JP2012083672A - Conductive roller used for electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive roller for an electrophotographic device and a method for manufacturing the roller, which has a surface layer having low surface roughness and high releasing property for a toner, includes an elastic layer having low hardness so as to easily obtain a nip with another member, and has excellent durability against friction by an external member such as a blade.SOLUTION: The conductive roller includes at least a rubber layer, an elastic layer and a surface layer successively formed on an outer circumference of a shaft core. The surface layer has a surface roughness of 2.5 μm or less in terms of Rzjis. The elastic layer contains a filler, in which the specific gravity of the filler is twice or more as the specific gravity of the elastic layer material constituting the elastic layer. The filler is unevenly present in a surface side of the elastic layer.

Description

  The present invention relates to a conductive roller used in an image forming apparatus using an electrophotographic system such as a digital printing machine, a copying machine, a printer, and a facsimile machine. Specifically, a charging roller for uniformly charging the photosensitive member, a developing roller for attaching toner to the electrostatic latent image formed on the photosensitive member, a toner image on the electrostatic latent image such as paper The present invention relates to a conductive roller for an electrophotographic apparatus such as a transfer roller for transferring to a recording material and a cleaning roller for removing residual toner and carrier.

Conventionally, in an electrophotographic apparatus, various kinds of conductive rollers as described above exhibiting a conductive or semiconductive region electric resistance of about 10 ³ to 10 ¹¹ in volume resistance have been used. For these conductive rollers, for the purpose of preventing contamination with toner or the like, it is adopted to reduce the surface roughness or to coat the surface with a releasable material.

  In general, in order to reduce the surface roughness of the conductive roller, a method of reducing the roughness of the rubber surface by surface polishing or the like has been proposed (for example, Patent Document 1).

  However, precision polishing of the rubber surface has a problem that it requires a lot of man-hours and a long time, and there is a limit that can reduce the surface roughness. In addition, the lower the roller rubber hardness, the harder it is to reduce the surface roughness by polishing.

  In addition, there is a technique in which a surface layer made of urethane resin or fluororesin is formed on the rubber surface of the conductive roller by coating such as spray or dip coating to improve releasability from toner. However, since such a resin material for coating is harder than rubber, the flexibility of the rubber roller is sacrificed and the roller nip width cannot be sufficiently obtained. Further, when the hardness of the resin material forming the surface layer is lowered, the flexibility as a rubber roller is not hindered, but the friction coefficient on the roller surface is increased.

  Patent Document 2 proposes a conductive roller in which fine particles are blended into a surface layer material to provide irregularities to reduce the friction coefficient, but has a disadvantage that the surface roughness becomes rough due to the irregularities. .

  Further, in Patent Document 3, there is a method in which the surface layer is made of a thermoplastic resin, and the conductive roller molded body is pressed against the mirror body heated to the softening temperature of the thermoplastic resin to reduce the surface roughness. Proposed. However, in this method, the thickness of the surface layer must be set to a certain extent, and it becomes difficult to obtain an appropriate nip width. In addition, since heat is applied from the surface of the conductive roller, a resin that softens at a temperature lower than the heat resistant temperature of the rubber that constitutes the roller must be selected as the surface layer material, and there are restrictions in selecting the material.

  The problem of the surface roughness is particularly remarkable in a wet electrophotographic apparatus using liquid toner. Liquid toner has a particle size that is a fraction of that of dry toner. To prevent toner from entering the surface of the conductive roller, the surface roughness of the roller is preferably less than the toner particle size. . On the coating surface that is formed by spray coating, etc., some of the irregularities derived from the droplets when leaving the droplets leave marks on the painted surface, so there is a limit to smoothness and the surface roughness must be sufficiently small. As a result, it is not suitable for use for wet electrophotography.

  On the other hand, when a release material is used as a surface layer, for example, in a transfer roller, the purpose is to prevent image dropout during primary transfer, and the ability to follow irregularities of recording materials such as paper during secondary transfer. For the purpose of increasing the thickness, it is desirable that the structure has a surface layer having a very thin thickness and high releasability, and the base rubber hardness is low. However, in the conventional technique, it is very difficult to reduce the surface roughness of the conductive roller by making the surface layer thin and the rubber hardness low.

  In addition, the transfer roller and developing roller receive external force from printing media such as paper, or other sliding members that contact the surface of other rubber rollers, metal rollers, cleaning blades, etc. However, there is a problem that stress applied to the conductive roller is concentrated on the surface layer of the thin film, causing cracking or peeling of the surface layer.

  Thus, it has been impossible to make a conductive roller having a thin surface layer with excellent durability against external friction while maintaining a high-quality image.

JP 2007-86318 Japanese Patent Laid-Open No. 2001-100549 Japanese Patent Laid-Open No. 2003-131460

  An object of the present invention is to have a surface layer having a small surface roughness and a high releasability from the toner, an elastic layer having a low hardness so that a nip can be easily obtained from other members, a blade, etc. It is an object of the present invention to provide a conductive roller for an electrophotographic apparatus having excellent durability against friction from the outside and a manufacturing method thereof.

  As a result of intensive studies to solve the above problems, the present inventors have formed a tube-shaped article consisting of two layers of a surface layer and an elastic layer by centrifugal molding using a cylindrical mold, A method of manufacturing a conductive roller for an electrophotographic apparatus by coating a roller main body (a core body coated with a rubber layer) has been adopted. By this method, the state of the inner surface of the cylindrical mold is transferred to the surface of the surface layer. Therefore, if a mold having a mirror surface on the inner surface is used, the surface layer can be made into a mirror surface. Also, by setting the hardness of the elastic layer formed on the inside of the surface layer to be low, when the resulting conductive roller is used as a transfer roller, it prevents the image from being lost and follows the irregularities on the surface of the recording material. It was possible to improve the performance. Furthermore, an electrophotographic apparatus having excellent durability against external friction and the like while maintaining a high-quality image by adding a filler with a high specific gravity in the elastic layer and unevenly distributing the filler to the surface layer side in the elastic layer A conductive roller was obtained.

  Based on this knowledge, further research is being conducted to realize the optimal balance by realizing the surface releasability, surface smoothness, surface layer friction durability, elastic layer hardness that makes it easy to obtain a nip, etc., required for conductive rollers. Repeatedly, the present invention has been completed.

  That is, the present invention provides the following conductive roller.

  Item 1 A conductive roller comprising at least a rubber layer, an elastic layer, and a surface layer in order on the outer periphery of the shaft core body, wherein the surface layer has a surface roughness of Rzjis of 2.5 μm or less, and the elastic layer Includes a filler, the specific gravity of the filler is twice or more the specific gravity of the elastic layer material constituting the elastic layer, and the filler is unevenly distributed on the surface side of the elastic layer. roller.

  Item 2 The conductive roller according to Item 1, wherein the surface layer has a thickness of 10 μm or less.

  Item 3. The conductive roller according to Item 1 or 2, wherein the surface layer contains a fluororesin.

  Item 4. The conductive roller according to any one of Items 1 to 3, wherein the elastic layer contains a cured product of liquid urethane rubber.

Item 5. A method of manufacturing a conductive roller,
(1) A process of producing a rubber roller body by vulcanizing and molding a rubber composition on a shaft core;
(2) A step of forming a surface layer by injecting a material containing a fluororesin into the inner surface of a cylindrical mold having a surface roughness of 2 μm Rzjis or less, and performing centrifugal molding.
(3) A step of injecting an elastic layer material containing a filler into the inner surface of the surface layer obtained in (2) above, centrifugally forming the elastic layer to produce a bilayer membrane (coating layer tube), Here, the specific gravity of the filler is not less than twice the specific gravity of the elastic layer material, and (4) the outer surface of the rubber roller body obtained in the above (1) and the two-layer film obtained in the above (3) A step of superposing and heating the inner surface of the elastic layer of the (coating layer tube),
Manufacturing method.

