JP2012063590A - Charging member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging member in which permanent deformation is hard to occur.SOLUTION: A charging member includes an elastic body layer 12 on a conductive support 11 in which the elastic body layer is formed by a cured and unvulcanized rubber blend including binder polymer containing butadiene rubber (A) and 1, 2-syndiotactic polybutadiene (B); and conductive particles.

Description

  The present invention relates to a charging member.

  In recent years, an electrophotographic apparatus such as a copying machine or an optical printer, and an image forming apparatus such as an electrostatic recording apparatus employ a contact charging method as a charging method for a photosensitive member or a dielectric. In the contact charging method, a member to be charged by applying a voltage (referred to as a charging member) is brought close to or in contact with the surface of the object to be charged, and the surface of the object to be charged is charged. Generally, using a rubber roller type charging member having a semiconductive elastic layer formed on a shaft of a metal core, the surface of the photosensitive member is charged by rotating while pressing against the photosensitive member. .

  In such an elastic layer of the charging roller, an ionic conductive agent or conductive particles are blended as a conductive agent into urethane, acrylic urethane, acrylic ester, NBR (nitrile rubber), epichlorohydrin or the like to make it semiconductive. Used. The charging member is required to ensure uniform contact with the photosensitive member in the roller axis direction in order to uniformly charge the photosensitive member.

  Further, it has been pointed out that the charging member is permanently deformed as a result of press contact between the photosensitive member and the charging member for a long period of time, and an abnormal image is generated due to excessive current from the nip portion. Also, problems have been pointed out such that the deformed portion non-uniformly contacts the photoconductor when the roller rotates, causing exposure unevenness and causing image defects. In particular, in recent years, with the improvement of the process speed and the high definition of image quality in electrophotography, there is a problem that an image defect occurs even with a slight permanent deformation of the charging member. For such a problem, Patent Document 1 discloses that the elastic layer has a coating layer, and maintains a low hardness while reducing the permanent deformation when the photosensitive member and the charging member are pressed against each other for a long time. A charging member is disclosed.

JP-A-10-319676

  An object of the present invention is to provide a charging member that is less prone to permanent deformation.

  According to the present invention, there is provided a charging member having an elastic layer on a conductive support, wherein the elastic layer contains a butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). And a charged member made of a cured product of an unvulcanized rubber mixture containing conductive particles.

  In the charging member of the present invention, permanent deformation when brought into contact with the photosensitive member for a long time is reduced, and set image defects are reduced.

1 is a schematic cross-sectional view of an example of an electrophotographic apparatus to which the present invention can be applied. It is a typical sectional view of an example of the charging roller of the present invention.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to this embodiment.

<< Charging member >>
The charging member of the present invention is a charging member having an elastic layer on a conductive support. Further, the charging member of the present invention can load the elastic layer on the conductive support. The charging member of the present invention can have a highly conductive support and an elastic layer composed of at least one layer on the support. The elastic layer contains butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). The elastic layer is a cured product of an unvulcanized rubber mixture, and the unvulcanized rubber mixture includes a binder polymer containing butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). And conductive particles.

  In addition, a binder polymer means the polymer component mix | blended in order to provide an elastic body layer formation ability among the unvulcanized rubber mixtures used in order to form a charging member. The content ratio of the butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B) in the binder polymer is the sum of the butadiene rubber (A) and the 1,2-syndiotactic polybutadiene (B). Is preferably 5% by mass or more. If it is 5 mass% or more, the reduction of the effect by having too little content of these components can be prevented easily.

  The binder polymer can be composed of butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). There are cis 1,4 structure, trans 1,4 structure, and vinyl structure (1,2 structure) in the butadiene monomer unit bond structure of butadiene rubber. Conformational structures include syndiotactic, atactic and isotactic. In the present invention, the butadiene rubber (A) does not contain 1,2-syndiotactic polybutadiene.

  The unvulcanized rubber mixture can be obtained by dispersing conductive particles in a binder polymer containing 1,2 syndiotactic polybutadiene (B) and butadiene rubber (A). The elastic layer used in the present invention can be made of a vulcanized rubber mixture obtained by curing this unvulcanized rubber mixture. The unvulcanized rubber mixture and the vulcanized rubber mixture can be semiconductive.

