JP2000098761A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a high-quality image having an excellent transfer characteristic to be always outputted by providing a device with a backup roller whose outside diameter is smaller than the inside diameter of an intermediate transfer medium and which is brought into contact with the inside surface of the intermediate transfer medium and a pressure roller brought into contact with the outside surface of the intermediate transfer medium at a contact part between the backup roller and supplying an image carrier between the pressure roller and the intermediate transfer medium. SOLUTION: This device is constituted of the intermediate transfer medium 23 arranged adjacently to a latent image holding body 22, the backup roller 24 having the smaller outside diameter than the inside diameter of the medium 23 and the pressure roller 55. The roller 24 is brought into contact with the inside of the medium 23 so as to drive it. When a distance between the surface of the roller 24 and the surface of the holding body 23 is set to be 3 mm, for example, the medium 23 is expanded toward the holding body 22 side by the elasticity of itself and lightly brought into contact with the surface of the holding body 22 with extremely small pressure. Thus, developer 28 on the holding body 22 is efficiently transferred on the medium 23 by an electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus using a liquid developer or a dry developer.

[0002]

2. Description of the Related Art An electrophotographic apparatus using a liquid developer has an advantage which cannot be realized by a dry electrophotographic apparatus, and its value is recently being reconsidered. That is, since a very fine toner having a submicron size can be used,
It is economical because high image quality can be realized, sufficient image density can be obtained with a small amount of toner, and it can achieve the same texture as printing (for example, offset printing), and energy can be saved because toner can be fixed on paper at a relatively low temperature. Is a major advantage of wet electrophotography over dry electrophotography.

On the other hand, the conventional wet electrophotography using a liquid developer includes the following essential problems, and for a long time has allowed the sole use of the dry technology. One of these problems is a problem in the transfer process.

[0004] The first problem in transfer is deterioration of image quality. That is, conventionally, in the transfer step, the developer adhering to the latent image holding member was directly subjected to the electric field transfer to the sheet, so that the transfer unevenness due to the electric field fluctuation according to the unevenness of the sheet surface occurred. In addition, transfer failure was likely to occur due to variations in the electrical characteristics of the paper and environmental dependence. These issues are
The quality of the transferred image was significantly deteriorated.

[0005] A second problem in transfer is an environmental problem due to the adhesion of a solvent to paper. In the electric field transfer of a liquid developer, toner particles, which are charged particles, move in a solvent by an electrophoresis phenomenon and are transferred to paper. Therefore, in electric field transfer, a predetermined amount of solvent must be interposed between the latent image holding member and the sheet, and as a result, a large amount of solvent adheres to the sheet after transfer. This solvent is partially volatilized in the fixing process by heat and released outside the machine,
It caused problems such as odor and adverse effects on the human body due to inhalation of steam. Further, the paper discharged outside of the apparatus after fixing still contains a large amount of solvent, and when a user with allergic nature touches this, dermatitis such as eczema may be caused.

In order to solve such a problem, a method has been proposed in which toner particles with a predetermined amount of solvent are temporarily transferred from a latent image holding member to an intermediate transfer medium, and then transferred to paper. US Patent Nos. 5,148,222 and 5,16
Nos. 6,734, 5,208,637 and the like disclose a method of transferring toner particles from a latent image holding member to an intermediate transfer medium by an electric field, and then transferring the toner particles to paper by pressure (and heat). I have. Also, Japanese Patent Publication No. 46-4167
No. 9 and JP-A-62-280882 disclose a method of using pressure (and heat) for both transfer to an intermediate transfer medium and transfer to paper without using electric field transfer.

Since it is relatively easy to form the intermediate transfer medium from a material having a smooth surface and a small variation or variation in electric resistance, the image quality is deteriorated by the transfer as compared with the case where the electric field is directly transferred to the paper. Is dramatically improved. Even when the image is transferred to the intermediate transfer medium by pressure and heat, the deterioration of the image quality is significantly suppressed.

