JP2009122592A - Conductive rubber roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive rubber roller which controls high viscosity in forming, in which conductive carbon black is distributed uniformly, which has moderate hardness and small resistance unevenness, which can form a uniform image, and which is excellent in bleeding resistance. <P>SOLUTION: This conductive rubber roller has a conductive elastic layer 2 on a conductive support body 1. The conductive elastic layer is formed by crosslinking rubber compositions containing acrylonitrile butadiene rubber (A) having a specific SP value, synthetic rubber (B) having a specific SP value and a specific weight average molecular weight, and conductive carbon black (C). The rubber compositions are contained as in the conditions that (a)/(b) is 4.00-20.0 and (a)/(c) is 1.30-4.95, where the mass of the acrylonitrile butadiene rubber (A) is (a), the mass of the synthetic rubber (B) is (b), and the mass of the conductive carbon black (C) is (c). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conductive rubber roller that can be used for a charging roller, a transfer roller, a developing roller and the like provided in an electrophotographic apparatus using an electrophotographic process.

  2. Description of the Related Art Conventionally, conductive rubber rollers in a form suitable for a charging roller, a transfer roller, a developing roller, and the like are used in contact charging and contact transfer type electrophotographic apparatuses using an electrophotographic process. The conductive rubber roller has a cored bar and a conductive elastic layer on its outer periphery, and a multi-layered configuration where a surface layer is provided on the outside of the conductive elastic layer for resistance adjustment and prevention of dirt / bleeding as necessary. It is often said.

  In an electrophotographic apparatus, the charging roller performs uniform charging by contact with the photoconductor, the developing roller transports uniform toner as a thin film, and other transfer rollers and the like also ensure their functions. It is required to maintain such a nip width. For this reason, this type of conductive rubber roller is required to have a low hardness suitable for use while maintaining the nip width by pressure contact, and to have sufficient recovery against deformation due to pressure contact. .

Furthermore, the conductive rubber roller is often used with a controlled resistance value in a semiconductive region (a range of about 10 ⁴ to 10 ¹⁰ Ωcm). When an ionic conductive agent such as a quaternary ammonium salt is used as a conductive agent for imparting conductivity, a relatively stable resistance value can be easily obtained. However, when the surface layer is thin, When a large amount of the agent is added, the photoreceptor may be contaminated by bleeding. Moreover, the cost of the ionic conductive agent is relatively high, and a method of adding conductivity by adding carbon black is used when contamination is suppressed as much as possible or when importance is attached to the cost.

  In general, as carbon black has a smaller primary particle size, a larger nitrogen adsorption specific surface area, and a larger DBP absorption, the effect of imparting conductivity to the resin molded body is greater. However, carbon black having such physical properties has a large change in resistance and dispersion state with respect to the addition amount and dispersion time, and tends to make it difficult to control the resistance value and dispersion state. Furthermore, for example, when a conductive rubber roller is used as a charging roller, if the dispersion state is poor, images such as white stripes and white spots are overcharged in a minute low resistance portion where carbon black is unevenly distributed. Defects may occur. On the other hand, in a minute high resistance portion where the carbon amount is small and unevenly distributed, charging may be insufficient and image defects such as black spots and black stripes may occur.

  As a means of controlling the dispersion state and resistance value of carbon black, a method of controlling the resistance by using medium structure carbon black instead of high structure carbon black having a large DBP oil absorption (Patent Document 1) is reported. Has been. However, when carbon black with medium structure is used in the conductive elastic layer, it is necessary to increase the amount of carbon black added, the hardness of the conductive rubber roller becomes high, and it is difficult to secure an appropriate nip amount. There is a problem of becoming.

  In addition, when the conductive elastic layer is formed into a roller shape by extrusion molding or the like, the molding composition for the conductive elastic layer containing a large amount of carbon black has a high viscosity, and the fluidity at the time of extrusion is lowered, and the roller The resistance unevenness in the circumferential direction tends to increase. Furthermore, there may be a problem that voids are generated without sufficient degassing of moisture.

  In response to these problems, a method of adding a large amount of plasticizer to reduce the viscosity of the molding composition for the conductive elastic layer, and a softening agent to reduce the hardness of the resulting conductive elastic layer There is also a way to do it. However, when the electrophotographic apparatus is stopped for a long period of time, a certain portion of the conductive elastic layer is pressed, and a low molecular weight substance such as a plasticizer may bleed from the portion to contaminate the photoreceptor. . Therefore, a method for suppressing bleed by cross-linking of liquid rubber after extrusion together with the effect of plasticization during extrusion molding by adding liquid rubber having a low molecular weight instead of a softener or plasticizer (Patent Documents 2 to 4) Has been reported.

However, when the thickness of the surface layer is made thinner, or when only the surface treatment such as UV treatment is performed and the surface layer is not provided, the liquid rubber having a low molecular weight may cause bleeding. It is considered that there may be cases where the effect of suppressing contamination is not sufficient. In addition, depending on the type and blending amount of carbon black and the compatibility and blending amount of base rubber and liquid rubber, the dispersibility of carbon black will decrease, and sufficient (optimum) flow will occur in the composition for forming a conductive elastic layer. Sexuality may not be obtained. For this reason, resistance nonuniformity becomes large in the conductive elastic layer, and the hardness is increased, so that a sufficient nip cannot be obtained. As a result, the image uniformity may be impaired in the electrophotographic apparatus.
Japanese Patent Application Laid-Open No. 07-053860 JP 05-224501 A Japanese Patent No. 3100625 Japanese Patent No. 311537

  The object of the present invention is to suppress the increase in the viscosity of the rubber composition during molding, the conductive carbon black is uniformly dispersed, has an appropriate hardness, has little resistance unevenness, can form a uniform image, and is resistant to bleeding. An object of the present invention is to provide a conductive rubber roller having excellent properties.