  The conductive roller of the present invention can realize all of surface releasability, surface smoothness, low hardness of the elastic layer, and surface layer friction durability. Since these effects are generally in a trade-off relationship, they cannot be realized with conventional conductive rollers.

  Therefore, the conductive roller of the present invention can be suitably used for a transfer roller, a developing roller, a charging roller, a cleaning roller, etc. used in an image forming apparatus using an electrophotographic system.

It is a cross-sectional schematic diagram of the tube covering electroconductive roller of this invention. It is a schematic diagram of the apparatus used for film forming of each layer which comprises the covering tube in an Example. The mass concentration measurement location of the filler in the elastic layer in the electroconductive roller of this invention is shown.

1: Surface layer 2: Elastic layer 3: Coating layer Tube 4: Rubber layer 5: Core metal (shaft core)
6: Location of surface layer and elastic layer 7: Driving roller A: 10% of elastic layer thickness from interface between surface layer and elastic layer toward rubber layer side B: Near central region of elastic layer thickness ( 10% area in the middle of the elastic layer thickness)
C: 10% of the elastic layer thickness from the interface between the rubber layer and the elastic layer toward the surface layer side

Hereinafter, embodiments of the electroconductive roller for an electrophotographic apparatus (particularly, a transfer roller) of the present invention will be described.
I. Molding of Roller Body The roller body of the present invention means a rubber roller before covering a tube-shaped molded article composed of at least two layers of a surface layer and an elastic layer, which will be described later, and the outer side of the core metal part (shaft core body) 5 A rubber part 4 is provided around the base (see FIG. 1).

  As a material of the core metal (shaft core body), for example, a conductive shaft made of SUS (stainless steel), an aluminum alloy, steel with rust prevention such as electroless nickel plating, or a conductive pipe is used. be able to. In particular, in the case of a large transfer roller having a diameter exceeding φ100 mm, it is preferable to use an aluminum alloy pipe in order to reduce the weight. As the material of the aluminum alloy, A6063, A5056, and the like are typically employed from the viewpoint of availability and cost.

  Examples of rubber (base rubber) forming the roller body include acrylonitrile butadiene rubber (NBR), epichlorohydrin rubber, urethane rubber, and the like. Of these, NBR and epichlorohydrin rubber are preferable.

  The NBR is a copolymer of acrylonitrile and butadiene, and includes one containing a carboxyl group, one partially crosslinked, one blended with vinyl chloride, and the like. Specific NBR grades include, for example, Nipol DN003, 1041L, 1031, 1001, DN101L, DN103, DN115, 1042AL, 1052J, PB5501NF, PB5502NF, VN1000 (manufactured by Nippon Zeon Co., Ltd.), JSR N215L, N222L, Examples include N222SH, N220S, N230SL, N230S, N230SH, N520, N640H, and PN30A (above, manufactured by JSR Corporation).

  The epichlorohydrin rubber is, for example, a copolymer of epichlorohydrin and an alkylene oxide such as ethylene oxide or propylene oxide; a ternary copolymer containing allyl glycidyl ether having an unsaturated bond as a third component in addition to the above components. A homopolymer of epichlorohydrin; and a copolymer of epichlorohydrin and allyl glycidyl ether. Specific grades of this epichlorohydrin rubber include epichromer H, C, D, CG, CG-102, CG-104, CG-105, CG-107, CG-109 (above, manufactured by Daiso Corporation), Zecron 1000. , 1100, 2000, 3100, 3101, 3102 (manufactured by Nippon Zeon Co., Ltd.).

  As the rubber forming the roller body, epichlorohydrin rubber or NBR may be used alone, or a blend of two or more kinds of epichlorohydrin rubbers or epichlorohydrin rubber and the like for the purpose of adjusting electric resistance, vulcanization speed, etc. A blend with NBR may be used, and another type of rubber such as styrene butadiene rubber (SBR) or ethylene-propylene-diene rubber (EPDM) may be blended as necessary.

  For the vulcanization of the rubber composition forming the roller body, a normal sulfur vulcanization system can be applied as long as the rubber has an unsaturated bond. The sulfur used for the sulfur vulcanization is usually added in an amount of about 0 to 5 parts by weight with respect to 100 parts by weight of the base rubber. As this sulfur, the recovered sulfur is pulverized into fine powder. This includes, for example, Jinhua stamp fine powder sulfur 150 mesh, 200 mesh, 300 mesh (above, manufactured by Tsurumi Chemical Co., Ltd.).

  In sulfur vulcanization, a vulcanization accelerator can be added to improve vulcanizate properties, particularly compression set and processing stability. The addition amount of the vulcanization accelerator is usually about 0.5 to 10 parts by weight, preferably about 1 to 3 parts by weight with respect to 100 parts by weight of the base rubber. Examples thereof include thiazoles, thioureas, thylliums, dithiocarbamates and guanidines. As the vulcanization accelerator, one or more of these (about 2 to 6 types) can be used.

  Examples of thiazoles include 2-mercaptobenzothiazole such as Accel M (trade name, manufactured by Kawaguchi Chemical Co., Ltd.), and examples of thioureas include diethylthiourea such as Accel EUR (manufactured by Kawaguchi Chemical Industry Co., Ltd.). Are tetramethylthiuram disulfide such as Accel TMT (manufactured by Kawaguchi Chemical Co., Ltd.), dithiocarbamates such as zinc dimethyldithiocarbamate such as Accel PZ (manufactured by Kawaguchi Chemical Co., Ltd.), and guanidines such as Examples thereof include diphenylguanidine such as Accel D (manufactured by Kawaguchi Chemical Co., Ltd.).

  The rubber composition forming the roller body can be filled with about 0 to 30 parts by weight of a softening agent with respect to 100 parts by weight of the base rubber. As a result, the composition can be made to have a relatively low hardness, assist in mixing and dispersion of the compounding agent in the composition, facilitate the molding operation such as extrusion, and increase the adhesiveness of the unvulcanized rubber. It can be made easier. Specific examples of the softener include paraffinic oil, naphthenic oil, aromatic oil, phthalic acid derivative, isophthalic acid derivative, adipic acid derivative, and phosphoric acid derivative.

  Examples of the softener for paraffinic oil include Diana Process Oil PW-32 and PW-90, and examples of a softener for naphthenic oil include Diana Process Oil NS-24, NS-100, NM-26, and NF-90. Examples of the aromatic oil softener include Diana Process Oil AC-460, AE-24, AH-58 (all of which are manufactured by Idemitsu Kosan Co., Ltd.).

  Usually, one or two kinds of softeners are appropriately used, and if necessary, different kinds of oils may be added together so as to blend naphthenic oil and paraffinic oil. In addition, considering the abrasiveness of the surface of the rubber layer when used as a roller, black sub, white sub, cocoon sub, golden factis, neo factis, sulfur-free factis (above, product name manufactured by Tenma Sub Chemical Co., Ltd.) Such sub (factis) can also be used in an amount of about 5 to 50 parts by weight per 100 parts by weight of the base rubber.

  A reinforcing agent such as carbon black or a silica-based filler can be added to the rubber composition forming the roller body of the present invention. The added amount is usually about 0 to 80 parts by weight, preferably 0 to 80 parts by weight with respect to 100 parts by weight of the base rubber so that the rubber kneadability is good and the composition has low hardness. About 40 parts by weight of a reinforcing agent can be added.

