oe (71.6 to 278.5 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 190 to 300%, preferably 195 to 300%; a surface roughness Ra (of the coating film) of usually not more than 8.5 nm, preferably 2.0 to 8.0 nm, more preferably 2.0 to 7.5 nm; a Young's modulus (relative value to a commercially available video tape: and AV T-120 produced by Victor Company of Japan, Limited) of usually 124 to 160, preferably 126 to 160; a linear absorption (of the coating film) of usually 1.20 to 5.00 μm

−1

, preferably 1.30 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

10

Ω/cm

2

, preferably not more than 7.5×10

9

Ω/cm

2

, more preferably not more than 5.0×10

9

Ω/cm

2

.

As to the electromagnetic performance of the magnetic recording medium of the first and third aspects in the present invention in which the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler, in the case where magnetic particles having a coercive force value of not less than 250 Oe (19.9 kA/m) and less than 800 Oe (63.7 kA/m) is used therein, the output at a recording frequency of 4 MHz is usually not less than +1.0 dB, preferably not less than +1.5 dB when the output is expressed by a relative value on the basis of a reference tape produced by the same method as used in the present invention except that alumina is used as a filler in an amount of 7.0 parts by weight based on 100 parts by weight of the magnetic particles; and in the case where magnetic particles having a coercive force value of 800 to 4,000 Oe (63.7 to 318.3 kA/m) are used in such a magnetic recording medium, the output at a recording frequency of 7 MHz is usually not less than +1.0 dB, preferably not less than +1.5 dB.

As to the electromagnetic performance of the magnetic recording medium of the second and fourth aspects in the present invention in which the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler, in the case where magnetic particles having a coercive force value of not less than 250 Oe (19.9 kA/m) and less than 800 Oe (63.7 kA/m) are used therein, the output at a recording frequency of 4 MHz is usually not less than +1.5 dB, preferably not less than +2.0 dB when also expressed by the same relative value as described above; and in the case where magnetic particles having a coercive force value of 800 to 4,000 Oe (63.7 to 318.3 kA/m) are used, the output at a recording frequency of 7 MHz is usually not less than +1.5 dB, preferably not less than +2.0 dB.

As to the durability of the magnetic recording medium using as a filler the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat, the running durability time thereof is usually not less than 20 minutes, preferably not less than 22 minutes, more preferably not less than 24 minutes when measured by the below-described method. Further, the degree (rank) of contamination of the magnetic head under the above condition is usually B or A, preferably A.

As to the durability of the magnetic recording medium using as a filler the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat, the running durability time thereof is usually not less than 22 minutes, preferably not less than 24 minutes, more preferably not less than 26 minutes. Further, the degree (rank) of contamination of the magnetic head under the above condition is usually B or A, preferably A.

The magnetic recording medium according to the fifth aspect of the present invention in which the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler and the non-magnetic undercoating layer is disposed between the non-magnetic base film and the magnetic recording film, has a coercive force value of usually 250 to 4,000 Oe (19.9 to 318.3 kA/m), preferably 300 to 4,000 Oe (23.9 to 318.3 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 165 to 300%, preferably 170 to 300%; a surface roughness Ra (of the coating film) of usually not more than 9.5 nm, preferably 2.0 to 9.0 nm, more preferably 2.0 to 8.5 nm; a linear absorption (of the coating film) of usually 1.30 to 5.00 μm

−1

, preferably 1.35 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

9

Ω/cm

2

, preferably not more than 7.5×10

8

Ω/cm

2

, more preferably not more than 5.0×10

8

Ω/cm

2

.

The magnetic recording medium according to the sixth aspect of the present invention in which the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler and the non-magnetic undercoating layer is disposed between the non-magnetic base film and the magnetic recording film, has a coercive force value of usually 250 to 4,000 Oe (19.9 to 318.3 kA/m), preferably 300 to 4,000 Oe (23.9 to 318.3 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 170 to 300%, preferably 175 to 300%; a surface roughness Ra (of the coating film) of usually not more than 9.0 nm, preferably 2.0 to 8.5 nm, more preferably 2.0 to 8.0 nm; a linear absorption (of the coating film) of usually 1.35 to 5.00 μm

−1

, preferably 1.40 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

9

Ω/cm

2

, preferably not more than 7.5×10

8

Ω/cm

2

, more preferably not more than 5.0×10

8

Ω/cm

2

.

The magnetic recording medium according to the seventh aspect of the present invention in which the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler, magnetic metal particles containing iron as a main component or magnetic alloy particles containing iron as a main component are used as magnetic particles and the non-magnetic undercoating layer is disposed between the non-magnetic base film and the magnetic recording film, has a coercive force value of usually 800 to 3,500 Oe (63.7 to 278.5 kA/m), preferably 900 to 3,500 Oe (71.6 to 278.5 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 190 to 300%, preferably 195 to 300%; a surface roughness Ra (of the coating film) of usually not more than 8.5 nm, preferably 2.0 to 8.0 nm, more preferably 2.0 to 7.5 nm; a linear absorption (of the coating film) of usually 1.30 to 5.00 μm

−1

, preferably 1.35 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

9

Ω/cm

2

, preferably not more than 7.5×10

8

Ω/cm

2

, more preferably not more than 5.0×10

8

Ω/cm

2

.

The magnetic recording medium according to the eighth aspect of the present invention in which the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat are used as a filler, magnetic metal particles containing iron as a main component or magnetic alloy particles containing iron as a main component are used as magnetic particles and the non-magnetic undercoating layer is disposed between the non-magnetic base film and the magnetic recording film, has a coercive force value of usually 800 to 3,500 Oe (63.7 to 278.5 kA/m), preferably 900 to 3,500 Oe (71.6 to 278.5 kA/m); a squareness (residual magnetic flux density Br/saturation magnetic flux density Bm) of usually 0.85 to 0.95, preferably 0.86 to 0.95; a gloss (of the coating film) of usually 195 to 300%, preferably 200 to 300%; a surface roughness Ra (of the coating film) of usually not more than 8.0 nm, preferably 2.0 to 7.5 nm, more preferably 2.0 to 7.0 nm; a linear absorption (of the coating film) of usually 1.35 to 5.00 μm

−1

, preferably 1.40 to 5.00 μm

−1

; and a surface resistivity (of the coating film) of usually not more than 1.0×10

9

Ω/cm

2

, preferably not more than 7.5×10

8

Ω/cm

2

, more preferably not more than 5.0×10

8

Ω/cm

2

.

As to the electromagnetic performance of the magnetic recording medium of the fifth and seventh aspects in the present invention, which has a non-magnetic undercoat layer and contains as a filler the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat, in the case where magnetic particles having a coercive force value of not less than 250 Oe (19.9 kA/m) and less than 1,200 Oe (95.5kA/m) is used therein, the output value at a recording frequency of 4 MHz is usually not less than +1.2 dB, preferably not less than +1.7 dB; and in the case where magnetic particles having a coercive force value of 1,200 to 4,000 Oe (95.5 to 318.3 kA/m) are used in such a magnetic recording medium, the output value at a recording frequency of 7 MHz is usually not less than +1.2 dB, preferably not less than +1.7 dB.

As to the electromagnetic performance of the magnetic recording medium of the sixth and eighth aspects in the present invention, which has a non-magnetic undercoat layer and contains as a filler the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat, in the case where magnetic particles having a coercive force value of not less than 250 Oe (19.9 kA/m) and less than 1,200 Oe (95.5kA/m) is used therein, the output value at a recording frequency of 4 MHz is usually not less than +1.7 dB, preferably not less than +2.2 dB; and in the case where magnetic particles having a coercive force value of 1,200 to 4,000 Oe (95.5 to 318.3 kA/m) are used in such a magnetic recording medium, the output value at a recording frequency of 7 MHz is usually not less than +1.7 dB, preferably not less than +2.2 dB.

As to the durability of the magnetic recording medium of the fifth and seventh aspects in the present invention which has a non-magnetic undercoat layer and uses as a filler the black composite hematite particles coated with no hydroxides and/or oxides of aluminum and/or silicon coat, the running durability time is usually not less than 24 minutes, preferably not less than 25 minutes, more preferably not less than 26 minutes. Further, the degree (rank) of contamination of the magnetic head under the above condition is usually B or A, preferably A.

As to the durability of the magnetic recording medium of the sixth and eighth aspects in the present invention which has a non-magnetic undercoat layer and uses as a filler the black composite hematite particles coated with hydroxides and/or oxides of aluminum and/or silicon coat, the running durability time is usually not less than 25 minutes, preferably not less than 26 minutes, more preferably not less than 27 minutes. Further, the degree (rank) of contamination of the magnetic head under the above condition is usually B or A, preferably A.

Next, the process for producing the black composite hematite particles according to the present invention, is described.

The coating of the hematite particles as core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds, may be conducted (i) by mechanically mixing and stirring the hematite particles as core particles together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds; or (ii) by mechanically mixing and stirring both the components together while spraying the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds onto the hematite particles as core particles. In these cases, substantially whole amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds added can be applied onto the surfaces of the hematite particles as core particles.

In order to uniformly coat the surfaces of the hematite particles as core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds, it is preferred that the hematite particles as core particles are preliminarily diaggregated by using a pulverizer.

As apparatus (a) for mixing and stirring the core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds to form the coating layer thereof, and (b) for mixing and stirring carbon black fine particles with the particles whose surfaces are coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds to form the carbon black coat, there may be preferably used those apparatus capable of applying a shear force to the particles, more preferably those apparatuses capable of conducting the application of shear force, spaturate force and compressed force at the same time.

As such apparatuses, there may be exemplified wheel-type kneaders, ball-type kneaders, blade-type kneaders, roll-type kneaders or the like. Among them, wheel-type kneaders are preferred.

Specific examples of the wheel-type kneaders may include an edge runner (equal to a mix muller, a Simpson mill or a sand mill), a multi-mull, a Stotz mill, a wet pan mill, a Conner mill, a ring muller, or the like. Among them, an edge runner, a multi-mull, a Stotz mill, a wet pan mill and a ring muller are preferred, and an edge runner is more preferred.

Specific examples of the ball-type kneaders may include a vibrating mill or the like. Specific examples of the blade-type kneaders may include a Henschel mixer, a planetary mixer, a Nawter mixer or the like. Specific examples of the roll-type kneaders may include an extruder or the like.

In addition, by conducting the above-mentioned mixing or stirring treatment (a) of the hematite particles as core particles together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds, at least a part of the alkoxysilane compounds and the fluoroalkylsilane compounds coated on the hematite particles as core particles may be changed to the organosilane compounds and fluoroalkyl organosilane compounds, respectively.

In order to coat the surfaces of the core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds as uniformly as possible, the conditions of the above mixing or stirring treatment may be appropriately controlled such that the linear load is usually 2 to 200 Kg/cm (19.6 to 1960 N/cm), preferably 10 to 150 Kg/cm (98 to 1470 N/cm), more preferably 15 to 100 Kg/cm (147 to 980 N/cm); and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.

The amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds added, is preferably 0.15 to 45 parts by weight based on 100 parts by weight of the hematite particles as core particles. When the amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds added is less than 0.15 part by weight, it may become difficult to form the carbon black coat in such an amount enough to improve the blackness of the obtained black composite hematite particles.

On the other hand, when the amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds added is more than 45 parts by weight, a sufficient amount of the carbon black coat can be formed on the surface of the coating layer, but it is meaningless because the blackness of the composite particles cannot be further improved by using such an excess amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds.

Next, the carbon black fine particles are added to the hematite particles coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds, and the resultant mixture is continuously mixed and stirred to form a carbon black coat on the surfaces of the coating layer composed of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds.

In addition by conducting the above-mentioned mixing or stirring treatment (b) of the carbon black fine particles together with the hematite particles coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds, at least a part of the alkoxysilane compounds and the fluoroalkylsilane compounds coated on the hematite particles may be changed to the organosilane compounds and fluoroalkyl organosilane compounds, respectively.

In the case where the alkoxysilane compounds and the fluoroalkylsilane compounds are used as the coating compound, after the carbon black coat is formed on the surface of the coating layer, the resultant black composite hematite particles may be dried or heat-treated, for example, at a temperature of usually 40 to 200° C., preferably 60 to 150° C. for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours, thereby forming a coating layer composed of the organosilicon compounds (1) and the fluoroalkyl organosilicon compounds (3), respectively.

It is preferred that the carbon black fine particles are added little by little and slowly, especially about 5 to 60 minutes.

In order to form carbon black coat onto the coating layer composed of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds as uniformly as possible, the conditions of the above mixing or stirring treatment can be appropriately controlled such that the linear load is usually 2 to 200 Kg/cm (19.6 to 1960 N/cm), preferably 10 to 150 Kg/cm (98 to 1470 N/cm), more preferably 15 to 100 Kg/cm (147 to 980 N/cm); and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.

The amount of the carbon black fine particles added, is preferably 1 to 30 parts by weight based on 100 parts by weight of the hematite particles as core particles. When the amount of the carbon black fine particles added is less than 1 part by weight, it may become difficult to form the carbon black coat in such an amount enough to improve the blackness of the obtained composite particles. On the other hand, when the amount of the carbon black fine particles added is more than 30 parts by weight, a sufficient blackness of the resultant composite particles can be obtained, but the carbon black tend to be desorbed from the surface of the coating layer because of too large amount of the carbon black adhered, resulting in deteriorated dispersibility in a vehicle.

At least a part of the surface of the hematite particles as core particles may be coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon, in advance of mixing and stirring with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, the terminal-modified polysiloxanes or the fluoroalkylsilane compounds.

The coating of the hydroxides and/or oxides of aluminum and/or silicon may be conducted by adding an aluminum compound, a silicon compound or both the compounds to a water suspension in which the hematite particles are dispersed, followed by mixing and stirring, and further adjusting the pH of the suspension, if required, thereby coating the surfaces of the hematite particles with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon. The thus obtained particles coated with the hydroxides and/or oxides of aluminum and/or silicon are then filtered out, washed with water, dried and pulverized. Further, the particles coated with the hydroxides and/or oxides of aluminum and/or silicon may be subjected to post-treatments such as deaeration treatment and compaction treatment.

As the aluminum compounds, there may be exemplified aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride or aluminum nitrate, alkali aluminates such as sodium aluminate, or the like.

The amount of the aluminum compound added is 0.01 to 50.00% by weight (calculated as Al) based on the weight of the hematite particles. When the amount of the aluminum compound added is less than 0.01% by weight, it may be difficult to sufficiently coat the surfaces of the hematite particles with hydroxides or oxides of aluminum or silicon, thereby failing to improve the dispersibility in a vehicle. On the other hand, when the amount of the aluminum compound added is more than 50.00% by weight, the coating effect is saturated and, therefore, it is meaningless to add such an excess amount of the aluminum compound.

As the silicon compounds, there may be exemplified water glass #3, sodium orthosilicate, sodium metasilicate, colloidal silica or the like.

The amount of the silicon compound added is 0.01 to 50.00% by weight (calculated as SiO

2

) based on the weight of the hematite particles. When the amount of the silicon compound added is less than 0.01% by weight, it may be difficult to sufficiently coat the surfaces of the hematite particles with hydroxides or oxides of silicon, thereby failing to improve the dispersibility in a vehicle. On the other hand, when the amount of the silicon compound added is more than 50.00% by weight, the coating effect is saturated and, therefore, it is meaningless to add such an excess amount of the silicon compound.

In the case where both the aluminum and silicon compounds are used in combination for the coating, the total amount of the aluminum and silicon compounds added is preferably 0.01 to 50.00% by weight (calculated as a sum of Al and SiO

2

) based on the weight of the hematite particles.

Next, the process for producing the magnetic recording medium according to the present invention is described.

The magnetic recording medium according to the first aspect of the present invention can be produced by an ordinary method, i.e., by coating the surface of the non-magnetic base film with a magnetic coating composition comprising magnetic particles, a binder resin, black composite hematite particles as a filler and a solvent to form a magnetic recording layer thereon, and then magnetically orienting the magnetic recording layer.

The magnetic recording medium according to the fifth aspect of the present invention can be produced by an ordinary method, i.e., by coating the surface of the non-magnetic base film with a non-magnetic coating composition comprising non-magnetic particles, a binder resin and a solvent to form a coating film thereon; drying the coating film to form a non-magnetic undercoat layer; coating the surface of the non-magnetic undercoat layer with a magnetic coating composition comprising magnetic particles, a binder resin, black composite hematite particles and a solvent to form a magnetic recording layer thereon, and then magnetically orienting the magnetic recording layer.

Upon kneading and dispersing the non-magnetic coating composition and magnetic coating composition, as kneaders, there may be used, for example, twin-screw kneader, twin-screw extruder, pressure kneader, twin-roll mill, triple-roll mill or the like; and as dispersing devices, there may be used ball mill, sand grinder, attritor, disper, homogenizer, ultrasonic dispersing device or the like.

The coating of the non-magnetic coating composition and magnetic coating composition may be conducted using gravure coater, reverse-roll coater, slit coater, die coater or the like. The thus obtained coating film may be magnetically oriented using counter magnet, solenoid magnet or the like.

As the solvents, there may be exemplified those ordinarily used for the production of conventional magnetic recording media such as methyl ethyl ketone, toluene, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran or a mixture thereof.

The total amount of the solvent(s) used in the non-magnetic coating composition or magnetic coating composition is 65 to 1,000 parts by weight based on 100 parts by weight of the non-magnetic particles or magnetic particles. When the amount of the solvent used is less than 65 parts by weight, the viscosity of the obtained non-magnetic coating composition or magnetic coating composition may be too high, so that it is difficult to coat such a composition. When the amount of the solvent used is more than 1,000 parts by weight, the amount of the solvent vaporized upon coating may be too large, resulting in industrial disadvantages.

In the case where the black composite hematite particles having an average diameter of 0.08 to 1.0 μm and comprising hematite particles as core particles which may be coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon; a coating layer formed on surface of each core particle and comprising an organosilicon compound; and a carbon black coat formed on the organosilicon coating, are used as a black filler to be incorporated into the magnetic recording layer, there is obtained the magnetic recording medium capable of exhibiting not only an excellent durability and a good electromagnetic performance, but also a low light transmittance and a small surface resistivity.

The reason why the magnetic recording medium according to the present invention has an excellent durability and a good electromagnetic performance, is considered as follows. That is, due to the fact that the amount of carbon black desorbed from the surface of each black composite hematite particle is very small, respective components present in the system, especially the magnetic particles are well dispersed without being adversely affected by carbon black. Further, since carbon black coat is formed onto the surface of each black composite hematite particle, irregularities are formed thereon. Therefore, the magnetic particles are prevented from contacting with each other because such black composite hematite particles having surface irregularities are interposed therebetween, so that the magnetic particles tends to be packed with a high density in the magnetic recording layer.

Especially, in the case of using the alkoxysilane compounds or the fluoroalkylsilane compounds, metalloxane bonds (≡Si—O—M, wherein M represents a metal atom contained in the hematite particle as core particle, such as Si, Al or Fe) are formed between the metal elements such as Si, Al or Fe which are contained within the hematite particle or present at the surface thereof, and alkoxy groups of the alkoxysilane compounds or the fluoroalkylsilane compounds on which the carbon black coat is formed, so that the organosilicon compounds onto which the carbon black coat is formed, can be more strongly bonded to the surface of the hematite particle. Further, in the case of using the polysiloxanes or modified polysiloxanes, the functional groups in the polysiloxanes or modified polysiloxanes onto which the carbon black coat is formed, are strongly bonded to the surface of the hematite particle.

