JPH09305039A - Picture forming device, its bias roll and manufacture of the roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture forming device which is capable of obtaining a high quality picture by preventing sheets of paper from being contaminated due to toner transited on a bias roll at the time of non-transfer, etc. SOLUTION: The picture forming device is constituted of an intermediate transfer belt with which a toner image carried on an image carrier is primarily transferred in a secondary transfer part thereof, the bias roll 2 with which a non-fixed toner image on the intermediate transfer belt is secondarily transferred on a recording medium P and a backup roll 3 for supporting the belt from the rear surface of the intermediate transfer belt in a position opposed to the bias roll. the bias roll consists of a core bar 2a, a core layer 2b in which a foamed rubber material such as EPDM and urethane rubber fixed to the outer periphery thereof is used as a constricting component, a skin layer 2c and coating layer 2d in which a material having a small surface energy with a surface roughness of <=15μm and a film thickness of 5 to 30μm is used as a constituting component. The volume resistivity of the bias roll is in the range of 10<4> to 10<7> >cm, and the hardness of the bias roll is in the range of 20 to 45 deg. Asker C.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus using an electrophotographic method, such as a laser printer, a facsimile, and a composite OA device thereof.
More specifically, an image forming apparatus that temporarily transfers a toner image formed on an image carrier to an intermediate transfer belt and then secondarily transfers the toner image onto a recording medium such as paper to obtain a reproduced image. The present invention also relates to a bias roll that secondarily transfers a toner image that is primarily transferred onto a recording medium, and a manufacturing method thereof.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system is a laser in which a uniform charge is formed on an image carrier composed of a photoreceptor made of an inorganic or organic photoconductive material and an image signal is modulated. After forming an electrostatic latent image with light or the like, the electrostatic latent image is developed with charged toner to obtain a visualized toner image. Then, this toner image is transferred to a recording medium such as a paper through an intermediate transfer body or directly to obtain a required reproduced image. In the system that uses the method of primary transfer of the toner image formed on the image carrier to the intermediate transfer body and secondary transfer of the toner image on the intermediate transfer body to the recording medium, a conductive bias roll is used. A bias roll type image forming apparatus is known in which a recording medium is pressed against an intermediate transfer member and a toner image is electrostatically transferred by the action of an electric field. The bias roller transfer method for performing electrostatic transfer while applying a transfer voltage to a conductive bias roll includes a backup roll that receives a pressing force of the bias roll and forms a path for a transfer current.

Conventional examples of image forming apparatuses adopting the above method are disclosed in, for example, Japanese Patent Laid-Open Nos. 6-95521 and 6-124049. FIG. 6 is an explanatory diagram of a secondary transfer portion in the transfer device disclosed in the former publication. In the figure, the intermediate transfer member 01 is stretched by a backup roll 02 and a plurality of support rollers 03, and moves in the arrow direction. Further, in the secondary transfer portion, a bias roll 05 for applying a transfer voltage from the power source 04 to the backup roll 02, and a backup roll 02 pressed and rotated to form a transfer current path based on the transfer voltage. It is equipped with an electrode roll (earth roll) 06. As the bias roll 05, a metal roll made of aluminum is used. When a transfer voltage is applied between the bias roll 05 and the backup roll 02 from the power source 04, the toner image on the intermediate transfer body 01 is transferred onto the paper P. Further, the latter publication discloses an image forming apparatus in which a bias roll (transfer roller) is formed by a cored bar and the next elastic member covering the outer peripheral surface thereof. As the elastic member, an elastic body made of EPDM in which a conductive agent is dispersed and whose volume resistivity is set to 10 ⁷ to 10 ¹⁰ Ωcm, or a PFA tube having a thickness of 50 μm and a volume resistivity of 10 ⁸ to 10 ⁹ Ωcm is coated. An epichlorohydrin rubber having a volume resistivity of 10 ⁸ to 10 ⁹ Ωcm is used.

[0004]

However, Japanese Patent Application Laid-Open No. 6-9552 uses a metal roll as the bias roll.
In the transfer device disclosed in Japanese Unexamined Patent Publication No. 1, the sheet P is pressed against the backup roll 02 by the bias roll 05 via the intermediate transfer member 01, so that the toner image is electrostatically transferred by the action of the electric field. The load of the pressing force by the bias roll 05 is concentrated on the transfer portion. As a result, the toner image is aggregated to increase the charge density, which in turn may cause discharge inside the toner layer to change the polarity of the toner. Due to such factors, the above-described conventional technique has a problem in that an image quality defect occurs in a hollow character in which a line image is missing. As a countermeasure against this problem, the bias roll needs to have a low Asker C hardness of 20 to 45 °. As a method of reducing the hardness of the rubber material,
There are a) a method of blending a rubber material with a low molecular weight component such as a plasticizer, and b) a method of using the rubber material as a foam. But,
The former method a) in which a low-molecular component is blended is not preferable because the low-molecular component exuding from the roll surface adversely affects the image quality as a contaminant.

In the transfer device disclosed in the above-mentioned Japanese Patent Laid-Open No. 6-95521, a sheet of paper P passes through the bias roll 05 and the next sheet of paper P is conveyed to the bias roll 05. There is a problem that the toner remaining on the transfer body 01 is transferred to the bias roll 05, and this causes back stain on the paper P. In order to solve this problem, for example, c) a method of cleaning the bias roll with a cleaning blade or the like, and d) an electric field in the direction in which toner is displaced to the image carrier during non-transfer is applied between the bias roll and the image carrier. A forming method, etc. have been proposed. However, in the method c), when the hardness of the bias roll is relatively low as in the method b), it is difficult to sufficiently exert the scraping action by the cleaning blade. On the other hand, when the bias roll is made of a rubber material having a large friction coefficient such as urethane rubber or EPDM (ethylene propylene diene rubber) disclosed in the above-mentioned JP-A-6-124049, the bias roll is rubbed by a blade. Is not practical because it is damaged or the rotation torque increases. In the method d), the bias roll is pressed into contact with the image carrier to be deformed into a concave shape, so that the adhered toner is pressed by the bias roll and easily aggregates. Therefore, a high electric field is required for sufficient cleaning, which is not preferable.

[0006] As a measure for preventing such back stain on the recording medium, there is a method of coating the foamed rubber body with a fluorine-based resin as described in the above method b). For example, JP-A-6-14
No. 9097 discloses that the surface of a foamed elastic body such as silicone rubber or urethane rubber is partly formed into fine spots by a fluorine resin or a silicone resin for the purpose of preventing contamination of the surface of the photosensitive drum by a bleeding component such as a plasticizer. A transfer roller coated on the same is disclosed. Further, in Japanese Unexamined Patent Publication No. 6-175470, a conductive film layer formed of a soluble fluororesin mixed with a conductive material for the purpose of preventing the development of a mesh image due to non-uniform charging of a charged body under a low humidity environment. Discloses a conductive roll coated with a foamed elastic layer such as EPDM. However, since all of the above-mentioned foamed elastic bodies have large surface roughness due to the unevenness of the foamed cells remaining on the surface, even if the surface is coated with a fluorine-based resin, the scraping action by the cleaning blade can be sufficiently exerted. I can't.

In order to fully exert the scraping action, for example, a roller transfer device having a rubber lining layer coated with a resin having a good releasing property is disclosed in Japanese Patent Laid-Open No. 20897/1992.
No. 3 discloses this. Similarly, there is a method of coating a foamed elastic body with a fluorine-based resin having a small surface energy, for example, the above-mentioned PFA (perfluoroalkyl vinyl ether resin) tube material. For example, the following method is known for coating the rubber roll with this tube material. One method e) is to process a predetermined film material into a tube shape to inflate it by pressurizing a fluid such as air from the inside, insert a rubber roll into the tube material, and then reduce the pressure of the fluid to shrink it. There is a processing method for forming a surface layer by doing so. As another method f), a tube material is stretched on the inner surface of a cylinder-shaped mold and attached in a tube shape, and a liquid rubber material is injected therein, and vulcanized and cured to form a film-covered rubber roll. There is a method of molding.

Since the tube (film) material used in both the above-mentioned processing methods is provided with an elongation of 50 to 200% during processing, the characteristic of the tube material is 50 to 200% in the elastic region. Deformation amount of is required. Within this elongation range, the tube material cannot be made thinner than 50 μm in order to coat the tube material without breaking the tube material. However, when the rubber roll is coated with a tube material thicker than 50 μm, the hardness (Asker C) of the rubber roll increases by about 15 to 20 °. Therefore, there is a problem that a low hardness, Asker C 20 to 45 ° bias roll satisfying the hardness condition for avoiding the occurrence of the hollow character described above cannot be stably obtained.

