JP4646662B2 - Conductive roller - Google Patents

Description

  The present invention relates to a conductive roller, and more particularly to a conductive roller used in an electrophotographic copying apparatus such as a copying machine, a facsimile machine, and a printer.

  In recent years, in an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, and a printer, a contact method has become common instead of a corona discharge method in order to prevent generation of ozone. In the contact type image forming apparatus, a roll-shaped conductive member, that is, a conductive roller, is frequently used as a developing roller, a transfer roller, a charging roller, a paper feeding roller, a cleaning roller, a pressure roller for fixing, and the like. Yes.

  In order to obtain a high-quality image using the image forming apparatus, the conductive roller needs to have a low hardness, and usually includes a shaft and an elastic layer disposed on the outer periphery of the shaft. It is. Here, the elastic layer of the conductive roller is mainly composed of solid rubber components such as natural rubber (NR), epichlorohydrin rubber (ECO), ethylene / propylene / diene rubber (EPDM), acrylonitrile / butadiene rubber (NBR), etc. A rubber composition containing a conductive agent such as carbon black, a metal oxide, or an ionic conductive agent in order to impart conductivity, and a large amount of a softening agent to further reduce the hardness. Is commonly used.

JP-A-5-117434 International Publication No. 91/10942 Pamphlet

  However, when a rubber composition containing a large amount of softener is used for the elastic layer of the conductive roller, the compression set of the elastic layer of the conductive roller becomes large, and image unevenness occurs due to deformation at the time of roll pressure contact. There was a problem such as. There is also a problem that the softening agent bleeds on the surface of the conductive roller and contaminates the photoreceptor.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a conductive roller having a low hardness, a small compression set and a low roller resistance, without causing the softener to bleed.

  As a result of diligent studies to achieve the above object, the present inventors have formulated liquid polyisoprene rubber as a softening agent together with a conductive agent in polybutadiene rubber and polyisoprene rubber having a high cis-1,4-bond content. By using a rubber composition in which the blending ratio of these components is in a specific range for the elastic layer of the conductive roller, the softening agent does not bleed on the surface, and the hardness is low and the compression set is small. Furthermore, the present inventors have found that a conductive roller having a low roller resistance can be obtained, and have completed the present invention.

  That is, the conductive roller according to the present invention is a conductive roller comprising a shaft and an elastic layer formed on the outer periphery of the shaft. The component (A): cis-1,4-bond content is 90% or more. Polybutadiene rubber and polyisoprene rubber are blended with (B) component: liquid polyisoprene rubber and (C) component: conductive agent, and polybutadiene rubber (BR) and polyisoprene rubber in component (A). The mass ratio (BR / IR) to (IR) is 90/10 to 60/40, the blending amount of component (B) is 10 to 40 parts by mass with respect to 100 parts by mass of component (A), C) A rubber composition having a component content of 12.4 to 20.1% by mass is used for the elastic layer. Here, the microstructure of the polybutadiene rubber and the polyisoprene rubber can be obtained by an infrared absorption spectrum method. Liquid polyisoprene rubber is liquid at room temperature (25 ° C.).

  In another preferred embodiment of the conductive roller of the present invention, the rubber composition for an elastic layer further contains (D) component: an organic peroxide. Here, the content of the component (D) in the elastic layer rubber composition is preferably in the range of 0.5 to 2.0 mass%. The organic peroxide is particularly preferably 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane.

  In another preferred embodiment of the conductive roller of the present invention, the conductive agent is carbon black.

  According to the present invention, in a conductive roller comprising a shaft and an elastic layer formed on the outer periphery of the shaft, the elastic layer has a high cis-1,4-bond content relative to polybutadiene rubber and polyisoprene rubber. By using a rubber composition in which liquid polyisoprene rubber is blended as a softening agent together with a conductive agent, and the blending ratio of these components is in a specific range, the softening agent does not bleed on the surface, and the hardness is low. In addition, it is possible to provide a conductive roller having a small compression set and a low roller resistance.