  When the present inventors added a specific amount of a synthetic rubber having a specific weight average molecular weight, which is mainly composed of acrylonitrile butadiene rubber and having a SP value lower than that of acrylonitrile butadiene rubber, the former is the sea part of the continuous phase and the latter is The knowledge of forming discontinuous islands was obtained. At that time, carbon black is unevenly distributed in the sea part of acrylonitrile butadiene rubber having a high SP value, and the island part of the latter synthetic rubber having a low SP value has a low carbon black content, so that the increase in hardness due to the carbon black is avoided. It has been found that rubber elasticity is increased. Such a conductive elastic layer has good fluidity at the time of manufacture, and the obtained conductive elastic layer has low hardness due to the island, bleed resistance due to the sea, and uniform conductivity. Based on this finding, the present invention has been completed.

That is, the present invention is a conductive rubber roller having a conductive elastic layer on a conductive support,
The conductive elastic layer has an acrylonitrile butadiene rubber (A) having an SP value of 19.2 (MPa) ^1/2 or more and 21.0 (MPa) ^1/2 or less, and an SP value of 15.6 (MPa). Synthetic rubber (B) having a weight average molecular weight of 40,000 or more and 80,000 or less, and conductive carbon black (C), which is ^1/2 or more and 18.6 (MPa) ^1/2 or less, When the mass of the acrylonitrile butadiene rubber (A) is (a), the mass of the synthetic rubber (B) is (b), and the mass of the conductive carbon black (C) is (c), (a) / (b) Is 4.00 or more and 20.0 or less, (a) / (c) is 1.30 or more and 4.95 or less, and the total of (a) and (b) is 100 parts by mass of the rubber component. The rubber composition is 95 parts by mass or more and 100 parts by mass or less. The present invention relates to a characteristic conductive rubber roller.

  The conductive rubber roller of the present invention suppresses an increase in the viscosity of the rubber composition during molding, the conductive carbon black is uniformly dispersed, has an appropriate hardness, has little resistance unevenness, and can form a uniform image. Excellent bleed resistance.

  The conductive rubber roller of the present invention has a conductive elastic layer on a conductive support.

  The conductive support is not particularly limited as long as it has conductivity and has a strength capable of supporting the conductive elastic layer. As the material, for example, SUS, iron, copper, stainless steel, brass, conductive plastic, conductive elastomer and the like can be used. The shape of the conductive support may be a cylindrical shape having a hollow central portion in addition to the columnar shape. Examples of the outer diameter of the conductive support include 4.0 to 8.0 mm.

  The conductive elastic layer is formed by crosslinking a rubber composition containing acrylonitrile butadiene rubber (A), synthetic rubber (B), and conductive carbon black (C). And it has a sea island structure which has the sea part containing an acrylonitrile butadiene rubber (A) and the island part containing a synthetic rubber (B).

[Acrylonitrile butadiene rubber (A)]
The acrylonitrile butadiene rubber (A) contained in the rubber composition has acrylonitrile units and butadiene units. The acrylonitrile unit having a cyano group is highly polar, that is, has a large SP value (Solubility Parameter) and is excellent in dispersibility of the conductive carbon black (C). Butadiene units have good crosslinkability, and the glass transition temperature of acrylonitrile butadiene rubber may be high, so that the molecular mobility of the rubber after vulcanization is low and the effect of suppressing bleeding of low molecular weight substances is high. Furthermore, unlike epichlorohydrin rubber, which is a polar rubber having similar properties, it does not have a halogen group (chlorine), so that contamination of the photoreceptor due to chlorine can be suppressed.

  The acrylonitrile butadiene rubber (A) is preferably a random copolymer of acrylonitrile and butadiene because it has non-crystalline properties and suppresses an increase in hardness.

  The larger the acrylonitrile unit content, the higher the polarity of the acrylonitrile butadiene rubber (A) and the higher the SP value, and the conductive carbon black can be easily contained in the sea part constituted by the acrylonitrile butadiene rubber (A). . By adjusting the acrylonitrile unit amount, the content of the conductive carbon black in the sea can be adjusted. In addition, as the acrylonitrile unit content increases, the molecular motion of the acrylonitrile butadiene rubber (A) decreases, the bleed resistance of the conductive elastic layer improves, the crack growth rate due to ozone decreases, and the ozone degradation resistance increases. Although improved, rubber elasticity is reduced.

The acrylonitrile unit content in the acrylonitrile butadiene rubber (A) is preferably 31% by mass or more and less than 36% by mass (generally referred to as medium-high nitrile). If the content of the acrylonitrile unit is within this range, the SP value of the acrylonitrile butadiene rubber (A) can be in the range of 19.2 (MPa) ^1/2 or more and 21.0 (MPa) ^1/2 or less. . The content of acrylonitrile units in the acrylonitrile butadiene rubber (A) can be determined by measuring the nitrogen content in the copolymer by the semi-micro Kjeldahl method described in JIS K6384 (2001) and adopting the value obtained by calculation. .

  Further, the butadiene unit in the acrylonitrile butadiene rubber (A) imparts rubber elasticity, and the conductive elastic layer imparts good rubber elasticity even in cold regions. The butadiene unit may be either a 1,4-butadiene unit or a 1,2-butadiene unit, but is preferably a 1,4-butadiene unit. The content of butadiene units in the acrylonitrile butadiene rubber (A) is preferably 64% by mass or more and 69% by mass or less.

