JPH08123206A - Liquid developing device - Google Patents

Abstract

PURPOSE: To provide a liquid developing device capable of completely removing liquid remaining on a photoreceptor without exerting any adverse influence on an obtained image and having simple structure. CONSTITUTION: This liquid developing device is provided with a cylindrical developing roller having a high electric resistor whose electric resistance is >=10<7> Ω.cm in volume resistance on its surface and having a conductive material whose electric resistance is <=1/100 of the high electric resistor inside. The cylindrical developing roller is constituted of a roller obtained by coating the periphery of a center roller with porous elastic body, and the high electric resistor existing on the surface of the roller is an electrostatically flocked fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid developing device for electrophotography.

[0002]

2. Description of the Related Art Xerographic electrophotographic copying methods are widely used as general copying methods.
In this copying method, the electrostatic latent image formed on the photoconductor is visualized with toner, transferred to a copy sheet, and then fixed if necessary to obtain a desired copy. There are dry and wet methods. Among them, there are a liquid spray developing method and a liquid developing method in a wet developing method using a liquid developer, and the former is formed by atomizing an ink or a dye solution to charge it.
This is a method of developing by spraying this onto a photoreceptor. The latter is
This is a method in which a toner suspended in a petroleum-based liquid (carrier liquid) is attached to an electrostatic latent image on a photoconductor by electrophoresis, which is a general method as a wet method.

When the toner particles are attached to the electrostatic latent image by the liquid developing method, it is necessary to allow a conductive substance (developing electrode) to exist near the surface of the photosensitive member in order to faithfully reproduce the original image. In addition, it is desirable that the amount of liquid remaining on the surface of the photoreceptor immediately before transfer be small. This is because when a large amount of liquid is used, a large amount of liquid is transferred to the copy paper, and therefore the amount of energy for drying is large, and the gas generated from the liquid (petroleum-based hydrocarbon gas) makes the operator uncomfortable, This is because it may adversely affect safety and the environment. In order to satisfy the above requirements, liquid development is carried out by various methods. A method using two or more developing rollers or a reverse roller near the photoconductor removes residual liquid on the surface of the photoconductor in a non-contact manner. The method to do is realized. In addition, the developing roller used for liquid development has a conductive substance inside so as to form the above-mentioned developing electrode, but the developing roller surface that contacts the surface of the photoreceptor may be an insulator. Yes, and if the surface is conductive, the electrostatic latent image is compromised.

By the way, when the residual liquid on the surface of the photoreceptor is removed by the developing roller, an elastic roller having a foam layer having open cells on the surface is used as the developing roller so that the residual liquid is well absorbed by the roller. preferable. However, this elastic roller has a problem that air bubbles are crushed at the time of pressure contact with the photoconductor and the quality of the copy is deteriorated. The above-mentioned conductive substance (developing electrode) is effective in preventing fogging and eliminating edge effects, and it is preferable to allow it to exist in the vicinity of the photoreceptor. Therefore, attempts have been made to add conductive powder such as carbon powder to the foam portion of the elastic roller having the foam, or to cover the foam portion with a wire mesh. However, in the former case, there are problems such as deterioration in flexibility and mechanical strength of the foamed portion, and in the latter case, the wire mesh often disturbs the electrostatic latent image. Note that the edge effect is an effect in which an edge portion of an image obtained from an electrostatic latent image is darker than others, and this effect occurs because a large amount of toner adheres to a place where the voltage contrast is strong. This can be prevented by the presence of a conductive substance near the photoconductor.