The reason why the magnetic recording medium according to the present invention exhibits a low light transmittance, is considered as follows. That is, the low light transmittance is attributed to the excellent blackness of the black composite hematite particles contained in the magnetic recording layer. More specifically, in the black composite hematite particles of the present invention, carbon black fine particles which behave as an agglomarated matter caused by usually fine particles, are adhered on the surfaces of the hematite particles through the organosilicon compounds, so that the carbon black coat is uniformly and densely formed on the surface thereof. Therefore, the effect and function of the carbon black are more remarkably exhibited.

The reason why the magnetic recording medium according to the present invention exhibits a small surface resistivity, is considered as follows. That is, due to the fact that the black composite hematite particles are uniformly dispersed in the magnetic recording layer, the carbon black coat uniformly and densely formed onto the surfaces thereof is continuously contacted with each other.

In the magnetic recording medium according to the present invention, as a black filler, there are used the black composite hematite particles capable of preventing the deterioration of electromagnetic performance even when added in an amount sufficient to enhance the durability, and of reducing an amount of carbon black fine particles added together therewith, due to sufficient blackness thereof. As a result, the magnetic recording medium has an excellent durability and a good electromagnetic performance and, therefore, is suitable for high-density recording.

Since the amount of carbon black fine particles used is very small, the magnetic recording medium according to the present invention is favorable from standpoints of safety and hygiene.

The black composite hematite particles of the present invention have an excellent dispersibility in vehicle upon the production of a magnetic coating composition and, therefore, are excellent in handling and processing properties, thereby providing industrial and economical advantages.

Further, the magnetic recording medium having the non-magnetic undercoating layer, since the black composite hematite particles having an excellent blackness and a low volume resistivity are used as a filler, has a smooth surface, a low light transmittance and a small surface resistivity. Therefore, the magnetic recording medium of the present invention is more suitable as those for high-density recording.

EXAMPLES

The present invention is described in more detail by Examples and Comparative Examples, but the Examples are only illustrative and, therefore, not intended to limit the scope of the present invention.

Various properties were measured by the following methods.

(1) The average particle diameter, the average major axial diameter and average minor axial diameter of hematite particles, black composite hematite particles and carbon black fine particles were respectively expressed by the average of values (measured in a predetermined direction) of about 350 particles which were sampled from a micrograph obtained by magnifying an original electron micrograph by four times (×80,000) in each of the longitudinal and transverse directions.

(2) The aspect ratio of the particles was expressed by the ratio of average major axial diameter to average minor axial diameter thereof. The plate ratio of the particles was expressed by the ratio of the average plate surface diameter to the average thickness thereof.

(3) The geometrical standard deviation of particle diameter was expressed by values obtained by the following method. That is, the particle sizes were measured from the above magnified electron micrograph. The actual particle sizes and the number of the particles were calculated from the measured values. On a logarithmic normal probability paper, the particle sizes were plotted at regular intervals on the abscissa-axis and the accumulative number (under integration sieve) of particles belonging to each interval of the particle sizes were plotted by percentage on the ordinate-axis by a statistical technique.

The particle sizes corresponding to the number of particles of 50% and 84.13%, respectively, were read from the graph, and the geometrical standard deviation was calculated from the following formula:

Geometrical standard deviation={particle sizes corresponding to 84.13% under integration sieve}/{particle sizes (geometrical average diameter) corresponding to 50% under integration sieve}

The closer to 1 the geometrical standard deviation value, the more excellent the particle size distribution.

(4) The specific surface area was expressed by the value measured by a BET method.

(5) The amount of Mn, Al and Si which were present within hematite particles or black composite hematite particles, or on surfaces thereof, and the amount of Si contained in the organosilicon compounds, were measured by a fluorescent X-ray spectroscopy device 3063 (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to JIS K0119 “General rule of fluorescent X-ray analysis”.

(6) The amount of carbon black coat formed on the surface of the black composite hematite particles was measured by “Horiba Metal, Carbon and Sulfur Analyzer EMIA-2200 Model” (manufactured by Horiba Seisakusho Co., Ltd.).

(7) The thickness of carbon black coat formed on the surfaces of the black composite hematite particles is expressed by the value which was obtained by first measuring an average thickness of carbon black coat formed onto the surfaces of the particles on a photograph (×5,000,000) obtained by magnifying (ten times) a micrograph (×500,000) produced at an accelerating voltage of 200 kV using a transmission-type electron microscope (JEM-2010, manufactured by Japan Electron Co., Ltd.), and then calculating an actual thickness of carbon black coat formed from the measured average thickness.

(8) The desorption percentage (T %) of carbon black desorbed from the black composite hematite particles was measured by the following method.

That is, 3 g of the black composite hematite particles and 40 ml of ethanol were placed in a 50-ml precipitation pipe and then was subjected to ultrasonic dispersion for 20 minutes. Thereafter, the obtained dispersion was allowed to stand for 120 minutes, and separated the carbon black desorbed from the black composite hematite particles on the basis of the difference in specific gravity therebetween. Next, the thus separated black composite hematite particles were mixed again with 40 ml of ethanol, and the obtained mixture was further subjected to ultrasonic dispersion for 20 minutes. Thereafter, the obtained dispersion was allowed to stand for 120 minutes, thereby separating the black composite hematite particles and carbon black desorbed, from each other. The thus separated black composite hematite particles were dried at 100° C. for one hour, and then the carbon content thereof was measured by the “Horiba Metal, Carbon and Sulfur Analyzer EMIA-2200 Model” (manufactured by HORIBA SEISAKUSHO CO., LTD.). The desorption percentage (T %) was calculated according to the following formula:

T

(%)={(

W

a

−W

e

)/

W

a

}×100

wherein W

a

represents an amount of carbon black initially formed on the black composite hematite particles; and W

e

represents an amount of carbon black which still remains on the black composite hematite particles after the above desorption test.

The closer to zero the desorption percentage (T %), the smaller the amount of carbon black desorbed from the black composite hematite particles.

(9) The blackness of the hematite particles and black composite hematite particles was measured by the following method. That is, 0.5 g of sample particles and 1.5 ml of castor oil were intimately kneaded together by a Hoover's muller to form a paste. 4.5 g of clear lacquer was added to the obtained paste and was intimately kneaded to form a paint. The obtained paint was applied on a cast-coated paper by using a 6-mil (150 μm) applicator to produce a coating film piece (having a film thickness of about 30 μm). The thus obtained coating film piece was measured according to JIS Z 8729 by a multi-light source spectrographic colorimeter MSC-IS-2D (manufactured by Suga Testing Machines Manufacturing Co., Ltd.) to determine an L* value of calorimetric indices thereof. The blackness was expressed by the L* value measured.

Here, the L* value represents a lightness, and the smaller the L* value, the more excellent the blackness.

(10) The volume resistivity of the hematite particles and the black composite hematite particles was measured by the following method.

That is, first, 0.5 g of a sample particles to be measured was weighted, and press-molded at 140 Kg/cm

2

(13,720 kPa) using a KBr tablet machine (manufactured by Simazu Seisakusho Co., Ltd.), thereby forming a cylindrical test piece.

Next, the thus obtained cylindrical test piece was exposed to an atmosphere maintained at a temperature of 25° C. and a relative humidity of 60% for 12 hours. Thereafter, the cylindrical test piece was set between stainless steel electrodes, and a voltage of 15V was applied between the electrodes using a Wheatstone bridge (model 4329A, manufactured by Yokogawa-Hokushin Denki Co., Ltd.) to measure a resistance value R (Ω).

The cylindrical test piece was measured with respect to an upper surface area A (cm

2

) and a thickness t

0

(cm) thereof. The measured values were inserted into the following formula, thereby obtaining a volume resistivity X (Ω·cm).

X

(Ω·cm)=

R

×(

A

/t

0

)

(11) The viscosity of the coating composition was obtained by measuring the viscosity of the coating composition at 25° C. at a shear rate D of 1.92 sec

−1

by using “E type viscometer EMD-R” (manufactured by Tokyo Keiki, Co., Ltd.).

(12) The magnetic properties of the magnetic particles and magnetic recording medium were measured under an external magnetic field of 795.8 kA/m (10 kOe) by “Vibration Sample Magnetometer VSM-3S-15 (manufactured by Toei Kogyo, Co., Ltd.)”.

(13) The gloss of the surface of the coating film of the magnetic recording layer was measured at an angle of incidence of 45° by “glossmeter UGV-5D” (manufactured by Suga Shikenki, Co., Ltd.).

(14) The surface roughness Ra is expressed by the average value of the center-line average roughness of the profile curve of the surface of the coating film of the magnetic recording layer by using “Surfcom-575A” (manufactured by Tokyo Seimitsu Co., Ltd.).

(15) The light transmittance is expressed by the linear adsorption coefficient calculated by substituting the light transmittance measured by using “UV-Vis Recording Spectrophotometer UV-2100” (manufactured by Shimazu Seisakusho, Ltd.) for the following formula. The larger the value, the more difficult it is for the magnetic recording medium to transmit light:

Linear adsorption coefficient (μm

−1

) {l n (l/t)}/FT wherein t represents a light transmittance (−) at λ=900 nm, and FT represents thickness (μm) of the coating film used for the measurement.

(16) The electromagnetic performance was expressed by a relative value of an output of a magnetic recording medium (tape) with respect to that of a reference tape which outputs were measured by reproducing signals recorded at a frequency of 4 MHz or 7 MHz by setting a relative speed between magnetic tape and magnetic head to 5.8 m/s, using a DRUM TESTER BX-3168 (manufactured by BELDEX Co., Ltd.).

The reference tape was produced by the same method as used in the present invention except that the black composite hematite particles in the magnetic coating composition were replaced with alumina (tradename: AKP-30, produced by Sumitomo Kagaku Co., Ltd.), and the alumina was added in an amount of 7.0 parts by weight based on 100 parts by weight of the magnetic particles.

(17) The durability of the magnetic medium was evaluated by the following running durability and the head contamination.

The running durability was evaluated by the actual operating time under the conditions that the load was 9.6 N (200 gw) and the relative speed of the head and the tape was 16 m/s by using “Media Durability Tester MDT-3000” (manufactured by Steinberg Associates). The longer the actual operating time, the higher the running durability.

(18) The head contamination was evaluated by visually observing the magnetic head after running the magnetic tape under a load of 19.6 N (200 gw) for 30 minutes by setting a relative speed between the magnetic tape and the magnetic head to 16 m/s, using a MEDIA DURABILITY TESTER MDT-3000 (manufactured by Steinberg Associates Co. Ltd.). The evaluation results were classified into the following four ranks. The A rank represents the smallest head contamination.

A: Not contaminated

B: Slightly contaminated

C: Contaminated

D: Severely contaminated

(19) The friction coefficient of the magnetic recording medium was determined by measuring a frictional force between a surface of the magnetic tape and a metal surface (aluminum polished surface) using a tensile tester TENSILON (manufactured by Shimadzu Seisakusho Co., Ltd.), and expressed by the ratio of the measured value to the load.

(20) The surface resistivity of the coating film of the magnetic recording layer was measured by the following method. That is, the coating film to be measured was exposed to the environment maintained at a temperature of 25° C. and a relative humidity of 60%, for not less than 12 hours. Thereafter, the coating film was slit into 6 mm width, and the slit coating film was placed on two metal electrodes having a width of 6.5 mm such that a coating surface thereof was contacted with the electrodes. 1.7 N (170 gw) were respectively suspended at opposite ends of the coating film so as to bring the coating film into close contact with the electrodes. D.C. 500 V was applied between the electrodes, thereby measuring the surface resistivity of the coating film.

(21) The strength of the non-magnetic undercoat layer was expressed the Young's modulus obtained by “Autograph” (produced by Shimazu Seisakusho Co., Ltd.). The Young's modulus was expressed by the ratio of the Young's modulus of the coating film to that of a commercially available video tape “AV T-120” (produce by Victor Company of Japan, Limited). The higher the relative value, the more favorable.

(22) The thickness of each of the non-magnetic base film, the non-magnetic undercoat layer and the magnetic recording layer constituting the magnetic recording medium was measured in the following manner by using “Digital Electronic Micrometer R351C” (manufactured by Anritsu Corp.) The thickness (A) of a base film was first measured. Similarly, the thickness (B) (B=the sum of the thicknesses of the base film and the non-magnetic undercoat layer) of a non-magnetic substrate obtained by forming a non-magnetic undercoat layer on the base film was measured. Furthermore, the thickness (C) (C=the sum of the thicknesses of the base film, the non-magnetic undercoat layer and the magnetic recording layer) of a magnetic recording medium obtained by forming a magnetic recording layer on the non-magnetic substrata was measured. The thickness of the non-magnetic undercoat layer is expressed by (B)−(A), and the thickness of the magnetic recording layer is expressed by (C)−(B).

Example 1

Production of Black Non-magnetic Composite Particles

20 kg of Mn-containing hematite particles shown in the electron micrograph (×20,000) of

FIG. 1

(average particle size: 0.30 μm; geometrical standard deviation value: 1.46; BET specific surface area value: 3.6 m

2

/g; Mn content: 13.3% by weight (calculated as Mn) based on the weight of the particle; blackness (L* value): 22.6; volume resistivity: 2.0×10

7

Ω·cm), were deagglomerated in 150 liters of pure water using a stirrer, and further passed through a “TK pipeline homomixer” (tradename, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times, thereby obtaining a slurry containing the Mn-containing hematite particles.

Successively, the obtained slurry containing the Mn-containing hematite particles was passed through a transverse-type sand grinder (tradename “MIGHTY MILL MHG-1.5L”, manufactured by Inoue Seisakusho Co., Ltd.) five times at an axis-rotating speed of 2,000 rpm, thereby obtaining a slurry in which the Mn-containing hematite particles were dispersed.

The particles in the obtained slurry which remained on a sieve of 325 meshes (mesh size: 44 μm) was 0%. The slurry was filtered and washed with water, thereby obtaining a filter cake containing the Mn-containing hematite particles. After the obtained filter cake containing the Mn-containing hematite particles was dried at 120° C., 11.0 kg of the dried particles were then charged into an edge runner “MPLTV-2 Model” (tradename, manufactured by Matsumoto Chuzo Tekkosho Co., Ltd.), and mixed and stirred at 294 N/cm (30 Kg/cm) and a stirring speed of 22 rpm for 30 minutes, thereby lightly deagglomerating the particles. 220 g of methyl triethoxysilane (tradename: “TSL8123”, produced by TOSHIBA SILICONE CO., LTD.) was mixed and diluted with 200 ml of ethanol to obtain a methyl triethoxysilane solution. The methyl triethoxysilane solution was added to the deagglomerated Mn-containing hematite particles under the operation of the edge runner. The Mn-containing hematite particles were continuously mixed and stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 45 minutes.

Next, 1,100 g of carbon black fine particles A shown in the electron micrograph (×20,000) of

FIG. 2

(particle shape: granular shape; average particle size: 0.022 μm; geometrical standard deviation value: 1.68; BET specific surface area value: 134 m

2

/g; and blackness (L* value): 16.6; pH value: 3.4; DBP oil absorption: 89 ml/100 g) were added to the Mn-containing hematite particles coated with methyl triethoxysilane for 10 minutes while operating the edge runner. Further, the mixed particles were continuously stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 60 minutes to form the carbon black coat on the coating layer composed of methyl triethoxysilane, thereby obtaining black composite hematite particles.

The obtained black composite hematite particles were heat-treated at 105° C. for 60 minutes by using a drier to evaporate water, ethanol or the like which were remained on surfaces of the black composite hematite particles. As shown in the electron micrograph (×20,000) of

FIG. 3

, the resultant black composite hematite particles had an average particle diameter of 0.31 μm. In addition, the black composite hematite particles showed a geometrical standard deviation value of 1.46, a BET specific surface area value of 9.3 m

2

/g, a blackness (L* value) of 17.5 and a volume resistivity of 9.2×10

3

Ω·cm. The desorption percentage of the carbon black from the black composite hematite particles was 6.7%. The amount of a coating organosilane compound produced from methyl triethoxysilane was 0.30% by weight (calculated as Si). The amount of the carbon black coat formed on the coating layer composed of the organosilane compound produced from methyl triethoxysilane is 9.05% by weight (calculated as C) based on the weight of the black composite hematite particles (corresponding to 10 parts by weight based on 100 parts by weight of the Mn-containing hematite particles). The thickness of the carbon black coat formed was 0.0024 μm. Since no carbon black was recognized on the electron photograph of

FIG. 3

, it was confirmed that a whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed of the organosilane compound produced from methyl triethoxysilane.

For a comparative purpose, the Mn-containing hematite particles not coated with methyl triethoxysilane and the carbon black fine particles were mixed and stirred together by an edge runner in the same manner as described above, thereby obtaining treated particles as shown in the electron photograph (×20,000) of FIG.

4

. As shown in

FIG. 4

, it was recognized that the carbon black fine particles were not adhered on the Mn-containing hematite particles, and the individual particles were present separately.

Production of Magnetic Recording Medium

100 parts by weight of Co-coated acicular magnetite particles (average major axial diameter: 0.24 μm, aspect ratio: 7.1, BET specific surface area: 31.3 m

2

/g, coercive force value: 714 Oe (56.8 kA/m), saturation magnetization value: 83.1 emu/g (83.1 Am

2

/kg), Co content: 2.26 wt. %), 10.0 parts by weight of vinyl chloride-vinyl acetate copolymer resin (tradename: MR-110, produced by Nippon Zeon Co., Ltd.), 23.3 parts by weight of cyclohexanone, 10.0 parts by weight of methyl ethyl ketone, 1.0 part by weight of carbon black fine particles (produced by Mitsubishi Chemical Corp., average diameter: 26 nm, BET specific surface area: 130 m

2

/g) and 7.0 parts by weight of the above obtained black composite hematite particles were kneaded together for 20 minutes using a kneader. The obtained kneaded material was diluted by adding 79.6 parts by weight of toluene, 110.2 parts by weight of methyl ethyl ketone and 17.8 parts by weight of cyclohexanone thereto, and then the resultant mixture was mixed and dispersed for 3 hours by a sand grinder, thereby obtaining a dispersion.

The obtained dispersion was mixed with 33.3 parts by weight of a solution prepared by dissolving 10.0 parts weight (solid content) of polyurethane resin (tradename: TI-1075, produced by Sanyo Kasei Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone and cyclohexanone (weight ratio: 1/1), and the resultant mixture was mixed and dispersed for 30 minutes by a sand grinder. Thereafter, the obtained dispersion was passed through a filter having a mesh size of 1 μm. The obtained filter cake was mixed while stirring with 12.1 parts by weight of a solution prepared by dissolving 1.0 part by weight of myristic acid and 3.0 parts by weight of butyl stearate in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), and with 15.2 parts by weight of a solution prepared by dissolving 5.0 parts by weight of trifunctional low molecular weight polyisocyanate (tradename: E-31, produced by Takeda Yakuhin Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), thereby producing a magnetic coating composition.

The obtained magnetic coating composition had the following composition:

Magnetic particles

100

parts by weight

Vinyl chloride-vinyl

10

parts by weight

acetate copolymer resin

Polyurethane resin

10

parts by weight

Black composite hematite

7.0

parts by weight

particles (filler)

Carbon black fine

1.0

part by weight

particles

Myristic acid

1.0

part by weight

Butyl stearate

3.0

parts by weight

Trifunctional low molecular

5.0

parts by weight

weight polyisocyanate

Cyclohexanone

56.6

parts by weight

Methyl ethyl ketone

141.5

parts by weight

Toluene

85.4

parts by weight

The obtained magnetic coating composition had a viscosity of 2,380 cP.