The acrylonitrile butadiene rubber (A) has an SP value in the range of 19.2 (MPa) ^1/2 or more and 21.0 (MPa) ^1/2 or less. When the acrylonitrile butadiene rubber (A) has an SP value in this range, it is possible to make the conductive carbon black unevenly distributed in the sea part together with the SP value of the synthetic rubber (B) described later.

  As the SP value, a value obtained by an intrinsic viscosity method can be adopted. The intrinsic viscosity method is a method that utilizes the fact that the intrinsic viscosity of a rubber in a solvent shows a maximum value when the SP value of the rubber matches the SP value of the solvent. In other words, rubber is dissolved in solvents having various SP values, the intrinsic viscosity is measured, and the SP value of the rubber is obtained from the SP value of the solvent that gives the maximum intrinsic viscosity.

  The acrylonitrile butadiene rubber (A) preferably has a Mooney viscosity of 20 ML (1 + 4) 100 ° C. or higher and 50 ML (1 + 4) 100 ° C. or lower. If the Mooney viscosity is 20 ML (1 + 4) 100 ° C. or higher, the dispersibility of the conductive carbon black (C) and the filler can be improved, and if it is 50 ML (1 + 4) 100 ° C. or lower, the conductive carbon black (C) and the compounding quantity of a filler can be increased. The Mooney viscosity can be a value measured by a measurement method based on JIS K6300-1.

  The weight average molecular weight of such acrylonitrile butadiene rubber (A) is preferably 200,000 to 400,000. The weight average molecular weight of the acrylonitrile butadiene rubber (A) corresponds to that having the Mooney viscosity.

  The weight average molecular weight can be determined by the following measuring method.

  This is performed using a GPC (gel permeation chromatography) apparatus (HLC-8120GPC: manufactured by Tosoh Corporation) using THF (tetrahydrofuran) as a solvent. The sample is prepared as follows. Put the sample in THF and let stand for several hours, then shake well and mix well with THF, and let stand for more than 48 hours. After that, a sample processed by a sample processing filter (pore size 0.5 μm, Myshori disk H-25-5: manufactured by Tosoh Corporation) is used as a GPC sample. The sample concentration is adjusted to be 0.2 to 0.5 wt%.

The measurement was performed by stabilizing a column (TSKgel SuperHM-M: manufactured by Tosoh Corporation) in a heat chamber at 40 ° C., and flowing THF as a solvent at a flow rate of 0.6 ml / min through the column at this temperature. Inject approximately 100 μl. In measuring the molecular weight of a sample, the molecular weight distribution of the sample is calculated from the relationship between the logarithmic value of a calibration curve prepared from several types of monodisperse polystyrene standard samples and the count value. As a standard polystyrene sample for preparing a calibration curve, one having a molecular weight of about 10 ² to 10 ⁷ manufactured by Tosoh Corporation is used, and it is appropriate to use at least about 10 standard polystyrene samples. An RI (refractive index) detector is used as the detector.

[Synthetic rubber]
The synthetic rubber (B) contained in the rubber composition constitutes an island part in the conductive elastic layer, and has an SP value of 15.6 (MPa) ^1/2 or more, 18.6 (MPa). ^1/2 or less. The SP value of the synthetic rubber (B) preferably has a difference of 1.0 or more from the SP value of the acrylonitrile butadiene rubber (A) because a stable sea-island structure can be formed. When the synthetic rubber (B) has such an SP value, the conductive carbon black (C) can be unevenly distributed in the sea part of the acrylonitrile butadiene rubber (A). For this reason, the rubber composition at the time of manufacture is imparted with high good fluidity and the like, and in the conductive elastic layer, the strength of the island portion due to the conductive carbon black (C) is suppressed, and the island of high elasticity and low hardness High elasticity and low hardness are maintained by the part.

  The synthetic rubber (B) preferably has a weight average molecular weight of 40,000 or more and 80,000 or less and is a liquid rubber at room temperature. When the weight average molecular weight of the synthetic rubber (B) is 40,000 or more, the conductive carbon black (C) is alienated during kneading of the rubber composition at the time of production, and the conductive carbon black (C) on the island is removed. It is possible to obtain a conductive elastic layer that prevents penetration and has low hardness and excellent bleed resistance. Moreover, if the weight average molecular weight of a synthetic rubber (B) is 80,000 or less, the fluidity | liquidity at the time of manufacture is high, and the resistance nonuniformity which arises in a conductive elastic layer can be suppressed.

  Examples of the synthetic rubber (B) include butadiene rubber, isoprene rubber, styrene butadiene rubber, ethylene propylene rubber, butyl rubber and the like, and these can be used alone or in combination of two or more. Of these, butadiene rubber and isoprene rubber are preferably included, and butadiene rubber is particularly preferable.

  The butadiene rubber includes polycis-1,4-butadiene, polytrans-1,4-butadiene, and poly1,2-butadiene, but polycis-1,4-butadiene and polytrans-1,4-butadiene react. The speed is low, which is preferable in terms of high elasticity and flexibility. Since poly1,2-butadiene has high reactivity and high hardness, the content in the butadiene rubber is preferably 0.1% by mass or more and 10% by mass or less.

  As the content of these isomers in the butadiene rubber, a value obtained by an infrared absorption spectrum analysis method or a Morero method can be adopted.

