JP2012042700A - Charging roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging roll which suppresses occurrence of toner filming on a roll surface, and also occurrence of a ghost image, shaving of a photoreceptor surface, and removal of roughness forming particles contained in a protective layer.SOLUTION: In a charging roll, in which an electroconductive rubber foam layer is laid on the outer peripheral surface of a shaft body and a protective layer is provided on the outside of the electroconductive rubber foam layer by using a synthetic resin composition containing a synthetic resin material and roughness forming particles, the electroconductive rubber foam layer has on its surface layer part a skin layer having an aperture ratio of 0.5% to 20% and its hardness is 0.02 N/mmor less. The charging roll is constituted in such a manner that the hardness X(N/mm) of the synthetic resin material and the hardness Y(N/mm) of the roughness forming particles satisfy all of prescribed conditional expressions (1) to (3), and the thickness a(μm) of the protective layer and the average particle diameter b(μm) of the roughness forming particles satisfy a prescribed conditional expression (4).

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roll used for charging an image carrier made of an electrophotographic photosensitive member or an electrostatic recording dielectric in an image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic system. It is.

  In an image forming apparatus (hereinafter referred to as an electrophotographic apparatus) such as a copying machine, a printer, or a facsimile using an electrophotographic system, an image carrier such as a photoconductor (drum) is brought into contact with an outer peripheral surface of a charging roll, A so-called roll charging method (contact charging method) in which the surface of the image carrier is charged by rotating the image carrier and the charging roll mutually is widely adopted.

  As a charging roll used in such a roll charging method, generally, a plurality of layers in which two or more layers made of different materials are sequentially laminated so that various required characteristics can be effectively exhibited. A roll having a layer structure is widely adopted.

  For example, the stress applied to the toner and the photoconductor is reduced even after long-term use, and the base layer around the shaft (core metal) as a conductor for the purpose of reducing the manufacturing cost, 2. Description of the Related Art Conventionally, a charging roll having a structure in which a conductive rubber foam layer made of a low hardness conductive rubber foam is provided and a protective layer is provided on the outer side has been widely used. In particular, for such a two-layered charging roll, the resistance of the roll itself is made uniform and the shape of the product is made highly accurate, and also exhibits excellent anti-sagging properties even during long-term pressure contact with the photoreceptor. Thus, it has been proposed to use a continuous foam tube having a skin layer on the surface as the base layer (see Patent Document 1).

  In addition, for the purpose of suppressing the occurrence of charging unevenness on the roll surface and obtaining a good image, the outermost layer of the charging roll has been conventionally applied to various synthetic resin materials and rubber materials such as particles for forming roughness. It has been proposed to use a composition obtained by blending predetermined particles (see Patent Documents 2 to 4).

  However, the inventors of the present application have been studying a conventional charging roll in which a protective layer including particles such as roughness forming particles is provided on the outside of a conductive rubber foam layer having a skin layer on the surface. As a result, it has been found that a so-called ghost image may be generated due to uneven charging (afterimage phenomenon) on the roll surface. That is, in the roll charging method (contact charging method), the photosensitive member is charged by causing discharge in a slight gap (dischargeable region) in the contact portion between the charging roll and the photosensitive member. In the conventional charging roll having the configuration, the gap (dischargeable region) is small, and the charging property to the photosensitive member is not sufficient, and as a result, a ghost image may be generated.

  Further, in a charging roll provided with a protective layer containing particles such as roughness forming particles as the outermost layer, the surface of the photoreceptor may be scraped by particles in the protective layer due to long-term use. In addition, there is a problem that particles may fall off from the protective layer and various image defects such as spot images and image unevenness may occur.

JP 2009-237532 A JP 2005-91455 A JP 2007-178559 A JP 2007-264491 A

  The present invention has been made in the background of such circumstances, and the problem to be solved is to suppress the occurrence of toner filming on the roll surface, and to An object of the present invention is to provide a charging roll that suppresses the occurrence of abrasion on the body surface and the drop-off of the particles for forming the roughness contained in the protective layer.