As described above, in the conventional bias roller transfer method, since the bias roll having both hardness and surface characteristics could not be obtained, the toner transferred to the bias roll at the time of non-transfer was removed and the recording medium of the recording medium was removed. There is a problem in that a good image cannot be obtained because there is no effective means for preventing back stain. (Because the above description "Remove the toner transferred to the bias roll during transfer when not transferring" and "When transferring, etc." below in the original application specification are considered to be incorrect or inaccurate, please refer to " We will remove the toner that has transferred to the bias roll and correct it to "at the time of non-transfer." Thank you for your understanding.) Therefore, the present invention solves the above problems. An image forming apparatus capable of reliably preventing contamination of paper by toner transferred to a bias roll during non-transfer and obtaining a high-quality image, and the bias roll and the same roll. It is to provide a manufacturing method of.

[0010]

Means for Solving the Problems The inventors of the present invention have earnestly studied means for efficiently removing the toner transferred to the bias roll in the bias roller transfer method in which a toner image is secondarily transferred using an intermediate transfer member. When I piled up,
By interposing a skin layer between the surface layer with a small surface energy and the foamed elastic body, it is possible to reduce the hardness of the bias roll and the film thickness and surface roughness of the surface layer to a mutually satisfactory range. Then, the present invention has been completed based on such knowledge. That is, the image forming apparatus of the present invention includes an image carrier on which an electrostatic latent image corresponding to image information is formed, and a developing device which visualizes the electrostatic latent image formed on the image carrier as a toner image with toner. , An intermediate transfer belt on which the toner image carried on the image carrier is primarily transferred, a bias roll for secondarily transferring an unfixed toner image on the intermediate transfer belt to a recording medium, and an intermediate transfer belt facing the bias roll. It is composed of a backup roll that supports from the back side of the bias roll,
The contact angle between the core metal, the core layer composed of the EPDM foamed rubber material or urethane foam rubber fixed to the outer peripheral surface of the core metal, the skin layer, and the water droplet when displayed by the wettability of water is It is composed of a coating layer having a film thickness of 5 to 30 μm, which is composed of a material having a small surface energy of 90 ° or more, and has a resistance per unit area between the core metal and the outer surface of the coating layer of 10 ⁴ to 10 ⁷ Ωcm. And the hardness of the bias roll is in the range of 20 to 45 ° in terms of Asker C hardness. The present invention also includes the above-mentioned bias roll and the manufacturing method thereof.

The image forming apparatus of the present invention further comprises the above-mentioned image carrier, developing device, intermediate transfer belt, bias roll and backup roll. The bias roll is provided on the core metal and the outer peripheral surface of the core metal. A film composed of a material having a small surface energy in which a contact angle between a core layer having a fixed foamed rubber material as a constituent component, a skin layer, and a water droplet when expressed as wettability of water is 90 ° or more. Thickness 5
Consists of a ~30μm coating layer, the resistance per unit area between the metal core and the coating layer outer surface ¹⁰⁴ to
Within the range of 10 ⁷ Ωcm, the surface roughness R of the coating layer
z is 15 μm or less, and the bias roll hardness is in the range of 20 to 45 ° in terms of Asker C hardness. The present invention also includes the above bias roll.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
FIG. 1 is an explanatory diagram of a secondary transfer portion in the image forming apparatus of the present invention. In the figure, a backup roll 3 is arranged at a position facing the bias roll 2 via an intermediate transfer belt 1 carrying an unfixed toner image that has been primarily transferred. To support. An electrode roll 4 for applying a transfer voltage to the bias roll 2 is pressed against the backup roll 3. The bias roll 2 is grounded, and the electrode roll 4 is connected to the power source 5. A cleaning blade 6 made of polyurethane or the like is in contact with the surface of the bias roll 2. As the intermediate transfer belt 1, a belt formed by mixing various resins or rubber materials with an appropriate amount of a conductive agent such as carbon black and molding it to a thickness of 0.05 to 0.15 mm is used, and the surface resistivity thereof is 10 ⁸ to 10 ^{8. 14}
It is adjusted within the range of Ω / □. Examples of various resins include acrylic resin, polyvinyl chloride, polyester, polycarbonate, polyamide, and polyimide.

The bias roll 2 constituting the transfer electrode is
While the toner image carried on the image carrier is primarily transferred onto the intermediate transfer belt 1, the toner image carried on the transfer belt 1 is separated from the transfer belt 1, and the toner image carried on the transfer belt 1 is recorded on a recording medium such as a paper P (hereinafter referred to as a recording medium). , Which is typified by the paper P), is configured to be pressed against the transfer belt 1 and pressed against the backup roll 3. Bias roll 2 above
Is a core layer 2b having a rubber material such as an EPDM foamed rubber material or urethane foam rubber fixed to the outer peripheral surface of the core metal 2a as a constituent component, and a material having a small surface energy as a constituent component via a skin layer 2c. The coating layer 2d has a three-layer structure. In addition, the coating layer 2d
When the surface roughness Rz is less than or equal to a predetermined value described below, the core layer 2b can be made of any foamed rubber material. A conductive agent is dispersed in these layers (2b to 2d) in order to adjust the resistance. Examples of the conductive agent dispersed in each layer include carbon black, graphite, copper,
Metals or alloys such as aluminum, copper alloys, stainless steel (SUS), tin oxide, zinc oxide, titanium oxide, indium oxide, antimony oxide, potassium titanate, SnO
₂ -In ₂ O ₃ composite oxide, fine powder such as SnO ₂ -Sb ₂ O ₅ composite oxide such as conductive metal oxide is used. Among them, carbon black is preferable because it has good dispersibility with rubber materials and various resins.

In the bias roll, the resistance per unit area between the core metal and the outer surface of the coating layer (hereinafter referred to as the volume resistivity of the bias roll) is 10 ⁴ to 10 ⁷ Ωcm.
In the range. If this volume resistivity is lower than 10 ⁴ Ωcm, an air gap may occur between the sheet conveyed during the secondary transfer and the bias roll, in which case discharge occurs. On the other hand, if the volume resistivity is higher than 10 ⁷ Ωcm,
The balance with the resistance of the backup roll is lost, and the transfer latitude that can maintain a high-quality toner image is narrowed. In any case, if the volume resistivity of the bias roll is not within the above range, poor image quality may occur, and the preferable range is 10 ^4.5 to 10 ⁶ Ωcm. The hardness of the bias roll is 20 to 45 ° in Asker C hardness.
(Hereinafter, hardness is represented by Asker C).
That is, when the foamed rubber rolls (2b, 2c) are coated with a thin film of a material having a small surface energy in which a conductive agent is dispersed, it is costly to manufacture a roll having a hardness lower than 20 °. Further, when the hardness is higher than 45 °, the nip pressure between the intermediate transfer belt and the intermediate transfer belt pressed against the paper is increased more than necessary, and the graininess of the image quality is deteriorated.
Occurrence of a hollow character, that is, a line image is missing.

The core metal functions as an electrode and a supporting member of the bias roll, and is made of, for example, a metal or alloy such as aluminum, iron, copper alloy, SUS, chromium,
It is made of a conductive material such as iron or synthetic resin plated with nickel or the like. The outer diameter of the core metal is usually 10 to 20 m
m. As described above, the core layer is made of a conductive agent-dispersed EPDM rubber material or urethane rubber foam. Here, the EPDM rubber material means EPDM alone or a blend rubber with another rubber material containing 50% by weight or more of EPDM. Further, when the surface roughness Rz described later of the coating layer is 15 μm or less, the foamed material is not limited to the above foamed material, and any foamed rubber material can be used. Specific examples thereof include, in addition to the above EPDM and urethane rubber, isoprene rubber, chloroprene rubber, butyl rubber, epichlorohydrin rubber, norbornene rubber, silicone rubber, fluorine rubber, acrylic rubber, SBR (styrene-butadiene rubber), NBR ( Examples thereof include foamed rubber materials such as acrylonitrile-butadiene rubber) and acrylonitrile-butadiene-styrene rubber, and blended materials thereof may be used. Among them, silicone rubber, urethane rubber,
EPDM and the like are preferably used.

