JP2011013271A - Charging roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging roll including a surface layer having a relatively uniform thickness, capable of effectively suppressing occurrence of image failures.SOLUTION: The charging roll includes: a conductive rubber foam layer formed on the outer peripheral surface of a shaft body; and the surface layer formed outside the conductive rubber foam layer. The conductive rubber foam layer includes a skin layer having an opening ratio of 0.5 to 15%, on the surface layer part. The surface layer is formed by applying an aqueous emulsion-based material which is prepared using synthetic resin aqueous emulsion or rubber latex and roughness forming particles, with water as dispersion medium, on the surface of the conductive rubber foam layer.

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 is widely employed in which the surface of the image carrier is charged by rotating the image carrier and the charging roll relative to each other.

  In 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. The layer structure is widely adopted, for example, a conductive rubber foam layer made of a low hardness conductive rubber foam is provided as a base layer around a shaft body (core metal) as a conductor, Further, various charging rolls having a structure in which a surface layer as a protective layer is provided outside are proposed and used (see Patent Document 1).

  Here, in the charging roll having the multilayer structure as described above, the surface layer, which is the outermost layer, is often set to be relatively thin. For this reason, in many cases, such a liquid material is prepared in advance by using a liquid material obtained by dissolving various synthetic resins or rubbers in a predetermined solvent or by dispersing synthetic resins or the like in a predetermined dispersion medium. A surface layer is provided by applying (coating) the surface of the conductive rubber foam layer. And in the liquid material used there, it is possible to widen the selection range of a synthetic resin or the like that can be dissolved or dispersed, and to advantageously ensure applicability to the surface of the conductive rubber foam layer. From the viewpoint, conventionally, organic substances such as methyl ethyl ketone have been widely used as solvents or dispersion media.

  However, when using liquid materials (organic liquid materials) using organic substances such as methyl ethyl ketone, facilities that properly treat the organic substances contained therein are required from the viewpoint of environmental considerations and safety. As a result, there is a problem that the manufacturing cost increases. Moreover, in producing a charging roll having the structure as described above, when an organic liquid material is used, depending on the material of the conductive rubber foam layer that is the coated part, or depending on the type of organic substance as a solvent, There is a possibility that wrinkles due to swelling may occur on the surface of the conductive rubber foam layer, and there is also a problem that it is difficult to ensure a smooth surface property required particularly during durable use in the finally obtained charging roll.

  On the other hand, in order to solve such problems, it has been proposed to use a liquid material (aqueous liquid material) using water as a solvent or a dispersion medium instead of the organic liquid material described above. For example, in Patent Document 2 (Japanese Patent Application Laid-Open No. 9-96946), an electrophotographic charging roll comprising a foam layer on the outer peripheral surface of a core material and a coating layer on the surface of the foam, the coating layer Has been proposed using an aqueous emulsion resin material.

  However, an aqueous liquid material such as an aqueous emulsion resin material is generally known to have many problems to be solved in the coating process since it has a low viscosity and requires time for drying. In particular, in the case of an aqueous liquid material in which roughness forming particles such as resin particles are blended, when this is applied to the surface of the conductive rubber foam layer described above, the specific gravity of the roughness forming particles, the synthetic resin, etc. Due to the difference in specific gravity with other components, there was a problem that a thin film portion and a thick film portion were formed in the dried coating film, and it was difficult to obtain a coating film (surface layer) with a uniform thickness. . Such a charging roll having a surface layer with a non-uniform thickness may cause various image defects. In order to solve such problems, it is conceivable to mix a leveling agent in the material. However, the leveling agent is mixed in the finally obtained charging roll (set resistance) and durability. There is a problem that image quality is reduced and image defects (ghosts) are likely to occur.

Japanese Patent No. 3277619 JP-A-9-96946

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is that it has a surface layer with a relatively uniform thickness and is effective in generating image defects. An object of the present invention is to provide a charging roll that can be suppressed.