When the infrared absorption spectrum analysis method is performed by ATR, a sample can be directly measured. Specifically, Porishisu 1,4 butadiene 733Cm ^-1, poly trans-1,4-butadiene 966Cm ^-1, poly 1,2-butadiene corresponding respective content in the peak intensity at 912cm ^-1 To do. From the spectral intensity Ac ₁ of cis-1,4 polybutadiene, the spectral intensity At ₁ of trans-1,4 polybutadiene, and the spectral intensity Av ₁ of poly 1,2-butadiene, the content mass ratio can be determined as follows.
Polycis-1,4 butadiene (% by mass) = [Ac ₁ / (Ac ₁ + At ₁ + Av ₁ )] × 100
Polytrans-1,4 butadiene (% by mass) = [At ₁ / (Ac ₁ + At ₁ + Av ₁ )] × 100
Poly 1,2-butadiene (mass%) = [Av ₁ / (Ac ₁ + At ₁ + Av ₁ )] × 100
The Morero method is effective when the cis content is high. A sample dissolved in carbon disulfide at a certain concentration is subjected to infrared transmission measurement in a fixed cell having an optical path length of 1 mm. The absorbance Ac _{2 of the} obtained polycis-1,4-butadiene, the absorbance At _{2 of} polytrans-1,4-butadiene, and the absorbance Av _{2 of} poly1,2-butadiene are obtained using the following formula.
C = (1.7455Ac ₂ -0.0151Av ₂₎
V = (0.3746Av ₂ -0.0070Ac _{2)
T = (0.4292At 2 -0.0129Av 2 -0.0454Ac} 2).
Polycis-1,4-butadiene (% by mass) = [C / (C + V + T)] × 100
Polytrans-1,4-butadiene (mass%) = [T / (C + V + T)] × 100
Poly 1,2-butadiene (mass%) = [V / (C + V + T)] × 100
[Conductive carbon black]
The conductive carbon black (C) contained in the rubber composition has conductivity that can impart desired conductivity to the conductive rubber roller, and is used unevenly in the sea as described above. As the conductive carbon black (C), specifically, conductive carbon black of ketjen black and acetylene black; carbon black for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT is used. be able to.

  The average primary particle diameter of the conductive carbon black (C) is preferably 20 nm or more, more preferably 24 nm or more. Moreover, 45 nm or less is preferable, More preferably, it is 38 nm or less. If the average primary particle diameter of the conductive carbon black (C) is within the above range, the viscosity of the rubber composition, the aggregation in the rubber composition, the hardness of the conductive elastic layer, and the fluctuation of the resistance value are suppressed. Further, conductivity can be imparted to the conductive elastic layer.

  A value obtained by the following measuring method can be adopted as the average primary particle size of the conductive carbon black. Take an image of tens of thousands of times with an electron microscope, select 100 carbon black particles arbitrarily, obtain (maximum diameter + minimum diameter) / 2 for each particle as the primary particle diameter, and average the average value of the average primary particles. It can be adopted as the diameter.

  Content in the rubber composition of the said acrylonitrile butadiene rubber (A), a synthetic rubber (B), and electroconductive carbon black (C) is the following ranges. When the mass of the acrylonitrile butadiene rubber (A) is (a), the mass of the synthetic rubber (B) is (b), and the mass of the conductive carbon black (C) is (c), (a) / (b) Is 4.00 or more and 20.0 or less, and (a) / (c) is 1.30 or more and 4.95 or less. When (a) / (b) is within this range, a conductive elastic layer having a sea-island structure in which acrylonitrile butadiene rubber (A) is the sea part and synthetic rubber (B) is the island part can be obtained. Further, if (a) / (b) is 4.00 or more, the conductive elastic layer has bleed resistance and can suppress photoconductor contamination, and the flow unevenness at the time of manufacture can be suppressed and uniform. A conductive elastic layer having conductivity is obtained. If (a) / (b) is 20.0 or less, it can suppress that the rubber composition at the time of manufacture becomes high viscosity, and can suppress that a conductive elastic layer becomes high hardness. it can. Moreover, if (a) / (c) is 1.30 or more, the conductive elastic layer is prevented from becoming hard and has an appropriate nip. When (a) / (c) is 4.95 or less, by containing a sufficient amount of conductive carbon black, the conductive elastic layer has a uniform resistance value and a stable electrical resistance. Become.

  Further, when the mass of the conductive carbon black (C) contained in the sea part is (cA) and the mass of the conductive carbon black (C) contained in the island part is (cB), [(cA) / ( a)]> [(cB) / (b)] is preferably satisfied. When the content of the conductive carbon black (C) in the sea part and the island part satisfies this range, the conductive elastic layer has bleed resistance, low hardness, and conductive uniformity. In order to contain the conductive carbon black (C) in the sea part and the island part in such a range, it can be achieved by adjusting the SP values of the sea part and the island part as described above.

  The rubber composition may contain other rubber components as long as the functions of the acrylonitrile butadiene rubber (A), the synthetic rubber (B), and the conductive carbon black (C) are not impaired. Examples of such rubber components include EPDM (ethylene-propylene-diene-copolymer), natural rubber, epichlorohydrin rubber, SBR (styrene butadiene rubber), CR (chloroprene), silicon rubber, urethane rubber, fluorine rubber, and the like. be able to. These can be used alone or in combination of two or more. These other rubber components are composed of 95 parts by mass or more of (a) and (b) with respect to 100 parts by mass of all the rubber components including acrylonitrile butadiene rubber (A) and synthetic rubber (B). , And used in the range of 0 to 5 parts by mass so as to be in the range of 100 parts by mass or less. If content of another rubber component is 5 mass parts or less, the influence on the characteristic of acrylonitrile butadiene rubber (A) or a synthetic rubber (B) will be suppressed.

  The rubber composition further includes a plasticizer, a filler, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, an anti-scorch agent as necessary, as long as no adverse effects such as bleeding and an increase in hardness occur. Additives such as dispersants, lubricants, and acid acceptors can be added as appropriate.

  A method for forming a conductive elastic layer by crosslinking the rubber composition will be described below.