The thickness of the core layer is preferably in the range of 4 to 10 mm. Also, the size of the bubbles formed in the core layer varies depending on the type of rubber material, foam molding method, etc.
The average cell diameter is generally adjusted in the range of 40 to 1200 μm. In order to manufacture a bias roll having predetermined hardness and surface characteristics, for example, in the case of EPDM foamed rubber material, the average cell diameter is in the range of 50 to 300 μm,
Further, in the case of foamed urethane rubber, it is preferably in the range of 50 to 1000 μm. Average cell diameter is 40μ
When it is smaller than m, not only a bias roll having stable characteristics cannot be obtained, but also the hardness of the bias roll is 45 °.
Higher. On the other hand, when the average cell diameter is larger than 1200 μm, the internal structure of the bias roll becomes uneven, and the bias roll having stable volume resistivity and hardness cannot be obtained.

The skin layer for covering the surface of the core layer is provided to eliminate the unevenness due to foam cells on the surface of the bias roll and to adjust the hardness of the bias roll within the range of 20 to 45 °. This skin layer is
i) coating and molding a non-foamed rubber material in which a conductive agent is dispersed on the surface of the core layer, ii) coating and adhering the film or tube (hereinafter referred to as a tube) on the surface of the core layer, and
iii) It is formed by molding a dense surface layer at the same time as the core layer when foaming an unfoamed elastic material containing a conductive agent, a foaming agent, etc. The rubber material forming the skin layer is not particularly limited, and the same non-foamed rubber material as the one exemplified as the constituent component of the core layer is used. In particular, it is preferable to use the same rubber material as the foam material of the core layer. In that case, the adhesion between both layers is good, and when the molding method iii) is adopted, the core layer and the skin layer can be molded at the same time.

In order to control the surface roughness and hardness of the bias roll, the thickness of the skin layer is generally 10 μm to.
It is preferably in the range of 1.50 mm. For example, when the foam is an EPDM foam rubber material, the thickness is 10 to 8
In the range of 00 μm, 10 μm for urethane foam rubber
It is preferably in the range of 1.50 mm. In the method of forming the skin layer, when i) the surface of the core layer is coated with the rubber material, it is generally within a range of 0.10 to 1.50 mm,
For example, in the case of an EPDM foamed rubber material, it is 0.20 to 0.8.
0 mm, and 0.20 to 1.5 for urethane foam rubber
The thickness of the skin layer may be adjusted within the range of 0 mm. ii) When adhering the tube material to the surface of the core layer, a tube material having a thickness in the range of 50 to 500 μm is used. iii) When molded simultaneously with the core layer, a skin layer having a thickness in the range of 10 to 200 μm can be easily formed. Further, the surface roughness Rz of the skin layer is 2
It is preferable that the thickness be 0 μm or less. In that case, a coating layer having a surface roughness Rz of 15 μm or less can be easily formed.

The coating layer is made of a material having a small surface energy in which a conductive agent is dispersed. Here, as described above, the “material having a small surface energy” has a contact angle with a water droplet of 90 ° or more when the wettability of water is displayed. The wettability of water is displayed using the material before dispersion of the conductive agent that constitutes the semiconductive coating layer as a test piece, and the contact angle between the plane of the test piece and the water droplet as a scale. More specifically, when water drops are placed on the surface of the test piece, the surface tension γs of the test piece, the interfacial tension γi between the liquid and the test piece, and the surface tension γl of the liquid are balanced, and as shown in FIG. Form the shape of. At this time, if the droplet is small and the influence of gravity can be ignored, the following Young's equation holds. That is, the “material having a small surface energy” in the present invention means a material having the contact angle θ of 90 ° or more. γs = γi + γlcosθ

As a material having a small surface energy, polytetrafluoroethylene (tetrafluoroethylene:
TFE), polyvinylidene fluoride, polychlorotrifluoroethylene, PFA, ethylene-TFE copolymer, TF
E-hexafluoropropylene copolymer (FEP), ethylene-chlorotrifluoroethylene copolymer, TFE
-Fluorine resins such as PFA copolymer and PFA-FEP copolymer, polydimethylsiloxane, polymethylphenylsiloxane, dimethylsiloxane-methylphenylsiloxane copolymer, dimethylsiloxane-methylvinylsiloxane copolymer, dimethylsiloxane- Examples thereof include silicone rubber or resin such as methyltrifluoropropylsiloxane copolymerization. Since these materials have low surface energy, they have a property that toner is difficult to adhere to the surface of the bias roll. Coating layer thickness is 5
˜30 μm. In the secondary transfer section, the bias roll is repeatedly pressed and rotated to the backup roll through the paper and the intermediate transfer belt, and when the film thickness is less than 5 μm, the coating layer is worn and the skin layer is not formed. May be exposed. On the other hand, the film thickness is 3
When it exceeds 0 μm, when the skin layer is coated with the above-mentioned material containing a conductive agent by a coating method, liquid sagging easily occurs on the surface, and it becomes difficult to stably form a smooth and uniform coating film. When the film thickness of the coating layer is within the above range, a bias roll having a hardness within the range of 20 to 45 ° can be stably obtained.

In order to fully exert the scraping action of the cleaning boule, it is desirable that the surface of the bias roll is smooth. In the present invention, the surface roughness Rz of the coating layer is generally adjusted to 15 μm or less. However, the bias roll having the core layer made of the EPDM foam rubber material or the urethane foam rubber does not cause the back stain of the paper due to the incomplete scraping action, so that the surface roughness Rz of the coating layer is not always 15 μm.
It is not necessary to adjust to m or less. Such surface roughness Rz
The coating layer having a can be easily formed by adopting a coating method such as a spray method. According to the coating method, a coating layer having a surface roughness Rz of 15 μm or less is formed by adjusting the film thickness in the range of 15 to 30 μm on the skin layer having a surface roughness Rz of 20 μm or less. Surface roughness Rz of coating layer formed
Is larger than 15 μm, the surface roughness Rz is set to 15 μm by appropriately setting the polishing conditions such as the feed speed of the grindstone, the rotation speed of the bias roll, and the other processing time.
It can be adjusted to m or less. This is the same when the surface roughness Rz of the skin layer is adjusted to 20 μm or less. The surface roughness Rz in the present invention is determined according to JIS B
The value obtained according to the ten-point average roughness according to 0610.

In the bias roll as described above, the resistance per unit area between the core metal and the outer surface of the skin layer (hereinafter referred to as the volume resistivity of the foamed rubber roll) is 10 ⁴ to 1
The volume resistivity of the coating layer is 1 in the range of 0 ⁷ Ωcm.
It is preferable to set in the range of 0 ² to 10 ⁵ Ωcm.
For that purpose, the ratio of the conductive agent mixed in the foamed rubber roll is 5 to 30 wt%, although it depends on the type of the conductive agent.
, The ratio of the conductive agent blended in the coating layer is 1
It is preferably in the range of 0 to 30 wt%. When the blending ratio is out of the above ranges, it is not only difficult to adjust the volume resistivity of the bias roll to the desired range. For example, when the blending ratio exceeds 30 wt%, the hardness of the bias roll is 45%. ° May be higher. By setting the volume resistivity of the foamed rubber roll and the coating layer in the above range, the volume resistivity of the bias roll obtained by synthesizing these resistances is 10 ⁴ to 10 ^{7 above.}
It can be set arbitrarily within the range of Ωcm. Therefore, the foamed rubber roll can have a degree of freedom in volume resistivity.

Backup roll 3 which constitutes the counter electrode
Is a roll in which an appropriate amount of the conductive agent is mixed with an insulating rubber roll such as EPDM, silicone rubber or urethane rubber. The surface resistivity is preferably in the range of 10 ⁸ to 10 ¹⁰ Ω / □, and the hardness is preferably in the range of 58 to 73 °.
The material forming the electrode roll 4 is not particularly limited as long as it is a metal or an alloy having good electrical conductivity, and for example, SUS, copper, aluminum or the like is used. From this electrode roll 4 through the backup roll 3 -2 to-
A transfer voltage of 5 kV is applied to the bias roll 2. When the transfer voltage is lower than 2 kV (absolute value), the strength of the electric field for transferring the unfixed toner image on the intermediate transfer belt 1 onto the paper P is insufficient. On the other hand, if the voltage is higher than 5 kV, the change in surface resistivity of the backup roll 3 becomes large during long-term use, which is not preferable. In the above secondary transfer portion, the electrode roll 4 is not necessarily a necessary member, and for example, a cored bar provided on the backup roll 3 can be used as an electrode member.

