Patent Grant
7783235
1. Field of the Invention
The present invention relates to a development apparatus, and an image formation apparatus such as a copying machine, a printer, and a facsimile apparatus that forms an image using the development apparatus.
2. Description of the Related Art
Conventionally, a development apparatus that develops an image with toner that hops on a surface of a toner supporting object, such as a toner conveyance substrate, is known wherein toner adsorbed by a developing roller or a magnetic carrier is not used.
For example, Patent Reference 1 discloses a development apparatus that includes a cylindrical toner supporting object that includes two or more electrodes arranged at a predetermined pitch in a circumferential direction. There, two adjacent electrodes constitute a pair, and electrode pairs are repeatedly arranged. Between two electrodes of an electrode pair, an alternating current (AC) electric field is formed. Then, the toner on one electrode of the pair is floated (hops) and lands on the other electrode, and vice versa. With a rotational drive of the cylindrical toner supporting object, the toner, which repeats hopping, is conveyed to a development position. At the development position, the toner that hops to the vicinity of a latent image on a latent image supporting object is pulled to the latent image by the electric field, and adheres to the latent image without descending toward the electrode of the toner supporting object. With this configuration, the toner that is hopping is used instead of the toner that is adsorbed by the developing roller, the magnetic carrier, etc. In this way, a low voltage development that cannot be realized with a conventional 1-component development method or a 2-component development method is realized. For example, the toner can be selectively adhered at a low voltage such as dozens V between an image part and a non-image part.
[Patent Reference 1] JPA H3-21967
[Disclosure of Invention]
[Objective of Invention]
According to the development apparatus disclosed by Patent Reference 1, by rotationally driving the toner supporting object, the toner that is supported on the surface of the cylindrical toner supporting object is conveyed to a position where a roller made from urethane foam is contacted so that the thickness of the toner on the surface of the toner supporting object may be regulated. However, since the roller made from the urethane foam is easily deformed when contacting an object, it is difficult to make the thickness of the toner uniform on the surface of the toner supporting object. Further, since the central section in an axial direction of the toner supporting object that is not supported by a bearing tends to sag, the thickness of the toner tends to be greater at the central section in a direction perpendicular to a surface moving direction of the surface of the toner supporting object than both ends. For this reason, according to the development apparatus of Patent Reference 1, the toner thickness tends to be uneven, and, therefore, development concentration tends to be uneven.
The present invention provides a development apparatus and an image formation apparatus that substantially obviate one or more of the problems caused by the limitations and disadvantages of the related art.
Specifically, the present invention provides a development apparatus and an image formation apparatus that employ a hopping method wherein the development consistency unevenness due to the toner thickness unevenness is reduced.
Features of embodiments of the present invention are set forth in the description that follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Problem solutions provided by an embodiment of the present invention may be realized and attained by a development apparatus and an image formation apparatus particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention.
[Means for Solving Problem]
To achieve these solutions and in accordance with an aspect of the invention, as embodied and broadly described herein, an embodiment of the invention provides a development apparatus and an image formation apparatus as follows.
An aspect of the embodiment provides a development apparatus, wherein toner supported on the surface of a toner supporting object hops on the surface by an electric field and moves with a movement of the surface to a position that counters a latent image supporting object so that the toner is transferred to a latent image formed on the latent image supporting object after the toner is passed through a toner thickness regulation position constituted by a regulating member. There, the regulating member is made of a flexible material, one end of which regulating member is supported, and the other end (free end) of which regulating member contacts the toner supporting object.
According to another aspect of the embodiment, in the development apparatus, the surface of the toner supporting object is endlessly moving, and the electric field is formed all over the circumference of the surface in the endless moving direction.
According to another aspect of the embodiment, in the development apparatus, the flexible material for the regulating object contains a material that promotes friction electrification on to the regular electrification polarity side of the toner when the flexible material comes into sliding contact with the toner on the surface of the toner supporting object.
According to another aspect of the embodiment, in the development apparatus, a main component of the toner is one of polyester and styrene acrylics, and the flexible material is made from one or a combination of silicone resin, nylon resin, melamine resin, acrylic resin, poly vinyl alcohol (PVA), urethane, quaternary ammonium salt, and a nigrosine system dye.
According to another aspect of the embodiment, in the development apparatus, the flexible material is made of a conductive material.
Another aspect of the embodiment provides an image formation apparatus that includes the development apparatus as described above for superposing two or more toner images on the latent image supporting object.
