JP2000056576A - Wet type electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve development with high picture quality without fogging or edge distortion, when adopting constitution that uses a high-viscosity liquid toner showing nonvolatility, by enhancing the cohesion of a developing toner layer applied on a photoconductor. SOLUTION: The photoconductor 10 of a wet type electrophotographic device is charged by a charging device and then exposed by an exposure device to form an electrostatic latent image. A developing roller 22 causes the toner particles of a liquid developing solution to cling to the photoconductor 10 according to an electric field formed between the developing roller 22 and the photoconductor 10. The developing solution is supplied to the developing roller 22 as it is drawn by a plurality of continuous rotating rollers. The final-stage rotating roller 23 of a developing solution application means has conductivity at least on its surface and a bias voltage is supplied to the final-stage rotating roller 23. The toner particles of the liquid developing solution applied to the surface of the final-stage rotating roller 23 are made to cohere according to the electric field generated between the rollers 22, 23 by the bias voltage and are made to migrate toward the developing roller 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet type electrophotographic apparatus using a non-volatile, high-viscosity liquid toner, and more particularly to a wet type electrophotographic apparatus capable of developing high-quality images without fogging.

[0002]

2. Description of the Related Art In an electrophotographic apparatus in which an electrostatic latent image is formed on a photosensitive member (photosensitive drum), toner is adhered to the image, and the image is transferred to paper and fixed, a dry type using powder toner is widely used. Used.

However, the powder toner has a problem that the toner is scattered, and the toner particles have a particle size of 7 to 10 μm.
There is a problem that the resolution is poor due to the large value of m.

Therefore, when high resolution is required, a wet type using a liquid toner is used. Liquid toner has toner particles as small as about 1 μm,
Due to the large charge amount, disturbance of the toner image hardly occurs,
This is because high resolution can be realized.

In a conventional wet-type electrophotographic apparatus, a low-viscosity liquid toner in which a toner is mixed with an organic solvent at a ratio of 1 to 2% is used as a developing solution. However, such a developer uses an organic solvent that is harmful to the human body, and has a large problem of causing environmental problems since a large amount of the developer is used due to a low toner concentration.

[0006] Against this background, a wet type using a high-viscosity, high-concentration developer constituted by dispersing a high-concentration toner in silicone oil or the like is described in International Publication No. WO95 / 08792. An invention of an electrophotographic apparatus has been disclosed.

The use of this liquid toner has the advantages that the problem of harm to the human body does not occur, and that the high toner concentration eliminates the need to use a large amount of developer.

[0008] As disclosed in International Publication No. WO95 / 08792, even when such a high-viscosity, high-concentration liquid toner developing solution is used, conventionally, the same concept as when a powder toner is used is used. A configuration in which a developing solution is applied to a developing roller or a developing belt according to the above, and the developing roller or the like is brought into contact with the photoreceptor, whereby toner is adhered to the photoreceptor on which the electrostatic latent image is formed. Has been adopted. In addition, "International publication number WO95 / 08792"
Uses a developing belt.

That is, when applying the powder toner to the developing roller, a configuration is adopted in which the powder toner is applied to the developing roller by using a purely mechanical contact method. Therefore, even when such a high-viscosity, high-concentration liquid toner showing non-volatility is used, a configuration is adopted in which a developing solution is applied to a developing roller or the like using a purely mechanical contact method. The surface that mechanically contacts the developing roller or the like is configured to have a high surface accuracy so that a developing solution is applied to the developing roller or the like.

[0010]

When a non-volatile, high-viscosity, high-concentration liquid toner is used, the high-viscosity toner is prevented from adhering to the non-exposed portion of the electrostatic latent image formed on the photosensitive member. Before applying the liquid toner,
A pre-wet process of applying a pre-wet liquid such as silicon oil to the photoconductor is performed.

However, according to such a conventional technique, the toner adheres to the non-exposed portion of the electrostatic latent image on the photosensitive member to which the toner does not adhere even when the pre-wet process is performed. However, there is a problem that image noise occurs.

