JP6946149B2 - Electrophotographic rollers, process cartridges and electrophotographic image forming equipment - Google Patents

Description

The present invention relates to an electrophotographic roller, a process cartridge and an electrophotographic image forming apparatus.

An electrophotographic image forming apparatus adopting an electrophotographic method (hereinafter, may be referred to as an "electrophotograph apparatus") is mainly an electrophotographic photosensitive member (hereinafter, may be simply referred to as a "photoreceptor") and charging. It is equipped with an apparatus, an exposure apparatus, a developing apparatus, a transfer apparatus, and a fixing apparatus. Members having a roller shape, a blade shape, and the like are preferably used for the charging device, the developing device, and the transfer device. A roller-shaped member (hereinafter referred to as an "electrophotographic roller") is particularly preferred in these devices. Taking a charging device as an example, an electrophotographic roller is placed in contact with or close to the surface of a photoconductor, and is photosensitized by applying a voltage (a voltage of only DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage). It plays a role in charging the surface of the body.

Patent Document 1 discloses a charging member having a conductive resin layer as a surface layer, which is shown below. That is, this charging member contains bowl-shaped resin particles having openings in the conductive resin layer, and the surface of the charging member has an uneven shape derived from the openings and edges of the bowl-shaped resin particles. Have. The charging member further has a crack at the bottom of the bowl-shaped resin particles, in which the conductive resin layer communicates with the surface of the charging member.

Further, according to Patent Document 1, according to the charging member, the contact pressure is relaxed by elastically deforming the edge portion of the bowl-shaped resin particles when they come into contact with the photoconductor, and the photoconductor is non-uniform. It is described that it is possible to suppress sharpening.

Japanese Unexamined Patent Publication No. 2011-237470

The present inventors have developed an electrophotographic roller capable of exhibiting better charging performance when used as a charging member in order to further increase the process speed when forming an electrophotographic image. Recognized that it is necessary.

One aspect of the present invention is to provide an electrophotographic roller capable of exhibiting stable charging performance even when used as a charging member in an electrophotographic image forming apparatus having a higher process speed. Is.

Another aspect of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus that contribute to the formation of a high-quality electrophotographic image.

According to one aspect of the present invention, an electrophotographic roller having a conductive shaft core and a conductive resin layer as a surface layer on the shaft core.
The conductive resin layer contains a binder and a plurality of solid resin particles.
A bowl-shaped resin particle having an opening is held in a state where the opening is exposed on the surface of the electrophotographic roller.
The surface of the electrophotographic roller has a concave portion derived from the opening of the bowl-shaped resin particles and a convex portion derived from the edge of the opening of the bowl-shaped resin particles.
At least two of the solid resin particles are in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles.
When the bowl-shaped resin particles are orthographically projected onto the surface of the shaft core, the projection circle formed on the surface of the shaft core is defined as the first projection circle.
The solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are formed on the surface of the shaft core when the solid resin particles are projected onto the surface of the shaft core. When the projection circles are the second projection circle and the third projection circle, respectively.
The bowl-shaped resin particles and the solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are
At least a part of the second projection circle overlaps with the first projection circle, and at least a part of the third projection circle overlaps with the first projection circle, and
A line segment passing through the center of gravity of the second projection circle and the center of gravity of the third projection circle extends parallel to the axial direction of the axis, and intersects with a straight line passing through the center of gravity of the first projection circle. Positioned to have,
Provided by an electrophotographic roller characterized by satisfying the following mathematical formulas (1) and (2), where G is the compressive elastic modulus of the conductive resin layer and J is the compressive elastic modulus of the solid resin particles. Will be done.
Formula (1)
G <J
Formula (2)
0.1 MPa ≤ G ≤ 10 MPa.

Further, according to another aspect of the present invention, there is provided a process cartridge having the above-mentioned electrophotographic roller and configured to be detachably attached to the main body of the electrophotographic image forming apparatus.

Further, according to another aspect of the present invention, an electrophotographic image forming apparatus including the electrophotographic roller is provided.

According to one aspect of the present invention, it is possible to obtain an electrophotographic roller capable of exhibiting stable charging performance even when used as a charging member in an electrophotographic image forming apparatus having a higher process speed. can.

Further, according to another aspect of the present invention, it is possible to obtain a process cartridge and an electrophotographic image forming apparatus that contribute to the formation of a high-quality electrophotographic image.

It is a partial cross-sectional view of two examples in the vicinity of the surface of the roller for electrophotographic of the present invention. It is explanatory drawing of two examples of the projection circle with respect to a bowl-shaped resin particle and a solid resin particle which concerns on this invention. It is sectional drawing which shows two examples of the roller for electrophotographic of this invention. It is explanatory drawing of the cross section of the bowl-shaped resin particle which concerns on this invention. It is a three-dimensional explanatory drawing of five examples in the shape of a bowl-shaped resin particle which concerns on this invention. It is explanatory drawing of the plunge cut type grinding machine which can be used when manufacturing the roller for electrophotographic of this invention, and FIGS. It is a figure and a side view. It is explanatory drawing of an example of the electrophotographic image forming apparatus of this invention. It is explanatory drawing of an example of the process cartridge of this invention.

According to the study by the present inventors, the charged member according to Patent Document 1 has a defect caused by the occurrence of abnormal discharge from the charged member to the electrophotographic photosensitive member when applied to an electrophotographic image forming apparatus having a high process speed. An electrophotographic image having the above may be formed.

The present inventors speculate the cause of the abnormal discharge as follows. That is, it is derived from the opening of the bowl-shaped resin particles existing on the surface of the charged member when the charged member according to Patent Document 1 comes into contact with the electrophotographic photosensitive member (hereinafter, also referred to as “photoreceptor”). The edges may be excessively elastically deformed. Hereinafter, the excessive elastic deformation of the edge portion may be referred to as "deflection". When the edge is bent, a gap for generating a stable discharge between the charged member and the photoconductor is not secured, and the discharge from the charged member on the upstream side of the nip to the photoconductor is insufficient. As a result, excessive discharge will occur on the downstream side of the nip. It is considered that abnormal discharge occurs due to the imbalance of discharge upstream and downstream of the nip.

Therefore, the present inventors have not impaired the excellent effect of the charging member according to Patent Document 1, and even at the nip with the photoconductor, the edge derived from the opening of the bowl-shaped resin particles is not easily bent for electrophotographic. Repeated studies aimed at obtaining rollers.

As a result, it was found that an electrophotographic roller having the following configuration is effective in achieving the above object.
(I) It has a conductive shaft core and a conductive resin layer as a surface layer on the shaft core;
(Ii) The conductive resin layer contains a binder and a plurality of solid resin particles, and holds the bowl-shaped resin particles having openings in a state where the openings are exposed on the surface of the electrophotographic roller. Yes;
(Iii) The surface of the electrophotographic roller has a recess derived from the opening of the bowl-shaped resin particles and a convex portion derived from the edge of the opening of the bowl-shaped resin particles;
(Iv) At least two of the solid resin particles are in contact with the outer wall surface of the shell forming the recess of the bowl-shaped resin particles;
(V) When the bowl-shaped resin particles are orthographically projected onto the surface of the shaft core, the projection circle formed on the surface of the shaft core is defined as the first projection circle.
When the solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are projected onto the surface of the shaft core, they are formed on the surface of the shaft core. When the projection circles are the second projection circle and the third projection circle, respectively.
The bowl-shaped resin particles and the solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are
At least a part of the second projection circle overlaps with the first projection circle, and at least a part of the third projection circle overlaps with the first projection circle, and
A line segment passing through the center of gravity of the second projection circle and the center of gravity of the third projection circle extends parallel to the axial direction of the axis, and intersects with a straight line passing through the center of gravity of the first projection circle. Located to have;
(Vi) When the compressive elastic modulus of the conductive resin layer is G and the compressive elastic modulus of the solid resin particles is J, the following mathematical formulas (1) and (2) are satisfied:
Formula (1)
G <J
Formula (2)
0.1 MPa ≤ G ≤ 10 MPa.

When such an electrophotographic roller is used as a charging member (charging roller), for example, it is possible to prevent the bowl-shaped resin particles from bending at the nip with the photoconductor. The reason is that the bowl shape is formed by contacting the outer wall surface of the shell of the bowl-shaped resin particles with at least two solid resin particles so as to have a specific positional relationship with the bowl-shaped resin particles. It is considered that this is because the bending of the edge portion from which the opening of the resin particles is derived is appropriately limited. As a result, it is considered that the imbalanced state of the charge amount on the upstream side and the downstream side of the nip due to the bending can be eliminated, and the occurrence of abnormal discharge can be suppressed.

The electrophotographic roller according to the present invention can be used as a charging roller, but can also be used as a developing roller and a transfer roller. Hereinafter, the electrophotographic roller of the present invention will be described mainly focusing on the charging roller, but the present invention is not limited to these embodiments.

<Roller for electrophotographic>
The electrophotographic roller according to one aspect of the present invention has a conductive shaft core body and a conductive resin layer as a surface layer arranged on the shaft core body.

FIG. 3 shows a schematic cross-sectional view showing two examples of the roller for electrophotographic of the present invention. As shown in FIG. 3A, the electrophotographic roller of the present invention has a conductive shaft core 12 and a conductive resin layer 13. Further, in the electrophotographic roller of the present invention, as shown in FIG. 3B, another layer (for example, for example) is formed between the conductive shaft core body 12 and the conductive resin layer 13 which is a surface layer. It can have a conductive elastic layer 14). The conductive resin layer 13 can also have properties as a conductive elastic layer, and the roller for electrophotographic of the present invention has a configuration having a plurality of conductive elastic layers as shown in FIG. 3 (b). It may be.

The conductive shaft core 12 and the (sequentially) laminated (each) layer (for example, the conductive elastic layer 14 and the conductive resin layer 13 shown in FIG. 3B) are adhered to each other. It may be adhered via an agent.
The adhesive used at this time is preferably conductive. As the conductive adhesive, those known in the field of electrophotographic apparatus can be appropriately used. The adhesive may include, for example, a binder and a conductive agent. Examples of this binder include thermosetting resins and thermoplastic resins, and known binders such as urethane-based, acrylic-based, polyester-based, polyether-based, and epoxy-based binders can be used. The conductive agent for imparting conductivity to the adhesive can be appropriately selected from conductive fine particles and the like, which will be described later and can be used for making the conductive resin layer conductive. These conductive agents may be used alone or in combination of two or more.