[Effectiveness of Invention]
According to the embodiment of the present invention, it is possible to support all the areas of the supporting end of the flexible member serving as the regulating member by a supporting member in the direction perpendicular to the surface moving direction of the toner supporting object. For this reason, compared with the case wherein a roller is supported only at end areas by bearings, bending (sag) at the central position can be reduced. Further, the flexible material can be a member, such as a blade, that does not produce an elastic deformation in thickness directions. As a result, the toner thickness unevenness due to elastic deformation in the thickness directions of the regulating member, and the toner thickness unevenness due to bending of the regulating member in the axial direction are reduced compared with the case wherein the roller made from urethane foam is used as the regulating member. Accordingly, the uneven development consistency due to the uneven toner thickness on the surface of the toner supporting object can be reduced compared with the conventional configuration.
In the following, embodiments of the present invention are described with reference to the accompanying drawings.
First, experiments conducted by the Inventors hereto concerning the present invention are described. With reference to
The toner layer 5 was formed on the substrate 4 by developing a solid black image with a 2-component development apparatus that is not illustrated. The toner was of a polyester system, and has a particle diameter of about 6 μm. The amount of electrification of the toner formed into a thin film on the substrate 4 was about −22 μC/g. Then, an AC voltage was applied to the electrodes as shown in
Four samples of the substrate 4 were manufactured, wherein the electrode pitch p between the electrodes 21, 22, 23, and so on was differentiated, namely, p=50, 100, 200, and 400 μm. Then, the degree of flare activity was observed with a high-speed camera, changing Vmax V that is a voltage difference between a positive peak and a negative peak of the voltage of the AC voltage applied to the electrodes 21, 22, 23, and so on from the AC power supply 6. Results are obtained as shown in
Here, the degree of flare activity was obtained by a sensory evaluation wherein a situation of the toner not moving but sticking to the surface of the substrate 4 was evaluated in 5 levels. As shown in
Further, in order to determine an influence of an electrical property of the surface of the substrate 4, a volume specific resistance of the surface layer 3 of the substrate 4 was changed, and the degree of the flare activity was similarly evaluated. The material of the surface layer 3 was a silicone system resin, and the amount of carbon particles contained in the silicone system resin was changed so that the surface layer 3 (thickness of which surface layer 3 is about 5 μm) has a volume specific resistance between 107 and 1014 Ω-cm. As a typical example, the electrode pitch was 50 μm. Then, experiment results were obtained as shown in
From the experiment results, it was determined that an appropriate volume specific resistance of the surface layer 3 ranged between 109 and 1012 Ω-cm. Otherwise, if the volume specific resistance of the surface layer 3 was too high, the surface of the substrate 4 remained being charged by friction of the surface layer 3 and the toner that repeated hopping. The charge causes the surface voltage of the substrate 4 to fluctuate, and a bias voltage for development became unstable. To the contrary, if the conductivity of the surface layer 3 was too high, a charge leak (short circuit) occurred between the electrodes 21, 22, 23, and so on, and the bias voltage was degraded. That is, the specific resistance of the surface layer 3 had to be appropriate (i.e., between 109 and 1012 Ω-cm) such that the charge accumulated on the surface layer 3 on the substrate 4 could be properly discharged to the electrodes 21, 22, 23, and so on. In addition, the range of the volume specific resistance was determined through experiments using the experimental system shown in
The inventors hereto further conducted an observation of the degree of flare activity with two kinds of the surface layer 3; namely, one was made of silicone system resin and the other was made of fluorine system resin. This was to determine the influence of a friction electrification characteristic of the surface of the substrate 4. The volume specific resistance of the surface layer 3 of both the silicone system resin and the fluorine system resin was made to be 1011-1012 Ω-cm by distributing a small quantity of carbon particles. Then, the degree of flare activity was observed by applying an AC bias to the electrodes 21, 22, 23, and so on from the AC power supply 6. With the surface layer 3 of the silicone system resin, the flare state was maintained for a long time. With the surface layer 3 of the fluorine system resin, the flare quickly disappeared and the toner stuck to the substrate 4.
After the observation, an amount of electrification of the toner on the substrate 4 was measured. With the surface layer 3 of the silicone system resin, the amount of electrification of the toner on the substrate 4 was a little smaller than an initial stage. With the surface layer 3 of the fluorine system resin, the amount of electrification of the toner on the substrate 4 was almost lost. Next, toner that was not charged was rubbed onto the surface layer 3. In the case of the surface layer 3 of the silicone system resin, the toner acquired a positive polarity charge. In the case of the surface layer 3 of the fluorine system resin, the toner acquired almost no charge, or a slight negative polarity charge. Given that the flare phenomenon is a process wherein the toner collides with the surface of the substrate 4 for a great number of times, the surface layer 3 is desirably made of a material that gives a positive polarity charge to the toner, rather than a material that discharges the toner. That is, a friction electrification series of materials can be referenced, and the surface layer 3 is desirably made of, e.g., a glass system, and a material used in a carrier coat of 2-component developer.