In these proposals, since the transfer is performed on paper by heat and pressure, the problem seen in the case of electric field transfer does not occur. Furthermore, the solvent adhering to the intermediate transfer medium can be vaporized or sucked by heating or air suction prior to pressure transfer to the paper, so that the solvent adhesion to the paper is significantly reduced. Can be. In the case of transferring to paper by pressure, such an improvement is possible because no solvent is required.

However, these proposals still have the following problems in practical use. First, when transferring toner particles to an intermediate transfer medium by an electric field, the intermediate transfer medium needs to be made of a material having conductivity and elasticity. This requirement is the same in the transfer of a dry developer, and when an excessively high pressure is applied to the developer, the adhesive force between the developer and the latent image holding member is increased, and it is difficult to transfer by an electric field. .

Therefore, conventionally, it has been attempted to use a conductive rubber as an intermediate transfer medium to realize elasticity and conductivity at the same time. However, generally, when conductivity is imparted to rubber by adding conductive carbon or the like, the flexibility of the rubber is impaired, and it becomes difficult to obtain soft contact. for that reason,
A rubber having a relatively high hardness had to be used, and the latent image holding member and the intermediate transfer medium had to face each other with extremely high precision in order to obtain a soft contact.

[0011] Such demands have required the use of high-precision parts, resulting in increased costs and reduced yield in the manufacturing process. Further, since the rubber swells due to the petroleum-based solvent contained in the liquid developer and changes its thickness, the operator has to frequently adjust the positional relationship between the intermediate transfer medium and the latent image holding member. Furthermore, in selecting a conductive rubber material capable of suppressing such swelling as much as possible, there is a problem that the range of selection is extremely narrow and involves a great deal of difficulty.

On the other hand, in the method of transferring the toner particles to the intermediate transfer medium by pressure, the above-mentioned problem relating to the electric field transfer can be avoided, but the following problem newly arises. In this case, the toner particles are transferred mainly based on the surface energy of each member or the difference in releasability. That is, the toner particles are transferred to the intermediate transfer medium only when the releasability of the surface of the latent image holding member exceeds the releasability of the intermediate transfer medium.

The relationship of the releasability must be established between the intermediate transfer medium and the sheet. Therefore, a clear order of releasability must be realized between the latent image carrier, the intermediate transfer medium, and the paper, and the selection range of constituent materials for these parts has been significantly narrowed.

Further, when used for a long period of time, the surface of each member is contaminated with a developer or the like, so that the surface condition changes, and it is difficult to maintain the above-described order. All of these problems have resulted in deterioration of transfer characteristics and, consequently, deterioration of image quality.

Although the description has been given mainly of the case where the liquid developer is used, most of the above-mentioned problems are also caused in the electrophotographic apparatus using the dry developer. That is, the problem of image quality deterioration when the developer is transferred directly from the latent image holding member to the paper by electric field, the problem that the electric field transfer becomes difficult when the paper or the intermediate transfer medium is strongly pressed against the latent image holding member, The order of releasability between components is important when transferring images by using a developer, and problems such as restrictions on material selection and reduction in durability are common issues when dry developer is used. Had become.

[0016]

As described above, in the electrophotographic apparatus using the conventional liquid developing technique, there is a problem that a harmful solvent contained in the developer is easily attached to the paper and discharged outside the apparatus. was there. In addition, in electric field transfer, image quality is degraded due to irregularities on the paper surface and excessive contact pressure, and in pressure transfer, there are issues such as restrictions on the material selection range of component parts and poor durability. A similar problem arises in an electrophotographic apparatus using the same.

The present invention has been made under such circumstances,
An object of the present invention is to provide an electrophotographic apparatus capable of always realizing good transfer characteristics and high-quality image output in both a wet electrophotographic apparatus and a dry electrophotographic apparatus. It is another object of the present invention to provide an electrophotographic apparatus capable of minimizing the release of a solvent of a developer in a wet electrophotographic apparatus.