The thus obtained magnetic coating composition was passed through a filter having a mesh size of 1 μm. Thereafter, the magnetic coating composition was coated on a 14 μm-thick polyester base film using a slit coater having a gap width of 45 μm and the magnetic recording medium obtained was oriented and dried in a magnetic field, thereby forming a magnetic layer having a thickness of 3.9 μm on the base film. The surface of the obtained magnetic layer was calendered and smoothened by an ordinary method, and then the obtained film was slit into a width of ½ inch (1.27 cm). The obtained tape was allowed to stand in a curing oven maintained at 60° C., for 24 hours, and sufficiently cured therein, thereby producing a magnetic tape. The magnetic layer of the obtained magnetic tape had a thickness of 3.4 μm.

The obtained magnetic tape had a coercive force value of 743 Oe (59.1 kA/m), a squareness (Br/Bm) of 0.87, a gloss of 180%, a surface roughness (Ra) of 6.8 nm, a linear absorption of 1.26 μm

−1

and a surface resistivity of 1.2×10

9

Ω/cm

2

. As to the electromagnetic performance of the obtained magnetic tape, the output thereof at a recording frequency of 4 MHz was +2.1 dB. Further, as to the durability of the magnetic tape, the running durability time was not less than 30 minutes, and the head contamination was A.

Meanwhile, the measurement of the electromagnetic performance was conducted using a reference tape 1 described in Tables 8 and 9 hereinafter.

Core Particles 1 to 5:

Various hematite particles were prepared by known methods. The same procedure as defined in Example 1 was conducted by using the thus hematite particles, thereby obtaining deagglomerated hematite particles as core particles.

Various properties of the thus obtained hematite particles are shown in Table 1.

Core Particles 6:

The same procedure as defined in Example 1 was conducted by using 20 kg of the diaggregated Mn-containing hematite particles (core particles 1) and 150 liters of water, thereby obtaining a slurry containing the Mn-containing hematite particles. The pH value of the obtained re-dispersed slurry containing the Mn-containing hematite particles was adjusted to 10.5, and then the concentration of the solid content in the slurry was adjusted to 98 g/liter by adding water thereto. After 150 liters of the slurry was heated to 60° C., 2722 ml of a 1.0 mol/liter NaAlO

2

solution (corresponding to 0.5% by weight (calculated as Al) based on the weight of the Mn-containing hematite particles) was added to the slurry. After allowing the obtained slurry to stand for 30 minutes, the pH value of the slurry was adjusted to 7.5 by using acetic acid. After further allowing the resultant slurry to stand for 30 minutes, the slurry was subjected to filtration, washing with water, drying and pulverization, thereby obtaining the Mn-containing hematite particles whose surface was coated with hydroxides of aluminum.

Main production conditions are shown in Table 2, and various properties of the obtained Mn-containing hematite particles are shown in Table 3.

Core Particles 7 to 10:

The same procedure as defined above for the production of the core particles 6, was conducted except that kinds of core particles and kinds and amounts of additives used in the above surface treatment were changed variously, thereby obtaining surface-treated hematite particles.

The essential treating conditions are shown in Table 2, and various properties of the obtained surface-treated hematite particles are shown in Table 3.

Examples 2 to 11 and Production Comparative Examples 1 to 5

The same procedure as defined in Example 1 was conducted except that kinds of the core particles, addition or non-addition of alkoxysilane, kinds and amounts of alkoxysilane added, treating conditions of an edge runner used in the alkoxysilane-coating process, kinds and amounts of the carbon black fine particles added, and treating conditions of an edge runner used in the process for forming the carbon black coat, were changed variously, thereby obtaining black composite hematite particles. As a result of the observation by an electron microscope, liberated carbon black fine particles were not recognized in the black composite hematite particles obtained in Examples 2 to 11. Therefore, it was confirmed that a substantially whole amount of the carbon black used in Examples 2 to 11 contributed to the formation of the carbon black coat on the coating layer composed of an organosilane compound produced from the alkoxysilane.

Various properties of the carbon black fine particles A to F used, are shown in Table 4. The essential treating conditions are shown in Table 5, and various properties of the obtained black composite hematite particles are shown in Table 6.

Example 12 to 21, Comparative Examples 6 to 12

Production of Magnetic Recording Medium

The same procedure as defined in Example 1 was conducted except for varying the kind of the magnetic particles, the kind and amount of the black composite hematite particles added, thereby producing a magnetic recording medium.

Various properties of the magnetic particles (1) to (6) used, are shown in Table 7.

The shape of the magnetic particles (3) is plate shape. In the Table 7, the average major axis diameter, average minor axis diameter and aspect ratio of the magnetic particles (3) means an average plate surface diameter, an average thickness and a plate ratio (average plate surface diameter/average thickness), respectively.

The main producing conditions of reference tapes using the magnetic particles shown in Table 8 and various properties are shown in Table 9.

The main producing conditions of the magnetic recording medium shown in Table 8 and various properties are shown in Table 9 and 10.

Example 22

Production of Black Non-magnetic Composite Particles

20 kg of Mn-containing hematite particles (average particle size: 0.30 μm; geometrical standard deviation value: 1.46; BET specific surface area value: 3.6 m

2

/g; Mn content: 13.3% by weight (calculated as Mn) based on the weight of the particle; blackness (L* value): 22.6; volume resistivity: 2.0×10

7

Ω·cm), were deagglomerated in 150 liters of pure water using a stirrer, and further passed through a “TK pipeline homomixer” (tradename, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times, thereby obtaining a slurry containing the Mn-containing hematite particles.

Successively, the obtained slurry containing the Mn-containing hematite particles was passed through a transverse-type sand grinder (tradename “MIGHTY MILL MHG-1.5L”, manufactured by Inoue Seisakusho Co., Ltd.) five times at an axis-rotating speed of 2,000 rpm, thereby obtaining a slurry in which the Mn-containing hematite particles were dispersed.

The particles in the obtained slurry which remained on a sieve of 325 meshes (mesh size: 44 μm) was 0%. The slurry was filtered and washed with water, thereby obtaining a filter cake containing the Mn-containing hematite particles. After the obtained filter cake containing the Mn-containing hematite particles was dried at 120° C., 11.0 kg of the dried particles were then charged into an edge runner “MPUV-2 Model” (tradename, manufactured by Matsumoto Chuzo Tekkosho Co., Ltd.), and mixed and stirred at 30 Kg/cm (294 N/cm) and a stirring speed of 22 rpm for 30 minutes, thereby lightly deagglomerating the particles.

110 g of methyl hydrogen polysiloxane (tradename: “TSF484”, produced by TOSHIBA SILICONE CO., LTD.) were added to the deagglomerated Mn-containing hematite particles under the operation of the edge runner. The Mn-containing hematite particles were continuously mixed and stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 45 minutes.

Next, 1,100 g of carbon black fine particles A shown in the electron micrograph (×20,000) of

FIG. 2

(particle shape: granular shape; average particle size: 0.022 μm; geometrical standard deviation value: 1.68; BET specific surface area value: 134 m

2

/g; and blackness (L* value): 16.6; pH value: 3.4; DBP oil absorption: 89 ml/100 g) were added to the Mn-containing hematite particles coated with methyl hydrogen polysiloxane for 10 minutes while operating the edge runner. Further, the mixed particles were continuously stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 60 minutes to form the carbon black coat on the coating layer composed of methyl hydrogen polysiloxane, thereby obtaining black composite hematite particles.

The obtained black composite hematite particles were dried at 105° C. for 60 minutes by using a drier to evaporate water or the like which were remained on surfaces of the black composite hematite particles. As shown in the electron micrograph, the resultant black composite hematite particles had an average particle diameter of 0.32 μm. In addition, the black composite hematite particles showed a geometrical standard deviation value of 1.45, a BET specific surface area value of 8.9 m

2

/g, a blackness (L* value) of 17.9 and a volume resistivity of 8.6×10

3

Ω·cm. The desorption percentage of the carbon black from the black composite hematite particles was 6.8%. The amount of an organosilane compound coating layer composed of methyl hydrogen polysiloxane was 0.44% by weight (calculated as Si). The amount of the carbon black coat formed on the coating layer composed of methyl hydrogen polysiloxane is 9.04% by weight (calculated as C) based on the weight of the black composite hematite particles (corresponding to 10 parts by weight based on 100 parts by weight of the Mn-containing hematite particles). The thickness of the carbon black coat formed was 0.0024 μm. Since no carbon black was recognized on the electron photograph, it was confirmed that a whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed of methyl hydrogen polysiloxane.

Production of Magnetic Recording Medium

100 parts by weight of Co-coated acicular magnetite particles (average major axial diameter: 0.24 μm aspect ratio: 7.1, BET specific surface area: 31.3 m

2

/g, coercive force value: 714 Oe (56.8 kA/m), saturation magnetization value: 83.1 emu/g (83.1 Am

2

/kg), Co content: 2.26 wt. %), 10.0 parts by weight of vinyl chloride-vinyl acetate copolymer resin (tradename: MR-110, produced by Nippon Zeon Co., Ltd.), 23.3 parts by weight of cyclohexanone, 10.0 parts by weight of methyl ethyl ketone, 1.0 part by weight of carbon black fine particles (produced by Mitsubishi Chemical Corp., average diameter: 26 nm, BET specific surface area: 130 m

2

/g) and 7.0 parts by weight of the above obtained black composite hematite particles were kneaded together for 20 minutes using a kneader. The obtained kneaded material was diluted by adding 79.6 parts by weight of toluene, 110.2 parts by weight of methyl ethyl ketone and 17.8 parts by weight of cyclohexanone thereto, and then the resultant mixture was mixed and dispersed for 3 hours by a sand grinder, thereby obtaining a dispersion.

The obtained dispersion was mixed with 33.3 parts by weight of a solution prepared by dissolving 10.0 parts weight (solid content) of polyurethane resin (tradename: TI-1075, produced by Sanyo Kasei Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone and cyclohexanone (weight ratio: 1/1), and the resultant mixture was mixed and dispersed for 30 minutes by a sand grinder. Thereafter, the obtained dispersion was passed through a filter having a mesh size of 1 μm. The obtained filter cake was mixed while stirring with 12.1 parts by weight of a solution prepared by dissolving 1.0 part by weight of myristic acid and 3.0 parts by weight of butyl stearate in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), and with 15.2 parts by weight of a solution prepared by dissolving 5.0 parts by weight of trifunctional low molecular weight polyisocyanate (tradename: E-31, produced by Takeda Yakuhin Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), thereby producing a magnetic coating composition.

The obtained magnetic coating composition had the following composition:

Magnetic particles

100

parts by weight

Vinyl chloride-vinyl

10

parts by weight

acetate copolymer resin

Polyurethane resin

10

parts by weight

Black composite hematite

7.0

parts by weight

particles (filler)

Carbon black fine particles

1.0

part by weight

Myristic acid

1.0

part by weight

Butyl stearate

3.0

parts by weight

Trifunctional low molecular

5.0

parts by weight

weight polyisocyanate

Cyclohexanone

56.6

parts by weight

Methyl ethyl ketone

141.5

parts by weight

Toluene

85.4

parts by weight

The obtained magnetic coating composition had a viscosity of 2,560 cP.

The thus obtained magnetic coating composition was passed through a filter having a mesh size of 1 μm. Thereafter, the magnetic coating composition was coated on a 14 μm-thick polyester base film using a slit coater having a gap width of 45 μm, and the magnetic recording medium obtained was oriented and dried in a magnetic field, thereby forming a magnetic layer having a thickness of 4.0 μm on the base film. The surface of the obtained magnetic layer was calendered and smoothened by an ordinary method, and then the obtained film was slit into a width of ½ inch (1.27 cm). The obtained tape was allowed to stand in a curing oven maintained at 60° C., for 24 hours, and sufficiently cured therein, thereby producing a magnetic tape. The magnetic layer of the obtained magnetic tape had a thickness of 3.5 μm.

The obtained magnetic tape had a coercive force value of 754 Oe (59.3 kA/m), a squareness (Br/Bm) of 0.88, a gloss of 183%, a surface roughness (Ra) of 6.7 nm, a linear absorption of 1.28 μm

−1

and a surface resistivity of 4.8×10

8

Ω/cm

2

. As to the electromagnetic performance of the obtained magnetic tape, the output thereof at a recording frequency of 4 MHz was +2.3 dB. Further, as to the durability of the magnetic tape, the running durability time was not less than 30 minutes, and the head contamination was A.

Meanwhile, the measurement of the electromagnetic performance was conducted using a reference tape 1 described in Tables 8 and 9 hereinafter.

Examples 23 to 32 and Comparative Examples 13 to 17

The same procedure as defined in Example 22 was conducted except that kind of core particles to be treated; addition or non-addition of polysiloxane compound in the coating treatment, kind and amount of polysiloxane compound added, treating conditions of edge runner in the coating treatment; kind and amount of carbon black fine particles added, and treating conditions of edge runner used in the forming process of the carbon black coat, are varied, thereby obtaining black composite hematite particles.

The black composite hematite particles obtained in Examples 23 to 32 were observed by an electron microscope. As a result, almost no liberated carbon black fine particles were recognized. Therefore, it was confirmed that a substantially whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed the polysiloxane formed on each core particle.

Main production conditions are shown in Table 13, and various properties of the obtained black magnetic acicular composite particles are shown in Table 14.

Examples 33 to 42 and Comparative Examples 16 to 18

The same procedure as defined in Example 22 was conducted except that kind of core particles to be treated, addition or non-addition of a modified polysiloxane compound in the coating treatment, kind and amount of the modified polysiloxane compound added, treating conditions of edge runner in the coating treatment, kind and amount of carbon black fine particles added, and treating conditions of edge runner used in the forming process of the carbon black coat, were varied, thereby obtaining black composite hematite particles.

The black composite hematite particles obtained in Examples 33 to 42 were observed by an electron microscope. As a result, almost no liberated carbon black fine particles was recognized. Therefore, it was confirmed that a substantially whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed of modified polysiloxane.

Main production conditions are shown in Table 15, and various properties of the obtained black composite hematite particles are shown in Table 16.

Examples 43 to 52 and Comparative Examples 19 to 21

The same procedure as defined in Example 22 was conducted except that kind of core particles to be treated, addition or non-addition of a terminal-modified polysiloxane compound in the coating treatment, kind and amount of the terminal-modified polysiloxane compound added, treating conditions of edge runner in the coating treatment, kind and amount of carbon black fine particles added, and treating conditions of edge runner used in the forming process of the carbon black coat, were varied, thereby obtaining black composite hematite particles.

The black composite hematite particles obtained in Examples 43 to 52 were observed by an electron microscope. As a result, almost no liberated carbon black fine particles was recognized. Therefore, it was confirmed that a substantially whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed of terminal-modified polysiloxane.

Main production conditions are shown in Table 17, and various properties of the obtained black composite hematite particles are shown in Table 18.

Example 53 to 82, Comparative Examples 22 to 30

Production of Magnetic Recording Medium

The same procedure as defined in Example 22 was conducted except for varying the kind of the magnetic particles, the kind and amount of the black composite hematite particles added as a filler, thereby producing a magnetic recording medium.

The main producing conditions of the magnetic recording medium shown in Tables 19 to 20 and various properties are shown in Tables 21 and 24.

Example 83

Production of Black Composite Hematite Particles

20 kg of Mn-containing hematite particles (average particle size: 0.30 μm; geometrical standard deviation value: 1.46; BET specific surface area value: 3.6 m

2

/g; Mn content: 13.3% by weight (calculated as Mn) based on the weight of the particle; blackness (L* value): 22.6; volume resistivity: 2.0×10

7

Ω·cm), were deagglomerated in 150 liters of pure water using a stirrer, and further passed through a “TK pipeline homomixer” (tradename, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times, thereby obtaining a slurry containing the Mn-containing hematite particles.

Successively, the obtained slurry containing the Mn-containing hematite particles was passed through a transverse-type sand grinder (tradename “MIGHTY MILL MHG-1.5L”, manufactured by Inoue Seisakusho Co., Ltd.) five times at an axis-rotating speed of 2,000 rpm, thereby obtaining a slurry in which the Mn-containing hematite particles were dispersed.

The particles in the obtained slurry which remained on a sieve of 325 meshes (mesh size: 44 μm) was 0%. The slurry was filtered and washed with water, thereby obtaining a filter cake containing the Mn-containing hematite particles. After the obtained filter cake containing the Mn-containing hematite particles was dried at 120° C., 11.0 kg of the dried particles were then charged into an edge runner “MPUV-2 Model” (tradename, manufactured by Matsumoto Chuzo Tekkosho Co., Ltd.), and mixed and stirred at 30 Kg/cm (294 N/cm) and a stirring speed of 22 rpm for 30 minutes, thereby lightly deagglomerating the particles.

220 g of tridecafluorooctyl trimethoxysilane (tradename “TSL8257”, produced by TOSHIBA SILICONE CO., LTD.) were added to the deagglomerated Mn-containing hematite particles under the operation of the edge runner. The Mn-containing hematite particles were continuously mixed and stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 45 minutes.

Next, 1,100 g of carbon black fine particles A shown in the electron micrograph (×20,000) of

FIG. 2

(particle shape: granular shape; average particle size: 0.022 μm; geometrical standard deviation value: 1.68; BET specific surface area value: 134 m

2

/g; and blackness (L* value): 16.6; pH value: 3.4; DBP oil absorption: 89 ml/100 g) were added to the Mn-containing hematite particles coated with tridecafluorooctyl trimethoxysilane for 10 minutes while operating the edge runner. Further, the mixed particles were continuously stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 60 minutes to form the carbon black coat on the coating layer composed of tridecafluorooctyl trimethoxysilane, thereby obtaining black composite hematite particles.

The obtained black composite hematite particles were heat-treated at 105° C. for 60 minutes by using a drier to evaporate water or the like which were remained on surfaces of the black composite hematite particles. As shown in the electron micrograph, the resultant black composite hematite particles had an average particle diameter of 0.32 μm. In addition, the black composite hematite particles showed a geometrical standard deviation value of 1.45, a BET specific surface area value of 9.1 m

2

/g, a blackness (L* value) of 17.8 and a volume resistivity of 9.0×10

3

Ω·cm. The desorption percentage of the carbon black from the black composite hematite particles was 6.7%. The amount of a organosilane compound coating produced from tridecafluorooctyl trimethoxysilane was 0.11% by weight (calculated as Si). The amount of the carbon black coat formed on the coating layer composed of the organosilane compound produced from tridecafluorooctyl trimethoxysilane is 9.02% by weight (calculated as C) based on the weight of the black composite hematite particles (corresponding to 10 parts by weight based on 100 parts by weight of the black Mn-containing hematite particles). The thickness of the carbon black coat formed was 0.0024 μm. Since no liberated carbon black fine particles was recognized on the electron photograph, it was confirmed that a whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed of the organosilane compound produced from tridecafluorooctyl trimethoxysilane.

Production of Magnetic Recording Medium

100 parts by weight of Co-coated acicular magnetite particles (average major axial diameter: 0.24 μm, aspect ratio: 7.1, BET specific surface area: 31.3 m

2

/g, coercive force value: 714 Oe (56.8 kA/m), saturation magnetization value: 83.1 emu/g (83.1 Am

2

/kg), Co content: 2.26 wt. %), 10.0 parts by weight of vinyl chloride-vinyl acetate copolymer resin (tradename: MR-110, produced by Nippon Zeon Co., Ltd.), 23.3 parts by weight of cyclohexanone, 10.0 parts by weight of methyl ethyl ketone, 1.0 part by weight of carbon black fine particles (produced by Mitsubishi Chemical Corp., average diameter: 26 nm, BET specific surface area: 130 m

2

/g) and 7.0 parts by weight of the above obtained black composite hematite particles were kneaded together for 20 minutes using a kneader. The obtained kneaded material was diluted by adding 79.6 parts by weight of toluene, 110.2 parts by weight of methyl ethyl ketone and 17.8 parts by weight of cyclohexanone thereto, and then the resultant mixture was mixed and dispersed for 3 hours by a sand grinder, thereby obtaining a dispersion.

