Thermal transfer recording medium

Abstract

A thermal transfer recording medium includes a sheet-like base member and a hot-melt ink layer containing a colorant and a hot-melt material. The hot-melt ink layer contains a hot-melt material having a melting point Tm of 70.degree. to 90.degree. C., a complex elastic modulus of 10.sup.6 Pa to 10.sup.7 Pa at 100.degree. C., and a pour point Tp of 150.degree. C. or more, the hot-melt ink layer is in an amorphous or microcrystalline state and satisfies condition I/I.sub.0 .ltoreq.0.9 where I is the diffraction peak intensity in a range of 21.3.degree. to 21.5.degree. originated from an ethylene-based crystal and measured by an x-ray diffraction method, and I0 is the halo intensity in a range of 16.degree. to 17.degree. originated from an amorphous part, or the hot-melt ink layer contains a low-melting point crystalline material having a specific acid value and a specific saponification value and 15 to 30 wt % of a specific copolymer resin whose ethylene content is 65 to 80 wt % and a melt index of 60 or less.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal transfer recording medium for transferring a hot-melt recording medium to a transfer medium by using a thermal head.

2. Description of the Related Art

A method of transferring a thermal transfer recording medium against a transfer medium on a thermal head at a predetermined pressure to melt a hot-melt colorant layer (ink layer) of the thermal transfer recording medium with thermal energy applied from the thermal head and to transfer the colorant layer to the transfer medium has been conventionally employed to transfer the thermal transfer recording medium to the transfer medium. During this transfer, most of the hot-melt colorant layer on the thermal transfer recording medium is transferred to the transfer medium. In order to perform recording using a thermal transfer recording medium, a thermal transfer recording medium having an area equal to or larger than a recording area is required. For this reason, a recording method using a thermal transfer recording medium is more expensive than an electrophotographic method and an ink-jet method.

In order to reduce the recording cost, a multi-time thermal transfer recording medium which can be used a plurality of times has been developed. An example of such a multi-time thermal transfer recording medium is described in Published Unexamined Japanese Patent Application No. 54-68253. In this example, a micro porous layer is formed using a resin, and a thermal ink is impregnated in the pores of the porous layer, thereby forming a thermal transfer recording medium. In this thermal transfer recording medium, the thermal ink is transferred from the pores to a transfer medium due to a permeation phenomenon. However, it takes a long period of time to melt the thermal ink with heat and cause it to permeation through the pores. The printing speed is low due to the above phenomenon, and the exudation amount of the thermal ink is also limited. As a result, it is difficult to obtain a transfer image having a high density. A proposal similar to the above prior art is made in Published Unexamined Japanese Patent Application No. 55-105579, but the same problem as described above is also posed.

Published Unexamined Japanese Patent Application No. 56-89984 discloses a multi-time thermal transfer recording medium in which an organic pigment (e.g., carbon black), a fine powder of a metal or metal oxide (e.g., aluminum or aluminum oxide), or any other inorganic pigment is added as a filler in a solid ink layer of the recording medium. A solid ink layer in the thermal transfer recording medium has a porous layer formed by the filler blended in the recording medium and a solid ink impregnated in the pores of the porous layer. The solid ink can be obtained by dissolving or dispersing a colorant such as a dye or pigment in a low-melting resin. When heat is applied to this recording medium, the solid ink is melted and exudes from the porous layer, and the exuded ink is transferred to a transfer medium. However, even this recording medium is not suitable for high-speed transfer due to the same reason as that of the micro porous layer made of the resin. In addition, it is difficult to obtain a transfer image having a high density. When a filler such as carbon black which can be is used as a colorant is used, the filler tends to be partially transferred together with a solid ink, and a color of transfer image tends to be turbidity in color recording.

Along with the recent developments of information equipments, a high-speed, compact, high-precision printer serving as an information output device has been developed. However, the multi-time thermal transfer recording medium cannot cope with high-speed printing due to poor heat response. The resultant image has poor printing quality and a low density.

A problem unique to the multi-time thermal transfer recording medium is degradation of the surface of the thermal transfer recording medium used a plurality of times, and the degraded part of medium may stain the entire surface of the transfer medium brought into tight contact therewith for image transfer. This stain tends to become conspicuous when the thermal response of the thermal transfer recording medium is increased to perform high-speed recording. When a recording equipment becomes more compact, the temperature inside the equipment during the operation is increased to stain the transfer medium more. When the equipment is heated to a high temperature as described above, problems unique to heat are posed. One problem is a reverse transfer phenomenon, i.e., an incomplete transfer phenomenon in which even if a hot-melt layer of the thermal transfer recording medium is melted and transferred to the transfer medium, it returns to the thermal transfer recording medium without being transferred to the transfer medium. Another problem is an incomplete traveling phenomenon of the thermal transfer recording medium with respect to the transfer medium, which is caused such that the hot-melt layer serves as an adhesive layer to adhere the thermal transfer recording medium to the transfer medium.

There is another method to reduce the recording cost without using the same thermal transfer recording medium a plurality of times. According to this method, the feed speeds of the thermal transfer recording medium and the transfer medium are not set in the proportion of 1:1. The feed speed of the thermal transfer recording medium is lower than that of the transfer medium (n time speed) to reduce the recording cost. This printing is called n-time speed printing.

Published Unexamined Japanese Patent Application No. 60-178088 discloses a thermal transfer recording medium characterized in that an overcoating layer containing a resin and a wax as major constituents is formed on a hot-melt ink layer. When such an overcoating layer is formed, a rubbed stain caused by a pressure acting on the thermal transfer recording medium and the transfer medium and a difference between the feed speeds of the thermal transfer recording medium and the transfer medium can be prevented. However, the n-time speed printing has a low absolute speed of the thermal transfer recording medium with respect to a thermal head. For this reason, an excessive melting phenomenon of the thermal transfer recording medium by heat accumulated in the thermal head tends to occur. A rubbed stain caused by melting of the ink upon printing and a tailing stain caused by the high viscosity of the melted ink material tend to occur.

Published Unexamined Japanese Patent Application No. 2-204092 discloses a thermal transfer recording medium and a thermal transfer recording method using a thermal transfer ink constituted by a hot-melt binder consisting of an ethylene-vinyl acetate copolymer and a wax and a colorant disposed in this binder to define a shear strength of the thermal transfer ink at room temperature (25.degree. C.), thereby preventing a tailing stain. However, the shear strength representing the mechanical strength of the material at room temperature is not strongly associated with the tailing stain caused by the high viscosity of the molten material in view of physical properties. For this reason, there is no n-time speed thermal transfer recording medium which produces a high-density image, is suitable for high-speed transfer, and can satisfactorily solve the conventional problems described above.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a thermal transfer recording medium, wherein a hot-melt ink layer is transferred stepwise from the ink layer surface which is contact with a transfer medium in a direction of depth of the ink layer to cope with high-speed printing, achieve stable transfer characteristics and stable traveling of the ink layer even at high temperatures without causing stains, and assure sufficiently high printing quality and a sufficiently high density.

It is another object of the present invention to provide a thermal transfer recording medium suitable for multi-time use and n-time speed printing, wherein a hot-melt ink layer is transferred stepwise in the longitudinal direction of the thermal transfer recording medium to cope with high-speed printing, provide an image having sufficiently high printing quality and a sufficiently high density, eliminate a rubbed stain and a tailing stain even at high temperatures.

According to an aspect of the present invention, there is provided a thermal transfer recording medium comprising:

a sheet-like base member; and

a hot-melt ink layer, formed on the sheet-like base member, containing a colorant and a hot-melt material, and selectively heated, melted, and transferred to a transfer medium,

wherein the hot-melt material has a melting point Tm of 70.degree. to 90.degree. C., a complex elastic modulus of 106 Pa to 107 Pa at 100.degree. C., and a pour point Tp of not less than 150.degree. C.

