JP4784858B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having an intermediate transfer belt.

  Conventionally, an electrophotographic image forming apparatus (wet image forming apparatus) using a liquid developer is known. The developer used in the wet image forming apparatus is obtained by suspending solids (toner particles) in an electrically insulating organic solvent (carrier liquid). The particle diameter of the toner particles is 2 μm or less, usually Since it is extremely fine, about 1 μm or less, it is possible to achieve higher image quality than a dry image forming apparatus using powder toner particles of about 7 μm.

  The carrier liquid constituting the developer has a function of making the toner particles charged and further uniformly dispersed in addition to preventing the toner particles from scattering around 1 μm. It also has a role to make it easy to move by action. As described above, the carrier liquid is a component necessary for toner storage, toner conveyance, development, and transfer processes, but also adheres to non-image areas, and excessive carrier liquid after development causes transfer disturbance and the like. Therefore, the carrier liquid is usually removed (squeezed) from the developer on the photosensitive member and the intermediate transfer member.

In addition, when an intermediate transfer belt or a secondary transfer belt is used in a wet image forming apparatus, liquid developer (carrier liquid and solid content) adhering to the belt surface is removed by a cleaning blade. (Patent Document 1).
JP 2002-189354 A

  By the way, the deposit (liquid developer) to be cleaned in the intermediate transfer belt is generally subjected to carrier removal as described above, so that the solid content is increased, so that it is intermediate like “wet powder”. It adheres to the surface of the transfer belt. Further, the developer remaining on the intermediate transfer belt after being transferred to paper absorbs the carrier liquid on the paper, so that the solid content rate is further increased and requires a force for cleaning, and particularly a soft (low elastic modulus) belt. Then, it was confirmed that the belt surface was deformed by the cleaning blade and the belt was lost.

SUMMARY An advantage of some aspects of the invention is that the liquid developer adhered on the intermediate transfer belt can be cleaned without breaking the belt.
For this purpose, the image forming apparatus of the present invention transfers an image carrier, a developing unit for developing a liquid developer containing toner and a carrier liquid, and an image developed on the image carrier by the developing unit, A transfer belt wound around a transfer roller and a tension roller; a transfer backup roller that contacts the transfer roller via the transfer belt and transfers an image transferred to the transfer belt onto a transfer material; and the transfer belt A cleaning liquid application member that contacts the transfer roller and applies a cleaning liquid, and applies a bias voltage between the cleaning liquid application member and the transfer roller, and the cleaning liquid application member It is a roller having a value Rs, and has a relationship of resistance value Rt and Rs> Rt of the transfer backup roller.
The present invention is characterized by comprising a cleaning roller that contacts the transfer belt and a cleaning blade that contacts the cleaning roller and cleans the cleaning roller.
Further, the present invention is characterized in that the cleaning liquid is a carrier liquid.

  The present invention uses a cleaning roller as a cleaning member for the intermediate transfer belt, and a cleaning liquid application member at a position facing the roller for stretching the intermediate transfer belt on the upstream side in the rotation direction of the intermediate transfer belt with respect to the cleaning roller. By disposing and applying the cleaning liquid, the soft intermediate transfer belt can be cleaned without breaking.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the embodiment of the present invention. Development units 30Y, 30M, 30C, and 30K are arranged at the lower part of the image forming apparatus, and the intermediate transfer belt 40 and the secondary transfer unit 60 are arranged for the image forming unit of each color arranged in the center of the image forming apparatus. Arranged at the top of the image forming apparatus.

  The image forming unit includes image carriers 10Y, 10M, 10C, and 10K, charging rollers 11Y, 11M, 11C, and 11K, and exposure units 12Y, 12M, 12C, and 12K (not shown). The exposure units 12Y, 12M, 12C, and 12K have an optical system such as a semiconductor laser, a polygon mirror, and an F-θ lens. The image bearing members 10Y, 10M, 10C, and 10K are provided by charging rollers 11Y, 11M, 11C, and 11K. Are uniformly charged and irradiated with laser light modulated based on the input image signal by the exposure units 12Y, 12M, 12C, and 12K, and on the charged image carriers 10Y, 10M, 10C, and 10K. An electrostatic latent image is formed on the surface.

  The developing units 30Y, 30M, 30C, and 30K generally include liquid developers of respective colors including the developing rollers 20Y, 20M, 20C, and 20K, yellow (Y), magenta (M), cyan (C), and black (K). Developer containers (reservoirs) 31Y, 31M, 31C, 31K to be stored, and developer supply rollers for supplying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K 32Y, 32M, 32C, 32K and the like, and the electrostatic latent images formed on the image carriers 10Y, 10M, 10C, and 10K are developed with liquid developers of respective colors.