The bias roll of the present invention can be manufactured, for example, as follows depending on the difference in the skin layer forming methods i) to iii). i) A method of coating and molding a non-foamed rubber material in which a conductive agent is dispersed on the surface of the core layer. In order to adjust the conductivity and hardness, a conductive agent such as carbon black, a filler such as a metal oxide or a non-metal oxide, and foaming. A foaming rubber compound is prepared by adding agents, vulcanizing agents and the like to a rubber material such as an unfoamed EPDM rubber material or a urethane rubber material. In order to form a foamed elastic body having a predetermined conductivity and hardness, it is important to adjust the amount of foaming agent and foaming conditions. Next, after the kneaded product of the foamed rubber compound is molded by an extruder, it is heated to foam and vulcanize the rubber material to form a tubular foamed elastic body. After that, a core metal is press-fitted and fixed in the cavity of the foamed elastic body, and the surface of the foamed elastic body is polished to form a core layer, if necessary. Next, the core metal is positioned at the center of the mold, and the rubber compound from which the foaming agent has been removed is coated on the outer peripheral surface of the core layer by a tube crosshead extruder, or the outer peripheral surface of the core layer and the inner surface of the mold are covered. After being injected in between, it is vulcanized to form a skin layer on the outer peripheral surface of the core layer. At this time, the thickness of the skin layer is generally 0.10 to 1.50 mm, for example 0.20 when the foam is a foamed EPDM rubber material.
~ 0.80 mm, 0.20 in the case of urethane foam rubber
Molded to ~ 1.50 mm. The rubber material in the rubber compound does not necessarily have to be the same as that of the core layer. The surface roughness Rz of the molded skin layer is 2
When it is larger than 0 μm, it is preferable to carry out polishing if necessary. The same applies to the following methods ii) and iii).

The molded foamed rubber roll is then coated with a dispersion liquid in which a conductive agent such as carbon black is dispersed in a material having a small surface energy on the surface of the skin layer to give a film thickness of 5 to 5.
A 30 μm coating layer is formed. As the above-mentioned dispersion liquid, an aqueous emulsion paint containing a urethane-modified TFE resin (Emuralon 345E: manufactured by Nippon Acheson Co., Ltd.)
Alternatively, a paint containing TFE-PFA copolymer (Belflon: manufactured by NOF CORPORATION) and the like, and carbon black is preferably used. These paints can be applied from room temperature to 150
It is used as a two-part type that crosslinks at a relatively low temperature up to ° C. Further, FEP-based conductive paint (GLS-213R: manufactured by Daikin Industries, Ltd.) is also preferably used. The method for applying the dispersion liquid is not particularly limited, and examples thereof include a brush coating method, a spray method, a dipping method, and a roll coater method. Among them, the spray method is a method in which the dispersion liquid is sprayed from a sprayer while rotating with a core metal having a foamed rubber roll fixed as an axis, and the formation of a coating layer is simple.
Moreover, the film thickness can be easily adjusted. When the surface roughness Rz of the formed coating layer is larger than 15 μm, it is preferable to carry out polishing. In particular, when the core layer is made of a rubber material other than EPDM foam rubber material or urethane foam rubber, the following methods ii) and ii
The same applies to i), but polishing is performed so that the surface roughness Rz is 15 μm or less.

Ii) Method of coating and adhering the tube material of the conductive agent on the surface of the core layer A smooth tube material having a thickness of about 50 to 500 μm is attached to the inner surface of the cylindrical mold. Then, the same foam rubber compound as in the above method i) is injected into the inside of the tube material and then foamed and vulcanized to form a core layer, and at the same time, the core layer and the tube material are bonded. When the adhesion between the tube material to be the skin layer and the core layer is poor, it is preferable to apply an adhesive in advance to the inner surface of the tube material. After that, the coating layer is formed in the same manner as the method i). iii) Method of molding a skin layer at the same time as a core layer at the time of molding an unfoamed rubber compound A foamed rubber compound is prepared in the same manner as in the above method i), and the kneaded product is extruded by an extruder and sent to a crosshead. Wrap around the outer circumference of gold. Next, the cored bar is supported on a mold to heat the foamed rubber compound, and the foamed elastic body is fixed to the cored bar to form a core layer, and at the same time, the inner surface of the mold has a thickness of 10 to 200 μm. To form a dense skin layer. After that, the coating layer is formed in the same manner as the method i). Furthermore, instead of the coating method, after coating the skin layer on the core layer molded as described above or on the foam rubber roll,
The above-mentioned methods e) and f) for coating a tube material having a small surface energy may be adopted.

The operation of the present invention is as follows. In addition,
The numbers in parentheses correspond to the components of the numbers given in FIG. The electrostatic latent image formed on the image carrier (19) according to the image information is developed by the toner in the developing device (21),
It is visualized as an unfixed toner image. This toner image is
In the primary transfer part while being carried by the image carrier (19),
The image is transferred onto the intermediate transfer belt 1. When transferring a multicolor image, primary transfer is repeated for each color of the toner contained in the developing device (21). When the primary transfer of the toner image from the image carrier (19) onto the intermediate transfer belt 1 is completed and the intermediate transfer belt 1 carrying the toner image of a desired hue moves to the secondary transfer portion, The paper P is conveyed to the secondary transfer portion in synchronism with the above. At this time, the bias roll 2 is in pressure contact with the transfer belt 1 whose back side is supported by the backup roll 3. Then, when the sheet P passes through the secondary transfer portion while receiving the pressure contact force between the bias roll 2 and the backup roll 3, for example, a transfer voltage having the same polarity as the charging polarity of the toner image is applied from the electrode roll 4. By
The toner image carried on the transfer belt 1 is secondarily transferred onto the sheet P from the surface of the intermediate transfer belt 1.

According to the image forming apparatus of the first aspect and the bias roll of the fifth aspect, the bias roll 2 is used.
Has a three-layer structure in which a core layer 2b having a foamed rubber material as a constituent component, a skin layer 2c, and a coating layer 2d having a material having a small surface energy as a constituent component are sequentially laminated on the outer peripheral surface of a core metal 2a. Therefore, the surface of the bias roll 2 is coated with a material having a small surface energy without any unevenness due to the foam cells, so that the toner transferred to the bias roll 2 at the time of non-transfer is easily cleaned by the cleaning member such as the cleaning blade 6. Can be removed. The thickness of the coating layer 2d is 5 to 3
Since it is in the range of 0 μm, the roll hardness required as a transfer roll can be stably obtained in the range of 20 to 45 °. Therefore, in a state where the bias roll 2 is pressed against the intermediate transfer belt 1 via the paper P, the bias roll 2 is electrostatically transferred by the action of the electric field in the secondary transfer portion.
Since the load of the pressing force due to is not concentrated, the image quality defect of the hollow character in which the line image is lost does not occur. Moreover, since the volume resistivity of the bias roll 2 is in the range of 10 ⁴ to 10 ⁷ Ωcm, an appropriate transfer electric field is generated in the secondary transfer portion that transfers the unfixed toner image on the intermediate transfer belt 1 onto the paper P. A good quality transferred image is obtained by the action.

According to the image forming apparatus of the second aspect of the present invention, the volume resistance of the foamed rubber rolls (2b, 2c) is adjusted so that the volume resistivity of the bias roll 2 necessary for forming the above-mentioned transferred image of good quality can be obtained. The resistivity is set in the range of 10 ⁴ to 10 ⁷ Ωcm, and the volume resistivity of the coating layer 2d is set to the range of 10 ² to 10 ⁵ Ωcm, which is lower than that of the foamed rubber roll. Therefore, compared with the variation in the volume resistivity of the core layer 2b, the foam rubber roll and the coating layer 2 are
The variation (standard deviation value) of the volume resistivity 10 ⁴ to 10 ⁷ Ωcm of the bias roll 2 obtained by combining the resistances of d can be further reduced.

According to the image forming apparatus of the third aspect, E
The average cell diameter of the core layer 2b having a PDM-based foamed rubber material as a constituent is in the range of 50 to 300 μm, and the thickness of the skin layer 2c having an EPDM-based rubber material as a constituent is 10 to 10.
It is in the range of 800 μm, the resin component of the coating layer 2d is a fluorine resin, and carbon black is dispersed as a conductive agent in each layer (2b to 2d). Therefore, in combination with setting the film thickness of the coating layer 2d in the range of 5 to 30 μm, the hardness of the bias roll 2 as a transfer roll can be obtained more stably in the range of 20 to 45 °. . Moreover, the bias roll 2 is made of an inexpensive material. According to the image forming apparatus of the fourth aspect, the core layer 2 containing urethane foam rubber as a constituent component.
The average cell diameter of b is in the range of 50 to 1000 μm, and the thickness of the skin layer 2c containing urethane rubber as a constituent is 10
coating layer 2d in the range of μm to 1.50 mm
The resin component is a fluorine-based resin, and carbon black is dispersed as a conductive agent in each layer (2b to 2d). Therefore, similarly to the third aspect of the invention, the hardness of the bias roll 2 can be obtained more stably in the range of 20 to 45 °.