The shape of the electrophotographic roller is not particularly limited. However, when used as a charging roller, for example, the shape may be as follows from the viewpoint of improving the driven rotation with the photoconductor in the central portion of the charging roller in the longitudinal direction (perpendicular to the paper surface shown in FIG. 3). preferable. That is, it is preferable that the charging roller has a crown shape in which the central portion in the longitudinal direction is the thickest and the portion becomes thinner toward both ends in the longitudinal direction. The preferred range of crown amount defined below is 30 μm or more and 200 μm or less. The crown amount is the average value of the difference between the outer diameter D2 of the central portion in the longitudinal direction of the electrophotographic roller and the outer diameters D1 and D3 at positions 90 mm apart from the central portion in the direction of both ends, and is the average value of the following formula (3). ) Is the value calculated.

Formula (3)
Crown amount = D2- (D1 + D3) / 2

(Conductive shaft core)
The conductive shaft core 12 has conductivity and has a function of supporting a conductive resin layer or another layer provided on the conductive shaft core body 12. The material constituting the shaft core is not particularly limited, and examples of the material include metals such as iron, copper, stainless steel, aluminum, and nickel, and alloys thereof. Further, the shape of the shaft core is not particularly limited, but it is preferably a cylindrical shape.

(Conductive resin layer)
The conductive resin layer 13 is arranged as a surface layer of an electrophotographic roller and includes at least a binder, bowl-shaped resin particles, and (plural) solid resin particles. The conductive resin layer can further contain other components (for example, conductive fine particles and the like).

The thickness of the conductive resin layer is preferably 1.0 mm or more and 5.0 mm or less. The thickness of the conductive resin layer means the thickness from the surface of the shaft core body (if an intermediate layer is formed, the intermediate layer thereof) to the surface of the conductive resin layer. When measuring the thickness of the conductive resin layer, for example, the thickness of any 10 points of the conductive resin layer is measured, and the average value thereof is taken as the thickness of the conductive resin layer. An observation device such as a video micro or an electron microscope can be used for the measurement.

Hereinafter, each component contained in the conductive resin layer will be described in detail. Note that FIG. 1 shows two examples of partial cross-sectional views in the vicinity of the surface of the electrophotographic roller of the present invention, more specifically in the vicinity of the surface of the conductive resin layer.

(I) Binder As the binder (reference numeral 6 in FIG. 1) contained in the conductive resin layer, for example, known rubber and resin can be used.

Examples of the rubber include natural rubber (for example, polyisoprene rubber), vulcanized rubber thereof, and synthetic rubber.
Examples of synthetic rubber include the following. Ethylene propylene rubber, styrene butadiene rubber (SBR), silicone rubber, urethane rubber, isopropylene rubber (IR), butyl rubber, acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), acrylic rubber, epichlorohydrin rubber and fluorine rubber.

As the resin, for example, a resin such as a thermosetting resin or a thermoplastic resin can be used. Of these, fluororesins, polyamide resins, acrylic resins, polyurethane resins, acrylic urethane resins, silicone resins, and butyral resins are preferable from the viewpoint of low cost and versatility.
One of these binders may be used alone, or two or more of these binders may be mixed and used. Further, a plurality of monomers which are raw materials of these binders may be used for copolymerization, and the obtained copolymer may be used as a binder.

Among these, it is particularly preferable to use NBR as the binder from the viewpoint of controlling the compressive elastic modulus of the conductive resin layer. For example, by appropriately adjusting the amount of nitrile of NBR, the amount of sulfur as a vulcanizing agent, and the type, combination and amount of the vulcanization accelerator, the compressive elasticity of the conductive resin layer can be adjusted to a specific range described later. The rate can be easily controlled.

The content ratio of the binder in the conductive resin layer is preferably 30% by mass or more and 70% by mass or less.

(II) Bowl-shaped resin particles The conductive resin layer can contain a plurality of bowl-shaped resin particles (reference numeral 3 in FIG. 1). The bowl-shaped resin particles 3 can be resin particles having a rounded inner wall surface defined by the shell 4.

As shown in FIG. 1, at least a part of the bowl-shaped resin particles 3 contained in the conductive resin layer has an opening (opening) 1, and this opening is exposed on the surface of the electrophotographic roller. The bowl-shaped resin particles 3 are held in the conductive resin layer (binder 6). By holding the bowl-shaped resin particles in such a state, it is possible to suppress the bending that occurs when the bowl-shaped resin particles vibrate due to rubbing against the photoconductor.
It is sufficient that some of the bowl-shaped resin particles contained in the conductive resin layer are held in the conductive resin layer in this state. That is, for example, the conductive resin layer may contain bowl-shaped resin particles (hollow-shaped resin particles described later) before the opening is formed. That is, in the present invention, at least a part of the bowl-shaped resin particles contained in the conductive resin layer (including the hollow-shaped resin particles) is exposed on the surface of the electrophotographic roller in the above state. I just need to be there.

Further, as shown in FIG. 1, the surface of the roller for electrophotographic photography has a recess 1a derived from an opening 1 of a bowl-shaped resin particle exposed on the surface and a bowl-shaped resin particle exposed on the surface. It has a convex portion 2a derived from the edge 2 of the opening 1.
The bowl-shaped resin particles having an opening are composed of the shell 4 and can have a cavity inside. That is, the recess 1a derived from the opening 1 of the bowl-shaped resin particles can be composed of the inner wall surface of the shell 4 forming the recess.
The bowl-shaped resin particles are held in the conductive resin layer with the opening exposed on the surface, and a concave portion derived from the opening and a convex portion derived from the edge of the opening are formed on the surface of the electrophotographic roller. It can be confirmed by the following method.
That is, it can be confirmed by observing the surface of the electrophotographic roller with an observation device such as a video micro or an electron microscope.

Next, FIGS. 5A to 5E show five examples of bowl-shaped resin particles 3 having an opening 1. The shape of the opening 1 contained in the bowl-shaped resin particles is not particularly limited, and various shapes can be used. For example, as shown in FIGS. 5A and 5B, the edge (edge portion of the opening) may have a flat shape, or as shown in FIGS. 5C to 5E, the edge may have a flat shape. It may have irregularities.

However, the bowl-shaped resin particles having this opening preferably have a shape that satisfies some of the following conditions.

First, as shown in FIG. 4, the distance 16 between the apex 16a of the convex portion derived from the edge of the opening of the bowl-shaped resin particles and the bottom portion 16b of the concave portion defined by the shell of the bowl-shaped resin particles is set. The range is preferably as follows. That is, the distance 16 is preferably 5 μm or more and 100 μm or less, and more preferably 8 μm or more and 80 μm or less. Hereinafter, the distance may be referred to as a "height difference". By setting this distance 16 within the range of 5 to 100 μm, the contact pressure can be relaxed more reliably.

The apex 16a of the convex portion is the highest (thick) portion (thickness) of the convex portion in the height (thickness) in the direction perpendicular to the outer surface of the axial core body (vertical direction on the paper surface in FIG. 4). Point) means. Further, the bottom portion 16b of the recess means the lowest portion of the recess at a height in the direction perpendicular to the outer surface of the shaft core body.

Further, the ratio of the distance (height difference) 16 to the maximum diameter 15 of the bowl-shaped resin particles shown in FIG. 4, that is, the [maximum diameter] / [height difference] of the resin particles is 0.8 or more. It is preferably 0 or less. By setting it within this range, the above-mentioned contact pressure can be reduced more reliably.

The maximum diameter 15 of the bowl-shaped resin particles is preferably 5 μm or more and 150 μm or less, and more preferably 8 μm or more and 120 μm or less.
The ratio of the maximum diameter 15 of the bowl-shaped resin particles to the minimum diameter 17 of the opening shown in FIG. 5, that is, the [maximum diameter] / [minimum diameter of the opening] of the bowl-shaped resin particles is 1. It is preferably 1 or more and 4.0 or less. By setting this ratio within this range, the above-mentioned contact pressure can be reduced more reliably.

The thickness of the shell of the bowl-shaped resin particles is preferably 0.1 μm or more and 3 μm or less, and more preferably 0.2 μm or more and 2 μm or less. By setting the thickness of the shell within the range of 0.1 to 3 μm, the edge can be elastically deformed more flexibly, and as a result, the contact pressure can be more reliably relaxed. The maximum thickness of the shell is preferably 3 times or less, more preferably 2 times or less of the minimum thickness.

The maximum diameter 15, the distance 16, the minimum diameter 17 of the opening, and the thickness of the shell of the bowl-shaped resin particles having an opening can be specified by the following methods.
That is, an arbitrary point of the conductive resin layer is cut out over 500 μm by a focused ion beam (trade name: FB-2000C, manufactured by Hitachi, Ltd.) by 20 nm, and a cross-sectional image thereof is taken. Then, the images of the same bowl-shaped resin particles are combined to calculate a three-dimensional image of the bowl-shaped resin particles. From the stereoscopic image, as shown in FIGS. 4 and 5, the maximum diameter 15, the distance (height difference) 16 and the minimum diameter 17 of the opening are calculated. Further, from this three-dimensional image, the difference between the outer diameter (of the shell) and the inner diameter is calculated at any five points of the bowl-shaped resin particles, and the thickness of the shell at the five points is calculated. Such work is performed on 10 arbitrary bowl-shaped resin particles. Then, the same measurement was performed at 10 points in the longitudinal direction of the electrophotographic roller (perpendicular to the paper surface in FIG. 3), and from the average value of each data of a total of 100 resin particles obtained, the above maximum diameter was obtained. Specify 15, the distance 16, the minimum diameter 17 of the opening, and the thickness of the shell.