The obtained dispersion was mixed with 33.3 parts by weight of a solution prepared by dissolving 10.0 parts weight (solid content) of polyurethane resin (tradename: TI-1075, produced by Sanyo Kasei Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone and cyclohexanone (weight ratio: 1/1), and the resultant mixture was mixed and dispersed for 30 minutes by a sand grinder. Thereafter, the obtained dispersion was passed through a filter having a mesh size of 1 μm. The obtained filter cake was mixed while stirring with 12.1 parts by weight of a solution prepared by dissolving 1.0 part by weight of myristic acid and 3.0 parts by weight of butyl stearate in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), and with 15.2 parts by weight of a solution prepared by dissolving 5.0 parts by weight of trifunctional low molecular weight polyisocyanate (tradename: E-31, produced by Takeda Yakuhin Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), thereby producing a magnetic coating composition.

The obtained magnetic coating composition had the following composition:

Magnetic particles

100

parts by weight

Vinyl chloride-vinyl

10

parts by weight

acetate copolymer resin

Polyurethane resin

10

parts by weight

Black composite hematite

7.0

parts by weight

particles (filler)

Carbon black fine particles

1.0

part by weight

Myristic acid

1.0

part by weight

Butyl stearate

3.0

parts by weight

Trifunctional low molecular

5.0

parts by weight

weight polyisocyanate

Cyclohexanone

56.6

parts by weight

Methyl ethyl ketone

141.5

parts by weight

Toluene

85.4

parts by weight

The obtained magnetic coating composition had a viscosity of 2,048 cP.

The thus obtained magnetic coating composition was passed through a filter having a mesh size of 1 μm. Thereafter, the magnetic coating composition was coated on a 14 μm-thick polyester base film using a slit coater having a gap width of 45 μm, and the magnetic recording medium obtained was oriented and dried in a magnetic field, thereby forming a magnetic layer having a thickness of 3.9 μm on the base film. The surface of the obtained magnetic layer was calendered and smoothened by an ordinary method, and then the obtained film was slit into a width of ½ inch (1.27 cm). The obtained tape was allowed to stand in a curing oven maintained at 60° C., for 24 hours, and sufficiently cured therein, thereby producing a magnetic tape. The magnetic layer of the obtained magnetic tape had a thickness of 3.4 μm.

The obtained magnetic tape had a coercive force value of 746 Oe (59.4 kA/m), a squareness (Br/Bm) of 0.88, a gloss of 182%, a surface roughness (Ra) of 6.8 nm, a linear absorption of 1.23 μm

−1

and a surface resistivity of 8.6×10

8

Ω/cm

2

. As to the electromagnetic performance of the obtained magnetic tape, the output thereof at a recording frequency of 4 MHz was +2.3 dB. Further, as to the durability of the magnetic tape, the running durability time was not less than 30 minutes, and the head contamination was A.

Meanwhile, the measurement of the electromagnetic performance was conducted using a reference tape 1 described in Tables 8 and 9 hereinafter.

Examples 84 to 93 and Comparative Examples 31 to 33

The same procedure as defined in Example 83 was conducted except that kind of core particles to be treated; addition or non-addition of fluoroalkylsilane compound in the coating treatment, kind and amount of fluoroalkylsilane compound added, treating conditions of edge runner in the coating treatment; kind and amount of carbon black fine particles added, and treating conditions of edge runner used in the forming process of the carbon black coat, are varied, thereby obtaining black composite hematite particles.

The black composite hematite particles obtained in Examples 84 to 93 were observed by an electron microscope. As a result, almost no liberated carbon black fine particles were recognized. Therefore, it was confirmed that a substantially whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed the fluoroalkyl organosilane compound produced from the fluoroalkylsilane compound, formed on each core particle.

Main production conditions are shown in Table 13, and various properties of the obtained black magnetic acicular composite particles are shown in Table 14.

Main production conditions are shown in Table 25, and various properties of the obtained black composite hematite particles are shown in Table 26.

Examples 94 to 103 and Comparative Examples 34 to 36

Production of Magnetic Recording Medium

The same procedure as defined in Example 83 was conducted except for varying the kind of the black composite hematite particles, the kind and amount of the carbon black fine particles added, thereby producing a magnetic recording medium.

The main producing conditions of the magnetic recording medium shown in Table 27 and various properties are shown in Table 28.

Example 104

Production of Black Non-magnetic Composite Particles

20 kg of Mn-containing hematite particles (average particle size: 0.30 μm; geometrical standard deviation value: 1.46; BET specific surface area value: 3.6 m

2

/g; Mn content: 13.3% by weight (calculated as Mn) based on the weight of the particle; blackness (L* value): 22.6; volume resistivity: 2.0×10

7

Ω·cm), were deagglomerated in 150 liters of pure water using a stirrer, and further passed through a “TK pipeline homomixer” (tradename, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times, thereby obtaining a slurry containing the Mn-containing hematite particles.

Successively, the obtained slurry containing the Mn-containing hematite particles was passed through a transverse-type sand grinder (tradename “MIGHTY MILL MHG-1.5L”, manufactured by Inoue Seisakusho Co., Ltd.) five times at an axis-rotating speed of 2,000 rpm, thereby obtaining a slurry in which the Mn-containing hematite particles were dispersed.

The particles in the obtained slurry which remained on a sieve of 325 meshes (mesh size: 44 μm) was 0%. The slurry was filtered and washed with water, thereby obtaining a filter cake containing the Mn-containing hematite particles. After the obtained filter cake containing the Mn-containing hematite particles was dried at 120° C., 11.0 kg of the dried particles were then charged into an edge runner “MPLTV-2 Model” (tradename, manufactured by Matsumoto Chuzo Tekkosho Co., Ltd.), and mixed and stirred at 30 Kg/cm (294 N/cm) and a stirring speed of 22 rpm for 30 minutes, thereby lightly deagglomerating the particles.

165 g of methyl triethoxysilane (tradename: “TSL8123”, produced by TOSHIBA SILICONE CO., LTD.) was mixed and diluted with 200 ml of ethanol to obtain a methyl triethoxysilane solution. The methyl triethoxysilane solution was added to the deagglomerated Mn-containing hematite particles under the operation of the edge runner. The Mn-containing hematite particles were continuously mixed and stirred at a linear load of 60 Kg/cm (588 N/cm) and a stirring speed of 22 rpm for 20 minutes.

Next, 1,925 g of carbon black fine particles B (particle shape: granular shape; average particle size: 0.022 μm; geometrical standard deviation value: 1.78; BET specific surface area value: 133.5 m

2

/g; and blackness (L* value): 14.6; pH value: 3.4; DBP oil absorption: 84 ml/100 g) were added to the Mn-containing hematite particles coated with methyl triethoxysilane for 10 minutes while operating the edge runner. Further, the mixed particles were continuously stirred at a linear load of 30 Kg/cm (294 N/cm) and a stirring speed of 22 rpm for 30 minutes to form the carbon black coat on the coating layer composed of methyl triethoxysilane, thereby obtaining black composite hematite particles.

The obtained black composite hematite particles were heat-treated at 80° C. for 120 minutes by using a drier to evaporate water, ethanol or the like which were remained on surfaces of the black composite hematite particles. As shown in the electron micrograph, the resultant black hematite composite particles had an average particle diameter of 0.31 μm. In addition, the black non-magnetic composite particles showed a geometrical standard deviation value of 1.46, a BET specific surface area value of 7.8 m

2

/g, a blackness (L* value) of 17.6 and a volume resistivity of 6.8×10

3

Ω·cm. The desorption percentage of the carbon black from the black composite hematite particles was 7.8%. The amount of a coating organosilane compound produced from methyl triethoxysilane was 0.22% by weight (calculated as Si). The amount of the carbon black coat formed on the coating layer composed of the organosilane compound produced from methyl triethoxysilane is 14.78% by weight (calculated as C) based on the weight of the black composite hematite particles (corresponding to 17.5 parts by weight based on 100 parts by weight of the Mn-containing hematite particles). The thickness of the carbon black coat formed was 0.0024 μm. Since no liberated carbon black fine particles was recognized on the electron photograph, it was confirmed that a whole amount of the carbon black used contributed to the formation of the carbon black coat on the coating layer composed of the organosilane compound produced from methyl triethoxysilane.

Production of Non-magnetic Substrate: Formation of Non-magnetic Undercoat Layer on Non-magnetic Base Film

12 g of the non-magnetic particles 1 (hematite particles: particle shape: spindle shape; average major axis diameter: 0.187 μm; average minor axis diameter: 0.0240 μm; aspect ratio: 7.8:1; geometrical standard deviation value: 1.33; BET specific surface area value: 43.3 m

2

/g; blackness (L* value): 32.6; volume resistivity: 8.6×108 Ω·cm) shown in the Table 31, were mixed with a binder resin solution (30% by weight of vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone, and each of the obtained mixtures (solid content: 72% by weight) was kneaded by a plast-mill for 30 minutes.

Each of the thus-obtained kneaded material was charged into a 140 ml-glass bottle together with 95 g of 1.5 mmφ glass beads, a binder resin solution (30% by weight of polyurethane resin having a sodium sulfonate group and 70% by weight of a solvent (methyl ethyl ketone:toluene=1:1)), cyclohexanone, methyl ethyl ketone and toluene, and the obtained mixture was mixed and dispersed by a paint shaker for 6 hours to obtain a non-magnetic coating composition.

The thus-obtained non-magnetic coating composition was as follows:

Non-magnetic particles 1

100

parts by weight

Vinyl chloride-vinyl acetate

10

parts by weight

copolymer resin having a sodium

sulfonate group

Polyurethane resin having a

10

parts by weight

sodium sulfonate group

Lubricant (myristic acid:

2

parts by weight

butyl stearate = 1:1)

Cyclohexanone

56.9

parts by weight

Methylethyl ketone

142.3

parts by weight

Toluene

85.4

parts by weight

The viscosity of the obtained non-magnetic coating composition was 310 cP.

The non-magnetic coating composition obtained was applied to a polyethylene terephthalate film of 12 μm thick to a thickness of 55 μm by an applicator, and the coating film was then dried, thereby forming a non-magnetic undercoat layer. The thickness of the non-magnetic undercoat layer was 3.4 μm.

The thus obtained non-magnetic undercoat layer had a gloss of 193%, and a surface roughness Ra of 8.2 nm. The Young's modulus (relative value) thereof was 123. The linear adsorption coefficient (of the coating film) thereof was 1.01 μm

−1

; and the surface resistivity thereof was 1.1×10

14

Ω/cm

2

.

Production of Magnetic Recording Medium: Formation of Magnetic Recording Layer

100 parts by weight of Co-coated acicular magnetite particles (average major axial diameter: 0.23 μm, aspect ratio: 7.3:1, BET specific surface area: 30.3 m

2

/g, coercive force value: 726 Oe (57.8 kA/m), saturation magnetization value: 81.9 emu/g (81.9 AM

2

/kg), Co content: 2.22 wt. %), 10.0 parts by weight of vinyl chloride-vinyl acetate copolymer resin (tradename: MR-110, produced by Nippon Zeon Co., Ltd.), 23.3 parts by weight of cyclohexanone, 10.0 parts by weight of methyl ethyl ketone, 1.0 part by weight of carbon black fine particles (produced by Mitsubishi Chemical Corp., average diameter: 26 nm, BET specific surface area: 130 m

2

/g) and 7.0 parts by weight of the above obtained black composite hematite particles were kneaded together for 20 minutes using a kneader. The obtained kneaded material was diluted by adding 79.6 parts by weight of toluene, 110.2 parts by weight of methyl ethyl ketone and 17.8 parts by weight of cyclohexanone thereto, and then the resultant mixture was mixed and dispersed for 3 hours by a sand grinder, thereby obtaining a dispersion.

The obtained dispersion was mixed with 33.3 parts by weight of a solution prepared by dissolving 10.0 parts weight (solid content) of polyurethane resin (tradename: TI-1075, produced by Sanyo Kasei Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone and cyclohexanone (weight ratio: 1/1), and the resultant mixture was mixed and dispersed for 30 minutes by a sand grinder. Thereafter, the obtained dispersion was passed through a filter having a mesh size of 1 μm. The obtained filter cake was mixed while stirring with 12.1 parts by weight of a solution prepared by dissolving 1.0 part by weight of myristic acid and 3.0 parts by weight of butyl stearate in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), and with 15.2 parts by weight of a solution prepared by dissolving 5.0 parts by weight of trifunctional low molecular weight polyisocyanate (tradename: E-31, produced by Takeda Yakuhin Kogyo Co., Ltd.) in a mixed solvent containing methyl ethyl ketone, toluene and cyclohexanone (weight ratio: 5/3/2), thereby producing a magnetic coating composition.

The obtained magnetic coating composition had the following composition:

Magnetic particles

100

parts by weight

Vinyl chloride-vinyl

10

parts by weight

acetate copolymer resin

Polyurethane resin

10

parts by weight

Black composite hematite

7.0

parts by weight

particles (filler)

Carbon black fine particles

1.0

part by weight

Myristic acid

1.0

part by weight

Butyl stearate

3.0

parts by weight

Trifunctional low molecular

5.0

parts by weight

weight polyisocyanate

Cyclohexanone

56.6

parts by weight

Methyl ethyl ketone

141.5

parts by weight

Toluene

85.4

parts by weight

The obtained magnetic coating composition had a viscosity of 2,816 cP.

The thus obtained magnetic coating composition was passed through a filter having a mesh size of 1 μm and then was coated on the obtained non-magnetic undercoat layer using a slit coater, and the obtained product was oriented and dried in a magnetic field, thereby forming a magnetic layer on the non-magnetic undercoat layer. The surface of the obtained magnetic layer was calendered and smoothened by an ordinary method, and then the obtained film was slit into a width of ½ inch (1.27 cm). The obtained tape was allowed to stand in a curing oven maintained at 60° C., for 24 hours, and sufficiently cured therein, thereby producing a magnetic tape. The magnetic layer of the obtained magnetic tape had a thickness of 3.4 μm.

The obtained magnetic tape had a coercive force value of 754 Oe (60.0 kA/m), a squareness (Br/Bm) of 0.88, a gloss of 194%, a surface roughness (Ra) of 6.8 nm, a linear absorption of 1.36 μm

−1

and a surface resistivity of 6.8×10

7

Ω/cm

2

. As to the electromagnetic performance of the obtained magnetic tape, the output thereof at a recording frequency of 4 MHz was +2.3 dB. Further, as to the durability of the magnetic tape, the running durability time was 29.2 minutes, and the head contamination was A.

Meanwhile, the measurement of the electromagnetic performance was conducted using a reference tape 5 described in Tables 33 and 34 hereinafter.

Examples 105 to 116 and Comparative Examples 37 to 40

Production of Black Composite Hematite Particles

The same procedure as defined in Example 104 was conducted except that kind of core particles to be treated; addition or non-addition of alkoxysilane, polysiloxane and silicon compound in the coating treatment, kind and amount of the alkoxysilane, polysiloxane and as a coupling agent silicon compound added, treating conditions of edge runner in the coating treatment, and kind and amount of carbon black fine particles added and treating conditions of edge runner used in the forming process of the carbon black coat, are changed variously, thereby obtaining black composite hematite particles. When the black composite hematite particles obtained in Examples 105 to 116 were observed by an electron microscope, no liberated carbon black fine particles were recognized. Therefore, it was confirmed that a substantially whole amount of carbon black used contributed to the formation of the carbon black coat on the coating layer composed of an organosilane compound obtained from alkoxysilane or the polysiloxane.

Main production conditions are shown in Table 29, and various properties of the obtained black composite hematite particles are shown in Table 30.

All of the additives used in Examples 112 to 114 were polysiloxane (“TSF484” (tradename, produced by Toshiba Silicone Co. Ltd.): methyl hydrogen polysiloxane; “BYK-080” (tradename, produced by BYK Chemie Japan Co., Ltd.): modified polysiloxane; “TSF-4770” (tradename, produced by Toshiba Silicone Co. Ltd.): terminal-carboxyl-modified polysiloxane).

Production of Non-magnetic Substrate: Formation of Non-magnetic Undercoat Layer on Non-magnetic Base Film

By using the non-magnetic particles 1 to 6, non-magnetic undercoat layers were formed in the same way as in Example 104.

Various properties of the non-magnetic particles are shown in Table 31.

Main production conditions and various properties of the obtained non-magnetic undercoating layer are shown in Table 32.

Reference Tapes 5 to 8

By using the non-magnetic undercoating layers and magnetic particles, reference tapes were produced. The main producing conditions are shown in Table 33 and various properties of the reference tapes are shown in Table 34.

Examples 117 to 128 and Comparative Examples 41 to 44

Production of Magnetic Recording Medium: Formation of Magnetic Recording Layer

Magnetic recording media were produced in the same way as in Example 104 except for varying the kind and amount of magnetic particles and black composite hematite particles as a filler.

The main producing conditions are shown in Table 35 and various properties are shown in Table 36.