[0018]

According to a first aspect of the present invention, there is provided a latent image forming means for forming an electrostatic latent image on a latent image holding member, and a developer supplied to the electrostatic latent image to form a visible image. Developing means, and a transfer means for transferring the visible image onto an image carrier, wherein the transfer means is arranged so as to be in contact with or close to the latent image holding member. An intermediate transfer medium comprising a rotatable flexible cylinder, means for forming an electric field between the intermediate transfer medium and the latent image carrier, and an intermediate diameter having an outer diameter smaller than the inner diameter of the intermediate transfer medium; A backup roller disposed in the intermediate transfer medium so as to be in contact with the inner surface of the intermediate transfer medium at a position different from a position where the medium and the latent image holding member face each other, and the intermediate transfer in a contact portion with the backup roller Arranged to contact the outer surface of the media A pressure roller, and means for supplying an image carrier between the pressure roller and the intermediate transfer medium, wherein the pressure roller is pressed by a backup roller via the intermediate transfer medium, The backup roller does not contact the intermediate transfer medium in a portion other than the pressing portion, whereby the intermediate transfer medium does not come into strong contact with the latent image holding member, and the intermediate transfer medium does not contact the intermediate image holding member. An electrophotographic apparatus is provided, in which a visible image on a transfer medium is transferred.

According to a second aspect of the present invention, there is provided a latent image forming means for forming an electrostatic latent image on a latent image holding member, a developing means for supplying a developer to the electrostatic latent image to visualize the electrostatic latent image, Transfer means for transferring a visible image on an image carrier, an electrophotographic apparatus,
An intermediate transfer medium, wherein the transfer unit is arranged so as to be in contact with or close to the latent image holding member; a unit that forms an electric field between the intermediate transfer medium and the latent image holding member; And a means for supplying an image carrier between the pressing member and the intermediate transfer medium, wherein the intermediate transfer medium is formed on a rigid substrate and a surface of the rigid substrate. Means for providing an elastic layer and a flexible conductive layer formed on the surface of the elastic layer, and pressing the pressing member against the intermediate transfer medium with a pressure exceeding an elastic limit of the elastic layer. And a means for supporting the intermediate transfer medium so as to be in elastic contact with or close to the latent image holding member.

According to a third aspect of the present invention, there is provided a latent image forming means for forming an electrostatic latent image on a latent image holding member, a developing means for supplying a liquid developer to the electrostatic latent image to visualize the latent image, Transfer means for transferring the visible image onto an image carrier, wherein the transfer means is opposed to the latent image holding member so as to be in contact with or close to the latent image holding member. Means for forming an electric field between the intermediate transfer medium and the latent image holding member, a pressing member pressed against the intermediate transfer medium, and supplying an image carrier between the pressing member and the intermediate transfer medium A means for suspending and driving the conductive belt, a means for lightly contacting a flexible portion of the belt with the latent image holding member, The pressing means is strongly pressed against the belt, and is pressed against the image carrier. It provides an electrophotographic apparatus, characterized in that it comprises a means for transferring and fixing the serial developer. According to the electrophotographic apparatus configured as described above, it is possible to always output a high-quality image.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an electrophotographic apparatus according to one embodiment of the present invention. In FIG. 1, a latent image holding member 1 is formed of a photosensitive drum having an organic or amorphous silicon photosensitive layer provided on a conductive substrate. The latent image carrier 1 is uniformly charged by a well-known corona charger or scorotron charger 2a.
Upon receiving the exposure 3a by the image-modulated laser beam, an electrostatic latent image is formed on the surface.

Thereafter, the developing device 4 for storing the liquid developer
The visualization of the electrostatic latent image is performed by a. The liquid developer or toner adhering to the electrostatic latent image may be directly transferred to a sheet by the transfer device 5 in the transfer step, but here, the second charger 2b and the second laser exposure 3b continue here. A second electrostatic latent image is formed, and the first developing device 4
This is developed by a second developing device 4b that stores a second developer of a different color from the liquid developer stored in a. Therefore, after the second development, two color toner images are formed on the latent image holding member 1.