The average particle size of the bowl-shaped resin particles based on the spherical approximation is preferably 10 μm or more from the viewpoint of forming the surface uneven shape, and preferably 100 μm or less from the viewpoint of compression set. Further, the average particle size of the bowl-shaped resin particles based on the spherical approximation is more preferably 30 μm or more from the viewpoint of suppressing the pot-shaped image, and more preferably 60 μm or less from the viewpoint of toner contamination.

The average particle size of the bowl-shaped resin particles by spherical approximation can be specified by the following method. That is, first, 10 bowl-shaped resin particles are arbitrarily selected from the surface of the electrophotographic roller. Then, these bowl-shaped resin particles are orthographically projected onto the surface of the axial core body, and the plane parallel to the plane of the projection portion is used as a cut plane, and the focused ion beam (for example, trade name: FB-2000C, Hitachi, Ltd.) is focused by 20 nm. Take a cross-sectional image of each while cutting out with (manufactured by). Then, based on these cross-sectional images, the diameters close to the sphere are calculated for each of the selected 10 bowl-shaped resin particles, and the average value thereof is the average particle size obtained by the spherical approximation of the bowl-shaped resin particles. And.

It is preferable that the surface state of the electrophotographic roller, that is, the surface state of the conductive resin layer is controlled as follows by the uneven shape of the bowl-shaped resin particles exposed on the surface. The ten-point average roughness (Rzjis) is preferably 5 μm or more and 65 μm or less, and more preferably 10 μm or more and 50 μm or less.
The average unevenness interval (Sm) on the surface is preferably 30 μm or more and 200 μm or less, and more preferably 40 μm or more and 150 μm or less. By setting Rzjis in the range of 5 to 65 μm and Sm in the range of 30 to 200 μm, the contact pressure can be reduced more reliably. The method for measuring the ten-point average roughness (Rzjis) of the surface and the unevenness average interval (Sm) of the surface conforms to the standard of surface roughness in JIS B 0601-1994.
A specific method for producing bowl-shaped resin particles will be described later.

(III) Solid Resin Particles A plurality of solid resin particles (reference numeral 5 in FIG. 1) are contained in the conductive resin layer. Solid resin particles are particles in which the inside of the particles is filled with resin. That is, the particles do not contain gas inside the particles, or even if they contain gas, the particles have a very small amount and are 0.1% or less in terms of volume.

The material of the solid resin particles is not particularly limited, and examples thereof include polyethylene resin, acrylic resin, urethane resin, silicone resin, amino resin, polyester resin, polyamide resin, polycarbonate resin, epoxy resin, and melamine resin. However, the resin constituting the solid resin particles preferably contains a resin selected from a polyethylene resin and an acrylic resin from the viewpoint of satisfying both the mathematical formulas (1) and (2) described later, and is composed of these resins. Is preferable. With these resins, the hardness of the solid resin particles and the degree of dispersion in the binder tend to be desired values, which is particularly advantageous in satisfying these mathematical formulas.

The content ratio (content) of the solid resin particles in the conductive resin layer is preferably in the following range with respect to 100 parts by mass of the resin solid content in the conductive resin layer. That is, from the viewpoint of forming the conductive resin layer, it is preferably 1 part by mass or more and 40 parts by mass or less, and more preferably 4 parts by mass or more and 20 parts by mass or less from the viewpoint of suppressing the pot-shaped image.

The average particle size of the solid resin particles contained in the conductive resin layer based on the spherical approximation is preferably 1 μm or more from the viewpoint of suppressing the pot-shaped image, and preferably 50 μm or less from the viewpoint of forming the surface uneven shape. Further, the average particle size of the solid resin particles based on the spherical approximation is more preferably 10 μm or more from the viewpoint of further suppressing the pot-shaped image, and more preferably 30 μm or less from the viewpoint of toner contamination.
The average particle size of the solid resin particles by spherical approximation can be confirmed by the same method as that of the bowl-shaped resin particles.

The ratio of the average particle size of the bowl-shaped resin particles to the solid resin particles (the average particle size of the bowl-shaped resin particles: the average particle size of the solid resin particles) is 9: 1 to 1: 1 (preferably 5). : 1 to 1: 1) is preferable. This is because the solid resin particles can more efficiently mitigate vibrations that cause bending.

Examples of the solid resin particles include trade names: XM-220 and PM-200 (all materials: polyethylene resin, manufactured by Mitsui Kagaku Co., Ltd.), trade names: MBX-5, MBX-50 (all materials: materials: Acrylic resin, manufactured by Sekisui Chemical Co., Ltd.), trade name: Epostal M05 (material: melamine resin, manufactured by Nippon Shokubai Co., Ltd.) can be used.

-Compressive elastic modulus In the present invention, when the compressive elastic modulus of the conductive resin layer is G and the (average) compressive elastic modulus of the solid resin particles contained in the conductive resin layer is J, the following mathematical formula (1) and Satisfy formula (2).

Formula (1)
G <J
Formula (2)
0.1 MPa ≤ G ≤ 10 MPa

When each compressive elastic modulus satisfies these mathematical formulas, it is possible to suppress the bending of the bowl-shaped resin particles existing on the surface of the roller for electrophotographic photography.
Specifically, when the G is less than 0.1 MPa, the holding force of the deflection in the electrophotographic roller is reduced, and the effect of suppressing the pot-shaped image due to the abnormal discharge is reduced. Further, when the G exceeds 10 MPa, the harmful effect of promoting scratches and wear on the contact object such as the photoconductor by the high-hardness solid resin particles is greater than the increase in the effect of suppressing the pot-shaped image due to the abnormal discharge. Become.
Further, when G> J, the hardness of the binder contained in the conductive resin layer increases, and adverse effects such as toner contamination occur.

Therefore, it is essential that the compressive elastic moduli G and J satisfy G <J and 0.1 MPa ≦ G ≦ 10 MPa. Further, it is more preferable that these compressive elastic moduli satisfy G <J and 1.0 MPa ≦ G ≦ 10 MPa from the viewpoint of increasing the bending suppressing effect.

These compressive elastic moduli can be specified by measuring the indentation elastic modulus using a picodenter HM500 (trade name, manufactured by Fisher Instruments Co., Ltd.) based on ISO14577. As the indenter, an indenter (Vickers pyramid) having a square pyramid-shaped diamond indenter having a square base and a facing angle of 136 ° sandwiching the apex can be used.

The measurement is performed at the central portion and both end portions (positions of 90 mm each from the central portion in the both end directions) in the longitudinal direction of the electrophotographic roller. Specifically, using a microscope, 10 points each of the non-existent portion of the solid resin particles were arbitrarily selected from the central portion and both end portions, and the indentation elastic modulus was measured, and a total of 30 measurements were obtained. The average value of the values is defined as the compressive elastic modulus G of the conductive resin layer.

Next, using a microscope, 10 points of the solid resin particles exposed on the surface of the electrophotographic roller are arbitrarily selected from the central portion and both end portions, and the indentation elastic modulus is measured. When there are no exposed solid resin particles on the surface of the electrophotographic roller, the surface of the electrophotographic roller is trimmed to expose the solid resin particles to the surface for measurement. Then, the average value of the obtained 30 measured values is defined as the (average) compressive elastic modulus J of the solid resin particles.

-Arrangement of bowl-shaped resin particles and solid resin particles The bowl-shaped resin particles contained in the conductive resin layer and the solid resin particles satisfy the following conditions (iv) and (v).
(Iv) At least two, more preferably 2.0 or more, of one bowl-shaped resin particle held in the conductive resin layer, with respect to the outer wall surface of the shell forming the recess. Solid resin particles come into contact.
(V) When the bowl-shaped resin particles are orthographically projected onto the surface of the shaft core, the projection circle formed on the surface of the shaft core is defined as the first projection circle.
When two of the solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are projected onto the surface of the shaft core, the shaft core When the projection circles formed on the surface are the second projection circle and the third projection circle, respectively.
The bowl-shaped resin particles and the solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are
At least a part of the second projection circle overlaps with the first projection circle, and at least a part of the third projection circle overlaps with the first projection circle, and
A line segment passing through the center of gravity of the second projection circle and the center of gravity of the third projection circle extends parallel to the axial direction of the axis, and intersects with a straight line passing through the center of gravity of the first projection circle. Positioned to have.

・ Condition (iv)
As shown in FIG. 1, at least two solid resin particles 5 are in contact with the outer wall surface 4a of the shell 4 forming the recess 1a of the bowl-shaped resin particles 3.

The number of solid resin particles in contact with the outer wall surface 4a of one bowl-shaped resin particle is at least two, more preferably 2.0 or more. In addition, for example, when three or three or more solid resin particles are in contact with the outer wall surface 4a, at least two of them satisfy the condition (v) described later.

At least a part of the solid resin particles contained in the conductive resin layer may be arranged at a position satisfying the condition (iv). Therefore, other solid resin particles may be present, for example, exposed on the surface of the electrophotographic roller (for example, in a partially chipped form or in a form at the time of addition), or a bowl-shaped resin. It may be included in the conductive resin layer (binder) without coming into contact with the particles. Further, there may be one in which only one solid resin particle is in contact with the outer wall surface of the bowl-shaped resin particle.

However, among the solid resin particles contained in the conductive resin layer, the (number) ratio of the solid resin particles arranged at specific positions satisfying these conditions is determined from the viewpoint of suppressing the pot-shaped image. It is preferably 5.0% or more and 30.0% or less from the viewpoint of compression set.
The method for specifying the number of solid resin particles in contact with the outer wall surface of the bowl-shaped resin particles will be described later.

・ Condition (v)
First, a bowl-shaped resin particle and a projection circle corresponding to two of the solid resin particles in contact with the outer wall surface of the resin particle will be described. FIG. 2 shows two examples of a bowl-shaped resin particle and a projected circle on the solid resin particle.

As shown in FIG. 2, the projection circle formed on the surface (outer surface) of the shaft core body when the bowl-shaped resin particles are orthographically projected onto the surface of the shaft core body is defined as the first projection circle 7. Next, a projection circle formed on the surface of the shaft core when each of the two solid resin particles in contact with the outer wall surface 4a of the bowl-shaped resin particles is positively projected onto the surface of the shaft core. Let each of be a second projection circle 8 and a third projection circle 9. Although the outer surface of the shaft core is actually a curved surface as shown in FIG. 3, it can be regarded as a flat surface because of the relative size difference with these resin particles.