  The intermediate transfer belt 40 is an endless elastic belt member, is wound around a driving roller 41 and a tension roller 42, and is stretched between the image transfer members 10Y, 10M, and 50K at the primary transfer portions 50Y, 50M, 50C, and 50K. It is rotationally driven by the drive roller 41 while abutting 10C and 10K. The primary transfer sections 50Y, 50M, 50C, and 50K are arranged such that the primary transfer rollers 51Y, 51M, 51C, and 51K are opposed to each other with the image transfer bodies 10Y, 10M, 10C, and 10K interposed between the intermediate transfer belt 40 and the image transfer bodies 10Y, Using the contact position with 10M, 10C, and 10K as the transfer position, the developed toner images of the respective colors on the image carriers 10Y, 10M, 10C, and 10K are sequentially superimposed and transferred onto the intermediate transfer belt 40, and full color toner is transferred. Form an image.

  The toner images formed on the plurality of image carriers (photoconductors) 10 are sequentially transferred to the intermediate transfer belt 40 where the toner images are sequentially transferred onto the sheet material, and then transferred onto the sheet material. In transferring the toner image to the sheet material in the process, even if the sheet material surface is not smooth due to the fiber, etc., as a means for improving the secondary transfer characteristics following the non-smooth sheet material surface, A flexible elastic belt member is used.

The configuration of the intermediate transfer belt will be described with reference to FIG.
The intermediate transfer belt 40 has a base material layer 40a (eg, thickness) made of a polyimide material that has excellent bending durability and is less stretched by belt tension and has excellent heat resistance even when there is a heating step in the coating step of covering the elastic layer. 100 μm), urethane rubber (hardness JIS-A30 °), etc., elastic layer 40b (eg, thickness 200 μm) covering the surface of the base material layer 40a, coat layer 40C (eg, thickness 10 μm) made of fluororesin ), And an image is formed on the coat layer 40C by primary transfer. The width of the belt is 324 mm, and the volume resistance value of the belt is about log 10 Ωcm (resistance value of all layers).

  The secondary transfer unit 60 of FIG. 1 has a secondary transfer roller 61 disposed opposite to the belt drive roller 41 with the intermediate transfer belt 40 interposed therebetween, and further includes a secondary transfer roller cleaning blade 62 and a developer recovery unit 63. Is placed. In the secondary transfer unit 60, the sheet material conveyance path L is adjusted in accordance with the timing at which a full-color toner image or a single-color toner image formed by superimposing colors on the intermediate transfer belt 40 reaches the transfer position of the secondary transfer unit 60. Then, a sheet material such as paper, film or cloth is conveyed and supplied, and a single color toner image or a full color toner image is secondarily transferred to the sheet material. A fixing unit (not shown) is disposed in front of the sheet material conveyance path L, and a single color toner image or a full color toner image transferred onto the sheet material is fused and fixed to a recording medium (sheet material) such as paper. Image formation on the final sheet material is completed. Even if the surface of the secondary transfer roller 61 is a sheet material that is not smooth due to fiber or the like, the surface is coated with an elastic body as a means for improving the secondary transfer characteristics following the non-smooth sheet material surface. It is composed of rollers. This is an elastic belt employed in the intermediate transfer belt 40 that sequentially transfers the toner images formed on the plurality of image carriers 10 in order to be superimposed and supported on the intermediate transfer belt 40, and then collectively transferred to a sheet material. The purpose is the same as that of the member.

  Next, the image forming unit and the developing unit will be described. FIG. 3 is a cross-sectional view showing main components of the image forming unit and the developing unit. Since the configurations of the image forming unit and the developing unit for each color are the same, the following description will be made based on the yellow (Y) image forming unit and the developing unit.

  The image forming unit includes a cleaning device including a latent image eraser 16Y, an image carrier cleaning blade 17Y, and a developer recovery unit 18Y along the rotation direction of the outer periphery of the image carrier 10Y, a charging roller 11Y, an exposure unit 12Y, and a development unit. A cleaning device including a developing roller 20Y of 30Y, an image carrier squeeze roller 13Y, an image carrier squeeze roller cleaning blade 14Y, and a developer recovery unit 15Y, which are associated with the development roller 20Y, is provided. In the developing unit 30Y, a cleaning blade 21Y, a developer supply roller 32Y using an anilox roller, and a compression roller 22Y are disposed on the outer periphery of the developing roller 20Y, and a liquid developer stirring roller 34Y is disposed in the liquid developer container 31Y. The developer supply roller 32Y is accommodated.