Next, experiment results of another system as shown in
The system further includes a substrate B that is installed countering the substrate A at a gap d μm. The substrate B is constituted like the substrate 4. The surface layer 3 is made into a white coat layer so that measurement with an optical measurement instrument (a catoptrical light consistency measuring instrument) of an amount of toner to be transferred here by subsequent work is facilitated. Then, dependability of an amount of toner transition to the substrate B to the development gap d μm was investigated, wherein four combinations of Vmax V and p μm were used, all of which combinations give Vmax V/p μm=4. Note that the flare was stably formed where Vmax V/p μm is equal to 4 regardless of other conditions as shown in
This can be taken as a condition under which influences of an electric field curtain formed on the toner supporting object (substrate B) do not reach the electrostatic latent image electric field or the toner image on the latent image supporting object (substrate A). Under this condition, not only an isolated dot can be correctly developed at, for example, 1200 dpi and 2400 dpi without scavenging, but also a very high definition toner image superposition can be realized without causing the color mixture of the toner in the development apparatus, and without disturbing the toner image previously formed on the latent image supporting object when forming an image by an image forming process like the toner image superposition on the latent image supporting object (substrate A) as described above.
By the way, conventional development apparatuses used by image formation apparatuses, such as a copying machine, a printer, and a facsimile apparatus, often employ one of a 2-component development method, and a 1-component development method. The 2-component development method is suitable for high-speed development, and currently is a mainstream method for a medium to high-speed image formation apparatus. According to the 2-component development method, in order to obtain high definition, the developer at a position contacting the electrostatic latent image on the latent image supporting object has to be very minute. For this purpose, miniaturization of the diameter of carrier particles is progressing, and a particle diameter of about 30 μm is commercially available.
The 1-component development method, which requires a small and lightweight mechanism, is a mainstream of a low speed image formation apparatus at present. According to the 1-component development method, the toner supported on the surface of a developer supporting object, such as a developing roller, is used for development without hopping. Specifically, in order to form a thin toner layer on the developing roller, a toner regulating member, such as a blade and a roller, is made to contact the toner on the developing roller, and the toner is then electrified by friction with the developing roller and the toner regulating member. The electrified thin toner layer formed on the developing roller is carried to the development position, and the electrostatic latent image on the latent image supporting object is developed. Here, the 1-component development method can be classified into two types. One is a contacting type, and the other is a non-contacting type. As for the former, the developing roller and the latent image supporting object make contact; and as for the latter, the developing roller and latent image supporting object do not make contact.
For example, JPA H3-100575 discloses a hybrid method wherein the 2-component development method and the 1-component development method are combined such that shortcomings of one are complemented by the other.
For example, JPA H3-113474 discloses a method of developing a minute uniform dot of a high resolution. According to the method, a wire, to which a high frequency bias is applied, is provided to the development unit that is based on the hybrid method as described above so that a toner cloud is obtained in the development unit. In this way, a high resolution dot can be developed.
Further, JPA H3-21967 (Patent Reference 1) discloses a method of efficiently and stably forming the toner cloud, wherein an electric-field curtain is formed on a rotation roller.
Further, JPA 2003-15419 discloses a development apparatus wherein a developer is conveyed by an electric-field curtain by a progressive-wave electric field. Further, JPA H9-269661 discloses a development apparatus that includes two or more magnetic poles for almost uniformly adsorbing a carrier of about one layer on the circumference of a developing roller. Further, JPA 2003-84560 discloses a development apparatus wherein a periodic conductive electrode pattern is formed on a developer supporting body for supporting a non-magnetic toner through an insulation member, and an electric-field gradient is generated near the developer supporting body surface by providing a predetermined bias voltage to the electrode so that a non-magnetic toner is adhered to the developer supporting object and conveyed by the developer supporting object.
It is increasingly required that the conventional 2-component development provide high-definition capability. It is required that the dot size of a pixel be equivalent to or even smaller than the present diameter of the carrier particles. From the viewpoint of reproducibility of an isolated dot, the diameter of the carrier particles should be smaller than now. However, the smaller is the diameter, the smaller becomes the permeability of the carrier particles. Small particle carrier tends to be disassociated from a developing roller. If the disassociated carrier particles are adhered to a latent image supporting object, various side effects can occur such as damaging the latent image supporting object in addition to producing a faulty image.
