JP2005300666A - Foam conductive rubber roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foam conductive rubber roller whose electric resistance value is uniform over the circumferential surface thereof. <P>SOLUTION: In the foam conductive rubber roller provided with a foam rubber layer on a conductive shaft body, at least chemical foaming agent, sulfur and thiazole-based vulcanization accelerator are blended in the rubber composition of the foam rubber layer, and the thiazole-based vulcanization accelerator is blended in the form of vulcanization accelerator master batch that flocculated substance whose average diameter is ≤40 μm exists by three or less per unit area (mm<SP>2</SP>) of an optional position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a foamed conductive rubber roller such as a charging roller, a transfer roller, and a developing roller that is preferably used around a photosensitive member in an image forming apparatus such as a copying machine or a printer using an electrophotographic system.

  Conventionally, in an image forming apparatus for office automation equipment such as a copying machine and a printer, a non-contact charging method in which a high voltage is applied by corona discharge has been used. However, this charging method has a problem that harmful ozone is generated with corona discharge. Therefore, in recent years, image formation using a contact charging method in which a conductive rubber roller to which a voltage is applied is pressed against the surface of the photoconductor to charge the surface of the insulator has become the mainstream. A conductive rubber roller is used for each process such as charging and transfer around a photosensitive drum using a body.

  Conventionally, such conductive rubber roller is an electronic conductive rubber imparted with conductivity by filling a conductive filler such as carbon black into a rubber such as ethylene propylene diene rubber (EPDM) or styrene butadiene rubber (SBR). A composition is used. However, in the conductive filler filling system, the electric resistance varies depending on the filling amount and dispersion state of the conductive filler, the molding conditions of the rubber composition, etc., and the electric resistance depends on the applied voltage (voltage dependence) and is uniform. There was a problem that it was difficult to obtain an image. As a method for solving such a problem, it is known to use a polar rubber such as acrylonitrile butadiene rubber (NBR) or epichlorohydrin rubber. Polar rubber exhibits ionic conductivity because of the presence of polar groups in the polymer, and the rubber material itself is conductive, so there is little variation in resistance, and the voltage dependence of electrical resistance is small, making it suitable for conductive rubber rollers. It is known.

  In addition to the above-described electrical characteristics (electrical resistance, electrical resistance unevenness, environmental dependence, voltage dependence), the conductive rubber roller as described above should have a moderately low hardness in order to improve adhesion to the drum. Is desired. When the roller hardness is high, the nip width with the photosensitive drum or the like becomes small. For example, in the case of a transfer roller, the transfer rate is reduced, and image defects are likely to occur due to wear or damage on the surface of the photoreceptor. On the other hand, if the hardness is too low, it is too soft and the compression set becomes large and the durability is inferior, and the conveying force becomes too strong and the image tends to be defective.

  Examples of the method for reducing the hardness of the conductive rubber roller include a method using various additives such as a softener and a plasticizer. The conductive rubber roller added with the softener and the plasticizer is brought into contact with the photosensitive drum. When used, various additives having a low molecular weight bleed out from the conductive rubber roller and adhere to the surface of the photoconductor, which easily causes problems such as image deterioration and photoconductor contamination. Therefore, a method of obtaining a foamed elastic rubber roller using a chemical foaming agent is generally used to reduce the hardness of the conductive rubber roller (for example, Patent Document 1).

  Chemical foaming is a method of blending a rubber component with a chemical foaming agent and heating and foaming, and the most common chemical foaming agent is an organic foaming agent. An organic blowing agent is a substance that decomposes chemically and releases gas under the influence of heat. In this method, since the generated gas is quickly released in a certain temperature range, relatively large bubbles are formed, and it is possible to obtain a conductive roller having low hardness and excellent elasticity.

Further, the rubber composition used for the conductive rubber roller often uses sulfur vulcanization. In this case, thiazole compounds such as dibenzothiazyl disulfide and 2-mercaptobenzothiazole are used as the primary vulcanization accelerator, and thiuram compounds and dithiocarbamic acid compounds are used as secondary vulcanization accelerators as necessary. In many cases, the presence of a thiazole vulcanization accelerator is important in obtaining a conductive rubber roller.
JP 2002-115714 A

  However, when a foamed rubber is obtained using a chemical foaming agent, if there is a compound that causes poor dispersion in the rubber composition, the foamed state is affected, and there is a tendency to generate a location where abnormal foaming occurs. In particular, when flocculation accelerator aggregates are present, abnormal foaming is likely to occur. As a result, the electrical resistance of the abnormally foamed portion is increased, the electrical resistance varies, and the formed image is disturbed. There is.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a foamed conductive rubber roller having no abnormal foam cell and having a uniform electric resistance value on the outer peripheral surface of the roller.