Similarly, third and fourth developments are performed.
A full-color toner image is formed on the latent image holding member 1.
The toner image is transferred to a sheet by the transfer device 5, and may be transferred directly to the sheet or to the sheet 10 via the intermediate transfer medium 6 as illustrated in FIG. May be. In the transfer from the latent image holding member 1 to the intermediate transfer medium 6 and the transfer from the intermediate transfer medium 6 to the paper 10, any of the transfer using an electric field and the transfer using pressure (and heat) can be used. .

Many liquid developers can generally be fixed on paper at room temperature. However, fixing may be performed by heating the pressure roller 8 or the like. Such an image forming process is described in, for example, US Pat. No. 5,570,173 and US Pat.
No. 0,675, which is a conventionally known process.

FIG. 2 shows an embodiment according to the first invention.
2 shows an enlarged view of the transfer device. The transfer device 21 shown in FIG.
The intermediate transfer medium 23 is formed of a flexible endless tube which is in contact with or close to the latent image holding member 22, a backup roller 24 having an outer diameter smaller than the inner diameter of the endless tube, and a pressure roller 25. I have. The paper 26 is carried between the pressure roller 25 and the intermediate transfer medium 23 by a transport device (not shown), and is sandwiched between them.

The intermediate transfer medium 23 has an inner diameter of 55 m, for example.
m, a polyimide endless tube having a thickness of 120 μm and a length of 240 mm. By dispersing conductive carbon in the material, a conductivity in the range of 1 Ωcm to 10 ¹⁴ Ωcm, more preferably 10 ⁴ Ωcm to ^{10 10} Ωc
m (for example, 10 ⁸ Ωcm). A transfer voltage in the range of 500 V to 2500 V, more preferably in the range of 800 V to 1800 V, is applied to the intermediate transfer medium 23 by the bias power supply 27, and a transfer electric field is formed between the intermediate transfer medium 23 and the latent image holding member 22. ing.

A backup roller 24 having an outer diameter of, for example, 50 mm and a roller length of 240 mm is rotatably supported inside the intermediate transfer medium 23, and is driven in a counterclockwise direction by a driving device (not shown). It is rotated so that the outer peripheral speed is substantially equal to the outer peripheral speed of the latent image holding member 22. The backup roller 24 contacts the inside of the intermediate transfer medium 23 and drives the intermediate transfer medium 23 so that the surface thereof has a high friction coefficient such as urethane rubber.
It is made of silicon rubber, NBR, or a foam thereof.

When the pressure roller 25 is pressed against the backup roller 24 and is rotated clockwise at the same outer peripheral speed as the backup roller 24, the intermediate transfer medium 23 held therebetween is Rotates counterclockwise at almost the same peripheral speed as.

Each member of the transfer device is set as described above,
When the distance between the surface of the backup roller 24 and the surface of the latent image holding member 22 is set to, for example, 3 mm, the intermediate transfer medium 23 swells toward the latent image holding member 22 due to its own elasticity. The portion opposite to the portion sandwiched between the two protrudes toward the latent image holding member 22 and comes into light contact with the surface of the latent image holding member 22 with an extremely small pressure.

With such a configuration, "light elastic contact" required for electric field transfer can be easily realized. In order to obtain more stable contact, a tape-like auxiliary member is stretched by a spring along the peripheral surface of the intermediate transfer medium at portions of both ends of the intermediate transfer medium 23 that are not involved in the image, and It is desirable to stabilize the downward bulge (overhang).

In FIG. 2, the developer 28 on the latent image carrier 22 is efficiently transferred to the intermediate transfer medium 23 by such a setting. According to experiments performed by the inventors, it has been found that the transfer efficiency always exceeds 95%, and usually shows a transfer efficiency of 100% or close thereto.

