JP2019124900A - Electrophotographic charging member, process cartridge and electrophotographic image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging member for electrophotographic which contributes to suppression of strong electric discharge derived from a convex portion of a surface and suppression of a white-out image. SOLUTION: This is a charging member for electrophotographic having a conductive substrate, a conductive elastic layer and an insulating surface layer in this order. The elastic layer contains a binder and has a plurality of bowl-shaped resin particles as a substrate of the elastic layer. The particles are held on the surface opposite to the side facing the opening, and the particles have an opening and an edge around the opening and a gap connected to the opening, and each of the particles has an opening and an edge facing the substrate of the elastic layer. It is held by the elastic layer so as to be exposed from the surface opposite to the side facing the substrate, the surface of the surface layer opposite to the side facing the substrate constitutes the surface of the charging member, and the surface of the charging member is a void. A line segment having a plurality of concave portions derived from the above and a plurality of convex portions derived from the edge, and connecting the apex and the center of rotation of the substrate in a cross section including the apex of the convex portion orthogonal to the longitudinal direction of the charging member. Through the space of the recesses, the surface layer has a specific volumetric resistance and film thickness. [Selection diagram] Fig. 2

Description

  The present invention relates to a charging member for electrophotography, a process cartridge and an electrophotographic image forming apparatus.

  An image forming apparatus adopting an electrophotographic method mainly includes an electrophotographic photosensitive member (hereinafter, also simply referred to as a “photosensitive member”), a charging device, an exposure device, a developing device, a transfer device, and a fixing device. Many contact charging devices are employed as the charging device. The contact charging device applies a DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage to a charging member (typically, a charging roller) disposed in contact with or in close proximity to the surface of the photoconductor. To charge the surface of

  With the recent increase in speed and life of electrophotographic apparatuses, the charging member is required to stably charge a member to be charged for a long time.

  To address this problem, Patent Document 1 discloses a charging roller in which a conductive layer having a convex portion derived from resin particles is provided on the surface of the charging roller. Further, Patent Document 2 discloses a charging roller having a concave portion derived from an opening of a bowl-shaped resin particle and a convex portion derived from an edge of an opening of a bowl-shaped resin particle on the surface. There is.

JP, 2008-276026, A JP, 2011-248353, A

  When the photosensitive member is charged using the charging members according to Patent Document 1 and Patent Document 2, a surface potential corresponding to the surface shape is formed on the surface of the charging member by an applied voltage. A surface potential higher than that of the non-convex portion is formed at the convex portion derived from the resin particle contained in the surface layer of the charging member or the convex portion derived from the edge of the bowl-shaped resin particle. Therefore, in the convex portion of the surface of the charging member, stronger discharge occurs with the photosensitive member than in the non-convex portion. Therefore, in the portion of the surface of the photosensitive member corresponding to the convex portion on the surface of the charging member, the charging potential is higher than that of the surrounding portion.

  In particular, when forming a high-definition low-density image, the exposure intensity by the exposure device becomes weak. For this reason, it is difficult to make the surface portion of the photosensitive member whose charging potential has become high as described above, a surface potential suitable for developing toner after exposure. As a result, on the electrophotographic image, the toner may not be transferred to a portion to which the toner is originally to be transferred, and white spots may occur in the electrophotographic image.

  One aspect of the present invention is directed to the provision of a charging member for electrophotography that contributes to the suppression of a strong discharge originating from the convex portion of the surface of the charging member and the suppression of a white spot image. Another aspect of the present invention is directed to the provision of a process cartridge and an electrophotographic image forming apparatus which contribute to the suppression of a strong discharge originating from the convex portion on the surface of the charging member and the suppression of the white spot image.

According to one aspect of the invention:
A charging member for electrophotography comprising a conductive substrate, a conductive elastic layer, and an insulating surface layer in this order,
The elastic layer contains a binder and holds a plurality of bowl-shaped resin particles on the surface of the elastic layer opposite to the side facing the substrate,
The bowl-shaped resin particle has an opening, an edge around the opening, and a void connected to the opening, and each of the bowl-shaped resin particles has the opening and the edge formed by the elastic layer. The elastic layer so as to be exposed from the side opposite to the side facing the substrate,
The surface of the surface layer opposite to the side facing the substrate constitutes the surface of the charging member,
The surface of the charging member has a plurality of recesses derived from the void and a plurality of projections derived from the edge,
In a cross section orthogonal to the longitudinal direction of the charging member and including the apex of the projection, a line connecting the apex and the rotation center of the base passes through the space of the recess,
The volume resistivity of the surface layer is 1.0 × 10 ¹⁶ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less, and
There is provided a charging member for electrophotography, wherein the film thickness of the surface layer is 1 μm or more and 5 μm or less.

According to another aspect of the present invention, there is provided a process cartridge detachably configured to a main body of an electrophotographic image forming apparatus, comprising:
There is provided a process cartridge having the charging member for electrophotography.

  According to still another aspect of the present invention, there is provided an electrophotographic image forming apparatus comprising: an electrophotographic photosensitive member; and a charging member arranged to charge the electrophotographic photosensitive member, wherein the charging member is the above-mentioned. An electrophotographic image forming apparatus, which is a charging member of

  According to one aspect of the present invention, there is provided a charging member for electrophotography, which contributes to the suppression of a strong discharge originating from the convex portion on the surface of the charging member and the suppression of a blank image. Further, according to another aspect of the present invention, there are provided a process cartridge and an electrophotographic image forming apparatus which contribute to the suppression of a strong discharge originating from the convex portion on the surface of the charging member and the suppression of the white spot image.

It is a schematic cross section which shows the structural example of the charging member which concerns on this invention. It is a cross-sectional schematic diagram of an example of the bowl-shaped resin particle of a charging member. It is a cross-sectional schematic diagram for demonstrating the dimension of an example of the bowl-shaped resin particle of a charging member. It is a figure for demonstrating the mechanism which expresses the effect of this invention, (A) is a cross-sectional schematic diagram in the case of the resin particle of bowl shape, (B) is a cross-sectional schematic diagram in the case of solid resin particle. It is a schematic diagram which shows the structure of the corona discharge surface treatment apparatus used in the Example. It is a schematic diagram which shows the structure of the apparatus which performs discharge light observation of the charging member used in the Example. FIG. 1 is a schematic cross-sectional view of an example of an electrophotographic image forming apparatus according to the present invention. It is a cross-sectional schematic diagram of an example of the process cartridge which concerns on this invention. It is a schematic diagram which shows the surface finish grinding apparatus used in the Example. FIG. 6 is a cross-sectional schematic view of typical bowl-shaped resin particles of the charging member obtained in Comparative Example 3;

  The charging member according to an aspect of the present invention includes a conductive substrate, a conductive elastic layer, and an insulating surface layer in this order. The elastic layer contains a binder. The elastic layer is formed by holding a plurality of bowl-shaped resin particles on the surface of the elastic layer opposite to the side facing the substrate. The bowl-shaped resin particles have an opening, an edge around the opening, and an air gap connected to the opening. Each of the bowl-shaped resin particles is held by the elastic layer so that the opening and the edge are exposed from the surface of the elastic layer opposite to the side facing the substrate.

  The inventors of the present invention have estimated the reason why the occurrence of white spots on the electrophotographic image can be suppressed even when forming a low density electrophotographic image by the charging member as follows.

  First, as a charging member according to the conventional example, as shown in FIG. 4 (B), solid and conductive resin particles (4b) are exposed from the surface of the conductive elastic layer (1b) and insulating surface The charging member in which the layer (1a) covers the resin particles (4b) and the conductive elastic layer (1b) will be described.

  The surface layer of the charging member is opposite in polarity to the applied voltage. Here, the case where a negative voltage is applied to the conductive substrate of the charging member is considered.

  In the discharge space, when the strength of the electric field exceeds a certain value (which can be obtained by Paschen's law), gas molecules in the air are ionized, electrons and positive ions are generated, and the first discharge occurs. Next, the generated electrons collide with many gas molecules in the air in the process of moving according to the applied electric field, and move toward the photoreceptor while forming an electron avalanche. At the tip of the electronic avalanche, collisions of electrons and gas molecules occur. Therefore, the electron avalanche progresses while increasing the discharge charge amount, and eventually electrons accumulate on the surface of the photosensitive member. That is, the surface of the photosensitive member is charged.

  The generated positive ions move in the opposite direction to the photosensitive member, ie, to the surface of the charging member. Here, when the volume resistivity of the surface layer of the charging member is low, the positive charge of positive ions transferred to the surface of the charging member passes through the surface layer and escapes to the conductive elastic layer and the conductive substrate. . However, when the volume resistivity of the surface layer is high, that is, the surface layer is insulating, the positive charge of positive ions can not pass through the surface layer (1a) and the surface of the surface layer (1a) Accumulate in That is, the surface layer charges up positively. FIG. 4 (B) schematically shows this.

  As described above, when the surface layer is positively charged up, the accumulated positive charge can offset the negative electric field generated by the applied voltage, and the strong discharge can be suppressed. However, as shown in FIG. 4B, in the case where only a convex shape by solid conductive resin particles (4b) is present as the convex portion, the electric field is only offset as a whole, and the convex portion is not It is insufficient to fill in the difference in electric field strength with the convex portion.

  On the other hand, in the charging member according to the present embodiment, as shown in FIG. 4A, the surface having convex portions (2d in FIG. 2) and concave portions (2c in FIG. 2) derived from bowl-shaped resin particles It has a surface layer to be charged up. This makes it possible to reduce the difference in electric field strength between the convex portion and the non-convex portion.