That is, the present inventor has achieved the object of the present invention by the following means.
In a foamed conductive rubber roller in which a foamed rubber layer is provided on a conductive shaft, at least a chemical foaming agent, sulfur and a thiazole vulcanization accelerator are blended in the rubber composition of the foamed rubber layer, By blending the vulcanization accelerator in the form of a vulcanization accelerator masterbatch having an average diameter of 40 μm or less per unit area (mm ² ) of 3 or less per unit area (mm ² ),
By using a thiazole compound having a maximum particle size of 25 μm or less as a raw material for the vulcanization accelerator master batch,
When the content of the thiazole compound in the vulcanization accelerator master batch is 40 to 90% by mass,
When the Mooney viscosity (ML1 + 4, 50 ° C.) of the vulcanization accelerator master batch is 30 to 110,
The object of the present invention was achieved by the rubber component of the rubber composition containing at least one of acrylonitrile butadiene rubber and epichlorohydrin rubber.

  According to the present invention, it is possible to prevent the occurrence of abnormal foam cells. As a result, a foamed conductive rubber roller having a uniform electrical resistance value on the outer peripheral surface of the roller can be obtained, and it is possible to provide a high-quality image by using it around a photosensitive drum in an electrophotographic apparatus, particularly a transfer roller. Become.

Hereinafter, the foamed conductive rubber roller of the present invention will be described in detail. The foamed conductive rubber roller of the present invention is provided with a foamed rubber layer on a conductive shaft, and at least a chemical foaming agent, sulfur and a thiazole vulcanization accelerator are blended in the rubber composition of the foamed rubber layer. The foamed conductive rubber roller. The rubber composition used in the present invention uses sulfur as a vulcanizing agent and a thiazole vulcanization accelerator as a primary vulcanizing agent. In the present invention, the thiazole-based vulcanization accelerator is blended in the form of a vulcanization accelerator masterbatch in which aggregates having an average diameter of 40 μm or less are 3 or less per unit area (mm ² ) at an arbitrary position. is important. If the average diameter of the aggregates exceeds 40 μm, or if the average diameter is 40 μm or less and the number of aggregates per unit area (mm ² ) at an arbitrary position is more than 3, the thiazole-based vulcanization in the rubber composition after kneading There is a high possibility that agglomerates of the accelerator exist, abnormal foaming occurs, and the electric resistance unevenness of the obtained foamed conductive rubber roller becomes large. In addition, thiazole compounds can be blended in the rubber composition as powders, but they may be scattered during weighing or kneading, which is undesirable for hygiene and is not easy to mix into rubber materials. Since it is inferior in processability, it is preferable to mix | blend with a rubber composition in the form of a vulcanization accelerator masterbatch. Moreover, the polymer used for the binder of a masterbatch is not specifically limited, However, It is preferable to use the polymer compatible with the rubber component of a rubber composition.

  The vulcanization accelerator master batch is preferably made from a thiazole compound having a maximum particle size of 25 μm or less. When the maximum particle size of the thiazole compound exceeds 25 μm, the average diameter of the aggregates in the master batch tends to increase, abnormal foaming is likely to occur, and the roller resistance value may vary.

  Examples of the thiazole compound used as a vulcanization accelerator include dibenzothiazyl disulfide and 2-mercaptobenzothiazole. A thiazole compound capable of obtaining a desired vulcanization rate and vulcanized rubber characteristics can be used. These may be selected and used, and these may be used alone or in combination.

  The amount of sulfur and thiazole-based compound used in the present invention is not particularly limited, and an amount capable of obtaining a desired vulcanization speed and vulcanized rubber properties may be added. It is preferable to mix 0.1-5 mass parts with respect to the above. When the amount of the thiazole compound is less than 0.1 parts by mass, it is difficult to obtain the effect as a vulcanization accelerator, and when the amount exceeds 5 parts by mass, there is a possibility of blooming.