  As carbon black, for example, SAF carbon (average particle size 18-22 μm) such as Asahi # 90 (manufactured by Asahi Carbon Co., Ltd.), Seast 9 (manufactured by Tokai Carbon Co., Ltd.), Dia Black-A (manufactured by Mitsubishi Chemical), ISAF carbon (average particle size 19-29 μm) such as Asahi # 80 (Asahi Carbon Co., Ltd.), Show Black N220 (Showa Cabot Co., Ltd.), Seest 6 (Tokai Carbon Co., Ltd.), Asahi # 70 (Asahi Carbon) Co., Ltd.), Seast S (Tokai Carbon Co., Ltd.), Dia Black-H (Mitsubishi Chemical Co., Ltd.) and other HAF carbon (26-30 μm), Asahi 60H (Asahi Carbon Co., Ltd.), Seast 116 (Tokai) (Manufactured by Carbon Co., Ltd.), Dia Black N550M (manufactured by Mitsubishi Chemical Corporation), etc. 5 μm), Asahi # 60, # 60 U (above, manufactured by Asahi Carbon Co., Ltd.), Seest SO, FM (above, manufactured by Tokai Carbon Co., Ltd.), Dia Black-E, EY (above, manufactured by Mitsubishi Chemical Corporation), etc. FEF carbon (average particle size 40-52 μm), Asahi # 50, # 50U, # 51 (above, manufactured by Asahi Carbon Co., Ltd.), Seast S (manufactured by Tokai Carbon Co., Ltd.), Dia Black R (manufactured by Mitsubishi Chemical Corporation) SRF carbon (average particle size of 58 to 94 μm) and the like are exemplified.

  Examples of the silica-based filler include dry silica such as Aerosil 200, 300, 380, R972 (manufactured by Nippon Aerosil Co., Ltd.) and Leolosil QS13, QS30, QS38, QS102 (manufactured by Tokuyama Co., Ltd.), Carplex #. 67, # 80, # 100, 22S, CS-5 (above, manufactured by Shionogi Pharmaceutical Co., Ltd.), Shilton A (manufactured by Mizusawa Chemical Industry Co., Ltd.), Toxeal AL-1 (manufactured by Tokuyama Co., Ltd.), NipSeal NA (Nippon Silica) Examples thereof include wet silica such as (manufactured by Co., Ltd.).

  In addition, activated calcium carbonate such as white gloss flower CC, DD, O, U (manufactured by Shiraishi Kogyo Co., Ltd.), special calcium carbonate such as white gloss flower A, (manufactured by Shiroishi Kogyo Co., Ltd.), Mythron Paper ) Magnesium silicate, Hytron, Microlite, Hilac SS (made by Takehara Chemical Industry Co., Ltd.), Wiener Clay A (Hard Clay: Kawamo Co., Ltd.), Hard Top Clay, Soft Clay Clay (aluminum silicate) such as crown clay (Shiraishi Calcium Co., Ltd.), silane modified clay such as ST-100, ST-200, ST-301 (Shiraishi Calcium Co., Ltd.) You may use together.

  Further, if necessary, an increase filler of about 5 to 100 parts by weight with respect to 100 parts by weight of the base rubber may be added for the purpose of dimensional stability and low cost. Light fillers such as Green Ball (manufactured by Inoue Lime Industry Co., Ltd.), Tama Pearl TP-121 (manufactured by Okutama Kogyo Co., Ltd.) and Silver W (manufactured by Shiroishi Kogyo Co., Ltd.), Whitelon SSB (Shiraishi Co., Ltd.) Heavy calcium carbonate such as Calcium Co., Ltd., Sunlite # 100 (Takehara Chemical Co., Ltd.), NS # 100 (Nitto Flour Chemical Co., Ltd.) and Super S (Maruo Calcium Co., Ltd.), JET- S (manufactured by Asada Milling Co., Ltd.), talc GTA, CTA1, CTA2, fine talc (manufactured by Kunimine Kogyo Co., Ltd.), MS, MS-P, MS-A, SS, S (manufactured by Nihon Talc Co., Ltd.) Talc (talc) such as zinc oxide, zinc oxide 2 types (manufactured by Sakai Chemical Industry Co., Ltd.), aluminum sulfate, barium sulfate, calcium sulfate , Titanium oxide, molybdenum disulfide and the like, and usually one to several types are used together with the reinforcing filler.

  In addition, the rubber of the roller body when applied to a transfer roller or the like is provided with a conductivity imparting agent, for example, carbon black, zinc oxide, tin oxide, titanium oxide, or the like as necessary for providing semiconductivity. Depending on the type, generally 0.5 to 30 parts by weight of the conductive material and ion conductive materials such as various metal ion salts, quaternary ammonium salts and lithium ion-based salts with respect to 100 parts by weight of the base rubber A degree can be appropriately added.

  Further, if necessary, about 0.3 to 5 parts by weight of a lubricant or an internal mold release agent can be added to 100 parts by weight of the base rubber in order to improve rubber kneadability and extrudability. Usually 0.5 to 1 part by weight can be added to such an extent that blooms, bleeds and poor fusion are not caused.

  Examples of the lubricant and internal mold release agent include low molecular weight polyethylene such as Mitsui High Wax 100P (manufactured by Mitsui Petrochemical Co., Ltd.), stearic acid such as FA-KR (manufactured by Nippon Oil & Fats Co., Ltd.), and plastrozine (Fujisawa Pharmaceutical Co., Ltd.). Fatty acid amides such as Armowax EBS (manufactured by Lion Akzo), sorbitan monolaurate (lauric acid sorbitan ester) such as Rheodor SP-L10 (manufactured by Kao Corporation), Struktol WB222 Examples include polyhydric alcohol fatty acid esters such as (Sill & Seillacher (Germany)), silicone oils such as KF96 (manufactured by Shin-Etsu Chemical Co., Ltd.), paraffin wax, and montan wax.

In blending the rubber composition, it is preferable to prioritize the aim of volume resistivity and rubber hardness as the rubber physical properties after vulcanization. That is, the volume resistivity of the vulcanized rubber is usually about 10 ³ to 10 ¹² Ω · cm, preferably 10 from the viewpoint of assisting the delivery of toner by electrical control as a material constituting the main body of the conductive roller. It is adjusted to about ⁵ to 10 ¹⁰ Ω · cm. The hardness of the vulcanized rubber is usually 80% or less, preferably 40 ° to 60 °, type A hardness (JIS K6253), considering that the flexibility of the surface of the conductive roller by the coated elastic tube described later is not impaired. It is preferable that

  The roller body is manufactured by coating the rubber composition on a metal core (shaft core body) and vulcanization molding. The molding method is not particularly defined, and various conventionally known methods can be used. For example, the rubber composition kneaded product is preformed into a pipe shape with a single screw extruder, the preformed product is vulcanized at 160 ° C. for 20 to 80 minutes, and then a metal core (shaft core body) is inserted. After bonding and polishing the surface, the roller body can be obtained by cutting to the required dimensions. Of course, if the trumpet-like rebound shape at the end of the roller at the time of cutting is a concern, it may be polished after cutting. The vulcanization time may be determined by determining the optimum vulcanization time using a vulcanization test rheometer (eg, curast meter). Further, the vulcanization temperature may be determined by raising or lowering the temperature as necessary. In order to reduce the photoreceptor contamination and compression set, it is preferable to set the conditions so that a sufficient vulcanization amount can be obtained.

  The diameter of a roller main body is 30-350 mm normally, Preferably it is 80-300 mm. When the size of the roller body is large, for example, when the diameter exceeds 100 mm, an extruder that can extrude the rubber kneaded product is rare, so the above method cannot be adopted, but the rubber kneaded material is dispensed into a sheet. It is only necessary to wrap around the outer periphery of the cored bar (shaft core body) coated with an adhesive and compression-mold it with a two-part mold. The roller body is then obtained in the same way.

