JP2002202663A - Developing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of preventing the surface staining of the non-image part of a latent image carrier without using a pre-wetting device for coating the latent image carrier with a pre-wetting liquid in order to prevent the surface staining of the non-image part of the latent image carrier, and an image forming device using the developing device. SOLUTION: The surface of a two-layer forming roller 43 is uniformly coated with developer 18 by a coating roller 44 at a developer coating part C. The thin layer of the developer 18 on the roller 43 is carried to a developer transfer part A and formed to two layers, that is, a carrier liquid layer 18b and a toner particle layer 18a by two-layer forming bias. The developer 18 formed to the two layers advances to a developing part B so that carrier liquid comes into contact with the surface of a photoreceptor 10Y first. Thus, the surface of the photoreceptor 10Y is covered with the carrier liquid in the developer 18 and the toner particles in the developer 18 carried on a developing roller 42 do not directly come into contact with the non- image part of the photoreceptor 10Y. Therefore, the toner particles are completely prevented from adhering to the non-image part of the photoreceptor 10Y without using the pre-wetting device, so that the surface staining of the non-image part is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image formed on a latent image carrier with a liquid developer, and an image forming apparatus such as a copying machine or a printer using the developing device. More specifically, the present invention relates to a developing device and an image forming apparatus capable of preventing background contamination of a non-image portion of a toner image formed on the latent image carrier without using a pre-wet device.

[0002]

2. Description of the Related Art As a developing device of this type, a liquid developer in which charged toner particles are dispersed in an electrically insulating liquid (dielectric carrier) is applied in a thin layer on a developer carrying member. 2. Description of the Related Art There is known an image forming apparatus that develops an electrostatic latent image formed on a latent image carrier with a liquid developer applied on the carrier to form a toner image on the latent image carrier (for example, JP-A-11-174851). In this developing device, the liquid developer applied to the developer carrier comes into contact with the surface of the latent image carrier in a developing section where the developer carrier and the latent image carrier face each other. The toner particles in the liquid developer applied to the developer carrier adhere to the electrostatic latent image formed on the latent image carrier by the action of the developing electric field (electric field) formed in the developing section. Thereby, the electrostatic latent image is formed into a toner image (developed).

Here, a developing electric field formed in the developing section is set to a potential and a polarity such that the toner particles do not adhere to a region (non-image portion) of the latent image carrier where no toner image is formed. Have been. In this type of conventional developing device, the liquid developer applied on the developer carrier carries the latent image carrier despite the development electric field set as described above in the developing section. It has been confirmed that the toner particles in the liquid developer slightly adhere to the non-image portion of the latent image carrier due to contact with the non-image portion, thereby causing background stain on the non-image portion. This is because when the liquid developer applied on the developer carrier enters the developing section, the liquid developer may directly contact the surface of the latent image carrier without receiving much action by the developing electric field. It is considered one of the causes.

As one method of preventing background contamination of the non-image portion, it is conceivable to sufficiently increase a developing electric field formed in the developing portion. That is, a method of increasing the potential difference between the surface potential of the non-image portion of the latent image carrier and the surface potential of the developer carrier can be considered. However, in such a method, an abnormal discharge easily occurs between the developer carrier and the latent image carrier. Therefore, in this method,
The abnormal discharge may cause a problem that the latent image carrier is destroyed.

Therefore, in an image forming apparatus using this type of developing device, generally, for example, Japanese Patent Laid-Open No.
As described in Japanese Patent No. 52255, prior to development of an electrostatic latent image formed on a latent image carrier, a pre-wet liquid composed of a colorless electrically insulating liquid is applied to the surface of the latent image carrier in advance. The method is adopted. As described above, the pre-wet liquid is applied to the surface of the latent image carrier in advance, so that the liquid developer applied on the developer carrier and the non-image portion of the latent image carrier come into direct contact. Disappears. Accordingly, the toner particles in the liquid developer are prevented from adhering to the non-image portion of the latent image carrier, and the occurrence of background stain on the non-image portion is prevented.

[0006]

However, in the case of using the above-described method of applying a pre-wet liquid to the surface of the latent image carrier in advance to prevent background contamination of the non-image area,
It is necessary to dispose a pre-wet liquid applying device for applying a pre-wet liquid to the latent image carrier at an appropriate position around the latent image carrier. Therefore, in an image forming apparatus equipped with such a pre-wet liquid coating device, the peripheral length of the surface of the latent image carrier, that is, when the latent image carrier is formed by an endless photosensitive belt, Perimeter length of photoreceptor belt,
When the latent image carrier is formed of a photosensitive drum, it is necessary to increase the outer diameter of the photosensitive drum.

As described above, in the image forming apparatus in which the pre-wet liquid coating apparatus is arranged, the size of the latent image carrier is increased, so that the size of the apparatus body is increased and the cost of the latent image carrier itself is increased. Or Further, in this type of image forming apparatus, a container for storing the pre-wet liquid, a replenishing pump for replenishing the pre-wet liquid, and the like are required. There is also a risk that the size and cost will increase.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent a non-image portion of a latent image carrier from being stained with a pre-wet on a latent image carrier. An object of the present invention is to provide a developing device capable of preventing background contamination of a non-image portion of a latent image carrier without using a pre-wet device for applying a liquid, and an image forming apparatus using the developing device.

[0009]

In order to achieve the above object, the present invention is directed to a first method in which at least charged toner particles move while carrying a liquid developer dispersed in an electrically insulating liquid. And a developer transfer portion facing the first developer support via the liquid developer carried on the first developer support, and the developer transfer portion The liquid developer transferred from the first developer carrier is carried and moved, and an electrostatic latent image is formed via the liquid developer transferred from the first developer carrier. The latent image carrier that has been brought into contact with the developing unit, and the electrostatic latent image on the latent image carrier due to toner particles in the liquid developer transferred from the first developer carrier in the developing unit. A second developer carrier for developing the first developer carrier and the second developer carrier.
The direction in which the toner particles are moved toward the second developer carrier between the surface potential of the first developer carrier and the surface potential of the second developer carrier. And a bias applying means for applying a bias so that a potential difference is generated.