TABLE 1

Core

Properties of hematite particles

particles

Kind

Particle shape

Core

Mn-containing hematite

Granular

particles 2

particles

Core

Mn-containing hematite

Granular

particles 2

particles

Core

Hematite particles

Granular

particles 3

Core

Hematite particles

Granular

particles 4

Core

Hematite particles

Acicular

particles 5

Properties of hematite particles

Average major

axial diameter

(average

Average minor

Aspect

Core

particle size)

axial diameter

ratio

particles

(μm)

(μm)

(-)

Core

0.32

—

—

particles 1

Core

0.18

—

—

particles 2

Core

0.11

—

—

particles 3

Core

0.29

—

—

particles 4

Core

0.23

0.029

7.9:1

particles 5

Properties of hematite particles

Geometrical

BET specific

standard

surface area

Core

deviation value

value

Mn content

particles

(-)

(m

2

/g)

(wt. %)

Core

1.49

3.1

13.1

particles 1

Core

1.41

7.8

15.6

particles 2

Core

1.35

15.3

—

particles 3

Core

1.41

3.8

—

particles 4

Core

1.38

35.6

—

particles 5

Properties of hematite particles

Volume resistivity

Blackness

Core

value

(L* value)

particles

(Ω.cm)

(-)

Core

1.8 × 10

7

22.4

particles 1

Core

2.3 × 10

7

24.4

particles 2

Core

7.6 × 10

8

35.5

particles 3

Core

6.4 × 10

8

32.1

particles 4

Core

3.6 × 10

8

34.0

particles 5

TABLE 2

Surface-treatment step

Kind of

Additive

Core

core

Calculated

Amount

particles

particles

Kind

as

(wt. %)

Core

Core

Sodium

Al

0.5

particles 6

particles 1

aluminate

Core

Core

Water glass

SiO

2

0.2

particles 7

particles 2

#3

Core

Core

Aluminum

Al

0.5

particles 8

particles 3

sulfate

Water glass

SiO

2

1.5

#3

Core

Core

Sodium

Al

1.0

particles 9

particles 4

aluminate

Colloidal

SiO

2

1.0

silica

Core

Core

Aluminum

Al

5.5

particles 10

particles 5

sulfate

Core

Core

Sodium

Al

2.0

particles 11

particles 4

aluminate

Surface-treatment step

Core

Coating material

particles

Kind

Calculated as

Amount (wt. %)

Core

A

Al

0.49

particles 6

Core

S

SiO

2

0.18

particles 7

Core

A

Al

0.48

particles 8

S

SiO

2

1.45

Core

A

Al

0.97

particles 9

S

SiO

2

0.97

Core

A

Al

5.21

particles 10

Core

A

Al

1.90

particles 11

Note;

A: Hydroxide of aluminum

S: Oxide of silicon

TABLE 3

Properties of surface-treated hematite

particles

Average major

axial diameter

(average

Average minor

Aspect

Core

particles size)

axial diameter

ratio

particles

(μm)

(μm)

(-)

Core

0.32

—

—

particles 6

Core

0.18

—

—

particles 7

Core

0.11

—

—

particles 8

Core

0.29

—

—

particles 9

Core

0.23

0.030

7.7:1

particles 10

Core

0.29

—

—

particles 11

Properties of surface-treated hematite

particles

Geometrical

BET specific

standard

surface area

Core

deviation value

value

Mn content

particles

(-)

(m

2

/g)

(wt. %)

Core

1.47

3.8

13.0

particles 6

Core

1.40

7.5

15.6

particles 7

Core

1.35

17.1

—

particles 8

Core

1.41

5.1

—

particles 9

Core

1.38

35.2

—

particles 10

Core

1.41

5.2

—

particles 11

Properties of surface-treated hematite

particles

Volume resistivity

Blackness

Core

value

(L* value)

particles

(Ω.cm)

(-)

Core

3.2 × 10

7

22.6

particles 6

Core

4.8 × 10

7

25.1

particles 7

Core

9.3 × 10

8

35.6

particles 8

Core

6.8 × 10

8

32.3

particles 9

Core

5.1 × 10

8

34.6

particles 10

Core

7.6 × 10

8

32.5

particles 11

TABLE 4

Properties of carbon black fine particles

Geometrical

Average

standard

Kind of carbon

particle

deviation

black fine

Particle

size

value

particles

shape

(μm)

(-)

Carbon black A

Granular

0.022

1.68

Carbon black B

Granular

0.022

1.78

Carbon black C

Granular

0.015

1.56

Carbon black D

Granular

0.030

2.06

Carbon black E

Granular

0.024

1.69

Carbon black F

Granular

0.028

1.71

Properties of carbon black fine

particles

Kind of carbon

BET specific

black fine

surface area value

pH value

particles

(m

2

/g)

(-)

Carbon black A

134.0

3.4

Carbon black B

133.5

3.4

Carbon black C

265.3

3.7

Carbon black D

84.6

8.0

Carbon black E

113.6

10.8

Carbon black F

800.0

7.0

Properties of carbon black fine

particles

Kind of carbon

Blackness

black fine

DBP oil absorption

(L* value)

particles

(ml/100 g)

(-)

Carbon black A

89

16.6

Carbon black B

84

14.6

Carbon black C

57

15.2

Carbon black D

95

17.0

Carbon black E

102

16.2

Carbon black F

200

15.3

TABLE 5

Production of black composite

hematite particles

Coating with alkoxysilane

Examples

Additive

and

Amount

Comparative

Kind of core

added (part

Examples

particles

Kind

by weight)

Example 2

Core

Methyl

1.0

particles 1

triethoxysilane

Example 3

Core

Methyl

2.0

particles 2

trimethoxysilane

Example 4

Core

Dimethyl

1.0

particles 3

dimethoxysilane

Example 5

Core

Phenyl

0.5

particles 4

triethoxysilane

Example 6

Core

Isobutyl

5.0

particles 5

trimethoxysilane

Example 7

Core

Methyl

3.0

particles 6

triethoxysilane

Example 8

Core

Methyl

1.5

particles 7

triethoxysilane

Example 9

Core

Methyl

2.0

particles 8

triethoxysilane

Example 10

Core

Methyl

5.0

particles 9

trimethoxysilane

Example 11

Core

Dimethyl

0.5

particles 10

dimethoxysilane

Comparative

Core

—

—

Example 1

particles 1

Comparative

Core

Methyl

1.0

Example 2

particles 1

triethoxysilane

Comparative

Core

Dimethyl

0.5

Example 3

particles 3

dimethoxysilane

Comparative

Core

Methyl

0.005

Example 4

particles 3

triethoxysilane

Comparative

Core

γ-aminopropyl

1.0

Example 5

particles 1

triethoxysilane

Production of black composite hematite

particles

Coating with alkoxysilane

Examples

Coating amount

and

Edge runner treatment

(calculated as

Comparative

Linear load

Time

Si)

Examples

(N/cm)

(Kg/cm)

(min)

(wt. %)

Example 2

588

60

30

0.15

Example 3

294

30

30

0.40

Example 4

441

45

20

0.22

Example 5

588

60

25

0.06

Example 6

294

30

30

0.72

Example 7

441

45

20

0.45

Example 8

588

60

30

0.22

Example 9

294

30

60

0.29

Example 10

441

45

20

0.96

Example 11

588

60

30

0.11

Comparative

—

—

—

—

Example 1

Comparative

588

60

20

0.15

Example 2

Comparative

588

60

30

0.11

Example 3

Comparative

588

60

30

7 × 10

−4

Example 4

Comparative

588

60

30

0.13

Example 5

Production of black composite

hematite particles

Examples

Coating of carbon black

and

Carbon black

Comparative

Amount added

Examples

Kind

(part by weight)

Example 2

B

8.5

Example 3

B

5.0

Example 4

C

5.0

Example 5

C

10.0

Example 6

D

15.0

Example 7

B

15.0

Example 8

B

12.0

Example 9

C

10.0

Example 10

C

15.0

Example 11

D

20.0

Comparative

B

10.0

Example 1

Comparative

—

—

Example 2

Comparative

B

0.01

Example 3

Comparative

C

5.0

Example 4

Comparative

D

10.0

Example 5

Production of black composite hematite

particles

Coating with carbon black

Examples

Amount coated

and

Edge runner treatment

(calculated as

Comparative

Linear load

Time

C)

Examples

(N/cm)

(Kg/cm)

(min)

(wt. %)

Example 2

588

60

20

7.82

Example 3

441

45

30

4.75

Example 4

294

30

30

4.76

Example 5

441

45

60

9.08

Example 6

294

30

25

13.03

Example 7

588

60

20

13.04

Example 8

294

30

30

10.71

Example 9

441

45

45

9.09

Example 10

588

60

30

13.03

Example 11

588

60

45

16.60

Comparative

588

60

30

9.06

Example 1

Comparative

—

—

—

—

Example 2

Comparative

294

30

60

0.01

Example 3

Comparative

588

60

45

4.75

Example 4

Comparative

588

60

30

9.00

Example 5

TABLE 6

Properties of black composite hematite

particles

Average

major axial

diameter

Geometerical

Examples

(average

Average

standard

and

particle

minor axial

Aspect

deviation

Comparative

size)

diameter

ratio

value

Examples

(μm)

(μm)

(-)

(-)

Example 2

0.32

—

—

1.49

Example 3

0.18

—

—

1.40

Example 4

0.11

—

—

1.36

Example 5

0.30

—

—

1.41

Example 6

0.23

0.031

7.4:1

1.38

Example 7

0.32

—

—

1.49

Example 8

0.19

—

—

1.41

Example 9

0.12

—

—

1.36

Example 10

0.30

—

—

1.41

Example 11

0.23

0.031

7.4:1

1.38

Comparative

0.33

—

—

—

Example 1

Comparative

0.32

—

—

1.47

Example 2

Comparative

0.11

—

—

—

Example 3

Comparative

0.11

—

—

—

Example 4

Comparative

0.33

—

—

—

Example 5

Properties of black composite hematite

particles

Examples

BET specific

and

surface area

Blackness

Comparative

value

Mn content

(L* value)

Examples

(m

2

/g)

(wt. %)

(-)

Example 2

5.0

11.9

17.3

Example 3

7.4

14.5

18.4

Example 4

17.6

—

19.8

Example 5

6.8

—

18.7

Example 6

41.3

—

18.3

Example 7

4.6

11.0

17.1

Example 8

9.3

13.5

17.3

Example 9

16.6

—

19.3

Example 10

7.8

—

18.7

Example 11

42.6

—

18.1

Comparative

16.6

11.9

22.2

Example 1

Comparative

4.6

12.9

23.1

Example 2

Comparative

14.8

—

36.4

Example 3

Comparative

21.0

—

29.7

Example 4

Comparative

10.7

11.8

22.1

Example 5

Properties of black composite hematite

particles

Volume

Carbon black

Thickness of

Examples and

resistivity

desorption

carbon black

Comparative

value

percentage

coated

Examples

(Ω.cm)

(%)

(μm)

Example 2

6.4 × 10

3

7.1

0.0023

Example 3

7.8 × 10

3

8.2

0.0021

Example 4

2.3 × 10

4

6.4

0.0022

Example 5

9.4 × 10

3

8.9

0.0023

Example 6

8.6 × 10

3

8.8

0.0024

Example 7

5.3 × 10

3

4.3

0.0025

Example 8

6.5 × 10

3

1.5

0.0024

Example 9

9.3 × 10

3

3.6

0.0024

Example 10

8.4 × 10

3

4.3

0.0024

Example 11

6.6 × 10

3

4.6

0.0025

Comparative

8.7 × 10

6

68.3

—

Example 1

Comparative

2.5 × 10

7

—

—

Example 2

Comparative

5.2 × 10

8

—

—

Example 3

Comparative

1.3 × 10

8

47.3

—

Example 4

Comparative

6.8 × 10

6

51.6

—

Example 5

TABLE 7

Properties of magnetic

particles

Average

Average

major axial

minor axial

Magnetic

Kind of magnetic

diameter

diameter

particles

particles

(μm)

(μm)

Magnetic

Co-coated magnetite

0.180

0.0252

particles 1

particles

Magnetic

Magnetic metal

0.135

0.0191

particles 2

particles

Magnetic

Ba ferrite

0.053

0.0160

particles 3

particles

Magnetic

Co-coated magnetite

0.181

0.0250

particles 4

particles

Magnetic

Magnetic metal

0.133

0.0188

particles 5

particles

Magnetic

Ba ferrite

0.052

0.0159

particles 6

particles

Properties of magnetic particles

Geometrical

standard

BET specific

deviation

Aspect

surface area

Magnetic

value

ratio

value

particles

(-)

(-)

(m

2

/g)

Magnetic

1.35

7.1:1

41.6

particles 1

Magnetic

1.38

7.1:1

53.5

particles 2

Magnetic

1.21

3.3:1

58.2

particles 3

Magnetic

1.36

7.2:1

41.7

particles 4

Magnetic

1.37

7.1:1

53.4

particles 5

Magnetic

1.21

3.3:1

58.2

particles 6

Properties of magnetic particles

Coercive force

Saturation

Magnetic

value

magnetization value

particles

(kA/m)

(Oe)

(Am

2

/kg)

(emu/g)

Magnetic

77.0

968

78.6

78.6

particles 1

Magnetic

178.3

2,240

138.2

138.2

particles 2

Magnetic

199.7

2,510

52.6

52.6

particles 3

Magnetic

75.8

953

78.3

78.3

particles 4

Magnetic

175.9

2,210

135.2

135.2

particles 5

Magnetic

199.0

2,500

52.6

52.6

particles 6

TABLE 8

Production conditions of reference

tape

Magnetic particles

Amount blended

Reference tape

Kind

(part by weight)

Reference tape 1

Magnetic particles

100.0

used in Example 1

Reference tape 2

Magnetic particles 1

100.0

Reference tape 3

Magnetic particles 2

100.0

Reference tape 4

Magnetic particles 3

100.0

Production conditions of

Properties

reference tape

of magnetic

Filler

coating

Amount blended

composition

(part by

Viscosity

Reference taper

Kind

weight)

(cP)

Reference tape 1

Al

2

O

3

7.0

2,623

Reference tape 2

Al

2

O

3

7.0

2,511

Reference tape 3

Al

2

O

3

7.0

8,795

Reference tape 4

Al

2

O

3

7.0

6,418

TABLE 9

Properties of reference tape

Coercive force value

Reference

(Oe)

Squareness

Gloss

tape

(kA/m)

(Oe)

(-)

(%)

Reference

59.5

748

0.81

134

tape 1

Reference

79.2

995

0.83

148

tape 2

Reference

182.8

2,297

0.82

181

tape 3

Reference

196.6

2,471

0.80

155

tape 4

Properties of reference tape

Surface

Electromagnetic

roughness

Linear

performance

Reference

Ra

absorption

4 MHz

7 MHz

tape

(nm)

(μm

−1

)

(dB)

(dB)

Reference

12.6

1.10

±0

—

tape 1

Reference

11.8

1.08

—

±0

tape 2

Reference

10.4

1.15

—

±0

tape 3

Reference

12.3

1.11

—

±0

tape 4

Properties of reference tape

Durability

Surface

Running

resistivity

Reference

durability time

Head

value

tape

(min)

contamination

(Ω.cm

2

)

Reference

23.2

A

1.2 × 10

10

tape 1

Reference

22.5

A

4.3 × 10

10

tape 2

Reference

21.0

B

2.6 × 10

10

tape 3

Reference

21.8

B

7.9 × 10

10

tape 4

TABLE 10

Production conditions of magnetic

recording medium

Magnetic particles

Examples and

Amount blended

Comparative

(part by

Examples

Kind

weight)

Example 12

Magnetic particles used

100.0

in Example 1

Example 13

Magnetic particles used

100.0

in Example 1

Example 14

Magnetic particles 1

100.0

Example 15

Magnetic particles 1

100.0

Example 16

Magnetic particles 1

100.0

Example 17

Magnetic particles 1

100.0

Example 18

Magnetic particles 1

100.0

Example 19

Magnetic particles 1

100.0

Example 20

Magnetic particles 2

100.0

Example 21

Magnetic particles 3

100.0

Comparative

Magnetic particles used

100.0

Example 6

in Example 1

Comparative

Magnetic particles used

100.0

Example 7

in Example 1

Comparative

Magnetic particles 1

100.0

Example 8

Comparative

Magnetic particles 1

100.0

Example 9

Comparative

Magnetic particles 1

100.0

Example 10

Comparative

Magnetic particles 1

100.0

Example 11

Comparative

Magnetic particles 1

100.0

Example 12

Properties of

Production conditions of

magnetic

magnetic recording medium

coating

Examples and

Filler

composition

Comparative

Amount blended

Viscosity

Examples

Kind

(part by weight)

(cP)

Example 12

Example 1

7.0

2,380

Example 13

Example 2

7.0

2,560

Example 14

Example 3

10.0

2,355

Example 15

Example 4

14.0

2,074

Example 16

Example 5

21.0

2,150

Example 17

Example 6

7.0

2,022

Example 18

Example 7

7.0

3,072

Example 19

Example 8

15.0

2,944

Example 20

Example 9

10.0

8,832

Example 21

Example 10

7.0

5,594

Comparative

Core

7.0

2,893

Example 6

particles 1

Comparative

Core

7.0

3,098

Example 7

particles 3

Comparative

Comparative

7.0

3,302

Example 8

Example 1

Comparative

Comparative

7.0

3,456

Example 9

Example 2

Comparative

Comparative

7.0

2,867

Example 10

Example 3

Comparative

Comparative

7.0

3,456

Example 11

Example 4

Comparative

Comparative

7.0

3,200

Example 12

Example 5

TABLE 11

Properties of magnetic

recording medium

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Example 12

Reference

59.8

752

tape 1

Example 13

Reference

59.9

753

tape 1

Example 14

Reference

79.8

1,003

tape 2

Example 15

Reference

79.3

996

tape 2

Example 16

Reference

79.4

998

tape 2

Example 17

Reference

80.6

1,013

tape 2

Example 18

Reference

79.5

999

tape 2

Example 19

Reference

79.8

1,003

tape 2

Example 20

Reference

183.1

2,301

tape 3

Example 21

Reference

203.8

2,561

tape 4

Properties of magnetic recording medium

Squareness

Gloss

Examples

(−)

(%)

Example 12

0.86

189

Example 13

0.86

182

Example 14

0.88

196

Example 15

0.88

198

Example 16

0.88

189

Example 17

0.88

191

Example 18

0.89

191

Example 19

0.88

193

Example 20

0.89

235

Example 21

0.86

218

Properties of magnetic recording medium

Electromagnetic

Surface

Linear

performance

roughness

absorption

4 MHz

7 MHz

Examples

Ra (nm)

(μm

−1

)

(dB)

(dB)

Example 12

6.4

1.63

+2.2

—

Example 13

7.1

1.64

+2.1

—

Example 14

6.0

1.53

—

+2.1

Example 15

5.8

1.56

—

+2.2

Example 16

6.3

1.58

—

+2.3

Example 17

6.0

1.53

—

+2.2

Example 18

6.2

1.57

—

+2.0

Example 19

5.9

1.59

—

+2.1

Example 20

6.0

1.86

—

+2.3

Example 21

5.6

1.48

—

+2.1

Properties of magnetic recording medium

Durability

Running

Surface

durability

Head

resistivity

Examples

time (min)

contamination

value (Ω/cm

2

)

Example 12

27.3

A

7.4 × 10

7

Example 13

≧30

A

7.8 × 10

7

Example 14

26.8

B

1.3 × 10

8

Example 15

28.3

A

2.4 × 10

8

Example 16

26.5

A

7.6 × 10

7

Example 17

≧30

A

5.4 × 10

7

Example 18

≧30

A

3.8 × 10

7

Example 19

≧30

A

1.6 × 10

8

Example 20

28.8

A

3.8 × 10

7

Example 21

26.1

B

3.4 × 10

8

TABLE 12

Properties of magnetic

recording medium

Comparative

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Comparative

Reference

58.8

739

Example 6

tape 1

Comparative

Reference

59.0

741

Example 7

tape 1

Comparative

Reference

79.5

999

Example 8

tape 2

Comparative

Reference

79.0

993

Example 9

tape 2

Comparative

Reference

78.7

989

Example 10

tape 2

Comparative

Reference

79.6

1,000

Example 11

tape 2

Comparative

Reference

63.3

796

Example 12

tape 2

Properties of magnetic recording medium

Surface

Comparative

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Comparative

0.84

158

10.3

Example 6

Comparative

0.85

152

10.7

Example 7

Comparative

0.84

138

9.8

Example 8

Comparative

0.84

156

10.1

Example 9

Comparative

0.85

153

10.3

Example 10

Comparative

0.84

138

11.2

Example 11

Comparative

0.84

136

9.6

Example 12

Properties of magnetic recording medium

Linear

Electromagnetic performance

Comparative

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Comparative

1.23

+0.7

—

Example 6

Comparative

1.08

+0.3

—

Example 7

Comparative

1.21

—

−0.2

Example 8

Comparative

1.20

—

+0.1

Example 9

Comparative

1.06

—

+0.2

Example 10

Comparative

1.21

—

±0.0

Example 11

Comparative

1.24

—

−0.1

Example 12

Properties of magnetic recording medium

Durability

Running

Surface

Comparative

durability

Head

resistivity

Examples

time (min)

contamination

value (Ω/cm

2

)

Comparative

17.8

C

8.6 × 10

9

Example 6

Comparative

13.2

C

9.3 × 10

10

Example 7

Comparative

15.3

C

7.6 × 10

9

Example 8

Comparative

15.0

C

1.4 × 10

10

Example 9

Comparative

10.3

D

2.4 × 10

10

Example 10

Comparative

11.2

C

1.8 × 10

10

Example 11

Comparative

14.6

C

9.3 × 10

9

Example 12

TABLE 13

Production of black composite

hematite particles

Coating with polysiloxane

Examples and

Additive

Comparative

Kind of core

Amount added

Examples

particles

Kind

(part by weight)