  A primary transfer roller 51Y of the primary transfer portion is disposed along the intermediate transfer belt 40 at a position facing the image carrier 10Y, and an intermediate transfer belt squeeze roller 53Y, a backup roller 54Y, an intermediate transfer belt are disposed downstream of the moving direction. An intermediate transfer belt squeeze device 52Y including a belt squeeze roller cleaning blade 55Y and a developer recovery unit 56Y is disposed.

FIG. 4 is a diagram illustrating the squeeze device 52Y.
The squeeze device 52Y is provided between the colors of the intermediate transfer belt, and the squeeze roller 53Y is for removing the carrier liquid contained in the liquid developer on the intermediate transfer belt 40, and rotates at the same speed as the intermediate transfer belt. is doing. The squeeze roller 53Y is configured by winding a PFA tube 20 μm around a surface layer of urethane rubber (hardness JIS-A 30 °) having a thickness of 2 mm (outside diameter φ14 mm) on a φ10 mm metal shaft, and has a roller width of 307 mm. A squeeze backup roller 54Y (φ10 mm metal shaft) is disposed opposite to the intermediate transfer belt 40 and is in contact with the intermediate transfer belt at a linear pressure of about 50 gf / cm. The actual resistance value of the roller is about Log4Ω, and a bias voltage of +150 V is applied between the squeeze roller 53Y and the squeeze backup roller 54Y so that the solid content in the developer is not removed. The squeeze roller 54Y is cleaned by contact with a cleaning blade 55Y made of urethane rubber (hardness JIS-A 70 °). With these configurations, the carrier liquid of the liquid developer is squeezed out on the intermediate transfer belt 40 and stored in the developer recovery unit 56Y.

  The image carrier 10Y is a photosensitive drum made of a cylindrical member having a width wider than about 320 mm of the developing roller 20Y and having a photosensitive layer formed on the outer peripheral surface thereof. For example, the image carrier 10Y rotates in a clockwise direction as shown in FIG. To do. The photosensitive layer of the image carrier 10Y is composed of an organic image carrier or an amorphous silicon image carrier. The charging roller 11Y is disposed upstream of the nip portion between the image carrier 10Y and the developing roller 20Y in the rotation direction of the image carrier 10Y, and a bias having the same polarity as the charging polarity of the developing toner particles is applied from a power supply device (not shown). Then, the image carrier 10Y is charged. The exposure unit 12Y irradiates laser light onto the image carrier 10Y charged by the charging roller 11Y on the downstream side in the rotation direction of the image carrier 10Y with respect to the charging roller 11Y, thereby forming a latent image on the image carrier 10Y. To do.

  The developing unit 30Y includes a compression roller 22Y, a developer container 31Y that stores a liquid developer in which toner is dispersed in a carrier liquid in an approximate weight ratio of about 25%, a developing roller 20Y that carries the liquid developer, and a liquid developer. The developer supply roller 32Y, the regulating blade 33Y, the stirring roller 34Y, and the liquid developer carried on the developing roller 20Y for compressing (forming a film) are maintained in a uniform dispersed state by stirring the developer and supplying the developer to the developing roller 20Y. ) A developing roller cleaning blade 21Y for cleaning the compression roller 22Y and the developing roller 20Y.

  The liquid developer accommodated in the developer container 31Y is a low concentration (about 1 to 2 wt%) and low viscosity, which is generally used in the past, using Isopar (trademark: Exxon) as a carrier liquid. It is not a volatile liquid developer having volatility, but a non-volatile liquid developer having a high concentration and high viscosity and having non-volatility at room temperature. That is, in the liquid developer in the present invention, a solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin is introduced into a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. It is a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) which is added together with a dispersant and has a toner solid content concentration of about 25%.

  The developer supply roller 32Y is a cylindrical member that rotates in a clockwise direction as shown in FIG. 3, for example, and is unevenly formed by a spiral groove that is finely and uniformly so as to easily carry the developer on the surface. An anilox roller having a surface formed on the surface. The groove dimensions are such that the groove pitch is about 130 μm and the groove depth is about 30 μm. The developer supply roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. The stirring roller 34Y and the developer supply roller 32Y may be in sliding contact with each other, but may be arranged in a distant relationship.