In order to solve such a problem, the present invention is provided with a conductive rubber foam layer on the outer peripheral surface of the shaft body, and on the outside of the conductive rubber foam layer, a synthetic resin material and roughness are provided. A charging roll provided with a protective layer using a synthetic resin composition containing particles for forming, and (A) the conductive rubber foam layer is a skin layer having an opening ratio of 0.5 to 20%. The surface layer portion has a hardness of 0.02 N / mm ² or less. (B) Hardness of the synthetic resin material: X (N / mm ² ) and hardness of the roughness forming particles: Y (N / mm ² ) satisfies all of the following conditional expressions (1) to (3), and (C) the thickness of the protective layer: a (μm) and the average particle size of the roughness forming particles: b (μm) The gist of the present invention is a charging roll characterized by satisfying the following conditional expression (4).

  In such a charging roll according to the present invention, the synthetic resin material is advantageously an acrylic resin aqueous emulsion, a urethane resin aqueous emulsion, or an alcohol-soluble polyamide.

As described above, the charging roll according to the present invention has a skin layer having an aperture ratio of 0.5 to 20% as a base layer as a base layer in the surface layer portion, and a conductive foam having a hardness of 0.02 N / mm ² or less. Since the body layer is employed and the hardness of the entire roll is kept low, the occurrence of toner filming on the roll surface is effectively suppressed. In addition, when the protective layer is formed using a synthetic resin composition containing a synthetic resin material and roughness forming particles, the hardness of the synthetic resin material: X and the hardness of the roughness forming particles: Y Since all the predetermined conditional expressions (1) to (3) are satisfied and the thickness of the protective layer: a and the average particle diameter of the roughness forming particles: b satisfy the conditional expression (4), the roll surface In addition to effectively suppressing the occurrence of toner filming in the toner, it is also possible to effectively suppress the occurrence of ghost images, the photoconductor surface scraping, and the loss of roughness forming particles contained in the protective layer. .

  In addition, when an acrylic resin aqueous emulsion, urethane resin aqueous emulsion, or alcohol-soluble polyamide is used as the synthetic resin material, the thickness of the protective layer can be made more uniform, thereby reducing image defects. Generation can be effectively suppressed.

It is an axis perpendicular cross-section explanatory drawing which shows an example of the charging roll according to this invention.

  Hereinafter, the present invention will be described in detail with appropriate reference to the drawings.

  FIG. 1 schematically shows an exemplary embodiment of a charging roll according to the present invention in a cross-section in a direction perpendicular to the axis. In FIG. 1, a charging roll 10 is a conductive rubber foam that is a base layer in order from the inner side to the outer side in the roll radial direction on the outer peripheral surface of a metal conductive shaft (core metal) 12. The layer 14 and the protective layer 16 which is the outermost layer are each integrally formed with a predetermined thickness.

  The conductive shaft body 12 is not particularly limited as long as it is made of a conductive metal, and examples are made of iron, stainless steel (SUS), free-cutting steel (SUM), and the like. I can do it. In addition, the conductive shaft body 12 may be subjected to a plating treatment or the like, and an adhesive, a primer, or the like may be applied to the outer peripheral surface as necessary. In addition, the shape of the conductive shaft body 12 may be a pipe-shaped hollow cylindrical body other than the rod-shaped solid body as shown in FIG.

In the charging roll 10 according to the present invention, first, the conductive rubber foam layer 14 integrally formed on the outer peripheral surface of the conductive shaft 12 has a skin layer with an opening ratio of 0.5 to 20%. 18 in the surface layer portion, and its hardness is 0.02 N / mm ² or less.