In order to prevent the carrier from disassociating, attempts have been made, e.g., by raising the permeability of the carrier particles by selecting an appropriate material, and by strengthening the magnetism of a magnet included in the developing roller. However, development works have reached an extreme of difficulty in balance between the cost and high definition. Further, requirements for miniaturization of an apparatus lead to reduction of the diameter of the developing roller, which makes it further difficult to design a developing roller with a powerful magnetic field for preventing the carrier disassociation.
First of all, since the 2-component development method is a process of forming a toner image by an ear, called a magnetic brush, of a 2-component developer rubbing an electrostatic latent image, unevenness tends to be produced when developing an isolated dot due to the heterogeneity of the ear. Even though an improvement in quality of the image is possible by forming an alternating current (AC) electric field between the developing roller and the latent image supporting object, it is difficult to completely remove the unevenness of the image due to fundamental unevenness of the ear of the developer.
Further, in order to raise transfer efficiency of a process of transferring the toner image developed on the latent image supporting object, and in order to raise cleaning efficiency of a process of cleaning the toner that remains on the latent image supporting object after transfer, non-electrostatic adhesion of the toner to the latent image supporting object has to be reduced as much as possible. As a method of reducing the non-electrostatic adhesion of the toner to the latent image supporting object, a friction coefficient of the surface of the latent image supporting body may be reduced. However, if the friction coefficient is small, the ear of the 2-component developer may smoothly pass through the development position, which causes the development efficiency and dot reproducibility to be degraded.
According to the 1-component development method, the toner layer on the developing roller is fully press-contacted to the toner regulating member; for this reason, toner response to the electric field at the development position is poor. Accordingly, it is a usual practice to form a powerful alternating current (AC) electric field between the developing roller and the latent image supporting object in order to obtain high definition. However, even if the AC electric field is formed, it is difficult to stably develop the toner at a constant rate for the electrostatic latent image, and it is difficult to uniformly develop the minute dot of a high resolution. Further, according to the 1-component development method, a great stress is applied to the toner when the toner is formed in lamination on the developing roller, which causes the toner, which is recycled in the development apparatus, to be quickly degraded. With the degradation of the toner, the toner tends to be uneven. For this reason, the 1-component development method is not generally suitable for a high speed/high durability image formation apparatus.
According to the hybrid method (JPA H3-100575), although the size and the number of components of the development apparatus are increased, some problems are overcome. Nevertheless, the same problem as the 1-component development method remains at the development position, that is, it is difficult to develop a minute and uniform dot in high resolution.
Although high stability and high definition development may be realized by the method disclosed by JPA H3-113474, the configuration of the development apparatus becomes complicated.
Further, the method disclosed by JPA H3-21967 (Patent Reference 1) may be excellent in obtaining small and high-definition development; however, the Inventors hereto have discovered that, in order to obtain the ideal high definition, conditions concerning such as electric-field curtain forming and development are restrictive. In other words, unless image formation is carried out under the restrictive conditions, merits of the method cannot be enjoyed at all; not only that, the image quality is degraded. Further, according to this method, the toner is conveyed while hopping on the toner supporting object to a development position by a movement of the toner supporting object; however, this problem (limited conditions) is common to the method disclosed by JPA 2002-341656, wherein the toner is conveyed to the development position only by a hopping movement, not by a movement of the toner supporting object.
Further, for an image formation process wherein a first toner image is formed on the latent image supporting object, then a second toner image, then a third toner image, and so on, one by one, the development method has to be such that the toner image(s) already formed on the latent image supporting object is not disturbed. According to the non-contacting 1-component development method and the toner cloud development method disclosed by JPA H3-113474, it is possible to form color toner images one by one on the latent image supporting object. However, since an alternating current (AC) electric field is formed between the latent image supporting object and the developing roller, a part of the toner tends to be torn off from the toner image already formed on the latent image supporting object, and the torn-off toner enters the development apparatus. That is, the image on the latent image supporting object is disturbed by this, and further a problem is posed that the toner in the development apparatus is mixed with another color. This is a vital problem for acquiring a high-definition image. A method of generating a toner cloud, wherein no alternating current (AC) electric field is formed between the latent image supporting object and the developing roller, is required.
The toner cloud may be generated by the methods disclosed by JPA H3-21967 (Patent Reference 1), and JPA 2002-341656 described above; however, merits of the methods cannot be enjoyed unless strict conditions are met as described above; otherwise, they are completely ineffective. If the conditions are not appropriate, the toner cloud cannot be generated. Even if the toner cloud is generated, a part of the toner in the toner layer on the latent image supporting object is mixed into the development apparatus of the next color, causing image disturbance and color mixture.