Then, the obtained three projection circles satisfy the following conditions (v-1) and (v-2).
First, at least a part of each of the second projection circle 8 and the third projection circle 9 corresponding to the two solid resin particles overlaps with the first projection circle 7 (condition (v-1)). Further, the line segment 11 passing through the center of gravity 8a of the second projection circle and the center of gravity 9a of the third projection circle is parallel to the axial direction of the axis core (for example, the direction perpendicular to the paper surface shown in FIG. 3). It has an intersection with a straight line 10 passing through the center of gravity 7a of the first projection circle (condition (v-2)). In the above condition (v-1), the entire second projection circle and the third projection circle may overlap the first projection circle, or a part of them may overlap the first projection circle. May be good.

Examples of the arrangement of the projection circles satisfying such conditions include the case where the center of gravity 8a of the second projection circle and the center of gravity 9a of the third projection circle exist on both sides of the straight line 10. Specifically, the arrangement shown in FIGS. 2A and 2B can be mentioned.

By arranging the bowl-shaped resin particles and the solid resin particles at positions that satisfy the above conditions (iv) and (v), the following can be achieved. That is, the solid resin particles can absorb the vibration of the axial core body of the electrophotographic roller in the rotation direction, and the bending of the bowl-shaped resin particles can be suppressed.

It can be confirmed by the following method that the bowl-shaped resin particles and the solid resin particles are arranged at positions satisfying the above conditions (iv) and (v) in the conductive resin layer.

That is, first, 10 bowl-shaped resin particles that are held in a state where the openings are exposed on the surface of the electrophotographic roller are selected. Then, for each of the bowl-shaped resin particles, a cross-sectional image of a range including the surrounding solid resin particles is taken, and based on each cross-sectional image, the solid resin particles in contact with the outer wall surface of each bowl-shaped resin particle. Are extracted respectively. Next, the center of gravity of each of these solid resin particles is obtained from the cross-sectional image. From the center of gravity and the cross-sectional image, it is determined whether the solid resin particles in contact with the outer wall surface of the resin particles in each bowl shape satisfy the above condition (v).

Next, for each of the resin particles, the number of solid resin particles in contact with the outer wall surface of the bowl-shaped resin particles that satisfy the condition (v) is determined. When the average value of the number is 2 or more (preferably 2.0 or more), the bowl-shaped resin particles and the solid resin particles contained in the conductive resin layer are subject to these conditions (iv) and It is determined that (v) is satisfied.

By producing the roller for electrophotographic of the present invention using the primary kneaded product described later, the bowl-shaped resin particles and the solid resin particles can be easily placed at positions satisfying the above conditions (iv) and (v). Can be placed in.

(IV) Other Components-Conductive Fine Particles The conductive resin layer can contain known conductive fine particles in order to exhibit conductivity. Examples of the conductive fine particles include conductive metal oxides, metal fine particles and carbon black. Further, these conductive fine particles may be used alone or in combination of two or more.

The content of the conductive fine particles in the conductive resin layer is preferably 2 parts by mass or more and 200 parts by mass or less from the viewpoint of imparting conductivity to 100 parts by mass of the binder, and from the viewpoint of controlling conductivity. , 20 parts by mass or more and 80 parts by mass or less is more preferable.
The average particle size of the conductive fine particles is preferably 0.01 μm or more and 0.9 μm or less, and more preferably 0.01 μm or more and 0.5 μm or less, from the viewpoint of controlling conductivity.

-Ion conductive agent and insulating particles The conductive resin layer may contain an ion conductive agent, insulating particles and the like in addition to the above-mentioned materials.

Examples of the ionic conductive agent include _{perchlorates of LiClO 4} and NaClO ₄ , and quaternary ammonium salts. These ionic conductive agents may be used alone or in combination of two or more.

Examples of the insulating particles include the following. Zinc oxide, tin oxide, indium oxide, titanium oxide (titanium dioxide, titanium monoxide, etc.), iron oxide, silica, alumina, magnesium oxide, zirconium oxide, strontium titanate, calcium titanate, magnesium titanate, barium titanate, Calcium dilconate, barium sulfate, molybdenum disulfide, calcium carbonate, magnesium carbonate, hydrotalcite, dolomite, talc, kaolin clay, mica, aluminum hydroxide, magnesium hydroxide, zeolite, wolastonite, silica soil, glass beads , Bentnite, montmorillonite, hollow glass spheres, particles of organic metal compounds and organic metal salts, etc.
The blending ratio of the ionic conductive agent and the insulating particles in the conductive resin layer can be appropriately set and is not particularly limited.

(V) Volume resistivity of the conductive resin layer The volume resistivity of the conductive resin layer is 1 × 10 ² Ω · cm or more and 1 × 10 ¹⁶ Ω · cm or less in an environment of a temperature of 23 ° C. and a relative humidity of 50%. Is preferable. Within this range, charging on the photoconductor by electric discharge and transfer of the toner developed on the photoconductor on paper can be performed more efficiently.

The volume resistivity of the conductive resin layer can be obtained as follows. First, the conductive resin layer is cut out from an electrophotographic roller into strips having a length of 5 mm, a width of 5 mm, and a thickness of 1 mm. The vertical, horizontal, and thickness directions of the electrophotographic roller shown in FIG. 3 are the axial direction (vertical direction to the paper surface), the rotation direction, and the thickness direction (from the surface of the conductive resin layer to the axis core body, respectively). (Direction toward the center).
Then, metal is vapor-deposited on both sides of the obtained strip-shaped conductive resin layer to prepare an electrode and a guard electrode, and a sample for measurement is obtained. If the conductive resin layer cannot be cut out as a thin film, a conductive resin composition described later for forming the conductive resin layer is applied onto an aluminum sheet to form a coating film, and the coating film surface is coated. A metal is vapor-deposited to prepare a measurement sample.

Next, a voltage of 200 V is applied to the obtained measurement sample using a micro ammeter (trade name: ADVANTEST R8340A ULTRA HIGHRESISTANCE METER, manufactured by Advantest Co., Ltd.). Then, the current after 30 seconds is measured, and the volume resistivity is obtained by calculating from the film thickness and the electrode area.
The volume resistivity of the conductive resin layer can be adjusted by the conductive fine particles and the ionic conductive agent blended in the conductive resin layer.

(Conductive elastic layer)
In the electrophotographic roller of the present invention, one or a plurality of conductive elastic layers may be formed between the conductive shaft core and the conductive resin layer which is the surface layer. The conductive elastic layer can contain a binder, a conductive agent and other components (additives such as insulating particles and a plasticizer). As the binder, known rubbers and resins as described above can be appropriately used in the conductive resin layer. Further, as the conductive agent, known conductive agents such as carbon black and conductive metal oxide can be appropriately used.
The conductive elastic layer may have the same composition as the above-mentioned conductive resin layer, that is, the conductive elastic layer contains hollow-shaped resin particles, solid resin particles, and the like, which will be described later. You may. The (total) thickness of the conductive elastic layer arranged between the shaft core and the conductive resin layer is preferably 1.0 μm or more and 10.0 μm or less from the viewpoint of conductivity and adhesiveness.

<Manufacturing method of rollers for electrophotographic>
The electrophotographic roller of the present invention can be produced, for example, by a method for manufacturing an electrophotographic roller having the following steps.
-A step of forming a preliminary coating layer containing a binder, hollow-shaped resin particles (bowl-shaped resin particles before an opening is formed), and (plural) solid resin particles on a conductive shaft core. (Preliminary coating layer forming step).
-A step (polishing step) of forming a conductive resin layer by polishing a part of the surface of hollow resin particles contained in the preliminary coating layer by polishing the surface of the preliminary coating layer.

In addition, the method for manufacturing an electrophotographic roller may also have the following steps.
-A process of preparing a conductive shaft core (shaft core preparation process).
-A step of surface-treating or heat-treating the conductive resin layer (treatment step).

Further, the pre-coating layer forming step can include the conductive resin composition preparation step and the pre-coating layer forming step shown below.
-Step of preparing a conductive resin composition containing (s) thermoexpandable microcapsules (a plurality of solid resin particles) and a binder (which is a precursor of bowl-shaped resin particles) (Preparation of conductive resin composition) Process).
-A step of forming a pre-coating layer by coating the conductive resin composition on the conductive shaft core and applying heat (pre-coating layer forming step).

In addition, the conductive resin composition preparation step can include the following steps.
-A step of kneading heat-expandable microcapsules, solid resin particles (s) and a first binder to prepare a primary kneaded product (primary kneaded product preparation step).
-A step of preparing a conductive resin composition (secondary kneaded product) by kneading the primary kneaded product, the second binder, and an additive (for example, a conductive agent) if necessary (secondary kneaded product). Preparation process).
Each step will be described in detail below.

(Axial core body preparation process)
As the conductive shaft core body, those known in the field of electrophotographic apparatus can be appropriately used. Specifically, a cylindrical stainless steel shaft core or the like can be used, and if necessary, a conductive adhesive can be applied to the surface thereof.

(Preliminary coating layer forming step)
When preparing the conductive resin layer, first, on the conductive shaft core, a binder, hollow resin particles (which are precursors of bowl-shaped resin particles), solid resin particles, and if necessary, other components are used. A coating layer (preliminary coating layer) containing components is prepared.
The thickness of the preliminary coating layer is preferably 2.0 mm or more from the viewpoint of polishing workability, and preferably 6.0 mm or less from the viewpoint of polishing workability.

As the binder and the solid resin particles, those described above in the description of the conductive resin layer can be appropriately used. Among them, from the viewpoint of controlling the compressive elastic modulus of the conductive resin layer, it is preferable to use NBR as the binder, and it is preferable to use one containing polyethylene resin or acrylic resin as the solid resin particles.
As the above other components, for example, a conductive agent (conductive fine particles, ionic conductive agent, etc.), a plasticizer, a bulking agent, a vulcanizing agent, a vulcanization accelerator, an antiaging agent, a foaming agent, etc. may be arbitrarily used. can.