  Here, FIG. 2 is referred to. FIG. 2 is a cross-sectional view of a cross section orthogonal to the longitudinal direction of the charging member according to the present embodiment and including the apex of the convex portion. The charging member has a recess (2c) derived from the void (2a) of the bowl-shaped resin particle (201) and a protrusion (2d) derived from the edge (2h) around the opening on the surface, It has an upable surface layer (1a).

  When a negative voltage is applied to the base of the charging member, an electric field is concentrated at the top (2e) of the convex portion (2d). On the other hand, the electric field formed on the surface of the recess (2c) derived from the void (2a) of the bowl-shaped resin particle (201) present below the protrusion (2d) is weaker than that of the protrusion, and It is weaker than the flat part of the charging roller surface. Furthermore, since the concave portion (2c) has the chargeable surface layer (1c), the electric field formed on the concave surface is even weaker.

  Therefore, in the portion (4a) surrounded by the broken line shown in FIG. 4A, a positively charged portion capable of canceling out the strong negative electric field of the convex portion can be formed on the surface of the concave portion under the convex portion. Therefore, in the convex portion (2d) derived from the edge, the effect of offsetting the negative electric field is greater than in the non-convex portion, and the difference in electric field strength between the convex portion and the non-convex portion can be reduced. . As a result, it is possible to suppress the occurrence of white spots even when forming a low density electrophotographic image.

  Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited thereby. In addition, although a charging roller is described in detail as a charging member for electrophotography, the shape of the charging member is not limited to the roller shape.

<Configuration>
The charging roller shown in FIG. 1 comprises a conductive substrate (1c), a conductive elastic layer (1b) provided on the conductive substrate, and an insulating surface layer provided on the conductive elastic layer. And (1a) in this order.

<Conductive substrate>
As the conductive substrate, a substrate made of a conductive material can be used, for example, a support (for example, a metal (including an alloy) formed of iron, copper, stainless steel, aluminum, an aluminum alloy, or nickel) A cylindrical metal can be used.

<Conductive elastic layer>
The conductive elastic layer (1b) includes a binder and a plurality of bowl-shaped resin particles (201). The elastic layer can include conductive particles to express its conductivity. Each of the bowl-shaped resin particles (201) has one opening (2b), an edge (2h) of the opening, and a gap (2a) connected to the opening. The bowl-shaped resin particles have a shape in which hollow resin particles are open. The opening (2b) and its edge (2h) are exposed from the outer peripheral surface of the elastic layer (1b) (that is, the surface opposite to the side facing the base). The void (2a) is defined by the inner wall surface of the resin particle (201) and the opening (2b).

(Binder of conductive elastic layer)
A known rubber or resin can be used as the binder contained in the conductive elastic layer. As rubber | gum, natural rubber, that which carried out the vulcanization process of this, a synthetic rubber can be mentioned, for example. The following are mentioned as a synthetic rubber. Ethylene propylene rubber, styrene butadiene rubber (SBR), silicone rubber, urethane rubber, isoprene rubber (IR), butyl rubber, acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), acrylic rubber, epichlorohydrin rubber and fluororubber. As the resin, for example, a resin such as a thermosetting resin or a thermoplastic resin can be used. Among them, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, acrylic urethane resin, silicone resin and butyral resin are more preferable. These may be used alone or in combination of two or more. Moreover, it is good also as a copolymer by copolymerizing the monomer which is a raw material of these binders. The conductive elastic layer may be formed by adding a crosslinking agent or the like to a prepolymerized binder raw material and curing or crosslinking.

(Conductive particles)
The conductive elastic layer can contain known conductive particles in order to develop conductivity. Specific examples of the conductive fine particles include metal oxides, metal fine particles, carbon black and the like. In addition, these conductive fine particles can be used alone or in combination of two or more. As a standard of content of conductive particles in a conductive elastic layer, it is 2-200 mass parts, especially 5-100 mass parts to 100 mass parts of binders.

(Other components that make up the conductive elastic layer)
In addition to the above, the conductive elastic layer may contain insulating particles, and additives such as a softening oil and a plasticizer for adjusting the hardness. It is preferable to use a polymer type plasticizer as the plasticizer, and the weight average molecular weight thereof is preferably 2000 or more, more preferably 4000 or more. Furthermore, resin particles other than anti-aging agents, fillers, processing aids, tackifiers, anti-tack agents, dispersing agents and roughening particles may be contained as materials imparting various functions. The following may be mentioned as resin particles. Polymethyl methacrylate particles, polyethylene particles, silicone rubber particles, polyurethane particles, polystyrene particles, amino resin particles, or phenol resin particles.

<Surface layer>
The outer peripheral surface of the surface layer (1a) (surface opposite to the side facing the substrate) constitutes the surface of the charging roller. Therefore, the outer peripheral surface of the elastic layer (1b) is covered with the surface layer (1a) including the portion exposed from the outer peripheral surface of the elastic layer of the bowl-shaped resin particle (201). As a result, the surface of the charging roller has a plurality of concave portions (2c) derived from the voids (2a) of the plurality of resin particles (201) and a plurality derived from the edges (2h) of the plurality of resin particles (201). And a convex portion (2d) of

  In order to capture and charge up the positive charge generated by the discharge, the volume resistivity and the film thickness of the surface layer are in the following ranges.

(Film thickness of surface layer)
The film thickness of the insulating surface layer (1a) is 1 μm or more and 5 μm or less. By setting the film thickness to 1 μm or more, the positive charge on the charged up surface layer can be held in the surface layer without being released to the conductive substrate. Further, by setting the film thickness to 5 μm or less, discharge can be sufficiently generated, stabilization of the discharge can be achieved, and uniform charging can be performed without causing charging failure. The film thickness of the surface layer can be measured by cutting the cross section of the charging roller with a sharp blade and observing the obtained sample with an optical microscope or an electron microscope.

(Volume resistivity of surface layer)
The volume resistivity of the surface layer (1a) is 1.0 × 10 ¹⁶ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less. By setting the volume resistivity of the surface layer to 1.0 × 10 ¹⁶ Ω · cm or more, positive charges on the charged-up surface layer can be held on the surface layer without causing the conductive substrate to escape. The electric field concentrated on the convex portion can be relaxed. Further, by setting the volume resistivity of the surface layer to 1.0 × 10 ¹⁸ Ω · cm or less, the amount of positive charge accumulated in the surface layer can be properly made, and the discharge can be stabilized, so that the photosensitive member Uniform charging can be performed without causing charging failure.

(Measurement of volume resistivity of surface layer)
The volume resistivity of the surface layer can be measured using an atomic force microscope (AFM) and a measurement value measured by the conductivity mode. First, the surface layer (1a) of the charging roller is cut into sheet pieces using a manipulator, and metal deposition is performed on one side of the sheet piece. A DC power supply is connected to the metal-deposited surface, a voltage is applied, the free end of the cantilever is in contact with the other surface of the surface layer, and a current image is obtained through the AFM body.
From the current image, the current value at 100 randomly selected surfaces is determined, and the average of the 10 lower current values of the measured current values, the film thickness of the sheet piece, and the contact area of the cantilever , Volume resistivity can be calculated.
The measurement environment can be a temperature of 23 ° C. and a relative humidity of 50%.

(How to check charge up)
The charge up can be confirmed by applying a charge to the surface of the charge roller by corona discharge or the like and then measuring the surface potential.

Specifically, the charge amount measuring device (trade name: DRA-2000L, manufactured by QEA) is disposed such that the gap between the grid portion and the surface of the charge roller is 1 mm. Then, a voltage of 8 kV is applied to the corona discharger to generate discharge to charge the surface of the charge roller, and the surface potential of the charge roller may be measured after 10 seconds after the discharge is completed.
The measurement environment can be a temperature of 23 ° C. and a relative humidity of 50%.

(Material of surface layer)
As a resin for forming the surface layer (1a), a resin capable of setting the volume resistivity of the surface layer to 1 × 10 ¹⁶ Ω · cm or more and 1 × 10 ¹⁸ Ω · cm or less is used. Examples of such resins include fluorine resins, polyamide resins, acrylic resins, polyurethane resins, silicone resins, butyral resins and polyolefin resins (for example, polyethylene resins) which exhibit the above-mentioned volume resistivity. In addition, a copolymer produced by reacting two or more kinds of monomers serving as raw materials of these resins, or reacting these resins as prepolymers with monomers serving as raw materials of other resins is used. It can also be done.

  Among these, in order to control the volume resistivity of the surface layer (1a) to a high resistance, it is preferable to use a resin having a polyolefin skeleton. Further, among resins having a polyolefin skeleton, resins having a polyisoprene skeleton are preferable. The polyisoprene skeleton has a large amount of carbon adjacent to a double bond in the skeleton, that is, carbon that is in the allyl position, and when the surface layer is charged up, it is easy to stably hold a positive charge. In addition, since the double bond is not conjugated, it is easy to stably control the volume resistivity of the surface layer with high resistance.

  Further, the resin of the surface layer is preferably a radiation disintegrable resin. The radiation-disintegrable resin is a resin in which molecular chain breakage is likely to occur as compared with the crosslinking reaction because unstable radicals are generated when radiation irradiation is performed. Examples of radiation-disintegrable resins are introduced in the literature such as Kenichi Kuwahara et al., "Radiation and Polymers" (Tsubaki Shoten, 1968).

  Whether the resin is a radiation-disintegrable resin can be determined by measuring the change in molecular weight of the resin before and after the process of applying radiation or energy corresponding thereto. When the charge roller surface holds a positive charge on the surface, radicals may be generated on the surface layer by prolonged use. When a radiation-disintegrable resin is used for the surface layer, the decay thereof generates an unstable radical, and this unstable radical can be used to achieve a state in which the radical always disappears in the surface layer. As a result, it is possible to prevent a phenomenon in which the resistance of the resin of the surface layer is lowered by the reaction with oxygen and water present on the surface of the surface layer.