Then, according to the image formation apparatus of the embodiment, the condition of Vmax V/p μm>1 is sufficed in view of the result of the experiment described above. The toner cloud can be surely generated with this configuration. Therefore, according to the embodiment, higher definition and smaller size are realized compared with the conventional techniques.
In addition, it is conceivable that the toner cloud is surely generated by the method disclosed by JPA 2002-341656, wherein the toner is electrostatically moved by an AC electric field of three or more phases, not by a mechanical movement of the toner supporting object, if the condition as described above is sufficed. However, according to the method, the toner may deposit on a conveyance substrate triggered by a toner that is not electrostatically conveyed by some chances, and as a result, operations stop. In order to solve this problem, JPA 2004-286837 proposes a structure having a combination of a fixed conveyance plate and a toner supporting object that moves on the surface of the fixed conveyance plate; nevertheless, this makes the mechanism highly complicated. Conversely, according to the image formation apparatus of the embodiment of the present invention, wherein the toner is conveyed to the development position by movement of the surface of the toner supporting object, which toner moves to and fro between the electrodes by hopping, the toner is not accumulated, and the mechanism is not complicated.
A manufacturing process of the toner supporting object 31 is described with reference to
A thin toner layer is formed on the protection layer 55 of the toner supporting object 31, like the substrate 4. When the AC voltage, serving as a bias voltage, as shown in
In addition, according to the example shown in
Residual toner that has not been used for the development returns from the development position to the magnet sleeve 57. Since the flare is formed, the amount of the toner that remains adhered to the toner supporting object 31 is very small. The toner that has returned from the development position by the toner supporting object 31 is easily scratched by the ear of the 2-component developer that follows the rotation of the magnet sleeve 57, and is homogenized/smoothed. By repeating this, an approximately constant amount of the toner flare is always formed on the toner supporting object 31. The 2-component development unit 56 stirs, conveys, and circulates the 2-component developer 63 in a container 60, for example, via circulation paddles 61 and 62, while the magnet sleeve 57 conveys a part of the 2-component developer 63 to the toner supporting object 31, and returns the unused toner.
In the following, described is the case wherein the latent image supporting object 58 uses an organic photo conductor that is 13 μm thick, and a latent image is formed using a laser writing unit of 1200 dpi. The latent image supporting object (photo conductor) 58 is rotationally driven by a driving unit that is not illustrated, is uniformly charged by an electrification apparatus, and is exposed by the laser writing unit such that the electrostatic latent image is formed. In this case, the electrostatic latent image is formed under conditions that an electrification voltage of the latent image supporting object (photo conductor) 58 is between −300 and −500 V, and a writing voltage for a solid image part is between 0 and −50 V.
The electrostatic latent image is developed by the toner that forms a flare on the toner supporting object 31, and turns into a toner image. At this time, conditions for producing a good single dot of 1200 dpi with the solid image part being satisfactorily printed without ground dirt for a toner made of particles 6 μm in diameter having an amount of electrification about −22 μC/g are as follows:
the gap between the toner supporting object 31 and the latent image supporting object (photo conductor) 58 is about 500 μm; and
the alternating-current (AC) bias is provided from the AC power source 59 to the electrodes of the toner supporting object 31, where the AC bias peaks at −400 V and 0 V, averaging at −200 V, at a frequency of 5 kHz. Further, the phase angle of the AC bias provided to the odd-numbered electrodes is the inverse of the AC bias provided to the even-numbered electrodes.
The toner image on the toner supporting object 31 is transferred by a transferring unit to a recording medium such as paper fed by a feeding unit, and is fixed to the recording medium by a fixing unit. Then, the recording medium is discharged outside.
If an excessive amount of toner is provided to the toner supporting object 31, the electric-field curtain is shielded by the charge of the toner, which makes it impossible to form the flare. In this view, a direct-current (DC) bias of about 200 V is provided between the magnet sleeve 57 and the toner supporting object 31 from a power source so that the amount of toner on the toner supporting object 31 is 0.2 mg/cm2. Incidentally, since the toner is diffused by flaring, some unevenness in toner transfer to the toner supporting object 31 from the magnet sleeve 57 does not cause a problem, a device for superposing an AC bias onto the direct-current bias between the magnet sleeve 57 and the toner supporting object 31 is unnecessary, and a device for strictly homogenizing the ear of the 2-component developer is also unnecessary.