Here, as a method for containing the hollow-shaped resin particles which become bowl-shaped resin particles, that is, which are precursors of the bowl-shaped resin particles, in the preliminary coating layer, for example, the following method is used. be able to. That is, it is a method using so-called heat-expandable microcapsules, which contains an encapsulating substance inside the particles, and the encapsulating substance expands when heat is applied, resulting in hollow resin particles.

Specifically, a conductive resin composition in which heat-expandable microcapsules and solid resin particles are dispersed in a binder is prepared (conductive resin composition preparation step), and this composition is placed on a conductive shaft core. To prepare a pre-coating layer by applying heat to the surface (pre-coating layer forming step). In the case of this method, the encapsulating substance of the heat-expandable microcapsules can be expanded by heat during drying, curing, cross-linking, etc. of the binder used for the preliminary coating layer to form hollow resin particles. At this time, as a method of controlling the particle size of the hollow resin particles after expansion, for example, a method of controlling the particle size of the unexpanded (before expansion) heat-expandable microcapsules can be preferably used. In this method, the particle size after expansion (hollow resin particles) is controlled by keeping the composition of the components (binder, inclusion substance, etc.) of the heat-expandable microcapsules constant and controlling the particle size. Can be done. For example, the volume average particle size of the heat-expandable microcapsules (before expansion) can be 1.0 μm or more and 100 μm or less. The volume average particle diameter of the hollow resin particles is preferably 10 μm or more and 100 μm or less.

Further, the particle size of the hollow resin particles may be controlled by appropriately controlling the binder and the inclusion substance to be blended in the heat-expandable microcapsules. With respect to this binder, for example, the particle size after expansion can be controlled by using an acrylate and / or methacrylate-based monomer and controlling the Tg (glass transition temperature) of the binder. With respect to the inclusion substance, for example, the particle size after expansion can be controlled by controlling the content and boiling point.

As a method of containing the hollow-shaped resin particles in the precoating layer, a method of containing the hollow-shaped particles in which the gas is previously contained inside the particles as it is can be considered. However, in the present invention, from the viewpoint of controlling the average particle size of the bowl-shaped resin particles, it is preferable to use a method using heat-expandable microcapsules as a means for forming the hollow-shaped resin particles.
Hereinafter, the heat-expandable microcapsules will be described.

-Heat-expandable microcapsules When using heat-expandable microcapsules, it is required to use a thermoplastic resin as a binder to be blended in the capsules. Examples of the thermoplastic resin include the following.
Acrylonitrile resin, vinyl chloride resin, vinylidene chloride resin, methacrylic acid resin, styrene resin, urethane resin, amide resin, methacrylnitrile resin, acrylic acid resin, acrylic acid ester resin, methacrylic acid ester resin.
Among these, it is preferable to use a thermoplastic resin consisting of at least one selected from acrylonitrile resin, vinylidene chloride resin and methacrylonitrile resin, which have low gas permeability and exhibit high impact resilience. These thermoplastic resins may be used alone or in combination of two or more. Further, a copolymer obtained by copolymerizing a monomer as a raw material of these thermoplastic resins may be used as a binder to be blended in the capsule.

The heat-expandable microcapsules can be produced by known production methods such as suspension polymerization method, interfacial polymerization method, interfacial sedimentation method and in-liquid drying method.

Hereinafter, the suspension polymerization method will be described as an example. First, the polymerizable monomer, the substance to be encapsulated in the heat-expandable microcapsules (encapsulating substance), and the polymerization initiator are mixed. Then, the obtained mixture is dispersed in an aqueous medium containing a surfactant and a dispersion stabilizer, and then suspension polymerization is carried out to prepare thermally expandable microcapsules. In addition, a compound having a reactive group that reacts with the functional group of the polymerizable monomer, an organic filler, and the like can be added to this mixture.

Examples of the polymerizable monomer include the following.
Acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, vinylidene chloride, vinyl acetate; acrylic acid ester (methyl acrylate, ethyl) Acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, isobornyl acrylate, cyclohexyl acrylate, benzyl acrylate); methacrylic acid ester (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, Isobornyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate); styrene-based monomer, acrylamide, substituted acrylamide, methacrylicamide, substituted methacrylicamide, butadiene, ε-caprolactam, polyether, isocyanate.
These polymerizable monomers may be used alone or in combination of two or more.

As the inclusion substance of the thermoplastic microcapsules, those which become gas and expand at a temperature equal to or lower than the softening point of the thermoplastic resin are preferable, and examples thereof include the following.
Low boiling liquids such as propane, propylene, butene, normal butane, isobutane, normal pentane, isopentane; high boiling liquids such as normal hexane, isohexane, normal heptane, normal octane, isooctane, normal decane, isodecane.
From the viewpoint of foamability, the amount of the inclusion substance used is preferably 1.0 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polymerizable monomer.

As the above-mentioned polymerization initiator, an initiator soluble in a polymerizable monomer is preferable, and for example, a known peroxide initiator (dicumyl peroxide or the like) and an azo initiator can be used. Of these, the azo initiator is preferable from the viewpoint of productivity. Examples of azo initiators are given below. 2,2'-azobisisobutyronitrile, 1,1'-azobiscyclohexane1-carbonitrile, 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile. Of these, 2,2'-azobisisobutyronitrile is preferable from the viewpoint of cost.
When a polymerization initiator is used, it is preferable to use 0.01 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the polymerizable monomer from the viewpoint of productivity.

As the surfactant, for example, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, and a polymer-type dispersant can be used. From the viewpoint of dispersibility, the amount of the surfactant used is preferably 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polymerizable monomer.

Examples of the dispersion stabilizer include the following. Organic fine particles (polystyrene fine particles, polymethyl methacrylate fine particles, polyacrylic acid fine particles, polyepoxide fine particles, etc.), silica (coloidal silica, etc.), calcium carbonate, calcium phosphate, aluminum hydroxide, barium carbonate, magnesium hydroxide, etc.
From the viewpoint of dispersibility, the amount of the dispersion stabilizer used is preferably 0.01 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polymerizable monomer.

Suspension polymerization is preferably carried out in a pressure-resistant container in a hermetically sealed state. Further, the above-mentioned raw material for polymerization may be suspended in a disperser or the like and then transferred to a pressure-resistant container for suspension polymerization, or may be suspended in a pressure-resistant container. The polymerization temperature is preferably 50 ° C. or higher and 120 ° C. or lower from the viewpoint of productivity. The polymerization reaction may be carried out at atmospheric pressure, but it is preferable to carry out the polymerization reaction under pressure (under atmospheric pressure plus 0.1 to 1 MPa) in order to prevent the inclusion substances from being vaporized. After completion of the polymerization reaction, solid-liquid separation and washing may be performed by centrifugation or filtration. When solid-liquid separation or washing is performed, then drying or pulverization may be performed at a temperature equal to or lower than the softening temperature of the resin (binder) constituting the thermally expanded microcapsules. Drying and pulverization can be performed by known methods, and air flow dryers, smooth air dryers and Nauter mixers can be used. Further, drying and crushing can be performed simultaneously by a crushing dryer. Surfactants and dispersion stabilizers can be removed by repeating washing and filtration after production.
From the above, heat-expandable microcapsules can be obtained.

-Conducting resin composition The conductive resin composition includes a binder (resin (rubber)), heat-expandable microcapsules and solid resin particles, and other components (for example, a conductive agent, a plasticizer, a bulking material, and a slipper). It can be produced by kneading various additives such as materials) with a kneader.

Here, in the present invention, the bowl-shaped resin particles and the plurality of solid resin particles are arranged at specific positions in the conductive resin layer. In order to achieve this particular arrangement, it is preferable to prepare the conductive resin composition by the following method. That is, when preparing the conductive resin composition, first, the heat-expandable microcapsules (which are the precursors of the bowl-shaped resin particles), the solid resin particles, and the (first) binder are kneaded in advance. , Prepare the primary kneaded product (master batch) (primary kneaded product preparation step). By preparing this primary kneaded product in advance, a plurality of solid resin particles can be easily attached to the heat-expandable microcapsules which are the precursors of the bowl-shaped resin particles.

Then, this primary kneaded product is further kneaded with a (second) binder and other components (additives such as a conductive agent and a vulcanizing agent) to prepare a conductive resin composition (secondary kneaded product). (Secondary kneaded product preparation step). At this time, at least a part of the binder and other components to be kneaded with the primary kneaded product may be separately kneaded in advance. Further, the same binder may be used for the first binder and the second binder, or different binders may be used.
Then, the obtained conductive resin composition (more specifically, heat-expandable microcapsules) is heated to a temperature equal to or higher than the expansion temperature of the capsule (for example, 150 ° C. or higher and 200 ° C. or lower) to be thermally expandable. Hollow resin particles can be formed from the microcapsules. As a result, it is possible to obtain hollow-shaped resin particles which are precursors of bowl-shaped resin particles in which a plurality of solid resin particles are held (attached) to the periphery (outer peripheral surface).
As described above, it is preferable to prepare the conductive resin composition by a two-step kneading operation.

The blending ratio of each component of the primary kneaded product is preferably as follows from the viewpoint of adhering the solid resin particles to the heat-expandable microcapsules. That is, it is preferable that the binder is 20% by mass or more and 50% by mass or less, the heat-expandable microcapsules are 20% by mass or more and 40% by mass or less, and the solid resin particles are 30% by mass or more and 50% by mass or less. In addition to these components, a plasticizer, a lubricant, or the like may be added to the primary kneaded product. The kneading temperature at the time of primary kneading is preferably −10 ° C. or higher and 50 ° C. or lower from the viewpoint of preventing pre-expansion of the heat-expandable microcapsules.

The reason why the solid resin particles can be attached around the shell of the heat-expandable microcapsules by performing the primary kneading is that the heat-expandable microcapsules and the solid resin particles are kneaded at a high concentration. Because it can be done. In addition, by adjusting the stirring speed of the disperser from the temperature rise due to kneading and the measured shearing force (the amount of electric power may be substituted), a plurality of solids are adjusted so that strong shearing is not applied. The resin particles can be easily brought into contact with the heat-expandable microcapsules in a particular arrangement.