  In addition, the thiazole compound content and Mooney viscosity in the vulcanization accelerator master batch are not particularly limited and may be adjusted as necessary, but the thiazole compound content is 40 to 90% by mass. The Mooney viscosity (ML1 + 4 50 ° C.) is preferably 30 to 110.

  When the content of the thiazole compound is less than 40% by mass, the compounding amount as a master batch is increased, which increases the cost, and also increases the amount of the binder in the rubber composition. May affect foaming. Moreover, when the content of the thiazole compound exceeds 90% by mass, the concentration of the thiazole compound in the masterbatch is too high, so there is a high possibility that an aggregate of the thiazole compound is generated in the masterbatch. Even after blending in the rubber composition, the aggregates may not be dispersed and the foamed state may be affected.

  Moreover, when the Mooney viscosity of the master batch is less than 30, the master batches may be fixed to each other, and the storage stability may be lacking. Conversely, when the Mooney viscosity of the masterbatch exceeds 110, the viscosity is too high and it takes time to disperse by kneading with the rubber material, resulting in poor work efficiency and may cause poor dispersion. .

  In the present invention, for example, a thiuram vulcanization accelerator or a dithiocarbamate vulcanization accelerator can be used as the secondary vulcanization accelerator, and a desired vulcanization speed and vulcanized rubber characteristics can be obtained. What is necessary is just to add as needed so that it may be obtained.

  The rubber component which comprises the rubber composition used for this invention will not be specifically limited if it is a rubber material which can use sulfur as a vulcanizing agent. Examples thereof include natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, and epichlorohydrin rubber. In addition, these rubber materials can be used alone or in combination, but the rubber material itself is conductive, so there is little variation in resistance, and the voltage dependence of electrical resistance is small, making it suitable for conductive rubber rollers. It is preferable to contain acrylonitrile butadiene rubber and / or epichlorohydrin rubber. In addition, what is necessary is just to adjust suitably content and a compounding ratio of an acrylonitrile butadiene rubber and / or epichlorohydrin type rubber so that it may become desired electric resistance.

  Examples of the chemical foaming agent used in the present invention include organic foaming agents such as azodicarbonamide, 4,4oxybis-benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, and inorganic such as sodium bicarbonate, ammonium bicarbonate, and sodium borohydride. Examples of the foaming agent include organic foaming agents from the viewpoint of dispersibility in a polymer. Among organic foaming agents, azodicarbonamide and 4,4oxybis-benzenesulfonylhydrazide, which are not sanitary and have no possibility of ignition, are preferably used. In addition, azodicarbonamide and 4,4oxybis-benzenesulfonylhydrazide are not only used alone, but also used in combination to adjust the foaming speed and the amount of foaming gas, or blended with foaming aids such as urea. It is also possible to do. Moreover, what is necessary is just to adjust a compounding quantity suitably so that it may become a desired foaming state, and 2-20 mass parts is normally mix | blended with respect to 100 mass parts of rubber components.

  Examples of the additive used in producing the conductive rubber roller used in the present invention include a vulcanization acceleration aid, a conductivity imparting agent, a softening agent, a plasticizer, and a filler. These additives are necessary. It may be added according to.

  In addition, the rubber composition used in the present invention can contain other components used in general rubber as required. For example, various fillers such as carbon black, calcium carbonate, clay, silica and talc, processing aids such as plasticizers, various anti-aging agents, vulcanization aids such as zinc oxide and stearic acid, and conductivity adjustment Various ionic conductive agents and the like are contained as necessary.

  The conductive rubber roller of the present invention is blended with various additives as necessary in the above-mentioned rubber, kneaded, extruded into a tube shape, vulcanized, and inserted into this with a conductive shaft, It is obtained by polishing to the shape of The vulcanization method is preferably steam vulcanization, but other vulcanization methods may be used. The vulcanization conditions are usually 140 to 180 ° C. and 10 to 120 minutes. Examples of the core material for the conductive shaft include conventionally used aluminum and stainless steel.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  Tables 1 and 2 show the blending ratios of the rubber compositions used in the examples and comparative examples. In addition, the unit of a compounding quantity is a mass part.

  First, the raw materials shown in Tables 1 and 2 were kneaded with an open roll to prepare rubber compositions of Examples and Comparative Examples.