According to the second aspect of the present invention, there is provided a thermal transfer recording medium comprising:

a sheet-like base member; and

a hot-melt ink layer, formed on the sheet-like base member, containing a colorant, an ethylene-based low-melting crystalline material, and an ethylene-based resin member, and selectively heated, melted, and transferred to a transfer medium,

wherein the hot-melt ink layer is set in an amorphous or microcrystalline state and satisfies the following condition:

I/I.sub.0 .ltoreq.0.9 where I is a diffraction peak intensity in a range of 21.3.degree. to 21.5.degree. originated from an ethylene-based crystal and measured by an x-ray diffraction method, and I.sub.0 is a halo intensity in a range of 16.degree. to 17.degree. originated from an amorphous part.

According to the third aspect of the present invention, there is provided a thermal transfer recording medium comprising:

a sheet-like base member; and

a hot-melt ink layer, formed on the sheet-like base and containing 30 to 50 wt % of a colorant, a low-melting crystalline material having an acid value of 5 to 40 mg KOH/g and a saponification value of 10 to 100 mg KOH/g, and 15 to 30 wt % of an ethylene-based resin material containing a copolymer resin of an ethylene monomer and a monomer containing a carbonyl group,

wherein the ethylene-based resin material has an ethylene content of 65 to 80 wt % and a melt index of not more than 60.

In these aspects of the present invention, the hot-melt ink layers have heat absorption peak curves preferably falling with a range of .+-.30.degree. C. of peak temperature thereof upon measurement using a differential scanning calorimeter (DSC).

According to the present invention, there is provided a thermal transfer recording medium which has good transfer characteristics in multi-time printing in a high-speed printer, can satisfy both high printing quality and a high image density, can prevent the surface of a transfer medium from stains, and has stable transfer characteristics and traveling characteristics even at high temperatures. There is also provided a thermal transfer recording medium capable of forming good transfer images at high speed without causing a decrease in resolution regardless of whether a transfer medium having high or low surface smoothness is used.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a graph showing heat absorption peak curves obtained by DSC measurements of one embodiment of a thermal transfer recording medium according to the present invention;

FIG. 2 is a graph showing a relationship between temperature and complex modulus at a frequency of 3 Hz with regard to a hot-melt ink layer according to Example 1-5;

FIG. 3 is a graph showing a relationship between temperature and complex modulus at a frequency of 3 Hz with regard to a hot-melt ink layer according to Control 1-5;

FIG. 4 is a graph showing an x-ray diffraction data obtained by Seemann-Bohlin method of an hot-melt ink layer according to Example 2-74 in condition that fixed angle of incidence is 0.1;

FIG. 5 is a graph showing an X-ray diffraction data obtained by Seemann-Bohlin method of an hot-melt ink layer according to Example 2-75 in the same condition as that in FIG. 4;

FIG. 6 is a graph showing an X-ray diffraction data obtained by Seemann-Bohlin method of an hot-melt ink layer according to Example 2-76 in the same condition as that in FIG. 4;

FIG. 7 is a graph showing an X-ray diffraction data obtained by Seemann-Bohlin method of an hot melt ink layer according to Example 2-77 in the same condition as that in FIG. 4;

FIG. 8 is a graph showing an X-ray diffraction data obtained by Seemann-Bohlin method of an hot melt ink layer according to Control 2-28 in the same condition as that in FIG. 4; and

FIG. 9 is a graph showing an X-ray diffraction data obtained by Seemann-Bohlin method of an hot melt ink layer according to Control 2-29 in the same condition as that in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Thermal transfer recording media according to the present invention have the following three preferred aspects.

A thermal transfer recording medium according to the first aspect comprises a sheet-like base member and a hot-melt ink layer, formed on the sheet-like base member, containing a colorant and a hot-melt material, wherein the hot-melt material has a melting point Tm of 70.degree. to 90.degree. C., a complex modulus of 10.sup.6 Pa to 10.sup.7 Pa at 100.degree. C., and a pour point Tp of 150.degree. C. or more.

The melting point Tm and the pour point Tp defined herein indicate melting and pour points obtained in a measurement of a complex modulus to be described below.

The complex modulus of material is determined by a so-called forced osillation method in which a sample is filled in an aluminum vessel having an inner diameter of 16 mm and a depth of 3 mm, an aluminum disc having a diameter of 12 mm is vertically vibrated by a vibrator at a frequency of 3 Hz sine wave, and an complex modulus is calculated in accordance with a displacement and a stress obtained.

At this time, the elastic modulus is represented by a complex modulus E* represented as follows:

E*=E'+iE" where E' is the storage elastic modulus, E" is the loss elastic modulus, and i is an imaginary number.

The magnitude of the complex modulus is represented as follows:

.vertline.E*.vertline.={(E').sup.2 +(E").sup.2 }.sup.1/2 The sample is heated by indirect heating such that a sample cell is heated in a thermostat using air as a medium. The heating rate is 0.5.degree. C./min.

The melting point Tm of a material is defined as a temperature corresponding to a magnitude of complex modulus of 5.times.10.sup.7 Pa when the material is heated.

The pour point Tp is defined as a temperature at which the loss elastic modulus (E') becomes larger than the storage elastic modulus (E"), i.e., a fluid state shifted from a rubbery state in viscoelasticity.

A thermal transfer recording medium according to the present invention can realize multi-time printing by stepwise transfer of a hot-melt ink layer. This can be achieved when a composition of materials in consideration of physical properties, are selected to cause a cohesive failure phenomenon inside a hot-melt material in the hot-melt ink layer.

A hot-melt material having a melting point Tm of 70.degree. C. or less cannot be used due to poor preservation performance at high temperatures. When the melting point Tm is 90.degree. C. or more, the melting temperature is shifted to a high temperature to cause degradation of transfer characteristics. The melting point Tm of a hot-melt material falls within the range of 70.degree. to 90.degree. C., and preferably 75.degree. to 85.degree. C. When the melting point Tm exceeds 85.degree. C., the material tends to cause degradation of transfer characteristics under low-temperature atmosphere, e.g., 0.degree. to 10.degree. C. However, when the melting point Tm is less than 75.degree. C., transfer characteristics of the material tends to degrade with regard to shelf life test at 55.degree. C. and long life test at ordinary temperature on the passage of time.

Preferably, this material may be easily melted by heating and may become fluid and deformed on a transfer medium by a transfer pressure. For this purpose, the material may have a complex modulus of 10.sup.7 Pa or less at 100.degree. C. In order to stabilize traveling of the material at a high temperature, the mechanical strength of the molten material is preferably high. For this purpose, the complex modulus is 10.sup.6 Pa or more. The complex modulus at 100.degree. C. preferably falls within the range of 8.times.10.sup.6 to 2.times.10.sup.6 Pa. When the complex modulus is less than 2.times.10.sup.6 Pa, pour point of the material is decreased almost in proportion to decrease in complex modulus due to almost constant melting point, thereby stains are tend to occurred on printing. On the other hand, when the complex modulus exceeds 8.times.10.sup.6 Pa, the material tends to deformation amount of a ink layer containing the material is decreased when transfer pressure is applied to the ink layer, this causes decrease in adhesive area between the ink layer and a transfer material, thereby transfer characteristics particularly with regard to a rough paper tends to be decreased.