In this developing device, the surface potential of the first developer carrier and the second potential are applied to the first developer carrier and the second developer carrier by the bias applying means. A bias is applied so as to generate a potential difference between the surface potential of the developer carrier and the direction in which the toner particles are moved toward the second developer carrier. Thereby, the first
The liquid developer transferred from the developer carrier to the second developer carrier is a surface layer mainly composed of the electrically insulating liquid due to the potential difference, and a bottom layer mainly composed of the toner particles. It is divided into two layers. That is, on the second developer carrier, a two-layered developer including an aggregation layer made of toner particles and an insulating liquid layer (hereinafter, referred to as a “two-layered developer”) Is carried. As a result, when the electrostatic latent image formed on the latent image carrier in the developing section comes into contact with the liquid developer carried on the developer carrier,
First, the insulating liquid which is the surface layer of the two-layered developer,
It comes into contact with the surface of the latent image carrier first. Thereby, the surface of the latent image carrier is covered with the insulating liquid in the liquid developer, and the toner particles in the liquid developer carried on the developer carrier are transferred to the non-image portion of the latent image carrier. No direct contact is made. As described above, this developing device can obtain the same effect as applying the pre-wet liquid to the surface of the latent image carrier without using the pre-wet device. Therefore, by using this developing device, it is possible to prevent toner particles in the liquid developer from adhering to the non-image portion of the latent image carrier, and to prevent the occurrence of background stain on the non-image portion. Become like

According to a second aspect of the present invention, in the developing device of the first aspect, the surface moving speed of the first developer carrier and the second developer carrier at the developer transfer portion, and the developing speed The surface movement speed of the second developer carrier and the latent image carrier in the portion is such that the toner particles in the liquid developer move from the first developer carrier to the second developer carrier in the developer transfer portion. The moving speed is set such that the moving speed can move on the surface of the developer carrier and move from the second developer carrier to the surface of the latent image carrier in the developing section.

By the way, the surface moving speed of the first developer carrier and the second developer carrier in the developer transfer section, and the second developer carrier and the latent carrier in the developing section When the surface moving speed with the image carrier increases,
A small amount of toner particles adhere to the non-image portion of the latent image carrier to cause background contamination, and the amount of toner particles adhering to the electrostatic latent image on the latent image carrier is reduced, so that development on the latent image carrier is performed. A phenomenon that the density of the applied toner image decreases may occur.
This is because the liquid developer carried on the second developer carrier enters the developing section in a state in which the liquid developer carried on the second developer carrier is not completely formed into a two-layer structure due to an increase in the surface moving speed. This is because the two-layered developer may pass through the developing unit even when the toner particles are incompletely moved to the electrostatic latent image on the latent image carrier even if the two-layered developer is two-layered. That is,
These phenomena are caused by a shortage of time required for the toner particles in the liquid developer to move to a predetermined portion in the developing section or the developer transfer section as the speed increases. It is a phenomenon. In this developing device, the surface moving speed of the first developer carrier and the second developer carrier in the developer transfer section, and the second developer carrier in the developing section and The surface movement speed with respect to the latent image carrier is such that the toner particles in the liquid developer can move from the first developer carrier to the surface of the second developer carrier at the developer transfer portion, The moving speed is set such that the developing unit can move from the second developer carrier to the surface of the latent image carrier. As a result, it is possible to sufficiently secure a time required for the toner particles in the liquid developer to move to a predetermined portion in the developing section or the developer transfer section. Therefore, after the liquid developer carried on the second developer carrier is surely formed into two layers at the developer transfer portion, the liquid developer enters the developing portion, and the non-image portion becomes dirty. Is eliminated. Further, the movement of the toner particles to the electrostatic latent image on the latent image carrier is surely performed, and the decrease in the density of the toner image is eliminated.

According to a third aspect of the present invention, in the developing device according to the first or second aspect, at least one surface of the first developer carrier and the second developer carrier, and the second developer carrier. At least one surface of the agent carrier and the latent image carrier has elasticity that is deformed by contact with the other surface.

In this developing device, the first developer bearing member and the second developer bearing member are brought into contact with each other at the developer transfer portion such that one surface bites into the other surface. Becomes possible. Further, the second developer carrier and the latent image carrier can be brought into contact with each other in the developing section such that one surface bites into the other surface. Thereby, the contact width between the first developer carrier and the second developer carrier at the developer transfer section (hereinafter, referred to as “developer transfer nip width”) and the second developer support nip width at the developer transfer section The contact width between the developer carrying member and the latent image carrying member (hereinafter referred to as “developing nip width”) can be arbitrarily set. Therefore, in this developing device, the toner particles in the liquid developer can be more stably and reliably electrostatically moved in the developer transfer section and the developing section.

According to a fourth aspect of the present invention, in the developing device of the first, second or third aspect, the surface of the first developer carrying member is provided at a portion downstream of the developer transfer portion in a developer moving direction. A first cleaning unit for cleaning, and a second cleaning unit for cleaning a surface of the second developer carrier at a position downstream of the developing unit in a developer moving direction. It is a feature.

In this developing device, the surface of the first developer carrying member is cleaned by the first cleaning means at a portion downstream of the developer transfer portion in the developer moving direction. Further, the surface of the second developer carrying member is cleaned by the second cleaning means at a portion downstream of the developer transfer portion in the developer moving direction. As a result, the toner amount of the liquid developer carried on the first developer carrier and the amount of toner particles of the two-layered developer carried on the second developer carrier are stabilized, and A toner image having stable image quality is formed on the body.

According to a fifth aspect of the present invention, in the developing device of the first, second, third or fourth aspect, the development of the liquid developer adhering to the second developer carrier and the latent image carrier is performed. The contact pressure between the second developer carrier and the latent image carrier in the developing unit was set such that the total amount immediately before passing through the developing unit and the total amount immediately after passing through the developing unit were equal. It is characterized by the following.