  Above all, when a resin having a polyolefin skeleton and being a radiation disintegrable type, for example, polyisobutylene is used, high resistance can be easily maintained strictly, and a surface layer particularly suitable for long-term use can be provided.

In order to maintain the volume resistivity of the surface layer at 1.0 × 10 ¹⁶ Ω · cm or more, it is preferable that the surface layer does not contain a conductive agent such as an ion conductive agent or conductive particles.

(Confirmation of whether the resin of the surface layer is radiation decay type)
By the following method, it can be confirmed whether or not the resin forming the surface layer is radiation disintegrating. First, the resin forming the surface layer is sampled, and the molecular weight of the resin is measured by gel permeation chromatography (GPC). Next, corona discharge treatment is applied to the charging roller, and then the resin constituting the surface layer of the charging roller is sampled, and the molecular weight is measured by GPC. If the molecular weight is reduced before and after the corona discharge, the resin is radiation disintegrating. If the molecular weight is increasing, the resin is a radiation crosslinkable resin.

  In GPC measurement, the target resin is put in a solvent to form a solution. As this solvent, a solvent capable of dissolving 1% by mass or more of the resin may be selected. The sampled resin may be immersed in a selected solvent, and after a certain period of time has elapsed, GPC measurement may be performed on the solution portion taken out by filtration.

  Specifically, depending on the target resin, the solvent may be toluene, chlorobenzene, tetrahydrofuran (THF), trifluoroacetic acid, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), formic acid, etc. The choice of the most soluble solvent is possible.

(Other additives)
If necessary, other additives may be added to the surface layer (1a) to the extent that the effects of the present invention are not impaired. It is preferable to contain a silicone additive from the viewpoint of increasing the surface layer resistance and imparting slipperiness. In addition, the surface layer may be subjected to modification, introduction of a functional group or a molecular chain, surface treatment with a release agent, and the like, as long as the effects of the present invention are not impaired.

(Method of forming surface layer)
Here, a method of forming the surface layer (1a) will be described. The method of forming the elastic layer (1b) will be described later. The surface layer (1a) can be formed by an application method such as electrostatic spray application, dipping application, ring application and the like. Further, a method of curing and molding the material into a predetermined shape in a mold can also be used. Among these, it is preferable to form a surface layer by applying a coating liquid containing the material of the surface layer on the surface of the elastic layer by a coating method, drying, and curing by heating or ultraviolet irradiation. This is to form a surface layer uniformly on the surface of the conductive elastic layer (1b) within a specific film thickness range.

  Moreover, physical properties such as dynamic friction and surface free energy can be adjusted by surface-treating the surface layer. Specifically, the surface layer may be irradiated with active energy rays. As an active energy ray, an ultraviolet ray, an infrared ray, an electron beam etc. are mentioned.

<Surface shape of charging roller>
The form of the surface shape of the charging roller will be described in detail below.

  As shown in FIG. 2, in the bowl-shaped resin particle (201), an opening (2b), an edge (2h), and a void (2a) are present. The outer wall surface of the resin particle (201) is covered with the elastic layer (1b). The elastic layer (1b) is not present on the inner wall surface of the bowl-shaped resin particle (201) and is not present on the edge (2h). The outer peripheral surface of the elastic layer (1b) is covered with the inner wall surface and the edge (2h) of the bowl-shaped resin particle (201) by the surface layer (1a). On the surface of the charging roller, there are a recess (2c) derived from the air gap (2a) and a protrusion (2d) derived from the edge (2h).

  Of the convex portions (2d), the point (2e) most projecting outward on the side opposite to the base (1c) is referred to as a “convex apex”. Further, as shown in FIG. 2, a point (2g) where the rotation axis of the charging roller exists in a cross section including the convex apex (2e) and orthogonal to the longitudinal direction (rotational axis direction) of the charging roller ) Of "rotation center" or simply "rotation center". In the case where two convex portions exist in the cross section shown in FIG. 2, the convex portion having the point protruding to the outermost side is a convex portion derived from the edge of the bowl-shaped resin particle (201).

  In the cross section shown in FIG. 2, a line segment (2f) connecting the convex apex (2e) and the rotation center (2g) passes through the space (2i) of the recess (2c).

    When discharge is generated from the convex portion (2d), the electric field is concentrated on the convex apex (2e). In order to suppress the strong electric field concentrated on the convex apex (2e), the discharge direction from the convex, that is, the direction connecting the convex apex (2e) and the rotation center (2g), is closer to the rotation center than the convex It is effective that there is a site for weakening the discharge from the convex portion.

  It is preferable that 70% or more of the bowl-shaped resin particles having the above-mentioned shape be present, and it is more preferable to be 90% or more.

  The electric field formed in the concave portion (2c) is weak because the distance to the photosensitive member is longer than the convex portion (2d) or the non-convex concave portion, and the electric field of the convex portion present on the photosensitive member side than the concave portion (2c) Attenuating effect is strong. Therefore, in order to weaken the electric field of the convex portion (2d) as described above, it is effective for the concave portion to be present on the base (1c) side with respect to the convex apex. That is, it is effective that the line segment (2f) passes through the space (2i) of the recess (2c).

  Preferred shapes are described with reference to FIG. Similar to FIG. 2, FIG. 3 shows a cross section orthogonal to the longitudinal direction of the charge roller, including the convex apex (2e). First, the distance between the convex apex (2e) and the height average surface (3a) of the charging roller surface is defined as the convex apex height (3b) (hereinafter, for convenience, the convex apex height is also referred to as "Ho"). . Next, a point at which a line segment (2f) connecting the convex apex (2e) and the rotation center (2g) intersects the surface of the recess (2c) of the bowl-shaped resin particle is taken as an intersection (3c). The distance between the convex apex (2e) and the intersection (3c) is referred to as a convex apex-concave surface distance (3d) (hereinafter also referred to as "PL" for convenience). At this time, it is preferable that the ratio of the convex apex height to the convex apex-concave surface distance, that is, the value of PL / Ho be 2 or more and 10 or less. That is, it is preferable that the distance PL be equal to or more than twice and equal to or less than 10 times the convex vertex height Ho. This is because the electric field of the convex portion becomes stronger depending on the height of the convex apex, while the electric field strength of the concave surface decreases as the concave surface gets farther from the convex apex, and the effect of weakening the electric field of the convex is strong In order to When PL / Ho is 2 or more, the effect of attenuating the electric field of the convex portion becomes strong, and when it is 10 or less, stable discharge is easy.

  Further, in order to further reduce the concentration of the electric field at the convex apex (2e), it is preferable to set the convex apex height Ho to 3 μm or more and 10 μm or less. A stable discharge becomes easy by setting it as 3 micrometers or more, and it is easy to optimize electric field concentration of a convex part, and to perform an electric field attenuation effectively by setting it as 10 micrometers or less.

(How to check the surface shape of the charging roller)
The surface shape can be confirmed as follows.
First, for the surface of the charging roller, an elevation profile of the surface is created using a confocal microscope or the like, and the highest point among the projections (2d) from the height average surface of the charging roller surface, that is, Search for a convex vertex (2e). Using a focused ion beam method, a cross section (a cross section orthogonal to the longitudinal direction) is cut out in a direction parallel to the circumferential direction of the charging roller from the convex apex (2e) of the bowl-shaped resin particle (201). At this time, an ion beam is cut out to at least the center of the conductive substrate (1c) to prepare a sample sheet in a state where the rotation center (2 g) can be known. With respect to the sample sheet, a cross-sectional image of the surface shape may be taken using a scanning electron microscope (SEM) or a confocal microscope to confirm that the shape is as shown in FIG.

  Further, in the height profile and the cross-sectional image obtained, it is possible to measure the above-mentioned convex vertex to concave surface distance PL (3 d) and the convex vertex height Ho (3 b). This measurement is performed, for example, on the central part of a total of 66 areas when the charging roller is divided roughly into 11 in the longitudinal direction and into 6 in the circumferential direction, and the average value of the respective measured values is The surface distance PL (3d) and the convex vertex height Ho (3b) may be used.

(Method of forming surface shape of charging roller)
First, a conductive resin composition in which hollow resin particles (hereinafter sometimes referred to as "hollow particles") are dispersed is prepared, and an elastic layer (1b) is formed on the conductive substrate (1c). As an example of a method of forming a conductive resin composition on a conductive substrate, this coating is cured by an application such as electrostatic spray application, dipping application, roll application, and subsequent drying, heating, crosslinking steps, etc. There is a way to Moreover, the method of adhere | attaching the layer of the sheet | seat shape or tube shape which film-formed and hardened the conductive resin composition to a predetermined | prescribed film thickness to a conductive base is also mentioned. Moreover, the method of coat | covering a conductive substrate with this sheet-shaped or tube-shaped layer is mentioned. Furthermore, there is a method in which the conductive resin composition is placed in a mold in which the conductive substrate is disposed and cured to be molded. Further, in particular, when the binder is rubber, the conductive substrate (1c) and the unvulcanized rubber composition are integrally extruded using an extruder equipped with a crosshead, and after drying, heating and crosslinking steps. Also, the conductive resin composition can be formed on the conductive substrate. The crosshead is an extrusion mold which is used to form a coating layer on a rod-like material such as an electric wire or wire, and which is installed at the tip of a cylinder of an extruder.

  By polishing the surface (peripheral surface) of the conductive elastic layer (1b) formed on the conductive substrate (1c), the surface shape of the specific elastic layer as shown in FIG. 2 described above is formed. be able to. As a method of polishing the surface, cylindrical polishing or tape polishing can be used. In addition, after the primary surface treatment using cylindrical polishing method, heat treatment is performed in an atmosphere containing oxygen gas to further promote curing of the bowl-shaped resin particles (particularly, the convex portions thereof), and thereafter a tape is obtained. There is also a method of forming a surface shape by performing secondary surface treatment by polishing.