The material of the intermediate transfer medium 23 is as follows.
In addition to polyimide, resins such as polyester, Teflon, and polypropylene, urethane rubber, silicone rubber, N
An elastomer such as BR or a flexible metal tube such as nickel or stainless steel can be used. In the case of a resin system, the thickness is desirably in the range of 50 to 300 μm, more preferably 70 to 180 μm. If the thickness is too small, the contact with the latent image holding member is unstable, and if the thickness is too large, the flexibility is reduced and the contact pressure with the latent image holding member increases, resulting in poor transfer. The metal tube preferably has a thickness in the range of 30 to 200 μm.

The ratio L1 / L2 of the inner diameter L1 of the intermediate transfer medium 23 and the outer diameter L2 of the backup roller 24 is 1.
01 to 1.30, more preferably 1.03 to 1.30.
It is desirably within the range of 1. If the ratio is excessively small, high processing and assembling accuracy is required. If the ratio is excessively large, driving of the intermediate transfer medium and contact with the latent image holding member become unstable.

The nip width between the intermediate transfer medium 23 and the latent image holder 22 is in the range of 0 mm to 20 mm, more preferably 2 m
It is desirable to set in the range of m to 10 mm. When the contact pressure is extremely low, the liquid developer adhering to the surface of the latent image holding member 22 pushes up the intermediate transfer medium, so that the intermediate transfer medium is effectively in the vicinity of the latent image holding member. However, also in this case, the transfer is reliably performed by electrophoresis using the transfer electric field. Even when there is a minute gap between the intermediate transfer medium and the developer surface, the transfer is performed by the elongation phenomenon of the developer due to the electric field.

On the other hand, in transfer to paper, pressure transfer by high pressure can be realized. For example, as the backup roller 24, a hard rubber having a rubber hardness of 40 to 100 degrees, more preferably 60 to 80 degrees is used, and as the pressing roller 25, a metal roller or a hard roller obtained by applying a fluorine process to the metal roller is used. Then, an extremely high pressure can be applied to the sheet 26 and the developer 28 that comes into contact with the sheet 26.

In the pressure transfer, the higher the applied pressure, the higher the transfer efficiency can be obtained.
The transfer efficiency to paper can always be maintained at a value close to 100%. As a result of the experiment, the contact pressure between the pressure roller 25 and the backup roller 24 was 500 g / cm ^{2 to} 100 g / cm ^2.
00 g / cm ² , more preferably 1500 g / c
It has been found that a range of m ^{2 to} 6000 g / cm ² is desirable.

FIG. 3 shows the layer structure of the intermediate transfer medium. FIG.
(A) has the simplest layer configuration and is composed of only the conductive base 31. In pressure transfer to paper, it is desirable that the intermediate transfer medium has a releasing property to ensure the transfer of the developer. Therefore, as the conductive substrate 31, a fluorine-based resin, a resin whose surface has been subjected to a fluorination treatment, or a silicone-based resin is more preferably used.

The layer structure shown in FIG.
2 is provided with a surface release layer 33 made of a release material such as a fluorine-based or silicone-based material on the surface thereof, and has a structure capable of further improving the release property. If conductivity is imparted to the surface release layer 33, more reliable electric field transfer is realized. Further, if the surface release layer 33 is formed of a porous material, more preferably a porous material having pores extending in the thickness direction, the liquid developer transferred from the latent image holding member is directed to the surface direction of the intermediate transfer medium. To prevent the image from bleeding and causing blur of the image, thereby maintaining a sharper image.

The layer structure shown in FIG. 3 (c) is such that an elastic layer 34 is provided on the lowermost layer, whereby a proper elasticity can be imparted at the time of pressure transfer. In this case, a rigid body can be used as the drive roller 24 in FIG.

In FIG. 2, when a solvent removing device 29 for removing the solvent from the liquid developer transferred from the latent image holding member 22 to the intermediate transfer medium 23 is added, the adhesion of the solvent to the paper 26 can be more reliably performed. Can be reduced. As the solvent removing device 29, a suction device using air, a device using liquid absorbing properties of a porous body such as a sponge, or the like can be applied.