In order to solve the above problems, Japanese Patent Publication No.
JP-A-8-30581 discloses an electrophotographic liquid developing device in which at least a surface of the peripheral surface that can come into contact with other members is made of an insulating material, and most of the outer peripheral portion has an electrode effect. A rotating member has been proposed. However, this member uses a wire net that is substantially covered with an insulating film as an insulating material, and prevents the image forming toner from being scraped by the projections of the wire net and that a wire net trace is formed on a copy. It is extremely difficult to prevent. Tokiko Sho 58-
No. 30578, an elastic roller provided with an elastic material layer and a surface layer which is not deformed in a surface in contact with the photosensitive drum even when the elastic material layer is deformed, and a photosensitive drum surface using the elastic roller The liquid removal method has been proposed.
However, also in this case, there is the same problem as when the rotating member for electrophotographic liquid development described in Japanese Patent Publication No. 58-30581 is used.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems encountered in liquid development of electrophotography, and sufficiently removes the liquid remaining on the photoreceptor without adversely affecting the obtained image. It is an object of the present invention to provide a liquid developing apparatus which can be removed without any problem, and which is capable of both developing with a single developing roller and removing liquid remaining on a photoconductor.

[0007]

The present inventors have completed the present invention as a result of intensive research to solve the above problems. That is, according to the present invention, the volume resistivity is 10 ⁷ Ω · cm or more, and the thickness is 5 to 200.
A liquid developing apparatus comprising a cylindrical developing roller having a uniform high electric resistance of μm on the surface thereof and having a conductive material whose electric resistance is 1/100 or less of that of the high electric resistance inside. Will be provided. Further, according to the present invention, the developing roller is composed of a roller in which a central roller is covered with a porous elastic body, and the high electric resistance existing on the surface of the roller is a fiber to which electrostatic flocking is applied. The above liquid developing apparatus is provided.

The inventors of the present invention have a simpler structure than a developing device using a plurality of developing rollers if there is no problem even if both developing and residual liquid removal are performed with one developing roller.
The apparatus using one developing roller was considered to be advantageous, and a detailed investigation was attempted on a copying apparatus described in Japanese Patent Publication No. 58-30581 which has one developing roller. This device is a device whose outline is described in FIG. 1, and the detailed structure of the contact portion between the photosensitive drum and the developing roller is the device described in FIG. In the figure, 1 is a photosensitive drum, 2 is a latent image forming means section, 3 is a developing unit section, 4 is a transfer means section, 5 is a cleaning section, 6 is a rotary shaft of the photosensitive drum, 7 is a developing solution tank, 8 Is a developing roller, 9 is a squeezing roller, 10 is a central roller of the developing roller, 11 is an elastic foamed body, 12 is a wire mesh partially coated with insulating paint, 12A is an insulating material,
12B represents a metal, and 13 represents a developing solution.

In the apparatus shown in FIG. 1, an elastic foam body 11 made of polyurethane foam is provided around a central roller 10, and the outer side of the elastic foam body 11 is covered with a wire net 12, and then the photosensitive drum 1 of the wire net.
A developing roller coated with an insulating paint is provided on a portion contacting with. In addition, since the apparatus is provided with the wire mesh 23, fogging and edge effects are prevented. In copying using the apparatus shown in FIG. 1, the photosensitive drum 1 rotates about the rotary shaft 6 in the direction of the arrow. Then, toner is attached to the electrostatic latent image formed on the photosensitive drum 1 by the latent image forming unit 2 in the developing unit 3 to make it visible, and this visible image (toner image) is transferred to the transfer unit. After being transferred to the copy paper at 4, the cleaning unit 5 removes the unnecessary electrostatic latent image and the unnecessary developing solution on the photosensitive drum, and the photosensitive drum 1 is initialized.

The developing section 3 is provided with a developer tank 7, a developing roller 8 and a diaphragm roller 9, and the developing roller 8
The elastic foam 11 can easily contain a developing solution. Further, the developing roller 8 is so moved that the contact portion between the developing roller 8 and the photosensitive drum 1 is entrained and moves in the same direction at a constant speed.
Is provided with a drive unit (not shown). The developing roller 8 and the squeezing roller 9 are arranged in the developing solution 13 so as to be able to come into pressure contact with each other, and the developing solution contained in the elastic foam 11 is exchanged by the pressure contact between the two. Development (formation of a toner image) is performed with the developer supplied to the surface of the photoconductor drum 2 by the developing roller 8, and the residual liquid after development is removed by the elastic foam 11 of the developing roller 8. That is, in the developing roller 8 pressed against the photosensitive drum 1 at the portion B shown in FIG. 1, the developer contained in the elastic foam 11 is squeezed and supplied to the portion A of FIG. As a result, the electrostatic latent image is developed with a fresh developer, and at the portion C where the developing roller is released from the pressure contact, the liquid on the photosensitive drum is sufficiently absorbed, and the amount of liquid around the toner image is reduced. be able to.