  FIG. 1 is a schematic configuration example of an electrophotographic apparatus to which the charging member of the present invention can be applied, and has a charging member. Reference numeral 21 denotes an electrophotographic photosensitive member (image carrier) as a member to be charged. The electrophotographic photosensitive member in FIG. 1 includes a conductive support 21b such as aluminum and a photosensitive layer 21a formed on the support 21b. A drum-shaped electrophotographic photosensitive member as a basic constituent layer. It is rotationally driven at a predetermined peripheral speed in the clockwise direction in the figure around the support shaft 21c.

  A charging roller 1 is disposed in contact with the electrophotographic photosensitive member 21 to charge (primary charging) the electrophotographic photosensitive member to a predetermined polarity and potential, and the charging member of the present invention can be used. The charging roller 1 includes a cored bar 11 that is a conductive support and an elastic body layer 12 formed on the cored bar 11. Both ends of the cored bar 11 are pressed on the electrophotographic photosensitive member 21 by pressing means (not shown). Followed by rotation drive.

  The electrophotographic photosensitive member 21 is contact-charged to a predetermined polarity / potential by applying a predetermined direct current (DC) bias of the core metal 11 by the rubbing power source 23a. The electrophotographic photosensitive member 21 whose peripheral surface is charged by the charging roller 1 is then subjected to exposure of target image information (laser beam scanning exposure, slit exposure of a document image, etc.) by an exposure device 24, so that the peripheral surface has a target. An electrostatic latent image corresponding to the image information is formed.

  The electrostatic latent image is then successively visualized as a toner image by the developing member 25. This toner image is then synchronized with the rotation of the electrophotographic photosensitive member 21 from a paper feeding unit (not shown) by the transfer unit 26 and transferred at a proper timing between the electrophotographic photosensitive member 21 and the transfer unit 26. Are sequentially transferred to the transfer material 27 conveyed to the substrate. The transfer means 26 in FIG. 1 is a transfer roller, and the toner image on the electrophotographic photosensitive member 21 side is transferred to the transfer material 27 by charging from the back of the transfer material 27 with the opposite polarity to the toner.

  The transfer material 27 having received the transfer of the toner image on the surface is separated from the electrophotographic photosensitive member 21 and conveyed to a fixing means (not shown) to receive image fixing and output as an image formed product. Alternatively, in the case of forming an image on the back side, it is conveyed to a re-conveying means (not shown) to the transfer unit.

  The peripheral surface of the electrophotographic photosensitive member 21 after the image transfer is subjected to pre-exposure by a pre-exposure device 28 serving as pre-exposure means, and residual charges on the electrophotographic photosensitive drum are removed (static elimination). Known means can be used for the pre-exposure means 28. For example, an LED chip array, a fuse lamp, a halogen lamp, and a fluorescent lamp can be preferably exemplified.

The peripheral surface of the electrophotographic photosensitive member 21 from which the charge has been removed is cleaned by the cleaning member 29 after removal of adhering contaminants such as toner remaining after transfer, and is repeatedly used for image formation.
The charging roller 1 may be driven and driven by the electrophotographic photosensitive member 21 driven to move the surface, may not be rotated, or has a predetermined circumference in the forward or reverse direction in the surface moving direction of the electrophotographic photosensitive member 21. You may make it actively rotate at a speed.

For example, when the electrophotographic apparatus is used as a copying machine, exposure is performed as follows. That is, reflected light or transmitted light from a document, or reading a document as a read signal, scanning a laser beam based on this signal, driving an LED array, or driving a liquid crystal shutter array, etc. Done.
Examples of the electrophotographic apparatus that can use the charging member of the present invention include copying machines, laser beam printers, LED printers, and electrophotographic application apparatuses such as an electrophotographic plate making system.

  In addition to the charging roller, the charging member of the present invention can also be used as a developing member, a transfer member, a charge eliminating member, and a conveying member such as a paper feed roller.

  The charging member of the present invention can be composed of a cored bar as a conductive support and a semiconductive elastic layer provided on the outside (surface) thereof. FIG. 2 shows a schematic diagram of a charging roller as an example of the charging member of the present invention. The charging roller is composed of a cored bar 11 and an elastic body layer 12 provided on the outer periphery thereof, and a surface layer 13 can be provided outside the elastic body layer 12 if necessary.

<Conductive support>
The conductive support supports a conductive elastic layer, a surface layer, and the like provided thereon, and has a strength that can sufficiently withstand a load caused by contact with a member to be charged. Examples of the shape include a columnar shape and a cylindrical shape when the charging member has a roller shape. Examples of the material of the conductive support include metal (made of alloy) such as iron, copper, stainless steel, aluminum, aluminum alloy, and nickel. These conductive supports may be subjected to a surface treatment such as plating for the purpose of scratch resistance and rust prevention within a range not impeding the conductivity.