When the contact pressure between the second developer carrier and the latent image carrier in the developing section is unnecessarily high, a part of the liquid developer entering the developing section may be charged by the second developer carrier. 2
May be blocked by the contact between the developer carrier and the latent image carrier. The liquid developer blocked before the developing unit is agitated by the contact movement between the second developer carrier and the latent image carrier, so that the liquid developer is double-layered in the developer transfer unit. The two-layered developer is disturbed. For this reason, in this case, the pre-wetting effect on the surface of the latent image carrier by the two-layered developer is reduced, and the toner particles easily adhere to the non-image portion of the latent image carrier. In this developing device, the contact pressure between the second developer carrier and the latent image carrier in the developing section is changed by the liquid adhered to the second developer carrier and the latent image carrier. The total amount of the developer immediately before passing through the developing section is set to be equal to the total amount immediately after passing through the developing section. This prevents the liquid developer entering the developing section from being blocked by the contact between the second developer carrier and the latent image carrier. Therefore, in this developing device, the two-layered developer carried on the second developer carrier is not disturbed in the developing section, and the toner concentration of the two-layered developer is not reduced. The two-layered developer ensures that the surface of the latent image carrier is pre-wet, and that the toner density of the toner image is prevented from lowering. As a result, adhesion of toner particles to the non-image portion of the latent image carrier can be suppressed to a minimum, and a toner image having a target toner concentration can be formed.

The invention according to claim 6 is the invention according to claims 1, 2, 3, and 4.
Or the total amount of the liquid developer adhering on the first developer carrier and the second developer carrier immediately before passing through the developer transfer portion, and Wherein the contact pressure between the second developer carrier and the latent image carrier at the developer transition section is set so that the total amount immediately after passing through the developer transition section is equal. It is.

Similarly to the developing section, even when the contact pressure between the first developer carrier and the second developer carrier at the developer transfer section is unnecessarily large, the developer transfer section can be used. A part of the liquid developer entering the liquid developer may be blocked by the contact between the first developer carrier and the second developer carrier. As described above, when a part of the liquid developer is blocked before the developer transfer portion, the amount of the two-layered developer formed into two layers at the developer transfer portion becomes insufficient. As a result, the amount of the electrically insulating liquid in the liquid developer that functions as the prewetting liquid is insufficient, and the prewetting effect on the surface of the latent image carrier by the two-layered developer is reduced. In this developing device, the contact pressure between the first developer carrier and the second developer carrier at the developer transfer section is increased by the contact pressure between the first developer carrier and the second developer carrier. The total amount of the liquid developer adhering to the body immediately before passing through the developer transfer portion is set to be equal to the total amount immediately after passing through the developer transfer portion. As a result, the liquid developer entering the developer transfer section is not blocked by the contact between the first developer carrier and the second developer carrier. Therefore, in this developing device, the amount of the two-layered developer at the developer transfer portion does not become insufficient, and the surface of the latent image carrier can be reliably pre-wet with the two-layered developer. Become like As a result, the adhesion of toner particles to the non-image portion of the latent image carrier can be suppressed to a minimum.

[0021] The invention of claim 7 is based on claims 1, 2, 3,
In the developing device of 4, 5, or 6, the liquid developer is
A liquid developer applying means for applying a thin layer to the first developer carrier is provided.

In this developing device, the liquid developer is applied to the first developer carrier in a thin layer by the liquid developer applying means. Thus, the first
By applying the liquid developer to the developer carrying member using the liquid developer applying means, the amount of the liquid developer carried on the first developer carrying member and entering the developer transfer portion can be reduced. , It is possible to make the amount suitable for two-layering.

According to an eighth aspect of the present invention, in the developing device according to the seventh aspect, the liquid developer applying means comprises a contact applying member which is in contact with the first developer carrier, and a surface potential of the contact applying member is provided. Wherein the contact coating member and the first developer carrier are electrically short-circuited so that the surface potential of the first developer carrier and the surface potential of the first developer carrier are the same. is there.

When there is a potential difference between the surface potential of the contact coating member and the surface potential of the first developer carrier, the liquid developer is applied to the first developer carrier by the contact coating member. At this time, the toner particles in the liquid developer are biased due to the electric action due to the potential difference. Then, due to the bias of the toner particles, the amount of the toner particles of the liquid developer applied to the first developer carrier becomes uneven. In this developing device, since the contact coating member and the first developer carrier are electrically short-circuited, the surface potential of the contact coating member and the surface potential of the first developer carrier are reduced. Have the same potential. Thereby, the toner particles in the liquid developer applied to the first developer carrier by the contact applying member are not biased by the electric action, and the toner concentration of the liquid developer can be made uniform. Will be possible.
Therefore, in this developing device, a toner image having a stable image quality can be formed on the latent image carrier by the two-layered developer having a stable toner concentration.

According to a ninth aspect of the present invention, a latent image carrier on which an electrostatic latent image is formed, and an electrostatic latent image formed on the latent image carrier, wherein at least charged toner particles are electrically insulating liquid And a developing device that develops with a liquid developer dispersed therein to form a toner image on the latent image carrier.
It is characterized in that 4, 5, 6, 7 or 8 developing devices are used.

In this image forming apparatus, the developing device according to the first, second, third, fourth, fifth, sixth, seventh or eighth aspect is used as the developing device. This makes it possible to sufficiently prevent the toner particles in the liquid developer from adhering to the non-image portion of the latent image carrier, and to prevent the occurrence of background stain on the non-image portion, so that the image quality is stabilized. A toner image can be formed.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a wet color electrophotographic copying machine (hereinafter, referred to as a color copying machine) which is a wet image forming apparatus will be described below. FIG.
1 is a schematic configuration diagram of a main part of a color copying machine according to the present embodiment. The color copying machine is provided with image forming units 1Y, 1M, 1C, and 1Bk for each color for forming a color image in a color image forming process.
Each image forming unit includes a photoconductor 10 as a latent image carrier.
Y, 10M, 10C, 10Bk, wet developing device 40Y,
40M, 40C, 40Bk, etc., respectively.
In this embodiment, the image forming units 1Bk are for black, 1C is for cyan, 1M is for magenta, 1Y is for yellow, and the photoconductors 10Y, 10M, 10C,
It is configured to form visible images with different print colors on 10Bk. Further, each of the photoconductors 10Y, 10Y
M, 10C, and 10Bk have a part of their respective peripheral surfaces exposed from the openings of the housings of the image forming units 1Y, 1M, 1C, and 1Bk, and are arranged to be rotatable in the direction of arrow A, respectively.

Around the respective photoconductors, an optical writing device 2 as an exposure unit for writing an original light image on the surface of each photoconductor, a charging roller 3 as a charging unit for uniformly charging the surface of each photoconductor, A photoreceptor cleaning blade 4 as a photoreceptor cleaning means for removing residual toner on the surface of each photoreceptor, a charge removing lamp 5 as a charge removing means for removing residual charge on the surface of each photoreceptor, and the like are provided.