  Hereinafter, the conductive roller of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an example of a conductive roller of the present invention. The illustrated conductive roller 1 includes a shaft 2 and an elastic layer 3 formed on the outer periphery of the shaft 2. In the conductive roller of the present invention, the elastic layer 3 has (A) component: polybutadiene rubber and polyisoprene rubber having a cis-1,4-bond content of 90% or more, and (B) component: liquid polyisoprene. A rubber and (C) component: a conductive agent are blended, and the mass ratio (BR / IR) of the polybutadiene rubber (BR) and the polyisoprene rubber (IR) in the component (A) is 90/10 to 60 / 40 is a rubber composition in which the blending amount of component (B) is 10 to 40 parts by weight with respect to 100 parts by weight of component (A) and the content of component (C) is 12.4 to 20.1% by weight. It is characterized by using.

  Since the rubber composition used for the elastic layer 3 of the conductive roller of the present invention contains liquid polyisoprene rubber having a molecular weight larger than that of a normal softener as a softener, there is no bleeding out of the softener. In the rubber composition, the polybutadiene rubber having a high cis-1,4-bond content, the polyisoprene rubber and the liquid polyisoprene rubber form a sea-island structure, and the rubber composition has a sufficient hardness. Low and compression set is also sufficiently small. Further, in the above rubber composition, the conductive agent of (C) component is more unevenly distributed in the polybutadiene rubber of (A) component than the liquid polyisoprene rubber of (B) component, and a conductive path is formed. The resistance of the composition itself is low, and the roller resistance of the conductive roller can be made sufficiently low.

The rubber composition for an elastic layer comprises a polybutadiene rubber having a cis-1,4-bond content of 90% or more and a polybutadiene rubber having a cis-1,4-bond content of 90% or more as a rubber component, ie, component (A). And isoprene rubber. Although not particularly limited, the high cis polybutadiene rubber preferably has a vinyl bond content of 5% or less and a Mooney viscosity ML _{1 + 4} (100 ° C.) in the range of 25-60, The high cis polyisoprene rubber preferably has a vinyl bond content of 5% or less and a Mooney viscosity ML _{1 + 4} (100 ° C.) in the range of 65 to 90. If the Mooney viscosity ML _{1 + 4} (100 ° C) of the polyisoprene rubber is less than 65, there is a problem in the blending of the rubber components. If it is higher than 90, the structure of the conductive agent such as carbon black is destroyed in the kneading process. End up. In addition, you may mix | blend another rubber component with the said rubber composition in the range which does not injure the objective of this invention.

  In the component (A) of the rubber composition for an elastic layer, the mass ratio (BR / IR) of the high cis-polybutadiene rubber (BR) to the high cis-polyisoprene rubber (IR) is 90/10 to 60/40. Range. When the content of high cis-BR in the component (A) exceeds 90% by mass, the rubber composition is deteriorated by kneading with a kneader of the rubber composition, or buggy or sheet punching occurs in the sheeting operation. On the other hand, when the content of high cis-BR in the component (A) is less than 60% by mass, the rubber composition is closely adhered to the rotor by kneading with a kneader, or the rubber composition is It may stick to the roll.

  The rubber composition for an elastic layer contains liquid polyisoprene rubber as a softener, that is, the component (B). When the liquid polyisoprene rubber is solid, the structure of a conductive agent such as carbon black is easily broken during kneading, and good conductivity cannot be obtained. Although not particularly limited, the liquid polyisoprene rubber preferably has a weight average molecular weight (Mw) of 20,000 to 50,000.