On the other hand, since the amount of the toner necessary for forming a solid image on the latent image supporting object (photo conductor) 58 is 0.4 mg/cm2, it is necessary to make the moving speed of the toner supporting object 31 equal to or greater than twice the moving speed of the latent image supporting object (photo conductor) 58 so that a sufficient amount of the toner is provided to the development position. Accordingly, the moving speed of the toner supporting object 31 is made 2.5 times the latent image supporting object (photo conductor) 58 in this embodiment. A moving direction of the toner supporting object 31 may be the same as a moving direction of the latent image supporting object (photo conductor) 58 as shown in
With the system described above, it was confirmed that high-definition development of a 1200 dpi dot was realized with satisfactory solid image nature without ground dirt at a linear speed of 300 mm/s of the latent image supporting object (photo conductor) 58.
The contact position serves as a toner thickness regulation position, at which the thickness of the toner layer on the toner supporting object 31 is regulated for a uniform thickness when the toner layer enters this position. In this way, the thickness of the thin toner layer on the surface of the toner supporting object 31 is regulated and made uniform.
The metering blade 68 is made of a flexible material such as a thin plate, a film, etc., that is not elastically deformed in a thickness direction. One end of the metering blade 68 is supported by a supporting member such as a bracket that is not illustrated, and the other end contacts the toner supporting object 31. According to this configuration, the whole area of the supported end of the metering blade 68 is supported by the supporting member in directions perpendicular to the movement of the surface of the toner supporting object 31 (that is, in directions penetrating the drawing paper). For this reason, bending at a central position can be reduced compared with a roller that can be supported only at both ends by the bearings. Further, since the metering blade 68 is made of the material that is not elastically deformed in the thickness direction, thickness unevenness of the toner due to the elastic deformation in the thickness direction is avoided. As described above, both thickness unevenness of the toner due to the elastic deformation in the thickness direction of the roller produced by a roller made of urethane foam and thickness unevenness of the toner due to bending in a direction of an axis of the roller are avoided. Accordingly, uneven development concentration due to the thickness unevenness of the toner on the surface of the toner supporting object 31 is reduced compared with the conventional practice.
The toner used by the image formation apparatus according to the embodiment is made of a base-material resin (the main material of the toner) that consists of polyester or styrene acrylics that has a negative regular electrification polarity. Further, both a latent image part and a uniformly charged part (background) of the latent image supporting object (photo conductor) 58 are made into the same polarity as the regular electrification polarity of the toner (that is, the negative polarity according to this example), and the toner is selectively adhered to the latent image part, a voltage of which is smaller than the background so that the so-called reversal development is performed.
The metering blade 68 serving as the regulating member is made of a material that promotes friction electrification on to the side of the regular electrification polarity of the toner (negative polarity according to this example) when the metering blade 68 is in sliding contact with the toner on the surface of the toner supporting object 31. That is, the toner is located at a more negative position on a friction electrification series than the metering blade 68. The metering blade 68 is made of a material that realizes the relationship described above, e.g., organic materials such as silicone, nylon, melamine resin, acrylic resin, PVA, and urethane. In addition, the fourth class ammonium salt, and a nigrosine system dye, etc., may be used. Further, a mixture of two or more of the materials listed above may be used.
According to the image formation apparatus that includes the metering blade 68, friction electrification onto the side of the regular electrification polarity of the toner is promoted by sliding contact with the toner on the surface of the toner supporting object 31. In this way, degradation of the image quality due to conveying a toner with poor electrification to the development position can be reduced.
Here, the toner supporting object 31 includes the protection layer 3 as shown in
Alternatively, a toner that has a positive regular electrification polarity may be used. In this case, the metering blade 68 and the protection layer 3 are made of a material that promotes friction electrification by sliding contact with the toner on to the side of the positive polarity.
The electrification series of a toner is that of the toner as a whole including additives such as silica, and titanium oxide to the toner base-material resin (particles). A position in the electrification series of a toner may be determined as follows. That is, the toner on a surface-protection layer is in sliding contact with one of the metering blade 68 and the protection layer 3 for a predetermined time, then the toner is extracted by attraction, then an amount of electrification of the extracted toner is measured by an electro meter. If a measurement result shows an increase in the amount of electrification to the negative polarity of the toner, the toner is determined to have the more negative position in the electrification series than the metering blade 68 or the protection layer 3, as applicable. Further, if the measurement result shows an increase in the amount of electrification to the positive polarity of the toner, the toner is determined to have the more positive position in the electrification series than the metering blade 68 or the protection layer 3, as applicable.
Further, a middle layer may be provided between the protection layer 3 and the electrodes. The material of the middle layer may be, e.g., Ti, Sn, Fe, Cu. Cr, Ni, Zn, Mg, Al, TiO2, SnO2, Fe2O3, Fe3O4, CuO, Cr2O3, NiO, ZnO, MgO, and Al2O3.