Each of the image forming units 1Y, 1M, 1
Above C and 1Bk, an intermediate transfer belt 60 as an intermediate transfer member is provided. This intermediate transfer belt 60
Denotes an intermediate transfer belt driving roller 62 composed of a plurality of stretching rollers, and image forming units 1Y, 1M, 1C, and 1B.
k primary transfer rollers 63Y, 63M, 63C, 63Bk
As a result, it is stretched to have a predetermined tension, and can be moved in the direction of the arrow in the figure.

Further, an intermediate transfer belt cleaning blade 70 as a belt cleaning means for cleaning the surface of the intermediate transfer belt 60 is provided so as to face the portion where the intermediate transfer belt 60 is wound around the primary transfer roller 63Y. On the other hand, a secondary transfer roller 80 is provided so as to face a portion where the intermediate transfer belt 60 is wound around the intermediate transfer belt driving roller 62. The secondary transfer roller 80 is a conductive roller to which a secondary transfer bias for transferring (secondary transfer) the toner image on the intermediate transfer belt 60 to a transfer sheet P as a transfer material is applied.

Each of the wet developing devices 40Y, 40M, 40C,
40Bk each have substantially the same configuration, and a liquid developer (hereinafter simply referred to as “developer”) in which at least charged toner particles are dispersed in an electrically insulating liquid (hereinafter, referred to as “carrier liquid”) is used. "). Here, 100 to 10000 mP in which toner particles of each color are dispersed in a carrier liquid at a high concentration.
A high viscosity developer 18 of a · s is used.

As shown in FIGS. 1 and 2, each of the wet developing devices is provided with a developer tank 41 for storing the developer 18 and a second developing unit B provided so as to be in contact with the surface of each photoconductor.
A developing roller 42 as a developer carrying member, a two-layered roller 43 as the first developer carrying member provided so as to be in contact with the developing roller 41 at a developer transfer portion A, and The developer roller 18 is disposed so as to be immersed in the developer 18 in the developer tank 41, and the application roller 44 as a developer application unit that applies the pumped developer 18 to the two-layered roller 43 in the developer application section C. Have.

Next, the image forming operation of the color copying machine will be described. Here, each of the image forming units 1Y, 1
M, 1C, and 1Bk each perform image formation based on the same principle. Therefore, here, only the yellow image forming process on the photoconductor 10Y located on the left end side in FIG. 1 will be described. 10M, 10C, 10
The description of the image forming process for Bk is omitted.

1 and 2, the photosensitive member 10Y is uniformly charged by the charge from the charging roller 3 while rotating in the direction of the arrow. Thereafter, the surface of the uniformly charged photoreceptor 10Y is irradiated with a laser beam modulated based on yellow image information from the optical writing device 2. Thus, an electrostatic latent image (yellow latent image) based on the yellow image information is formed on the surface of the photoconductor 10Y. The yellow latent image formed on the photoconductor 10Y is developed by the developer (yellow developer) 18 of the wet developing device 40Y corresponding to the photoconductor 10Y. Thereby, the photoconductor 10Y
A yellow toner image is formed thereon.

The application roller 44 uniformly applies the developer 18 pumped by its rotation to the surface of the two-layered roller 43 at the developer application section C. In this process, the developer 18
Is formed into a thin film, and a thin layer of the developer 18 having a certain thickness is formed on the two-layer roller 43. The thin layer of the developer 18 on the two-layer roller 43 is transported by the rotation of the two-layer roller 43 to the developer transfer portion A where the two-layer roller 43 and the developing roller 42 are in contact. . And
In the developer transfer section A, the thin layer of the developer 18 on the two-layer roller 43 is formed into two layers: a surface layer mainly composed of a carrier liquid and a bottom layer mainly composed of toner particles. (Details are described later).

The two-layered developer is applied to the developing section B where the developing roller 42 and the photoconductor 10Y are in contact with each other. Approach the surface first. Thus, the surface of the photoconductor 10Y is covered with the carrier liquid in the developer 18. As described above, the surface of the photoconductor 10Y is covered with the carrier liquid in the developer 18, so that the toner particles in the developer 18 carried on the developing roller 42 are directly transferred to the non-image portion of the photoconductor 10Y. No more contact. As a result, in this color copying machine, the same effect as when the pre-wet liquid is applied to the surface of the photoreceptor 10Y without using the pre-wet device as described above can be obtained. Therefore, in this color copying machine, the developer 18 is applied to the non-image area of the photoreceptor 10Y.
It is possible to sufficiently prevent the adhesion of toner particles inside,
It is possible to prevent the occurrence of background stain on the non-image portion.

A developing bias as a developing voltage is applied to the developing roller 42 (the method of applying the developing bias will be described later in detail). As a result, in the developing section, the toner particles in the developer 18 carried by the developing roller 42 are electrostatically transferred to a portion on the photoreceptor 10Y where the yellow electrostatic latent image is formed. Adhere to. As a result, a yellow toner image is formed on the photoreceptor 10Y based on the yellow image information. Here, the developer remaining on the developing roller 42 that has not been used for development is removed by the developing roller cleaning blade 45 and returned to the inside of the developer tank 41. Also,
Of the developer 18 carried on the two-layer roller 43, the developer remaining on the two-layer roller 43 without being transferred to the developing roller 42 is removed by the two-layer roller cleaning blade 46, and the developer is removed. It is returned inside the tank 41.
Further, the surplus developer pumped up by the application roller 44 is removed by the metering blade 47 and returned to the inside of the developer tank 41.

As shown in FIG. 2, the developing roller cleaning blade 45 and the core of the two-layer roller 43 were electrically disposed via a first bias power supply 48. Further, the roller cleaning blade 45
Was grounded via a second bias power supply 49.

Then, the yellow toner image formed on the photoreceptor 10Y is primarily transferred by the primary transfer roller 63Y to the intermediate transfer belt 60 which rotates in the direction of the arrow in synchronization with the photoreceptor 10Y. On the other hand, the developer remaining on the photoconductor 10Y after the transfer is removed by the photoconductor cleaning blade 4 to prepare for the next image formation.