  As a result, a part of the shell of the hollow resin particle is removed to form a bowl shape having an opening, and the opening (2b) of the obtained bowl-shaped resin particle (201) and the resin particle (201) are obtained. An air gap (2a) defined by the inner wall can be formed. The opening (2b) is directed to the opposite side of the elastic layer (1b) from the side facing the base.

  By covering the outer peripheral surface of the elastic layer (1b) thus obtained with the surface layer (1a) as described above, the recess (2c) derived from the void (2a) and the bowl-shaped resin particle It is possible to obtain a surface shape having a convex portion (2d) derived from the edge (2h) of the opening.

  In order to make the value of PL / Ho 2 or more and 10 or less, it is preferable to carry out the polishing in the tape polishing method in the same direction as the polishing performed in the cylindrical polishing. The average abrasive grain of the polishing tape used in the tape polishing method is preferably 0.1 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm.

  In order to set the value of Ho to 3 μm or more and 10 μm or less, the rotation speed of the roller in the tape polishing method is preferably 500 rpm or more and 6000 rpm or less, and more preferably 1000 rpm or more and 3000 rpm or less.

<Resin constituting hollow particle and bowl-shaped resin particle>
The resin of the hollow particles and the bowl-shaped resin particles is preferably a resin having a polar group from the viewpoint of low gas permeability in order to maintain the hollow shape, and a resin having a unit represented by the following formula (1) preferable.

  In formula (1), A is at least one selected from the following formulas (2), (3) and (4). R1 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

  Specifically, acrylonitrile resin, vinyl chloride resin, vinylidene chloride resin, methacrylic acid resin, styrene resin, butadiene resin, urethane resin, amide resin, methacrylonitrile resin, acrylic acid resin, acrylic acid ester resin, and methacrylic acid ester resin One or more resins selected from the group consisting of

  Among them, radiation disintegrable resins are preferred in view of long-term use. The convex portion (2e) derived from the edge of the bowl-shaped resin particle is likely to generate radicals since the electric field is concentrated, and the surface layer of the convex portion may be embrittled by long-term use. When the surface layer of the convex portion is embrittled, the surface layer may be lost due to the contact with the photosensitive member, the bowl-shaped resin particles (201) may be exposed, and a strong discharge may be generated therefrom.

  On the other hand, radiation-disintegrable resins are considered to generate unstable radicals upon irradiation with radiation and to cause cleavage of molecular chains in the vicinity of the radical generation site.

  Therefore, by forming the bowl-shaped resin particle (201) with a radiation-disintegrable resin, radicals generated by the concentration of the electric field become unstable radicals. Unstable radicals react with the resin in the bowl-shaped resin particles and disappear due to the instability before the surface layer is destroyed. Therefore, the present inventors estimate that embrittlement of the surface layer does not occur due to long-term use.

  A preferable radiation-disintegrable resin for the bowl-shaped resin particles is a thermoplastic resin comprising at least one selected from an acrylonitrile resin, a vinylidene chloride resin, and a methacrylonitrile resin.

  On the other hand, a radiation crosslinking resin is mentioned as a resin in which a new bond such as molecular crosslinking is formed and the molecular structure tends to be large in response to irradiation of radiation. Since the radiation crosslinkable resin generates stable radicals, the reaction with the surrounding material is increased and oxidation and formation of by-products proceed as compared with the radiation disintegrable resin. Therefore, it is considered that the embrittlement of the surface layer due to long-term use is likely to occur as compared with the radiation disintegrable resin.

(Confirmation of radiation decay type for bowl-shaped resin particles)
The confirmation of whether the resin of the bowl-shaped resin particle is a radiation-disintegrable type may be performed in the same manner as the method of confirming the radiation-disintegrable resin for the resin of the surface layer described above. Specifically, it is possible to sample the bowl-shaped resin particles forming the surface shape of the charging roller and measure the molecular weight of the resin particles by gel permeation chromatography (GPC). Next, corona discharge treatment is applied to the charging roller, and then, the resin particles in the bowl shape forming the surface shape of the charging roller are sampled, and the molecular weight is measured by GPC. And, if the molecular weight after the corona discharge is smaller than the molecular weight before the corona discharge, the resin in the resin particle is a radiation disintegrating type. On the other hand, when the molecular weight is increasing, the resin is a radiation crosslinking resin.

  This GPC measurement can be performed in the same manner as the GPC measurement to confirm whether the resin of the surface layer is a radiation-disintegrable type.

(Hollow particles)
As hollow particles to be dispersed in the binder of the conductive elastic layer, for example, resin particles that are already hollow during the dispersion can be used. Alternatively, it is possible to exemplify a method using thermally expandable microcapsules, which contain an inclusion substance inside the particles and expand the inclusion substance by applying heat to form hollow resin particles.

  In this method, a conductive resin composition in which thermally expandable microcapsules are dispersed in a binder of the conductive elastic layer is prepared, the conductive substrate is coated with this composition, and drying, curing, or crosslinking is performed. Can. In this method, the encapsulated material can be expanded by the heat of drying, curing, or crosslinking of the conductive elastic layer binder to form hollow resin particles. At that time, the particle diameter can be controlled by controlling the temperature condition.

(Manufacturing method of thermally expandable microcapsule)
As the substance to be contained in the thermally expandable microcapsule, for example, a substance capable of expanding into a gas at a temperature lower than the softening point of the thermoplastic resin constituting the bowl-shaped resin particle is preferable, and the following may be mentioned as specific examples. . Low boiling liquids such as propane, butene, normal butane, isobutane, normal pentane, and isopentane; high boiling liquids such as normal hexane, isohexane, normal heptane, normal octane, isooctane, normal decane, and isodecane.

  The above-mentioned thermally expandable microcapsules can be produced by known methods such as suspension polymerization, interfacial polymerization, interfacial sedimentation, in-liquid drying and the like. For example, in the suspension polymerization method, a polymerizable monomer, a substance to be encapsulated in the thermally expandable microcapsule, and a polymerization initiator are mixed. Then, after this mixture is dispersed in an aqueous medium containing a surfactant and a dispersion stabilizer, suspension polymerization can be performed. In addition, the compound which has a reactive group which reacts with the functional group of a polymerizable monomer, and an organic filler can also be added.

  The following can be illustrated as a polymerizable monomer. Acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, vinylidene chloride, vinyl acetate; acrylic ester (methyl acrylate, ethyl Acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, isobornyl acrylate, cyclohexyl acrylate, benzyl acrylate; methacrylic acid esters (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, Isobornyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate); styrenic monomerア ク リ ル, acrylamide, substituted acrylamide, methacrylamide, substituted methacrylamide, butadiene, ε-caprolactam, polyether, isocyanate. These polymerizable monomers can be used singly or in combination of two or more.

  The polymerization initiator is not particularly limited, but an initiator soluble in the polymerizable monomer is preferable, and known peroxide initiators and azo initiators can be used. Of these, azo initiators are preferred. Examples of azo initiators are listed below. 2,2'-azobisisobutyronitrile, 1,1'-azobiscyclohexane 1-carbonitrile, 2,2'-azobis-4-methoxy-2,4-dimethyl valeronitrile. Among these, 2,2'-azobisisobutyronitrile is preferable. Also preferred is dicumyl peroxide. The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

  As surfactants, anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, and polymer type dispersants can be used. The amount of surfactant used is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the polymerizable monomer. The following may be mentioned as dispersion stabilizers. Organic fine particles (polystyrene fine particles, polymethyl methacrylate fine particles, polyacrylic acid fine particles and polyepoxide fine particles), silica (colloidal silica), calcium carbonate, calcium phosphate, aluminum hydroxide, barium carbonate, magnesium hydroxide and the like. The use amount of the dispersion stabilizer is preferably 0.01 to 20 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

  Suspension polymerization is preferably carried out in a sealed manner using a pressure resistant vessel. The polymerizable raw material may be suspended by a disperser or the like and then transferred to a pressure resistant container for suspension polymerization, or may be suspended in the pressure resistant container instead of being suspended by a disperser or the like. The polymerization temperature is preferably 50 ° C to 120 ° C. The polymerization may be carried out at atmospheric pressure, but may be carried out under pressure (at a pressure of 0.1 to 1 MPa added to the atmospheric pressure) so as not to vaporize the substance to be encapsulated in the thermally expanded microcapsules. preferable. After completion of the polymerization, solid-liquid separation and washing may be performed by centrifugation or filtration. In the case of solid-liquid separation or washing, thereafter, drying or pulverization may be performed at a temperature equal to or lower than the softening temperature of the resin constituting the thermally expanded microcapsule. Drying and pulverization can be carried out by a known method, and a flash dryer, a forward wind dryer, a Nauta mixer and the like can be used. Drying and grinding can also be carried out simultaneously by means of a grinding dryer. Surfactants and dispersion stabilizers can be removed by repeated washing and filtration after production.

<Electrophotographic apparatus>
An electrophotographic image forming apparatus according to an aspect of the present invention has a charging member for electrophotography. The charging member according to an aspect of the present invention can be used in an electrophotographic image forming apparatus.

  A schematic configuration of an example of the electrophotographic image forming apparatus is shown in FIG. This electrophotographic apparatus is composed of the following components and the like. Electrophotographic photosensitive member, charging device for charging electrophotographic photosensitive member, latent image forming device for performing exposure, developing device for developing latent image on toner image, transfer device for transferring toner image to transfer material, on electrophotographic photosensitive member A cleaning device that recovers the transfer residual toner, and a fixing device that fixes the toner image. The roller-shaped charging member according to the present invention can be used as a charging roller included in the charging device of the electrophotographic image forming apparatus.