The kneading temperature of the secondary kneading when preparing the conductive resin composition (secondary kneading product) is preferably 30 ° C. or higher and 100 ° C. or lower from the viewpoint of preventing the pre-expansion of the heat-expandable microcapsules.

Examples of the kneader used for producing the conductive resin composition include a ribbon blender, a Nauter mixer, a Henschel mixer, a super mixer, a Banbury mixer and a pressure kneader.
When a vulcanizing agent or a vulcanization accelerator is used as the additive, when these additives are kneaded into the conductive resin composition, the progress of vulcanization of the resin (rubber) due to an increase in temperature is prevented. Therefore, it is preferable to perform kneading using an open kneader such as an open roll.
The primary kneading and the secondary kneading may be performed under the same kneading conditions (kneading machine, kneading temperature, kneading time, etc.) or under different kneading conditions.

-Method for forming the preliminary coating layer As a specific method for forming the preliminary coating layer from the conductive resin composition, for example, a method using an extrusion molding apparatus equipped with a crosshead can be mentioned. As this method, for example, the conductive resin composition is coaxially coated on the conductive shaft core body coated with an adhesive as a central axis, and the conductive shaft core body and the composition are coated. Can be mentioned as a method of integrally extruding. The crosshead is a device generally used for coating electric wires and wires, and is used by being attached to a rubber discharge portion of a cylinder of an extruder.

Further, as a specific method for forming the preliminary coating layer from the conductive resin composition, for example, a method of forming a rubber tube, inserting an adhesive-coated conductive shaft core into the tube, and adhering the tube. Can be mentioned. Another example is a method in which an unvulcanized rubber sheet is coated on a conductive shaft core body coated with an adhesive, and vulcanization is performed in a mold.
Then, if necessary, the preliminary coating layer can be obtained by drying, curing, cross-linking, or the like. When forming the preliminary coating layer using the heat-expandable microcapsules, it is required to heat the conductive resin composition at least once above the expansion temperature of the capsules before the polishing step described later. .. This heating operation may be performed at the same time as the vulcanization operation, for example, or may be performed at the same time as the drying operation of the conductive resin composition applied on the shaft core body.

(Polishing process)
Next, the surface of the obtained preliminary coating layer is polished to form a conductive resin layer. By this polishing step, a part of the surface (opening part) of the hollow resin particles contained in the preliminary coating layer is removed by polishing, and a part of the hollow resin particles is opened. Bowl-shaped resin particles. Then, a concave portion due to the opening of the bowl-shaped resin particles and a convex portion due to the edge of the opening of the bowl-shaped resin particles are formed. By undergoing this polishing step, the bowl-shaped resin particles having an opening exposed on the surface and the plurality of solid resin particles adhering to the outer wall surface of the bowl-shaped resin particles are conductive in a specific arrangement. A resin layer can be obtained.

Here, when the polishing step is performed, hollow resin particles are exposed on the surface of the preliminary coating layer according to the thickness of the preliminary coating layer, and convex portions derived from the hollow resin particles are formed. It is considered that the preliminary coating layer contains hollow resin particles. In the polishing step, the polishing method can be appropriately selected according to these situations. As the polishing method, for example, a cylindrical polishing method or a tape polishing method can be used. However, in particular, when hollow resin particles are included in the preliminary coating layer, it is necessary to significantly bring out the difference in the polishability of the materials, so that the condition of polishing faster is preferable. From this point of view, it is more preferable to use the cylindrical polishing method. Examples of the cylindrical polishing machine include a traverse type NC cylindrical polishing machine and a brand cut type NC cylindrical polishing machine. However, among the cylindrical polishing methods, it is more preferable to use the brand cut method from the viewpoint that the longitudinal direction of the electrophotographic roller can be polished at the same time and the polishing time can be shortened.

A specific polishing method will be described with reference to the explanatory view of the brand cut type polishing machine shown in FIG. Here, FIG. 6A is a front view of the branding cut type polishing machine, and FIG. 6B is a side view of the branding cutting type polishing machine.

First, the cylindrical polishing grindstone 20 and the roller (preliminary coating roller) 21 having the shaft core and the preliminary coating layer are arranged so that the axial directions of the two are parallel to each other. Next, both ends of the pre-covering roller are held by the holding device 22 that holds the exposed portion (shaft core body portion) of the pre-covering roller. Reference numeral 23 indicates the rotation direction of the precoating roller, and reference numeral 24 indicates the rotation direction of the cylindrical polishing grindstone.
Then, a cylindrical polishing grindstone is made to penetrate into the outer surface of the preliminary coating layer (cutting), and the surface of the preliminary coating layer is ground (intrusion step). At that time, the rotation speed of the brand cut type cylindrical polishing grindstone is preferably 1000 rpm or more and 4000 rpm or less, and more preferably 2000 rpm or more and 4000 rpm or less. The penetration speed of the cylindrical polishing wheel into the preliminary coating layer is preferably 5 mm / min or more and 30 mm / min or less, and more preferably 10 mm / min or more and 30 mm / min or less.

Next, if necessary, after the cylindrical polishing grindstone is intruded (invasion step), an operation of acclimatizing the polished surface of the preliminary coating layer (intrusion step) may be performed. Specifically, this operation is preferably performed within 2 seconds at an intrusion rate of 0.1 to 0.2 mm / min.
Further, if necessary, a spark-out operation (process) (polishing operation at an intrusion speed of 0 mm / min) may be performed at the final cutting end point, and this operation time may be 3 seconds or less. preferable.

In the polishing step, the rotation speed of the precoating roller to be polished is preferably set to 50 rpm or more and 500 rpm or less, and more preferably 200 rpm or more.
By performing the polishing step satisfying these conditions, unevenness due to the opening of the bowl-shaped resin particles can be more easily formed on the surface of the preliminary coating layer.

(Processing process)
Next, from the viewpoint of controlling physical properties such as hardness, electric resistance, and friction coefficient on the surface of the conductive resin layer, the surface of the conductive resin layer whose surface has been polished is surface-treated with ultraviolet rays or electron beams. Heat treatment may be performed by hot air or an infrared generator. However, from the viewpoint of efficiently changing these physical properties, it is preferable to perform heat treatment with a hot air furnace. The heat treatment temperature is preferably 160 ° C. or higher and 200 ° C. or lower from the viewpoint of forming surface hardness and deteriorating the binder.

<Electrophotograph image forming apparatus>
The electrophotographic image forming apparatus includes an electrophotographic roller according to an aspect of the present invention. FIG. 7 shows a schematic view of one aspect of the electrophotographic image forming apparatus. This electrophotographic apparatus can be used from an electrophotographic photosensitive member, a charging apparatus for an electrophotographic photosensitive member, a latent image forming apparatus for exposing, a developing apparatus, a transfer apparatus, a cleaning apparatus for residual transfer toner on an electrophotographic photosensitive member, a fixing apparatus, and the like. It is configured.

The electrophotographic photosensitive member 39 is a rotary drum type having a photosensitive layer on a conductive substrate. The electrophotographic photosensitive member 39 is rotationally driven at a predetermined peripheral speed (process speed) in the direction indicated by the arrow. The charging device has a contact-type charging roller 30 that is contact-arranged by being brought into contact with the electrophotographic photosensitive member 39 with a predetermined pressing force. The charging roller 30 is a driven rotation that rotates according to the rotation of the electrophotographic photosensitive member 39, and charges the electrophotographic photosensitive member 39 to a predetermined potential by applying a predetermined DC voltage from the charging power source 40.
As a latent image forming apparatus (not shown) for forming an electrostatic latent image on the electrophotographic photosensitive member 39, an exposure apparatus such as a laser beam scanner is used. An electrostatic latent image is formed by irradiating the uniformly charged electrophotographic photosensitive member 39 with the exposure light 31 corresponding to the image information.

The developing apparatus has a developing sleeve or a developing roller 32 arranged in close proximity to or in contact with the electrophotographic photosensitive member 39. A toner 33 electrostatically processed to have the same polarity as the charge polarity of the electrophotographic photosensitive member 39 is subjected to reverse development to develop an electrostatic latent image to form a toner image.
The transfer device has a contact type transfer roller 34. The toner image is transferred from the electrophotographic photosensitive member 39 to a transfer material 35 such as plain paper. The transfer material 35 is conveyed by a paper feeding system (not shown) having a conveying member.
The cleaning device has a blade-type cleaning member 36 and a collection container 37, and after transfer, mechanically scrapes and collects the transfer residual toner remaining on the electrophotographic photosensitive member. Here, it is possible to omit the cleaning device by adopting the simultaneous development cleaning method in which the transfer residual toner is collected by the developing device.
The fixing member 38 is composed of a heated roller or the like, fixes the transferred toner image on the transfer material 35, and discharges the transferred toner image to the outside of the machine.

The electrophotographic roller of the present invention can be used as at least one of a charging roller, a developing roller and a transfer roller in an electrophotographic apparatus.

<Process cartridge>
The process cartridge of the present invention has the roller for electrophotographic of the present invention, and is characterized in that it is detachably attached to and detachable from the main body of the electrophotographic apparatus. FIG. 8 shows a schematic configuration diagram of an example of the process cartridge of the present invention. This process cartridge integrates an electrophotographic photosensitive member 39, a charging roller 30, a developing roller 32, a cleaning member 36, and the like, and is configured to be removable from the electrophotographic apparatus. Further, the electrophotographic roller of the present invention can be used as at least one of a charging roller and a developing roller in a process cartridge.

Hereinafter, the present invention will be described in more detail with reference to specific production examples and examples, but the technical scope of the present invention is not limited thereto.