To explain this problem more specifically, the liquid toner is transported while thinly extending from the toner reservoir using an applicator roller to form a toner layer on the developing roller, and the toner layer contacts the photosensitive member. Consider a developing device in which the charged toner adheres to the exposed portion of the photoconductor in accordance with the electric field between them. At this time, in the nip portion between the developing roller and the applicator roller, the toner layer receives the compression pressure from both rollers, but when it comes to the nip outlet, the compression pressure is released. By receiving a tensile force due to its own viscosity and the adhesive force to the roller surface, it is separated so that it can be broken off at both sides, and at that time the toner around the periphery is involved,
As shown in FIG. 6, in a state where the toner particles are dispersed in the carrier liquid, fine stripe-shaped unevenness (irregularity) remains on the developing roller.

For example, the content of toner particles is 20% wt,
Developing with a liquid toner having a viscosity of 600 mPa.S, and observing the edges of the dots or fine lines, it was found that the edges were disordered. This is because the toner tends to flow because the cohesive force of the developed toner layer on the photoreceptor is low. This is because separation is not clearly performed. On the other hand, when the content of the toner particles is set to 10% and the same toner layer thickness is formed on the developing roller and developed, the edge portion of the dot or the thin line becomes very sharp due to the good movement characteristics. However, the image density is reduced due to an insufficient amount of toner particles. Further, when the toner layer thickness is increased by the decrease in density, fogging or edge disturbance is likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to a configuration using a non-volatile, high-viscosity liquid toner. It is an object of the present invention to provide a new wet-type electrophotographic apparatus which enables high-quality development without fogging or edge disturbance.

Further, the present invention makes it possible to use a liquid toner having a relatively low toner concentration without increasing the cohesive force of the developed toner layer so that the amount of toner particles is not insufficient and the image density is not reduced. It is intended to be.

[0016]

The photosensitive member 10 is charged by a charging device 11 and then exposed by an exposure device 12 to form an electrostatic latent image. Pre-wet device 13
Applies a prewetting liquid to the surface of the photoreceptor 10.

The developing device 14 is provided in association with yellow / magenta / cyan / black and uses a non-volatile, high-viscosity liquid toner as a liquid developer. The developing roller (developing solution support) 22 contacts the photoreceptor 10 to supply the liquid developer so as to maintain a two-layer structure with the pre-wet liquid film on the photoreceptor 10, and The developing solution is supplied to the developing roller 22 which causes the toner particles of the liquid developing solution to adhere to the photoreceptor 10 in accordance with the electric field generated between the developing device and the developing solution applying means. As a result, a toner layer is formed on the developing roller 22. The developing solution applying means is constituted by a plurality of rotating rollers connected to each other, and is configured to carry the supplied liquid developing solution while applying the liquid developing solution to the surface while being stretched by the rotating rollers. The final-stage rotating roller 23 of the developer application means has at least a surface having conductivity, and a bias voltage is supplied to the final-stage rotating roller 23, and the final-stage rotating roller 23 is generated between the final-stage rotating roller 23 and the developing roller 22 by the bias voltage. According to the applied electric field, the toner particles of the liquid developer applied to the surface of the final-stage rotating roller 23 are aggregated and moved to the developing roller 22 side.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail according to embodiments. In the present invention, a non-volatile high-viscosity liquid toner is used as a liquid developer, and the liquid toner is obtained by dispersing solid particles such as a pigment in a liquid carrier (oil).

FIG. 1 shows the overall configuration of a wet electrophotographic apparatus provided with the present invention.

As shown in FIG. 1, a wet electrophotographic apparatus according to the present invention comprises a photosensitive member 10, a charging device 11, and an exposure device 1.
2, a pre-wetting device 13, a developing device 14, an intermediate transfer member 15, a blade 16, a charge removing device 17, a heating device 18, and a pressure roller 19.