  In order to solve such a problem, the present invention provides a charging roll in which a conductive rubber foam layer is provided on the outer peripheral surface of the shaft body, and a surface layer is further provided on the outer side thereof. The porous rubber foam layer has a skin layer with an open area ratio of 0.5 to 15% in the surface layer part, and the surface layer comprises a synthetic resin aqueous emulsion or rubber latex, and roughness forming particles. The gist of the present invention is a charging roll prepared by using an aqueous emulsion material in which the dispersion medium is water.

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

  As described above, in the charging roll according to the present invention, the conductive rubber foam layer provided on the outer peripheral surface of the shaft body has a skin layer having an opening ratio of 0.5 to 15% in the surface layer portion. Therefore, a dispersion medium prepared using a predetermined aqueous emulsion material, that is, an aqueous emulsion or rubber latex of a synthetic resin, and a particle for forming roughness is formed on the surface of the conductive rubber foam layer. When the aqueous emulsion material is applied according to various methods and then dried, the thickness of the surface layer, which is the dried body of the coating film, becomes relatively uniform. Therefore, the charging roll according to the present invention can effectively suppress the occurrence of various image defects.

  In addition, when an acrylic resin aqueous emulsion or a urethane resin aqueous emulsion is used as the above-described synthetic resin aqueous emulsion, the above-described effects can be more advantageously enjoyed.

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

  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 outermost layer (protective layer) 16 are 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, the conductive rubber foam layer 14 integrally formed on the outer peripheral surface of the conductive shaft 12 has the skin layer 18 having an opening ratio of 0.5 to 15%. There is a great feature where it is in the surface layer.

  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. Further, in the charging roll (10) of the present invention in which the surface layer (16) is formed using an aqueous emulsion material described later, the aqueous emulsion material is the surface of the conductive rubber foam layer (14). The (non-opening and opening) are effectively impregnated, and 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 can be effectively suppressed.

  Here, the aperture ratio (%) in this specification and claims means what is calculated as follows. That is, with respect to the conductive rubber foam layer before the surface layer is formed, at three locations in the axial center and both ends, three times at each location, that is, nine times in total, using an optical microscope such as a laser microscope 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.

  On the other hand, if the open area ratio of the skin layer (18) in the conductive rubber foam layer (14) is too small, the object of the present invention may not be effectively achieved, while the open area ratio of the skin layer (18). If is too large, it may be difficult to form the surface layer (16), or the thickness of the surface layer (16) may be non-uniform, 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 15%.

  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 the organic foaming agent 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.

  On the other hand, the surface layer (16) in the charging roll (10) according to the present invention is an aqueous emulsion system in which the dispersion medium is water prepared using a synthetic resin aqueous emulsion or rubber latex and roughness forming particles. Formed of material. As described above, the conductive rubber foam layer (14) in the present invention has a skin layer having an opening ratio within a predetermined range on the surface layer portion. In contrast, even when an aqueous emulsion-based material containing roughness forming particles (20) is used, the thickness of the finally obtained surface layer (16) is relatively uniform, and therefore, charging with which image defects are unlikely to occur. It becomes a roll (10).

Here, the synthetic resin aqueous emulsion means one in which synthetic resin particles are dispersed in water as a dispersion medium. In the present invention, any conventionally known synthetic resin aqueous emulsion can be used, but an acrylic resin aqueous emulsion or urethane resin aqueous emulsion is particularly preferably used.
In the case of a commercially available aqueous emulsion of a synthetic resin, it is used as it is or by adding water as necessary when preparing a material.

  The rubber latex used in the present invention is not particularly limited. For example, natural rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), and nitrile rubber (NBR). And rubber latex composed of butyl rubber (IIR), hydrogenated NBR, fluorine rubber, urethane rubber, ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), halogenated butyl rubber, and the like. These rubber latices can be used alone or in combination of two or more.

  Furthermore, examples of the roughness forming particles (20) include urethane resin particles, (meth) acrylic resin particles, urea resin particles, various synthetic resin particles such as amide resin particles, rubber particles, silica particles, and silicone particles. It is possible. Even in these roughness forming particles, it is of course possible to use them alone or in combination of two or more. In addition, as the particles for roughness formation, those having an average particle diameter of about several μm to 30 μm are usually used.