<Manufacturing example 1>
[Preparation of Capsule Particle 1]
An aqueous mixture of 4000 parts by mass of ion-exchanged water, 2 parts by mass of colloidal silica and 0.15 parts by mass of polyvinylpyrrolidone as a dispersion stabilizer was prepared. Next, an oil-based mixed solution consisting of 50 parts by mass of acrylonitrile, 45 parts by mass of methacrylonitrile, 5 parts by mass of methyl methacrylate, 12.0 parts by mass of isopentane, and 0.75 parts by mass of dicumyl peroxide was prepared. 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 was stirred and mixed with a homogenizer for 3 minutes, charged into a nitrogen-substituted polymerization reaction vessel, and reacted at 60 ° C. for 20 hours under stirring at 100 rpm to prepare a reaction product. The obtained reaction product was repeatedly filtered and washed with water, and then dried at 80 ° C. for 5 hours to prepare capsule particles. Capsule particles (heat-expandable microcapsules) 1 were obtained by crushing the obtained capsule particles with a sonic classifier and classifying them. The volume average particle diameter of the capsule particles 1 measured by the method shown below was 20.0 μm.

[Measurement of volume average particle size of capsule particles]
The volume average particle size of the capsule particles was measured using a laser diffraction type particle size distribution meter (trade name: Coulter LS-230 type particle size distribution meter, manufactured by Coulter). An aqueous module was used for the measurement, and pure water was used as the measurement solvent. The inside of the measurement system of the particle size distribution meter was washed with pure water for about 5 minutes, 10 mg of sodium sulfite was added to the measurement system as an antifoaming agent, and a background function was performed. Next, 3 drops of a surfactant (sodium stearate aqueous solution) was added to 50 ml of pure water, and 10 mg of a measurement sample (capsule particles after classification treatment) was further added. The aqueous solution in which the sample was suspended was dispersed with an ultrasonic disperser for 3 minutes to prepare a test sample solution. This test sample solution is gradually added into the measurement system of the measuring device, and the concentration of the test sample in the measuring system is adjusted so that the PIDS (Polaration Intensity Differential Scattering) on the screen of the device is 45% or more and 55% or less. And the measurement was performed. The volume average particle size was calculated from the obtained volume distribution.

<Manufacturing example 2>
[Preparation of capsule particles 2]
Capsule particles 2 were obtained in the same manner as in Production Example 1 except that the amount of isopentane was changed to 6.0 parts by mass and the rotation speed of the homogenizer was changed to 200 rpm. The volume average particle size of the capsule particles 2 was 8.0 μm.

<Manufacturing example 3>
[Preparation of capsule particles 3]
Capsule particles 3 were obtained in the same manner as in Production Example 1 except that the amount of isopentane was changed to 15.0 parts by mass and the rotation speed of the homogenizer was changed to 80 rpm. The volume average particle size of the capsule particles 3 was 33.5 μm.

<Manufacturing example 4>
[Preparation of primary kneaded product 1]
The materials shown in Table 1 below were kneaded with a closed mixer (volume 5 L) for 15 minutes to obtain a primary kneaded product 1. The amount to be charged was adjusted so that the following materials had the following ratio and the total amount was 3000 g. The rotation speed of the mixer was adjusted so that the material temperature during kneading was 60 ° C. or lower.

<Manufacturing Examples 5 and 6>
[Preparation of primary kneaded products 2 and 3]
The primary kneaded products 2 and 3 were prepared in the same manner as in Production Example 4 except that the amounts of NBR and solid resin particles to be blended were changed. Specifically, the amounts of NBR and solid resin particles to be blended were changed to 35% by mass and 35% by mass in Production Example 5 (primary kneaded product 2), respectively, and in Production Example 6 (primary kneaded product 3). , 30% by mass and 40% by mass.

<Manufacturing example 7>
[Preparation of primary kneaded product 4]
The primary kneaded product 4 was produced in the same manner as in Production Example 4, except that the materials used for producing the primary kneaded product were changed to the contents and ratios shown in Table 2 below.

<Manufacturing Examples 8 and 9>
[Preparation of primary kneaded products 5 and 6]
The primary kneaded products 5 and 6 were prepared in the same manner as in Production Example 7 except that the amounts of NBR and solid resin particles to be blended were changed. Specifically, in Production Example 8 (primary kneaded product 5), the amounts of NBR and solid resin particles to be blended were changed to 35% by mass and 35% by mass, respectively, and in Production Example 9 (primary kneaded product 6). , 30% by mass and 40% by mass.

<Manufacturing example 10>
[Preparation of primary kneaded product 7]
The primary kneaded product 7 was produced in the same manner as in Production Example 4, except that the materials used for producing the primary kneaded product were changed to the contents and ratios shown in Table 3 below.

<Manufacturing Examples 11 and 12>
[Preparation of primary kneaded products 8 and 9]
Primary kneaded products 8 and 9, respectively, were prepared in the same manner as in Production Example 10 except that the amounts of NBR and solid resin particles to be blended were changed. Specifically, the amounts of NBR and solid resin particles to be blended were changed to 30% by mass and 40% by mass in Production Example 11 (primary kneaded product 8), respectively, and in Production Example 12 (primary kneaded product 9). , 25% by mass and 45% by mass.

<Manufacturing Examples 13 and 14>
[Preparation of primary kneaded products 10 and 11]
The type of solid resin particles to be blended was changed to solid resin particles (trade name: PM-200 (material: polyethylene resin), average particle size 10.5 μm, Mitsui Chemicals, Inc.). Other than that, the primary kneaded product 10 (Production Example 13) and the primary kneaded product 11 (Production Example 14) were produced in the same manner as in Production Examples 5 and 6, respectively.

<Manufacturing example 15>
[Preparation of primary kneaded product 12]
The primary kneaded product 12 was produced in the same manner as in Production Example 4, except that the materials used for producing the primary kneaded product were changed to the contents and ratios shown in Table 4 below.

<Manufacturing Examples 16-18>
[Preparation of primary kneaded products 13 to 15]
The type of solid resin particles to be blended was changed to solid resin particles (trade name: MBX-5 (material: acrylic resin), average particle size 5.6 μm, Sekisui Chemical Co., Ltd.). Other than that, primary kneaded products 13, 14 and 15 (Production Examples 16, 17 and 18) were prepared in the same manner as in Production Examples 5, 6 or 15.

<Manufacturing Examples 19 to 21>
[Preparation of primary kneaded products 16-18]
The type of solid resin particles to be blended was changed to solid resin particles (trade name: Epostal M05 (material: melamine resin), average particle size 5.6 μm, Nippon Shokubai Co., Ltd.). Other than that, primary kneaded products 16, 17 and 18 (Production Examples 16 to 19) were prepared in the same manner as in Production Examples 5, 6 and 15, respectively.

<Manufacturing example 22>
[Preparation of primary kneaded product 19]
The primary kneaded product 19 was produced in the same manner as in Production Example 4, except that the materials used for producing the primary kneaded product were changed to the contents and ratios shown in Table 5 below.

[Example 1]
(Conductive shaft core preparation process)
A thermosetting resin (polyphenol resin) containing 10% by mass of carbon black is applied to a cylindrical substrate made of stainless steel with a diameter of 6 mm and a length of 252.5 mm, and the dried product is used as a conductive shaft core. Prepared as a body.

(Preliminary coating layer forming step)
-Step of Preparing Conductive Resin Composition The materials shown in Table 6 below were added to a closed mixer adjusted to 50 ° C. and kneaded for 15 minutes to obtain an A kneaded rubber composition.

Next, the materials shown in Table 7 below were kneaded for 10 minutes in a two-roll machine cooled to a temperature of 25 ° C. to obtain a B kneaded rubber composition (conductive resin composition).

-Preliminary coating layer forming step Next, using an extrusion molding apparatus equipped with a crosshead, the outer peripheral surface of the above-mentioned conductive shaft core is coated with the above-mentioned B kneaded rubber composition to a thickness of 1.0 mm. bottom. The roller after extrusion was heated at 160 ° C. for 1 hour in a hot air furnace to vulcanize the B kneaded rubber composition to form a rubber layer.

Next, both ends of the rubber layer were cut off to make the length of the rubber layer in the axial direction 224.2 mm. Subsequently, the rubber layer was heated at a temperature of 160 ° C. for 1 hour to prepare a roller having a pre-coating layer having a thickness of 3.5 mm (hereinafter, also referred to as “pre-coating roller”). By the heat generated by these vulcanization operations, the capsule particles in the B kneaded rubber composition were thermally expanded to form hollow resin particles.

(Polishing process)
The outer peripheral surface of the pre-covered roller was polished using a brand-cut type cylindrical grinding machine shown in FIG. Specifically, a pitrified grindstone was used as the polishing abrasive grains, the abrasive grains were green silicon carbide (GC), and the particle size was 100 mesh. The rotation speed of the precoating roller was 350 rpm, and the rotation speed of the polishing wheel was 2050 rpm. Polishing was performed by setting the intrusion (cutting) speed to 20 mm / min and the spark-out time (time at a cutting of 0 mm) to 0 seconds. As a result, a part of the surface of the hollow resin particles contained in the preliminary coating layer was ground to obtain a conductive roller having a conductive resin layer in which the openings of the bowl-shaped resin particles were exposed on the surface. The thickness of the conductive resin layer was adjusted to 1.5 mm. The crown amount of this conductive roller was 120 μm.

(Processing process)
The obtained conductive roller was heated in a hot air furnace at a temperature of 190 ° C. for 1 hour to obtain an electrophotographic roller 1. The following measurements and evaluations were performed on the electrophotographic roller 1.

(Average particle size of bowl-shaped resin particles and number of solid resin particles in contact with bowl-shaped resin particles)
Arbitrarily 10 bowl-shaped resin particles exposed on the surface of the electrophotographic roller 1 were selected. Then, the 10 bowl-shaped resin particles and the solid resin particles around the 10 bowl-shaped resin particles are focused by 20 nm each with a plane parallel to the plane of the projection portion orthographically projected onto the surface of the axis core as a cut plane (trade name). : FB-2000C, manufactured by Hitachi, Ltd.), and a cross-sectional image was taken while cutting out. For each of the 10 bowl-shaped resin particles obtained, a spherically approximated diameter was calculated based on each cross-sectional image, and the average value was taken as an average particle size based on the spherically approximated bowl-shaped resin particles. In addition, the number of solid resin particles in contact with the resin particles in each bowl shape was counted from the obtained cross-sectional images.
As a result, the average particle size of the bowl-shaped resin particles of the electrophotographic roller 1 by spherical approximation was 50.2 μm. The number of solid resin particles in contact with the bowl-shaped resin particles was 2.6.