According to the detailed examination results by the present inventors, the following problems were recognized in the liquid developing apparatus disclosed in the above patent. The present invention provides a liquid developing device that solves these problems. Since there is an insulated wire mesh on the surface of the developing roller, when the liquid on the surface of the photoconductor drum is absorbed and removed, the toner is scraped off from the surface of the photoconductor drum on which the toner image is formed. By being transferred to the surface of the photoconductor drum via the toner, a mesh-like toner image is formed on the surface of the photoconductor drum. The high electric resistance on the surface of the developing roller is essentially only the insulating paint on the surface of the wire mesh, and the counter electrode necessary for forming the developing electric field is the wire mesh on the surface of the developing roller. It is difficult to form a suitable developing electric field because the gap between the counter electrode and the counter electrode is too narrow, and therefore it is not possible to give a sufficient image density gradation to the copied image.

The developing roller used in the liquid developing apparatus of the present invention has a surface made of a material having a volume resistance of 10 ⁷ Ω · cm or more and high electrical resistance and elasticity, and the inside thereof is 1/100 of the electric resistance of the surface. It is a cylindrical roller formed of a material having the following electric resistance. The surface portion having high electrical resistance has a thickness of 5 to 200 μm, preferably 10 to 50 μm.
It is desirable to set m. Further, it is desirable that a porous elastic body having a thickness of 2 to 30 mm, preferably 5 to 20 mm is present between the central roller and the high electric resistance surface. In this liquid developing device, since the degree of adhesion between the photoconductor and the developing roller is high, it is possible to sufficiently remove the residual liquid on the surface of the photoconductor even if the developing roller does not have continuous bubbles, and remains on the surface of the photoconductor after development. The liquid amount can be 0.2 mg / cm ² or less. Incidentally, in the device of FIG. 1, the liquid amount is about 1.7 mg / cm ² .

In the liquid developing apparatus of the present invention, the surface of the developing roller and the surface of the photoreceptor are exposed to light at a pressure of 0.01 to 1.0 kg / cm ² , preferably 0.05 to 0.2 kg / cm ^2. Since the residual liquid on the surface of the body is removed, the surface of the developing roller is preferably formed of a material that does not mechanically damage the toner image during pressure contact. As a material having both this property and high electric resistance, natural and synthetic polymers can be mentioned.
The latter is particularly preferable. Specifically, acrylic-based, nylon-based, polyester-based synthetic fibers or synthetic resins, or polynosic fibers (trade name of high-polymer strength staple fibers) are preferable. Of these, nylon 66 fiber and resin and polynosic fiber are particularly preferable. Further, it is preferable that these synthetic resins are present on the surface of the developing roller in the form of fine particles having a roundness such as spheres or in the form of fibers, and in particular, they are present in the form of fibers that have been flocked by electrostatic flocking. The reason why the transplanted fibrous material is preferable is
This is because the developer is easy to supply and remove due to the high flexibility and the capillary phenomenon. Therefore, the fiber has a thickness of 5
It is preferably denier or less, preferably 3 denier or less, and is flexible and has a good affinity with the developer. In addition,
If the fibers are too thick or too hard, the toner image may be damaged.