The charging device 11 applies a voltage of about 700 V
To be charged. The exposure device 12 forms an electrostatic latent image on the photoconductor 10 by exposing the photoconductor 10 using a laser beam having a wavelength of 780 nm so that the potential of the exposed portion becomes about 100 V.

The pre-wetting device 13 is 2.5 to 20 cS
Silicon oil having a viscosity of about t is applied to the surface of the photoconductor 10 in a thickness of 4 to 10 μm. Here, the pre-wet apparatus 13 may execute the pre-wet processing before the exposure processing performed by the exposure apparatus 12, or may execute the pre-wet processing after the exposure processing.

The developing device 14 is provided in correspondence with yellow / magenta / cyan / black and has a voltage of about 400 V to 6 V.
As described later with reference to FIG. 2, a liquid toner having a toner viscosity of 400 to 4000 mPa · S and a carrier viscosity of 20 cSt is applied to the liquid toner by using applicator rollers 23 to 25 connected thereto. Is transported while being thinly spread to form a toner layer having a thickness of 2 to 3 μm on the developing roller (developing solution support) 22.
By supplying the positively charged toner to the photoconductor 10 according to the electric field between the photoconductor 10 and the toner, the toner adheres to the exposed portion of the photoconductor 10 charged to about 100V.

According to the pre-wet layer applied by the pre-wet device 13, it is possible to prevent the toner from adhering to the non-exposed portion of the photoreceptor 10, as shown in FIG.

The intermediate transfer member 15 is biased to about -800 V, and the photosensitive member 1 is moved according to an electric field between the intermediate member 15 and the photosensitive member 10.
The toner attached to 0 is transferred. This intermediate transfer member 15
First, yellow toner adhered to the photoconductor 10 is transferred, then magenta toner adhered to the photoconductor 10 is transferred, and then cyan toner adhered to the photoconductor 10 is transferred. Then, the black toner attached to the photoconductor 10 is transferred.

The blade 16 removes toner and pre-wet liquid remaining on the photoreceptor 10. The neutralization device 17 neutralizes the photoconductor 10.

The heating device 18 melts the toner attached to the intermediate transfer member 15 by heating the surface of the intermediate transfer member 15. The pressure roller 19 fixes the toner of the intermediate transfer body 15 melted by the heating device 18 on the print medium.
Thus, using the heating device 18 and the pressure roller 19,
Since a configuration is adopted in which the toner adhered to the intermediate transfer body 15 is melted and fixed on the print medium without heating the print medium, print media other than paper can be handled.

FIG. 2 shows a developing roller 22 in contact with the photoreceptor (drum) 10 and a series of applicator rollers 23 to 25 for supplying a developing solution thereto. The applicator roller includes an applicator final-stage roller 23 in contact with the developing roller 22, and one or more other rollers. The number of applicator rollers is roller 23,
Although three rollers 24 and 25 are illustrated, the developing roller 22 is generally provided with an appropriate number of rollers necessary for thin and uniform spreading of the developer. The roller 22 contacts the photoreceptor 10 to supply the liquid developer so as to maintain a two-layer structure with the film of the pre-wet liquid on the photoreceptor 10, and according to the electric field between the photoreceptor 10, This is a developing roller that causes positively charged toner particles of the liquid developer to adhere to the photoconductor 10. The roller 23 is the last roller of the developer transport applicator roller. Most of the developer toner particles can be moved toward the developing roller 22 by the bias potential between the developing roller 22 and the final roller 23 of the applicator. it can.

Further, any remaining toner on the developing roller 22 and any pre-wet adhering to the developing roller 22 are removed, and the liquid toner newly supplied onto the developing roller 22 is always supplied with the developing roller 22 in a clean state. For this purpose, a blade 26 can be provided on the developing roller 22 so as to impinge on the rotating direction of the developing roller 22 and the counter direction after passing the developing point. Alternatively, a roller 27 for scraping residual toner accumulated in the contact portion between the blade 26 and the developing roller 22 can be additionally provided.