<Elastic body layer>
The elastic layer contains butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). The elastic layer is a cured product of an unvulcanized rubber mixture containing a binder polymer containing butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B) and conductive particles. Further, the elastic body layer is a cured product of an unvulcanized rubber material containing conductive particles as a dispersion in a binder polymer containing butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). Can be configured.

  Polybutadiene bonding modes (bonding structures) prepared by polymerizing butadiene include a cis 1,4 structure, a trans 1,4 structure, and a vinyl structure (1,2 bond). Further, the stereoregularity of the bonding mode includes syndiotactic, isotactic, and atactic. Butadiene rubber (A) is a kind of polybutadiene, and means stereoregularity other than syndiotactic. Therefore, in the present invention, the 1,2-syndiotactic polybutadiene-containing butadiene rubber means a binder polymer in which 1,2-syndiotactic polybutadiene (B) is contained in the butadiene rubber (A).

Generally, when the content of the cis 1,4 structure in the bonded structure is high, the tensile strength of the crosslinked product and the elongation at the time of cutting tend to increase, and when the content of the cis 1,4 structure is low, the roll winding There is a tendency for adherence to decrease. For this reason, it is preferable that the content rate of the cis 1,4 structure in the coupling | bonding structure of the butadiene monomer unit of the butadiene rubber (A) used for this invention is 94 mass% or more. If it is 94 mass% or more, it will become especially favorable mechanical strength and it will be excellent especially in workability. In addition, the content rate of cis 1,4 structure in the coupling | bonding structure of the butadiene monomer unit of butadiene rubber (A) can be measured by carrying out a ¹³ C-NMR analysis of raw material rubber. The raw rubber means a rubber that is not mixed with a binder polymer.

Specific measurement conditions are shown below.
Measuring apparatus: FTNMR apparatus JNM-EX400 (trade name, manufactured by JEOL Ltd.)
Observation frequency: 75.4 MHz
recycle delay: 1S
flip angle: 90 °
Data points: 32768
Integration count: 10,000 times Decoupling: gated decoupling (without NOE)
Measurement temperature: Sample for room temperature measurement: 100 mg of a measurement sample was placed in a sample tube having a diameter of 10 mm, and CDCl ₃ (containing 0.05% tetramethylsilane (TMS)) was added as a solvent. By this method, the molar ratio of the bonding mode of the butadiene rubber (A) was calculated from the measured peak area ratio, and converted into mass to obtain the content of the cis 1,4 structure.

  The 1,2 syndiotactic polybutadiene (B) used in the present invention is a polybutadiene having a 1,2 bond and a syndiotactic structure. 1,2-syndiotactic polybutadiene (B) has a crystal structure such as fine fibrous crystals, and has a reinforcing effect due to the bonding force between the crystal interface and butadiene rubber (A).

  Therefore, conductive particles are dispersed in a binder polymer containing 1,2 syndiotactic polybutadiene (B) and butadiene rubber (A), and a cured product of the resulting unvulcanized rubber mixture is used as an elastic layer. The following effects can be easily obtained.

  That is, at the time of low deformation, the crystal interface part plays a role like a crosslinking point, the polymer chain hardly moves in the rubber, and the permanent deformation becomes small. In particular, as in the case of contact with a photoreceptor in an electrophotographic apparatus, the permanent deformation when contacted for a long time with a weak force is reduced, and image defects are reduced. When the content of the cis 1,4 structure is increased, the tensile strength is increased, so that the force for supporting the 1,2-syndiotactic polybutadiene crystal is increased when subjected to pressure from the photoreceptor.

  In the present invention, the content of the cis 1,4 structure is preferably 94% by mass or more, and the permanent deformation in contact with the photoreceptor is smaller than that in the case of less than 94% by mass, and image defects are reduced. To do.

  The fiber diameter of the 1,2-syndiotactic polybutadiene fibrous crystal used in the present invention is preferably 0.1 μm or less. This is because the fiber diameter decreases, the area of the crystal interface increases, and the interaction with the butadiene rubber (A) increases. If crystals having a fiber diameter of 0.1 μm or less are contained in the butadiene rubber (A), the permanent deformation when contacting with the photoreceptor becomes smaller.