  In the rubber composition for an elastic layer, the amount of component (B) is in the range of 10 to 40 parts by mass with respect to 100 parts by mass of component (A). When the blending amount of the liquid polyisoprene rubber as the component (B) is less than 10 parts by mass with respect to 100 parts by mass of the component (A), the Mooney viscosity of the rubber composition becomes too high, and the structure destruction of the conductive agent such as carbon black may occur. As a result, good conductivity cannot be obtained. Moreover, when the compounding quantity of (B) component exceeds 40 mass parts with respect to 100 mass parts of (A) component, the Mooney viscosity of a rubber composition will become low too much and kneading | mixing with a kneader etc. will become difficult.

The rubber composition for an elastic layer contains a conductive agent as the component (C). By adding a conductive agent to the rubber composition, the resistance value of the rubber composition can be adjusted as appropriate, and the roller resistance of the conductive roller using the rubber composition can be adjusted to a desired range. Here, the conductive roller of the present invention is not particularly limited, but the roller resistance is preferably 10 ³ to 10 ⁹ Ω.

As the conductive agent, an electronic conductive agent such as carbon black is preferable. Here, as the carbon black, carbon black for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, MT, etc., carbon black for color subjected to oxidation treatment, pyrolytic carbon black, ketjen black And conductive carbon such as acetylene black. These carbon blacks may be used alone or in combination of two or more. The carbon black is not particularly limited, but preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 30 to 250 m ² / g and a DBP (dibutyl phthalate) absorption of 120 to 250 mL / 100 g. .

  The content rate of (C) component in the said rubber composition for elastic layers is the range of 12.4-20.1 mass%. When the content of the conductive agent is less than 12.4% by mass in the rubber composition, the conductivity of the rubber composition is low, and the desired conductivity cannot be imparted to the conductive roller. When the content exceeds 20.1% by mass, the conductivity of the roller is low. It becomes too high and a good image cannot be obtained.

  The rubber composition preferably further contains an organic peroxide as a crosslinking agent, that is, the component (D). When the rubber composition is crosslinked with an organic peroxide, it is easier to form a C—C bond than when vulcanized with sulfur, and the compression set of the rubber composition is reduced. As the organic peroxide, 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane is particularly preferable in that odor is less generated in the crosslinking step.

  The content of the component (D) in the rubber composition for an elastic layer is preferably in the range of 0.5 to 2.0% by mass. When the organic peroxide content of the component (D) is less than 0.5% by mass in the rubber composition, the rubber composition cannot be sufficiently crosslinked, compression set increases, and when it exceeds 2.0% by mass, The hardness of the rubber composition becomes too high, and a conductive roller having a desired hardness cannot be obtained. Here, the conductive roller of the present invention using the rubber composition preferably has an Asker C hardness of 45 to 75 degrees, and preferably has a compression set of 10% or less.

  The rubber composition for an elastic layer contains various compounding agents commonly used in the rubber industry, in addition to the components (A), (B), (C), and (D), such as fillers. , Stearic acid and the like can be appropriately selected and blended within a range not impairing the object of the present invention. As these compounding agents, commercially available products can be suitably used. In addition, the said rubber composition mix | blends (A) component with (B) component and (C) component, and various compounding agents selected suitably as needed, and is well-known using a kneader, a roll, etc. It can be manufactured by the method.

  The shaft 2 of the conductive roller of the present invention is not particularly limited as long as it has good conductivity. For example, a metal core made of a metal such as iron, stainless steel, aluminum, or the like is hollowed out. A metal shaft such as a metal cylinder can be used.