The above-described steps are sequentially repeated by the image forming unit corresponding to each color and the intermediate transfer belt 60 for each of the monochromatic images of yellow, magenta, cyan, and black, so that the intermediate transfer belt 60 A superimposed full-color image is formed.

The full-color image formed on the intermediate transfer belt 60 is collectively transferred onto the transfer paper P conveyed from a paper feed unit (not shown) by a predetermined secondary transfer bias applied to the secondary transfer roller 80. Next is transferred. After the completion of the secondary transfer, the transfer paper P is separated from the intermediate transfer belt 60,
A fixing process is performed by a fixing roller 91 and a pressure roller 92 of a fixing device 90 as a fixing unit, and the sheet is discharged outside the apparatus.

(First Embodiment) In this embodiment, each member of the above color copying machine is constructed as follows. As the photoconductors 10Y, 10M, 10C, and 10Bk, amorphous silicon photoconductors having a diameter of 30 mm were used, and their cores were grounded. The surface movement speed of this photoconductor is 15
0 mm / sec. The charging roller 3 has a diameter of 1
A 4 mm epichlorohydrin rubber roller was used. The surface moving speed of the charging roller 3 is 150 mm / sec.
And The charging potential on the photosensitive member charged by the charging roller 3 was +600 V. As the optical writing device 2,
The LD writing method was used. The potential of the image portion (electrostatic latent image) after exposure was set to 50V. As the static elimination lamp 5,
An LED array was used. Photoconductor cleaning blade 4
, Urethane rubber was used. Intermediate transfer belt 60
As a material, a conductive urethane rubber layer having a thickness of 1.5 mm was formed on a base material made of a stainless steel belt having a thickness of 0.1 mm. The surface movement speed of the intermediate transfer belt 60 was 150 mm / sec. Urethane rubber was used as the intermediate transfer belt cleaning blade. An epichlorohydrin rubber roller having a diameter of 20 mm was used as the primary transfer roller 63Y. Primary transfer roller 63
As M, 63C and 63Bk, epichlorohydrin rubber rollers having a diameter of 14 mm were used. The bias potential of each primary transfer roller was -300 V (constant voltage control).
The intermediate transfer belt drive roller 62 has a diameter of 20 mm.
Epichlorohydrin rubber roller was used. As the secondary transfer roller 80, an epichlorohydrin rubber roller having a diameter of 20 mm was used. The current flowing from the secondary transfer roller 80 to the intermediate transfer belt 60 was -100 μA. As the fixing roller 91, a roller in which a 30 mm-diameter hollow aluminum core including a halogen heater was covered with a semiconductive PFA tube having a thickness of 50 μm was used. The surface temperature of the fixing roller 91 was 95 ° C. The potential of the core of the fixing roller 91 was 0 V (ground). As the pressure roller 92, a semiconductive PF having a thickness of 100 μm is formed on a base material formed of conductive silicone rubber having a diameter of 30 mm.
A tube coated with A was used. Pressure roller 92
, The current flowing through the fixing roller 91 was −500 μA (constant current control).

On the other hand, the wet developing devices 40Y, 40M,
Each member of 40C and 40Bk was constituted by the following.
As the application roller 44, a stainless gravure roller having a diameter of 20 mm was used. The surface moving speed of the gravure roller was 250 mm / sec in a direction opposite to the surface moving speed of the two-layer roller 43 in the developer application section C, which is the contact part with the two-layer roller 43. As the metering blade 47, a stainless steel blade having a thickness of 0.5 mm was used. As the two-layered roller 43, an elastic layer made of conductive silicone rubber (volume resistivity: 10 ⁶ Ω · cm, hardness: Shore A · 50 °) having a diameter of 20 mm is formed around a stainless steel core rod having a diameter of 5 mm. The elastic layer was covered with a conductive PFA tube (volume resistivity: 10 ⁷ Ω · cm) having a thickness of 50 μm. Further, the surface moving speed of the two-layered roller 43 is 15 degrees in the same direction as the surface moving speed of the developing roller 42 in a developer transfer portion which is a contact portion with the developing roller 42.
0 mm / sec. As the two-layer roller cleaning blade 46, a stainless steel blade having a thickness of 0.5 mm was used. The developing roller 42 has a diameter of 5 mm.
An elastic layer made of low-hardness silicone rubber (hardness: Shore A: 5 °) having a diameter of 20 mm is formed around a stainless steel core rod, and a 50 μm-thick conductive PFA tube (volume resistivity) is formed around the elastic layer. : 10 ⁵ Ω · cm). Further, the surface moving speed of the developing roller 42 is set at a developing portion which is a contact portion with the photosensitive member.
150 mm / sec in the same direction as the surface movement speed of the photoconductor
And As the developing roller cleaning blade, a stainless steel blade having a thickness of 0.5 mm was used. First
Is a constant voltage power supply of 500V.
The second bias power supply 49 was a constant voltage power supply of 250V. The nip width of the developer transfer portion A was 5 mm. The nip width of the developing section B was 5 mm. The nip width of the developer application section C was 1 mm.

Further, in the wet developing process of this embodiment, as shown in FIG. 2, the core of a two-layered roller 43 which is entirely conductive, and the coating roller (gravure roller) 44, They are grounded so that they have the same potential. Therefore, the toner particles in the developer 18 applied to the two-layered roller 43 by the application roller 44 are not biased by the electric action, and the toner concentration of the developer 18 is made uniform. As a result, the concentration of the developer 18 supplied to the concave portion of the gravure roller serving as the application roller 44 is always constant, and a uniform thin layer of the developer having a stable concentration can be formed on the two-layer roller 43. . In other words, if the application roller (gravure roller) 44 and the two-layered roller 43 are not at the same potential, the toner particles in the concave portion of the gravure roller perform electrophoresis in the developer application section C. Therefore, it is difficult to stably form a thin layer of the developer 18 having a uniform concentration on the two-layer roller 43.

On the other hand, in the developer transfer area A and the development area B, it is necessary to form a nip area having a width that allows sufficient electrophoresis of toner particles dispersed in the developer 18. For this reason, for example, the developing roller 42 is desirably made of a material made of an elastic body having sufficiently low hardness. In view of this, the developing roller 42 in the present embodiment has an elastic layer formed by using a silicone rubber having a Shore A · 5 ° hardness as described above as its base material.