After the transfer to the paper, the intermediate transfer medium 2
An intermediate transfer medium cleaner 30 for removing the developer remaining on the surface of No. 3 may be provided. This cleaner 30
For example, well-known blade cleaning, web cleaning, sponge cleaning, brush cleaning, and the like can be applied. Of course, 100%
If the transfer efficiency can be maintained, this cleaner becomes unnecessary.

FIG. 4 shows an embodiment according to the second invention.
2 shows an enlarged view of the transfer device. The transfer device 41 shown in FIG.
It is composed of an intermediate transfer roller 42 and a pressure roller 47. The intermediate transfer roller 42 includes a roller base 43, an elastic layer 44 provided on the surface thereof, and a conductive layer 45 provided on the outer periphery thereof. In the intermediate transfer roller 42, the conductive layer 45 is lightly in contact with the latent image holding member 46 or is disposed in the vicinity of the latent image holding member 46. The conductive layer 45 has a bias power supply 48.
, And the developer 48 is transferred to the intermediate transfer roller 42 by the electric field.

The function of the intermediate transfer roller 42 is separated so that soft elasticity is exhibited by the elastic layer 44 and surface conductivity is exhibited by the conductive layer 45. There is no need to impart conductivity to the elastic layer 44, and the elastic layer 44 can be made of an extremely flexible soft elastic material such as urethane foam. Accordingly, extremely light elastic contact with the latent image holding member 46 is realized, thereby achieving high transfer efficiency and high image quality by electric field transfer.

The term "elastic contact" refers to a contact under a pressure that does not exceed the elastic limit of the elastic layer. Elastic layer 4
As for 4, the sponge hardness is 2 kg to 100 kg, more preferably 5 to 50 k, as measured by JIS-K-6401.
For example, urethane foam or silicone foam in the range of g, or a foam of rubber such as NBR, urethane rubber, silicone rubber, or EPDM is used. When a solid rubber is used, the rubber hardness is 5 to 40 degrees, more preferably 10 degrees with an A type hardness meter specified in JIS-K-6301.
It is preferable to use a material having an angle of up to 30 degrees. When a liquid developer is used, it is a matter of course that a material that is not easily attacked by a petroleum-based solvent must be used.

The developer 48 attached to the surface of the intermediate transfer roller 42 reaches the pressure contact position of the pressure roller 47 by the rotation of the roller, and is transferred to the paper 50. At this time, since the pressure roller 47 is pressed toward the roller base 43 with a pressure exceeding the elastic limit of the elastic layer 44 of the intermediate transfer roller 42, the pressure can be set to an extremely high pressure, and the developer 48 Can be transferred onto the paper 50 with high transfer efficiency. The appropriate range of the pressure setting at this time is the same as in the first invention.

The amount of deformation of the elastic layer 44 under the pressure of the pressure roller 47 affects the image quality. In particular, when the deformation amount due to the pressure is excessively large, a slight shift occurs in the moving speed of the interposed paper 50 and the latent image holding member 46, and the transfer image may be disturbed. The amount of deformation due to pressure is 5
mm or less, more preferably 0.5 mm to 2.
5 mm.

In order to realize this amount of deformation, the thickness of the elastic layer 44 is preferably in the range of 0.5 mm to 8 mm, more preferably 1 mm to 4 mm. If the thickness is too small, it will be difficult to maintain soft contact with the latent image holding member. Also in this case, the intermediate transfer roller 4
If the surface release layer shown in FIG. 3 is provided on the surface of No. 2, it goes without saying that more reliable pressure transfer is realized.

In order to more clearly show the meaning of the "pressure exceeding the elastic limit", FIG. 5 shows the relationship between the load applied to the elastic body and the amount of deformation. Here, the sponge hardness is 40 kg,
An example of a foam made of urethane foam having a thickness of 2 mm and a solid rubber made of urethane rubber having a rubber hardness of 60 degrees and a thickness of 2 mm will be described.