As described above, it is preferable that a porous elastic body be present between the central roller and the surface. This porous elastic body has an electric resistance of 1/100 or less of that of the surface and has an open surface. It is preferably a porous body having open pores. The presence of such continuous bubbles is advantageous in supplying the developing solution to the photoconductor and removing the residual solution from the surface of the photoconductor, as in the developing roller shown in FIG. Further, this portion is preferably formed of a material having an affinity for the developing solution and having resistance to dissolution and swelling in the developing solution. In the developing roller of the present invention, the central roller serves as the developing electrode when the porous elastic body is absent, while the elastic body serves as the developing electrode when the porous elastic body exists. Therefore, it is desirable that the electric resistance of the porous elastic body is 0 to 10 ⁵ Ω · cm, preferably 0 to 10 ³ Ω · cm. Therefore, conductive fine powder such as carbon powder is dispersed in the porous elastic body. Alternatively, it is desirable to use a conductive polymer or a mixture containing a conductive polymer as the material forming the porous elastic body. Specific examples of the porous elastic body used here are foams such as polyurethane and silicone resin.

[0015]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

Example 1 Three carbon steel developing rollers were removed from the developing section of a wet electrophotographic copying machine CT-5085 manufactured by Ricoh Co., Ltd., and the uppermost one of these rollers was manufactured by Soken Kagaku Co., Ltd. Acrylic particles are evenly adhered, and the thickness of the surface layer is 100 μm.
And An acrylic adhesive (manufactured by Soken Chemical Industry Co., Ltd .; trade name SK Dyne) is used for adhesion, and the thickness of the adhesive layer is approximately 50 μm.
m. The electric resistance of the acrylic particles is 10 ¹²
Ω · cm, and the electric resistance of the carbon steel roller was almost zero. One of the developing rollers processed as described above was returned to the original place of the copying machine. At this time, except for the bearings provided at both ends of the roller, the roller surface was brought into direct contact with the photoconductor. Further, the supply path of the developing solution is changed corresponding to the changing of the developing section so that the number of developing rollers is one, and the residual solution discharging path on the surface of the photoconductor is arranged so that both ends of the developing roller are in contact with the photoconductor. Was set up. When copying was performed using the modified copying machine described above in the same manner as before the modification, a good quality copy was obtained although the image density was slightly lower than that before the modification. Further, at the time of copying, there was about 0.2 mg / cm ² of residual liquid on the photoconductor, and the residual liquid amount could be greatly reduced from about 0.3 mg / cm ² before the modification.

Example 2 A conductive polyurethane foam having open cells around the same carbon steel roller as that processed in Example 1 (manufactured by Toyo Polymer Co., Ltd .; trade name: Rubycell; electric resistance value: 10)
⁴ Ω · cm) was provided to have a thickness of 10 mm, and a surface layer having a thickness of 100 μm, which was the same as in Example 1, was provided thereon. However, a foaming polyurethane adhesive (double face made by Toyo Ink Inc. with a carbon dioxide-based foaming agent added and mixed) was used to bond the acrylic fine particles in the surface layer and the polyurethane foam, and the underlying foam layer A liquid permeability was provided between the surface and the surface. The thickness of the adhesive layer was about 50 μm as in the case of Example 1. Except for the above, when copying was carried out by the same method as in Example 1, a good copied image was obtained with the same image density as in Example 1, and the residual liquid amount on the photoconductor was further than in Example 1. The small amount was about 0.1 mg / cm ² .

Example 3 Polynosic fibers (manufactured by Toyobo Co., Ltd .; electric resistance value: 10 ¹⁰ Ω · cm) were electrostatically flocked on the elastic roller coated with the conductive polyurethane foam used in Example 2. The formed roller was used as a developing roller. The electrostatic flocking was performed by a known method before foaming the polyurethane, and the polynosic fiber used had a length of 3 mm and a thickness of 5 denier. Except for the above, when copying was carried out by the same method as in Example 1, a high quality copied image having a higher density and a smoother overall impression than in Examples 1 and 2 was obtained. The copied image has the same image density and higher image quality as the copied image obtained by the copying machine before modification. The residual liquid amount on the photoconductor was 0.1 mg / cm ² or less.