  The electrophotographic photosensitive member (7b) is a rotary drum type having a photosensitive layer on a conductive substrate. The electrophotographic photosensitive member is rotationally driven at a predetermined circumferential speed (process speed) in the direction of the arrow.

  The charging device includes a contact charging member (hereinafter also referred to as "charging roller") (5a) having a roller shape which is disposed in contact by being brought into contact with the electrophotographic photosensitive member (7b) with a predetermined pressing force. Do. That is, the charging roller (5a) is arranged to be chargeable on the electrophotographic photosensitive member (7b), and is driven to rotate as the photosensitive member rotates. Then, the electrophotographic photosensitive member (7b) is charged by applying a DC voltage from a power source (7a). For a latent image forming device (not shown) for forming an electrostatic latent image on the electrophotographic photosensitive member (7b), an exposure device such as a laser beam scanner is used. An electrostatic latent image is formed by irradiating the uniformly charged electrophotographic photosensitive member (7b) with exposure light (7g) corresponding to the image information.

  The developing device has a developing sleeve or developing roller (7c) disposed in proximity to or in contact with the electrophotographic photosensitive member (7b). The developing device develops the electrostatic latent image of the toner electrostatically processed to the same polarity as the charging polarity of the electrophotographic photosensitive member by reversal development to form a toner image. The transfer device has a contact type transfer roller (7d). Thereby, the toner image is transferred from the electrophotographic photosensitive member to a transfer material such as plain paper. The transfer material is conveyed by a sheet feeding system (not shown) having a conveying member.

  The cleaning device has a blade type cleaning member (7f) and a recovery container (7h), and the transfer residual toner remaining on the electrophotographic photosensitive member (7b) after the developed toner image is transferred to the transfer material Mechanically scrape off and collect. Here, it is possible to dispense with the cleaning device by adopting a simultaneous development cleaning method in which the transfer residual toner is collected by the developing device. The toner image transferred to the transfer material passes between the fixing belt (7e) heated by a heating device (not shown) and a roller (7i) disposed opposite to the fixing belt, thereby transferring the transfer material. It is fixed in

<Process cartridge>
The process cartridge according to the present invention has a charging member for electrophotography, and is configured to be detachable from the main body of the electrophotographic image forming apparatus.

  A schematic configuration of an example of the process cartridge according to the present invention is shown in FIG. In this process cartridge, an electrophotographic photosensitive member (7b), a charging roller (5a), a developing roller (7c), a cleaning member (7f), a collection container (7h) and the like are integrated to form a main body of an electrophotographic image forming apparatus. It is configured to be removable. The charging member according to the present invention can be used as a charging roller included in this process cartridge.

Production Example 1: Production of Resin Particle A1
An aqueous mixed solution comprising 4000 parts by mass of ion-exchanged water, 9 parts by mass of colloidal silica as a dispersion stabilizer, and 0.15 parts by mass of polyvinylpyrrolidone was prepared. Next, an oily mixture comprising the following components was prepared. 50 parts by mass of acrylonitrile as a polymerizable monomer, 45 parts by mass of methacrylonitrile, 5 parts by mass of methyl acrylate, 12.5 parts by mass of normal hexane as an inclusion substance, and dicumyl peroxide 0.75 as a polymerization initiator Parts by mass. This oily mixture was added to the aqueous mixture, and 0.4 parts by mass of sodium hydroxide was further added to prepare a dispersion.

  The obtained dispersion is stirred and mixed for 3 minutes using a homogenizer, charged in a nitrogen-replaced polymerization reaction vessel, and polymerized at a temperature of 60 ° C. for 20 hours while stirring at 400 rpm to obtain a crude product as a crude product. Resin particles having a substance were prepared. The obtained crude product was repeatedly filtered and washed with water, and then dried at 80 ° C. for 5 hours to purify resin particles. The resin particles were crushed and classified using a sound wave type classifier to obtain a resin particle A1. Table 1 shows the formulations of the resin particles A1 to A8, the stirring conditions at the time of polymerization, and the volume average particle diameter.

<Production Example 2: Production of Resin Particle A2>
Resin particles A2 were obtained in the same manner as in Production Example 1 except that the classification conditions were changed.

<Production Examples 3 to 8: Production of Resin Particles A3 to A8>
A resin was prepared in the same manner as in Production Example 1 except that one or more of the amount of colloidal silica used, the type and amount of the polymerizable monomer, and the number of rotations of stirring at the time of polymerization were changed as shown in Table 1. The particles were produced and classified to obtain resin particles A3 to A8.

<Measurement of Volume Average Particle Size of Resin Particles>
The volume average particle diameter of the resin particles A1 to A8 was measured with a laser diffraction type particle size distribution analyzer (trade name: Coulter LS-230 particle size distribution analyzer, manufactured by Coulter, Inc.). For the measurement, an aqueous module was used, and pure water was used as a measurement solvent. The inside of the measurement system of the particle size distribution analyzer was washed with pure water for about 5 minutes, and 10 to 25 mg of sodium sulfite was added to the measurement system as a defoaming agent to execute a background function. Next, 3 to 4 drops of surfactant were added to 50 ml of pure water, and 1 mg to 25 mg of a measurement sample (resin particles) was further added. The aqueous solution in which the sample was suspended was subjected to a dispersion treatment with an ultrasonic disperser for 1 to 3 minutes to prepare a test sample solution. The test sample solution is gradually added into the measurement system of the measurement device to adjust the test sample concentration in the measurement system so that the polarization scattering intensity difference (PIDS) on the screen of the device is 45% or more and 55% or less. The measurements were taken. The volume average particle diameter Dv was calculated from the obtained volume distribution.

Production Example 9 Production of Surface Layer Coating Solution B1
12.9 parts by mass of polymeric MDI (trade name: Millionate MR-200, manufactured by Tosoh Corp.) was added to 100 parts by mass of a polyol (trade name: EPOL, manufactured by Idemitsu Kosan Co., Ltd.), and mixed with stirring. The methyl isobutyl ketone was added to this mixture so that solid content might be 5 mass%, and surface layer coating liquid B1 was obtained. Hereinafter, the resin, the solvent, and the liquid concentration which were used for manufacture of surface layer coating liquid B1-B12 were put together in Table 2.

Preparation Example 10 Preparation of Surface Layer Coating Solution B2
A surface layer coating solution B2 was obtained in the same manner as in Production Example 9 except that the solid content was adjusted to 10% by mass.

Production Example 11 Production of Surface Layer Coating Solution B3
A surface layer coating solution B3 was obtained in the same manner as in Production Example 9 except that the solid content was adjusted to 15% by mass.

Production Example 12 Production of Surface Layer Coating Solution B4
12.3 parts by mass of polymeric MDI (trade name: Millionate MR-200, manufactured by Tosoh Corporation) was added to 100 parts by mass of a hydroxyl group-terminated liquid polybutadiene (trade name: Poly bd, manufactured by Idemitsu Kosan Co., Ltd.), and mixed with stirring. The methyl isobutyl ketone was added to this mixture so that solid content might be 15 mass%, and surface layer coating liquid B4 was obtained.

Production Example 13 Production of Surface Layer Coating Solution B5
5 parts by mass of 1-hydroxy-cyclohexyl phenyl ketone (trade name: IRGACURE 184, manufactured by Toyotsu Chemi-Plass Co., Ltd.) as a polymerization initiator relative to 100 parts by mass of ultraviolet curable polyisoprene (trade name: UC-203M, manufactured by Kuraray) In addition, it was stirred and mixed. To this mixture was added methyl ethyl ketone so that the solid content was 15% by mass, to obtain a surface layer coating solution B5.

Production Example 14 Production of Surface Layer Coating Solution B6
Polymethyl methacrylate (trade name: Poly (methyl methacrylate) analytical standard, for GPC, 2,480,000, manufactured by Aldrich) was prepared. To this was added methyl ethyl ketone so that the solid content was 15% by mass, to obtain a surface layer coating solution B6.

Production Example 15 Production of Surface Layer Coating Solution B7
Toluene was added to the following polyisobutylene so that solid content might be 15 mass%, and surface layer coating liquid B7 was obtained.
Brand name: Polyisobutylene average Mw ̃4,200,000, average Mn ̃3,100,000 by GPC / MALLS, average Mv ̃4,700,000, manufactured by Aldrich.

Preparation Example 16 Preparation of Surface Layer Coating Solution B8
Toluene was added to polypropylene (trade name: Elmodu S901, manufactured by Idemitsu Kosan Co., Ltd.) so that the solid content was 8% by mass, to obtain a surface layer coating solution B8.

Production Example 17 Production of Surface Layer Coating Solution B9
A surface layer coating solution B9 was obtained in the same manner as in Production Example 16 except that the solid content was adjusted to 15% by mass.

Production Example 18 Production of Surface Layer Coating Solution B10
A surface layer coating solution B10 was obtained in the same manner as in Production Example 9 except that the solid content was adjusted to 1% by mass.

Production Example 19 Production of Surface Layer Coating Solution B11
A polyoxymethylene homopolymer (trade name: Polyoxymethylene-Homopolymer, manufactured by Aldrich), HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) with a solid content of 15% by mass Added to be. Thus, a surface layer coating solution was obtained.

Production Example 20 Production of Surface Layer Coating Solution B12
2-chlorophenol was added to polybutylene terephthalate (trade name: Polybutylene Terephthalate, manufactured by Aldrich) so that the solid content was 15% by mass, to obtain a surface layer coating solution B12.