II. Formation of Coating Layer 1 (Surface Layer) The surface layer in the conductive roller of the present invention comprises This is a layer formed on the outer side of the coating layer (tube) covering the roller body. It is a layer that becomes the surface of the finished conductive roller, and greatly affects the function as a roller. For example, in the case of a transfer roller, it is a layer for directly transferring toners of four colors (yellow, cyan, magenta, black) or more and superimposing and transferring the toners onto paper. In the case of the developing roller, the toner roller is a layer for transferring the toner from the surface of the roller called smoothing roller, which smoothes the toner, to the surface of the photosensitive member.

  The material for the surface layer is preferably a material containing a fluororesin from the viewpoint of facilitating release of the toner. Examples of such fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether (PFA), tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride copolymer (THV), and polyvinylidene fluoride. Ride (PVdF), a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer), or a mixture thereof. In addition, as for the copolymer of VDF and HFP, the ratio of HFP is preferable about 1-15 mol%.

  Of the fluororesin materials, polytetrafluoroethylene (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether (PFA) may be insufficiently adhered to the rubber constituting the elastic layer. In this case, urethane resin or acrylic resin may be used as the binder. Specifically, a coating material in which polytetrafluoroethylene (PTFE) or tetrafluoroethylene / perfluoroalkyl vinyl ether (PFA) is dispersed in these binders is used. Examples include Emuralon 345 ESD, JYL-601 ESD (Henkel Technologies Japan Co., Ltd.).

  On the other hand, a copolymer of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride (THV), polyvinylidene fluoride (PVdF), a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP) When a copolymer) or a mixture thereof is selected, since the inherent surface energy is relatively large, adhesion to rubber is relatively easy by using a primer or the like and can be used without a binder.

  Further, a fine powder of polytetrafluoroethylene (PTFE) may be added to these materials. In this case, the powder may be directly dispersed in a raw material solution to be described later, or a dispersion previously diluted with a solvent or the like may be used, and the polytetrafluoroethylene fine particle powder relative to the weight of the fluororesin raw material in the raw material solution The body can be added in an amount of not more than 20% by weight, preferably not more than 10% by weight.

The volume resistivity of the surface layer is usually 10 ¹³ Ω · cm or more, more preferably 10 ¹³ to 10 ¹⁵ Ω · cm. In addition, it is possible to control the semiconductivity by adding a conductive agent such as carbon black, but since the effect is limited and uniform dispersion is difficult, the surface layer does not contain a conductive agent. May be. Since the surface layer is not affected by the change in the environment (temperature, humidity, etc.), stable primary and secondary transfer of the toner is possible, and high image quality can be realized.

  The thickness of the surface layer is usually less than 10 μm, preferably 1 to 8 μm, and more preferably 2 to 7 μm. Within this range, the rubber elasticity effect of the elastic layer is suitably expressed while maintaining the durability of the surface layer.

  The static friction coefficient of the surface layer is preferably low in view of releasability, but it is preferable to provide a lower limit value from the viewpoint of ensuring cleaning properties, preventing the cleaning blade from squeaking, and preventing blade breakage. Therefore, the static friction coefficient is preferably 0.1 to 0.8, more preferably 0.15 to 0.5, and particularly preferably 0.2 to 0.4.

  Further, when considering the transfer roller, the surface layer is preferably flexible. This is because the effect of enveloping the toner can be expected, and the transfer efficiency of the primary transfer image, such as prevention of voids, can be improved. Specifically, the surface layer has a Rockwell hardness on an R scale according to JIS K7202 and is usually 100 degrees or less, preferably 80 degrees or less, particularly 40 to 80 degrees.

  The film formation of the surface layer will be described below by taking as an example the case of centrifugal molding of a fluororesin.

  First, the weight of the material is adjusted so that the finished surface layer has a desired thickness (for example, between 2 and 7 μm). The weighed surface layer material is dissolved in a solvent to obtain a liquid raw material, which is cast on the inner surface of a cylindrical mold and centrifuged. Solvents used include water; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as N, N-dimethylformamide and N, N-dimethylacetamide; Alternatively, a mixed solvent thereof or the like is used. The liquid raw material may have a solid content concentration of about 2 to 30% by weight.

  Centrifugal molding of the surface layer can be performed as follows using, for example, a cylindrical mold. The cylindrical mold has a mirror inner surface, specifically, a surface roughness of 2 μm Rzjis or less, preferably 1 μm Rzjis or less, more preferably 0.5 μm Rzjis or less, and the inner surface state of this mold is the outer surface of the surface layer of the conductive roller. Is transcribed. In addition, the inner surface of the mold can be blasted for the purpose of adjusting the roller surface layer so as to have uniform desired irregularities. In that case, it is preferable that the surface after the blasting process has the same roughness of 2 μm Rzjis or less. When the upper limit of the surface roughness of the inner surface of the mold is set to 2 μm Rzjis or less, the surface roughness of the roller surface layer can be reduced to 2.5 μm Rzjis or less. Can be transported. The roughness of the inner surface of the mold can be arbitrarily controlled by the count of the blast media used when the inner surface unevenness is imparted.

  Furthermore, it is preferable to apply a release agent to the inner surface of the cylindrical mold so that the film after curing of the raw material can be cleanly released from the inner surface of the cylindrical mold. As the release agent, a fluorine release agent, a silicone release agent, a semi-permanent release agent, or the like is used.

  The cylindrical mold is placed on a rotating roller and is indirectly rotated by the rotation of the roller. The size of the mold can be appropriately selected according to the desired size of the surface layer, that is, the outer diameter of the multilayer tube. After injecting the liquid raw material in an amount equivalent to obtaining the final thickness into the stopped cylindrical mold, the rotational speed is gradually increased to the speed at which the centrifugal force works, and the centrifugal force uniformly flows over the entire inner surface. Extend. Centrifugal molding is, for example, injecting a surface layer forming composition in an amount equivalent to obtaining the final thickness on the inner surface of a rotating drum (cylindrical mold) rotated to a centrifugal acceleration of 0.5 to 10 times the gravitational acceleration. Thereafter, the rotational speed is gradually increased, the rotation is increased to a centrifugal acceleration 2 to 20 times the gravitational acceleration, and the entire inner surface is cast by centrifugal force. Thereafter, the mixture is heated to evaporate the solvent and obtain a baked cured product. For the heating, a heat source such as a far-infrared heater is disposed around the mold, and indirect heating from the outside is performed. Usually, the temperature may be gradually raised from room temperature to about 120 to 200 ° C. and heated at the temperature after the temperature raising for about 0.5 to 2 hours. Thereby, the liquid raw material injected into the inner surface of the cylindrical mold is cured, and a seamless tube-like surface layer can be formed on the inner surface of the cylindrical mold.

III. Formation of Covering Layer 2 (Elastic Layer) The elastic layer in the conductive roller of the present invention is a layer formed on the inner side of the covering layer (tube) structure covering the roller body of I. above. And is formed of an elastic rubber material containing a filler, specifically, a cured product of liquid urethane rubber. For example, it is manufactured by adding a filler to an elastic layer material containing liquid urethane rubber, and applying and curing on the inner surface of the surface layer obtained in II. The elastic layer material may contain an electronic conductive agent or an ionic conductive agent as necessary.