  The regulating blade 33Y is composed of an elastic blade whose surface is covered with an elastic body, a rubber portion made of urethane rubber or the like that contacts the surface of the developer supply roller 32Y, and a metal plate or the like that supports the rubber portion. The Then, the film thickness and amount of the liquid developer carried and conveyed by the developer supply roller 32Y composed of an anilox roller are regulated and adjusted, and the amount of liquid developer supplied to the developing roller 20Y is adjusted. The rotation direction of the developer supply roller 32Y may be the opposite direction instead of the arrow direction shown in FIG. 3, and the regulating blade 33Y at that time requires an arrangement corresponding to the rotation direction.

  The developing roller 20Y is a cylindrical member having a width of about 320 mm, and rotates counterclockwise around the rotation axis as shown in FIG. The developing roller 20Y is provided with an elastic layer made of polyurethane rubber, silicon rubber, NBR or the like on the outer periphery of an inner core made of metal such as iron. The developing roller cleaning blade 21Y is made of rubber or the like that comes into contact with the surface of the developing roller 20Y. The developing roller 20Y is arranged downstream of the developing nip portion where the developing roller 20Y comes into contact with the image carrier 10Y in the rotation direction of the developing roller 20Y. The liquid developer remaining on the developing roller 20Y is scraped off and removed.

  Returning to FIG. 1, carrier oil is supplied from the carrier cartridges 1Y, 1M, 1C, and 1K to the developer containers 31Y, 31M, 31C, and 31K, and the developer is supplied from the developer cartridges 2Y, 2M, 2C, and 2K, respectively. Is done. On the other hand, the developer (mainly carrier liquid) squeezed by the squeeze rollers 13Y, 13M, 13C and 13K of each color image carrier, and the developer squeezed by the intermediate transfer belt squeeze devices 52Y, 52M, 52C and 52K (mainly The carrier liquid) is conveyed to the filter 5 through the developer conveyance path 3 by a pump action, and is collected by the secondary transfer roller cleaning blade 62 and collected in the developer collecting unit 63 (mainly carrier liquid) or Paper dust is also conveyed to the filter 5 through the developer conveyance path by a pump action. The carrier liquid from which solid content and paper dust are removed by the filter 5 so as not to cause the color mixing phenomenon is pooled in the carrier buffer tank 6 and supplied to the developer containers 31Y, 31M, 31C, and 31K through the carrier conveyance path 4. Yes. Of course, it may be supplied to each carrier cartridge.

  In the present invention, on the side of the belt cleaning backup roller 42 that stretches the intermediate transfer belt 40 together with the belt drive roller 41, a cleaning roller 70 is disposed so as to face the intermediate transfer belt 40 along the outer periphery thereof. . A cleaning blade 71 and a developer recovery container 72 are disposed on the outer periphery of the cleaning roller 70, and a cleaning liquid application member 75 is disposed at a position facing a roller (secondary transfer roller 41 in FIG. 1) that stretches the intermediate transfer belt. Is provided to facilitate removal of the developer (carrier liquid and solid content) adhering to the surface of the intermediate transfer belt, and this embodiment will be described with reference to FIGS.

FIG. 5 is a diagram illustrating a first embodiment in which a sponge roller is used as the cleaning liquid application member 75 and a bias voltage is applied between the cleaning roller 70 and the cleaning backup roller 42.
As described above, the intermediate transfer belt 40 is an endless elastic belt member, and is wound around and stretched between the secondary transfer roller 41 also serving as a driving roller and the cleaning backup roller 42 also serving as a tension roller. Deposits (liquid developer) remaining on the intermediate transfer belt after the secondary transfer are removed from the carrier liquid by each squeeze roller after the primary transfer, and the carrier liquid is absorbed by the transfer medium during the secondary transfer. The rate rises and requires more power for cleaning. Therefore, in the present embodiment, a sponge roller 75 as a cleaning liquid application member is disposed at a position facing the secondary transfer roller 41 so as to easily apply the cleaning liquid, and the liquid is applied on the intermediate transfer belt, A cleaning roller is used without using a cleaning blade so as not to damage the intermediate transfer belt. The liquid to be applied may be any liquid that can lower the solid content such as water and carrier liquid.

  A sponge roller as a liquid application member is formed by winding a urethane sponge (Asker A hardness 40 °) having a thickness of 5 mm (outside diameter φ20 m) around a metal shaft φ10 mm. The sponge roller is the same as the rotational peripheral speed of the intermediate transfer belt 40, and the rotational direction is rotating. However, it is not limited to this. The roller width is 310 mm, and it is lightly in contact with the intermediate transfer belt at a linear pressure of about 50 gf / cm. Further, by setting the sponge roller about 1.2 times faster than the peripheral speed of the belt, the scraping effect by the sponge roller can be obtained, so that cleaning can be facilitated.