  The conductive roller of the present invention can be used as a developing roller, a transfer roller, a charging roller, a toner supply roller, a paper feed roller, a cleaning roller, a fixing pressure roller, and the like of an image forming apparatus. The method for producing the conductive roller is not particularly limited. For example, the rubber composition is injected into a mold having a desired shape in which a metal shaft is disposed at the center and crosslinked. Can be manufactured.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

  Using a 3 L kneader manufactured by Moriyama Seisakusho, the rubber compositions having the compounding formulations shown in Tables 1 and 2 were kneaded to obtain an unvulcanized rubber composition. A predetermined amount of the unvulcanized rubber composition was injected into a mold on which a shaft was previously mounted, and heated in an oven heated to 170 ° C. for 30 minutes to crosslink the rubber composition. Next, the crosslinked roller was taken out of the mold, cooled, and then polished to a predetermined roller diameter using a polishing machine manufactured by Mizuguchi Seisakusho. The obtained conductive roller was allowed to stand at room temperature for 14 days to confirm the presence or absence of bleeding. Further, the hardness, compression set and static roller resistance of the conductive roller were measured by the following methods. The results are shown in Tables 1 and 2.

(1) Hardness The Asker C hardness of the roller was measured using an Asker C hardness meter [manufactured by Kobunshi Keiki Co., Ltd.].

(2) Compression set In accordance with JIS K-6301, a test piece having a diameter of 29 mm and a height of 12.7 mm is compressed 25% in the height direction and left in an oven at 70 ° C. for 22 hours. The residual strain at 30 minutes after the removal was determined.

(3) Roller resistance A load of 500 gf was applied to both ends of the roller, and the resistance of the roller was measured under the conditions of an applied voltage of 10 V, a room temperature of 25 ° C., and a humidity of 50% using a resistance measuring device R8340 (manufactured by Advantest) .

* 1 High cis-polybutadiene rubber manufactured by Nippon Zeon Co., Ltd., BR1220L, cis-1,4-bond content = 97%, Mooney viscosity ML _{1 + 4} (100 ° C.) = 29.
* 2 High cis polyisoprene rubber manufactured by Nippon Zeon Co., Ltd., IR2200L, cis-1,4-bond content = 98%, Mooney viscosity ML _{1 + 4} (100 ° C.) = 70.
* 3 Liquid polyisoprene rubber manufactured by Kuraray Co., Ltd., L-IR30, weight average molecular weight (Mw) = 29,000.
* 4 Toka Black manufactured by Tokai Carbon Co., TB # 5500, N ₂ SA = 225m ² / g, DBP oil absorption = 155mL / 100g.
* 5 Organic oxide manufactured by NOF Corporation, Perhexa TMH, 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane.

  As is apparent from Table 1, by making the BR / IR ratio in the component (A) in the range of 90/10 to 60/40, the workability of the rubber composition is improved and the hardness and compression permanent of the roller are improved. On the other hand, when the strain was out of this range, workability deteriorated.

  Further, as is apparent from Table 2, the roller resistance of the conductive roller could be controlled within a suitable range by setting the content of the conductive agent of component (C) in the range of 12.4 to 20.1% by mass.

It is sectional drawing of an example of the electroconductive roller of this invention.

Explanation of symbols

1 Conductive roller 2 Shaft 3 Elastic layer

Claims (5)

In a conductive roller comprising a shaft and an elastic layer formed on the outer periphery of the shaft,
Component (A): Polybutadiene rubber and polyisoprene rubber having a cis-1,4-bond content of 90% or more are blended with (B) component: liquid polyisoprene rubber and (C) component: conductive agent. The mass ratio (BR / IR) of the polybutadiene rubber (BR) and the polyisoprene rubber (IR) in the component (A) is 90/10 to 60/40, and the blending amount of the component (B) is ( A conductive roller characterized in that a rubber composition containing 10 to 40 parts by mass with respect to 100 parts by mass of component A and having a component (C) content of 12.4 to 20.1% by mass is used for the elastic layer.   The conductive roller according to claim 1, wherein the rubber composition for the elastic layer further contains (D) component: an organic peroxide.   The conductive roller according to claim 2, wherein the content of the component (D) in the rubber composition for an elastic layer is 0.5 to 2.0 mass%.   The conductive roller according to claim 2 or 3, wherein the organic peroxide is 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane.   The conductive roller according to claim 1, wherein the conductive agent is carbon black.

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