When preparing an aqueous emulsion material in which the dispersion medium is water, using a synthetic resin aqueous emulsion or rubber latex and roughness forming particles, a known conductive agent, crosslinking agent, filler, etc. Each of the various additives is blended at the same blending ratio as in the past, and the volume resistivity of the finally obtained surface layer (16) is generally about 1 × 10 ⁵ to 1 × 10 ¹³ Ω · cm. To be prepared.

  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 the desired range (0.5 to 15%).

  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 a 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 15%). 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 the surface of the conductive rubber foam layer 14 (the surface of the skin layer that is not open) with a laser. In addition, various conditions at the time of this laser irradiation are suitably determined so that an aperture ratio may be 0.5 to 15%.

-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 15% in the surface layer portion is obtained.

  And the aqueous emulsion type material 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. Is applied according to various conventionally known methods such as a roll coating method. Then, the surface layer 16 will be obtained by drying (and heating as needed) this coating film. The surface layer 16 is preferably formed to have a thickness of 0.3 to 50 μm, more preferably 0.5 to 20 μm.

  In the charging roll 10 of the present invention thus manufactured, since the conductive rubber foam layer 14 has the skin layer 18 opened at a predetermined opening ratio in the surface layer portion, the surface layer 16 is Even if it is formed using an aqueous emulsion material containing the roughness forming particles 20, the thickness thereof is relatively uniform, so that the occurrence of image defects can be effectively suppressed. It is a thing.

  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.

First, according to the blending ratio shown in the following Table 1, three types of foaming conductive rubber compositions as preparation materials for the conductive rubber foam layer (base layer) were prepared (blending examples 1 to 3). In preparing each composition, the following rubber materials were used.
-EPDM: Esprene 505 (trade name), manufactured by Sumitomo Chemical Co., Ltd.-NBR: Nipol DN3335 (trade name), manufactured by Nippon Zeon Co., Ltd.-Epichlorohydrin rubber: Epichromer CG102 (trade name), manufactured by Daiso Corporation-Carbon black: Ket Chain Black EC300J (trade name),
・ Ketjen Black International Co., Ltd. ・ Quaternary ammonium salt: Tetramethylammonium perchlorate ・ Zinc oxide: Zinc oxide 2 types (trade name), Sakai Chemical Industry Co., Ltd. ・ Stearic acid: Lunac S30 (trade name)・ Process oil: Diana Process Oil PW380 (trade name), manufactured by Idemitsu Kosan Co., Ltd. ・ Sulfur: manufactured by Karuizawa Seisen Co., Ltd.

On the other hand, according to the blending ratio shown in Table 2 below, three types of compositions (blending examples A to C) were prepared. As shown in Tables 3 and 4 below, these compositions were added to 450 parts by weight of water or an organic solvent (methyl ethyl ketone) as a dispersion medium to prepare an emulsion-based material as a surface layer forming material. In the preparation, the following synthetic resin aqueous emulsions and the like were used.
・ Acrylic resin aqueous emulsion: Boncoat SEP-119 (product name), manufactured by DIC Corporation ・ Urethane resin aqueous emulsion: Evaphanol HA107C (product name),
Made by Nikka Chemical Co., Ltd. ・ Isoprene rubber latex: TRH-70 (trade name), made by Resitex Corporation ・ Carbon black: CAB-O-JET 200 (trade name),
Cabot Specialty Chemicals, Inc. Acrylic resin particles: GM1001 (trade name), manufactured by Ganz Kasei Co., Ltd.

  Using the foamable conductive rubber composition (conductive rubber foam layer forming material) and emulsion material (surface layer forming material) prepared as described above, a charging roll was prepared according to the following method. In addition, in the following Table 3 and Table 4, each compounding example used when producing a conductive rubber foam layer (base layer) and a surface layer is shown together with evaluation results described later.

  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 Table 3 below was prepared on the surface layer of the conductive rubber foam layer (Examples 1 to 9). In addition, about the charging roll which concerns on Comparative Examples 1-12, laser irradiation was not implemented.