  Examples of the liquid urethane rubber include thermosetting polyurethane elastomers, and those having a type A hardness (JIS K6253) of 25 to 70 degrees, more preferably 35 to 55 degrees are particularly preferable. Specific examples include Pandex and Urehyper manufactured by DIC Corporation, Takenate manufactured by Mitsui Chemicals Polyurethane Corporation, and the like. In particular, in the case of a thermosetting polyurethane composition, a liquid blocked urethane prepolymer obtained by blocking the terminal isocyanate group with a blocking agent is used as a main component until a certain temperature is reached even when a curing agent is added. Is preferable in terms of processing because it can suppress curing.

  A filler having a specific gravity higher than that of the liquid urethane rubber (particularly thermosetting polyurethane elastomer) as the main material is added to the elastic layer, and the filler is unevenly distributed on the surface layer side in the elastic layer. It is characterized by. Here, the specific gravity of the filler refers to the true specific gravity of the filler. The surface layer side in the elastic layer refers to a portion within 10% of the elastic layer thickness from the surface layer side in the thickness direction of the elastic layer.

The specific gravity of the filler is desirably relatively large so as to be suitable for uneven distribution, and a metal-based or mineral-based hard filler is suitable for this. For example, it should be 2 times or more, preferably 2.1 to 10 times, more preferably 2.2 to 6 times the specific gravity of liquid urethane rubber (particularly thermosetting polyurethane elastomer) which is the main material of the elastic layer. In this case, it is easy to make it unevenly distributed by a method described later. The specific gravity of the filler is usually 2 to 10 g / cm ³ , preferably ³ to 7 g / cm ³ . For example, since the specific gravity of a normal thermosetting polyurethane elastomer is about 0.95 to 1.1, the specific gravity of the filler may be 2.2 or more.

  Examples of the filler include aluminum borate, potassium titanate, calcium silicate, boron nitride, aluminum nitride, aluminum oxide, titanium oxide, zirconium oxide, mica, talc, clay, hydrotalcite, silica, calcium carbonate, magnesium sulfate, Examples include zinc oxide, carbon black, and PTFE. Among these, aluminum borate, zirconium oxide, and mica are preferable. Further, the filler may be appropriately treated with a coupling agent or the like according to the combination of the filler and the rubber elastic layer.

  The shape of the filler is not particularly limited, and examples thereof include needles, particles, plates, spheres (true spheres), and fibers. Examples of needle fillers include aluminum borate such as Arbolex (manufactured by Shikoku Kasei Kogyo Co., Ltd.) and wollastonite such as wollastonite KGP-H45 (manufactured by Kansai Matec Co., Ltd.). Examples of particulate fillers For example, aluminum borate such as arbolite (manufactured by Shikoku Kasei Kogyo Co., Ltd.), zirconium oxide such as TMZ zirconium oxide (manufactured by Daiichi Rare Element Chemical Co., Ltd.), and SR-1 titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd.). Examples of the plate-like filler include barium sulfate such as barium sulfate HF (manufactured by Sakai Chemical Industry Co., Ltd.) and mica such as mica ME100 (manufactured by Coop Chemical Co., Ltd.), and spherical (true Examples of spherical fillers include true spherical silica such as true spherical silica SP30 (manufactured by Micron). . Of these, particulate or spherical shape is preferred.

  The volume average particle diameter (median diameter D50) of the filler is usually 0.3 to 40 μm, preferably 0.8 to 30 μm, and particularly preferably 1.0 to 20 μm. If the particle diameter is too large, a minute hardness distribution is generated on the belt surface and noise appears in the image, which is not preferable. Moreover, when the particle diameter is too small, when the filler is inclined toward the surface layer side by centrifugal force, it is difficult to cause the inclination, which is not preferable.

  The added amount of the filler is preferably 1.0 to 30.0 parts by weight, more preferably 5.0 to 15.0 parts by weight with respect to 100 parts by weight of the liquid urethane rubber contained in the elastic layer. preferable. If the amount of the filler is too large, the hardness of the entire elastic layer tends to be high and a good nip or image cannot be maintained.If the amount is too small, the portion in contact with the surface layer is soft, and stress concentration on the surface layer is reduced. There is a tendency that cannot be prevented.

Among the types of liquid urethane rubbers mentioned above, there is usually one having a volume resistivity of about 10 ⁹ Ω · cm to 10 ¹¹ Ω · cm without adjusting the resistance, and constitutes an elastic layer. It can be used as it is as a liquid urethane rubber. However, when further conductivity is desired, the resistance may be adjusted using an electronic conductive agent such as carbon black or an ionic conductive agent such as a lithium ion salt.

Among them, an ionic conductive agent using a lithium salt is usually in a liquid state, and even if added to a liquid urethane rubber, it is preferable because it does not hinder the uneven distribution of the above-mentioned high specific gravity filler. Examples of the ionic conductive agent using a lithium salt include lithium bisimide (CF ₃ SO ₂ ) ₂ NLi and lithium trismethide (CF ₃ SO ₂ ) ₃ CLi. Specific examples include Sanconol (manufactured by Sanko Chemical Co., Ltd.) and the like. In the type of a normal ionic conductive agent, the conductivity is considered to be manifested by moisture absorption, which causes the ionic conductivity to depend on the environment. However, this ionic conductive agent is considered to exhibit conductivity by movement of lithium ions due to molecular movement of oxygen, and is less dependent on the environment. It is used as a rubber constituting the elastic layer of the conductive roller of the present invention. Also suitable for use. When the ionic conductive agent is added, the addition amount is usually 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the liquid urethane rubber. Part.

  The liquid urethane material, the resistance of which has been adjusted by any method by adding the filler in this way, is introduced into the inner surface of the surface layer formed in the above II. The viscosity of the liquid urethane material is important for tilting the filler, and if necessary, dilute it appropriately with an ester solvent such as ethyl acetate or butyl acetate, or an aromatic hydrocarbon solvent such as toluene or xylene, and centrifuge. It can be adjusted to a viscosity suitable for molding.

  Examples of a method for forming the elastic layer include a method in which the elastic layer material is forcibly formed by rotationally molding (centrifugal molding) using a cylindrical mold so that filler is unevenly distributed on the surface layer side. The elastic layer material is uniformly applied on the inner surface of the surface layer of the rotating drum (cylindrical mold) on which the surface layer is formed, and centrifugal molding is performed. Thereafter, the rotating drum is moved to a gravitational acceleration of twice or more (preferably Heat treatment is performed while rotating at a centrifugal acceleration of 2 to 20 times. By setting the rotational speed of the rotating drum to a centrifugal acceleration that is at least twice the gravitational acceleration, a centrifugal force that is always greater than the gravitational acceleration is always applied to the raw material solution, so the filler with a higher specific gravity than liquid urethane rubber segregates on the surface layer side. It becomes easy.

  The molding temperature is gradually heated from room temperature, raised to about 110 to 160 ° C., which is below the heat resistance limit of urethane rubber, and kept in this state for about 0.5 to 2 hours to complete the curing.

  For the purpose of improving adhesion between the surface layer and the elastic layer, a method of applying a primer on the surface layer side by spraying, a method of adding a silane coupling agent to the liquid urethane material, a method of performing both, etc. You may take it.

The volume resistivity of the elastic layer is usually about 10 ⁵ to 10 ¹¹ Ω · cm, preferably about 10 ⁶ to 10 ¹⁰ Ω · cm, from the viewpoint that the toner is transferred by electrical control as a conductive roller.

  The thickness of the elastic layer is usually 50 to 1000 μm, preferably 100 to 500 μm, and more preferably 200 to 400 μm in consideration of the flexibility of the surface of the conductive roller and prevention of image displacement during use.