  In addition to the acrylonitrile butadiene rubber (A), synthetic rubber (B), and conductive carbon black (C), other rubber components and compounding agents are blended as necessary, and dispersed and kneaded using a kneader. A rubber composition for a conductive elastic layer for vulcanization is prepared. The kneader to be used may be a general one such as a pressure kneader, a Banbury mixer, an open roll, or the like.

  The rubber composition can be molded by extrusion molding, mold molding, or the like. As the mold molding, the rubber composition is injected into a cylindrical mold set with a conductive support and heated to mold, and the molded product is extruded together with the core metal using a vent type extruder equipped with a cross head. A method of forming a conductive elastic layer around the core metal can be mentioned. Examples of the extrusion molding include a method of extruding into a cylindrical shape with an extruder, cutting, inserting a cored bar, and molding a conductive elastic layer around the cored bar.

  Vulcanization (crosslinking) can be performed, for example, by heating at 160 ° C. for 30 minutes. In the case of mold molding, after molding, the mold may be taken out of the mold as it is, and then primary vulcanization may be performed in the mold, followed by secondary vulcanization. In the case of extrusion molding, vulcanization (crosslinking) can be performed by a method such as a vulcanizing can, a batch hot air oven, continuous vulcanization, or press vulcanization. Immediately after being extruded from the extruder, it is continuously vulcanized, and the vulcanized product can be cut and a cored bar can be inserted. In this case, secondary vulcanization can be performed after the core metal is inserted. In any method, it is preferable to prepare the end by forming a rubber layer on the conductive support and then cutting off the end. In particular, when the raw rubber composition is extruded together with the conductive support, it is preferable to prepare the end portion before vulcanization.

  The conductive elastic layer formed by crosslinking the rubber composition as described above may be subjected to a polishing process such as dry polishing or wet polishing in order to adjust surface characteristics and shape. The conductive elastic layer can be processed into a straight cylindrical shape or a crown shape in the longitudinal direction by polishing. The crown-shaped conductive elastic layer is preferable because it can press-contact the pressed body and form a uniform nip width.

  Thus, the thickness of the electroconductive elastic layer obtained can be made into the range of 0.5-5.0 mm, for example.

The conductive rubber roller having the conductive elastic layer preferably has a resistance value in the range of 1 × 10 ⁴ to 1 × 10 ⁷ Ωcm. Such a resistance value can be achieved by the conductive elastic layer.

A value obtained by the following measuring method can be adopted as the resistance value (Rr) of the conductive rubber roller. After leaving the conductive rubber roller in an NN (temperature 23 ° C., humidity 60%) environment for 24 hours or more, both ends of the conductive support are pressed against a SUS drum with a diameter of 30 mm by applying a load of 500 g to the SUS drum. Rotate at 30 rpm. In this state, a DC voltage of −200 V is applied from one of the conductive support portions, and the voltage applied to the 1 kΩ resistor connected in series to the SUS drum is measured for 3 seconds. Rr = 200 × 10 ³ / Vlove is obtained from the average value Vlove (V) of the measured values. At that time, the resistance unevenness of the conductive rubber roller can be obtained from the ratio Vrmax / Vrmin between the maximum value Vrmax and the minimum value Vrmin.

  Such a conductive rubber roller may have other functional layers in addition to the conductive elastic layer. Examples of such a functional layer include a surface layer such as a resistance adjusting layer provided on the outer side of the conductive elastic layer and a protective layer for preventing contamination and bleeding. Examples of surface layer materials are polyamide resin, polyurethane resin, polyvinyl butyral resin, fluororesin, polyester resin, acrylic urethane resin, etc. with flexibility, abrasion resistance, and mechanical strength, and added according to function Including blended products. Moreover, electrical resistance can also be adjusted by mix | blending a electrically conductive agent.

  Examples of the method for producing the surface layer include the following coating methods. Add additives such as a conductive agent to the solution in which the matrix resin is dissolved and disperse using a paint disperser such as a bead mill, sand mill, ball mill, paint shaker, etc., and dip coating, spray coating, roll coating It apply | coats on a conductive elastic layer by coating methods, such as. Next, the solvent is removed using a hot-air circulating dryer or an infrared drying furnace, and a surface layer is formed on the conductive elastic layer.

  As such a surface layer, the surface of the conductive elastic layer may be highly crosslinked by irradiating the surface of the conductive elastic layer with an energy beam such as electron beam, ultraviolet ray, X-ray, infrared ray, plasma or the like. This type of surface layer is low in cost, and can reduce the burden on the environment without using a solvent. Of these, the surface layer highly crosslinked by ultraviolet rays in particular has desired electrical characteristics, and also reduces adhesion and friction coefficient, so that toner and external additives can be prevented from adhering to the surface. ,preferable.

  The conductive rubber roller of the present invention can be used for a charging roller, a developing roller, or a transfer roller of an electrophotographic apparatus such as a copying machine, a laser beam printer, an LED printer, and an electrophotographic plate making system.

  An example of the conductive rubber roller of the present invention is shown in the schematic sectional view of FIG. The conductive rubber roller shown in FIG. 1 has a conductive elastic layer 2 and a surface layer 3 on a conductive support 1.

  An electrophotographic apparatus in which the conductive rubber roller of the present invention is suitably used will be described with reference to the schematic configuration diagram of FIG. The electrophotographic apparatus shown in FIG. 2 includes a photosensitive member 21, a charging roller 10 that uniformly charges the surface of the photosensitive member, an exposure unit 24 that forms an electrostatic latent image on the charged photosensitive member, and a photosensitive member. Developing means 25 for developing the carried electrostatic latent image as a toner image is sequentially provided. Further, a transfer roller 26 for transferring the toner image on the photoconductor to a transfer material 27 such as paper, a cleaning unit 28 for removing toner remaining on the surface of the photoconductor after the transfer of the toner image, and the like are provided.