Example 4 The thickness of the polynosic fiber used for flocking was 3 denier. Other than that, when copying was carried out in the same manner as in Example 3, a copy image of higher quality than that in Example 3 was obtained. Was given. That is, a copy image having the same image density and overall impression as that of the copy image of Example 3 and superior to the copy image of Example 3 in fine line reproducibility and sharpness was obtained. The amount of residual liquid on the photoconductor was 0.1 mg / cm ² .

Example 5 Instead of polynosic fibers, the electrical resistance was 2.5 × 10 ⁷ Ω.
・ Cm silicon carbide fiber (Tyranno fiber manufactured by Ube Industries, Ltd.)
The same high quality copied image as in Example 3 was obtained when copying was performed in the same manner as in Example 3 except for the above. The residual liquid amount on the photoconductor is about 0.1 mg / cm.
^{Was 2} .

Comparative Example 1 Instead of the polynosic fiber, the electric resistance value was about 10 ³ Ω · c.
m carbon fiber (manufactured by Mitsubishi Kasei Co., Ltd.) was used, and copying was carried out in the same manner as in Example 3 except for that, and when the fiber thickness was 5 denier (compared with Example 3), it was 3 denier. Also in the case (comparison with Example 4), the obtained copied image was seriously "blurred" or "scraped", and small characters could not be read.

Comparative Example 2 A copy was made in exactly the same manner as in Example 3 except that the amount of carbon contained in the conductive polyurethane foam rubicel was reduced and its electrical resistance was changed to 10 ⁹ Ω · cm.
The density of the obtained copy image was low, and the background portion was contaminated with toner. In addition, since the sharpness and resolution of the image are poor, it is difficult to read the characters.

[0023]

According to the liquid developing apparatus of the first aspect of the present invention, the residual liquid amount on the surface of the photoconductor can be made smaller than that of the conventional liquid developing apparatus, and the liquid developing apparatus has a simple structure for giving a high quality image. . Therefore, using this liquid developing device can reduce the amount of energy required to dry the paper on which the transferred image is formed, and also cause operator discomfort and adversely affect safety and environment. Less to do. In addition, high quality images can be provided at a low price. In the liquid developing device according to the second aspect, since the developing roller is provided with the porous elastic body having the open cells, the amount of residual liquid on the photoconductor can be further reduced and the image density can be increased. It is a liquid developing device. Claims 3 and 4
The liquid developing device of (1) is a liquid developing device capable of further improving the image quality because the surface of the developing roller is provided with fibers that have been flocked.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an outline of a conventional wet electronic copying machine using a liquid developing device.

FIG. 2 is a diagram illustrating a detailed structure of a contact portion between a photosensitive drum and a developing roller of a conventional liquid developing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Latent image forming means section 3 Developing device section 4 Transfer means section 5 Cleaning section 6 Rotating shaft of photoconductor drum 7 Developer tank 8 Developing roller 9 Squeezing roller 10 Central roller of developing roller 11 Elastic foam 12 Wire mesh 12A Insulating material 12B Metal 13 Developer

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Kazuyo Mizuno 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Akihiko Goto 1-3-6 Nakamagome, Ota-ku, Tokyo In stock company Ricoh (72) Inventor Masahide Yamashita 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Yoshitaka Kinoshita 1-3-6 Nakamagome, Tokyo Ota-ku In Ricoh Company

Claims (4)

[Claims] 1. A volume resistivity of 10 ⁷ Ωcm or more, a uniform high electrical resistance having a thickness of 5 to 200 μm is provided on the surface, and the electrical resistance is 1/10 of the high electrical resistance.
A liquid developing device comprising a cylindrical developing roller having a conductive material of 0 or less inside. 2. The liquid developing apparatus according to claim 1, wherein the developing roller is a roller having a central roller covered with a porous elastic body. 3. The liquid developing apparatus according to claim 1, wherein the high electric resistance body existing on the surface of the developing roller is a fiber having electrostatic flocking. 4. The liquid developing apparatus according to claim 3, wherein the fiber has a thickness of 5 denier or less.