  And by applying each emulsion system material shown in the following Table 3 and Table 4 on the surface of each base roll thus obtained in accordance with the roll coating method and drying at 120 ° C. for 30 minutes, 21 types of The charging roll was manufactured (Examples 1-9, Comparative Examples 1-12). The thickness of the obtained surface layer was measured by cutting the conductive rubber foam layer and the surface layer of the roll perpendicular to the shaft and observing the cross section with an optical microscope. The measurement results are also shown in Tables 3 and 4 below. In each of the charging rolls according to Comparative Examples 1 to 12, it was visually observed that the thickness of the surface layer was not uniform. In particular, in the charging rolls according to Comparative Examples 1 to 3, the conductive rubber foam layer is significantly impregnated with the emulsion material, and the thicknesses shown in Table 4 below are the thicknesses of the flat portions in the formed surface layer. Is measured.

  The following evaluations were performed on the obtained 21 types of charging rolls.

-Evaluation of coating unevenness image-
The charging roll was set in the cartridge of an actual machine (trade name: Color Laser Jet 3800dn, manufactured by Hewlett-Packard Company, the same applies hereinafter), and a black solid image and a 25% halftone pattern were output. Each obtained image was evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4 as “Coating unevenness images”.
○: Image density unevenness is not recognized at any charging roll pitch in any image.
Δ: In any of the images, although the image density unevenness is recognized at the charging roll pitch, it is within the allowable range.
X: In any of the images, remarkable image density unevenness is recognized at the charging roll pitch.

-Evaluation of speckled images-
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 “spot images”.
○: No speckled image is observed at the charging roll pitch in the image.
Δ: A spot image is observed at the charging roll pitch in the image, but it is within an allowable range.
X: A remarkable spot image is recognized by the charging roll pitch in the image.

-Evaluation of setability-
The charging roll was set in a cartridge of an actual machine, and left in a 40 ° C. × 95% RH environment for one week in that state, and then a 25% halftone pattern was output. The obtained images were evaluated according to the following criteria. The evaluation results are shown in Table 3 and Table 4 as “set property”.
A: No image streak is observed in the image at the charging roll pitch.
(Triangle | delta): Although an image stripe is recognized by the charging roll pitch in an image, it is in an allowable range.
X: Remarkable image streaks are observed in the image at the charging roll pitch.

-Evaluation of ghost images-
The charging roll was set in an actual cartridge, and an image in which the upper half was solid black and the lower half was 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 “ghost images”.
○: No solid black image is observed in the image.
Δ: Although a solid black afterimage is recognized in the image, it is within the allowable range.
X: A black solid afterimage is remarkably recognized in the image.

-Evaluation of durability-
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 3 and 4 as “durability”.
A: No toner fusion is observed on the surface of either the photosensitive drum or the charging roll.
Δ: Although toner fusion is observed on the surface of either the photosensitive drum or the charging roll, it does not significantly affect the output image.
X: Toner adhesion that adversely affects the output image is observed on the surface of either the photosensitive drum or the charging roll.

  As is apparent from the results of Tables 3 and 4, it was confirmed that the charging rolls (Examples 1 to 9) according to the present invention hardly cause image defects.

DESCRIPTION OF SYMBOLS 10 Charging roll 12 Shaft body 14 Conductive rubber foam layer 16 Surface layer 18 Skin layer 20 Roughness formation particle

Claims (2)

A charging roll in which a conductive rubber foam layer is provided on the outer peripheral surface of the shaft body, and a surface layer is provided on the outer side thereof,
The conductive rubber foam layer has a skin layer having an opening ratio of 0.5 to 15% in a surface layer portion, and the surface layer is an aqueous emulsion or rubber latex of synthetic resin, and particles for forming roughness. A charging roll characterized in that it is formed of an aqueous emulsion material prepared by using an aqueous emulsion material in which the dispersion medium is water. The charging roll according to claim 1, wherein the aqueous emulsion of the synthetic resin is an acrylic resin aqueous emulsion or a urethane resin aqueous emulsion.

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