  Image formation by such an electrophotographic apparatus will be described. A charging voltage from the applied power source 23 is applied to the charging roller 10 via the rubbing electrode 23a, and the surface of the photoreceptor in contact with the charging roller is charged. Next, the exposure unit, for example, a laser beam scanner or the like, performs exposure corresponding to the image information on the surface of the photoconductor, for example, attenuates the potential of the exposed portion to form an electrostatic latent image. On the other hand, in the developing means, a developing roller 25a, in which a negative toner having the same polarity as the charging polarity of the photosensitive member and applied to a developing bias voltage lower than that of the electrostatic latent image is formed in a film shape around it, is rotated to face the photosensitive member. Then, the toner is moved onto the electrostatic latent image on the photosensitive member and developed as a toner image.

  The transfer roller is pressed against the photosensitive member by a predetermined pressing force to form a transfer nip, and a reverse polarity of the toner from the power source 29 is applied to the back surface of the recording material 27 such as paper supplied from the paper feeding device to the transfer nip. A transfer bias voltage is applied via the transfer roller 26. The transfer roller rotates at the same peripheral speed as the photosensitive member, and the toner image on the photosensitive member is electrostatically transferred onto the recording material.

  Thereafter, the recording material is separated from the surface of the photoconductor, and the toner image on the recording material is fixed by heat and pressure between the fixing roller and the pressure roller in the fixing unit, and the recording material on which the permanent image is formed is outside the apparatus. Is discharged. In the double-sided image forming mode or the multiple image forming mode, the recording material is introduced into a recirculation conveyance mechanism (not shown) and reintroduced into the transfer nip portion.

  After the toner image is transferred, toner remaining on the photoconductor without being transferred is removed and collected from the photoconductor by a cleaning means. Further, the photosensitive member is irradiated with static elimination light by the charge removing means, the remaining latent image is erased, and the next image formation is awaited.

  In such an electrophotographic apparatus, the conductive rubber roller can be applied to the charging roller 10, the developing roller 25a, and the transfer roller 26. For example, in the charging roller, a conductive elastic layer 12 is provided on the surface of the conductive support 11, and a surface layer 13 is further provided thereon.

  For example, the above-mentioned constituent members can be used as a process cartridge in which two or more of a photosensitive member, a charging roller, a developing unit, a cleaning unit, and the like are combined and integrated to be detachable from the main body of the electrophotographic apparatus.

Hereinafter, the present invention will be described in more detail with reference to specific examples to which the conductive rubber roller of the present invention is applied, but the technical scope of the present invention is not limited thereto.
[Example 1]
The following components were kneaded with a pressure kneader for 20 minutes.
95 parts by mass of acrylonitrile butadiene rubber (A) (Nipol DN219: manufactured by Nippon Zeon Co., Ltd.) (acrylonitrile unit: 33.5% by mass, Mooney viscosity: 27.0 ML (1 + 4) 100 ° C., SP value 19.7 MPa ^{1 / 2} )
5 parts by mass of liquid butadiene rubber (B1) (LIR-300: manufactured by Kuraray Co., Ltd.) (weight average molecular weight (hereinafter referred to as Mw) 47,358, poly 1,2-butadiene 7.5% by mass, 17.0 MPa ^1/2 )
40 parts by mass of conductive carbon black (C1) (# 7360SB: manufactured by Tokai Carbon Co., Ltd.) (average primary particle size 28 nm)
20 parts by weight of calcium carbonate (Nanox # 30: manufactured by Maruo Calcium Co., Ltd.)
Zinc oxide 5 parts by mass (Zinc oxide 2 types: manufactured by Shodo Chemical Co., Ltd.)
1 part by weight of zinc stearate (zinc stearate: manufactured by NOF Corporation)
The obtained rubber composition was transferred to a 12-inch open roll, and the following were further added and kneaded for 15 minutes to prepare an unvulcanized rubber composition.
1 part by mass of di-2-benzothiazolyl disulfide (Noxeller DM-P: manufactured by Ouchi Shinsei Chemical Co., Ltd.)
Tetrabenzylthiuram disulfide 4 parts by mass (Noxeller TBzTD: Ouchi Shinsei Chemical Co., Ltd.)
0.8 parts by mass of sulfur Next, a cored bar (manufactured by SUS, φ6) was formed by an extrusion molding machine using a cross head set at 80 ° C. (50 mm diameter vent type extruder, L / D = 16, manufactured by EM Giken). The unvulcanized rubber composition was extruded into a cylindrical shape on the same axis centering around 0.0 mm and a length of 258.0 mm. Excess rubber up to 10.0 mm from the end of the mandrel was cut to make the length of the unvulcanized rubber composition on the mandrel to 238.0 mm, and then vulcanized at 160 ° C. for 1 hour in a hot air drying furnace. The vulcanized rubber roller was polished by dry polishing into a crown shape having an outer diameter of 8.5 mm at the center of the rubber and an outer diameter of the rubber end of 8.25 mm.

Furthermore, using a low-pressure mercury lamp, surface treatment is performed by irradiating with ultraviolet rays for 100 seconds while rotating the vulcanized rubber roller after polishing at 30 rpm with an ultraviolet intensity of 60 mW / cm ² to obtain a conductive rubber roller. It was. The resistance value of the conductive rubber roller was 1.0 × 10 ⁵ Ωcm.