The cohesive failure within the ink layer stably occurs at the central portion of a hot-melt ink layer when the hot-melt ink layer is set in a molten state and its mechanical strength does not greatly change in the direction of its thickness. A portion of the hot-melt ink layer close to a thermal head has a higher temperature than that of a portion of the hot-melt ink layer close to the transfer medium. In order to establish a condition for uniforming the mechanical strength, a range of temperature in melting condition and corresponding change in complex modulus may be minimized as possible.

According to the present invention, the above mechanical condition is established between 100.degree. C. and 150.degree. C., the pour point Tp of the hot-melt material is set to be 150.degree. C. or more. However, if the molecular weight of the resin is excessively increased, the elastic module of the entire ink layer is increased to result in a large cohesion force. As a result, an adhesive failure does not occur inside the ink layer. Therefore, the adhesive failure tends to occur at the interface between the ink layer and the transfer paper. When this cohesive failure does not occur, a transfer failure such as a reverse transfer phenomenon occurs. Therefore, the pour point Tp of the hot-melt material of ink layer is preferably 200.degree. C. or less. When the pour point Tp exceeds 200.degree. C., the adhesive failure of the ink tends to occur at the interface between the hot-melt ink layer and the transfer paper. As a result, a transfer error tends to occur.

A thermal transfer recording medium according to the second aspect of the present invention comprises a sheet-like base member and a hot-melt ink layer, formed on the sheet-like base member, containing a colorant, an ethylene-based low-melting crystalline material, and an ethylene-based resin, wherein the hot-melt ink layer is in an amorphous or microcrystalline state and satisfies the following condition:

I/I.sub.0 .ltoreq.0.9 where I is a diffraction peak intensity in a range of 21.3.degree. to 21.5.degree. originated from an ethylene-based crystal and measured by an X-ray diffraction method, and I.sub.0 is a halo intensity in a range of 16.degree. to 17.degree. originated from an amorphous part.

In order to perform high-speed printing, the hot-melt ink material must be quickly melted. In the thermal transfer recording medium according to the present invention, the intensity ratio I/I.sub.0 of the diffraction peak from the ethylene-based crystal to the halo intensity of the amorphous art is 0.9 or less, and crystallinity of the ethylene-based low-melting crystalline material may be remarkably low. For this reason, the hot-melt material is considered to be in a microcrystalline or amorphous state. This indicates that a low heat energy is required to melt crystal grains of wax constituting the low-melting crystalline material in a hot-melt ink layer as compared with the case in which large crystal are grown in a hot-melt ink layer, thereby melting speed of the crystal grains becomes high, and the hot-melt ink layer has a high sensitivity. The diffraction peak intensity ratio I/I.sub.0 is preferably 0.8 or less.

In the thermal transfer recording medium of the present invention, the ethylene-based low-melting crystalline material is properly mixed with an ethylene-based resin material to reduce crystallinity of the ethylene-based low-melting crystalline material, although the ethylene-based low-melting crystalline material has generally high crystallinity. Isolated wax portion from the hot-melt ink layer, which causes stains is very small in amount. Therefore, stains on printing even at high temperatures are minimized.

In order to properly mix the ethylene-based low-melting crystalline material and the ethylene-based resin material, they preferably have good compatibility. For this purpose, the ethylene-based low-melting crystalline material is preferably a material containing other functional groups in addition to the ethylene structure.

The ethylene-based resin material must have good affinity such as compatibility with the ethylene-based low-melting crystalline material and may have low crystallinity to reduce the crystallinity of the resultant material. The ethylene-based resin material preferably contains 25 wt % or more of a comonomer which is copolymelyzable with ethylene monomer.

The copolymer of ethylene and a comonomer is most preferably a random copolymer. The monomer reactivity ratio of the comonomer is preferably close to that of the ethylene monomer. Such a monomer preferably has a Q value (T. Alfrey, J. J. Bohrer, H. Mark, Copolymerization (1951)) of 1.0 or less, and more preferably 0.2 or less, which value is used as measures representing reactivity of monomers. The content of the ethylene-based resin material preferably falls within the range of 20 to 30 wt % to suppress reverse transfer, adhesion, and stains which are often problems unique to the multi-time thermal transfer recording medium.

In order to properly mix the ethylene-based low-melting crystalline material with the ethylene-based resin material, set the ethylene-based low-melting crystalline material in a microcrystalline or amorphous state in the hot-melt ink layer, and minimize the isolated wax portion which causes stains, the ratio of the content of the ethylene-based low-melting crystalline material for forming the hot-melt ink layer to the content of the ethylene-based resin material is preferably 1:1 to 1:3, and the content of the ethylene-based low-melting crystalline material preferably falls within the range of 30 to 50 wt %.

The thermal transfer recording media which satisfy the physical properties of the first and second aspects have compositions represented by, e.g., the third aspect to be described below.

A thermal transfer recording medium according to the third aspect of the present invention essentially consists of a sheet-like base member and a hot-melt ink layer, formed on the sheet-like base member, and the hot-melt ink layer contains 30 to 50 wt % of a colorant, a low-melting crystalline material having an acid value of 5 to 40 mg KOH/g and a saponification value of 10 to 100 mg KOH/g, and 15 to 30 wt % of ethylene-based resin material containing a copolymer resin of an ethylene monomer and a monomer containing carbonyl groups wherein the ethylene-based resin material has an ethylene content of 65 to 80 wt % and a melt index of 60 or less.

This thermal transfer recording medium can be achieved by improving affinity of the resin material with the ethylene-based low-melting crystalline material for forming the hot-melt ink layer. When a resin having poor affinity with the ethylene-based low-melting crystalline material is mixed with a wax as the ethylene-based low-melting crystalline material, the wax and the resin may be macroscopically mixed, but they are microscopically separated from each other. Therefore, the wax component which has a low mechanical strength causes stains of the transfer medium during transfer at high temperatures.

However, since both the wax and the resin used in the third aspect according to the invention have carbonyl groups, the resin has good affinity with the wax. In order to achieve good affinity of the resin with the wax, the ethylene-based low-melting crystalline material for forming the hot-melt ink layer has an acid value of 5 to 40 mg KOH/g and a saponification value of 10 to 100 mg KOH/g. At the same time, the ethylene-based resin material for forming the hot-melt ink layer is a copolymer resin of ethylene and a monomer containing a carbonyl group, and the ethylene content of the ethylene copolymer resin preferably falls within the range of 65 to 80 wt %.

When a resin having a high molecular weight and a melt index of 60 or less is used, the melt viscoelasticity is increased, and a high stain resistance and better medium traveling even at high temperature can be achieved. However, when the molecular weight is excessively increased, the melt viscoelasticity is excessively increased to tend to degrade the transfer characteristics. Therefore, the melt index of the resin is preferably 1 or more.

When the content of the resin is 15 wt % or less, the increasing effect of the melt viscoelasticity cannot be enhanced, and printing stains cannot be prevented. However, when the content of the resin exceeds 30 wt %, the melt viscoelasticity is excessively increased to result in a transfer error.

The following organic materials melted at predetermined temperatures can be ethylene-based low-melting crystalline materials each having a carbonyl group to form a hot-melt ink layer. Examples are paraffin oxide wax, carnauba wax, candelilla wax, rice wax, wood wax, beeswax, lanolin, coconut wax, wax oxide ester, emulsion type oxide wax, urethane type wax, alcohol type wax, oxide microcrystalline wax amide wax, waxes based on montan wax (e.g., bleached montan wax, nonbleached montan wax, purified wax, acid wax, ester wax, and partially saponified ester wax), PO wax, polyethylene oxide wax, rosin methylolamide, ester gum, and a higher fatty acid.