  Thus, by adopting the conductive rubber foam layer (14) having the skin layer (18) having an opening ratio within a predetermined range in the surface layer portion, the surface of the conductive rubber foam layer (14) is obtained. In addition, for example, when the protective layer (16) is formed using an emulsion material described later, the emulsion material effectively impregnates the surface (non-opening and opening) of the conductive rubber foam layer (14). At the same time, the roughness forming particles (20) are relatively uniformly dispersed on the surface of the conductive rubber foam layer (14) without agglomeration. As a result, in the charging roll (10) of the present invention, the thickness of the surface layer (16) becomes relatively uniform, so that the occurrence of image defects is effectively suppressed.

Further, since the hardness of the conductive rubber foam layer (14) is 0.02 N / mm ² or less, the hardness of the entire roll can be kept low, and the occurrence of toner filming on the roll surface can be effectively suppressed. It is done.

Here, if the opening ratio of the skin layer (18) in the conductive rubber foam layer (14) is too small, the above-described effects may not be enjoyed advantageously, while the skin layer (18) If the aperture ratio is too large, it may be difficult to form the protective layer (16), or the thickness of the protective layer (16) may be uneven, resulting in unevenness in the finally obtained image. . Therefore, in the charging roll (10) according to the present invention, the opening ratio of the skin layer (18) in the conductive rubber foam layer (14) is 0.5 to 20%. If the hardness of the conductive rubber foam layer (14) exceeds 0.02 N / mm ² , it may be difficult to suppress the occurrence of toner filming on the roll surface.

  The aperture ratio (%) in the present specification and claims means that calculated as follows. That is, with respect to the conductive rubber foam layer before the protective layer is formed, at three locations in the axial center and both ends, an optical microscope such as a laser microscope is used three times at each location, that is, nine times in total. Use to measure the opening area. The measured aperture area is divided by the observation area of the optical microscope, and the aperture ratio (%) in one measurement is calculated. And the average value of the aperture ratio (%) obtained by 9 times of measurement was computed, and this average value was made into the aperture ratio (%) in this specification and a claim.

Further, the hardness of the conductive rubber foam layer (14) means a value measured and calculated as follows. That is, the conductive rubber foam layer before the protective layer is formed is supported by the shaft (12) portions at both ends thereof, and a plate-like press against the surface of the supported conductive rubber foam layer. A jig having a surface (50 mm × 50 mm, thickness: 7 mm) is pressed at a speed of 10 mm / min, and the load per unit area (N / mm ² ) at the time of 0.25 mm displacement is measured. Such measurement is performed at four positions (positions rotated by 0 °, 90 °, 180 °, and 270 ° around the axial center) in the central portion in the axial direction of the conductive rubber foam layer, and the average of the four measurement results The value was calculated, and this average value was defined as the hardness (N / mm ² ) of the conductive rubber foam layer (14) in the present specification and claims.

  In the present invention, when forming the conductive rubber foam layer (14) having the skin layer (18) opened at a predetermined opening ratio, the foamable conductive rubber composition mainly composed of various rubber materials is used. Used. Examples of rubber materials that can be used in the present invention include epichlorohydrin rubber (ECO, CO, etc.), nitrile rubber (NBR), ethylene-propylene-diene rubber (EPDM), silicone rubber, urethane rubber, styrene-butadiene rubber (SBR), isoprene. Examples include rubber (IR), chloroprene rubber (CR), natural rubber (NR), and the like, and these can be used alone or in combination of two or more. In the present invention, ethylene propylene diene rubber (EPDM), epichlorohydrin rubber, nitrile rubber and the like are particularly preferably used.

  For such rubber materials, as in the past, a foaming agent and a conductive agent, and further, if necessary, a filler, an extender, a reinforcing agent, a processing aid, a curing agent, a vulcanizing agent, Various additives such as vulcanization accelerators, vulcanization aids, antioxidants, plasticizers, UV absorbers, pigments, silicone oils and surfactants are added to the extent that they do not impair the purpose of the present invention. It is blended as appropriate according to the purpose. Among them, in particular, the foaming agent, the vulcanizing agent, and the vulcanization accelerator greatly affect the formation of the skin layer (18) by heating under pressure, and therefore the selection of the type and blending amount is important. is there.