According to the method of manufacturing a bias roll for an image forming apparatus of the present invention, carbon black-dispersed EP is used.
Each of DM-based rubber materials is extrusion-molded to form a foamed core layer 2b and a non-foamed skin layer 2c, and then a carbon black-dispersed fluorine-based resin liquid is applied to the surface of the skin layer 2c to form a coating layer 2d. To form. Therefore, the hardness of the bias roll 2 can be stably obtained within the above range. Further, the thickness of the skin layer 2c is 0.20 to
It can be formed uniformly and surely within the range of 0.80 mm, and the thickness of the coating layer 2d can be easily adjusted by applying the fluororesin solution. Claim 7
According to the method of manufacturing a bias roll for an image forming apparatus of the present invention, a core layer is formed by foaming a urethane rubber material in which carbon black is dispersed, and then a liquid urethane in which carbon black is dispersed between the surface of the core layer and the inner surface of the mold. After injecting a rubber material and heating it to form a skin layer, a carbon black-dispersed fluorine resin solution is applied to the surface of the skin layer 2c to form a coating layer 2d. Therefore,
As in the sixth aspect of the invention, the hardness of the bias roll 2 is stably obtained within the above range. Further, the thickness of the skin layer 2c can be uniformly and surely formed within the range of 0.20 to 1.50 mm, and the thickness of the coating layer 2d can be easily adjusted by applying the fluororesin solution. You can

An image forming apparatus according to an eighth aspect of the invention and a bias roll according to the tenth aspect of the invention are characterized in that, in the first aspect and the fifth aspect of the invention, the core layer 2b comprises various foamed rubber materials as constituent components, and the coating layer further comprises The surface roughness Rz is limited to 15 μm or less. Therefore, the same operation as that of the first and fifth aspects of the invention is achieved. Moreover, since the surface of the bias roll 2 is smooth, the toner transferred to the bias roll 2 during non-transfer can be reliably removed by a cleaning member such as the cleaning blade 6. According to the image forming apparatus of the present invention, when the coating layer 2d having a film thickness of 15 to 30 μm is formed on the skin layer 2c having a surface roughness Rz of 20 μm or less, for example, by a coating method, the surface roughness is reduced. A bias roll 2 having a Rz of 15 μm or less is obtained. Such surface roughness Rz is determined by the core layer 2b and the skin layer 2
It can be obtained without being affected by the material of c. Therefore,
The ninth aspect of the invention has the same effect as the eighth aspect of the invention.

[0033]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples. (Image Forming Apparatus) FIG. 3 is an overall view of a digital color copying machine provided with an intermediate transfer belt as the image forming apparatus of the present invention. In FIG. 3, light emitted from an original illumination lamp 12 that moves along the lower surface of an original (not shown) placed on a platen 11 and reflected by the original is moved mirror unit 13, lens 14, fixed mirror. The image is converged on the CCD of the image reading unit via 15. The CCD converts the original image into an electric signal for each color by using a large number of photoelectric conversion elements and filters of three colors of red (R), green (G) and blue (B). This electric signal is input to the image processing circuit 16,
The image processing circuit 16 has an image memory that converts a document image reading signal input for each color into a digital signal and stores it.

The optical writing control device 17 reads out the image data of the image processing circuit 16 at a predetermined timing and outputs it to the light beam writing device 18. Light beam writing device 18
Writes an electrostatic latent image corresponding to each of the above colors on the image carrier 19 composed of a photosensitive drum that rotates in the direction of arrow A. Around the image carrier 19, a charging charger 20 for uniformly charging the surface of the image carrier 19, a developing unit 21 for developing the electrostatic latent image written on the image carrier 19 into a toner image of each color, and a developing unit 21 for each color. A transfer corotron 22 for primarily transferring the toner image onto the intermediate transfer belt 1, a cleaner unit 23 having a charge eliminator and a cleaning blade are arranged. The developing unit 21 includes black (K), yellow (Y), magenta
(M) and cyan (C) are provided with developing units containing toners of the respective colors, and the electrostatic latent images are developed and visualized with the toners of the respective colors. The intermediate transfer belt 1 includes a backup roll 3 and a belt transport roll 2 which the electrode roll 4 presses against.
It is stretched over 4, 25 and 26 and moves in the tangential direction while contacting the surface of the image carrier 19. In this embodiment, of the rolls (3, 24-26) that stretch the transfer belt 1, the belt transport roll 24 is used as a drive roll and the other rolls (3, 24-26) are set so that the transfer belt 1 moves in the direction of arrow B. , 25, 2
6) is configured as a driven roll. In order to prevent the transfer belt 1 from bending, the belt transport roll 26
Axis is biased in direction C by a spring (not shown).

On the back side of the intermediate transfer belt 1, the transfer corotron 22 is arranged in a primary transfer portion where the image carrier 19 and the surface of the transfer belt 1 are in contact with each other. On the other hand, on the front surface side of the transfer belt 1 carrying the unfixed toner image, facing the backup roll 3 and the belt transport roll 24,
Bias roll 2 and belt cleaner 2 respectively
7 are arranged. A portion where the bias roll 2 and the backup roll 3 face each other serves as a secondary transfer portion. Also,
Between the backup roll 3 and the belt transport roll 24, a peeling claw 28 for peeling the paper P carrying the secondary-transferred toner image from the transfer belt 1 is arranged. A cleaning blade 6 made of urethane rubber is always in contact with the surface of the bias roll 2 to remove foreign matter such as toner particles and paper powder attached at the time of secondary transfer.

An extractable paper feed tray 29 is provided in the lower portion of the main body of the image forming apparatus U, and a pickup roller 30 is arranged above it. This pickup roller 3
A pair of feed rolls 31 for preventing double feeding of the paper P, a paper transport roll 32, a guide member 33 for guiding the paper P, and a registration roll 34 are sequentially arranged on the downstream side of 0. On the downstream side of the secondary transfer section, a transport belt 3 for transporting a sheet P carrying a secondary-transferred toner image sequentially
5, a fixing device 36 for fixing the unfixed toner image on the paper P, a pair of discharge rolls 37 for discharging the paper P on which the fixed image is formed, and a paper discharge for mounting the discharged paper P A tray 38 is arranged.

(Operation of Image Forming Apparatus) The surface of the image carrier 19 rotating in the direction of arrow A is uniformly charged by the charging charger 20. This uniformly charged image carrier 1
An electrostatic latent image 9 is written by the light beam writing device 18. The electrostatic latent image on the image carrier 19 is developed by the developing unit 21 into an unfixed toner image. In the formation of this toner image, the toner image of the first color is first formed, and thereafter, every time the image carrier 19 makes one rotation, the toner images of the second color to the fourth color are formed. In this embodiment, K, Y, M, C
Color toner images are sequentially formed. The surface of the image carrier 19 is cleaned by the blade of the cleaner unit 23 after the toner image is transferred to the intermediate transfer belt 1. Here, the optical writing control device 17
Then, first, the K color digital signal of the first color is read and output to the light beam writing device 18. The writing device 18 writes an electrostatic latent image corresponding to K color on the surface of the image carrier 19. The electrostatic latent image corresponding to K color is developed into a visualized toner image of K color by the developing device K in the developing unit 21.
Move to the primary transfer part. In the primary transfer portion, the transfer corotron 22 arranged on the back surface side of the intermediate transfer belt 1 applies an electric field having a polarity opposite to the charging polarity of the toner image to the toner image of K color reaching the primary transfer portion. While being electrostatically attracted to the intermediate transfer belt 1, the primary transfer is performed by the movement of the intermediate transfer belt 1 in the arrow B direction.

The intermediate transfer belt 1 moves in the same cycle as the image carrier 19 while adsorbing and carrying the K toner image. When the transfer of the K toner image of the first color is completed, the output of the optical writing control device 17 outputs the Y color of the second color until the transfer start position of the K toner image on the transfer belt 1 reaches the primary transfer portion.
Writing of the electrostatic latent image of color is started. When the transfer start position of the transfer belt 1 carrying the K toner image reaches the primary transfer portion, the transfer corotron 22 transfers the Y toner image of the second color. Then, the transfer of the M toner image and the C toner image is performed in the same manner as the transfer of the Y toner image. In this way, a multiple toner image superimposed on each color is formed on the intermediate transfer belt 1. Until the toner image of each color is primarily transferred onto the intermediate transfer belt 1,
The bias roll 2, the peeling claw 28, and the belt cleaner 27 arranged on the front surface side of the transfer belt 1 are held at a retracted position separated from the intermediate transfer belt 1.