The following low-melting crystalline materials containing no carbonyl group can be effectively added to the above low-melting crystalline materials to adjust the melting points. Examples are paraffin wax, microcrystalline wax, low-molecular weight polyethylene wax, polyethylene oxide wax, and polyethylene wax. These materials are added in a total content of 10 wt % or less in the low-melting crystalline material so as to prevent isolation of the wax from the resin.

Preferable examples of the monomer containing a carbonyl group and copolymerized with ethylene are monomers such as methylmethacrylate, ethylmethacrylate, n-propylmethacrylate, iso-propylmethacrylate, methylacrylate, ethylacrylate, n-propylacrylate, isopropylacrylate, acrylic acid, methacrylic acid, maleic acid, and vinyl acetate. Examples of the ethylene copolymer according to the present invention are a bipolymer of one of the above monomers and ethylene, and a terpolymer. In addition, a monomer such as vinyl chloride or vinylidene chloride may be used in the ethylene-based terpolymer.

Examples of the colorant constituting the hot-melt ink layer are pigments and dyes such as carbon black, Fast Yellow G, Benzidine Yellow, Pigment Yellow, Indo Fast Orange, Irgadine Red, Carmine FB, Permanent Bordeaux FRR, Pigment Orange R, Lithol Red 2G, Lake Red C, Rhodamine FB, Rhodamine B, Phthalocyanine Blue, Pigment Blue, Brilliant Green B, Phthalocyanine Green, and quinacridone, as needed. When the content of these colorants is excessively large, transfer errors occur. However, when the content of the colorants is excessively small, storage stability at high temperatures is lost. Therefore, the content of the colorants preferably falls within the range of 30 to 50 wt %. When colorants to be added have large differences in specific gravity, the preferably contents of these colorants is possible to be out of the above range. The total content of the colorants preferably falls within the range of 20 to 40 vol %.

Use of large amounts of expensive dyes and pigments as ink materials is against the object for providing an inexpensive high-quality product. Additives such as silica, quartz sand, titanium oxide, zinc oxide, talc and the like may be effectively added to 50 vol % of the coloring component.

Not that example of a base material is polyethylene terephthalate, polyethylen naphthalate film, and polyphenylene sulfide film.

The cohesive failure within the hot-melt ink layer stably occurs at the central portion of the hot-melt ink layer when the hot-melt ink layer is in a molten state and its mechanical strength does not change much in the direction of its thickness. The portion of the hot-melt ink layer close to the thermal head has a higher temperature than that of the portion of the hot-melt ink layer closer to the transfer medium. In order to establish the condition for uniforming the mechanical strength, a range of temperature corresponding to temperature dependence complex modulus in the molten material must be minimized.

In the third aspect of the present invention, 15 to 30 wt % of the resin having a melt index of 60 or less are added to the material, and additionally, the affinity of the entire material system is controlled to set the pour point Tp of 150.degree. C. or more. The above mechanical condition is established between 100.degree. C. and 150.degree. C., thereby providing a thermal transfer recording medium which can cope with high-speed printing, satisfy high printing quality and a high image density, prevents the surface of the transfer recording medium from stains due to deterioration, and provide stable transfer and traveling characteristics even at high temperatures.

In order to set the pour point Tp of 150.degree. C. or more and the rubbery state of 150.degree. C. or more, the molecular weight of the resin must be increased. For this purpose, the melt index of the resin may be set to be 60 or less, and at the same time preferably 10 or more.

If the molecular weight of the resin is excessively increased, the elastic modulus of the ink hot-melt layer as a whole is excessively increased, this causes decrease in a deformation amount of the resin due to stress on transfer, thereby a contact area of the ink layer with the surface of a transfer medium is decreased to cause decrease of transfer characteristics, and the cohesion force is increased. As a result, the cohesive failure does not occur in the ink layer. An adhesive failure tends not to occur at the interface between the ink layer and the transfer paper. Transfer errors such as reverse transfer of the ink layer and adhesion of the ink layer tend to occur or in worst case ink layer act as adhesive between transfer recording medium and transfer medium.

In order to cope with high-speed printing, the hot-melt ink material must be quickly melted. This means that the hot-melt ink material must require only a low melting energy. The thermal properties (e.g., melting energy) of the material can be measured using the DSC (Differential Scanning Calorimeter). When DSC measurement of the hot-melt ink material is performed, a heat absorption peak curve can be obtained.

In order to obtain a thermal transfer recording medium which can cope with high-speed printing, is free from printing stains even at high temperatures, and exhibits stable traveling characteristics, this heat absorption peak curve must be as sharp as possible. That is, a peak curve is preferably obtained within the narrowest temperature range. If the heat absorption peak curve is broad, i.e., if melting characteristics are broad, it takes a long period of time to perfectly solidify the hot-melt ink material transferred to the transfer medium, and the ink material cannot be sufficiently adhered to the transfer medium. For this reason, when the thermal transfer recording medium is used a plurality of times, reverse transfer and adhesion tend to occur. During the transfer, a heat energy must be supplied at least to the temperature range in which the hot-melt ink material is perfectly melted. If the melting characteristics are broad, the above temperature range is shifted to high temperature side. In the multi-time thermal transfer recording medium, when the thickness of the hot-melt ink layer is increased to increase the number of times of transfer, the heat energy cannot be sufficiently supplied from the thermal head to the layer, the hot-melt ink material cannot be heated to the above temperature range, and transfer action may be started in this state. For this reason, when the melting characteristics are broad, incomplete printing tends to occur. In addition, when the melting characteristics are broad, the hot-melt ink material starts to soften at a low-temperature range, stains tend to be formed.

According to the thermal transfer recording medium of the present invention, since the heat absorption peak curve obtained by DSC measurement is sharp, i.e., since the hot-melt ink material can be melted within the narrow temperature range, the above problems are not posed. That is, the thermal transfer recording medium can cope with high-speed printing, is free from stains at high temperatures, and can travel stably. In order to prevent all of the reverse transfer, adhesion, and stains, melting is preferably within the range of .+-.30.degree. C. of the peak temperature point. Therefore, the heat absorption peak obtained by the DSC measurement preferably falls within the range of .+-.30.degree. C. of the peak temperature.

As described above, according to the present invention, there is provided a thermal transfer recording medium which has excellent transfer characteristics in multi-time printing at a high-speed printer, provides a high image density, is free from stains of the surface of the transfer recording medium, and has stable transfer and traveling characteristics even at high temperatures. There is also provided a thermal transfer recording medium capable of forming good transfer images at high speed without causing a decrease in resolution regardless of whether a transfer medium even having high or low surface smoothness is used.

EMBODIMENTS

The present invention will be described in detail by way of its embodiments and control.

EMBODIMENTS 1-1-1-5

Physical properties of waxes used in Embodiments 1-1 to 1-5 are shown in Table 1, and physical properties of resins used in Embodiments 1-1 to 1-5 are shown in Table 2.

TABLE 1______________________________________Table of Physical Properties of Waxes Melting Saponifica- Point Tm Acid Value tion ValueNo. .degree.C. mg KOH/g mg KOH/g______________________________________1 75 12 302 63 30 803 75 0 04 82 11 16______________________________________

Wax 2 in Table 1 has a melting point Tm of less than 70.degree. C., and wax 3 has an acid value and a saponification value which fall outside the ranges according to the present invention.

TABLE 2______________________________________Table of Physical Properties of Resins EthyleneNo. Content Comonomer Melt Index______________________________________1 72 Vinyl 20 acetate2 87 Vinyl 20 acetate3 72 Vinyl 300 Acetate4 75 Methyl- 20 methacrylate______________________________________

In Table 2 above, resin 2 has an ethylene content of 80 wt % or more, and resin 3 has a melt index of more than 60.