Production Example 21 Production of Conductive Rubber Composition C1
A closed mixer adjusted to 50 ° C. by adding a material other than NBR shown in the column of component (1) of Table 3 to 100 parts by mass of acrylonitrile butadiene rubber (NBR) (trade name: N230SV, manufactured by JSR) And kneading for 15 minutes. To this, the materials shown in the column of component (2) in Table 3 were added. Next, the mixture was kneaded for 10 minutes with a two-roll mill cooled to a temperature of 25 ° C. to obtain a conductive rubber composition C1. Hereinafter, resin particles used for each of the conductive rubber compositions C1 to C9 are summarized in Table 4.

<Production Examples 22 to 28: Production of Conductive Rubber Compositions C2 to C8>
Conductive rubber compositions C2 to C8 were obtained in the same manner as in Production Example 21 except that the resin particles were changed to A2 to A8, respectively.

Production Example 29 Production of Conductive Rubber Composition C9
A conductive rubber composition C9 is prepared in the same manner as in Production Example 21 except that solid high molecular weight polyethylene particles (trade name: Miperon XM-221U, made by Mitsui Chemicals, average particle size 25 μm) are used instead of the resin particles A1. Obtained.

Example 1
(Conductive substrate)
A conductive vulcanized adhesive (trade name: Metalloc U-20, manufactured by Toyo Chemical Laboratory) was applied to a stainless steel substrate having a diameter of 6 mm and a length of 252.5 mm and dried at a temperature of 80 ° C. for 30 minutes Was used as a conductive substrate.

(Conductive elastic layer)
Using an extrusion molding apparatus equipped with a crosshead, the circumferential surface was cylindrically coated with the conductive rubber composition C1 with the conductive substrate as the central axis. The thickness of the conductive rubber composition was adjusted to 1.75 mm.

  The extruded roller was vulcanized at 160 ° C. for 1 hour in a hot air furnace, and then the end of the rubber layer was removed to a length of 224.2 mm.

・ Primary surface treatment (cylindrical grinding)
The outer peripheral surface of the obtained roller was polished using a plunge-cut cylindrical polisher. A vitrified grindstone was used as a grinding stone, and the abrasive grains were green silicon carbide (GC) and the particle size was 100 mesh. The rotation speed of the roller at the time of this polishing was 350 rpm, and the rotation speed of the grinding wheel was 2050 rpm. Polishing was performed by setting the cutting speed to 20 mm / min and setting the spark out time (the time at a cutting of 0 mm) to 0 seconds, to fabricate a conductive roller having a conductive elastic layer. The thickness of the conductive elastic layer was adjusted to 1.5 mm. The crown amount of this roller (the average value of the difference between the outer diameter of the central portion and the outer diameter at a position 90 mm away from the central portion toward the both ends) was 120 μm.

Heat Treatment The cylindrically-polished roller was heat-treated at 180 ° C. for 1 hour in an air atmosphere using a hot air furnace to further cure the resin particles.

・ Secondary surface treatment (surface finish grinding) (tape grinding)
Using the surface finish grinding apparatus shown in FIG. 9, the obtained roller (9b) was subjected to surface finish grinding with a wrapping film (9a) while rotating at 1000 rpm to obtain a conductive elastic roller. The lapping film used was “lapping film WA abrasive grain # 2000 (trade name, manufactured by Sankyo Riken Co., Ltd.)” having an abrasive grain size of 9 μm. At this time, the polishing eyes of the cylindrical polishing machine and the surface finish grinding were in the same direction. Hereinafter, the same direction of polishing in the cylindrical polishing machine and the direction of surface finish grinding will be referred to as "forward polishing" and different ones will be referred to as "reverse polishing". The obtained conductive elastic roller has, on its surface, a convex portion derived from the edge of the opening of the bowl-shaped resin particle, and a void defined by the opening of the bowl-shaped resin particle and the inner wall of the resin particle It had a conductive elastic layer.

(Surface layer)
Surface layer coating liquid B1 was dip coated once on the obtained conductive elastic roller. In addition, as conditions for dipping application, the immersion time was 5 seconds, and the pulling speed from the surface layer coating liquid was 20 mm / s for the initial speed and 2 mm / s for the final speed. The velocity change from the initial velocity to the final velocity was linear with time.

  The conductive elastic roller pulled up from the surface layer coating solution was air dried at normal temperature for 30 minutes, and then dried with a hot air circulating dryer at a temperature of 80 ° C. for 1 hour and further at a temperature of 160 ° C. for 1 hour to obtain a charging roller. The following evaluation was performed about the charging roller obtained in this way.

<Shape and physical property evaluation>
(Bowl shape)
2 and 3 will be used in the following description of the bowl shape.

  First, it is confirmed that the plurality of convex portions (2d) and the plurality of concave portions (2c) exist on the surface of the charging roller.

  Measure according to the following method. The longitudinal position of the measurement point of the charging roller is the center, the position 20 mm away from the center, the position 40 mm apart, the position 60 mm apart, the position 80 mm apart, and the position 100 mm apart , A total of 11 places. A total of 66 points of six points (phase 0 °, 60 °, 120 °, 180 °, 240 °, and 300 °) in the circumferential direction of the charging roller are taken as measurement points for each of the 11 points in the longitudinal direction. Each of these measurement points is observed with a confocal microscope (trade name: Optics Hybrid, manufactured by Lasertec Corporation).

(Convex vertex height)
A height image of the surface of the charging roller was measured with a confocal microscope at the measurement point. The observation conditions were an objective lens 50 times, a pixel count of 1024 pixels, and a height resolution of 0.1 μm, and an image acquired from the surface shape was plane-corrected with a quadric surface. The normal direction was taken as the height direction with respect to the plane corrected image. The height profile is extracted from the plane-corrected image and averaged to obtain the height average surface (3a) of the charging roller surface at the measurement location. In the area where the height profile is higher and lower than the height average surface, these high and low parts are made convex (2d) and concave (2c) respectively (the height of these high and low parts) The values of are discontinuous at the boundaries between them). At each of the 66 measurement points in total, it was confirmed that one or more convex portions and concave portions were present. Select an arbitrary bowl-shaped resin particle (201) from the image of each measurement location, extract the cross-sectional profile around the convex part (2d) derived from the edge (2h) of the bowl-shaped resin particle, and select high The point furthest from the mean surface (3a) of the surface is taken as the convex vertex (2e). Further, the distance from the convex apex (2e) to the height average surface (3a) is taken as the convex apex height Ho (3b). The value (average value) of the convex vertex height Ho was 5.1 μm. However, this value is a value obtained by determining the convex vertex height Ho one by one for each of the 66 measurement points, and averaging the obtained 66 total Ho.

(Presence of a void)
Focused ion beam processing and observation apparatus (trade name: FB-2000C, Hitachi, Ltd.) A cross section perpendicular to the rotation axis of the charging roller passing through the convex apex (2e) of the bowl-shaped resin particle selected in the measurement of the convex apex height It cut out using the company make). At this time, it cut out to the depth which the rotation center (2g) of a conductive substrate exposed. Subsequently, the cross-sectional image was image | photographed by 1000 times using the scanning electron microscope (SEM) (brand name: S-4800, Hitachi High-Technologies company make). A total of 66 cross-sectional images were obtained, one for each of the 66 convex apexes.

  In each of a total of 66 cross-sectional images, whether or not the bowl-shaped particle having the convex apex has one opening 2b, an edge (2h) of the opening, and a gap (2a) connected to the opening I observed it.

(Specification of line segment (2f) and intersection point (3c))
In the cross-sectional image, a surface layer (1a) in which a line segment (2f) connecting the convex apex (2e) and the rotation center (2g) of the base of the charging roller (1c) is applied to the bowl-shaped resin particle. Of the points intersecting with the surface of, the point closest to the rotation center (2g) is taken as the intersection point (3c).

(A rule that the line segment (2f) passes through the space (2i) of the recess (2c))
In each of the total 66 cross-sectional images, it was observed whether the line segment (2f) passed through the space (2i). When the line segment (2f) does not intersect the surface of the surface layer (1a) applied to the bowl-shaped resin particle, the intersection point (3c) does not exist and the line segment (2f) does not pass through the space .

  In Tables 5 and 6, the ratio of the cross-sectional image in which the air gap (2a) exists and the line segment (2f) is confirmed to pass through the space (2i) to the total number of cross-sectional images (66) Is shown in%. In the table, the ratio is shown in the column of "presence of void and percentage of space passage of line segment 2f". In addition, when the space | gap (2a) existed, one opening (2b) and edge (2h) existed corresponding to the space | gap.

(Ratio of convex apex-concave surface distance PL and convex height Ho)
In the cross-sectional image, the distance PL (3d) between the convex apex (2e) and the intersection (3c) was determined. However, if the line segment (2f) does not intersect the surface of the surface layer (1a) applied to the bowl-shaped resin particle, PL does not exist because these intersection points (3c) do not exist. The average value of the distances PL that could be determined was 26.5 μm.

  Since the average value of Ho was 5.1 μm, PL / Ho is 5.2. Here, "PL / Ho" is a ratio of the average value of PL to the average value of Ho.

(Film thickness of surface layer)
The cross section of the surface layer was cut out using a sharp razor and observed at 1000 times using a digital microscope (manufactured by Keyence, trade name: VHX-5000). In each of three places which divided the longitudinal direction of the surface layer into three equally, a total of nine places of three places which divided the circumferential direction into three equally were made into a measurement place. Taking 360 μm × 240 μm as one field of view, the maximum value and the minimum value of the film thickness in one field of view were measured. Five fields of view were measured for each of the cross sections of one measurement point, and a total of 45 measurements were obtained. Among the 45 measured values, it was confirmed that the maximum value T _max was 1.2 μm, the minimum value T _min was 1.0 μm, and the film thickness was 1 μm to 5 μm. The average of 45 measurements was 1.1 μm.