  The method for preparing the binder polymer is not particularly limited, but a method for obtaining the binder polymer by dispersing 1,2-syndiotactic polybutadiene (B) in the butadiene rubber (A) will be described below as an example. At this time, the content of 1,2-syndiotactic polybutadiene (B) is the same as that of 1,2-syndiotactic polybutadiene (B), but the butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B). It can be calculated by dividing by the total mass of.

  Examples include a method of mixing raw materials using a closed mixer such as a Banbury mixer or a pressure kneader, a mixing method using an open type mixer such as an open roll, and the like. When 1,2-syndiotactic polybutadiene (B) is dispersed using these mixers, the crystals of 1,2-syndiotactic polybutadiene become fibrous with a fiber diameter of 0.2 to 0.8 μm. . When mixed with a mixer, crystals with a fiber diameter of less than 0.2 μm are difficult to obtain.

  Specific examples of the butadiene rubber (A) include BR71 (trade name) manufactured by Nippon Synthetic Rubber, BR1220L (trade name) manufactured by Nippon Zeon, and BR02LL (trade name) manufactured by Nippon Synthetic Rubber Co., Ltd. . Specific examples of 1,2-syndiotactic polybutadiene (B) include RB820 (trade name) manufactured by Nippon Synthetic Rubber.

  A method of dispersing 1,2-syndiotactic polybutadiene (B) in the butadiene rubber (A) other than the above mixing method will be described as an example.

  A butadiene rubber (A) is synthesized by polymerizing 1,3-butadiene in cis 1,4 using a polybutadiene polymerization catalyst composed of a cobalt compound and a halogen-containing organic aluminium compound in an organic solvent. Subsequently, 1,3-butadiene is added to the polymerization reaction mixture containing the butadiene rubber (A) as necessary, and 1,3-butadiene is converted into syndiotactic 1,2 using a cobalt compound-based polymerization catalyst. Polymerization is performed to synthesize 1,2 syndiotactic polybutadiene (B). Thereby, a binder polymer in which 1,2 syndiotactic polybutadiene (B) having a high degree of crystallinity is uniformly dispersed in the butadiene rubber (A) can be obtained. When 1,2 syndiotactic polybutadiene (B) is dispersed in butadiene rubber (A) by such a method, the crystal structure of 1,2 syndiotactic polybutadiene (B) has a fiber diameter of 0.02 to 0.001. It becomes a thin fiber structure of 1 μm. The resulting fiber diameter is smaller than when a mixer is used. For this reason, the area of the crystal interface of 1,2 syndiotactic polybutadiene (B) increases, the interaction with the butadiene rubber (A) becomes larger, and the case where it comes into contact with the photoconductor than when a mixer is used. The permanent deformation of becomes smaller. In addition, the dispersion state of 1,2 syndiotactic polybutadiene (B) in the butadiene rubber (A) is more preferable because it is particularly difficult to change due to the thermal history during processing. Examples of commercially available materials having such characteristics (a binder polymer in which 1,2-syndiotactic polybutadiene (B) is uniformly dispersed in butadiene rubber (A)) include VCR412, VCR617, and VCR450 (trade names, Ube Industries, Ltd.). Etc.). In this case, the mass of 1,2-syndiotactic polybutadiene (B) is measured from the amount remaining as a solid when the raw rubber is dissolved in hexane.

  The content of 1,2-syndiotactic polybutadiene (B) with respect to the total content of butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B) in the binder polymer and the elastic layer is 3.8 masses. % To 20% by mass is preferable. If it is 3.8% by mass or more, the elastic modulus can be easily prevented from becoming small, and the effect of reducing image defects due to permanent deformation when kept in contact with the photoreceptor for a long time can be easily prevented from being reduced. it can. In addition, if it is 20% by mass or less, the hardness becomes moderately high, resulting in poor contact with the photoreceptor when used as a charging member, and dirt such as toner and paper dust on the surface of the charging member during long-term use. It is possible to easily prevent non-uniform adhesion and image defects.

  The said electroconductive particle means a particle | grains required in order to express electroconductivity among the materials added in the process of manufacturing a charging member. Examples of the conductive particles include conductive carbon black such as carbon black, acetylene black, ketjen black, metal powder such as graphite, aluminum, nickel, tin oxide, titanium oxide, antimony oxide, Examples thereof include conductive metal oxides such as indium oxide, potassium titanate, antimony oxide-tin oxide composite oxide (ATO), and indium oxide-tin oxide composite oxide (ITO). These may be used alone or in combination of two or more.