Example 23

Core particles 1

TSF484

1.0

Example 24

Core particles 2

TSF484

5.0

Example 25

Core particles 3

KF99

2.0

Example 26

Core particles 4

L-9000

1.0

Example 27

Core particles 5

TSF484/L-45

0.5/1.5

Example 28

Core particles 6

TSF484

1.0

Example 29

Core particles 7

TSF484

5.0

Example 30

Core particles 8

KF99

2.0

Example 31

Core particles 9

L-9000

1.0

Example 32

Core particles 10

TSF484/L-45

0.5/1.5

Comparative

Core particles 1

TSF484

1.0

Example 13

Comparative

Core particles 3

TSF484

0.5

Example 14

Comparative

Core particles 3

TSF484

0.005

Example 15

Production of black composite hematite

particles

Coating with polysiloxane

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

Si) (wt. %)

Example 23

588

60

30

0.44

Example 24

294

30

45

2.13

Example 25

588

60

30

0.86

Example 26

441

45

20

0.43

Example 27

588

60

45

0.78

Example 28

588

60

30

0.44

Example 29

588

60

20

2.12

Example 30

294

30

30

0.86

Example 31

588

60

45

0.44

Example 32

441

45

30

0.81

Comparative

588

60

30

0.44

Example 13

Comparative

588

60

30

0.22

Example 14

Comparative

588

60

30

2 × 10

−3

Example 15

Production of black composite hematite

particles

Coating of carbon black

Examples and

Carbon black

Comparative

Amount added

Examples

Kind

(part by weight)

Example 23

B

10.0

Example 24

B

3.0

Example 25

C

5.0

Example 26

C

10.0

Example 27

D

7.5

Example 28

B

10.0

Example 29

B

3.0

Example 30

C

5.0

Example 31

C

10.0

Example 32

D

7.5

Comparative

—

—

Example 13

Comparative

B

0.01

Example 14

Comparative

C

3.0

Example 15

Production of black composite hematite

particles

Coating of carbon black

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

C) (wt. %)

Example 23

588

60

30

9.06

Example 24

588

60

45

2.90

Example 25

588

60

30

4.75

Example 26

294

30

20

9.09

Example 27

588

60

30

6.95

Example 28

588

60

45

9.06

Example 29

588

60

30

2.89

Example 30

441

45

20

4.72

Example 31

588

60

30

9.08

Example 32

441

45

45

6.93

Comparative

—

—

—

—

Example 13

Comparative

588

60

30

0.01

Example 14

Comparative

588

60

30

2.91

Example 15

TABLE 14

Properties of black composite hematite

particles

Average

major axial

Average

Examples

diameter

minor

Geometrical

and

(average

axial

Aspect

standard

Comparative

particle

diameter

ratio

deviation value

Examples

size) (μm)

(μm)

(−)

(−)

Example 23

0.32

—

—

1.48

Example 24

0.18

—

—

1.41

Example 25

0.11

—

—

1.35

Example 26

0.29

—

—

1.41

Example 27

0.23

0.029

7.9:1

1.38

Example 28

0.32

—

—

1.48

Example 29

0.19

—

—

1.42

Example 30

0.12

—

—

1.36

Example 31

0.30

—

—

1.41

Example 32

0.23

0.029

7.9:1

1.38

Comparative

0.32

—

—

1.48

Example 13

Comparative

0.11

—

—

1.35

Example 14

Comparative

0.12

—

—

1.36

Example 15

Properties of black composite hematite

particles

Examples

BET specific

Volume

and

surface area

Blackness

resistivity

Comparative

value

Mn content

(L* value)

value

Examples

(m

2

/g)

(wt. %)

(−)

(Ω· cm)

Example 23

4.4

12.2

18.3

5.6 × 10

3

Example 24

8.0

14.9

18.3

9.6 × 10

3

Example 25

15.3

—

20.9

2.6 × 10

4

Example 26

4.6

—

20.8

9.3 × 10

3

Example 27

36.4

—

18.6

1.4 × 10

4

Example 28

3.9

12.2

18.3

6.2 × 10

3

Example 29

8.3

14.9

20.9

1.7 × 10

4

Example 30

15.9

—

20.3

3.0 × 10

4

Example 31

4.4

—

20.2

9.8 × 10

3

Example 32

36.8

—

20.4

1.9 × 10

4

Comparative

3.9

12.9

21.2

3.6 × 10

7

Example 13

Comparative

15.5

—

35.9

5.8 × 10

8

Example 14

Comparative

18.6

—

25.7

3.3 × 10

8

Example 15

Properties of black composite hematite

particles

Examples and

Carbon black

Comparative

desorption percentage

Thickness of carbon

Examples

(%)

black coated (μm)

Example 23

7.3

0.0024

Example 24

8.9

0.0021

Example 25

8.6

0.0022

Example 26

6.9

0.0024

Example 27

9.1

0.0023

Example 28

4.6

0.0024

Example 29

3.2

0.0021

Example 30

4.8

0.0023

Example 31

4.2

0.0024

Example 32

1.6

0.0023

Comparative

—

—

Example 13

Comparative

—

—

Example 14

Comparative

67.2

—

Example 15

TABLE 15

Production of black composite

hematite particles

Coating with modified poly-

Examples and

siloxane Additive

Comparative

Kind of core

Amount added

Examples

particles

Kind

(part by weight)

Example 33

Core particles 1

BYK-080

1.0

Example 34

Core particles 2

BYK-310

2.0

Example 35

Core particles 3

BYK-322

5.0

Example 36

Core particles 4

TSF4446

1.0

Example 37

Core particles 5

YF3965

1.0

Example 38

Core particles 6

BYK-080

1.0

Example 39

Core particles 7

BYK-310

2.0

Example 40

Core particles 8

BYK-322

5.0

Example 41

Core particles 9

TSF4446

1.0

Example 42

Core particles 10

YF3965

1.0

Comparative

Core particles 1

BYK-080

1.0

Example 16

Comparative

Core particles 3

BYK-080

0.5

Example 17

Comparative

Core particles 3

BYK-080

0.005

Example 18

Production of black composite hematite

particles

Coating with modified polysiloxane

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

Si) (wt. %)

Example 33

588

60

30

0.17

Example 34

588

60

20

0.34

Example 35

441

45

45

0.85

Example 36

588

60

30

0.18

Example 37

294

30

25

0.16

Example 38

588

60

30

0.17

Example 39

441

45

30

0.33

Example 40

588

60

25

0.86

Example 41

294

30

45

0.17

Example 42

588

60

30

0.17

Comparative

588

60

30

0.17

Example 16

Comparative

588

60

30

0.08

Example 17

Comparative

588

60

30

6 × 10

−4

Example 18

Production of black composite hematite

particles

Coating of carbon black

Examples and

Carbon black

Comparative

Amount added

Examples

Kind

(part by weight)

Example 33

B

7.5

Example 34

B

5.0

Example 35

C

10.0

Example 36

C

15.0

Example 37

D

5.0

Example 38

B

7.5

Example 39

B

5.0

Example 40

C

10.0

Example 41

C

15.0

Example 42

D

5.0

Comparative

—

—

Example 16

Comparative

B

0.01

Example 17

Comparative

C

5.0

Example 18

Production of black composite hematite

particles

Coating of carbon black

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

C) (wt. %)

Example 33

441

45

45

6.95

Example 34

735

75

20

4.75

Example 35

588

60

20

9.08

Example 36

441

45

45

13.00

Example 37

588

60

30

4.76

Example 38

294

30

60

6.93

Example 39

588

60

30

4.74

Example 40

441

45

45

9.05

Example 41

735

75

20

13.03

Example 42

588

60

30

4.76

Comparative

—

—

—

—

Example 16

Comparative

588

60

30

0.01

Example 17

Comparative

588

60

30

4.73

Example 18

TABLE 16

Properties of black composite hematite

particles

Average

major axial

Average

Examples

diameter

minor

Geometrical

and

(average

axial

Aspect

standard

Comparative

particle

diameter

ratio

deviation value

Examples

size) (μm)

(μm)

(−)

(−)

Example 33

0.32

—

—

1.48

Example 34

0.18

—

—

1.41

Example 35

0.11

—

—

1.35

Example 36

0.29

—

—

1.41

Example 37

0.23

0.029

7.9:1

1.38

Example 38

0.32

—

—

1.48

Example 39

0.19

—

—

1.41

Example 40

0.12

—

—

1.35

Example 41

0.30

—

—

1.41

Example 42

0.23

0.029

7.9:1

1.38

Comparative

0.32

—

—

1.48

Example 16

Comparative

0.11

—

—

1.36

Example 17

Comparative

0.12

—

—

1.35

Example 18

Properties of black composite hematite

particles

Examples

BET specific

Volume

and

surface area

Blackness

resistivity

Comparative

value

Mn content

(L* value)

value

Examples

(m

2

/g)

(wt. %)

(−)

(Ω· cm)

Example 33

4.1

12.2

18.0

7.1 × 10

3

Example 34

8.3

14.9

18.1

8.2 × 10

3

Example 35

15.1

—

20.5

1.0 × 10

4

Example 36

4.3

—

20.5

8.5 × 10

3

Example 37

36.4

—

20.8

2.3 × 10

4

Example 38

4.1

12.3

18.4

7.4 × 10

3

Example 39

8.1

15.0

18.6

8.4 × 10

3

Example 40

15.8

—

20.6

1.7 × 10

4

Example 41

3.9

—

20.3

9.4 × 10

3

Example 42

36.8

—

20.6

2.5 × 10

4

Comparative

4.1

12.8

21.3

3.9 × 10

7

Example 16

Comparative

15.2

—

35.9

6.0 × 10

8

Example 17

Comparative

17.9

—

26.1

1.6 × 10

8

Example 18

Properties of black composite hematite

particles

Examples and

Carbon black

Comparative

desorption percentage

Thickness of carbon

Examples

(%)

black coated (μm)

Example 33

7.1

0.0023

Example 34

6.9

0.0022

Example 35

8.4

0.0024

Example 36

6.8

0.0025

Example 37

6.1

0.0023

Example 38

4.2

0.0024

Example 39

3.6

0.0023

Example 40

2.8

0.0024

Example 41

1.6

0.0024

Example 42

2.1

0.0023

Comparative

—

—

Example 16

Comparative

—

—

Example 17

Comparative

59.8

—

Example 18

TABLE 17

Production of black composite

hematite particles

Coating with terminal-

modified polysiloxane

Examples and

Additive

Comparative

Kind of core

Amount added

Examples

particles

Kind

(part by weight)

Example 43

Core particles 1

TFS4770

2.0

Example 44

Core particles 2

TFS4770

1.0

Example 45

Core particles 3

TFS4751

0.5

Example 46

Core particles 4

XF3905

5.0

Example 47

Core particles 5

YF3804

2.0

Example 48

Core particles 6

TFS4770

2.0

Example 49

Core particles 7

TFS4770

1.0

Example 50

Core particles 8

TFS4751

0.5

Example 51

Core particles 9

XF3905

5.0

Example 52

Core particles 10

YF3804

2.0

Comparative

Core particles 1

TFS4770

1.0

Example 19

Comparative

Core particles 3

TFS4770

1.0

Example 20

Comparative

Core particles 3

TFS4770

0.005

Example 21

Production of black composite hematite

particles

Coating with terminal-modified polysiloxane

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

Si) (wt. %)

Example 43

294

30

45

0.70

Example 44

588

60

20

0.35

Example 45

294

30

60

0.18

Example 46

588

60

20

1.75

Example 47

441

45

45

0.40

Example 48

441

45

30

0.69

Example 49

588

60

30

0.35

Example 50

588

60

20

0.17

Example 51

588

60

30

1.74

Example 52

588

60

20

0.41

Comparative

588

60

30

0.34

Example 19

Comparative

588

60

30

0.35

Example 20

Comparative

588

60

30

1 × 10

−3

Example 21

Production of black composite hematite

particles

Coating of carbon black

Examples and

Carbon black

Comparative

Amount added

Examples

Kind

(part by weight)

Example 43

B

10.0

Example 44

B

5.0

Example 45

C

7.5

Example 46

C

10.0

Example 47

D

7.5

Example 48

B

10.0

Example 49

B

5.0

Example 50

C

7.5

Example 51

C

10.0

Example 52

D

7.5

Comparative

—

—

Example 19

Comparative

B

0.1

Example 20

Comparative

C

5.0

Example 21

Production of black composite hematite

particles

Coating of carbon black

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

C) (wt. %)

Example 43

441

45

30

9.08

Example 44

294

30

60

4.76

Example 45

588

60

20

6.96

Example 46

294

30

45

9.09

Example 47

441

45

30

6.95

Example 48

441

45

45

9.07

Example 49

294

30

60

4.76

Example 50

588

60

30

6.96

Example 51

735

75

20

9.05

Example 52

588

60

30

6.95

Comparative

—

—

—

Example 19

Comparative

588

60

30

0.01

Example 20

Comparative

588

60

30

4.76

Example 21

TABLE 18

Properties of black composite hematite

particles

Average

major axial

Average

Examples

diameter

minor

Geometrical

and

(average

axial

Aspect

standard

Comparative

particle

diameter

ratio

deviation value

Examples

size) (μm)

(μm)

(−)

(−)

Example 43

0.32

—

—

1.48

Example 44

0.18

—

—

1.41

Example 45

0.12

—

—

1.35

Example 46

0.30

—

—

1.41

Example 47

0.23

0.029

7.9:1

1.38

Example 48

0.32

—

—

1.48

Example 49

0.19

—

—

1.40

Example 50

0.12

—

—

1.36

Example 51

0.30

—

—

1.41

Example 52

0.23

0.029

7.9:1

1.38

Comparative

0.32

—

—

1.48

Example 19

Comparative

0.11

—

—

1.36

Example 20

Comparative

0.12

—

—

1.36

Example 21

Properties of black composite hematite

particles

Examples

BET specific

Volume

and

surface area

Blackness

resistivity

Comparative

value

Mn content

(L* value)

value

Examples

(m

2

/g)

(wt. %)

(—)

(Ω· cm)

Example 43

4.4

12.4

18.3

6.2 × 10

3

Example 44

8.2

14.9

18.6

8.6 × 10

3

Example 45

15.1

—

20.7

1.5 × 10

4

Example 46

4.1

—

20.1

9.6 × 10

3

Example 47

35.9

—

20.6

1.8 × 10

4

Example 48

4.1

12.3

18.6

6.8 × 10

3

Example 49

8.1

15.0

18.8

9.4 × 10

3

Example 50

15.6

—

20.6

1.6 × 10

4

Example 51

4.2

—

19.9

1.1 × 10

4

Example 52

36.1

—

20.1

2.6 × 10

4

Comparative

3.8

12.9

21.5

3.9 × 10

7

Example 19

Comparative

17.2

—

35.6

5.4 × 10

8

Example 20

Comparative

19.1

—

25.8

1.9 × 10

8

Example 21

Properties of black composite hematite

particles

Examples and

Carbon black

Comparative

desorption percentage

Thickness of carbon

Examples

(%)

black coated (μm)

Example 43

5.3

0.0024

Example 44

6.1

0.0023

Example 45

7.2

0.0023

Example 46

8.9

0.0024

Example 47

9.1

0.0024

Example 48

1.3

0.0024

Example 49

2.6

0.0023

Example 50

3.2

0.0023

Example 51

4.4

0.0024

Example 52

1.8

0.0023

Comparative

—

—

Example 19

Comparative

—

—

Example 20

Comparative

61.2

—

Example 21

TABLE 19

Production conditions of magnetic

recording medium

Magnetic particles

Amount blended

Examples

Kind

(part by weight)

Example 53

Magnetic particles

100.0

used in Example 1

Example 54

Magnetic particles

100.0

used in Example 1

Example 55

Magnetic particle 1

100.0

Example 56

Magnetic particle 1

100.0

Example 57

Magnetic particle 1

100.0

Example 58

Magnetic particle 1

100.0

Example 59

Magnetic particle 1

100.0

Example 60

Magnetic particle 1

100.0

Example 61

Magnetic particle 2

100.0

Example 62

Magnetic particle 3

100.0

Example 63

Magnetic particles

100.0

used in Example 1

Example 64

Magnetic particles

100.0

used in Example 1

Example 65

Magnetic particle 1

100.0

Example 66

Magnetic particle 1

100.0

Example 67

Magnetic particle 1

100.0

Example 68

Magnetic particle 1

100.0

Example 69

Magnetic particle 1

100.0

Example 70

Magnetic particle 1

100.0

Example 71

Magnetic particle 2

100.0

Example 72

Magnetic particle 3

100.0

Example 73

Magnetic particles

100.0

used in Example 1

Example 74

Magnetic particles

100.0

used in Example 1

Example 75

Magnetic particle 1

100.0

Example 76

Magnetic particle 1

100.0

Example 77

Magnetic particle 1

100.0

Example 78

Magnetic particle 1

100.0

Example 79

Magnetic particle 1

100.0

Example 80

Magnetic particle 1

100.0

Example 81

Magnetic particle 2

100.0

Example 82

Magnetic particle 3

100.0

Production conditions of

magnetic recording medium

Properties of

Filler

magnetic

Amount

coating

blended

composition

(part by

Viscosity

Examples

Kind

weight)

(cP)

Example 53

Example 23

7.0

2,816

Example 54

Example 24

7.0

2,577

Example 55

Example 25

10.0

2,560

Example 56

Example 26

14.0

3,328

Example 57

Example 27

21.0

2,304

Example 58

Example 28

7.0

2,048

Example 59

Example 29

7.0

2,816

Example 60

Example 30

15.0

2,560

Example 61

Example 31

10.0

6,892

Example 62

Example 32

7.0

5,658

Example 63

Example 33

7.0

2,304

Example 64

Example 34

7.0

2,560

Example 65

Example 35

10.0

3,328

Example 66

Example 36

14.0

2,048

Example 67

Example 37

21.0

3,200

Example 68

Example 38

7.0

2,893

Example 69

Example 39

7.0

2,688

Example 70

Example 40

15.0

2,708

Example 71

Example 41

10.0

7,302

Example 72

Example 42

7.0

5,830

Example 73

Example 43

7.0

2,713

Example 74

Example 44

7.0

2,893

Example 75

Example 45

10.0

2,688

Example 76

Example 46

14.0

2,560

Example 77

Example 47

21.0

2,048

Example 78

Example 48

7.0

2,074

Example 79

Example 49

7.0

3,200

Example 80

Example 50

15.0

3,328

Example 81

Example 51

10.0

6,968

Example 82

Example 52

7.0

4,898

TABLE 20

Production conditions of magnetic

recording medium

Magnetic particles

Comparative

Amount blended

Examples

Kind

(part by weight)

Comparative

Magnetic particle 1

100.0

Example 22

Comparative

Magnetic particle 1

100.0

Example 23

Comparative

Magnetic particle 1

100.0

Example 24

Comparative

Magnetic particle 1

100.0

Example 25

Comparative

Magnetic particle 1

100.0

Example 26

Comparative

Magnetic particle 1

100.0

Example 27

Comparative

Magnetic particle 1

100.0

Example 28

Comparative

Magnetic particle 1

100.0

Example 29

Comparative

Magnetic particle 1

100.0

Example 30

Production conditions of

magnetic recording medium

Properties of

Filler

magnetic

Amount

coating

blended

composition

(part by

Viscosity

Examples

Kind

weight)

(cP)