(Volume resistivity of surface layer)
The volume resistivity of the surface layer was measured by the conductivity mode using an atomic force microscope (AFM) (trade name: Q-scope 250, manufactured by Quesant). First, the surface layer of the charging roller was cut into a sheet 2 mm wide and 2 mm long using a manipulator, and platinum deposition was applied to one side of this sheet. Next, connect a DC power supply (trade name: 6614C, Agilent) to the platinum-deposited surface and apply a voltage of 10 V, contact the free end of the cantilever with the other surface of this sheet, and pass through the AFM body A current image was obtained.

This measurement was performed on 100 randomly chosen surfaces throughout the surface layer. The average of the lower 10 current values of the obtained current value, and the average value of the film thickness of the surface layer measured as described above (average value of the maximum value T _max and the minimum value T _min ) The “volume resistivity” was calculated from The volume resistivity was 1.60 × 10 ¹⁶ Ω · cm. Although showing a volume resistivity in the column of "surface layer resistance" in Table 5 and 6, in these tables, for example, "1.60 × ^{10 16"} displays "1.60E + 16".

The conditions of measurement using AFM are shown below.
・ Measurement mode: contact
・ Cantilever: CSC17
・ Measurement range: 10 nm × 10 nm
・ Scan rate: 4 Hz
-Applied voltage: 10V.
The measurement environment was a temperature of 23 ° C. and a relative humidity of 50%.

(Charge up amount)
This evaluation is to confirm whether the manufactured charging roller has the charge-up performance as described above.

The surface potential of the charging roller due to corona discharge was measured using a charge amount measuring device (trade name: DRA-2000L, manufactured by QEA). Specifically, the corona discharger of the charge amount measuring device is disposed so that the gap between the grid portion and the surface of the charge roller is 1 mm. Then, a voltage of 8 kV is applied to the corona discharger to generate a discharge to charge the surface of the charging roller, and the surface potential of the conductive member after 10 seconds has elapsed after the discharge is measured. Details of the corona discharge treatment will be described later.
The measurement environment was a temperature of 23 ° C. and a relative humidity of 50%.

  Furthermore, in order to confirm the charge-up characteristic of the surface layer after long-term use, the above-mentioned measurement was performed also after endurance evaluation mentioned below.

(Confirmation of radiation disintegrating resin)
This evaluation is to determine whether or not the surface layer and the bowl-shaped resin particles are formed of a radiation-disintegrable resin. The confirmation of being a radiation-disintegrable resin is as follows. First, surface layer and bowl-shaped resin particles are sampled from a charge roller immediately after production which is not exposed to corona discharge, and the molecular weight of each is measured by gel permeation chromatography (GPC). Then, after corona discharge treatment is applied to the charging roller by a method described later, the surface layer of the charging roller and the bowl-shaped resin particles are sampled again, and the molecular weight is measured by GPC. Then, from the difference in molecular weight before and after corona discharge irradiation, it is determined whether or not the surface layer and the bowl-shaped resin particles are radiation-disintegrable. The details will be described below.

  First, 5 mg of each sample was collected from the surface layer of the charging roller and the bowl-shaped resin particles which were not exposed to corona discharge immediately after production. Select this solvent from among toluene, chlorobenzene, tetrahydrofuran (THF), trifluoroacetic acid, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and a soluble solvent. A sample solution having a concentration of 1% by mass was prepared. In addition, chlorobenzene was used as a solvent about the sample extract | collected from the surface layer of the charging roller.

  The weight average molecular weight Mw was measured using the prepared sample solution under the following conditions. The column was stabilized in a heat chamber at a temperature of 40 ° C., and the solvent used for dissolving the sample was flowed at a flow rate of 1 mL per minute as an eluent to the column at this temperature. 100 μL of this sample solution was injected into the column. In measuring the molecular weight of the sample, the molecular weight distribution of the sample was calculated from the relationship between the logarithmic value of the calibration curve and the retention time. The calibration curve was prepared using several types of monodispersed polystyrene standard samples (trade name: TSKgel standard polystyrene "0005202" to "0005211", manufactured by Tosoh Corporation). In addition, GPC gel permeation chromatograph (trade name: HLC-8120, manufactured by Tosoh Corp.) is used as a GPC device, and a differential refractive index detector (trade name: RI-8020, manufactured by Tosoh Corp.) is used as a detector. It was. For the column, three commercially available polystyrene gel columns (trade name: TSK-GEL SUPER HM-M, manufactured by Tosoh Corporation) were used in combination.

  Subsequently, the charge roller was subjected to corona discharge treatment as described below. Thereafter, the surface layer and the bowl-shaped resin particles were peeled off from the charging roller to measure the mass, and then the same solvent as that before the corona discharge was used to make a solution. Next, GPC measurement was performed in the same manner as before the corona discharge treatment to measure the mass average molecular weight Mw.

  When Mw before corona discharge treatment and after corona discharge treatment increased, it was a radiation crosslinking type, and when it decreased, it was considered as a radiation decay type. In the table of the evaluation results, in the case of the radiation disintegrable type, "〇" and in the case of the radiation cross-linked type, as "x".

(Corona discharge treatment)
The corona discharge treatment was performed using a corona discharge surface treatment apparatus manufactured by Kasuga Denki Co., Ltd. The working environment was a H / H environment (temperature 30 ° C., relative humidity 80% environment).

  The detailed method of corona discharge is demonstrated using FIG. Both end portions (5b) of the charging roller (5a) were fixed by supporting portions (5c). Next, the longitudinal direction of the aluminum corona electrode (5d) is parallel to the longitudinal direction of the charging roller (5a), and the surface of the corona electrode (5d) faces the surface of the charging roller (5a). It was adjusted. The distance between the surface of the corona electrode (5d) and the surface of the charging roller (5a) was 1 mm. The charging roller (5a) was rotated by rotating the support portion (5c) at a speed of 30 rotations per minute, and a state where 8 KV was applied from the power source (5e) to the electrode (5d) side was continued for 2 hours.

<Image evaluation>
(Discharge light observation)
It was confirmed as follows that the strong discharge from the convex portion of the charging roller surface was suppressed by the charge-up of the surface layer of the charging roller and the surface shape derived from the bowl-shaped resin particle. Specifically, first, in a state in which the charging roller (5a) was in contact with a glass plate imitating a photosensitive member, a discharge light moving image was obtained from a direction (back surface of glass) not in contact. Subsequently, the moving image which image | photographed the surface of the same location as the location which observed discharge light was acquired, and the behavior of the strong discharge from a convex part was observed by overlapping with the said discharge light animation. The specific procedure is shown below.

  First, an observation glass imitating an electrophotographic photosensitive member was prepared as follows. An indium tin oxide (ITO) film having a thickness of 5 μm was formed on one surface of a glass plate (300 mm long, 240 mm wide, 4.5 mm thick). Furthermore, 100 parts by mass of polycarbonate (trade name: Iupilon Z400, manufactured by Mitsubishi Gas Chemical Company, Ltd.) was dissolved in a mixed solvent of 650 parts by mass of chlorobenzene / 150 parts by mass of dimethoxymethane to prepare a coating liquid for charge transport layer. This charge transport layer coating solution is dip coated on the glass plate on which the ITO film is formed to form a coating film, and the coating film is dried at 110 ° C. for 30 minutes to form a charge transport layer having a thickness of 17 μm. A glass plate was prepared.

  Then, as shown in FIG. 6, the charging roller (5a) is 4.9 N at one end and 9.8 N in total at both ends from the surface side of the glass plate (6 a) after the film formation on which the ITO film is formed. A tool was created that can be pressed by the pressure of the spring. Further, the glass plate (6a) was made movable at the same speed as the image forming apparatus (Laserjet CP4525dn, manufactured by HP).

  Considering the glass plate (6a) as an electrophotographic photosensitive member, a high-speed camera is placed in the dark room from the lower side of the contact portion (the side opposite to the surface of the glass plate (6a)) via a high-speed gate. The discharge light of the charging roller (5a) was confirmed within a 1 mm square field of view. At this time, a 10 × objective lens was used. The high speed gate used is “I.I. unit C9527-2 (trade name, manufactured by Hamamatsu Photonics Co., Ltd.)”, and the high speed camera used is “FASTCAM-SA1.1 (product name: Hamamatsu Photonics Co., Ltd.). A voltage was applied to the charging roller under the same conditions as in the image forming apparatus (trade name: Laserjet CP4525dn, manufactured by HP).

  The shooting conditions were such that the voltage of -1200 V was applied while moving the glass plate in contact with the charging roller (5a) at 200 mm / sec, the gain of the high speed camera was 750, and the shooting speed was 3000 fps. Under this condition, imaging was performed for about 0.3 seconds, and a discharge light observation moving image was output. At the time of photographing, the sensitivity was appropriately adjusted to adjust the brightness of the photographed image.

  Next, in order to identify a location where a strong discharge occurs, a surface observation moving image to be superimposed on the discharge light observation moving image was photographed as follows. First, the observation glass was moved in a state of being in contact with the charging roller (5a) up to the shooting start position of the discharge light observation moving image. Next, the surface observation moving image was photographed while moving the observation glass at the same scanning speed and scanning distance as the discharge light observation moving image. The shooting conditions are high speed gate I. I. The moving image is the same as the moving image of the discharge light except that the unit gain is set to 500 and illumination is applied from the outside of the jig to reinforce the brightness. Thus, a surface shape observation moving image at the same position as the discharge light observation moving image was obtained.