  In the elastic layer, in addition to the above polymer (a binder polymer containing butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B)), other binder polymers can be blended and used. The polymer to be blended is not particularly limited, and specifically, natural rubber (NR), isoprene rubber (IR) styrene-butadiene (SBR), butyl rubber (IIR), ethylene-propylene-diene ternary. Copolymer rubber (EPDM), epichlorohydrin homopolymer (CHC), epichlorohydrin-ethylene oxide copolymer (CHR), epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (CHR-AGE), acrylonitrile-butadiene copolymer Examples thereof include a blend (NBR), a hydrogenated product of acrylonitrile-butadiene copolymer (H-NBR), a chloroprene rubber (CR), and an acrylic rubber (ACM, ANM).

  Furthermore, the elastic body layer is made of a material that is used as an elastic body layer, and if necessary, a filler, a processing aid, a crosslinking aid, a crosslinking accelerator, a crosslinking promotion aid, a crosslinking retardation, which are generally used as a rubber compounding agent. Agents, softeners, plasticizers, dispersants and the like can be added.

  As a method for forming the elastic body layer, an unvulcanized unvulcanized rubber mixture is extruded into a tube shape by an extruder, and the core metal is press-fitted into a product obtained by vulcanization molding (curing) with a vulcanizing can, A method of polishing the surface to obtain a desired outer diameter; a vulcanized rubber mixture after vulcanization is coextruded into a cylindrical shape around a core metal by an extruder equipped with a crosshead, and a mold having a desired outer diameter Examples thereof include a method of obtaining a molded product by fixing and heating inside.

The surface of the elastic layer may be subjected to surface modification by ultraviolet irradiation, electron beam irradiation or the like so that dirt such as toner and paper powder does not easily adhere. Furthermore, the charging member of the present invention can have a surface layer separately. As the surface layer, a known coating layer is generally used. For example, a binder polymer such as acrylic polymer, polyurethane, polyamide, polyester, polyolefin, silicone, carbon black, graphite, titanium oxide, tin oxide, etc. Oxides; conductive particles obtained by coating the surface of particles with metal such as Cu and Ag and metal oxides; and by appropriately dispersing ionic electrolytes such as LiClO ₄ , KSCN, NaSCN, and LiCF ₃ SO ₃ , A desired electric resistance value or a sol-gel film made of polysiloxane having an oxyalkylene group is used.

  As a method for forming the surface coating layer, a liquid obtained by dissolving or dispersing the surface layer material as described above in a solvent is applied to the surface of the elastic layer by a coating method such as dipping, ring coating, beam coating, roll coater, or spraying. And the like. In the present invention, a good image is obtained even when the surface layer is not provided, and it is preferable not to have a separate surface layer in addition to the elastic body layer in view of cost. The charging roller of the present invention can be provided with functional layers such as an adhesive layer, a diffusion prevention layer, a base layer, and a primer layer in addition to the elastic body layer and the surface coating layer as necessary.

  The present invention will be described in more detail with reference to the following examples, but these examples do not limit the present invention. In the following, commercially available high-purity products were used unless otherwise specified.

<Example 1>
(Preparation of unvulcanized rubber mixture)
The materials shown in Table 1 were kneaded and mixed A using a 6-liter pressure kneader (trade name: TD6-15MDX, manufactured by Toshin). At that time, A kneading mixing conditions were a filling rate of 60 vol%, a blade rotation number of 35 rpm, and mixing for 16 minutes to obtain an A kneading rubber composition (A kneading rubber mixture).

  Next, the materials shown in Table 2 were mixed in an open roll having a roll diameter of 12 inches. The mixing conditions were a front roll rotation speed of 8 rpm, a rear roll rotation speed of 10 rpm, and a roll gap of 2 mm for 20 minutes to obtain an unvulcanized rubber composition for an elastic layer.

(Charging roller molding)
Next, a conductive vulcanizing adhesive (commodity) is attached to the central portion 228 mm in the axial direction of the cylindrical surface of a cylindrical conductive mandrel having a diameter of 6 mm and a length of 252 mm (manufactured by Micron Seiko Co., Ltd., steel, surface is nickel-plated). Name: METALOC U-20, manufactured by Toyo Chemical Laboratory) was applied and dried at a temperature of 80 ° C. for 30 minutes.