  For example, as the foaming agent, conventionally known inorganic foaming agents and organic foaming agents can be blended. In the present invention, an organic foaming agent is advantageously used from the viewpoints that it can be easily foamed by thermal decomposition and that the decomposed product is excellent in compatibility with a rubber material as a matrix. Examples of such organic foaming agents include azodicarbonamide (ADCA), 4,4′-oxybis (benzenesulfonyl) hydrazide [OBSH], N, N′-dinitrosopentamethylenetetramine (DPT), and the like. I can do it.

  Examples of the conductive agent include carbon black such as ketjen black and acetylene black, graphite, metal powder, conductive metal oxide, and various ionic conductive agents such as tetramethylammonium perchlorate, trimethyloctadecylammonium perchlorate, Examples thereof include quaternary ammonium salts such as benzyltrimethylammonium chloride.

In the charging roll 10 according to the present invention, the protective layer 16 is provided on the outside of the conductive rubber foam layer 14 using the synthetic resin composition including the synthetic resin material and the roughness forming particles 20. The synthetic resin material and the roughness forming particles constituting the protective layer 16 satisfy predetermined conditions, and the thickness of the protective layer 16 and the average particle diameter of the roughness forming particles 20 Therefore, a great feature of the present invention exists. That is, in the present invention, the hardness of the synthetic resin material: X (N / mm ² ) and the hardness of the roughness forming particles 20: Y (N / mm ² ) are all the following conditional expressions (1) to (3). The thickness of the protective layer 16: a (μm) and the average particle size of the roughness forming particles 20: b (μm) satisfy the following conditional expression (4).

  Thus, in the protective layer 16 provided as the outermost layer, the hardness of the synthetic resin material and the hardness of the roughness forming particles 20 satisfy predetermined conditions, and the thickness of the protective layer 16 and the roughness forming particles 20 When the average particle diameter satisfies the predetermined condition, the charging roll 10 of the present invention can generate a ghost image, a photoconductor surface is scraped, and a rough layer included in the protective layer 16 when used in an actual machine. The falling off of the forming particles 20 is effectively suppressed.

  Here, the hardness of the synthetic resin material and the hardness of the particles for forming the roughness are indentation tests specified in ISO 14577-1 “Indentation test test and material parameter Part 1: Test method for hardness”. , And using the result, it was calculated in accordance with “A.2 Martens hardness HM” of the Annex A. In addition, when the synthetic resin material is an emulsion material, it is measured and calculated using the cured product as a sample.

  Moreover, the average particle diameter of the particle | grains for roughness formation means a volume average particle diameter (D50), and is measured based on JIS-Z-8825-1: 2001. Furthermore, the thickness of the protective layer is a sample having a size of about 1 mm in the roll axis direction, about 2 to 5 mm in the circumferential direction, and about 1 to 2 mm in the depth direction from the protective layer provided as the outermost layer of the charging roll. And a cross section of the sample is observed with a laser microscope and measured.

In the present invention, the hardness of the synthetic resin material: X (N / mm ² ) and the hardness of the roughness forming particles: Y (N / mm ² ) do not satisfy any of the following conditional expressions (1) to (3) In such a case, there is a possibility that the occurrence of toner filming on the roll surface and the scraping of the photoreceptor surface cannot be effectively suppressed. Further, when the protective layer thickness: a (μm) and the average particle diameter of the roughness forming particles: b (μm) do not satisfy the following conditional expression (4), generation of a ghost image or dropout of the particles is lost. May not be able to be advantageously prevented.