  The cleaning roller 70 disposed opposite to the cleaning backup roller 42 with the intermediate transfer belt 40 interposed therebetween has a diameter of 25 mm, and a core metal of 20 mm and urethane rubber having a hardness of JIS-A 30 ° of 2.5 mm is wound around the core metal. The roller has a width of 310 mm. The cleaning roller 70 is driven at the same speed as the intermediate transfer belt 40 in the follower direction. The resistance value of the cleaning roller is, for example, Log 4Ω, and by applying a bias voltage of about 400 V from the power source 73 to the cleaning roller, it is possible to perform good belt cleaning by attracting the charged solid content in the applied liquid. became. In addition, when the surface tension of the intermediate transfer belt surface layer is 20 dyne / cm and the surface tension of urethane on the cleaning roller surface layer is 40 dyne / cm, the adhesion to the cleaning roller is increased from the viewpoint of surface properties, so good cleaning is possible. It became. However, it is not limited to this relationship, and it is not limited to the urethane coat, and may be constituted by a fluorine coat layer or a tube around which a PFA tube is wound.

  The blade 71 for cleaning the cleaning roller 70 has a blade width of 317 mm. The urethane roller 70 is cleaned with a blade having a hardness of JIS-A 90 ° (thickness 2 mm, free length 6.5 mm) with respect to the roller rotation direction. It is made to contact in the counter direction. Since the counter has a high hardness, the cleaning roller can be subjected to blade cleaning. Although the contact angle is not particularly limited, good contact can be obtained when contact is made at 30 ° with a total load of 1 kgf, and the cleaned developer is recovered in the recovery container 72.

FIG. 6 is a diagram showing a second embodiment in which a bias voltage is applied between a sponge roller as a cleaning liquid application member and a secondary transfer roller.
This embodiment is different only in that a bias voltage is applied between the sponge roller and the secondary transfer roller, and the other configuration is the same as that of the first embodiment shown in FIG.
In the second embodiment, a bias voltage is applied to the sponge roller 75 for the purpose of floating the solid content adhering to the intermediate transfer belt 40, and the effect of peeling off the solid content from the intermediate transfer belt is obtained. In this case, it is necessary that the transfer current flows to the secondary transfer backup roller side through which the transfer material (paper) passes. For this reason, in particular, since the resistance of the paper is large, when the resistance value of the sponge roller is Rs and the resistance value of the secondary transfer backup roller is Rt, it is necessary to satisfy Rs> Rt. In this embodiment, Rs = Log6Ω and Rt = Log4Ω.

  In the example of FIGS. 5 and 6, the cleaning liquid application member is disposed to face the secondary transfer backup roller. However, the present invention is not limited to this, and the intermediate transfer belt is stretched. In this case, when a bias voltage is applied to the sponge roller as in the example of FIG. 6, Rs may be Log4Ω to Log8Ω, preferably Log6Ω.

  According to the present invention, since the soft intermediate transfer belt can be cleaned without being destroyed, the industrial utility value is great.

1 is a diagram illustrating an overall configuration of an image forming apparatus of the present invention. FIG. 4 is a diagram illustrating a configuration of an intermediate transfer belt. FIG. 3 is a diagram illustrating main components of an image forming unit and a developing unit. FIG. 6 is a diagram illustrating an intermediate transfer belt squeeze device. It is a figure explaining 1st Embodiment. It is a figure explaining 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 40 ... Intermediate transfer belt, 41 ... Secondary transfer roller, 42 ... Cleaning backup roller, 70 ... Cleaning roller, 71 ... Cleaning blade, 72 ... Collection container, 73 ... Bias power source, 75 ... Sponge roller, 76 ... Bias power source

Claims (3)

An image carrier;
A developing section for developing a liquid developer containing toner and carrier liquid;
The developed image is transferred to the image carrier by the developing unit, and a transfer belt wound around a transfer roller and a tension roller;
A transfer backup roller that contacts the transfer roller via the transfer belt and transfers the image transferred to the transfer belt to a transfer material;
A cleaning liquid application member that contacts the transfer roller via the transfer belt and applies a cleaning liquid;
A bias voltage is applied between the cleaning liquid application member and the transfer roller, the cleaning liquid application member is a roller having a resistance value Rs, and a resistance value Rt of the transfer backup roller;
Rs> Rt
An image forming apparatus having the following relationship: A cleaning roller in contact with the transfer belt;
A cleaning blade that contacts the cleaning roller and cleans the cleaning roller;
The image forming apparatus according to claim 1 , comprising: The image forming apparatus according to claim 1 or 2 cleaning liquid is the carrier liquid.

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