In the case where normal development is performed using a liquid toner without applying a bias potential to the applicator final-stage roller 23, the toner tends to flow because the cohesive force of the developed toner layer on the photoreceptor 10 is low. As described above, when the toner layer is dispersed at a high concentration on the developing roller 22, there are various problems such as the toner layer not being clearly separated at the edges of the image portion and the non-image portion.

This problem is caused by the applicator roller pair 23 to
The problem can be solved by applying a bias to the final stage roller 23 that is in contact with the developing roller 22 when the toner layer is formed on the developing roller 22 by the use of the roller 25. The applicator bias Vb is set to be higher by 150 to 300 V than the developing roller bias Va. As a result, in the case of positively charged toner particles, the toner particles move from the applicator final stage roller 23 to the developing roller 22,
An agglomerated uniform toner layer is formed on the developing roller 22.

FIG. 3 is a diagram for explaining the operation of moving the developer toner particles to the developing roller side by the potential difference, and shows details of the portion A indicated by a dotted circle in FIG. A bias voltage (Vb-Va) is applied between the developing roller 22 and the applicator final-stage roller 23 to apply an electric field to the nip portion of both rollers, thereby holding toner particles (solid particles) on the developing roller side. It is possible to increase the force and suction force. Thereby, the separation of the toner at the edges of the image portion and the non-image portion becomes clear, and the sharpness of the edge portion is improved.
Further, the applicator final stage roller 23 and the developing roller 22
By positively moving the toner particles between them by the bias force, the content of the toner particles increases on the developing roller side, and a sufficient image density can be obtained even when 10% wt toner is used. Observation of the toner state of the developing roller 22 and the applicator final stage roller 23 revealed that almost all of the toner particles had moved to the developing roller 22 side, and the toner content on the developing roller 22 was 2% of the initial content. A doubling was observed. After both rollers contacted, only the carrier oil component was present on the final applicator roller 23, and the carrier oil was coated on the agglomerated toner layer 28 on the developing roller 22. . Therefore, the actual toner layer thickness is equal or thin. Further, the toner layer 2
As a result, the carrier oil covering the upper portion of the No. 8 also functions as a pre-wet, resulting in an increase in margin for fogging. As a result, the hardness of the developing roller 22 can be increased, and the contact accuracy of the roller can be improved. Also, the pre-wet thickness can be reduced,
Pre-wet consumption can be suppressed. Further, when a liquid toner having a toner content of 10% by weight or less is used, the thickness of the carrier layer covering the toner layer is sufficiently large, and pre-wetless operation can be achieved.

The application of such a bias potential can be achieved by using a roller having at least a surface portion made of a conductive material as the last roller 23 of the applicator. The resistance value of the developing roller needs to be 10 ⁶ Ω or less, preferably 10 ⁴ Ω or less from the image density. When the resistance value of the applicator roller was changed and measured, when the current value flowing between the developing roller and the applicator roller was about several tens μA, the toner did not sufficiently move to the developing roller. On the other hand, when the current value was set to 100 μA or more, the movement of the toner occurred sufficiently, and a desired toner layer could be formed. Therefore, the resistance value of the applicator roller is set to 10 ⁵ to 10 ⁷
Ω or less. If the resistance value of the developing roller is higher than the resistance value of the applicator roller, the developing bias rises due to the applicator bias and fogging occurs, so that the resistance value of the developing roller needs to be low.

From the necessity of maintaining the image density, the toner layer thickness on the developing roller is 5 to 10 μm at a toner concentration of 20% wt.
m is formed. For this reason, when an applicator bias is applied using a roller having a surface roughness Rz of 10 μm or more (urethane roller having a hardness of JIS-A30 ゜, a resistance value of about 10-6 Ω) as the last roller 23 of the applicator, The toner layer on the developing roller had spot-like unevenness traced to the roller roughness. When a roller having a relatively smooth surface roughness (urethane roller having a hardness of JIS-A90 ° or more) was used as the final stage roller, the spot-like unevenness was not observed.