  As the synthetic resin material constituting the protective layer 16 of the present invention, it is possible to appropriately select and use one of various conventionally known synthetic resin materials according to the final charging roll. Is possible. Examples of the synthetic resin material include acrylic resin, urethane resin, nylon resin and acrylic styrene resin. In the present invention, a synthetic resin aqueous emulsion (emulsion) such as an acrylic resin aqueous emulsion or urethane resin aqueous emulsion is used. Material) and alcohol-soluble polyamides are particularly advantageously used. A liquid synthetic resin composition is prepared using these, and when this liquid synthetic resin composition is applied to the surface of the conductive rubber foam layer, the synthetic resin composition becomes a surface of the conductive rubber foam layer ( The non-openings and the openings) are effectively impregnated, and the roughness forming particles are relatively uniformly dispersed on the surface of the conductive rubber foam layer without agglomeration. Thereby, the thickness of the protective layer becomes relatively uniform, and the occurrence of image defects is effectively suppressed. In the case of using an emulsion-based material as the synthetic resin material, water is further added as necessary. In the case of using an alcohol-soluble polyamide as the synthetic resin material, various kinds of solvents such as methanol and ethanol are used as a dispersion medium. Alcohol is used. As water-based emulsion of synthetic resin, VONCOAT CP-6190, VONCOAT SA-6360, VONCOAT 550EF, VONCOAT VF-1040, VONCOAT CG-8400, BURNOCK WE-304 (above, product name: DIC Corporation), Takerak W series (Trade name: manufactured by Mitsui Chemicals Co., Ltd.), HUX320 (trade name: manufactured by ADEKA Co., Ltd.) and the like, and as an alcohol-soluble polyamide, resin EF30T (trade name: manufactured by Nagase ChemteX Corporation) I can do it.

  As the roughness forming particles (20), urethane resin particles, nylon resin particles, acrylic resin particles, melamine resin particles, various synthetic resin particles such as styrene resin particles, silica particles, and the like can be used. . These roughness forming particles can be used alone or in combination of two or more.

In preparing the synthetic resin composition for forming the protective layer in the charging roll of the present invention, various additives such as known conductive agents, cross-linking agents, and fillers are blended in the same blending ratio as before. The volume resistivity of the finally obtained protective layer (16) is generally adjusted to be about 1 × 10 ⁵ to 1 × 10 ¹³ Ω · cm.

  Incidentally, the charging roll 10 according to the present invention having the structure shown in FIG. 1 can be manufactured, for example, according to the following method.

  First, an unvulcanized unfoamed foam rubber layer that finally gives the conductive rubber foam layer 14 is prepared using the foamable conductive rubber composition as described above. Specifically, the foamable conductive rubber composition is formed into a tube shape.

  When the foamable conductive rubber composition is molded into a tube shape, any of the conventionally known molding methods including extrusion molding and mold molding can be adopted. From the viewpoint of productivity, etc. Advantageously, extrusion is employed. In extrusion molding, a general extrusion molding machine can be used, and an unvulcanized unfoamed foamable rubber layer is formed directly on the outer peripheral surface of the shaft body 12 or other core material. It is also possible.

  The unvulcanized unfoamed foamed rubber layer thus prepared is first heated under pressure to form a semi-vulcanized unfoamed foamed rubber layer having the skin layer 18 on the surface layer portion. By heating under pressure, foaming is suppressed inside the unvulcanized unfoamed foamable rubber layer, while vulcanization of the unvulcanized unfoamed foamable rubber layer proceeds, and thus the surface layer portion Thus, a semi-vulcanized unfoamed foam rubber layer having a skin layer 18 is obtained.

  In producing the charging roll according to the present invention, it is very significant to provide such a skin layer 18 first. That is, for the unvulcanized unfoamed foam rubber layer, first, the skin layer 18 is formed, and then the surface of the skin layer 18 is opened by a predetermined operation, whereby the conductive rubber foam layer 14 finally obtained is obtained. It is easy to adjust the aperture ratio on the surface of the film within a desired range. In addition, a shaft body and an unvulcanized unfoamed foamable rubber layer are coaxially arranged in a molding cavity of a cylindrical mold that has been widely used conventionally, and the mold is heated in this state to In the method of simultaneously foaming and vulcanizing the vulcanized unfoamed foamable rubber layer, it is difficult to control foaming. Therefore, the opening ratio of the surface of the finally obtained conductive rubber foam layer (18) is set. It is very difficult to make it within a desired range (0.5 to 20%).