Thermal transfer recording media were formed using the waxes shown in Table 1 and the resins shown in Table 2 in accordance with mixing ratios in Table 3 below.

TABLE 3______________________________________Composition of Embodiment Magnitude Melting of Complex Pour Resin Color- point Modulus PointWax No. No. ant (.degree.C.) (10.sup.6 Pa) (.degree.C.)______________________________________1-1 1 35% 1 35% 45% 78 8 1702 1 35% 4 35% 40% 82 8 1653 4 35% 1 35% 45% 85 7 1604 4 35% 4 35% 40% 87 9 1705 4, 25%+ 1, 12%+ 45% 78 4.3 155 2, 10% 3, 8%______________________________________ (The colorant was carbon black PRINTEX 35 available from Degussa AG, Germany.)

The samples in Embodiments 1-1 to 1-5 could cope with high-speed printing and provided satisfactory printing quality and high image densities. In addition, the surfaces of the transfer media were not stained by the samples of Embodiments 1-1 to 1-5. Stable transfer and traveling characteristics were obtained even at high temperatures.

More specifically, a printing test was performed at 35.degree. C. and a humidity of 85%. A printing density (solid black) measured by a Macbeth reflection densitometer was as high as 1.2 or more for the first printing cycle and was 1.0 or more for the third printing cycle. A satisfactory result was obtained in a shelf test of 55.degree. C..times.85%.times.96 H.

Compositions of Comparative Examples 1-1 to 1-5 are shown in Table 4 below.

TABLE 4______________________________________Composition of Comparative Example Magnitude Melting of Complex Pour Resin Color- point Modulus PointWax No. No. ant (.degree.C.) (10.sup.6 Pa) (.degree.C.)______________________________________1-1 2 35% 2 20% 45% 74 5 .times. 10.sup.6 1552 2 35% 2 25% 40% 69 8 .times. 10.sup.5 1353 2 35% 2 20% 45% 80 7 .times. 10.sup.6 1604 2 35% 3 25% 40% 87 9 .times. 10.sup.5 1455 3, 25%+ 1, 5%+ 45% 80 4 .times. 10.sup.6 120 4, 10% 3, 15%______________________________________

In the samples of Comparative Examples 1-1 to 1-5, printing stains were considerable at high and room temperatures, and there samples were found to be defective for multi-time printing.

In particular, multi-time printing of samples of Comparative Example 1-1 and 1-2 could be performed, but these samples were poor in shelf life. Multi-time printing of samples of Comparative Examples 1-3 and 1-4 could not be performed, and printing stains were also conspicuous.

The sample of Comparative Example 1-5 has almost similar melting point but has particularly lower melting point as compared with Example 1-5.

In comparison of both examples, printing stains occurred at ordinary temperature (25.degree. C.) and high temperature (35.degree. C.) in the case of Comparative Example 1-5 while no stains occurred at ordinary temperature and only a little stain occurred at high temperature.

Superiority of the thermal transfer recording media of the present invention over Comparative Examples 1-1 to 1-5 was confirmed by comparison between Embodiments 1-1 to 1-5 and Comparative Examples 1-1 to 1-4.

The thermal transfer recording media as described above can be used in conventional printers such as word processors and page printers when these media are housed in commercially available cases and used as ink ribbon cassettes which can set and be fed to a position at which they oppose paper. It is also apparent from the above result that these media are preferable as multi-time ink ribbons.

Embodiments 2-1-2-77

Materials of Embodiments 2-1 to 2-77 and Comparative Examples 2-1 to 2-29 are shown as follows. Physical properties of ethylene-based low-melting crystalline materials (waxes) are shown in Table 5, and physical properties of ethylene-based resin materials are shown in Table 6. For the sake of descriptive simplicity, the materials will be represented by symbols thereinafter.

Pigment: Carbon black pigment: p-1

PRINTEX 25 (tradename) available from Degussa Ag

TABLE 5______________________________________ Saponifi- Melting Acid cation Point Value Value (.degree.C.) mg KOH/g mg KOH/g______________________________________Ethylene-based Low- 75 12 30melting CrystallineWax: W-1Ethylene-based Low- 63 28 75melting CrystallineWax: W-2Ethylene-based Low- 83 14 38melting CrystallineWax: W-3Ethylene-based Low- 86 6 80melting CrystallineWax: W-4______________________________________ TABLE 6______________________________________ Ethylene Content Softening Melt Index (wt %) Point (.degree.C.)______________________________________Ethylene-based 400 72 40Resin: R-1Ethylene-based 150 72 40Resin: R-2Ethylene-based 15 72 40Resin: R-3______________________________________

Thermal transfer recording media of Embodiments 2-1 to 2-77 were formed such that hot-melt ink layers having compositions shown in Table 7 below were formed on polyester films having back coat layers consisting of heat-resistant smooth materials, respectively. The respective materials in Table 7 were represented by symbols described in Tables 5 to 6. The numerals in Table 7 represent wt %.

TABLE 7______________________________________Embodiment W-1 W-1 W-3 W-4 R-1 R-2 R-3 P-1______________________________________2-1 45 25 302 45 25 303 45 25 304 45 25 305 45 25 306 45 25 307 45 25 308 45 25 309 45 25 3010 45 20 3511 45 20 3512 45 20 3513 45 20 3514 45 20 3515 45 20 3516 45 20 3517 45 20 20 3518 45 20 3519 40 45 20 4020 40 20 4021 40 20 4022 40 20 4023 40 20 4024 40 20 4025 40 20 4026 40 20 4027 40 20 4028 35 20 4529 35 20 20 4530 35 4531 35 20 4532 35 20 4533 35 20 4534 35 20 4535 35 20 4536 35 20 4537 25 20 15 10 3038 25 20 10 15 3039 25 20 15 10 3040 25 20 10 15 3041 15 20 10 10 3042 15 20 10 10 3043 15 20 10 10 3044 15 20 10 10 3045 15 20 10 10 3046 15 20 10 10 3047 15 20 10 10 3048 15 20 10 10 3049 15 20 10 10 3050 15 20 6 14 4551 15 20 14 6 4552 15 20 6 14 4553 15 20 14 6 4554 15 20 6 14 4555 15 20 14 6 4556 15 20 6 14 4557 15 20 14 5 4558 15 20 6 14 4559 15 20 14 6 4560 15 20 6 14 4561 15 20 14 6 4562 25 10 8 12 4563 25 10 12 8 4564 25 10 8 12 4565 25 10 12 8 4566 25 10 8 12 4567 25 10 12 8 4568 25 10 8 12 4568 25 10 12 8 4570 25 10 8 12 4571 25 10 12 8 4572 25 10 8 12 4573 25 10 12 8 45______________________________________

Thermal transfer recording media of Comparative Examples 2-1 to 2-29 were formed such that hot-melt ink layers having compositions shown in Table 8 below were formed on polyester films having back coat layers heat-resistant smooth materials, respectively. The respective materials in Table 8 were represented by symbols described in Tables 5 and 6. The numerals in Table 8 represent wt %.