  The conductive elastic layer of the obtained conductive rubber roller was observed with a SEM at a magnification of several thousand times. From the observed image, the sea part which is the continuous phase and the island part of the discontinuous phase were confirmed. The SEM observation image was subjected to image processing using image processing software “image-pro plus” (Media Cybernetics), and the areas of the sea and the island were calculated. The area ratio between the sea part and the island part substantially corresponded to the mass ratio (a) / (b) of the acrylonitrile butadiene rubber (A) and the liquid butadiene rubber (B1) component. Therefore, it was easily found that the acrylonitrile butadiene rubber (A) formed the sea part where the continuous phase was formed, and the liquid butadiene rubber (B1) formed the island part of the discontinuous layer. Further, in the observed image, it was confirmed that most of the carbon black was unevenly distributed in the acrylonitrile butadiene rubber (A) component. Image processing is performed in the same manner as described above to calculate the area cA ′ of conductive carbon black observed in the sea component and the area cB ′ of conductive carbon black observed in the island component. From the ratio (cA ′) / (cB ′), (cA) / (cB) was confirmed. This confirmed that [(cA) / (a)]> [(cB) / (b)].

[hardness]
The obtained conductive rubber roller was left in an NN environment (temperature 23 ° C., humidity 60%) for 24 hours or longer. Thereafter, using a micro rubber hardness meter (MD-1 needle type-A, manufactured by Kobunshi Keiki Co., Ltd.), three points in the circumferential direction were measured in the peak hold mode at the center position in the longitudinal direction of the conductive rubber roller. . The results are shown in Table 1.

[Image uniformity]
The obtained conductive rubber roller was incorporated as a charging roller in a black all-in-one cartridge of a laser beam printer LBP5500 manufactured by Canon Inc. In this state, the cartridge was left in an LL environment (temperature 15 ° C., humidity 10%) for 24 hours, and then the cartridge was set in the LBP 5500 to output a halftone image and a practical image (photographic image). Observe the obtained image by visual inspection, depending on the presence or absence of image defects such as white / black spots, white / black streaks, black spots, etc. caused by non-uniform dispersion of carbon black, resistance unevenness, contact unevenness, etc. The evaluation was based on the following criteria. The results are shown in Table 1.
○: No image defect at all.
Δ: Although there is no image defect in a practical image, it is observed in a halftone image.
X: Image defects are observed in both the practical image and the halftone image.

[Photoconductor contamination]
The obtained conductive rubber roller was incorporated as a charging roller for a black all-in-one cartridge of a laser beam printer LBP5500 manufactured by Canon Inc. In that state, after being left in a constant temperature and humidity chamber at a temperature of 40 ° C. and a humidity of 95% for 7 days and then in an NN environment (temperature 23 ° C., humidity 60%) for 4 hours, this cartridge is set in the LBP5500, Output. Thereafter, the photoconductor was taken out from the cartridge, and the surface of the photoconductor was observed at a magnification of 100 using an optical microscope. Photoconductor contamination was evaluated according to the following criteria. The results are shown in Table 1.
◯: There is no defective image due to contamination of the photoreceptor in the halftone image, and no deposits or cracks due to bleeding are observed on the surface of the photoreceptor.
Δ: There is no image defect due to contamination of the photoreceptor in the halftone image, and there is no crack on the surface of the photoreceptor, but deposits are observed on the surface of the photoreceptor.
X: Image defect due to photoconductor contamination is observed in the halftone image, and deposits or cracks are generated on the surface of the photoconductor.

[Example 2]
A conductive rubber roller was prepared in the same manner as in Example 1 except that 90 parts by mass of acrylonitrile butadiene rubber (A) and 10 parts by mass of liquid butadiene rubber (B1) were prepared, and the hardness and resistance values were measured to form an image. The photoreceptor contamination was evaluated. The results are shown in Table 1.

[Example 3]
A conductive rubber roller was prepared in the same manner as in Example 1 except that 80 parts by mass of acrylonitrile butadiene rubber (A) and 20 parts by mass of liquid butadiene rubber (B1) were prepared, and the hardness and resistance values were measured to form an image. The photoreceptor contamination was evaluated. The results are shown in Table 1.

[Example 4]
Except for using liquid isoprene rubber (B2) (LIR-50: manufactured by Kuraray Co., Ltd.) (Mw 65, 194, 16.0 MPa ^1/2 ) instead of liquid butadiene rubber (B1), the same as in Example 2. A conductive rubber roller was produced. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 1.

[Example 5]
Except for using 40 parts by mass of conductive carbon black (C1), conductive carbon black (C2) (# 5500: manufactured by Tokai Carbon Co., Ltd.) (average primary particle size 25 nm) was used in the same manner as in Example 1. A conductive rubber roller was produced. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 1.

[Example 6]
The same as Example 3 except that conductive carbon black (C3) (G-116HM: manufactured by Tokai Carbon Co., Ltd.) (average primary particle size 38 nm) was used instead of 40 parts by mass of conductive carbon black (C1). A conductive rubber roller was prepared. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 1.

[Comparative Example 1]
A conductive rubber roller was prepared in the same manner as in Example 1 except that 98 parts by mass of acrylonitrile butadiene rubber (A) and 2 parts by mass of liquid butadiene rubber (B1) were used, and the hardness and resistance values were measured to form an image. The photoreceptor contamination was evaluated. The results are shown in Table 2.

[Comparative Example 2]
A conductive rubber roller was prepared in the same manner as in Example 1 except that 70 parts by mass of acrylonitrile butadiene rubber (A) and 30 parts by mass of liquid butadiene rubber (B1) were prepared, and the hardness and resistance values were measured to form an image. The photoreceptor contamination was evaluated. The results are shown in Table 2.