FIG. 4 shows the blade 29 abutting on the applicator final-stage roller 23. When the bias Vb is applied to the applicator final-stage roller 23 to perform development, as described above, almost all of the toner particles move to the developing roller 22 side, but a part of the carrier oil is transferred to the applicator final-stage roller. 23. This accumulates in the nip portion between the second applicator roller 24 and the toner, which is mixed with the toner conveyed from the roller 25, resulting in a phenomenon that the toner concentration is reduced and the formed toner layer is disturbed. For this reason, the blade 29 can be attached to the applicator final-stage roller 23 to remove the residual carrier oil.

FIG. 5 shows another example of bias application. As described above, the liquid developer having a reduced toner concentration remains on the applicator final-stage roller 23 because the roller for applying the bias and the roller for transporting the toner are the same, and are generated. A roller 3 for applying an applicator bias Vb separately from the toner conveying roller
By separately providing 0, it is possible to eliminate the influence of carrier oil remaining on the applicator final-stage roller 23.

[0037]

According to the present invention, when a configuration using a non-volatile, high-viscosity liquid toner is employed, at least the rotating roller (final stage rotating roller or a separately provided conductive roller) of the developing solution applying means is used. Make the surface conductive,
In addition, by supplying a bias voltage to the rotating roller, toner particles of the liquid developer applied to the surface of the rotating roller can be aggregated and moved to the developing roller side.

As described above, according to the present invention, by increasing the cohesive force of the developed toner layer on the photoreceptor, it becomes difficult for the toner to flow, and the separation of the toner layer at the edges of the image portion and the non-image portion is clearly performed. Therefore, high-quality image development without fogging or edge distortion can be achieved.

Further, the present invention makes it possible to use a liquid toner having a relatively low toner concentration without increasing the cohesive force of the developed toner layer so that the amount of toner particles is not insufficient and the image density is not reduced. As a result, a configuration in which the thickness of the pre-wet layer is reduced or the pre-wet is not used becomes possible.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a wet electrophotographic apparatus according to the present invention.

FIG. 2 shows a developing roller in contact with a photoreceptor and a series of applicator rollers for supplying a developing solution thereto.

FIG. 3 is a diagram for explaining an operation of moving developer toner particles to a developing roller side by a potential difference, and shows details of a portion A indicated by a dotted circle in FIG. 2;

FIG. 4 shows a blade for removing residual carrier oil on the last roller of the applicator.

FIG. 5 shows another example of bias application.

FIG. 6 is a diagram illustrating a state of a toner layer in a nip portion between a developing roller and an applicator roller.

FIG. 7 is a diagram illustrating the operation of a pre-wet layer on the surface of a photoconductor.

[Explanation of symbols]

 Reference Signs List 10 photoconductor (drum) 11 charging device 12 exposure device 13 pre-wet device 14 developing device 15 intermediate transfer member (roller) 16 blade 17 static eliminator 18 heating device 19 pressure roller 22 developing rollers 23, 24, 25 applicator roller 26 Blade 27 Roller 28 Toner layer 29 Blade 30 Bias applying roller

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hongo 98 Unoki-nu 98, Unoki-cho, Kawakita-gun, Ishikawa Pref. 2 Inside PFU Co., Ltd. (72) Masataka Takahata 98 Uno-nu 98, Unoki-cho, Kawakita-gun, Ishikawa No. 2 Inside PFU Co., Ltd. (72) Inventor Genji Ichida Unoki-cho, Unoki-cho, Kawakita-gun, Ishikawa 98-2 Inventor P72 Co., Ltd. (72) Inventor Shigeharu Okano Unoki-nu, Unokicho, Kawakita-gun, Ishikawa 98-2 PFU Co., Ltd. (72) Inventor Yasukazu Takeda Unoki Ki, Kawakita-gun, Ishikawa Prefecture 98-2 Infu Co., Ltd. (72) Inventor Shigenori Uesugi Unoki, Unoki-cho, Kawakita-gun, Ishikawa Prefecture No.98 No.2 Ffu Co., Ltd. F-term (reference) 2H073 AA02 BA01 BA11 BA13 CA32 2H074 AA03 AA06 BB50 B B61