IV. Formation of multi-layer roller (tube coating on roller body)
Finally, the roller body manufactured in the above I. is covered with the coating layer tube manufactured in the above III. To obtain the conductive roller of the present invention. That is, a roller body in which rubber is provided around a core metal (shaft core body), a covering layer tube composed of two layers of an integrated surface layer and an elastic layer, and an outer surface of the roller body rubber and the covering layer tube Are overlapped so that the inner surface (surface on the elastic layer side) is in contact. You may apply | coat an adhesive agent and a primer between both as needed. After the superposition of both, it is preferable that the space between the two is sealed. Thereafter, the laminated body is heat-treated to obtain a conductive roller in which the inner surface of the elastic layer and the outer surface of the roller body are bonded.

  Specific examples of the coalescence process will be given. Apply the primer thinly and uniformly on the inner surface of the coating film (tube) consisting of the surface layer and elastic layer formed on the inner surface of the cylindrical mold of III. . After applying a laminating adhesive or hot melt adhesive to the rubber outer surface of the roller body manufactured separately in I. above and air-drying, it is inserted into the inner surface of the elastic layer and fixed so as not to be displaced. Then, gently remove the coating film (tube) from the cylindrical mold. Immediately after this, the coating film adheres to the roller body by losing the support of the mold. If the shrinkage of the coating film (tube) is insufficient due to the size, etc., and the adhesion to the roller body is not sufficient, the air in both gaps can be evacuated and removed.

  Thereafter, heat treatment is performed at about 100 ° C. for about 20 to 60 minutes, and the adhesion between the roller body and the coating layer is completed simultaneously with the curing of the adhesive. If necessary, the completed conductive roller may be further annealed at about 120 ° C. for about 3 to 5 hours. Examples of the laminating adhesive include Takelac A-969 manufactured by Mitsui Chemicals Polyurethane Co., Ltd. and Tyforce NT-810 manufactured by DIC Co., Ltd. In addition, although use of said primer is arbitrary, it is preferable to use from the point of an adhesive strength improvement. Examples of the primer include DY39-067 manufactured by Toray Dow Corning Co., Ltd. Thus, the conductive roller of the present invention is obtained.

  The conductive roller has a coating film (tube) formed on the mirror surface inside the cylindrical mold as described above or a surface equivalent thereto, so the surface roughness Rzjis should be 2.5 μm or less. Can do. The surface roughness Rz is set to 2.5 μm or less because when the surface roughness Rz exceeds 2.5 μm, in the case of liquid toner having a particle size of about 1 μm, the toner is difficult to separate and the image deteriorates or is used endurancely. This is because may stick to the roller surface.

  On the other hand, if the surface roughness Rzjis is too small, the adhesion is increased due to the presence of an elastic layer on the base, and the dynamic friction coefficient of the surface increases. ) May occur. Therefore, the surface roughness Rzjis of the conductive roller is preferably 0.1 to 2.5 μm, more preferably 0.1 to 1.0 μm in order to prevent the blade from squeaking or breaking.

  The conductive roller is characterized in that the filler is unevenly distributed on the surface layer side in the elastic layer. The uneven distribution of the filler is about the filler on the surface layer side in the elastic layer. It can be expressed by the ratio of the mass concentration to the mass concentration of the filler at other locations. Specifically, it is as follows.

  Mass concentration M1 of filler contained in a region of 10% of the elastic layer thickness (A in FIG. 3) from the interface between the surface layer and the elastic layer toward the rubber layer side, a region in the middle of the elastic layer thickness (elastic layer thickness) 10% of the elastic layer thickness from the interface between the rubber layer and the elastic layer toward the surface layer side (in FIG. 3) The mass concentration M3 of the filler contained in C) is used. At this time, it is determined that the filler is inclined unevenly because M1> M2> M3. However, since the filler is concentrated on the surface layer side when the inclination is increased, the magnitude relationship between M2 and M3 is not necessarily important in that case.

  If the above equation is decomposed in more detail, the ratio (M1 / M3) of the concentration (M1 / M3) of the mass concentration M1 of the filler contained on the surface layer side of the elastic layer and the mass concentration M3 of the filler contained on the rubber layer side of the elastic layer is 2.0 or more is preferable, 3.0 or more is more preferable, and 3 to 100 is particularly preferable. Further, the ratio (M1 / M2) of the mass concentration M1 of the filler contained in the surface layer side of the elastic layer and the mass concentration M2 of the filler contained in the substantially central region of the thickness of the elastic layer is preferably 1.5 or more, 2.5 or more is more preferable, and 2.5 to 100 is particularly preferable.

  A larger mass concentration ratio (M1 / M3, M1 / M2) indicates that the filler is unevenly distributed on the surface layer side in the elastic layer. When M1 / M3 is 2.0 or more and M1 / M2 is 1.5 or more, the hardness of only the region in contact with the surface layer of the elastic layer is high, so stress concentration on the surface layer is avoided and high quality image is obtained. Since it can be set as the electroconductive roller which has the outstanding friction durability, maintaining this, it is preferable.

  Here, the mass concentration of the filler is measured by measuring the mass concentration of main elements constituting the filler with an energy dispersive X-ray analyzer (EDX) (acceleration voltage: 20 kV, irradiation time: 5 minutes). It is. For example, when the filler is aluminum borate, the aluminum concentration is measured, and when the filler is mica, the silicon concentration is measured.

  The conductive roller of the present invention produced as described above is suitably used as an electrophotographic roller such as a transfer roller, a charging roller, a developing roller, and a cleaning roller used in an image forming apparatus.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using a comparative example with an Example, this invention is not limited to these Examples.

The following evaluation described in this specification was performed as described below.
<Rubber and elastic layer material hardness>
According to JIS K6253, using a durometer A, a bulk (lumb) having a thickness of 6 mm was prepared and evaluated using a rubber material constituting the rubber layer of the roller body and an elastomer material constituting the elastic layer.
<Surface roughness>
Rzjis used for displaying the surface roughness is a ten-point average roughness defined as Rz in JIS B0601 (1994). In JIS B0601, Rz was revised by the 2001 standard revision, and replaced with Ry (maximum height) in 1994. Rz in 1994 was renamed Rzjis in 2001 for distinction.

  In this specification, the measurement of the surface roughness of the conductive roller and the roller main body (the shaft core before coating the multilayer tube with a rubber layer) is made in accordance with JIS B0601 (2001). Using a Keyence laser microscope VK-9700 measuring machine, the observation conditions were 1000 times the objective lens 20 times x eyepiece 50 times. Using the image of the surface obtained by observation, the line roughness was measured under the following measurement conditions.

Tilt correction: Surface tilt correction (automatic)
Cut-off: None Measurement length: 0.25mm
For each conductive roller, measure the four points at the same angle in the circumferential direction for each central axis direction, 3 places in total in the central axis direction, 30 mm from the center and both ends, and calculate the average value of all measured values. This was calculated as a measured value of the roller surface roughness Rzjis.
<Measurement of volume resistance of rubber layer of roller body>
For the volume resistance of the rubber layer of the roller body, the volume resistivity (LogΩ · cm) described in JIS K6911 measured under an applied voltage of 100 V was used as the roller volume resistance.
<Solid content concentration of surface layer and elastic layer>
The raw materials are precisely weighed, and the weight of the solid or liquid raw material at this time is Cg. In order to dissolve the raw material in the solvent on the electronic balance, the solvent is gradually added while stirring, and the final solution weight is set to Dg. The solid content concentration is given by the following formula.