Comparative

Comparative

7.0

2,893

Example 22

Example 13

Comparative

Comparative

7.0

3,304

Example 23

Example 14

Comparative

Comparative

7.0

3,925

Example 24

Example 15

Comparative

Comparative

7.0

3,862

Example 25

Example 16

Comparative

Comparative

7.0

3,568

Example 26

Example 17

Comparative

Comparative

7.0

3,302

Example 27

Example 18

Comparative

Comparative

7.0

3,302

Example 28

Example 19

Comparative

Comparative

7.0

3,046

Example 29

Example 20

Comparative

Comparative

7.0

4,188

Example 30

Example 21

TABLE 21

Properties of magnetic

recording medium

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Example 53

Reference

59.8

751

tape 1

Example 54

Reference

59.9

753

tape 1

Example 55

Reference

80.4

1,010

tape 2

Example 56

Reference

80.2

1,008

tape 2

Example 57

Reference

80.1

1,006

tape 2

Example 58

Reference

79.3

996

tape 2

Example 59

Reference

79.4

998

tape 2

Example 60

Reference

79.6

1,000

tape 2

Example 61

Reference

185.1

2,326

tape 3

Example 62

Reference

202.4

2,543

tape 4

Properties of magnetic recording medium

Surface

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Example 53

0.87

185

7.2

Example 54

0.88

183

7.5

Example 55

0.88

186

7.2

Example 56

0.89

188

7.0

Example 57

0.88

182

7.4

Example 58

0.90

191

6.4

Example 59

0.90

191

6.6

Example 60

0.89

183

7.3

Example 61

0.88

238

7.0

Example 62

0.87

206

6.0

Properties of magnetic recording medium

Linear

Electromagnetic performance

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Example 53

1.63

+2.1

—

Example 54

1.65

+2.5

—

Example 55

1.56

—

+2.2

Example 56

1.57

—

+2.4

Example 57

1.58

—

+2.3

Example 58

1.56

—

+2.7

Example 59

1.56

—

+3.0

Example 60

1.58

—

+2.1

Example 61

1.81

—

+5.0

Example 62

1.53

—

+4.0

Properties of magnetic recording medium

Durability

Running

Surface

durability

Head

resistivity

Examples

time (min)

contamination

value (Ω/cm

2

)

Example 53

26.2

A

6.3 × 10

7

Example 54

27.3

A

5.2 × 10

7

Example 55

26.6

A

2.6 × 10

8

Example 56

26.8

A

3.4 × 10

8

Example 57

26.9

A

8.6 × 10

7

Example 58

29.3

A

6.1 × 10

7

Example 59

≧30

A

1.6 × 10

7

Example 60

28.3

A

2.8 × 10

8

Example 61

26.6

A

4.1 × 10

7

Example 62

26.8

A

4.6 × 10

8

TABLE 22

Properties of magnetic

recording medium

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Example 63

Reference

59.8

751

tape 1

Example 64

Reference

59.7

750

tape 1

Example 65

Reference

79.5

999

tape 2

Example 66

Reference

79.4

998

tape 2

Example 67

Reference

80.1

1,006

tape 2

Example 68

Reference

80.4

1,010

tape 2

Example 69

Reference

80.2

1,008

tape 2

Example 70

Reference

80.1

1,006

tape 2

Example 71

Reference

184.3

2,316

tape 3

Example 72

Reference

201.5

2,532

tape 4

Properties of magnetic recording medium

Surface

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Example 63

0.88

183

7.3

Example 64

0.87

183

7.6

Example 65

0.88

185

7.3

Example 66

0.88

183

7.6

Example 67

0.87

186

7.2

Example 68

0.88

185

7.5

Example 69

0.88

183

7.3

Example 70

0.88

186

7.0

Example 71

0.88

236

7.3

Example 72

0.87

202

6.8

Properties of magnetic recording medium

Linear

Electromagnetic performance

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Example 63

1.61

+2.0

—

Example 64

1.63

+2.1

—

Example 65

1.53

—

+2.0

Example 66

1.50

—

+2.3

Example 67

1.51

—

+2.5

Example 68

1.53

—

+2.2

Example 69

1.55

—

+2.3

Example 70

1.56

—

+2.4

Example 71

1.86

—

+5.1

Example 72

1.50

—

+3.8

Properties of magnetic recording medium

Durability

Running

Surface

durability

Head

resistivity

Examples

time (min)

contamination

value (Ω/cm

2

)

Example 63

29.6

A

8.3 × 10

7

Example 64

28.8

A

8.7 × 10

7

Example 65

27.3

A

3.1 × 10

8

Example 66

26.8

A

2.6 × 10

8

Example 67

27.3

A

6.9 × 10

7

Example 68

28.3

A

5.9 × 10

7

Example 69

≧30

A

3.1 × 10

7

Example 70

≧30

A

2.2 × 10

8

Example 71

26.8

A

4.6 × 10

7

Example 72

26.3

A

1.8 × 10

8

TABLE 23

Properties of magnetic

recording medium

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Example 73

Reference

59.9

753

tape 1

Example 74

Reference

59.7

750

tape 1

Example 75

Reference

80.5

1,011

tape 2

Example 76

Reference

80.1

1,006

tape 2

Example 77

Reference

79.8

1,003

tape 2

Example 78

Reference

79.3

996

tape 2

Example 79

Reference

79.5

999

tape 2

Example 80

Reference

80.4

1,010

tape 2

Example 81

Reference

185.7

2,333

tape 3

Example 82

Reference

200.8

2,523

tape 4

Properties of magnetic recording medium

Surface

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Example 73

0.88

186

7.0

Example 74

0.87

188

6.7

Example 75

0.88

189

6.5

Example 76

0.89

191

6.0

Example 77

0.89

186

6.9

Example 78

0.88

189

6.4

Example 79

0.90

192

5.8

Example 80

0.88

190

6.2

Example 81

0.88

237

6.4

Example 82

0.87

201

6.4

Properties of magnetic recording medium

Linear

Electromagnetic performance

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Example 73

1.66

+2.4

—

Example 74

1.68

+2.2

—

Example 75

1.53

—

+2.6

Example 76

1.58

—

+2.2

Example 77

1.57

—

+2.5

Example 78

1.56

—

+2.3

Example 79

1.58

—

+2.1

Example 80

1.56

—

+2.6

Example 81

1.84

—

+5.5

Example 82

1.50

—

+4.5

Properties of magnetic recording medium

Durability

Running

Surface

durability

Head

resistivity

Examples

time (min)

contamination

value (Ω/cm

2

)

Example 73

26.9

A

6.9 × 10

7

Example 74

26.9

A

7.3 × 10

7

Example 75

27.1

A

2.6 × 10

8

Example 76

28.3

A

3.2 × 10

8

Example 77

28.0

A

8.3 × 10

7

Example 78

29.3

A

6.1 × 10

7

Example 79

29.6

A

4.4 × 10

7

Example 80

29.8

A

2.3 × 10

8

Example 81

27.7

A

4.4 × 10

7

Example 82

27.1

A

4.6 × 10

8

TABLE 24

Properties of magnetic

recording medium

Comparative

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Comparative

Reference

79.6

1,000

Example 22

tape 2

Comparative

Reference

79.0

993

Example 23

tape 2

Comparative

Reference

78.9

992

Example 24

tape 2

Comparative

Reference

79.3

996

Example 25

tape 2

Comparative

Reference

78.6

988

Example 26

tape 2

Comparative

Reference

78.7

989

Example 27

tape 2

Comparative

Reference

79.0

993

Example 28

tape 2

Comparative

Reference

79.2

995

Example 29

tape 2

Comparative

Reference

78.8

990

Example 30

tape 2

Properties of magnetic recording medium

Surface

Comparative

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Comparative

0.84

156

9.6

Example 22

Comparative

0.84

158

9.4

Example 23

Comparative

0.84

152

10.4

Example 24

Comparative

0.84

153

10.2

Example 25

Comparative

0.85

156

9.8

Example 26

Comparative

0.84

158

9.2

Example 27

Comparative

0.84

151

9.9

Example 28

Comparative

0.84

153

10.4

Example 29

Comparative

0.84

155

10.0

Example 30

Properties of magnetic recording medium

Linear

Electromagnetic performance

Comparative

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Comparative

1.21

—

+0.3

Example 22

Comparative

1.06

—

+0.2

Example 23

Comparative

1.21

—

0.0

Example 24

Comparative

1.22

—

+0.4

Example 25

Comparative

1.09

—

−0.1

Example 26

Comparative

1.22

—

−0.3

Example 27

Comparative

1.21

—

+0.3

Example 28

Comparative

1.09

—

+0.2

Example 29

Comparative

1.23

—

+0.2

Example 30

Properties of magnetic recording medium

Durability

Running

Surface

Comparative

durability

Head

resistivity

Examples

time (min)

contamination

value (Ω/cm

2

)

Comparative

15.0

C

1.9 × 10

10

Example 22

Comparative

14.3

C

3.2 × 10

10

Example 23

Comparative

14.1

C

2.1 × 10

10

Example 24

Comparative

12.2

C

1.6 × 10

10

Example 25

Comparative

10.6

C

3.6 × 10

10

Example 26

Comparative

11.3

C

2.4 × 10

10

Example 27

Comparative

13.8

C

1.9 × 10

10

Example 28

Comparative

14.3

C

3.1 × 10

10

Example 29

Comparative

11.9

C

2.6 × 10

10

Example 30

TABLE 25

Production of black composite

hematite particles

Coating with fluoroalkylsilane

Examples and

Additive

Comparative

Kind of core

Amount added

Examples

particles

Kind

(part by weight)

Example 84

Core

Tridecafluorooctyl

2.0

particles 1

trimethoxysilane

Example 85

Core

Heptadecafluorodecyl

4.0

particles 2

trimethoxysilane

Example 86

Core

Trifluoropropyl

3.0

particles 3

trimethoxysilane

Example 87

Core

Tridecafluorooctyl

1.5

particles 4

trimethoxysilane

Example 88

Core

Heptadecafluorodecyl

5.0

particles 5

trimethoxysilane

Example 89

Core

Tridecafluorooctyl

2.0

particles 6

trimethoxysilane

Example 90

Core

Heptadecafluorodecyl

4.0

particles 7

trimethoxysilane

Example 91

Core

Trifluoropropyl

3.0

particles 8

trimethoxysilane

Example 92

Core

Tridecafluorooctyl

2.5

particles 9

trimethoxysilane

Example 93

Core

Heptadecafluorodecyl

5.0

particles 10

trimethoxysilane

Comparative

Core

Tridecafluorooctyl

1.0

Example 31

particles 1

trimethoxysilane

Comparative

Core

Tridecafluorooctyl

0.5

Example 32

particles 3

trimethoxysilane

Comparative

Core

Tridecafluorooctyl

0.005

Example 33

particles 3

trimethoxysilane

Production of black composite hematite

particles

Coating with fluoroalkylsilane

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

Si) (wt. %)

Example 84

588

60

30

0.11

Example 85

294

30

30

0.19

Example 86

588

60

45

0.37

Example 87

441

45

45

0.08

Example 88

588

60

30

0.23

Example 89

294

30

30

0.10

Example 90

588

60

45

0.18

Example 91

441

45

45

0.36

Example 92

588

60

30

0.14

Example 93

294

30

30

0.23

Comparative

588

60

30

0.05

Example 31

Comparative

588

60

30

0.02

Example 32

Comparative

588

60

30

2 × 10

−4

Example 33

Production of black composite hematite

particles

Coating of carbon black

Examples and

Carbon black

Comparative

Amount added

Examples

Kind

(part by weight)

Example 84

B

7.5

Example 85

B

5.0

Example 86

C

5.0

Example 87

C

10.0

Example 88

D

10.0

Example 89

B

7.5

Example 90

B

5.0

Example 91

C

5.0

Example 92

C

10.0

Example 93

D

10.0

Comparative

—

—

Example 31

Comparative

B

0.01

Example 32

Comparative

C

5.0

Example 33

Production of black composite hematite

particles

Coating of carbon black

Examples and

Edge runner treatment

Coating amount

Comparative

Linear load

Time

(calculated as

Examples

(N/cm)

(kg/cm)

(min)

C) (wt. %)

Example 84

588

60

30

6.96

Example 85

588

60

30

4.75

Example 86

294

30

60

4.74

Example 87

294

30

30

9.09

Example 88

441

45

30

9.08

Example 89

441

45

45

6.97

Example 90

588

60

30

4.75

Example 91

588

60

20

4.75

Example 92

294

30

30

9.05

Example 93

294

30

30

9.08

Comparative

—

—

—

—

Example 31

Comparative

588

60

30

0.01

Example 32

Comparative

588

60

30

4.74

Example 33

TABLE 26

Properties of black composite hematite

particles

Average

major axial

Average

Examples

diameter

minor

Geometrical

and

(average

axial

Aspect

standard

Comparative

particle

diameter

ratio

deviation value

Examples

size) (μm)

(μm)

(−)

(−)

Example 84

0.32

—

—

1.48

Example 85

0.18

—

—

1.41

Example 86

0.11

—

—

1.35

Example 87

0.29

—

—

1.41

Example 88

0.23

0.029

7.9:1

1.38

Example 89

0.32

—

—

1.48

Example 90

0.19

—

—

1.42

Example 91

0.12

—

—

1.36

Example 92

0.30

—

—

1.41

Example 93

0.23

0.029

7.9:1

1.38

Comparative

0.32

—

—

1.49

Example 31

Comparative

0.11

—

—

1.35

Example 32

Comparative

0.12

—

—

1.35

Example 33

Properties of black composite hematite

particles

Examples

Volume

and

BET specific

Blackness

resistivity

Comparative

surface area

Mn content

(L* value)

value

Examples

value (m

2

/g)

(wt. %)

(−)

(Ω · cm)

Example 84

4.3

11.9

18.1

8.6 × 10

3

Example 85

8.1

14.3

18.3

9.0 × 10

3

Example 86

15.0

—

20.4

2.4 × 10

4

Example 87

4.1

—

20.2

9.8 × 10

3

Example 88

36.1

—

20.3

1.1 × 10

4

Example 89

3.8

11.8

18.2

8.9 × 10

3

Example 90

7.9

14.3

18.5

9.3 × 10

3

Example 91

15.6

—

20.5

2.6 × 10

4

Example 92

4.1

—

20.2

1.4 × 10

4

Example 93

35.9

—

20.0

1.9 × 10

4

Comparative

3.8

12.9

21.3

4.6 × 10

7

Example 31

Comparative

15.1

—

36.0

5.9 × 10

8

Example 32

Comparative

18.3

—

25.8

2.6 × 10

8

Example 33

Properties of black composite hematite

particles

Examples and

Carbon black

Comparative

desorption percentage

Thickness of carbon

Examples

(%)

black coated (μm)

Example 84

6.6

0.0024

Example 85

7.7

0.0023

Example 86

8.3

0.0023

Example 87

6.4

0.0024

Example 88

5.9

0.0024

Example 89

4.3

0.0023

Example 90

3.8

0.0022

Example 91

1.6

0.0023

Example 92

2.9

0.0024

Example 93

4.1

0.0024

Comparative

—

—

Example 31

Comparative

—

—

Example 32

Comparative

66.6

—

Example 33

TABLE 27

Production conditions of magnetic

recording medium

Examples and

Magnetic particles

Comparative

Amount blended

Examples

Kind

(part by weight)

Example 94

Magnetic particles used

100.0

in Example 1

Example 95

Magnetic particles used

100.0

in Example 1

Example 96

Magnetic particle 1

100.0

Example 97

Magnetic particle 1

100.0

Example 98

Magnetic particle 1

100.0

Example 99

Magnetic particle 1

100.0

Example 100

Magnetic particle 1

100.0

Example 101

Magnetic particle 1

100.0

Example 102

Magnetic particle 2

100.0

Example 103

Magnetic particle 3

100.0

Comparative

Magnetic particle 1

100.0

Example 34

Comparative

Magnetic particle 1

100.0

Example 35

Comparative

Magnetic particle 1

100.0

Example 36

Production conditions of

magnetic recording medium

Properties of

Filler

magnetic

Amount

coating

Examples and

blended

composition

Comparative

(part by

Viscosity

Examples

Kind

weight)

(cP)

Example 94

Example 84

7.0

2,541

Example 95

Example 85

7.0

2,464

Example 96

Example 86

10.0

2,711

Example 97

Example 87

14.0

2,832

Example 98

Example 88

21.0

2,659

Example 99

Example 89

7.0

2,720

Example 100

Example 90

7.0

2,791

Example 101

Example 91

15.0

2,883

Example 102

Example 92

10.0

7,156

Example 103

Example 93

7.0

5,938

Comparative

Comparative

7.0

2,844

Example 34

Example 31

Comparative

Comparative

7.0

2,304

Example 35

Example 32

Comparative

Comparative

7.0

3,685

Example 36

Example 33

TABLE 28

Properties of

magnetic recording

Examples and

medium

Comparative

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Example 94

Reference

59.7

750

tape 1

Example 95

Reference

59.5

748

tape 1

Example 96

Reference

80.1

1,006

tape 2

Example 97

Reference

80.4

1,010

tape 2

Example 98

Reference

80.5

1,012

tape 2

Example 99

Reference

79.7

1,001

tape 2

Example 100

Reference

79.8

1,003

tape 2

Example 101

Reference

80.3

1,009

tape 2

Example 102

Reference

183.9

2,311

tape 3

Example 103

Reference

201.3

2,530

tape 4

Comparative

Reference

79.3

996

Example 34

tape 2

Comparative

Reference

78.8

990

Example 35

tape 2

Comparative

Reference

79.4

998

Example 36

tape 2

Properties of magnetic recording medium

Examples and

Surface

Comparative

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Example 94

0.87

188

6.8

Example 95

0.87

186

6.9

Example 96

0.88

193

6.4

Example 97

0.88

196

6.2

Example 98

0.88

199

6.0

Example 99

0.89

198

6.2

Example 100

0.89

196

6.1

Example 101

0.89

196

6.3

Example 102

0.88

241

6.0

Example 103

0.87

210

6.0

Comparative

0.84

155

10.1

Example 34

Comparative

0.83

152

10.2

Example 35

Comparative

0.82

141

11.0

Example 36

Properties of magnetic recording medium

Electromagnetic

Examples and

Linear

performance

Comparative

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Example 94

1.65

+2.1

—

Example 95

1.66

+2.1

—

Example 96

1.54

—

+2.1

Example 97

1.58

—

+2.2

Example 98

1.58

—

+2.3

Example 99

1.54

—

+2.3

Example 100

1.56

—

+2.4

Example 101

1.58

—

+2.2

Example 102

1.83

—

+2.2

Example 103

1.49

—

+2.3

Comparative

1.22

—

±0.0

Example 34

Comparative

1.05

—

+0.3

Example 35

Comparative

1.20

—

+0.1

Example 36

Properties of magnetic recording medium

Durability

Examples and

Running

Surface

Comparative

durability

Head

resistivity

Examples

time (min)

contamination

(Ω/cm

2

)

Example 94

26.8

A

6.9 × 10

7

Exampie 95

28.5

A

8.3 × 10

7

Example 96

26.9

A

2.4 × 10

8

Example 97

28.3

A

4.8 × 10

8

Example 98

26.9

A

9.2 × 10

7

Example 99

29.6

A

6.1 × 10

7

Example 100

28.3

A

1.6 × 10

7

Example 101

≧30

A

2.3 × 10

8

Example 102

26.6

A

2.6 × 10

7

Example 103

26.0

A

1.9 × 10

8

Comparative

14.2

C

2.8 × 10

10

Example 34

Comparative

9.6

D

3.1 × 10

10

Example 35

Comparative

8.3

D

2.4 × 10

10

Example 36

TABLE 29

Production of black composite

hematite particles

Coating with alkoxysilane,

polysiloxane or silicon compound

Additive

Examples and

Amount added

Comparative

Kind of core

(part by

Examples

particles

Kind

weight)