According to the image formation apparatus of the embodiment, two or more electrodes of the toner supporting object 31 are in sliding contact for one of the electrode shafts 40A and 40B irrespective of the rotational position of the toner supporting object 31 as shown in
The inventors hereto prepared a printer testing machine having the same configuration as the image formation apparatus according to the embodiment described above, except that the electrodes of the toner supporting object 31 contact one of the electrode shafts 40A and 40B only when the rotational position of the toner supporting object 31 is at a predetermined position. Experiments were conducted for three different predetermined positions as follows.
(1) Experiment number 1: the rotational position that counters the development position
(2) Experiment number 2: the rotational position that counters the toner thickness regulation position, and the rotational position that counters the development position
(3) Experiment number 3: all areas from the rotational position that counters the toner thickness regulation position to the rotational position that counters the development position
In the experiments, a test image was printed with the printer testing machine, and evaluations were made about a distribution of toner electrification amounts, a convergence nature of toner electrification, and a presence of ground dirt. The distribution of the toner electrification amounts was evaluated as follows. That is, a printing operation (i.e., rotational drive of the toner supporting object 31) was halted during a test print, and the toner in an area just before the development position of the toner supporting object 31 was extracted. Then, with a commonly known technique, an amount of electrification of each toner particle in the extracted toner was measured, and the distribution of the electrification amounts was analyzed. Then, the distribution was classified into three categories, namely, great, medium, and small.
As for the convergence of the toner electrification amounts, an electrification range, which is equal to the standard deviation of the distribution of the electrification amounts, was analyzed. Then, the convergence was classified into three categories, namely, small, medium, and great that are expressed by ◯, Δ, and X, respectively, in Table 1 that follows. Since the toner electrification was saturated at a certain level, the better was the convergence of the electrification amounts (i.e., the smaller is the electrification range that is equal to the standard deviation), the more sufficiently was the toner electrified.
Further, for evaluating the presence of ground dirt, during test printing, the testing machine was suspended, and an adhesive transparent tape was attached to the background of the latent image supporting object (photo conductor) 58 such that the toner adhering to the background was removed by and transferred to the adhesive transparent tape. Then, the amount of the toner transferred to the tape was classified into four categories; namely, ⊚ (no toner transferred), ◯ (although there is a slight transfer of the toner, it is not visible), Δ (the transferred toner is visible), and X (the transferred toner is conspicuous).
Experiment results are shown in the following Table 1.
As shown in Table 1, as for the experiment number 1, the distribution of the toner electrification amounts was relatively great (Great), and the convergence of the toner electrification amounts was relatively small (X). This indicated that a part of the toner conveyed to the development position was not fully electrified. For this reason, as shown in Table 1, the ground dirt was produced (X) by the toner with poor electrification. Concerning the experiment number 2, the distribution of toner electrification amounts, the convergence of toner electrification amounts, and the ground dirt were improved compared with the experiment number 1. However, since the convergence of toner electrification amounts was not enough, the toner was slightly adhered to the background of the latent image supporting object (photo conductor) 58. According to the experiment number 3, since the best results were obtained concerning the distribution of toner electrification amounts and the convergence of toner electrification amounts, no ground dirt was generated. From the experiment results, it was concluded that the electrification of the toner on the surface of the toner supporting object 31 was promoted by hopping between the regulation position and the development position, wherein the toner and the protection layer 3 of the toner supporting object 31 were in sliding contact, and the friction electrification was promoted.
As described above, the image formation apparatus according to the embodiment, the electric field for hopping is formed all over the periphery of the surface of the toner supporting object 31 in the endless moving direction, friction electrification of the toner is promoted between the regulation position and the development position; in this way, generation of the ground dirt by poor electrification of the toner is reduced.
Next, examples of the image formation apparatus are described, wherein one or more features are added to the image formation apparatus of the embodiment as described above. Unless specified, the configuration of the image formation apparatus in the following examples is the same as that of the embodiment.
The inventors hereto prepared two kinds of the metering blade 68 for the printer testing machine, one consisting of a non-conductive material, and the other consisting of a conductive material. Then, the test image is continuously printed for a predetermined number of sheets, and adhesion nature of the toner to the metering blade 68 is evaluated in three categories, namely, X (adhesion is visible at a glance), ◯ (adhesion is slightly visible if an eye is well elaborated), and ⊚ (adhesion is not visible at all). Results are shown in the following Table 2.