  Here, the unvulcanized unfoamed foam rubber layer is preferably heated under pressure in a state where the shaft body 12 or other core material is inserted. However, in the unvulcanized unfoamed foamable rubber layer, it is difficult for heat to be transmitted to a portion in the vicinity of the shaft body 12 or the like (a portion on the inner side in the direction perpendicular to the shaft). This is because the skin layer can be advantageously formed only at the above-mentioned site.

  Further, various conditions when heating under such pressure, for example, pressure conditions, heating temperature, heating time, etc., are such that the vulcanization of the unvulcanized unfoamed foamed rubber layer is not completely completed (unvulcanized). The conditions under which the unfoamed foamed rubber layer is in a semi-vulcanized state) are the types and amounts of vulcanizing agents and vulcanization accelerators contained in the foaming conductive rubber composition, and will be described later. It is determined appropriately according to the method for opening the skin layer. Furthermore, when heating under pressure, a pressure oven or the like is used. In accordance with such appropriately selected conditions, a skin layer 18 having a thickness of about 10 to 100 μm is usually formed on the surface layer portion of the semi-vulcanized unfoamed foam rubber layer.

  The semi-vulcanized unfoamed foamable rubber layer having the skin layer formed on the surface layer portion thus obtained is replaced with the skin layer having an opening ratio within a predetermined range (0.5 to 20%). In order to obtain the conductive rubber foam layer 14, the following method can be exemplified.

-Method 1
The above-mentioned semi-vulcanized unfoamed foamable rubber layer is heated under normal pressure to cause foaming and vulcanization to proceed inside the semi-vulcanized unfoamed foamable rubber layer (18). The conductive rubber foam layer 14 having the surface layer portion is formed. Thereafter, the surface of the conductive rubber foam layer 14 is opened by irradiating a laser or the like on the surface of the conductive rubber foam layer 14 (the surface of the skin layer that is not open). In addition, various conditions at the time of this laser irradiation are suitably determined so that an aperture ratio may be 0.5 to 20%.

-Method 2-
After the skin layer of the above-mentioned semi-vulcanized unfoamed foam rubber layer is provided to be relatively thinner than that of the semi-vulcanized unfoamed foam rubber layer employed in the above method 1, the skin layer is heated under normal pressure, By making foaming and vulcanization proceed inside the vulcanized unfoamed foamable rubber layer, the conductive rubber foam layer 14 having a skin layer with an opening ratio of 0.5 to 20% in the surface layer portion is obtained.

  And the liquid synthetic resin which contains the particle | grains 20 for roughness formation mentioned above on the surface of the conductive rubber foam layer 14 which has the skin layer 18 which has the opening rate in the predetermined range obtained in this way is obtained. The composition is applied according to various conventionally known methods such as a roll coating method. Then, the protective layer 16 will be obtained by drying (and heating as needed) this coating film. The protective layer 16 is formed so that the thickness satisfies the conditional expression (4) between the thickness of the protective layer 16 and the average particle diameter of the roughness forming particles.

  In the charging roll 10 of the present invention thus manufactured, the conductive rubber foam layer 14 and the protective layer 16 are each configured to satisfy predetermined conditions. While effectively suppressing the occurrence of filming, it is also possible to effectively suppress the generation of ghost images, scraping of the surface of the photoreceptor, and dropping off of the roughness forming particles contained in the protective layer. It is.