In the foam, when the load is increased to increase the amount of deformation, when the amount of deformation reaches about 1.8 mm, the load increases rapidly, and a bending point appears on the deformation curve. Therefore, in this case, it can be determined that 1.8 mm is the elastic limit of this sample. On the other hand, in the case of solid rubber, the inclination of the straight line is steep, and no bending point occurs even when the load reaches 200 g / cm ² . Therefore, in this case, the elastic limit has not been reached. Even in solid rubber, if its hardness is low, a bending point occurs with a relatively low load,
It can be applied to the present invention.

FIG. 6 shows an embodiment according to the third invention.
1 shows a transfer device and its periphery. Transfer device 6 shown in FIG.
1 includes an intermediate transfer belt 62, a drive roller 63, a tension roller 64, and a pressure roller 65, which are disposed inside the belt and drive and stretch the belt 62.

The belt 62 has one of the layer configurations shown in FIG. 3 or another layer configuration based on the same concept as above, and a transfer voltage is applied to the conductive layer by a bias power supply 66. ing. The belt 62 is provided with the driving roller 6.
The contact with the latent image holding member 67 at the free side excluding the region in contact with the tension roller 3 and the tension roller 64 makes it possible to achieve extremely light pressure contact.

The developer or toner particles 68 transferred to the belt 62 at the position in contact with the latent image holding member 67 reach the pressure contact position with the pressure roller 65 by the traveling of the belt 62, where the paper 69 Is pressure-transferred. By heating any or all of the belt 62, the driving roller 63, and the pressure roller 65, the pressure transfer can be more reliably performed, and at the same time, the developer can be fixed on the paper. Of course, a separate heat fixing device may be provided after the transfer.

Since the pressure roller 65 is pressed by the drive roller 63 or the tension roller 64, a sufficient amount of pressure can be applied to the paper 69 and the toner particles 68 interposed therebetween. Thereby, highly efficient transfer can be realized. In this manner, a sufficiently small pressure can be applied in the electric field transfer and a sufficiently large pressure can be applied in the pressure transfer, so that a highly efficient transfer and a high quality transferred image can be obtained.

Also in the transfer device of the electrophotographic apparatus of the present invention, it is desirable to provide a device for removing the solvent from the developer on the belt and a cleaner for cleaning the belt surface after the transfer. Since the belt has a high degree of freedom in arrangement, it can be said that the belt is more advantageous in installing these members.

[0055]

As described above, according to the present invention,
An electrophotographic apparatus capable of stably obtaining high-efficiency transfer and a high-quality transferred image can be obtained by using either a liquid developer or a dry developer. In addition, when a liquid developer is used, the adhesion of the solvent to the paper can be suppressed to a minimum, so that the solvent can be prevented from being discharged outside the machine, and can be used in offices. A high performance wet electrophotographic apparatus can be provided.

Further, since the transfer from the latent image holding member to the intermediate transfer medium is performed by an electric field, and the transfer from the intermediate transfer medium to the paper is performed by pressure, the range of material selection is widened, and a less expensive and longer life electrophotographic apparatus is used. Can be realized. Also, in a so-called IOI (= Imageon Image) overlay development / batch transfer process, a color image superimposed on a latent image holding member can be reliably transferred to a sheet, and a high-quality color image is output. A great effect is achieved, for example.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an electrophotographic apparatus according to one embodiment of the present invention.

FIG. 2 is a sectional view showing a transfer unit of the electrophotographic apparatus according to the first invention.

FIG. 3 is a sectional view showing a layer configuration of an intermediate transfer medium of the electrophotographic apparatus according to the first invention.

FIG. 4 is a cross-sectional view showing a transfer unit of the electrophotographic apparatus according to the second invention.

FIG. 5 is a characteristic diagram of an elastic layer of an intermediate transfer medium of the electrophotographic apparatus according to the second invention.