TABLE 8______________________________________ComparativeExamples W-1 W-2 W-3 W-4 R-1 R-2 R-3 P-1______________________________________ 1 15 25 60 2 15 25 60 3 15 25 60 4 15 25 60 5 15 25 60 6 15 25 60 7 15 25 45 8 15 25 45 9 15 25 4510 40 15 4511 40 15 4512 40 15 4513 40 15 4514 40 15 4515 40 15 4516 40 15 2017 40 15 2018 40 15 2019 55 25 2020 55 25 2021 55 25 2022 55 25 2023 55 25 2024 55 25 2025 55 25 2026 55 25 2027 55 25 2028 40 15 15 3029 10 30 5 10 45______________________________________

Each of the thermal transfer recording media of Embodiments 2-1 to 2-77 and Comparative Examples 2-1 to 2-29 was cut into a rectangular piece having a size of 30 mm.times.5 mm. Both ends of each sample were fixed on a slide glass using pieces of an adhesive tape, thereby obtaining an X-ray diffraction measurement sample. The diffraction intensity of each thermal transfer recording medium was measured using a X-ray diffraction apparatus (available from Nihon Denshi KK). X-ray diffraction of thermal transfer recording medium was measured by Seemann-Bohlin Method. In the X-ray diffraction apparatus, when the incident angle of a monochromatic X-ray on each sample surface is set smaller than that in a common Bragg-Brentano Method (.theta.-2.theta. measurement). In this method, scattering of X-rays from the sheet-like base member is minized, a diffraction peak which cannot be normally detected, because it is concealed in the background, can be measured. The doncidion of measurement were as follows.

Target: Cu

Voltage: 50 KV

Fired incident angle: 0.1.degree.

The diffraction intensities of the thermal transfer recording media of Embodiments 2-1 to 2-77 and Comparative Examples 2-1 to 2-29 were measured by the this Seemann-Bohlin method. Diffraction peak intensities I (cps; count/sec.) from the ethylene-based crystals, the corresponding reflection angles 2.theta., halo intensities I.sub.0 (incident angle: 16.degree. to 17.degree.) of the amorphous parts, and intensity ratios I/I.sub.0 of the samples of Embodiments 2-1 to 2-77 were obtained from the resultant diffraction intensities and are summarized in Table 9, and those of the samples of Comparative Examples 2-1 to 2-29 are summarized in Table 10.

TABLE 9______________________________________ Reflection AngleEmbodiment (2.theta.) I (cps) I.sub.0 (cps) I/I.sub.0______________________________________2-1 21.4 1465 1703 0.86 2 21.2 1478 1760 0.84 3 21.4 1101 1932 0.57 4 21.4 1489 1673 0.89 5 21.3 1367 1627 0.84 6 21.0 1268 1838 0.69 7 21.1 1566 1956 0.80 8 21.1 1453 1863 0.78 9 21.4 1354 1634 0.7010 21.4 1436 1651 0.8711 21.4 1672 1990 0.8412 21.4 1252 1897 0.6613 21.4 1741 1956 0.8914 21.3 1655 1994 0.8315 21.3 1423 1801 0.7916 21.0 1462 1949 0.7517 21.3 1353 1879 0.7218 21.3 1368 1927 0.7119 21.3 1324 1697 0.7820 21.1 1323 1890 0.7021 21.2 1211 1922 0.6322 21.5 1534 1918 0.8023 21.0 1442 1803 0.8024 21.1 1329 1927 0.6925 21.4 1449 1882 0.7726 21.4 1458 1846 0.7927 21.5 1252 1869 0.6728 21.3 1347 1952 0.6929 21.2 1110 1947 0.5730 21.1 1252 1869 0.6331 21.1 1423 1923 0.7432 21.4 1294 1961 0.6633 21.3 1159 1964 0.5934 21.2 1191 1985 0.6035 21.2 1145 1877 0.6136 21.3 1297 1936 0.6737 21.3 1122 1700 0.6638 21.2 1168 1980 0.5939 21.2 1357 1967 0.6940 21.2 1249 1810 0.5741 21.1 1032 1811 0.5942 21.3 1145 1941 0.5743 21.4 1086 1975 0.5544 21.2 1223 1911 0.6445 21.2 1122 1781 0.6346 21.3 1045 1771 0.5947 21.4 1145 1974 0.5848 21.4 1355 1964 0.6949 21.4 1012 1879 0.5650 21.4 1257 1905 0.6651 21.4 1455 1993 0.7352 21.2 1221 1878 0.6553 21.2 1592 1990 0.8054 21.2 1697 1928 0.8855 21.2 1320 1886 0.7056 21.3 1604 1933 0.8357 21.3 1509 1818 0.7258 21.1 1431 1988 0.7959 21.3 1530 1937 0.8460 21.2 1761 2096 0.8361 21.0 1541 1857 0.7962 21.1 1523 1928 0.7963 21.4 1139 1651 0.6964 21.4 1333 1877 0.7165 21.3 1624 1957 0.8366 21.3 1430 1857 0.7767 21.3 1029 1744 0.5968 21.4 1199 1966 0.6169 21.1 1255 1992 0.6370 21.2 1453 1964 0.7471 21.2 1561 2001 0.7872 21.4 1175 1704 0.6973 21.1 1468 1906 0.7774 21.4 1200 1700 0.7175 21.4 885 1244 0.7176 21.3 1195 1709 0.7077 21.3 729 1266 0.58______________________________________ TABLE 10______________________________________ IncidentComparative AngleExample (2.theta.) I (cps) I.sub.0 (cps) I/I.sub.0______________________________________ 1 21.3 1763 1712 1.03 2 21.3 1934 1727 1.12 3 21.2 1972 1826 1.08 4 21.2 1835 1748 1.05 5 21.3 1769 1608 1.10 6 21.4 1888 1869 1.01 7 21.2 1902 1598 1.19 8 21.2 2134 2013 1.06 9 21.3 2374 2219 1.0710 21.2 1965 1638 1.2011 21.3 2540 2209 1.1512 21.4 2239 1736 1.2913 21.3 2341 2251 1.0414 21.3 1968 1587 1.2415 21.2 2546 2005 1.2716 21.3 2041 1759 1.1617 21.2 2328 2116 1.1018 21.3 1911 1874 1.0219 21.3 2544 1884 1.3520 21.3 2519 1634 1.4821 21.3 2312 1806 1.2822 21.2 2100 1533 1.3723 21.3 2344 1639 1.4324 21.4 2320 1706 1.3625 21.3 2178 1756 1.2426 21.3 2199 1653 1.3327 21.3 2308 1592 1.4528 21.4 2208 1768 1.2529 21.4 1963 1810 1.09______________________________________

Each of the thermal transfer recording media of Embodiments 2-1 to 2-77 and Comparative Examples 2-1 to 2-29 was mounted in a thermal transfer printer (Toshiba Personal Wordprocessor JW-95HP; printing speed: ANK 105 characters/sec.). A pattern of a character and a solid black portion was printed on thermal transfer paper (Becksmoothness: 400 sec.), and each ribbon sample was rewound to use the same position in the sample upon every printing of the pattern repeatedly. The reflection image densities of the resultant solid black transfer image patterns in the first and third printing cycles were measured using the Macbeth reflection densitometer RD 918.

Each of the thermal transfer recording media of Embodiments 2-1 to 2-77 and Comparative Examples 2-1 to 2-29 was caused to travel for printing using the above thermal transfer printer at 35xC and a humidity of 80% ten times, repeatedly. The high-temperature traveling characteristics of the thermal transfer recording media were examined during traveling, and adhesion and folding of the thermal transfer recording media, and traveling troubles were evaluated. Tailing stains at the ends of printed characters were visually evaluated for the printed characters, and fogging of the entire printed matters was visually evaluated. In addition, reverse transfer of the printed characters was also visually evaluated. The reflection image densities, printing stains, reverse transfer, and high-temperature traveling in the first and third printing cycles were checked, the results of Embodiments 2-1 to 2-77 are summarized in Table 11, and the results of Comparative Examples 2-1 to 2-29 are summarized in Table 12.