  In the above examples, “Nipol DN401L (acrylonitrile content: 18% by mass); manufactured by Nippon Zeon Co., Ltd.” is used for acrylonitrile butadiene rubber, and “Zeklon 3101 (ethylene oxide content: 31 mol%)” is used for epichlorohydrin rubber; "Made" was used. For zinc oxide, "Zinc oxide 2 types; manufactured by Hakusuitec Co., Ltd.", for stearic acid, "Stearic acid S; manufactured by Kao Corporation", for calcium carbonate, "Super SSS (heavy calcium carbonate)" "Maruo Calcium Co., Ltd." was used, "Asahi # 35; Asahi Carbon Co., Ltd." was used for carbon black, and "Sulfax 200S; Tsurumi Chemical Co., Ltd." was used for sulfur. Further, as the thiazole vulcanization accelerator, dibenzothiazyl disulfide was classified as “Accel DM; manufactured by Kawaguchi Chemical Industry Co., Ltd.”. Also, using the above dibenzothiazyl disulfide as a raw material powder, a thiazole vulcanization accelerator masterbatch containing acrylonitrile butadiene rubber “Nipol DN401L (acrylonitrile content 18% by mass); manufactured by Nippon Zeon Co., Ltd.” as a binder is prepared. And used. For azodicarbonamide, “Vinihol AC # LQ; made by Eiwa Kasei Co., Ltd.”, for 4, 4 oxybis-benzenesulfonyl hydrazide, “Neocerbon 1000S; made by Eiwa Kasei Co., Ltd.”, for urea, “Cell Paste A” Used by Eiwa Kasei Co., Ltd.

The maximum particle size of the thiazole compound dibenzothiazyl disulfide was measured using a laser diffraction / scattering particle size distribution analyzer “LA-920; manufactured by Horiba, Ltd.”. In addition, for the thiazole vulcanization accelerator master batch, a cubic test piece with a side of 5 mm was prepared, and an arbitrary part of the surface was observed using a scanning electron microscope “S-4300; manufactured by Hitachi High-Technologies Corporation” The number of aggregates present per unit area (mm ² ) at an arbitrary position and the average diameter were measured. The Mooney viscosity of the thiazole vulcanization accelerator masterbatch was measured using a Mooney viscometer “SMV-201; manufactured by Shimadzu Corporation” under a temperature condition of 50 ° C.

  The foamed conductive rubber rollers of the examples and comparative examples were extruded in a tube shape using an extruder and then vulcanized at 160 ° C for 30 minutes in a vulcanizer to produce a tube-shaped rubber vulcanizate. Then, a SUS shaft body having a diameter of 6 mm was press-fitted into the inner diameter portion of the tubular rubber vulcanizate to obtain a roller-shaped molded body. This molded body was prepared by polishing so that the outer diameter was 14 mm.

  Further, characteristics such as roller electrical resistance, circumferential unevenness of roller electrical resistance, roller hardness, and abnormal foam cell number were measured by the following methods.

<Roller electrical resistance>
In a normal temperature / humidity N / N environment (23 ° C x 50% RH), the shaft of the conductive rubber roller is pressure-bonded to an aluminum drum with an outer diameter of 30 mm and rotated at 0.5 Hz. In this state, the resistance value was measured while applying a voltage of 500 V between the shaft body and the aluminum drum.

<Roller electrical resistance unevenness>
In a normal temperature / humidity N / N environment (23 ° C x 50% RH), the roller body is pressed against an aluminum drum with an outer diameter of 30 mm and rotated at 0.5 Hz so that a total pressure of 1000 g is applied to the shaft of the conductive roller. In this state, the maximum value (logR _{1 (Max)} ) and the minimum value (logR _{1 (Min)} ) of the resistance value are measured while applying a voltage of 500 V between the shaft body and the aluminum drum. logR _{1 (Max)} -logR _{1 (Min)} ) was used as an index of resistance variation. Moreover, it evaluated based on the following evaluation criteria.
○: Measured value ≤ 1.05 (roller electrical resistance unevenness minimum)
Δ: 1.05 <measured value ≦ 1.09 (small roller electrical resistance unevenness)
×: 1.10 <measured value (large roller electrical resistance unevenness)

<Number of abnormal foam cells>
The foamed cells existing around the entire circumference of the roller were observed with a video micro “VH-8000; manufactured by Keyence Corporation”, and foamed cells having a diameter of 350 μm or more were judged as “abnormally foamed cells”. This operation was performed for 10 rollers, and the “number of abnormal foamed cells” existing per roller was calculated.
○: measured value ≦ 0.5
Δ: 0.5 <measured value ≦ 1.0 (small number of abnormal foam cells)
×: 1.0 <measured value (number of abnormal foamed cells)

<Roller hardness>
With the conductive core material at the end of the conductive rubber roller being received by the bearing, the pusher of the Asker C-type spring hardness tester (manufactured by Kobunshi Keiki Co., Ltd.) is pressed against the shaft body with a total pressure of 500g. Asker C hardness was measured.