The surface of the developing roller 42 needs to have a predetermined potential in order to form two layers of the developer 18 and develop an electrostatic latent image. However, when a conductive agent is added to the silicone rubber material in order to impart conductivity to the elastic layer, the rubber hardness of the elastic layer increases. Therefore, in the case of such a developing roller having a high rubber hardness, it is necessary to increase the contact force between the developing roller 42 and the photosensitive member in the developing section B in order to form the nip region. However, if the contact pressure between the developing roller 42 and the photosensitive member in the developing section B becomes too high, the two-layered developer carried on the developing roller 42 cannot pass through the developing section B.

Therefore, in the present embodiment, the elastic layer made of silicone rubber of the developing roller 42 has complete electrical insulation. Then, as shown in FIG. 2, a second bias power supply 49 is connected to the developing roller cleaning blade 45. As a result, the bias voltage applied to the developing roller cleaning blade 45 by the second bias power supply 49 changes the conductive surface layer (50 μm thick conductive PFA tube) of the developing roller 42 with which the developing roller cleaning blade 45 contacts. )
Is applied to the entire surface of the developing roller 42. As a result, the surface potential of the developing roller 42 becomes
The surface potential is about + 250V. Further, the two-layered roller 4 which contacts the developing roller 42 at the developer transfer portion A
3 is increased by the first bias power supply 48 to about +
500V.

FIGS. 3 (a), (b), (c), (d),
(E), (f), (g), (h) and (i) show symbols a, b, c, d, e, and e in FIG.
The state of the developer 18 at each part indicated by f, g, h, and i is shown. FIG. 3A shows the state of the developer 18 on the application roller (gravure roller) 44 immediately after passing through the metering blade 47. In this state, the developer 18 having a uniform concentration is measured and applied to the concave portion of the gravure roller. FIG. 3B shows the state of the developer 18 on the gravure roller immediately after passing through the developer application section C. Here, a part of the developer 18 measured and applied to the concave portion of the gravure roller is peeled off. FIG.
(C) shows the state of the developer thin layer applied on the two-layer roller 43. The thickness of this developer thin layer is 1
0 to 11 μm. FIG. 3D shows that the developer thin layer applied on the two-layer roller 43 is made into two layers by the action of the bias electric field (two-layer electric field) formed in the developer transfer portion A. The state is shown. In other words, the developer thin layer applied on the two-layered roller 43 has the toner particle layer 18a on the developer 18 side and the two-layered roller 43 side by the action of the two-layered electric field. Two layers are formed so that the carrier liquid layer 18b is formed.

The two-layered developer 18 is
When the carrier liquid layer 18b is released from the developer transfer portion A, it is separated in the carrier liquid layer 18b having a low cohesive force. As a result, as shown in FIG. 3E, a part of the carrier liquid layer passing through the developer transfer portion A is provided on the surface of the two-layer roller 43 on the downstream side of the developer transfer portion A in the developer transfer portion. Remain. The carrier liquid remaining on the two-layer roller 43 is removed by the two-layer roller cleaning blade 46 and the developer 1 is removed.
8 as a carrier component.

In this way, the developing roller 42
As shown in FIG. 3 (f), the surface layer is the carrier liquid layer 18
b, a two-layered developer in which the bottom layer is formed of the toner particle layer 18a is carried. Thereby, when the two-layered developer enters the developing section B, as shown in FIG. 3G, the carrier liquid layer 18b of the two-layered developer layer is first placed on the surface of the photoreceptor 10Y. Contact In this state, there is no opportunity for the toner particle layer 18a to come into direct contact with the photoconductor surface.

Here, a bias electric field having a polarity for displacing the toner particles facing the non-image portion toward the developing roller 42 is formed in the non-image portion on the photosensitive member surface in the developing portion B. This reliably prevents toner particles from adhering to the non-image area on the surface of the photoconductor (dirt). Further, the developing unit B
In the image area on the surface of the photoreceptor, a bias electric field having a polarity to move toner particles to the surface of the photoreceptor is formed. Thereby, the toner particles adhere to the electrostatic latent image on the photoconductor, and a toner image is formed on the photoconductor.

Then, the developer 1 in which the toner particles facing the non-image area on the photosensitive member surface are displaced toward the developing roller 42 side.
8 is left on the developing roller 42 when it is released from the developing section B, as shown in FIG. The developer 18 remaining on the developing roller 42 is removed by the developing roller cleaning blade 45 and the toner particle layer 1 is removed.
8a and the carrier liquid layer 18b are redispersed and reused. On the other hand, as shown in FIG. 3I, the toner particle layer 18a formed into a toner image on the photoreceptor proceeds to the transfer step to the intermediate transfer belt 60 as described above.

(Second Embodiment) The first embodiment described above
The process speed (surface moving speed of the photosensitive member) in the embodiment is 150 mm / sec, but only the process speed is changed to 300 mm / sec without changing the configuration of the first embodiment. However, when the speed of image formation is increased, the following problems occur. (1) Some toner particles adhere to the non-image area of the photoreceptor (smear of the non-image area). (2) The amount of toner particles adhering to the image area of the photoreceptor decreases (the density of the toner image decreases).

These disadvantages can be considered as the following phenomena, respectively. (1) The developer formed on the developing roller 42 is not completely two-layered. (2) The movement of the toner particles to the image area on the photoconductor is incomplete. That is, it is considered that all of these phenomena are caused by a shortage of time required for moving the toner particles in the developer transfer portion A or the developing portion B as the process speed is increased. .

Therefore, in order to increase the time required for moving the toner particles in the developer transfer area A or the development area B, it is necessary to increase the nip width in the developer transfer area A or the development area B. There is. However, if the contact pressure between the two-layered roller 43 and the developing roller 42 at the developer transfer portion A is increased in order to increase the nip width, as shown in FIG. This causes a phenomenon that the developer 18 carried on the two-layered roller 43 is blocked.

Since the flow of the blocked developer 18 is disturbed, the influence of the disturbance of the developer 18 is as follows.
It also extends to the developer layer in the developer transfer section A. As a result, it is difficult to uniformly form the developer carried on the developing roller 42 into two layers. Further, in a state in which the developer 18 is blocked at the upstream portion of the developer transfer portion A, the developer 18 between the entrance side and the discharge side of the developer 18 with the developer transfer portion A interposed therebetween. The total amount of components becomes uneven. That is, the total amount of the developer on the discharge side is smaller than the total amount of the developer on the entrance side. For this reason, in such a state, the developing roller 42
It becomes difficult to form a developer layer having a target thickness on the upper side, and the density itself of the toner image after the development process is reduced.