TABLE 11______________________________________Image DensityEmbodi- First Third Printing Reverse Travelingment Cycle Cycle STAINS Transfer Trouble______________________________________2-1 1.2 1.0 No No No 2 1.3 1.0 No No No 3 1.3 1.0 No No No 4 1.3 1.0 No No No 5 1.2 1.0 No No No 6 1.3 1.0 No No No 7 1.2 1.0 No No No 8 1.3 1.0 No No No 9 1.2 1.0 No No No10 1.3 1.0 No No No11 1.3 1.0 No No No12 1.3 1.0 No No No13 1.3 1.0 No No No14 1.3 1.0 No No No15 1.2 1.0 No No No16 1.2 1.0 No No No17 1.3 1.0 No No No18 1.2 1.0 No No No19 1.2 1.0 No No No20 1.3 1.0 No No No21 1.3 1.0 No No No22 1.3 1.0 No No No23 1.3 1.0 No No No24 1.3 1.0 No No No25 1.2 1.0 No No No26 1.3 1.0 No No No27 1.2 1.0 No No No28 1.3 1.0 No No No29 1.3 1.0 No No No30 1.3 1.0 No No No31 1.2 1.0 No No No32 1.3 1.0 No No No33 1.3 1.0 No No No34 1.3 1.0 No No No35 1.3 1.0 No No No36 1.3 1.0 No No No37 1.3 1.0 No No No38 1.3 1.0 No No No39 1.3 1.0 No No No40 1.3 1.0 No No No41 1.3 1.0 No No No42 1.3 1.0 No No No43 1.3 1.0 No No No44 1.3 1.0 No No No45 1.3 1.0 No No No46 1.3 1.0 No No No47 1.3 1.0 No No No48 1.3 1.0 No No No49 1.3 1.0 No No No50 1.2 1.0 No No No51 1.3 1.0 No No No52 1.3 1.0 No No No53 1.3 1.0 No No No54 1.3 1.0 No No No55 1.2 1.0 No No No56 1.2 1.0 No No No57 1.3 1.0 No No No58 1.3 1.0 No No No59 1.2 1.0 No No No60 1.3 1.0 No No No61 1.3 1.0 No No No62 1.2 1.0 No No No63 1.3 1.0 No No No64 1.3 1.0 No No No65 1.3 1.0 No No No66 1.2 1.0 No No No67 1.3 1.0 No No No68 1.3 1.0 No No No69 1.3 1.0 No No No70 1.3 1.0 No No No71 1.3 1.0 No No No72 1.3 1.0 No No No73 1.3 1.0 No No No74 1.3 1.0 No No No75 1.3 1.0 No No No76 1.3 1.0 No No No77 1.2 1.0 No No No :No______________________________________ TABLE 12______________________________________Image DensityEmbodi- First Third Printing Reverse Travelingment Cycle Cycle STAINS Transfer Trouble______________________________________2-1 0.3 0.3 Yes No No 2 0.2 0.1 Yes No No 3 0.2 0.1 Yes Yes Yes 4 0.4 0.2 Yes Yes No 5 0.3 0.3 Yes Yes No 6 0.3 0.1 Yes Yes Yes 7 0.2 0.2 Yes Yes Yes 8 0.3 0.3 Yes Yes Yes 9 0.1 0.1 Yes Yes Yes10 1.2 0.9 Yes No No11 1.1 1.0 Yes No No12 0.9 1.0 Yes No No13 1.2 1.0 Yes No No14 0.9 0.7 Yes No No15 1.3 1.0 Yes No No16 1.2 0.9 Yes No No17 1.0 0.8 Yes No No18 1.3 1.0 Yes No No19 1.4 0.6 Yes No No20 1.5 0.7 Yes No No21 1.3 1.0 Yes No No22 1.6 0.8 Yes No No23 1.4 0.7 Yes No No24 1.4 0.9 Yes No No25 1.5 1.0 Yes No No26 1.4 0.9 Yes No No27 1.3 0.9 Yes No No28 1.3 1.0 Yes No No29 1.4 0.8 Yes No No :No :Yes______________________________________

Each of the thermal transfer recording media of Embodiments 2-1 to 2-77 and Comparative Examples 2-1 to 2-29 was cut into a square piece having a side of 1 cm to obtain a DSC measurement sample. A DSC measurement of each sample at a heating rate of 5.degree. C./min. was performed. Typical examples of the resultant heat absorption peak curves are shown in FIG. 1.

Lines (indicated by dotted lines in FIG. 1) were drawn to connect two inflection points of the resultant DSC curves shown in FIG. 1 to obtain temperatures as the intersections between the straight lines and the DSC curves. Low temperatures were defined as ta, and high temperatures were defined as tb. Heat absorption peak temperatures of the DSC curves were defined as tp. Like the two DSC curves in FIG. 1, if two or more peaks regarded as heat absorption peaks were present, the largest magnitude of the peaks was selected, and the temperature corresponding to the selected peak was defined as tp. Therefore, the temperatures ta, tp, and tb were measured from the resultant DSC curves of Embodiments 2-1 to 2-73 and Comparative Examples 2-1 to -27, and the results are summarized in Tables 13 and 14.

TABLE 13______________________________________Embodiment ta (.degree.C.) tp (.degree.C.) tb (.degree.C.)______________________________________2-1 53 74 91 2 46 75 87 3 49 73 82 4 50 68 79 5 53 61 84 6 42 62 85 7 52 80 93 8 59 81 90 9 54 81 9310 58 76 9211 46 78 8712 53 74 9413 43 67 9114 44 62 8215 46 63 8116 54 82 9217 56 84 9618 52 83 9819 49 73 9320 44 70 9721 48 71 9722 40 64 9423 42 68 9724 41 70 9925 53 80 10126 57 81 9727 59 82 9928 40 77 10729 49 79 10330 54 76 10231 38 60 8632 36 62 8433 45 64 9034 59 85 10035 61 85 9936 56 82 10937 50 79 10138 59 80 10239 61 82 10940 57 81 11041 60 83 10442 51 79 9943 52 79 9444 47 73 10245 51 74 9846 45 72 9347 54 84 11348 53 81 11049 55 81 10650 52 77 10351 46 74 10052 52 76 10553 50 76 10654 41 70 9955 39 68 9056 42 69 9757 38 66 9158 53 81 10159 57 84 11060 56 80 10461 59 82 11162 52 78 9963 49 79 10764 51 76 10565 52 79 10166 43 70 9267 45 71 9768 40 69 9869 43 71 9370 52 80 10971 63 84 11472 56 85 11273 59 85 11074 48 84 8075 54 80 10776 58 83 11077 57 82 111______________________________________ TABLE 14______________________________________Comparative ExampleEmbodiment ta (.degree.C.) tp (.degree.C.) tb (.degree.C.)______________________________________2-1 31 77 103 2 29 79 98 3 35 74 110 4 36 62 100 5 28 60 94 6 31 64 99 7 48 82 109 8 54 81 112 9 50 85 11110 47 74 10911 38 77 10812 39 73 10213 31 64 9214 30 64 9015 34 62 8916 39 80 10617 43 82 11118 30 81 10819 36 70 9920 39 71 10321 32 69 11222 34 60 9523 35 63 9124 31 59 8925 40 79 10826 43 77 9927 51 80 11628 30 74 10229 38 75 107______________________________________ As can be apparent form Table 9, each thermal transfer recording medium according to the present invention has a diffraction peak intensity ratio I/I.sub.0 of 0.9 or less to result in low crystallinity, thereby providing a high sensitivity. This medium can cope with high-speed printing. This is apparent from the results in Tables 8 and 10. That is, an image density of 1.0 or more can be obtained in the third printing cycle. This medium is free from printing stains, reverse transfer, and traveling troubles. In addition, melting is completed within the range of .+-.30.degree. C. of the melting point, and the melting characteristic curve is sharp. Therefore, the thermal transfer recording medium according to the present invention can apparently and sufficiently cope with high-speed printing.