  Next, the unvulcanized rubber composition is simultaneously extruded into a cylindrical shape coaxially around the conductive support by extrusion molding using a crosshead, and the unvulcanized rubber composition is formed on the outer periphery of the conductive support. An unvulcanized rubber roller coated with was prepared. The extruder used was an extruder having a cylinder diameter of 45 mm and L / D = 20. The temperature during extrusion was adjusted to a head temperature of 100 ° C., a cylinder temperature of 110 ° C., and a screw temperature of 110 ° C. The extruder used was an extruder having a cylinder diameter of 45 mm and L / D = 20. The temperature during extrusion was adjusted to a head temperature of 100 ° C., a cylinder temperature of 110 ° C., and a screw temperature of 110 ° C.

  The obtained unvulcanized rubber roller was heated in a heating furnace in air at atmospheric pressure at a temperature of 160 ° C. for 30 minutes for vulcanization. After vulcanizing, both ends of the rubber of the vulcanized roller are cut off to make the length of the rubber part 232 mm, and then the rubber part is polished with a polishing machine (product name: LEO-600-F4-BME, manufactured by Mizuguchi Seisakusho). A vulcanized rubber roller having a crown-shaped elastic body layer having a part diameter of 8.4 mm and a central part diameter of 8.5 mm was obtained.

The surface of the obtained vulcanized rubber roller was subjected to surface modification treatment by irradiating with ultraviolet rays. The irradiation conditions were such that a low-pressure mercury lamp (Harrison Toshiba Lighting Co., Ltd.) was used to irradiate ultraviolet rays having a wavelength of 254 nm so that the integrated light amount was 8500 mJ / cm ² . The charging roller 1 was produced as described above.

(Image evaluation)
The charging roller 1 is mounted on a process cartridge (coaxially pressed to a φ30 mm photoconductor with a 5N load applied to both ends of the charging roller 1) and incorporated in an electrophotographic apparatus (trade name: LBP5050, manufactured by Canon). Images were printed and their initial images were evaluated. The following ranks were given for initial image defects.
A: An image with no defective image.
B: An image defect due to non-uniform charging occurred very slightly.
C: Image defect caused slightly due to uneven charging.
D: Image defect due to non-uniform charging is clearly generated.
In the initial image evaluation, the rank B or higher was set to a practical level.

Further, after the initial image evaluation, the cartridge was left in a harsh environment of 40 ° C./95% RH (relative humidity) for 30 days, and then incorporated into the same electrophotographic apparatus again to print an image. Based on the image after leaving the harsh environment, the set image defect due to permanent distortion of the charging roller after leaving the harsh environment was evaluated. The following ranks were given for image defects.
A: The image cannot be confirmed defective.
B: The image defect described above occurred slightly within the image end portion of 25 mm.
C: The above-mentioned image defect occurred slightly within the image edge portion of 50 mm.
D: The above-mentioned image defect occurred slightly on the entire image.
E: The above-mentioned image defect is clearly generated on the entire image.
In the image evaluation after leaving in a harsh environment, the rank D or higher was set to a practical level.
As a result of image evaluation using the charging roller 1, both the initial image and the image after being left in a harsh environment were in image rank A.

(Strain measurement)
The amount of deformation of the pressure contact portion of the charging roller 1 with the photosensitive member (the portion in contact with the photosensitive member) after being left in a harsh environment performed in image evaluation was measured. The measurement was performed with a general laser shape measuring machine (trade name: LS-5500, manufactured by Keyence Corporation), and the difference in roller diameter between the pressure contact portion and the non-pressure contact portion of the charging roller was defined as the strain amount.

(Measurement of hardness)
The hardness of the charging roller 1 was measured using a micro hardness meter MD-1 type (manufactured by Kobunshi Keiki Co., Ltd.) in a peak hold mode in a 23 ° C./55% RH environment. More specifically, place the charging roller on a metal plate, place a metal block, and fix it easily so that it does not roll, and measure accurately from the vertical direction to the center of the charging roller with respect to the metal plate. The value was read 5 seconds after the terminal was pressed. This was measured at 9 locations, 3 locations at both ends and the central portion 30-40 mm from the rubber end of the charging roller, and 3 locations in the circumferential direction, and the average of the measured values obtained was elastic. It was set as the hardness of the body layer. As a result, the hardness was 75.