Solid content concentration of each layer = C / D × 100 (%)
<Thickness of surface layer and elastic layer>
The thickness was measured as a mean value by measuring a total of 24 points of 3 points in the width direction and 8 points in the circumferential direction using a flat type probe of a contact-type film thickness measuring instrument.
<Volume resistivity of elastic layer>
The volume resistivity (Ω · cm) of the elastic layer was measured in a 23 ° C. and 55% RH environment using a resistance measuring instrument “HIRESTA UP / UR Blob” manufactured by Mitsubishi Chemical Corporation. A bulk is prepared from the same raw material as the elastomer composition constituting the elastic layer to prepare a sample, and an applied voltage of 100 V is applied to a total of nine places at three equal pitches in the width direction and three longitudinal (circumferential) directions. After 10 seconds, the volume resistivity was measured and expressed as a common logarithm of the average value. The measurement sample was measured after standing for 12 hours in an environment of 23 ° C. and 55% RH.
<Confirmation of uneven distribution of filler>
The belt cross section was sliced with a microtome, and gold vapor deposition was performed so that the vapor deposition thickness was 5 nm to prepare an observation sample. About the sample for observation, cross-sectional observation with the electron microscope (SEM: S-4800 by Hitachi, Ltd.) was performed.

  Further, the mass concentration M1 of the filler contained in the region of 10% of the elastic layer thickness from the interface between the surface layer and the elastic layer toward the rubber layer side, the region in the middle of the elastic layer thickness (the central layer of 10% of the elastic layer thickness) The mass concentration M2 of the filler contained in the region), and the mass concentration M3 of the filler contained in the region of 10% depth from the interface between the rubber layer and the elastic layer toward the surface layer side are expressed as EDX (Horiba Manufacturing Energy Dispersion X Measurement was performed with a line analyzer EMAX model 7593H, acceleration voltage: 20 kV, irradiation time: 5 minutes, and respective concentration ratios (M1 / M2, M1 / M3) were determined.

Example 1
(1) Manufacture of roller body First, 100 parts by weight of NBR as a base rubber, JSR N230S (manufactured by JSR Corporation), and dibutyl diglycol adipate (BXA, manufactured by Daihachi Chemical Industry Co., Ltd.) as a softener. 5 parts by weight, 5 parts by weight of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd.) as zinc oxide, 1 part by weight of Lunac S-20 (manufactured by Kao Corporation) as stearic acid, and Jinhua stamp fine powder sulfur as a vulcanizing agent 1.0 part by weight of 325 mesh, 1.0 part by weight of accelerator DM (manufactured by Kawaguchi Chemical Co., Ltd.) as a vulcanization accelerator, 0.5 part by weight of accelerator TS (manufactured by Kawaguchi Chemical Industry Co., Ltd.), and carbon black Asahi # 50 (Asahi Carbon Co., Ltd.) was weighed by 15 parts by weight. Each component was kneaded with a known rubber kneading roll to obtain an unvulcanized rubber composition for a roller.

  On the other hand, the thermosetting adhesive METALOC U-20 (trade name, manufactured by Toyo Chemical Research Laboratories) is applied to the surface of an aluminum alloy A6063 pipe core (shaft core) having an outer diameter of φ164 mm and a total length of the rubber bonded portion of 530 mm. After drying at room temperature for 30 minutes, it was dried by heating at 120 ° C. for 30 minutes. Next, the rubber composition for a roller obtained as described above is dispensed into a 5 mm thick sheet, wound around the core metal (shaft core) so as to be rotated twice, and a two-part mold is used. A 100-ton vacuum press (manufactured by Kotaki Seiki Co., Ltd.) was compression molded at a hot platen temperature of 170 ° C. for 45 minutes, and a rubber layer was vulcanized on the outer periphery of the core metal (shaft core body).

  Next, the rubber layer of this roller body is attached until a grinding wheel of GC120E is attached to the polishing machine and the grinding wheel is rotated at a speed of 2000 RPM until the outer diameter of the roller reaches 179.4 mm at a feed rate (traverse) of 200 mm / min. The rubber roller body was manufactured by polishing twice.

  The rubber roller body had a rubber hardness of type A53 degrees, a surface roughness of 6.3 μm Rzjis, and a volume resistivity of 7.5 (LogΩ · cm).

(2) Film formation of surface layer VDF-HFP copolymer resin (Kayner # 2821, made by Arkema: HFP 5 mol%, Rockwell hardness R75, which is a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) 30 g) was dissolved in a mixed solvent of 270 g of N, N-dimethylacetamide (DMAc) and 300 g of methyl ethyl ketone (MEK) to prepare a solution having a solid content concentration of 5% by weight.

  And 150g was extract | collected from this solution, and it shape | molded on the following conditions with the metal mold | die for tube shaping | molding which consists of a surface layer and an elastic layer.

  Molding device: A tube molding die composed of a surface layer and an elastic layer is a cylindrical die having an inner surface of φ180.5 mm and a width of 700 mm and having an inner mirror finish. The mold is placed on two rotating rollers. It was placed and placed in a state of rotating with the driving rotation of the roller. For example, see FIG. Since the surface roughness of the inner surface of the mold cannot be measured with a laser microscope that measures the sample, instead of using a direct contact surf coder SE-3400 (manufactured by Kosaka Laboratory Ltd.) 40 points were measured uniformly at 10 points in the central axis direction. As a result, the average was 0.25 μm Rzjis, the maximum was 0.33 μm Rzjis, and the minimum was 0.20 μm Rzjis.

  After the mold was rotated at a speed of 120 rpm (1.5 times the gravitational acceleration) and uniformly applied to the inner surface of the mold, the heating was started by changing the rotation speed to 150 rpm (2.3 times the gravitational acceleration). . The heating was performed at a temperature of 2 ° C./min up to 140 ° C., and heating was performed at that temperature for 60 minutes while maintaining its rotation. After forming a surface layer on the inner surface of the die, the die was cooled to room temperature. It was 5 micrometers when the thickness of the surface layer formed in the metal mold | die inner surface was measured with the eddy current type thickness meter.

(3) Film formation of elastic layer Aluminum borate having a specific gravity of 3.0 (Arbolex, volume) as a filler in a solution prepared by dissolving 125 g of polyurethane elastomer (Urehyper RUP1627, manufactured by DIC Corporation) having a specific gravity of 1.0 in 125 g of xylene 12.5 g of an average particle diameter (D50) of 20 μm, manufactured by Shikoku Kasei Kogyo Co., Ltd. was added, and uniform dispersion was performed using a ball mill. Furthermore, 10.0 g of CLH-5 (manufactured by DIC Corporation) was added as a curing agent and stirred. Thus, an elastic layer material having a solid content concentration of about 50% was obtained.

  The solution was uniformly applied to the inner surface of the surface layer on which the film had been formed in a state where the mold was rotated at a speed of 150 rpm (2.3 times the acceleration of gravity), and heating was started. The heating was performed at a rate of 2 ° C./min up to 130 ° C., and heating was performed at that temperature for 80 minutes while maintaining the rotation, thereby forming an elastic layer on the inner surface of the surface layer. Thereafter, the molded product in which the surface layer and the elastic layer were integrated was peeled off from the mold to complete the tube. The obtained tube had a thickness of 303 μm.

  As a preliminary test, the rubber hardness of a urethane rubber single film prepared with this urethane rubber master batch solution was measured and found to be 42 ° with Type A (JIS K6253). Similarly, the volume resistivity was measured and found to be 8.4 (LogΩ · cm).

(4) Cover adhesion of multilayer tube to roller body Primer DY39-067 (manufactured by Dow Corning Toray Co., Ltd.) was applied to the inner surface of the elastic layer of the tube formed in (3) above and air-dried. Dry laminating adhesive Takelac A-969 (Mitsui Chemical Polyurethane Co., Ltd.) was thinly applied to the rubber outer surface of the roller body of (1) above. A roller main body whose surface was treated with an adhesive was inserted and overlapped on the inner surface of the elastic layer of the primer-treated tube. Next, heating (80 to 120 ° C.) was performed for 1 hour in a state of being pressurized from the outside of the surface layer to complete the coating adhesion. Finally, both ends of the roller were cut to obtain a conductive roller having a rubber surface length of 530 mm. Since the surface layer of the obtained conductive roller was made of a fluororesin, the releasability was sufficient, and the surface roughness serving as a measure of smoothness was 0.85 μm Rzjis.