With regard to some of the above Examples and Comparative Examples, graphs showing relationship between temperature and complex modulus or X-ray diffraction data are represented in FIG. 2 to FIG. 9, for reference. FIG. 2 and FIG. 3 are graphs showing each relationship between temperature and complex modulus with regard to Example 1-5 and Comparative Example 1-5.

FIG. 4 to FIG. 9 are graphs showing X-ray diffraction dates with regard to Example 2-74 to 2-77 and Comparative Example 2-28 and 2-29, respectively.

In general, the thermal transfer recording medium as described above may be incorporated in a conventional cassette case to form an ink ribbon cassette.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative member, shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A thermal transfer recording medium comprising:

a base sheet; and

a hot-melt ink layer, formed on said base sheet, containing a colorant and a hot-melt material, which is selectively heated, melted, and transferred to a transfer medium,

wherein said hot-melt material has a melting point Tm of 70.degree. to 90.degree. C., a magnitude complex modulus of 10.sup.6 Pa to 10.sup.7 Pa at 100.degree. C., and a pour point Tp of not less than 150.degree. C.

2. A medium according to claim 1, wherein said hot-melt ink layer has a heat absorption peak curve obtained by measurement using a differential scanning calorimeter to fall within a range of .+-.30.degree. C. of a peak temperature.

3. A medium according to claim 1, wherein the pour point Tp falls within a range of 150.degree. C. to 200.degree. C.

4. A medium according to claim 1, wherein said colorant is a material selected form the group consisting of a pigment and a dye.

5. A multi-time thermal transfer recording medium comprising:

a base sheet; and

a hot-melt ink layer, formed on said base sheet, containing a colorant and a hot-melt material, which is selectively heated, melted, and transferred to a transfer medium,

wherein said hot-melt material has a melting point Tm of 70.degree. to 90.degree. C., a magnitude complex modulus of 10.sup.6 Pa to 10.sup.7 Pa at 100.degree., and a pour point Tp of not less than 150.degree. C.

6. A thermal transfer recording medium comprising:

a base sheet; and

a hot-melt ink layer, formed on said base sheet, containing a colorant, an ethylene-based crystalline material, and an ethylene-based resin material, which is selectively heated, melted, and transferred to a transfer medium,

wherein said hot-melt ink layer is set in an amorphous or microcrystalline state and satisfies the following condition:

I/I.sub.0 .ltoreq.0.9

wherein I is the diffraction peak intensity in the range of 21.3.degree. to 21.5.degree. originating from an ethylene-based crystal and I.sub.0 is the halo intensity in the range of 16.degree. to 17.degree. originating from an amorphous part when the hot-melt ink layer is measured by X-ray diffraction.

7. A medium according to claim 6, wherein said hot-melt ink layer has a heat absorption peak curve obtained by measurement using a differential scanning calorimeter to fall within a range of 35 30.degree. C. of a peak temperature.

8. A medium according to claim 6, wherein said hot-melt ink layer satisfies the following condition:

I/I.sub.0 .ltoreq.0.8.

9. A medium according to claim 6, wherein said colorant is a material selected from the group consisting of a pigment and a dye.

10. A medium according to claim 6, wherein 30 to 50 wt % of said crystalline material are contained in said hot-melt ink layer.

11. A medium according to claim 6, wherein 15 to 30 wt % of said ethylene-based resin material are contained in said hot-melt ink layer.

12. A medium according to claim 6, wherein 30 to 50 wt % of said colorant are contained in said hot-melt ink layer.

13. A medium according to claim 6, wherein said ethylene-based crystalline material is at least one material selected from the group consisting of a low-molecular weight polyethylene oxide wax, paraffin oxide wax, carnauba wax, candelilla wax, rice wax, wood wax, beeswax, lanolin, coconut wax, oxide wax ester, oxide wax, urethane wax, alcohol wax, amide wax, bleached montan wax, nonbleached montan wax, purified montan wax, oxide montan wax, ester wax, partially saponified ester montan wax, polyolefin wax, rosin, rosin methylolamide, ester gum, and a higher fatty acid.

14. A medium according to claim 6, wherein said ethylene-based resin material is a copolymer of ethylene and at least one monomer selected from the group consisting of methylmethacrylate, ethylmethacrylate, n-propylmethacrylate, iso-propylmethacrylate, methacrylate, ethylacrylate, n-propylacrylate, iso-propylacrylate, acrylic acid, methacrylic acid, maleic acid, vinyl acetate, vinyl chloride and vinylidene chloride.

15. A multi-time thermal transfer recording medium comprising:

a base sheet; and

a hot-melt ink layer, formed on said base sheet, containing a colorant, an ethylene-based crystalline material, and an ethylene-based resin material, which is selectively heated, melted, and transferred to a transfer medium,

wherein said hot-melt ink layer is set in an amorphous or microcrystalline state and satisfies the following condition:

I/I.sub.0 .ltoreq.0.9

where I is the diffraction peak intensity in the range of 21.3.degree. to 21.5.degree. originating from an ethylene-based crystal and I.sub.0 is the halo intensity in the range of 16.degree. to 17.degree. originating from an amorphous part when the hot-melt ink layer is measured by X-ray diffraction.

16. A thermal transfer recording medium comprising:

a base sheet; and

a hot-melt ink layer, formed on said base sheet and containing 30 to 50 wt % of a colorant, a crystalline material having an acid value of 5 to 40 mg KOH/g and a saponification value of 10 to 100 mg KOH/g, and 15-30 wt % of an ethylene-based resin containing a copolymer resin of ethylene and a monomer containing a carbonyl group,

wherein said ethylene-based resin material has an ethylene content of 65 to 80 wt % and a melt index of not more than 60.

17. A medium according to claim 16, wherein said ethylene-based resin material has a melt index of 10 to 60.

18. A medium according to claim 16, wherein said hot-melt ink layer has a heat absorption peak curve obtained by measurement using a differential scanning calorimeter to fall within a range of .+-.30.degree. C. of a peak temperature.

19. A medium according to claim 16, wherein 30 to 50 wt % of said crystalline material are contained in said hot-melt ink layer.

20. A medium according to claim 16, wherein 15 to 30 wt % of said ethylene-based resin material are contained in said hot-melt ink layer.

21. A medium according to claim 16, wherein 30 to 50 wt % of said colorant are contained in said hot-melt ink layer.

22. A medium according to claim 16, wherein 20 to 40 vol % of said colorant are contained in said hot-melt ink layer.

23. A medium according to claim 16, wherein said crystalline material is at least one material selected from the group consisting of paraffin wax oxide, carnauba wax oxide, candelilla wax, rice wax, wood wax, beeswax, lanolin, coconut wax, wax oxide ester, oxide wax, urethane wax, alcohol wax, amide wax, montan waxes, polyolefin wax, polyethylene wax oxide, rosin, rosin methylolamide, ester gum, and a higher fatty acid.

24. A medium according to claim 16, wherein said monomer containing said carbonyl group is at least one material selected from the group consisting of methylmethacrylate, ethylmethacrylate, n-propylmethacrylate, iso-propylmethacrylate, methylacrylate, ethylacrylate, n-propylacrylate, isopropylacrylate, acrylic acid, methacrylic acid, maleic acid, vinyl acetate, vinyl chloride, and vinylidene chloride.

25. A medium according to claim 16, wherein said medium is used as a multi-time thermal transfer recording medium.