(Processability evaluation)
Workability was evaluated according to the following criteria for kneading with a pressure kneader, sheeting with an open roll, and extrusion molding.
A: No problem.
B: Although workability is somewhat lowered, there is no problem.
C: Processing work is difficult.

(Measurement of 1,2-syndiotactic polybutadiene fiber diameter)
A sample is taken from the elastic layer of the charging roller by cutting with a sharp blade. From this sample, Leica EM FCS, product name: Leica EM FCS was used, and a diamond knife (made by Diatome, product name: Cryo dry 35 °) was used in an atmosphere of −120 ° C. to −50 ° C. and about 50 nm. An ultrathin section having a thickness of 5 mm was prepared. This ultrathin section was stained with osmium tetroxide and photographed with a transmission electron microscope at a direct observation magnification of 40,000 times. From a photographed image having a visual field size of 10 μm × 7 μm, the length (thickness) in the minor axis direction of 1,2-syndiotactic polybutadiene fiber in which the entire fiber is contained in the visual field is taken as the fiber diameter and measured. 0.02 to 0.1 μm.

  Similarly, charging rollers 2 to 15 described later were subjected to image evaluation, distortion measurement, hardness measurement, workability evaluation, and 1,2-syndiotactic polybutadiene fiber diameter measurement.

<Example 2>
The 1,2-syndiotactic polybutadiene-containing butadiene rubber in the A-kneaded rubber composition of Example 1 was changed to VCR 617 (manufactured by Ube Industries, Ltd., and the content mass ratio was 1,2-syndiotactic polybutadiene (B). : Butadiene rubber (A) = 17: 83, charged in the same manner as in Example 1, except that the butadiene monomer unit of butadiene rubber (A) has a cis 1,4 bond content of 98 mass%. Roller 2 was obtained. The obtained charging roller 2 was evaluated in the same manner as in Example 1.

<Example 3>
The 1,2-syndiotactic polybutadiene-containing butadiene rubber in the A-kneaded rubber composition of Example 1 was changed to VCR 450 (manufactured by Ube Industries, Ltd., and the content mass ratio was 1,2-syndiotactic polybutadiene (B): Butadiene rubber (A) = 3.8: 96.2, except that the butadiene monomer unit of the butadiene rubber (A) has a cis 1,4 bond content of 98% by mass in the bond structure). The charging roller 3 was obtained by this method. The obtained charging roller 3 was evaluated in the same manner as in Example 1.

<Example 4>
The 1,2-syndiotactic polybutadiene-containing butadiene rubber in the A-kneaded rubber composition of Example 1 was changed to VCR 800 (manufactured by Ube Industries, Ltd., and the content mass ratio was 1,2-syndiotactic polybutadiene (B): Example 1 except that butadiene rubber (A) = 5.3: 94.7 and cis 1,4 bond content in the bond structure of the butadiene monomer unit of butadiene rubber (A) was 98 mass%. The charging roller 4 was obtained by this method. The obtained charging roller 4 was evaluated in the same manner as in Example 1.

<Example 5>
A charging roller 5 was obtained in the same manner as in Example 1 except that 100 parts by mass of 1,2-syndiotactic polybutadiene-containing butadiene rubber in the kneaded rubber composition of Example 1 was changed to the material shown in Table 3. It was. The obtained charging roller 5 was evaluated in the same manner as in Example 1.

<Example 6>
Example 5 except that the blending amounts of butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B) in the kneaded rubber composition of Example 5 were changed to 70 parts by mass and 30 parts by mass, respectively. The charging roller 6 was obtained in the same manner as described above. The obtained charging roller 6 was evaluated in the same manner as in Example 1.

<Example 7>
The charging roller 7 was obtained in the same manner as in Example 1 except that 100 parts by mass of 1,2-syndiotactic polybutadiene-containing butadiene rubber in the kneaded rubber composition of Example 1 was changed to the material shown in Table 4. It was. The obtained charging roller 7 was evaluated in the same manner as in Example 1.

<Example 8>
A charging roller 8 was obtained in the same manner as in Example 1 except that 100 parts by mass of 1,2-syndiotactic polybutadiene-containing butadiene rubber in the kneaded rubber composition of Example 1 was changed to the material shown in Table 5. It was. The obtained charging roller 8 was evaluated in the same manner as in Example 1.

<Example 9>
Example 8 except that the blending amounts of butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B) in the kneaded rubber composition of Example 8 were changed to 70 parts by mass and 30 parts by mass, respectively. The charging roller 9 was obtained in the same manner as described above. The obtained charging roller 9 was evaluated in the same manner as in Example 1.