  Some examples of the present invention will be shown below to clarify the present invention more specifically. However, the present invention is not limited by the description of such examples. Needless to say. In addition to the following examples, the present invention includes various modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the above-described specific description. It should be understood that modifications, improvements, etc. can be made. In addition, the measurement of the hardness of the synthetic resin material in the following examples and comparative examples was specifically performed as follows.

-Measurement of hardness of synthetic resin material-
Measurement was performed using a Fisherscope H-100 (trade name) manufactured by Fischer Instruments. The thickness of the sample was 50 to 60 μm, and a Vickers indenter was used as the indenter, and the indenter indentation load was 1.0 mN and the indentation depth was 2.0 μm. Measurement was performed on 10 different points on the sample, and the average value was calculated.

-Measurement of hardness of roughness forming particles-
Measurement was performed using a Fisherscope H-100 (trade name) manufactured by Fischer Instruments. As the indenter, a flat tip having a square shape (50 μm × 50 μm) was used, the indentation indentation load was 1.0 mN, and the indentation depth was defined as the average particle diameter of the roughness forming particles as a sample. It was measured. Measurement was performed on 10 particles arbitrarily selected from those prepared as roughness forming particles, and the average value was calculated.

-Measurement of average particle size of roughness forming particles-
Measurement was performed using a laser diffraction particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., trade name: Microtrac HRA).

-Measurement of protective layer thickness-
Measurement was performed using a laser microscope (manufactured by Keyence Corporation, trade name: VK-9500).

  First, in accordance with the blending ratio shown in Table 1 below, a foamable conductive rubber composition was prepared as a material for forming a conductive rubber foam layer (base layer). In addition, the epichlorohydrin rubber used for preparation of the rubber composition is Epichromer DG (trade name) manufactured by Daiso Corporation.

  On the other hand, each of the combinations shown in Tables 4 and 5 below includes one of the synthetic resin materials shown in Table 2 below and one of the roughness forming particles (hereinafter also simply referred to as particles) shown in Table 3 below. Was used to prepare a synthetic resin composition as a protective layer forming material. Specifically, 100 parts by weight of a synthetic resin material, 10 parts by weight of particles, and 20 parts by weight of carbon black are added to 450 parts by weight of water or an organic solvent (methanol) as a dispersion medium, A liquid synthetic resin composition was prepared.

  Using the foamable conductive rubber composition (conductive rubber foam layer forming material) and the liquid synthetic resin composition (surface layer forming material) prepared as described above, a charging roll is formed according to the following method. Produced.

  Cylinder diameter: Using an extrusion molding device equipped with an extruded part having a diameter of 40φ and a cross-type head, the foamable conductive rubber composition is simultaneously extruded together with a core material (made of SUS304) having a predetermined diameter. A composite comprising an unvulcanized and unfoamed foamable rubber layer formed on the outer peripheral surface was obtained.

  The obtained composite was placed in a pressure oven, the inside of the oven was pressurized to 1 MPa, and then heated to 150 ° C. and heat-treated for 15 minutes. When the surface of the composite after the heat treatment (the surface of the semi-vulcanized unfoamed foam rubber layer) was visually observed, it was confirmed that no foam cells were found and a skin layer was formed.

  Thereafter, the pressure in the oven was reduced to normal pressure, and the core material was removed from the composite. The obtained rubber tube (semi-vulcanized unfoamed foam rubber layer) was subjected to a heat treatment at 150 ° C. for 30 minutes in an oven under normal pressure.

  Furthermore, after inserting a metal shaft having an outer diameter of 6φ into the obtained rubber tube, the surface of the rubber tube is irradiated with a laser so that the conductive rubber foam layer is integrated on the outer peripheral surface of the shaft. A base roll provided with a skin layer having an aperture ratio shown in Tables 4 and 5 below was prepared on the surface layer of the conductive rubber foam layer.