Example 105

Core

Methyl

1.0

particles 1

triethoxysilane

Example 106

Core

Methyl

2.0

particles 2

trimethoxysilane

Example 107

Core

Dimethyl

1.5

particles 3

dimethoxysilane

Example 108

Core

Phenyl

2.0

particles 4

triethoxysilane

Example 109

Core

Isobutyl

1.0

particles 5

trimethoxysilane

Example 110

Core

Methyl

1.5

particles 6

triethoxysilane

Example 111

Core

Methyl

1.5

particles 7

trimethoxysilane

Example 112

Core

TSF484

1.0

particles 8

Example 113

Core

BYK-080

1.0

particles 11

Example 114

Core

TSF4770

1.5

particles 10

Example 115

Core

Methyl

1.5

particles 1

triethoxysilane

Example 116

Core

Methyl

1.5

particles 1

triethoxysilane

Comparative

Core

—

—

Example 37

particles 1

Comparative

Core

Methyl

0.005

Example 38

particles 1

triethoxysilane

Comparative

Core

Methyl

1.0

Example 39

particles 1

triethoxysilane

Comparative

Core

γ-aminopropyl

1.0

Example 40

particles 1

triethoxysilane

Production of black composite hematite

particles

Coating with alkoxysilane, polysiloxane or

silicon compound

Coating amount

Examples and

Edge runner treatment

(calculated as

Comparative

Linear load

Time

Si)

Examples

(N/cm)

(kg/cm)

(min)

(wt. %)

Example 105

392

40

30

0.15

Example 106

441

45

30

0.39

Example 107

735

75

30

0.21

Example 108

588

60

20

0.13

Example 109

588

60

30

0.22

Example 110

588

60

20

0.23

Example 111

392

40

45

0.29

Example 112

588

60

20

0.65

Example 113

735

75

20

0.36

Example 114

441

45

35

0.34

Example 115

392

40

25

0.22

Example 116

735

75

20

0.23

Comparative

—

—

—

—

Example 37

Comparative

294

30

20

7 × 10

−4

Example 38

Comparative

294

30

20

0.15

Example 39

Comparative

294

30

20

0.13

Example 40

Production of black composite

hematite particles

Coating of carbon black

Examples and

Carbon black

Comparative

Amount added

Examples

Kind

(part by weight)

Example 105

A

15.0

Example 106

A

25.0

Example 107

B

7.5

Example 108

B

17.5

Example 109

C

10.0

Example 110

C

20.0

Example 111

D

10.0

Example 112

D

15.0

Example 113

B

12.5

Example 114

B

15.0

Example 115

E

15.0

Example 116

F

15.0

Comparative

B

15.0

Example 37

Comparative

C

15.0

Example 38

Comparative

D

35.0

Example 39

Comparative

D

15.0

Example 40

Production of black composite hematite

particles

Coating of carbon black

Coating amount

Examples and

Edge runner treatment

(calculated as

Comparative

Linear load

Time

C)

Examples

(N/cm)

(kg/cm)

(min)

(wt. %)

Example 105

588

60

20

13.01

Example 106

588

60

30

19.88

Example 107

392

40

30

6.92

Example 108

735

75

25

14.69

Example 109

392

40

45

9.05

Example 110

294

30

40

16.48

Example 111

735

75

30

9.00

Example 112

588

60

25

12.99

Example 113

588

60

20

11.04

Example 114

294

30

20

12.96

Example 115

588

60

20

13.00

Example 116

588

60

30

12.95

Comparative

294

30

20

13.01

Example 37

Comparative

294

30

20

13.00

Example 38

Comparative

294

30

20

25.88

Example 39

Comparative

294

30

20

12.99

Example 40

TABLE 30

Properties of black composite hematite particles

Average

major axial

Average

Examples

diameter

minor

Geometrical

and

(average

axial

Aspect

standard

Comparative

particle

diameter

ratio

deviation value

Examples

size) (μm)

(μm)

(—)

(—)

Example 105

0.32

—

—

1.48

Example 106

0.19

—

—

1.42

Example 107

0.11

—

—

1.37

Example 108

0.29

—

—

1.41

Example 109

0.23

0.029

7.9:1

1.37

Example 110

0.32

—

—

1.49

Example 111

0.18

—

—

1.41

Example 112

0.12

—

—

1.35

Example 113

0.29

—

—

1.40

Example 114

0.24

0.030

8.0:1

1.38

Example 115

0.32

—

—

1.49

Example 116

0.32

—

—

1.49

Comparative

0.32

—

—

—

Example 37

Comparative

0.32

—

—

—

Example 38

Comparative

0.32

—

—

—

Example 39

Comparative

0.32

—

—

—

Example 40

Properties of black composite hematite particles

Volume

and

BET specific

Blackness

resistivity

Comparative

surface area

Mn content

(L* value)

value

Examples

value (m

2

/g)

(wt. %)

(—)

(Ω · cm)

Example 105

7.4

11.3

17.4

4.0 × 10

3

Example 106

13.3

12.3

17.9

5.3 × 10

3

Example 107

17.6

—

19.6

8.4 × 10

3

Example 108

7.6

—

18.4

5.6 × 10

3

Example 109

38.9

—

18.3

7.9 × 10

3

Example 110

8.8

10.7

17.3

3.5 × 10

3

Example 111

10.0

13.9

18.0

6.0 × 10

3

Example 112

18.7

—

19.2

4.4 × 10

3

Example 113

7.5

—

18.6

5.1 × 10

3

Example 114

40.1

—

18.0

5.8 × 10

3

Example 115

7.6

11.2

17.4

1.6 × 10

3

Example 116

9.2

11.2

17.4

1.1 × 10

3

Comparative

15.8

11.4

19.2

4.1 × 10

6

Example 37

Comparative

14.2

11.3

19.6

2.6 × 10

6

Example 38

Comparative

16.6

9.6

19.2

1.6 × 10

5

Example 39

Comparative

12.8

11.3

19.9

1.3 × 10

6

Example 40

Properties of black composite hematite

particles

Examples and

Carbon black

Thickness of carbon

Comparative

desorption percentage

black coated

Examples

(%)

(μm)

Example 105

8.1

0.0025

Example 106

8.6

0.0026

Example 107

7.9

0.0023

Example 108

8.2

0.0024

Example 109

7.8

0.0024

Example 110

4.7

0.0026

Example 111

3.8

0.0024

Example 112

4.6

0.0025

Example 113

4.5

0.0024

Example 114

4.1

0.0024

Example 115

9.8

0.0026

Example 116

9.9

0.0027

Comparative

69.2

—

Example 37

Comparative

56.3

—

Example 38

Comparative

23.2

—

Example 39

Comparative

51.6

—

Example 40

TABLE 31

Properties of non-magnetic particles for non-

magnetic undercoat layer

Average

Average

Non-

major axial

minor axial

magnetic

Particle

diameter

diameter

particles

Kind

size

(μm)

(μm)

Non-

Hematite

Spindle-

0.187

0.0240

magnetic

particles

shaped

particles 1

Non-

Goethite

Acicular

0.240

0.0272

magnetic

particles

particles 2

Non-

Hematite

Acicular

0.143

0.0210

magnetic

particles

particles 3

Non-

Hematite

Acicular

0.115

0.0179

magnetic

particles

particles 4

Non-

Hematite

Acicular

0.143

0.0211

magnetic

particles

particles 5

Non-

Goethite

Acicular

0.240

0.0273

magnetic

particles

particles 6

Properties of non-magnetic particles for non-

magnetic undercoat layer

BET

Geometrical

specific

Coating

Non-

standard

surface

amount of

magnetic

Aspect

deviation

area value

Al

particles

ratio (−)

value (−)

(m

2

/g)

(wt. %)

Non-

7.8:1

1.33

43.3

—

magnetic

particles 1

Non-

8.8:1

1.37

86.3

—

magnetic

particies 2

Non-

6.8:1

1.37

54.9

0.98

magnetic

particles 3

Non-

6.4:1

1.35

58.3

—

magnetic

particles 4

Non-

6.8:1

1.37

55.6

—

magnetic

particles 5

Non-

8.8:1

1.35

88.1

—

magnetic

particles 6

Properties of non-magnetic particles for non-

magnetic undercoat layer

Amount of

carbon

black

coated

Volume

Non-

(calculated

resistivity

Blackness

magnetic

Al content

as C)

value

(L* value)

particles

(wt. %)

(wt. %)

(Ω · cm)

(−)

Non-

—

—

8.6 × 10

8

32.6

magnetic

particles 1

Non-

—

—

9.6 × 10

7

34.6

magnetic

particles 2

Non-

—

—

4.6 × 10

8

28.4

magnetic

particles 3

Non-

0.67

—

3.2 × 10

8

29.6

magnetic

particles 4

Non-

—

4.75

3.6 × 10

4

18.5

magnetic

particles 5

Non-

—

4.81

5.8 × 10

3

20.3

magnetic

particles 6

TABLE 32

Production of non-magnetic

Properties of

coating composition

non-magnetic

Weight ratio

coating

Kind of non-

of particles

composition

Undercoat

magnetic

to resin

Viscosity

layer

particles

(−)

(cP)

Undercoat

Non-magnetic

5.0

315

layer 1

particles 1

Undercoat

Non-magnetic

5.0

1,139

layer 2

particles 2

Undercoat

Non-magnetic

5.0

448

layer 3

particles 3

Undercoat

Non-magnetic

5.0

403

layer 4

particles 4

Undercoat

Non-magnetic

5.0

399

layer 5

particles 5

Undercoat

Non-magnetic

5.0

1,336

layer 6

particles 6

Properties of non-magnetic undercoat layer

Surface

Undercoat

Thickness

Gloss

roughness Ra

layer

(μm)

(%)

(nm)

Undercoat

3.4

191

8.2

layer 1

Undercoat

3.5

180

12.0

layer 2

Undercoat

3.4

205

6.3

layer 3

Undercoat

3.4

211

6.2

layer 4

Undercoat

3.4

199

7.1

layer 5

Undercoat

3.5

185

9.0

layer 6

Properties of non-magnetic undercoat layer

Surface

Young's modulus

Linear

resistivity

Undercoat

(relative

absorption

value

layer

value)

(μm

−1

)

(Ω/cm

2

)

Undercoat

124

1.03

1.5 × 10

14

layer 1

Undercoat

125

0.79

2.1 × 10

13

layer 2

Undercoat

126

1.01

3.5 × 10

13

layer 3

Undercoat

125

0.98

3.6 × 10

13

layer 4

Undercoat

125

1.52

4.1 × 10

9

iayer 5

Undercoat

129

1.49

2.3 × 10

10

layer 6

TABLE 33

Production conditions of reference tape

Magnetic particles

Undercoat

Amount blended

Reference

layer

(part by

tape

Kind

Kind

weight)

Reference

Undercoat

Magnetic

100.0

tape 5

layer 1

particles used

in Example 104

Reference

Undercoat

Magnetic

100.0

tape 6

layer 2

particles 4

Reference

Undercoat

Magnetic

100.0

tape 7

layer 3

particle 5

Reference

Undercoat

Magnetic

100.0

tape 8

layer 4

particle 6

Production conditions of

reference tape

Properties of

Filler

magnetic

Amount

coating

blended

composition

Reference

(part by

Viscosity

tape

Kind

weight)

(cP)

Reference

Al

2

O

3

7.0

2,611

tape 5

Reference

Al

2

O

3

7.0

2,590

tape 6

Reference

Al

2

O

3

7.0

8,753

tape 7

Reference

Al

2

O

3

7.0

6,392

tape 8

TABLE 34

Properties of reference tape

Coercive force value

Reference tape

(kA/m)

(Oe)

Reference tape 5

60.0

754

Reference tape 6

79.7

1,001

Reference tape 7

178.7

2,246

Reference tape 8

197.4

2,480

Properties of reference tape

Surface

Squareness

Gloss

roughness Ra

Reference tape

(−)

(%)

(nm)

Reference tape 5

0.82

136

12.5

Reference tape 6

0.83

147

11.9

Reference tape 7

0.82

180

10.6

Reference tape 8

0.80

157

12.0

Properties of reference tape

Electromagnetic

Linear

performance

absorption

4 MHz

7 MHz

Reference tape

(μm

−1

)

(dB)

(dB)

Reference tape 5

1.11

±0

—

Reference tape 6

1.08

—

±0

Reference tape 7

1.17

—

±0

Reference tape 8

1.10

—

±0

Properties of reference tape

Durability

Running

durability

Friction

Surface

Reference

time

Head

coefficient

resistivity

tape

(min)

contamination

(−)

(Ω/cm

2

)

Reference

23.5

A

0.32

1.6 × 10

10

tape 5

Reference

22.0

A

0.32

4.0 × 10

10

tape 6

Reference

20.6

B

0.35

3.8 × 10

10

tape 7

Reference

21.3

B

0.40

7.1 × 10

10

tape 8

TABLE 35

Production conditions of magnetic recording

medium

Magnetic particle

Examples and

Undercoat

Amount blended

Comparative

layer

(part by

Examples

Kind

Kind

weight)

Example 117

Undercoat

Magnetic

100.0

layer 1

particle 4

Example 118

Undercoat

Magnetic

100.0

layer 1

particle 4

Example 119

Undercoat

Magnetic

100.0

layer 1

particle 5

Example 120

Undercoat

Magnetic

100.0

layer 1

particle 5

Example 121

Undercoat

Magnetic

100.0

layer 1

particle 5

Example 122

Undercoat

Magnetic

100.0

layer 2

particle 5

Example 123

Undercoat

Magnetic

100.0

layer 3

particle 5

Example 124

Undercoat

Magnetic

100.0

layer 4

particle 6

Example 125

Undercoat

Magnetic

100.0

layer 5

particle 5

Example 126

Undercoat

Magnetic

100.0

layer 6

particle 5

Example 127

Undercoat

Magnetic

100.0

layer 3

particle 5

Example 128

Undercoat

Magnetic

100.0

layer 3

particle 5

Comparative

Undercoat

Magnetic

100.0

Example 41

layer 1

particle 4

Comparative

Undercoat

Magnetic

100.0

Example 42

layer 1

particle 4

Comparative

Undercoat

Magnetic

100.0

Example 43

layer 1

particle 5

Comparative

Undercoat

Magnetic

100.0

Example 44

layer 1

particle 5

Production conditions of

magnetic recording medium

Properties of

Filler

magnetic

Amount

coating

blended

composition

(part by

Viscosity

Examples

Kind

weight)

(cP)

Example 117

Example 105

7.0

2,864

Example 118

Example 106

7.0

2,560

Example 119

Example 107

10.0

5,680

Example 120

Example 108

14.0

5,762

Example 121

Example 109

21.0

4,140

Example 122

Example 110

7.0

6,243

Example 123

Example 111

7.0

7,250

Example 124

Example 112

15.0

3,834

Example 125

Example 113

10.0

6,326

Example 126

Example 114

7.0

5,813

Example 127

Example 115

7.0

5,216

Example 128

Example 116

7.0

4,896

Comparative

Comparative

7.0

2,768

Example 41

Example 37

Comparative

Comparative

7.0

2,832

Example 42

Example 38

Comparative

Comparative

7.0

10,240

Example 43

Example 39

Comparative

Comparative

7.0

9,680

Example 44

Example 40

TABLE 36

Properties of magnetic

Examples and

recording medium

Comparative

Reference

Coercive force value

Examples

tape

(kA/m)

(Oe)

Example 117

Reference

79.3

996

tape 2

Example 118

Reference

79.4

998

tape 2

Example 119

Reference

180.5

2,268

tape 3

Example 120

Reference

184.0

2,312

tape 3

Example 121

Reference

182.9

2,298

tape 3

Example 122

Reterence

182.3

2,291

tape 3

Example 123

Reference

181.7

2,283

tape 3

Example 124

Reference

206.1

2,590

tape 3

Example 125

Reference

182.5

2,293

tape 3

Example 126

Reference

184.3

2,316

tape 4

Example 127

Reference

180.5

2,268

tape 3

Example 128

Reference

181.1

2,276

tape 3

Comparative

Reference

177.5

2,231

Example 41

tape 3

Comparative

Reference

179.8

2,259

Example 42

tape 3

Comparative

Reference

180.5

2,268

Example 43

tape 3

Comparative

Reference

180.7

2,271

Example 44

tape 3

Properties of magnetic recording medium

Examples and

Surface

Comparative

Squareness

Gloss

roughness Ra

Examples

(−)

(%)

(nm)

Example 117

0.90

192

6.8

Example 118

0.90

193

6.9

Example 119

0.88

224

6.6

Example 120

0.89

230

6.4

Example 121

0.88

228

6.8

Example 122

0.89

233

6.5

Example 123

0.89

236

6.4

Example 124

0.88

202

6.6

Example 125

0.88

233

6.2

Example 126

0.89

230

6.0

Example 127

0.90

215

6.9

Example 128

0.90

213

7.0

Comparative

0.85

152

13.6

Example 41

Comparative

0.86

151

14.2

Example 42

Comparative

0.80

158

18.3

Example 43

Comparative

0.83

146

16.5

Example 44

Properties of magnetic recording medium

Electromagnetic

Examples and

Linear

performance

Comparative

absorption

4 MHz

7 MHz

Examples

(μm

−1

)

(dB)

(dB)

Example 117

1.35

+2.2

—

Example 118

1.37

+2.3

—

Example 119

1.36

—

+2.3

Example 120

1.41

—

+2.4

Example 121

1.42

—

+2.4

Example 122

1.42

—

+2.3

Example 123

1.46

—

+2.5

Example 124

1.48

—

+2.4

Example 125

1.50

—

+2.5

Example 126

1.43

—

+2.4

Example 127

1.35

—

+2.2

Example 128

1.36

—

+2.2

Comparative

1.16

—

+0.3

Example 41

Comparative

1.13

—

+0.1

Example 42

Comparative

1.19

—

−1.3

Example 43

Comparative

1.10

—

−1.3

Example 44

Properties of magnetic recording medium

Durability

Examples and

Running

Surface

Comparative

durability

Head

resistivity

Examples

time (min)

contamination

(Ω/cm

2

)

Example 117

27.2

B

7.3 × 10

7

Example 118

28.6

A

7.1 × 10

7

Example 119

27.2

B

9.4 × 10

7

Example 120

≧30

A

8.6 × 10

7

Example 121

26.9

B

6.9 × 10

7

Example 122

28.8

B

5.1 × 10

7

Example 123

≧30

A

4.3 × 10

7

Example 124

≧30

A

6.1 × 10

7

Example 125

28.6

A

1.3 × 10

7

Example 126

27.5

A

3.1 × 10

7

Example 127

25.0

B

3.2 × 10

7

Example 128

25.5

B

2.5 × 10

7

Comparative

11.6

D

7.6 × 10

9

Example 41

Comparative

14.6

C

8.6 × 10

9

Example 42

Comparative

15.2

C

8.3 × 10

9

Example 43

Comparative

12.3

C

7.6 × 10

9

Example 44

Number	Date	Country
11-125109	Apr 1999	JP
11-125115	Apr 1999	JP
11-125116	Apr 1999	JP
11-326190	Nov 1999	JP

Number	Name	Date	Kind
4089882	Takamizawa et al.	May 1978	A
4482623	Tabaru et al.	Nov 1984	A
4822850	Yashuda et al.	Apr 1989	A
5137783	Tanihara et al.	Aug 1992	A
5286291	Bernhardt et al.	Feb 1994	A
5686012	Hayashi et al.	Nov 1997	A
5876833	Suzuki et al.	Mar 1999	A
6024789	Kwan et al.	Feb 2000	A
6132743	Kuroda et al.	Oct 2000	A
6143403	Ejiri et al.	Nov 2000	A

Number	Date	Country
0165076	Dec 1985	EP
0176368	Apr 1986	EP
0825235	Feb 1998	EP
0913431	May 1999	EP
0957474	Nov 1999	EP
04157615	May 1992	JP

Magnetic recording medium

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (4)

US Referenced Citations (10)

Foreign Referenced Citations (6)

Non-Patent Literature Citations (1)