  When the mass concentration ratio (M1 / M2, M1 / M3) of aluminum borate by EDX was measured, they were M1 / M2 = 17.9 and M1 / M3 = 41.6.

  Further, since the elastic layer has a low hardness and is flexible, it can be suitably used as a transfer roller that has excellent image dropout phenomenon at the time of primary transfer at the time of printing and recording material unevenness at the time of secondary transfer.

Example 2
Instead of adding 12.5 g of a filler with a specific gravity of 3.0 to the elastic layer of Example 1 (3), TMZ zirconium oxide with a specific gravity of 5.8 (volume average particle diameter (D50) 1.3 μm, first rare element chemistry) 7 g of Kogyo Co., Ltd. was added. Otherwise, a conductive roller was produced in the same manner as in Example 1. When the mass concentration ratio (M1 / M2, M1 / M3) of zirconium oxide by EDX was measured, it was M1 / M2 = 3.1 and M1 / M3 = 5.0.

Example 3
Instead of adding 12.5 g of a filler having a specific gravity of 3.0 to the elastic layer of Example 1 (3), SR-1 titanium oxide having a specific gravity of 4.2 (volume average particle diameter (D50) of 1.2 μm, Sakai Chemical Industry) 18 g) was added. Otherwise, a conductive roller was produced in the same manner as in Example 1. When the mass concentration ratio (M1 / M2, M1 / M3) of titanium oxide by EDX was measured, it was M1 / M2 = 9.5 and M1 / M3 = 11.6.

Example 4
Instead of the filler having a specific gravity of 3.0 added to the elastic layer of Example 1 (3), a spherical silica SP30 having a specific gravity of 2.2 (volume average particle diameter (D50) 2.6 μm, manufactured by Micron) was added. . Otherwise, a conductive roller was produced in the same manner as in Example 1. When the mass concentration ratio (M1 / M2, M1 / M3) of true spherical silica by EDX was measured, it was M1 / M2 = 2.5 and M1 / M3 = 3.0.

Comparative Example 1
In place of the filler having a specific gravity of 3.0 added to the elastic layer of Example 1 (3), BF-300 (volume average particle diameter (D50) 8.0 μm, calcium shiroishi) which is a heavy calcium carbonate having a specific gravity of 1.3. Was added). Otherwise, a conductive roller was produced in the same manner as in Example 1. When the mass concentration ratio (M1 / M2, M1 / M3) of the diatomaceous earth filler by EDX was measured, it was M1 / M2 = 1.6 and M1 / M3 = 1.7.

Comparative Example 2
Instead of the filler having a specific gravity of 3.0 added to the elastic layer of Example 1 (3), Sigma RF006 (average fiber length 60 μm, manufactured by Whisker Co., Ltd.) which is a carbon fiber filler having a specific gravity of 1.7 was added. Otherwise, a conductive roller was produced in the same manner as in Example 1. When the mass concentration ratio (M1 / M2, M1 / M3) of the carbon fiber filler by EDX was measured, it was M1 / M2 = 1.1 and M1 / M3 = 1.2.

Comparative Example 3
The filler added to the elastic layer of Example 1 (3) was not added at all. Otherwise, a conductive roller was produced in the same manner as in Example 1.

Test example 1
Table 1 shows the results of evaluating the wear durability by incorporating the sample conductive rollers of Examples 1 to 4 and Comparative Examples 1 to 3 into the transfer unit.
<Abrasion durability test>
Paper feeding, energization, and driving tests were simultaneously performed under the following conditions, and surface layer cracking and peeling were evaluated according to the following evaluation criteria after driving tests equivalent to 1 million, 2 million, and 4 million sheets.

Drive speed: Roller outer peripheral speed 900 mm / sec. Energization: Power supply (Trek 610C) supplies a constant current of 50 .mu.A. Paper feed: Print roll paper is fed between the produced transfer roller and secondary transfer roller, and pseudo continuous. Reproduce the paper condition Cleaning mechanism: Cleaning blade made of urethane rubber (Rubber hardness type A 80 °)
The evaluation of cracking and peeling was performed by visually observing the belt after endurance for passing paper, and judged according to the following criteria.

○: No abnormality is observed on the roller surface △: A minute crack is observed ×: The crack grows into a clear crack, and peeling occurs around the crack

  In the examples, there was no cracking or peeling of the surface layer of the conductive roller, and only small cracks were observed in 4 million sheets only in Example 4, but it was judged that there was no adverse effect on the print quality.

  On the other hand, in each of the comparative examples, the conductive roller surface layer was cracked or peeled off at the early paper passing stage, suggesting that the surface layer wear was large due to the small filler specific gravity added to the elastic layer.

  Although consideration of the above phenomenon is still under study, if a filler is present on the surface layer side in the thickness direction of the elastic layer, when stress is applied to the roller surface from a contact member such as a cleaning blade, the stress depends on the presence or absence of the filler. By being finely dispersed, it is presumed that it is difficult to generate cracks, cracks and peeling of the surface layer, which are usually generated by stress concentration.

  In addition, the surface layer is a smooth surface without irregularities, and the presence of filler in the underlying elastic layer causes irregularities in the filler when contacted while visually smooth, which causes toner aggregation Dispersing the force is considered to contribute to the prevention of image dropout and the improvement of the followability to the recording material medium.

  As described above, the transfer roller of the embodiment does not easily wear even when stress and friction are applied from the outside with a cleaning blade or the like. Therefore, the above-described surface releasability, surface smoothness, and low hardness of the elastic layer. In addition to making it possible, it has become possible to have surface layer friction durability. Therefore, the conductive roller of the present invention can be used as a conductive roller for an electrophotographic apparatus having a good function balance in which toner transfer and conveyance characteristics are good and releasability, cleaning properties, and durability are excellent. all right.

Claims (5)

A conductive roller having at least a rubber layer, an elastic layer, and a surface layer in order on the outer periphery of the shaft core body, and the surface layer has a surface roughness of 2.5 μm or less in Rzjis. A conductive roller comprising a filler, wherein the specific gravity of the filler is twice or more that of the elastic layer material constituting the elastic layer, and the filler is unevenly distributed on the surface side of the elastic layer. The conductive roller according to claim 1, wherein the surface layer has a thickness of 10 μm or less. The conductive roller according to claim 1, wherein the surface layer contains a fluororesin. The conductive roller according to claim 1, wherein the elastic layer includes a cured product of liquid urethane rubber. A method for producing a conductive roller, comprising:
(1) A process of producing a rubber roller body by vulcanizing and molding a rubber composition on a shaft core;
(2) A step of forming a surface layer by injecting a material containing a fluororesin into the inner surface of a cylindrical mold having a surface roughness of 2 μm Rzjis or less, and performing centrifugal molding.
(3) A step of injecting an elastic layer material containing a filler into the inner surface of the surface layer obtained in (2) above, centrifugally forming the elastic layer to produce a bilayer membrane (coating layer tube), Here, the specific gravity of the filler is not less than twice the specific gravity of the elastic layer material, and (4) the outer surface of the rubber roller body obtained in the above (1) and the two-layer film obtained in the above (3) A step of superposing and heating the inner surface of the elastic layer of the (coating layer tube),
Manufacturing method.

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