Such a phenomenon that the developer 18 is blocked is similarly generated in the upstream portion of the developing section B even when the contact pressure between the developing roller 42 and the photosensitive member is increased. When the developer 18 is blocked at the upstream portion of the developing section B, the carrier liquid layer 18b in the two-layered developer formed on the developing roller 42 is disturbed. Cannot be obtained on the photoreceptor, thereby preventing the effect of preventing background contamination of the non-image area. Further, since the developer 18 is blocked at the upstream portion of the developing unit B, the total amount of the developer 18 that can pass through the developing unit B is reduced, so that the toner density of the toner image formed on the photoconductor is reduced. This leads to a problem of lowering.

Here, the proper maximum contact force in the developer transfer section A or the development section B is determined by the total amount of the developer 18 on the upstream side of the developer transfer section A or the development section B,
The determination can be made by confirming whether or not the total amount of the developer 18 on the downstream side is equal. Further, the total amount of the developer 18 can be known by measuring the weight per unit area of the developer 18 attached to the upstream side and the downstream side of the developing unit B.

In the second embodiment, the contact pressure between the two-layered roller 43 and the developing roller 42 in the developer transfer section A and the contact pressure between the developing roller 42 and the photosensitive member in the developing section B are increased. Without increasing the nip width between the two-layered roller 43 and the developing roller 42 in the developer transfer section A and the nip width between the developing roller 42 and the photosensitive member in the developing section B. is there. FIG. 5 shows the configuration of the second embodiment.

In this embodiment, each member of the above color copying machine is constructed as follows. As the application roller 44, a stainless gravure roller having a diameter of 20 mm was used. The surface moving speed of the gravure roller is 35 degrees opposite to the surface moving speed of the two-layered roller 43 in the developer application section C which is a contact portion with the two-layered roller 43.
0 mm / sec. As the metering blade 47, a stainless steel blade having a thickness of 0.5 mm was used. As the two-layered roller 43, a conductive silicone rubber having a diameter of 20 mm (volume resistivity: 10 ⁶ Ω · cm, hardness: Shore A · 5) is formed around a stainless steel rod having a diameter of 5 mm.
0 °) is formed, and around this elastic layer,
50 μm thick conductive PFA tube (volume resistivity: 1
0 ⁷ Ω · cm) was used coated with. Further, the surface moving speed of the two-layered roller 43 is set at the developer transfer portion, which is the contact portion with the developing roller 42, at the developing roller 42.
Of 300 mm / sec in the same direction as the surface moving speed of. As the two-layer roller cleaning blade 46,
A 0.5 mm thick stainless steel blade was used.

In the second embodiment, a second developer carrier which contacts the photoreceptor 10Y in the developing section B and develops the electrostatic latent image on the photoreceptor with the two-layered developer is used. In place of the developing roller 42 in the first embodiment, a conductive polyimide belt having a thickness of 0.1 mm (volume resistivity:
A developing belt 50 of 10 ⁵ Ω · cm) was used.
As a belt supporting roller for stretching the developing belt 50, a bias applying supporting roller 51 having a diameter of 14
using a stainless steel roller of 5 mm
As 2, a urethane rubber roller having a diameter of 14 mm was used. The surface moving speed of the developing belt 50 was 300 mm / sec in the same direction as the surface moving speed of the photoconductor 10Y in the developing section B. Further, a 1 mm thick urethane rubber cleaning blade was used as the belt cleaning blade 53 for removing the residual developer remaining on the developing belt 50 after the toner image was formed on the photosensitive member.

The first bias power supply 48 was a constant voltage power supply of 500V. The second bias power supply 49 is 250 V
Constant voltage power supply. The nip width of the developer transfer portion A is 1
0 mm. The nip width of the developing section B was 10 mm. The nip width of the developer application section C was 1 mm.

In the wet developing device according to the second embodiment, the second developer carrier is constituted by the developing belt 50. Therefore, the developer transfer nip width at the developer transfer portion A is changed. , And the developing nip width in the developing section B can be formed relatively easily. Therefore, the two-layered roller 43 in the developer transfer portion A
Even when the surface moving speed between the developing belt 50 and the photosensitive member in the developing section B and the surface moving speed between the developing belt 50 and the photosensitive member in the developing section B are increased, the toner particles in the developer 18 can be reliably moved. Can be applied to the image forming apparatus.

[0064]

According to the first to eighth aspects of the present invention, it is possible to obtain the same effect as applying a pre-wet liquid to the surface of a latent image carrier without using a pre-wet device. There is an excellent effect that it is possible to prevent toner particles in the liquid developer from adhering to the non-image portion of the image carrier and prevent the occurrence of background stain on the non-image portion.

In particular, according to the second aspect of the present invention, it is possible to sufficiently secure the time required for the toner particles in the liquid developer to move to a predetermined portion in the developing section or the developer transfer section. Therefore, after the liquid developer carried on the second developer carrying member is surely double-layered at the developer transfer portion, the liquid developer enters the developing portion, and the generation of background stain on the non-image portion is eliminated. Is done. Further, there is an excellent effect that the movement of the toner particles to the electrostatic latent image on the latent image carrier is reliably performed, and the decrease in the density of the toner image is eliminated.

Further, according to the third aspect of the present invention, the developer transfer nip width between the first developer carrier and the second developer carrier in the developer transfer section, and the second development in the developing section The developing nip width between the developer carrier and the latent image carrier can be set arbitrarily, and the toner particles in the liquid developer are more stably and reliably electrostatically transferred in the developer transfer portion and the developing portion. There is an excellent effect that can be moved to.

According to the fourth aspect of the present invention, the toner particles of the liquid developer carried on the first developer carrier and the two-layered developer carried on the second developer carrier are provided. There is an excellent effect that the amount is stable and a toner image with stable image quality is formed on the latent image carrier.