[Comparative Example 3]
Liquid butadiene rubber (B3) instead of liquid butadiene rubber (B1) (LIR-30: manufactured by Kuraray Co., Ltd.) (Mw 34,050, poly 1,2-butadiene 7.6 mass%, 17.0 MPa ^1/2 ) A conductive rubber roller was produced in the same manner as in Example 2 except that was used. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 2.
[Comparative Example 4]
Liquid butadiene rubber (B4) instead of liquid butadiene rubber (B1) (R-45HT: manufactured by Idemitsu Kosan Co., Ltd.) (Mw 3,580, poly 1,2-butadiene 20.0 mass%, 17.0 MPa ^1/2 ) A conductive rubber roller was produced in the same manner as in Example 2 except that was used. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 2.

[Comparative Example 5]
Except for using liquid acrylonitrile butadiene rubber (B5) (Nipol 1312: manufactured by Nippon Zeon Co., Ltd.) (Mw 9, 114, 19.7 MPa ^1/2 ) instead of liquid butadiene rubber (B1), the same as Example 2 A conductive rubber roller was prepared. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 2.

[Comparative Example 6]
Example 1 except that conductive carbon black (C4) (Seast 9H: manufactured by Tokai Carbon Co., Ltd.) (average primary particle diameter 18 nm) was used instead of 40 parts by mass of conductive carbon black (C1). A conductive rubber roller was prepared in the same manner as described above. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 2.

[Comparative Example 7]
Conductive rubber as in Example 3 except that conductive carbon black (C5) (# 4300: manufactured by Tokai Carbon Co., Ltd.) (average primary particle size 55 nm) was used instead of conductive carbon black (C1). A roller was produced. In the same manner as in Example 1, hardness and resistance values were measured, and image formation and photoreceptor contamination were evaluated. The results are shown in Table 2.

  From the results, it can be seen that the conductive rubber roller of the present invention is free from contamination of the photoreceptor, has little resistance unevenness, and has excellent image / resistance uniformity. In contrast, in Comparative Example 1, since the amount of the synthetic rubber (B) added is small, it can be seen that the viscosity and hardness are high, the resistance unevenness, and the image uniformity are inferior. In Comparative Example 2, since the amount of the synthetic rubber (B) was large, flow unevenness occurred during extrusion, resulting in poor image / resistance uniformity. It can be seen that Comparative Examples 3, 4, and 5 are inferior in photoreceptor contamination because the Mw of the synthetic rubber (B) is small. Furthermore, since the comparative example 4 has a large content ratio of poly1,2-butadiene of 20% by mass, it can be seen that the micro hardness increases and the resistance uniformity is inferior. In Comparative Example 5, since the SP value of the synthetic rubber (B) was the same as the SP value of the acrylonitrile butadiene rubber (A), it was confirmed that no sea island structure was formed. For this reason, the effect of suppressing the increase in hardness is small, and the image uniformity is inferior. In Comparative Examples 6 and 7, since the average primary particle diameter of the conductive carbon black (C) is different, the addition amount necessary for the desired resistance value is changed. Comparative Example 6 has large (a) / (c) and poor dispersibility of carbon black, resulting in large resistance unevenness, and Comparative Example 7 has low (a) / (c) and high Mooney viscosity. It can be seen that the resistance unevenness at the time increases and the image uniformity is inferior.

It is a schematic sectional drawing which shows a conductive rubber roller. It is a schematic block diagram which shows the electrophotographic apparatus using the conductive rubber roller of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 Conductive support body 2, 12 Conductive elastic layer 3, 13 Surface layer 10 Charging roller 21 Photoconductor 25a Developing roller 26 Transfer roller

Claims (6)

In a conductive rubber roller having a conductive elastic layer on a conductive support,
Conductive elastic layer
An acrylonitrile butadiene rubber (A) having an SP value of 19.2 (MPa) ^1/2 or more and 21.0 (MPa) ^1/2 or less,
A synthetic rubber (B) having an SP value of 15.6 (MPa) ^1/2 or more and 18.6 (MPa) ^1/2 or less, and a weight average molecular weight of 40,000 or more and 80,000 or less;
Conductive carbon black (C)
When the mass of the acrylonitrile butadiene rubber (A) is (a), the mass of the synthetic rubber (B) is (b), and the mass of the conductive carbon black (C) is (c), (a) / (b) Is 4.00 or more and 20.0 or less, (a) / (c) is 1.30 or more and 4.95 or less,
Conductivity characterized by being formed by crosslinking a rubber composition in which the total of (a) and (b) is 95 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the rubber component. Rubber roller.   The conductive rubber roller according to claim 1, wherein the acrylonitrile butadiene rubber (A) contains acrylonitrile units in a range of 31% by mass or more and less than 36% by mass.   The conductive rubber roller according to claim 1 or 2, wherein the synthetic rubber (B) contains at least one of butadiene rubber and isoprene rubber.   The conductive elastic layer has a sea-island structure having a sea part containing acrylonitrile butadiene rubber (A) and an island part containing synthetic rubber (B), and the mass of the conductive carbon black (C) contained in the sea part Is (cA), and the mass of the conductive carbon black (C) contained in the island is (cB), the claim that satisfies [(cA) / (a)]> [(cB) / (b)] Item 4. The conductive rubber roller according to any one of Items 1 to 3.   The conductive rubber roller according to claim 3 or 4, wherein the butadiene rubber has a poly1,2-butadiene content in the range of 0.1% by mass or more and 10% by mass or less.   The conductive rubber roller according to any one of claims 1 to 5, wherein the average primary particle diameter of the conductive carbon black (C) is 20 nm or more and 45 nm or less.

Images