On the other hand, the paper P stored in the paper feed tray 29
Are taken out one by one by a pickup roller 30 at a predetermined timing, and fed by a pair of feed rolls 31 and a paper transport roll 32, and a pair of registration rolls 3
The operation is temporarily stopped at step 4. The paper P is secondarily transferred from the registration roll 34 in synchronization with the multi-toner image of each color (K, Y, M, C) transferred onto the intermediate transfer belt 1 thereafter to the secondary transfer portion. Transported to the department. In the secondary transfer portion, the bias roll 2 is in pressure contact with the backup roll 3 via the transfer belt 1. Then, the conveyed paper P passes through the secondary transfer portion by the pressure contact conveyance between the rolls 2 and 3 and the movement of the transfer belt 1. At this time, the toner image adsorbed and carried on the transfer belt 1 is secondarily transferred from the surface of the intermediate transfer belt 1 onto the sheet P by electrostatic repulsion due to application of a transfer voltage having the same polarity as the charging polarity of the toner image from the electrode roll 4. Transcribed. When the bias roll 2 is pressed against the backup roll 3, the bias roll 2
Foreign particles such as toner particles attached to the surface are removed by the cleaning blade 6.

Although the transfer of the full-color image has been described above, in the case of forming a monochromatic image, the intermediate transfer belt 1 is used.
When, for example, a K-color toner image primary-transferred above moves to the secondary transfer section, the toner image is immediately transferred to the paper P. In the case of forming an image of a plurality of colors, the desired hue is selected, and when the multicolor toner image superimposed on those colors moves to the secondary transfer section, the toner image may be transferred to the paper P. . In the case of this multicolor image transfer, as described above, the rotation of the image carrier 19 and the movement of the intermediate transfer belt 1 are synchronized with each other so that the toner images of the respective colors accurately coincide with each other at the primary transfer portion. There is. As described above, the sheet P on which the toner image has been transferred in a desired hue is peeled by the operation of the peeling claw 28, is placed on the conveyance belt 35, and is conveyed to the fixing device 36. Then, in the fixing device 36, the unfixed toner image is fixed and fixed to the permanent image, and then the paper P is ejected to the paper ejection tray 38 by the pair of paper ejection rolls 37. When the secondary transfer is completed, the intermediate transfer belt 1
The surface of the sheet is cleaned by a belt cleaner 27 provided downstream of the secondary transfer portion to prepare for the next transfer.

(Secondary Transfer Member) The specific structure of the secondary transfer member in the image forming apparatus shown in FIG. 3 is as follows. As the intermediate transfer belt (1), polyimide having a thickness of 80 μm and a surface resistivity of 10 ¹² Ω / □ was used. As the bias roll (2), as shown in "Production of Bias Roll" below, SUS core metal (2a) having an outer diameter of 15 mm
On top, core layer (2b), skin layer (2c), coating layer
(2d) is laminated in sequence, length 325mm, outer diameter 28mm
Rolls were used. As the backup roll (3), a conductive silicone rubber molded to a thickness of 6.5 mm was used. Its hardness was 62 ° and its surface resistivity was 10 ⁹ Ω / □. The outer diameter of the backup roll (3) is 28 mm which is the same as that of the bias roll (2). A metal roll made of SUS having a diameter of 12 mm was used as the electrode roll (4).

(Production of Bias Roll) The bias roll shown in the examples was produced as follows. In addition, the following "parts" means "parts by weight" relative to 100 parts by weight of the rubber material. Example 1 A rubber material containing 1.5 wt% of sulfur as a vulcanizing agent and 0.6 wt% of tetramethylthiuram disulfide as a vulcanization accelerator (EPDM EP33: manufactured by Nippon Synthetic Rubber Co., Ltd.)
100 parts, 14 parts of Ketjen Black (manufactured by Lion Agzo Co., Ltd.) as a conductive agent, and FT carbon (Asahi Carbon
A foamed rubber compound having a composition ratio of 20 parts (manufactured by K.K. Co., Ltd.), 6 parts of p, p'-oxy-bis (benzenesulfonylhydrazide) as a foaming agent and 6 parts of mineral oil as a softening agent was kneaded by a kneader and roll kneading. This kneaded material was extruded into a tube shape by an extruder and heated in a vulcanizer at a temperature of 126 ° C. and a pressure of 1.5 kg / cm ² G under pressurized steam to foam and vulcanize. A SUS core metal (2a) having an outer diameter of 15 mm was press-fitted into the cavity of the obtained elastic foam, and the surface of the elastic foam was polished to form a core layer (2b) having an outer diameter of 28 mm.

Then, NBR and EPDM are mixed in a weight ratio of 4: 4.
Rubber material blended with 6 (NE40; Japan Synthetic Rubber)
10 parts of Ketjen black and 25 parts of FT carbon were added to 100 parts of K.K. and kneaded. The kneaded product was coated on the outer peripheral surface of the core layer (2b) by a tube crosshead extruder. At this time, the outer diameter of the core layer contracted to 27.5 mm due to the pressurization of the tube material. This tube material is placed in a vulcanizer at a temperature of 127 ° C and a pressure of 1.5.
It was heated under a pressurized steam of 5 kg / cm ² G to be vulcanized and adhered to the core layer. Then, the surface of the roll was ground and dimensioned, and the outer diameter of the foamed rubber roll (2b, 2c) having the skin layer (2c) adhered to the outer peripheral surface of the core layer was set to 28 mm. Further, an aqueous emulsion paint of urethane-modified TFE resin containing carbon black (Emullon 345E) was applied on the surface of the skin layer (2c) by a spray method, and then heated and cured at 100 ° C. for 35 minutes to give a film thickness of 1
A 5 μm coating layer (2d) was formed. Thus, the bias roll (2) having a three-layer structure was manufactured. In this bias roll, most of the cell diameter in the core layer is 5
The hardness was in the range of 0 to 300 μm, and the hardnesses of the foamed rubber roll and the bias roll were 36 ° and 40 °, respectively. The volume resistivities of the foamed rubber roll, coating layer and bias roll are 10 ^5.78 Ωcm and 1 respectively.
It was 0 ^4.55 Ωcm and 10 Ω ^5.32 cm.

Example 2 A kneaded product obtained by mixing a foaming agent with an elastic material having a composition ratio of 100 parts of polyether urethane and 15 parts of carbon black was extruded into a tube shape by an extruding machine and heated. It was foamed and vulcanized to form a foamed elastic body. A SUS core metal (2a) having an outer diameter of 15 mm coated with a hot-melt adhesive was press-fitted into the cavity of the foamed elastic body, and this was heat-bonded, and then the surface of the foamed elastic body was polished to a hardness of 13 °. To form a core layer (2b) having an outer diameter of 25.5 mm. A urethane elastic body material similar to the above elastic body material except that the formed core layer is positioned concentrically in a mold having an inner diameter of 28 mm and a foaming agent is removed between the outer peripheral surface of the core layer and the inner surface of the mold. Injected. Next, the inside of the mold was heated to 160 ° C. for vulcanization, and the elastic material was fixed to the outer peripheral surface of the core layer. After that, the surface of the molded foamed rubber roll was polished to form a skin layer (2c) having a surface roughness Rz of 20 μm and a thickness of 1.25 mm. Further, a coating layer (2d) was formed in the same manner as in Example 1 above. At this time, the surface roughness Rz of the coating layer (2d) was 15 μm. In this way, a three-layer bias roll
(2) was produced. In this bias roll (2), most of the cell diameters in the core layer were in the range of 0.2 to 1.0 mm, and the foamed rubber roll and the bias roll had hardnesses of 30 ° and 36 °, respectively. The volume resistivity of the foamed rubber roll, coating layer and bias roll is 10 ^5.46 Ωcm, 10 ^4.55 Ωcm and 10 ^5.18 Ω, respectively.
It was cm.