  The surface shape observation moving image thus obtained and the discharge light observation moving image are compared in detail, and on the surface of the charging roller, the number of convex portions (2d) in which a stronger discharge occurs than in the other portions than the convex portions (2d) I counted.

(Evaluation of whiteout image)
It was confirmed in the following manner that no white spot image was generated even at low density printing.

  An electrophotographic laser printer (trade name: Laserjet CP4525dn, manufactured by HP) was prepared as an electrophotographic apparatus. The manufactured charging roller was attached to a toner cartridge dedicated to the laser printer, and evaluation was performed under an environment of a temperature of 23 ° C. and a relative humidity of 50%.

  As an evaluation image, an image of 1 dot and 1 space at 600 dpi (image in which dots having a width of 1 dot and an interval of 1 dot are drawn in the direction orthogonal to the rotation direction of the photosensitive drum) was output. A digital microscope (manufactured by Keyence, trade name: VHX) is a place where the image density of the output image is 0.20 measured using a color reflection densitometer (trade name: X-Rite 500 series: manufactured by X-Rite). It observed at -5000). When observing a 2 mm square area, in the observation image to be obtained, "notch" a portion where a circular dot is partially missing, or a position where dots can not be formed where a dot should be. It was considered as "disappeared" and the number was counted. Theoretically 576 dots are drawn within 2 mm square.

  The above evaluation was performed in five areas when the charging roller was divided into five in the longitudinal direction, and the arithmetic mean value of the number of chips and disappearance was regarded as the evaluation value of the white spot image.

(Durable)
Next, an endurance test was conducted to measure the amount of change in the charge-up amount of the surface layer of the charging roller. In this test, it is confirmed that the resistance to radiation does not progress due to deterioration due to exposure to electric discharge and due to adhesion of the radiation disintegrating resin. The durability test uses a process cartridge and an electrophotographic apparatus similar to those used for the evaluation of the above-described whiteout image, and the H / H environment (temperature 30 ° C., relative humidity 80) that is more severe to the deterioration of the surface layer % Environment). In the endurance test, after outputting two images, the intermittent image forming operation of stopping the rotation of the photosensitive drum completely for about 3 seconds and resuming the output of two images is repeated to obtain 40,000 electrophotographic images. Output. The output image at this time is an image in which the letter “E” of the alphabet of 4 points in size is printed such that the coverage is 4% with respect to the area of A4 size paper.

  The same measurement as the measurement of the charge-up amount before the endurance was performed on the charge roller after the endurance, the charge-up amount after the endurance was determined, and the difference from the charge-up amount before the endurance was measured.

Examples 2 to 26
The manufacturing conditions of the charging roller were changed as shown in Table 5. The modifications described below were also made for Examples 4-5, 16-17 and 20-21, and Examples 15 and 19. The charging roller was produced and evaluated in the same manner as in Example 1 except for the above. Under the present circumstances, it confirmed that the location which convex part (2d) and recessed part (2c) adjoined in all the Examples has one or more in each point of a measurement location of a total of 66 places.

Examples 4-5, 16-17 and 20-21:
The drying method after application of the surface layer coating solution was changed to a method of air-drying at normal temperature for 30 minutes and then performing the method at a temperature of 160 ° C. for 1 hour with a hot air circulating dryer.

Examples 15 and 19:
After the application of the surface layer coating solution, it was changed to normal temperature air drying and hot air circulation drying, and ultraviolet irradiation was performed. As the conditions for ultraviolet irradiation, ultraviolet light with a wavelength of 254 nm was irradiated so that the integrated light amount became 9000 mJ / cm ² . A low pressure mercury lamp (manufactured by Toshiba Lightech Co., Ltd.) was used as the ultraviolet irradiation device.

Comparative Example 1
The manufacturing conditions of the charging roller were changed as shown in Table 6. In this example, heat treatment and surface finish grinding after cylindrical grinding were not performed. A charging roller was produced and evaluated in the same manner as in Example 1 except for the above. On the surface of this charging roller, there were convex portions derived from solid polyethylene particles, and there were no voids under the convex apexes, strong discharge from the convex shape was generated, and white spots were frequent.

Comparative Example 2
A charging roller was produced and evaluated in the same manner as in Example 1 except that the surface layer coating solution was not applied and the subsequent drying step was not performed. Since there was no chargeable layer on the surface layer of this charging roller, a strong discharge occurred and many white spots occurred.

Comparative Example 3
The manufacturing conditions of the charging roller were changed as shown in Table 6. In addition, the heat treatment method after cylindrical polishing was changed to a method of performing at 180 ° C for 30 minutes. A charging roller was produced and evaluated in the same manner as in Example 1 except for the above. In most of the 66 cross-sectional images, as shown in FIG. 10, the convex portion (2d) is curved, and the line segment (2f) does not pass through the space (2i). . A strong discharge occurred and there were many white spots. In the present example, the ratio PL / Ho was not determined.

Comparative Example 4
The manufacturing conditions of the charging roller were changed as shown in Table 6. In addition, the method for drying the surface layer after application of the surface layer coating solution was changed to a method in which air drying was performed for 30 minutes at normal temperature, and then the method was performed for 1 hour at a temperature of 120 ° C. with a hot air circulation dryer. A charging roller was produced and evaluated in the same manner as in Example 1 except for the above. The volume resistivity of the surface layer of the charging roller was low at 1.12 × 10 ¹⁵ Ω · cm, the surface layer was not charged up, strong discharge was generated from the convex portion, and white spots were many.

Comparative Example 5
The manufacturing conditions of the charging roller were changed as shown in Table 6. In addition, the immersion time was 1 second in the dipping application of the surface layer coating solution. A charging roller was produced and evaluated in the same manner as in Example 1 except for the above. The film thickness of the surface layer of this charging roller was 0.1 μm, and the surface layer was not charged up, and a strong discharge was generated from the projections, resulting in many white spots.

Comparative Example 6
The manufacturing conditions of the charging roller were changed as shown in Table 6. In addition, the immersion time was 24 seconds in the dipping application of the surface layer coating solution. A charging roller was produced and evaluated in the same manner as in Example 1 except for the above. The film thickness of the surface layer of the charging roller was as large as 6.1 μm, and the surface layer became overcharged. As a result, no discharge light was observed, causing charging failure of the photosensitive member, no image for evaluation was obtained in the image evaluation, and a solid black image was generated, which could not be evaluated.

Comparative Example 7
The manufacturing conditions of the charging roller were changed as shown in Table 6. In addition, the method for drying the surface layer after application of the surface layer coating solution was changed to a method in which air drying was performed for 30 minutes at normal temperature, and then the method was performed for 1 hour at a temperature of 180 ° C. with a hot air circulating dryer. A charging roller was produced and evaluated in the same manner as in Example 1 except for the above. The volume resistivity of this charging roller was 1.31 × 10 ¹⁸ Ω · cm, and the surface layer was charged up excessively because the volume resistivity was too high. As a result, no discharge light was observed, causing charging failure of the photosensitive member, no image for evaluation was obtained in the image evaluation, and a solid black image was generated, which could not be evaluated.

1a: surface layer 1b: elastic layer 1c: base 201: bowl-shaped resin particle 2a: void 2b: opening 2c of bowl-shaped resin particle: recess 2d: projection 2e: apex of projection 2f: apex of projection and Straight line 2g connecting the rotation centers of the substrate: rotation center of the substrate 2h: edge 2i of resin particles of bowl shape: space of concave portions 3a: height average surface of charging roller surface 3b: convex apex height 3c: line segment (2f) The intersection point with the recess (2c)

Claims (9)

A charging member for electrophotography comprising a conductive substrate, a conductive elastic layer, and an insulating surface layer in this order,
The elastic layer contains a binder and holds a plurality of bowl-shaped resin particles on the surface of the elastic layer opposite to the side facing the substrate,
The bowl-shaped resin particle has an opening, an edge around the opening, and a void connected to the opening, and each of the bowl-shaped resin particles has the opening and the edge formed by the elastic layer. The elastic layer so as to be exposed from the side opposite to the side facing the substrate,
The surface of the surface layer opposite to the side facing the substrate constitutes the surface of the charging member,
The surface of the charging member has a plurality of recesses derived from the void and a plurality of projections derived from the edge,
In a cross section orthogonal to the longitudinal direction of the charging member and including the apex of the projection, a line connecting the apex and the rotation center of the base passes through the space of the recess,
The volume resistivity of the surface layer is 1.0 × 10 ¹⁶ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less, and
The charging member for electrophotography, wherein the film thickness of the surface layer is 1 μm or more and 5 μm or less.   The length from the point of intersection of the apex of the projection and the rotation center of the base with the surface of the recess to the apex of the projection is twice or more and 10 times or less the height of the projection The charging member for electrophotography according to claim 1.   The charging member for electrophotography according to claim 1 or 2 whose height of said convex part is 3 micrometers or more and 10 micrometers or less.   The charging member for electrophotography according to any one of claims 1 to 3, wherein the surface layer contains a resin having a polyolefin skeleton.   The charging member for electrophotography according to any one of claims 1 to 4, wherein the polyolefin skeleton is a polyisoprene skeleton.   The charging member for electrophotography according to any one of claims 1 to 4, wherein the surface layer contains a radiation-disintegrable resin.   The charging member for electrophotography according to any one of claims 1 to 6, wherein the bowl-shaped resin particles contain a radiation-disintegrable resin. A process cartridge detachably configured to a main body of an electrophotographic image forming apparatus,
A process cartridge comprising the charging member for electrophotography according to any one of claims 1 to 7. An electrophotographic image forming apparatus comprising: an electrophotographic photosensitive member; and a charging member disposed to charge the electrophotographic photosensitive member,
An electrophotographic image forming apparatus, wherein the charging member is the charging member for electrophotography according to any one of claims 1 to 7.