Comparing the experiment number 5 with the experiment number 6 of Table 2, it is concluded that the conductive blade gives the better result than the non-conductive blade regarding the toner adhesion. This is considered to be because the toner is adhered by electrostatic force due to a counter charge (the toner being electrified in a polarity reverse to the toner) generated by sliding contact of the non-conductive material and the toner, while the conductive material does not generate such counter charge. In addition, with reference to the experiment number 4, in spite of using the conductive material for the metering blade 68, the evaluation result of adhesion of the toner is X (poor). This is considered to be because the hopping electric field is not formed at the regulation position, which promotes the adhesion of the toner by not making the toner hop on the surface of the toner supporting object 31 at the regulation position. In other words, by forming the hopping electric field at the regulation position, static electricity force that removes the toner from the surface of the regulating member is periodically generated; and as a result, the toner adhesion to the regulating member is reduced.
In view of above, the image formation apparatus according to Embodiment 1, the metering blade 68 is made of a conductive material such that the toner adhesion to the metering blade 68 is reduced. In addition, as described in the embodiment, the hopping electric field is formed all over the periphery of the toner supporting object 31. Therefore, the toner adhesion to the metering blade 68 is reduced also by making the toner hopping at the regulation position.
The development apparatuses 73K, 73Y, 73C, and 73M are for developing latent images in predetermined colors with toners of the corresponding colors, wherein the toner images of the colors are superposed on a belt-like organic photo conductor 69. The belt-like organic photo conductor 69 is wound around two rollers that are not illustrated, and rotationally driven by a driving unit that is not illustrated.
The image formation apparatus of Embodiment 2 includes image formation units 70K, 70Y, 70C, and 70M for forming images in two or more colors, for example, black, yellow, cyan, and magenta, respectively, that are shown on the left-hand side of the organic photo conductor 69 in
Then, the organic photo conductor 69 is uniformly charged by an electrification unit 71Y, and exposed by an optical beam 72Y modulated by image data for yellow color and provided by a writing unit (not illustrated) of the image formation unit 70Y such that an electrostatic latent image is formed. The electrostatic latent image turns into a toner image in yellow, and the toner image is developed by the development apparatus 73Y, which is configured the same as the development apparatus including the development unit 64 and the toner supporting object 31 shown in
Next, the organic photo conductor 69 is uniformly charged by an electrification unit 71C, and is exposed by an optical beam 72C modulated by image data for cyan color and provided by a writing unit that is not illustrated of the image formation unit 70C such that an electrostatic latent image in cyan is formed. The electrostatic latent image turns into a toner image in cyan color, which is then developed by the development apparatus 73C having the same configuration as the development apparatus including the development unit 64 and the toner supporting object 31 shown in
The organic photo conductor 69 is uniformly charged by an electrification unit 71M, and is exposed by an optical beam 72M modulated by image data for magenta color and provided by a writing unit (not illustrated) of the image formation unit 70M such that an electrostatic latent image in magenta is formed. The latent image is developed by the development apparatus 73M having the same configuration as the development apparatus including the development unit 64 and the toner supporting object 31 shown in
On the other hand, a recording medium such as paper is provided by a feeding unit that is not illustrated, and the full color image on the photo conductor 69 is transferred to the recording medium by a transfer roller 75, to which a transfer bias is provided by a power source. The full color image on the recording medium is fixed by a fixing unit 76, and the recording medium is discharged outside. After full color image transfer, residual toner on the photo conductor 69 is removed by a cleaner 77.
According to the image formation apparatus, since the toner images in four colors are formed on the same organic photo conductor 69, compared with the usual 4-color tandem system, position gap hardly occurs theoretically, and a high-definition full color image can be acquired.
In addition, according to the image formation apparatus as described above, both conditions of Vmax V/p μm>1 and p μm<d μm are sufficed in view of the results of the experiments described above. That is, no influences are affected in the toner image formed on the organic photo conductor 69, and no toner is transferred from a foregoing toner image formed on the organic photo conductor 69 to the development apparatus of a next color. In this way, high quality images are stably formed for a long period without problems such as scavenging and color mixture.
Although the embodiments are described about the image formation apparatus wherein the toner is conveyed to the development position by the surface movement of the toner supporting object while the toner is flared and hopping between two adjacent electrodes, the present invention can be applied to an image formation apparatus wherein, a toner is conveyed to a development position of a toner supporting object by repeatedly hopping from a certain electrode upward to an adjacent electrode in a direction from one end to the other of the toner supporting object like the method disclosed by JPA 2002-341656. Further, the present invention is also applicable to an image formation apparatus wherein the toner is conveyed to the development position by both hopping the toner and by movement of the surface of the toner supporting object.
Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Priority Application No. 2006-279541 filed on Oct. 13, 2006 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-279541 | Oct 2006 | JP | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20080089720 A1 | Apr 2008 | US |