<Kneading processability>
When the thiazole vulcanization accelerator was kneaded into a rubber material with an open roll, the quality of the workability was evaluated.

As a result of the above experiments, from Examples 1 to 5 and Comparative Examples 1 to 3, the agglomerates having an average diameter of 40 μm or less of thiazole vulcanization accelerator are 3 or less per unit area (mm ² ) at an arbitrary position. It turns out that it is important to mix | blend with the form of a vulcanization accelerator masterbatch. In the case of Comparative Example 1 where the average diameter of the agglomerates exceeds 40 μm, or Comparative Example 2 where the average diameter is 40 μm or less and there are more than 3 agglomerates per unit area (mm ² ), Occurrence increases, and the circumferential unevenness of the obtained foamed conductive rubber roller is large. Further, in Comparative Example 3 in which the thiazole-based vulcanization accelerator is blended as the raw material powder, scattering during kneading and mixing into the rubber material are not easy and are inferior in workability.

  Further, Examples 6 and 7 show that the vulcanization accelerator master batch is preferably made from a thiazole compound having a maximum particle size of 25 μm or less. That is, in Example 5 where the maximum particle size exceeds 25 μm, the average diameter in the master batch tends to be large, and there are many abnormal foam cells due to poor dispersion, and as a result, the roller electrical resistance unevenness tends to increase. .

  Next, from Examples 8 and 9, it can be seen that when the thiazole vulcanization accelerator of the present invention is used as a master batch, the content of the thiazole compound is more preferably 40 to 90% by mass. In Example 9 in which the content of the thiazole-based compound exceeds 90% by mass, there is a tendency that agglomerates present in the vulcanization accelerator master batch tend to increase, and as a result, the foamed conductive rubber roller obtained has an abnormal foam cell. There are many numbers, and the roller electric resistance unevenness tends to increase.

  Further, Examples 10 and 11 show that when the thiazole vulcanization accelerator of the present invention is used as a master batch, the Mooney viscosity (ML1 + 450) of the master batch is more preferably 30 to 110. That is, in Example 11 where the Mooney viscosity of the vulcanization accelerator exceeds 110, there is a possibility of poor dispersion due to kneading with the rubber component, and as a result, the number of abnormal foam cells increases in the resulting foamed conductive rubber roller. The roller electrical resistance unevenness may increase. In addition, when the Mooney viscosity of the master batch is less than 30, the master batches may be fixed to each other, and the storage stability may be lacking.

Claims (6)

In a foamed conductive rubber roller in which a foamed rubber layer is provided on a conductive shaft, at least a chemical foaming agent, sulfur and a thiazole vulcanization accelerator are blended in the rubber composition of the foamed rubber layer, Foam conductivity characterized by blending vulcanization accelerators in the form of a vulcanization accelerator masterbatch with 3 or less agglomerates with an average diameter of 40 μm or less per unit area (mm ² ) at any position Rubber roller.   The foamed conductive rubber roller according to claim 1, wherein the vulcanization accelerator master batch is made from a thiazole compound having a maximum particle size of 25 μm or less.   The foamed conductive rubber roller according to claim 1 or 2, wherein a content of the thiazole compound in the vulcanization accelerator master batch is 40 to 90% by mass.   The foamed conductive rubber roller according to any one of claims 1 to 3, wherein the Mooney viscosity (ML1 + 4, 50 ° C) of the vulcanization accelerator masterbatch is 30 to 110.   The foamed conductive rubber roller according to any one of claims 1 to 4, wherein the rubber component of the rubber composition contains at least one of acrylonitrile butadiene rubber and epichlorohydrin rubber. 6. A foamed conductive rubber roller used in an image forming apparatus for developing an electrostatic charge image on a photosensitive member with a developer, wherein the foamed conductive rubber roller is a transfer roller disposed on the photosensitive member. The foamed conductive rubber roller according to any one of the above.