Claims (6)

[Claims] An image support on which an electrostatic latent image is to be formed using a non-volatile, high-viscosity, high-concentration liquid toner as a liquid developer, and a film of a pre-wet liquid on the surface of the image support. A pre-wet liquid application unit for applying a liquid developer, supplying a liquid developer in contact with the image support, and toner particles of the liquid developer according to an electric field generated between the liquid support and the image support A developer support that adheres to the image support, and the liquid developer supplied is transported while being applied to the surface while being stretched by a continuous rotating roller,
A developer application means for applying a film of a liquid developer applied to the surface of the final-stage rotating roller by contacting the final-stage rotating roller with the developer support, to the contact surface of the developer support; In the wet-type electrophotographic apparatus, the final-stage rotating roller of the developer application means has at least a surface having conductivity, and a bias voltage is supplied to the final-stage rotating roller. In response to an electric field generated between the developer support and the developer support, the toner particles of the liquid developer applied to the surface of the final-stage rotating roller are aggregated and moved to the developer support. Wet electrophotographic apparatus. 2. The wet electrophotographic apparatus according to claim 1, wherein at least a surface of said developer support has conductivity lower than a resistance of a surface of said last rotating roller. . 3. The roller according to claim 1, wherein the surface of the final stage rotating roller is sufficiently smooth so that a film of the liquid developer applied to the surface of the developer support is made uniform. 4. The wet electrophotographic apparatus according to 1. 4. A blade for recovering a developer is provided at a position on the last-stage rotating roller after contact with the developer support. 4. The wet electrophotographic apparatus according to 1. 5. An image support on which an electrostatic latent image is formed using a high-viscosity, high-concentration liquid toner exhibiting non-volatility as a liquid developer, and a film of a pre-wet liquid on the surface of the image support. A pre-wet liquid application unit for applying a liquid developer, supplying a liquid developer in contact with the image support, and toner particles of the liquid developer according to an electric field generated between the liquid support and the image support A developing solution support for adhering the developing solution to the image support, a liquid developing solution to be supplied being spread by a rotating roller while being applied to the surface while being transported, and a rotating roller at the last stage contacting the developing solution support. A developer application means for applying a liquid developer film applied to the surface of the final-stage rotating roller on the contact surface of the developer support, wherein at least the surface is electrically conductive. Before having sex A conductive roller that rotates in contact with the developer support is provided separately from the final-stage rotating roller, a bias voltage is supplied to the conductive roller, and a bias voltage is applied between the conductive roller and the developer support. A wet electrophotographic apparatus comprising: aggregating toner particles of a liquid developer applied to the surface of the developer support in accordance with the generated electric field, and moving the toner particles to the developer support side. 6. An image support on which an electrostatic latent image is to be formed, wherein the liquid developer having a high viscosity is used as a liquid developer, and the liquid developer is supplied in contact with the image support. And a developer support for attaching toner particles of the liquid developer to the image support in accordance with an electric field generated between the developer and the image support, and the supplied liquid developer is extended by a rotating roller. While being applied to the surface while being conveyed, the last-stage rotating roller abuts on the developing solution support, and a film of the liquid developer applied to the surface of the last-stage rotating roller is applied to the developing solution support. A wet-type electrophotographic apparatus comprising: a developer application unit that applies the liquid to the contact surface; at least a surface of the final stage rotation roller of the developer application unit having conductivity; Is supplied with bias voltage The bias voltage aggregates toner particles of the liquid developer applied to the surface of the final-stage rotating roller in response to an electric field generated between the developer support and the developer support. The liquid electrophotographic apparatus according to claim 1, wherein the liquid toner has a toner concentration sufficiently low such that the carrier liquid also functions as a prewetting liquid by the action of the bias voltage.