(Secondary Transfer Test of Bias Roll) The image forming apparatus shown in FIG. 3 equipped with the bias rolls of Examples 1 and 2 was operated to evaluate the transfer image quality and the dirt on the back surface of the paper, and further to the bias roll. Cleaning blade
(6) The load torque due to the load was measured. The results are shown in Table 1 below. Further, as Comparative Examples 1 to 4, in place of the bias roll of the above example, 1) a bias in which a 50 μm-thick PFA tube was directly coated on a core layer made of foamed silicone rubber with a rubber material without forming a skin layer. Roll, 2) Bias roll in which the rubber material of the core layer and the skin layer that are not covered with the coating layer are made of silicone rubber, 3) Bias roll consisting only of the core layer of foamed silicone rubber, and 4) Foamed EPDM
Each of the vice rolls consisting of the core layer was used for the above test. Table 1 shows the results. The "dirt on the back surface of the paper" in Table 1 was evaluated by the number of rotations of the vice roll required for removing the toner.

[0046]

[Table 1] Transfer image quality ○: No image quality defect occurred ×: Image quality defect occurred −: Not evaluated, stain on the back side of the paper ○: 1 time △: 2 to 4 times ×: 5 times or more

In Comparative Example 1 in which the hardness of the bias roll is higher than 45 °, an image quality defect such as a hollow character of the transfer image quality occurred, and the transfer image quality became poor. Example 1,
As is clear from 2 and Comparative Example 1, by coating the surface of the bias roll with a material having a small surface energy, the adhesive force of the toner to the bias roll is reduced,
Since the scraping action of the cleaning blade can be fully exerted, the back surface of the paper is not stained. Further, in Comparative Example 2 in which the skin layer was not covered with the coating layer and the skin layer was the surface layer, the toner attached to the vice roll could not be sufficiently removed by one rotation. On the other hand, in Comparative Examples 3 and 4 in which foamed silicone rubber and foamed EPDM were used as the bias roll, since the friction coefficient of the foamed rubber was large, the load torque due to the cleaning blade was as large as 0.11 Nm. As a result, in the image forming apparatus shown in FIG. 3, the intermediate transfer belt slipped by the drive roller (belt transport roll 24) and did not rotate.

(Volume Resistivity of Bias Roll) FIG. 4 shows a method for measuring the volume resistivity of the foamed rubber roll and the bias roll. The measuring method of each roll is 3
24.5mm width (w) at several places (central part, both ends 50mm)
Wrap the copper tape in the circumferential direction of the roll, apply a voltage (V) of 20 V between the core metal of the roll and the copper tape, and read the current value (I) 10 seconds after the application of the voltage, The volume resistivity ρv (Ωcm) was calculated by the following formula. ρv = 2πwV / I · ln (r ₂ / r ₁ ) where r ₁ : outer diameter of core metal (15 mm) r ₂ : outer diameter of roll (28 mm)

Tables 2 and 3 show roll hardness and roll outer diameter in addition to the volume resistivity (log ρv) of the foamed rubber roll before and after coating with the coating layer, which was measured according to the measuring method shown in FIG. The volume resistivity of each roll shown in Examples and Comparative Examples of the present invention is obtained according to the above measuring method. The standard deviation values shown in the table, which represent variations in the roll resistance, were measured for each of 10 rolls at 3 locations in the axial direction of the roll shown in FIG. It was determined by the resistivity. As shown in Tables 2 and 3 below, it can be seen that the variation in the volume resistivity is small due to the coating of the coating layer of the foamed rubber roll, and the variation in roll hardness is also small due to the coating.

[0050]

[Table 2]

[Table 3]

Example 3 Two foamed silicone rubber compounds prepared by blending 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, a foaming agent, and silica into a silicone rubber containing 15% by weight of carbon black. Kneaded with rolls. This kneaded product was pressed into an SUS cored bar (2a) having an outer diameter of 15 mm by an extruder to be molded, and then heated at 230 ° C. for 3 hours in a mold to foam and vulcanize the core layer (b). ) And skin layer
(2c) was simultaneously molded. The surface of the molded foamed rubber roll having an outer diameter of 28 mm was polished to form a skin layer (2c) having a surface roughness Rz of 12 μm and a thickness of 100 μm. Further, a FEP-based conductive coating material (GLS-213R) containing 20 wt% of carbon black was applied to the surface of the skin layer (2c) by a spray method, and then heated and cured at 210 ° C. for 10 minutes to form a coating having a film thickness of 15 μm. Layer (2d) was formed. Surface roughness R of coating layer (2d) at this time
z was 9 μm. In the thus-produced bias roll (2) having a three-layer structure, the average cell diameter in the core layer was 100 μm, and the hardness was 35 °. Also,
The volume resistivity of foam rubber rolls (2b, 2c) is 10 ^5.3 Ω
cm, and the coating layer (2d) has a volume resistivity of 10
^{It is 2.1} Ωcm, and the volume resistivity of the bias roll (2) is 1
It was 0 ^4.6 Ωcm.

Example 4 A bias roll (2) was produced in the same manner as in Example 3 except that the skin layer (2c) was polished so that the surface roughness Rz was 17 μm. The surface roughness Rz of the surface of the obtained bias roll (2), that is, the coating layer (2d) is 1
It was 2 μm. Example 5 A bias roll (2) was produced in the same manner as in Example 3 except that the skin layer (2c) was polished so that the surface roughness Rz was 20 μm. Formed coating layer (2d)
The surface roughness Rz was 15 μm.

Comparative Example 5 The skin layer (2c) was ground to a surface roughness Rz of 22 μm, and the coating layer (2d) was formed to a film thickness of 10 μm.
A bias roll (2) having a hardness of 33 ° was manufactured in the same manner as in Example 3 except that the bias roll (2) was formed. At this time, the surface roughness Rz of the coating layer (2d) was 18 μm. Comparative Example 6 A bias roll (2) was produced in the same manner as in Example 3 except that the skin layer (2c) was polished so that the surface roughness Rz was 26 μm. Formed coating layer (2d)
The surface roughness Rz was 22 μm.

With respect to the bias rolls of Examples 3 to 5 and Comparative Examples 5 and 6, the transfer image quality and the stain on the back surface of the paper were evaluated. The evaluation criteria are the same as in the case of the "bias roll secondary transfer test". The results are shown in Table 4 below. Table 4 shows the surface roughness (Rz) of the skin layer and the film thickness and surface roughness (Rz) of the coating layer. The physical properties of each bias roll are all the same as those shown in Example 3 except for the above surface roughness and the hardness of Comparative Example 5.

[Table 4]

The thickness of the coating layer is 10 μm, 15 μ
The surface roughness (Rz) of the coating layer formed when the surface roughness (Rz) of the skin layer was changed in the bias rolls formed to m, 20 μm, 25 μm and 30 μm.
z) is shown in FIG. These bias rolls were manufactured according to the method described in Example 3 above. In FIG. 5, the thickness of the coating layer is 10 μm: ●, 15
μm: ○, 20 μm: ■, 25 μm: □, 30 μm: ▲
It is indicated by the reference symbol. As is clear from FIG. 5, the surface roughness of the skin layer is adjusted to 20 μm or less and the film thickness is adjusted to 15 to 3
When the coating layer is formed in the range of 0 μm, a bias roll having a surface roughness of 15 μm or less can be stably manufactured. Since such a bias roll is made of a material having a smooth surface and a small surface energy, the back surface of the paper is not contaminated with the toner during the secondary transfer, as shown in Table 4.

[0056]

According to the image forming apparatus and the bias roll of the present invention, the EPDM foamed rubber material or the core layer having urethane urethane rubber as a constituent component is formed on the outer peripheral surface of the cored bar with a small surface energy. It has a three-layer structure covered with a coating layer as a constituent. Alternatively,
The core layer fixed to the outer peripheral surface of the core metal is composed of a foamed rubber material, and the coating layer formed through the skin layer is composed of a material having a surface roughness of 15 μm or less and a small surface energy, and has a three-layer structure. . Therefore, since the surface of the bias roll is smooth without any unevenness due to the foamed cells, the toner hardly adheres, and even if the toner adheres, it can be easily removed by a cleaning blade or the like.
Further, since the thickness of the surface coating layer is in the range of 5 to 30 μm, a low-hardness bias roll can be stably obtained, so that the image quality of a hollow character in which a line image is hollow is not generated. , High quality transfer image can be obtained. According to the method for manufacturing a bias roll for an image forming apparatus of the present invention, a bias roll can be stably obtained within a hardness range of 20 to 45 °, and a skin layer having a uniform thickness can be reliably formed. Also, the thickness of the coating layer can be easily adjusted.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a secondary transfer unit in an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram of a contact angle that is a measure of surface energy.