According to the fifth aspect of the present invention, the two-layered developer carried on the second developer carrier is disturbed in the developing section, or the toner concentration of the two-layered developer decreases. The surface of the latent image carrier is reliably pre-wet by the two-layered developer, and the toner density of the toner image is prevented from lowering. Accordingly, there is an excellent effect that adhesion of toner particles to the non-image portion of the latent image carrier can be minimized, and a toner image having a target toner density can be formed.

According to the sixth aspect of the present invention, the amount of the two-layered developer in the developer transfer portion does not become insufficient, and the surface of the latent image bearing member can be reliably formed by the two-layered developer. As a result, it is possible to minimize the amount of toner particles adhering to the non-image area of the latent image carrier.

According to the seventh and eighth aspects of the present invention, the liquid developer is applied to the first developer carrier using the liquid developer applying means, so that the first developer carrier is applied. There is an excellent effect that the amount of the liquid developer carried on the developer and entering the developer transfer portion can be adjusted to an amount suitable for two-layer formation.

In particular, according to the invention of claim 8, since the surface potential of the contact coating member and the surface potential of the first developer carrier become the same potential, the first developer is applied by the contact coating member. There is an excellent effect that the toner particles in the liquid developer applied to the carrier are not biased due to the electric action, and the toner concentration of the liquid developer can be made uniform.

According to the ninth aspect, the first, second,
Since the developing device of 3, 4, 5, 6, 7, or 8 is used, it is possible to sufficiently prevent toner particles in the liquid developer from adhering to the non-image portion of the latent image carrier, and Since the occurrence of background stain on the image portion can be prevented, there is an excellent effect that a toner image with stable image quality can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a main part of a color copying machine according to an embodiment.

FIG. 2 is a schematic configuration diagram for explaining a configuration of a wet developing device used in the copying machine.

FIG. 3 is a schematic view showing a state of a developer at each part in the wet developing device.

FIG. 4 is a schematic perspective view showing a state in which a developer carried on a two-layered roller is blocked at an upstream portion of a developer transfer portion A of the wet developing device.

FIG. 5 is a schematic configuration diagram showing a configuration of a second example of the present invention.

[Explanation of symbols]

Reference Signs List 1Y, 1M, 1C, 1Bk Image forming unit 2 Optical writing device 3 Charging roller 4 Photoconductor cleaning blade 5 Static elimination lamp 10 Photoconductor 18 Developer 18a Toner particle layer 18b Carrier liquid layer 40Y, 40M, 40C, 40Bk Wet developing device 41 Developer tank 42 developing roller 43 two-layered roller 44 coating roller 45 developing roller cleaning blade 46 two-layered roller cleaning blade 47 metering blade 48 first bias power supply 49 second bias power supply 50 development belt 51 bias application support Roller 52 Driving support roller 53 Belt cleaning blade 60 Intermediate transfer belt 62 Intermediate transfer belt driving roller 63Y, 63M, 63C, 63Bk Primary transfer roller 70 Intermediate transfer belt cleaning blade 80 Secondary transfer roller 90 Fixing device 91 Fixing roller 92 Pressure roller P Transfer paper

Claims (9)

[Claims] 1. A first developer carrier that moves while carrying a liquid developer in which at least charged toner particles are dispersed in an electrically insulating liquid; and a first developer carrier that is carried by the first developer carrier. The liquid developer is brought into contact with the first developer carrier at a developer transfer portion facing the first developer carrier, and carries the liquid developer transferred from the first developer carrier at the developer transfer portion. And moves through the liquid developer transferred from the first developer carrier, and comes into contact with the latent image carrier on which the electrostatic latent image has been formed at the developing section facing the same. A second developer carrier for developing an electrostatic latent image on the latent image carrier with toner particles in the liquid developer transferred from the first developer carrier, and the first developer carrier The surface potential of the first developer carrier with respect to the second developer carrier and the second developer carrier.
The toner particles between the surface potential of the developer carrying member
And a bias applying means for applying a bias so as to generate a potential difference in a direction of moving the developer to the developer carrier. 2. The developing device according to claim 1, wherein a surface moving speed of the first developer carrier and the second developer carrier at the developer transfer portion, and a second speed of the second developer carrier at the developing portion. The surface movement speed between the developer carrier and the latent image carrier is such that the toner particles in the liquid developer are moved from the first developer carrier to the second developer carrier at the developer transfer portion. A second surface in the developing section.
Wherein the moving speed is set such that the moving speed can move from the developer carrier to the surface of the latent image carrier. 3. The developing device according to claim 1, wherein at least one surface of said first developer carrier and said second developer carrier, and said second developer carrier and said second developer carrier. A developing device characterized in that at least one surface of the latent image carrier has elasticity to be deformed by contact with the other surface. 4. The developing device according to claim 1, wherein the surface of the first developer carrier is cleaned at a portion downstream of the developer transfer portion in a developer moving direction. A developing device comprising: a cleaning unit; and a second cleaning unit that cleans a surface of the second developer carrier at a position downstream of the developing unit in a developer moving direction. . 5. The developing device according to claim 1, wherein the liquid developer adhering to the second developer carrier and the latent image carrier passes immediately before passing through the developing section. And the contact pressure between the second developer carrier and the latent image carrier in the developing unit is set so that the total amount of the second developer carrier and the total amount immediately after passing through the developing unit are equal. Developing device. 6. The developing device according to claim 1, wherein said liquid developer adhered on said first developer carrier and said second developer carrier is The second developer carrier and the latent image carrier in the developer transfer section are so set that the total amount immediately before passing through the developer transfer section is equal to the total amount immediately after passing through the developer transfer section. A developing device wherein a contact pressure with a body is set. 7. The liquid developer applying means according to claim 1, wherein said liquid developer is applied to said first developer carrier in a thin layer. A developing device comprising: 8. The developing device according to claim 7, wherein said liquid developer applying means comprises a contact applying member in contact with said first developer carrying member, and a surface potential of said contact applying member and said first developer carrying member. The developing device, wherein the contact coating member and the first developer carrier are electrically short-circuited so that the surface potential of the developer carrier becomes the same as the surface potential of the developer carrier. 9. A latent image carrier on which an electrostatic latent image is formed, and an electrostatic latent image formed on the latent image carrier, wherein at least charged toner particles are dispersed in an electrically insulating liquid. An image forming apparatus comprising: a developing device for developing with a liquid developer to form a toner image on the latent image carrier;
An image forming apparatus using the developing device of 7 or 8.