<Example 10>
A charging roller 10 was obtained in the same manner as in Example 1 except that the materials in the A-kneaded rubber composition of Example 1 were changed as shown in Table 6. The obtained charging roller 10 was evaluated in the same manner as in Example 1.

<Example 11>
60 parts by mass of styrene butadiene rubber in the kneaded rubber composition of Example 10 was changed to 70 parts by mass of nitrile butadiene rubber (trade name: JSR N230SV, manufactured by Nippon Synthetic Rubber Co., Ltd.), and 1,2-syndiotactic Polybutadiene-containing butadiene rubber (trade name: VCR 617, manufactured by Ube Industries, Ltd., content ratio is 1,2-syndiotactic polybutadiene (B): butadiene rubber (A) = 17: 83, butadiene rubber (A) The cis 1,4 bond content in the bond structure of the butadiene monomer unit was changed from 40 parts by mass to 30 parts by mass. Further, a charging roller 11 was obtained in the same manner as in Example 10 except that carbon black (trade name: Toka Black # 7360SB, manufactured by Tokai Carbon Co., Ltd.) was changed from 48 parts by mass to 32 parts by mass. The obtained charging roller 11 was evaluated in the same manner as in Example 1.

<Example 12>
The amounts of nitrile butadiene rubber and 1,2-syndiotactic polybutadiene-containing butadiene rubber in the A-kneaded rubber composition of Example 11 were changed to 95 parts by mass and 5 parts by mass, respectively. Further, a charging roller 12 was obtained in the same manner as in Example 11 except that carbon black (trade name: Toka Black # 7360SB, manufactured by Tokai Carbon Co., Ltd.) was changed from 32 parts by mass to 48 parts by mass. The obtained charging roller 12 was evaluated in the same manner as in Example 1.

<Comparative Example 1>
A charging roller 13 was obtained in the same manner as in Example 1 except that the material in the A-kneaded rubber composition of Example 1 was changed as shown in Table 7. The obtained charging roller 13 was evaluated in the same manner as in Example 1.

<Comparative example 2>
The styrene butadiene rubber in the kneaded rubber composition of Comparative Example 1 is butadiene rubber (trade name: BR1220L, manufactured by Nippon Zeon Co., Ltd., cis 1,4 bond content in the bond structure of the butadiene monomer unit of butadiene rubber (A). The charging roller 14 was obtained in the same manner as in Comparative Example 1 except that the amount was changed to 97% by mass). This butadiene rubber (trade name: BR1220L) does not contain 1,2-syndiotactic polybutadiene. The obtained charging roller 14 was evaluated in the same manner as in Example 1.

<Comparative Example 3>
The same method as Comparative Example 1 except that the styrene butadiene rubber in the kneaded rubber composition of Comparative Example 1 was changed to 1,2-syndiotactic polybutadiene (trade name: RB820, manufactured by Nippon Synthetic Rubber Co., Ltd.). Thus, a charging roller 15 was obtained. The obtained charging roller 15 was evaluated in the same manner as in Example 1.

  The evaluation results of the above examples and comparative examples are shown in Table 8 below.

  From this table, it can be seen that Comparative Examples 1 and 2 do not contain 1,2-syndiotactic polybutadiene (B) in the elastic layer, so that the image rank is lowered after leaving in a severe environment. In Comparative Example 3, only 1,2-syndiotactic polybutadiene (B) is present, and since the hardness is too high, when used as a charging member, poor contact with the photoreceptor occurs, and the rank of the initial image Since it decreases, practical use becomes difficult. In Comparative Example 3, since the initial image evaluation result was low, image evaluation after leaving the workability and harsh environment was not performed.

  Examples 1 to 12 are charging rollers of the present invention, and the image evaluation rank is D or more in all items, and good images having no practical problem are obtained. Moreover, Examples 1-12 do not have a surface layer, but it turns out that a favorable image can be obtained even with the structure only of an elastic body layer.

DESCRIPTION OF SYMBOLS 1 Charging roller 11 Core metal 12 Elastic body layer 13 Surface layer

Claims (1)

A charging member having an elastic layer on a conductive support,
The elastic layer is made of a cured product of an unvulcanized rubber mixture containing a binder polymer containing butadiene rubber (A) and 1,2-syndiotactic polybutadiene (B) and conductive particles. Charging member.

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