FIG. 3 is an overall view of an image forming apparatus shown as an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a method for measuring the volume resistivity of a foamed rubber roll and a bias roll.

FIG. 5 is a graph showing the relationship between the surface roughness of the skin layer and the surface roughness of the coating layer in the bias roll due to the difference in the film thickness of the coating layer.

FIG. 6 is an explanatory diagram of a secondary transfer unit in a conventional image forming apparatus.

[Explanation of symbols]

U ... Image forming apparatus, P ... Paper (recording medium), 1 ... Intermediate transfer belt, 2 ... Bias roll, 2a ... Core metal, 2b ... Core layer, 2c ... Skin layer, 2d ... Coating layer, 3 ... Backup roll, 19 ... Image carrier, 21 ... Developing unit (developing device).

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[Procedure amendment]

[Submission date] March 27, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

In order to fully exert the scraping action, for example, a roller transfer device having a rubber lining layer coated with a resin having a good releasing property is disclosed in Japanese Patent Laid-Open No. 20897/1992.
No. 3 discloses this. Similarly, a fluorine-based resin having a small surface energy, such as PFA ( tetrafluor
Polyethylene- perfluoroalkyl vinyl ether copolymer
(Coalescence ) There is a method of coating a foamed elastic material with a tube material. For example, the following method is known for coating the rubber roll with this tube material. One method e)
Is processed into a tube shape from a predetermined film material and inflated by pressurizing a fluid such as air from the inside, and after inserting a rubber roll into it, the pressure of the fluid is reduced to cause the surface to contract. There is a processing method for forming a layer. As another method f), a tube material is stretched on the inner surface of a cylinder-shaped mold and attached in a tube shape, and a liquid rubber material is injected therein, and vulcanized and cured to form a film-covered rubber roll. There is a method of molding.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

As described above, in the conventional bias roller transfer method, since the bias roll having both hardness and surface characteristics could not be obtained, the toner transferred to the bias roll at the time of non-transfer was removed and the recording medium of the recording medium was removed. There is a problem in that a good image cannot be obtained because there is no effective means for preventing back stain. Therefore, the present invention is intended to solve the above-mentioned problems, and it is possible to reliably prevent the contamination of the paper by the toner transferred to the bias roll during non-transfer and obtain a high-quality image. An object of the present invention is to provide a possible image forming apparatus, a bias roll for the image forming apparatus, and a method for manufacturing the same.

[Procedure 3]

[Document name to be amended] Statement

[Correction item name] 0053

[Correction method] Change

[Correction contents]

Comparative Example 5 The skin layer (2c) was polished so that the surface roughness Rz was 22 μm, and the coating layer (2d) had a film thickness of 10 μm.
The hardness is 33 in the same manner as in Example 3 except that the hardness is 33 μm.
A bias roll (2) of ° was manufactured. At this time, the surface roughness Rz of the coating layer (2d) was 18 μm. Comparative Example 6 A bias roll (2) was produced in the same manner as in Example 3 except that the skin layer (2c) was polished so that the surface roughness Rz was 26 μm. Formed coating layer (2d)
The surface roughness Rz was 22 μm.

Claims (10)

[Claims] 1. An image carrier on which an electrostatic latent image is formed according to image information, a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner, and an image carrier. An intermediate transfer belt to which the carried toner image is primarily transferred, a bias roll that secondarily transfers the unfixed toner image on the intermediate transfer belt to a recording medium, and the intermediate transfer belt is supported from the back side of the bias roll so as to face the bias roll. The bias roll comprises a cored bar, a core layer having EPDM foamed rubber material or urethane foam rubber fixed to the outer peripheral surface of the cored bar as a constituent component, a skin layer, and a water layer. A coating layer having a film thickness of 5 to 30 μm, which is composed of a material having a small surface energy having a contact angle with a water drop of 90 ° or more when expressed as wettability, and a core metal and a coating. Resistance per unit area between the outer surface is in the range of 10 ⁴ ~10 ⁷ Ωcm, and an image forming apparatus hardness of the bias roll is being in the range of 20 to 45 ° in Asker C hardness. 2. The bias roll according to claim 1, wherein the resistance per unit area between the cored bar and the outer surface of the skin layer is in the range of 10 ⁴ to 10 ⁷ Ωcm, and the volume resistivity of the coating layer is An image forming apparatus in the range of 10 ² to 10 ⁵ Ωcm. 3. The bias roll according to claim 1, wherein the core layer is made of the EPDM foamed rubber material in which carbon black is dispersed and has an average cell diameter of 50 to 300 μm, and the skin layer is formed in a thickness in which carbon black is dispersed. 10
An image forming apparatus made of an EPDM rubber material having a thickness of up to 800 μm, and a coating layer made of a fluorine resin in which carbon black is dispersed. 4. The bias roll according to claim 1, wherein the core layer is made of the urethane foam rubber having an average cell diameter of 50 to 1000 μm in which carbon black is dispersed,
The skin layer has a thickness of 10 μm in which carbon black is dispersed.
An image forming apparatus made of urethane rubber having a thickness of up to 1.50 mm, and a coating layer made of a fluororesin in which carbon black is dispersed. 5. A cored bar and an EP fixed to the outer peripheral surface of the cored bar
A material having a small surface energy, in which the contact angle between the core layer and the skin layer, each of which is a DM foam rubber material or urethane foam rubber, is 90 ° or more when the wettability of water is expressed. And a coating layer having a film thickness of 5 to 30 μm, the resistance per unit area between the core metal and the outer surface of the coating layer is in the range of 10 ⁴ to 10 ⁷ Ωcm, and the hardness is 20 in Asker C hardness. A bias roll for an image forming apparatus, which is in the range of up to 45 °. 6. A core fixed to the outer periphery of a core metal by extruding an EPDM rubber material containing at least carbon black and a foaming agent on the outer periphery of the core metal, heating this to foam and further vulcanizing it. After forming the layer, an EPDM rubber material containing at least carbon black is extruded and then heated to form a thickness of 0.20 to 0.80.
6. The method for producing a bias roll according to claim 5, wherein the core layer is coated with a skin layer having a thickness of mm, and a fluororesin in which carbon black is dispersed is applied to the surface of the skin layer for coating. 7. A core layer formed by foaming a urethane rubber material containing at least carbon black and a foaming agent in a mold centered on a core metal to form a core layer, and then fixed to the outer peripheral surface of the core metal. Is placed in the mold and a liquid urethane rubber material containing at least carbon black is injected between the core layer surface and the mold inner surface, and the urethane rubber material is heated to a thickness of 0.20 to 1 6. The method for manufacturing a bias roll according to claim 5, wherein a skin layer having a thickness of 0.50 mm is formed, and a fluororesin in which carbon black is dispersed is applied to the surface of the skin layer for coating. 8. An image carrier on which an electrostatic latent image is formed according to image information, a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner, and an image carrier. An intermediate transfer belt to which the carried toner image is primarily transferred, a bias roll that secondarily transfers the unfixed toner image on the intermediate transfer belt to a recording medium, and the intermediate transfer belt is supported from the back side of the bias roll so as to face the bias roll. When the bias roll is indicated by a core metal, a core layer having a foam rubber material fixed to the outer peripheral surface of the core metal as a constituent component, a skin layer, and water wettability. Of a coating layer having a film thickness of 5 to 30 μm, which is composed of a material having a small contact energy with a water droplet of 90 ° or less and a small surface energy, and the resistance per unit area between the core metal and the outer surface of the coating layer. There is in the range of 10 ⁴ to 10 ⁷ [Omega] cm, the surface roughness Rz of the coating layer is at 15μm or less, and 2 hardness bias roll Asker C hardness
An image forming apparatus having a range of 0 to 45 °. 9. The image forming apparatus according to claim 8, wherein the skin layer has a surface roughness Rz of 20 μm or less, and the coating layer has a thickness of 15 to 30 μm. 10. A contact angle between a core metal, a core layer composed of a foamed rubber material fixed to an outer peripheral surface of the core metal as a constituent component, a skin layer, and a water droplet when expressed as wettability of water is 90. A coating layer having a film thickness of 5 to 30 μm, which is composed of a material having a small surface energy of not less than 0 ° and having a resistance per unit area between the core metal and the outer surface of the coating layer of 10
^A bias roll for an image forming apparatus, characterized in that it is in the range of ⁴ to 10 ⁷ Ωcm, the surface roughness Rz of the coating layer is 15 μm or less, and the hardness is in the range of 20 to 45 ° in terms of Asker C hardness.