  And the liquid synthetic resin composition containing the synthetic resin material and particle | grains shown in following Table 4 and Table 5 was apply | coated to the surface of each base roll obtained in this way according to the roll coat method, and 30 degreeC was 30 degreeC. 19 types of charging rolls were manufactured by drying for a minute and forming a protective layer (Examples 1-11, Comparative Examples 1-8). In Tables 4 and 5 below, when the hardness of the synthetic resin material: X and the hardness of the roughness forming particles: Y satisfy all of the conditional expressions (1) to (3) of the present invention, When any one of the conditional expressions is not satisfied, x is indicated. In Tables 4 and 5 below, “b / a” indicates [average particle diameter of roughness forming particles: b (μm)] / [thickness of protective layer: a (μm)].

  The following evaluations were performed on the obtained 19 types of charging rolls.

-Evaluation of ghost images-
Set the charging roll in the cartridge of the actual machine (trade name: Color Laser Jet CP1215, manufactured by Hewlett-Packard Company, the same shall apply hereinafter). Output. The obtained images were evaluated according to the following criteria. The evaluation results are shown in Tables 4 and 5 as “ghost”.
A: No solid black afterimage is observed in the image.
○: Although a solid black afterimage is recognized in the image, it is within the allowable range.
(Triangle | delta): The black solid afterimage is recognized notably in an image.

-Evaluation of toner filming-
The charging roll was set in the cartridge of the actual machine, and 5% density images were output for the number of durable prints determined for the cartridge. Thereafter, each surface of the charging roll and the photosensitive drum was visually observed and evaluated according to the following criteria. The evaluation results are shown in Tables 4 and 5 as “toner filming”.
A: No toner fusion is observed on the surface of either the photosensitive drum or the charging roll.
X: Toner adhesion that adversely affects the output image is observed on the surface of either the photosensitive drum or the charging roll.

-Drum scraping evaluation-
The charging roll was set in the cartridge of the actual machine, and 5% density images were output for the number of durable prints determined for the cartridge. Thereafter, the surface of the photosensitive drum was visually observed and evaluated according to the following criteria. The evaluation results are shown in Tables 4 and 5 as “drum scraping”.
○: No defects are observed on the surface of the photosensitive drum.
X: Defects are observed on the surface of the photosensitive drum.

-Evaluation of image unevenness-
The charging roll was set in the actual cartridge and a 25% halftone pattern was output. The obtained images were evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4 as “image unevenness”.
○: Density unevenness of the image is not recognized at the charging roll pitch in the image.
X: Conspicuous image density unevenness is recognized in the image at the charging roll pitch.

  As is clear from the results of Tables 4 and 5, in the charging rolls according to the present invention (Examples 1 to 11), the occurrence of ghost images is suppressed and the occurrence of toner filming on the roll surface is suppressed. It has been recognized that this also suppresses the occurrence of abrasion on the surface of the photoreceptor and the loss of the particles for forming the roughness contained in the protective layer.

DESCRIPTION OF SYMBOLS 10 Charging roll 12 Shaft body 14 Conductive rubber foam layer 16 Protective layer 18 Skin layer 20 Roughness forming particles

Claims (2)

A conductive rubber foam layer is provided on the outer peripheral surface of the shaft body, and a protective layer is provided on the outside of the conductive rubber foam layer using a synthetic resin composition containing a synthetic resin material and roughness forming particles. The resulting charging roll,
The conductive rubber foam layer has a skin layer having an opening ratio of 0.5 to 20% in the surface layer portion, and has a hardness of 0.02 N / mm ² or less,
The hardness of the synthetic resin material: X (N / mm ² ) and the hardness of the roughness forming particles: Y (N / mm ² ) satisfy all of the following conditional expressions (1) to (3),
The thickness of the protective layer: a (μm) and the average particle diameter of the roughness forming particles: b (μm) satisfy the following conditional expression (4).
A charging roll characterized by that.

The charging roll according to claim 1, wherein the synthetic resin material is an acrylic resin aqueous emulsion, a urethane resin aqueous emulsion, or an alcohol-soluble polyamide.

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