FIG. 6 is a sectional view showing a transfer unit of the electrophotographic apparatus according to the third invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Latent image holder 2a, 2b, 2c, 2d ... Charger 3a, 3b, 3c, 3d ... Laser exposure 4a, 4b, 4c, 4d ... Developing device 5 ... Transfer device 23 ... Intermediate transfer medium 24 ... Backup roller 25 ... Pressing roller 26 ... Image carrier 28 ... Developer 43 ... Rigid base 44 ... Elastic layer 45 ... Flexible conductive layer 62 ... Conductive belt

Continuing from the front page (72) Inventor Yasushi Manesu 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Inventor Takashi Sasaki 1 Kosuka-Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Address: Inside Toshiba R & D Center (72) Inventor Hirohisa Miyamoto 1st in Komukai Toshiba-cho, Yuki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba R & D Center (72) Inventor: Koichi Tokomi Small, Yuki-ku, Kawasaki-shi, Kanagawa No. 1 Mukotoshiba-cho Toshiba R & D Center F-term (reference) 2H032 AA05 AA14 BA04 BA08 BA09 2H074 EE07

Claims (3)

[Claims] A latent image forming means for forming an electrostatic latent image on a latent image holding member; a developing means for supplying a developer to the electrostatic latent image to visualize the electrostatic latent image; An electrophotographic apparatus having a transfer unit for transferring the image on an image carrier, wherein the transfer unit comprises a rotatable flexible cylinder arranged to be in contact with or close to the latent image holding member. A transfer medium, means for forming an electric field between the intermediate transfer medium and the latent image holding member, and an outer diameter smaller than an inner diameter of the intermediate transfer medium, wherein the intermediate transfer medium faces the latent image holding member. A backup roller disposed in the intermediate transfer medium so as to be in contact with the inner surface of the intermediate transfer medium at a position different from that of the intermediate transfer medium; and a backup roller disposed in contact with the outer surface of the intermediate transfer medium in a contact portion with the backup roller. Pressure roller, and this Means for supplying an image carrier between a pressure roller and the intermediate transfer medium, wherein the pressure roller is pressed by a backup roller via the intermediate transfer medium, and the backup roller is The intermediate transfer medium does not contact the intermediate transfer medium at a portion, whereby the intermediate transfer medium does not come into strong contact with the latent image holding member, and the transfer of the visible image of the intermediate transfer medium from the latent image holding member to the intermediate transfer medium does not occur. An electrophotographic apparatus characterized by being performed. 2. A latent image forming means for forming an electrostatic latent image on a latent image holding member, a developing means for supplying a developer to the electrostatic latent image to visualize the electrostatic latent image; An electrophotographic apparatus having a transfer unit that transfers the image onto an image carrier, wherein the transfer unit is disposed opposite to the latent image holding member so as to be in contact with or close to the latent image holding member; and Means for forming an electric field between the latent image holding member, a pressing member pressed against the intermediate transfer medium, and means for supplying an image carrier between the pressing member and the intermediate transfer medium, The intermediate transfer medium includes a rigid substrate, an elastic layer formed on the surface of the rigid substrate, and a flexible conductive layer formed on the surface of the elastic layer. Means for pressing the intermediate transfer medium with a pressure exceeding the elastic limit of the elastic layer, Electrophotographic apparatus, characterized in that the intermediate transfer medium and means for supporting such that the resilient contact or close proximity to the latent image holding member. 3. A latent image forming means for forming an electrostatic latent image on a latent image holding member; a developing means for supplying a liquid developer to the electrostatic latent image to visualize the electrostatic latent image; Transfer means for transferring an image onto an image carrier, wherein the transfer means is opposed to the latent image holding member so as to be in contact with or close to the latent image holding member; Means for forming an electric field between a medium and the latent image holding member,
A pressure member pressed against the intermediate transfer medium, and a unit for supplying an image carrier between the pressure member and the intermediate transfer medium, wherein the intermediate transfer medium includes a conductive belt, Means for suspending and driving a belt, means for lightly contacting the flexible portion of the belt with the latent image holding member, and pressing the pressing means against the belt, An electrophotographic apparatus comprising: means for transferring and fixing a developer.