(Arrangement of bowl-shaped resin particles and solid resin particles)
Arbitrarily 10 bowl-shaped resin particles exposed on the surface of the electrophotographic roller 1 were selected. Then, the 10 bowl-shaped resin particles and the solid resin particles around the 10 bowl-shaped resin particles are focused by 20 nm each with a plane parallel to the plane of the projection portion orthographically projected onto the surface of the axis core as a cut plane (trade name). : FB-2000C, manufactured by Hitachi, Ltd.), and a cross-sectional image was taken while cutting out. Based on each cross-sectional image, solid resin particles in contact with the outer wall surface of each bowl-shaped resin particle were extracted. Next, the centers of gravity of these solid resin particles were obtained from the cross-sectional images. From the obtained center of gravity and the cross-sectional image, it was determined whether the solid resin particles in contact with the outer wall surface of the resin particles in each bowl shape satisfy the above condition (v). Then, for the arbitrary 10 bowl-shaped resin particles, the average value of the number of solid resin particles in contact with the outer wall surface of the bowl-shaped resin particles satisfying the condition (v) confirmed by the above method is calculated. I asked. As a result, in the ten arbitrarily selected bowl-shaped resin particles contained in the conductive resin layer of the electrophotographic roller 1, the number of solid resin particles satisfying the above condition (v) is 2.6. there were.
Therefore, it was found that the bowl-shaped resin particles and the solid resin particles contained in the conductive resin layer of the electrophotographic roller 1 were arranged at positions satisfying the above conditions (iv) and (v).

In Tables 8 and 10 described later, "Y" indicates that the bowl-shaped resin particles and the solid resin particles satisfy the conditions (iv) and (v), and "N" indicates that the conditions (iv) and (v) are not satisfied. It was written as.

(Measurement of compressive elastic modulus in conductive resin layer and solid resin particles)
The compressive elastic modulus (pushing elastic modulus) of the electrophotographic roller 1 (more specifically, the conductive resin layer) was measured using a picodenter HM500 (trade name, manufactured by Fisher Instrument Co., Ltd.). As the indenter, an indenter (Vickers pyramid) having a square pyramid-shaped diamond indenter having a square base and a facing angle of 136 ° sandwiching the apex was used. The measurement was performed at the central portion and both end portions of the electrophotographic roller 1 in the longitudinal direction (positions of 90 mm each in the direction from the central portion to both ends). First, using a microscope, 10 points each of the non-existent parts of the solid resin particles were arbitrarily selected from the central part and both ends, and the compressive elastic modulus of a total of 30 points was measured. Then, an average value was calculated from the obtained 30 measured values, and the average value was taken as the compressive elastic modulus G of the conductive resin layer.

Next, using a microscope, 10 points each of the central portion and both end portions where the solid resin particles are exposed on the surface of the conductive resin layer surface are arbitrarily selected, and a total of 30 points are compressed. The elastic modulus was measured. Then, an average value was calculated from the obtained 30 measured values, and the average value was taken as the compressive elastic modulus J of the solid resin particles. When the solid resin particles exposed on the surface of the conductive resin layer were not present, the surface of the conductive resin layer was trimmed to expose the solid resin particles to the surface.
The G of the electrophotographic roller 1 measured by the above method was 0.5 MPa, and J was 30 MPa.
In Tables 8 and 10 described later, the case where the above G and J satisfy the relationship of G <J is described as "Y", and the case where the above G and J do not satisfy is described as "N".

(Image evaluation)
-As an evaluation device for evaluating the occurrence of a spot-like image due to abnormal discharge, HP Color LaserJet Enterprise CP4525n (trade name) manufactured by Hulet Packard Co., Ltd., which is an electrophotographic image forming device having the configuration shown in FIG. 7, is used as a process speed. Was used after high-speed modification so that the value was 370 mm / sec. The process cartridge has been changed to a spring that can be equipped with a charging roller having an outer diameter of 8.5 mm and can be pressed with 2.45 N (0.25 kgf) at one end and 4.9 N (0.5 kgf) at both ends. The laser printer was modified by appropriately adjusting the settings of the high-voltage power supply, the gears of the motor, and the paper transport. Further, by changing the fixing position of the developing blade and sandwiching a spacer between the developing blade and the process cartridge container, the amount of toner supported on the developing roller was adjusted to ^{0.50 mg / cm 2.}

The electrophotographic roller 1 was set as a charging roller in the process cartridge, and was acclimatized to a low temperature and low humidity environment having a temperature of 15 ° C. and a relative humidity of 10% for 24 hours, and then image evaluation was performed.

After outputting 20,000 images, a halftone image (an image in which a horizontal line having a width of 1 dot and an interval of 2 dots is drawn in a direction perpendicular to the rotation direction of the electrophotographic photosensitive member) was output. Then, the obtained halftone image was visually observed, and the presence or absence of a spot-like image due to abnormal discharge was evaluated based on the following criteria.

-Evaluation Criteria Rank 1: No spot-like images are found.
Rank 2: Only slight spot-like images are observed.
Rank 3: A spot-like image is partially recognized at the pitch of the charging roller, but there is no problem in practical use.
Rank 4: Pochi-shaped images are conspicuous, and deterioration in image quality is observed.
The evaluation result of the electrophotographic roller 1 was rank 1.

[Examples 2, 3, 10 to 18]
The electrophotographic rollers 2, 3, 10 to 18, respectively, were subjected to the same method as in Example 1 except that the primary kneaded product 1 shown in Table 7 was changed to the primary kneaded products 2, 3 and 10 to 18, respectively. It was prepared and measured and evaluated in the same manner as in Example 1. The result of the image evaluation of the electrophotographic rollers 2, 3, 10 to 12 was rank 1, and the result of the image evaluation of the electrophotographic rollers 13 to 15 was rank 2. Moreover, the result of the image evaluation of Examples 16 to 18 was rank 3.

[Examples 4 to 6]
In these examples, the type of binder shown in Table 6 above was changed to NBR (trade name: N222L, manufactured by JSR Corporation), and the sulfur was changed from 1.0 part to 1.2 parts. Further, the primary kneaded product 1 shown in Table 7 was changed to a primary kneaded product 4 in Example 4, a primary kneaded product 5 in Example 5, and a primary kneaded product 6 in Example 6. Except for these, rollers 4 to 6 for electrophotographic were prepared by the same method as in Example 1, and the same measurement and evaluation as in Example 1 were performed. The results of image evaluation of the electrophotographic rollers 4 to 6 were all rank 1.

[Examples 7 to 9]
In these examples, the type of binder shown in Table 6 above was changed to NBR (trade name: N250SL, manufactured by JSR Corporation), and sulfur was changed from 1.0 part to 0.8 part. Further, the primary kneaded product 1 shown in Table 7 was changed to a primary kneaded product 7 in Example 7, a primary kneaded product 8 in Example 8, and a primary kneaded product 9 in Example 9. Except for these, rollers 7 to 9 for electrophotographic were prepared by the same method as in Example 1, and the same measurement and evaluation as in Example 1 were performed. The results of image evaluation of the electrophotographic rollers 7 to 9 were all rank 1.

Table 8 below shows the respective components used in each example, the measurement and evaluation results of the obtained electrophotographic roller, and the like.

[Comparative Example 1]
In the preparation of the B kneaded rubber composition (conductive resin composition), the electrophotographic roller 19 was produced by the same method as in Example 1 except that the following points were changed. Specifically, the materials shown in Table 6 above are kneaded for 15 minutes in a closed mixer adjusted to 50 ° C., and then 6.0 parts by mass of capsule particles 1 and solid resin particles (commodity) are added to the kneaded product. Name: XM-220, average particle size 30.2 μm, 6.0 parts by mass of Mitsui Chemicals, Inc. were added as powder. Further, the materials shown in Table 9 below were added, and these materials were kneaded for 10 minutes in a two-roll machine cooled to a temperature of 25 ° C. to prepare a conductive resin composition.

The obtained electrophotographic roller 19 was measured and evaluated in the same manner as in Example 1. As a result, the average particle size of the bowl-shaped resin particles contained in the conductive resin layer of the electrophotographic roller 19 was 50.2 μm. The number of solid resin particles in contact with the bowl-shaped resin particles was 0. The G of the electrophotographic roller 19 was 0.5 MPa, and the J was 30 MPa.
Further, the result of the image evaluation of the electrophotographic roller 19 was rank 4.

[Comparative Example 2]
When the B kneaded rubber composition (conductive resin composition) was prepared, 12.0 parts by mass of the primary kneaded product 19 was added instead of adding 6.0 parts by mass of the capsule particles 1 as a powder. Made an electrophotographic roller 20 in the same manner as in Comparative Example 1. The obtained electrophotographic roller 20 was measured and evaluated in the same manner as in Example 1. The result of the image evaluation of the electrophotographic roller 20 was rank 4.

[Comparative Example 3]
The type of binder shown in Table 6 above was changed to NBR (trade name: N222L, manufactured by JSR Corporation), and the sulfur content was changed from 1.0 part to 1.7 parts. Further, the primary kneaded product 1 shown in Table 7 above was changed to the primary kneaded product 16. Except for these, roller 21 for electrophotographic photography was prepared in the same manner as in Example 1, and the same measurement and evaluation as in Example 1 were performed. The result of the image evaluation of the electrophotographic roller 21 was rank 4.
The components used in each comparative example, the measurement and evaluation results of the obtained electrophotographic roller, and the like are shown in Table 10 below.

1: Aperture (opening)
1a: Concave 2: Edge 2a: Convex 3: Bowl-shaped resin particles 4: Shell 4a: Outer wall surface 5: Solid resin particles 6: Binder 7: First projection circle 7a: Center of gravity 8 of the first projection circle : Second projection circle 8a: Center of gravity of second projection circle 9: Third projection circle 9a: Center of gravity of third projection circle 10: Center of gravity of first projection circle parallel to the axial direction of the axis core 11: A line segment passing through the center of gravity of the second projection circle and the center of gravity of the third projection circle 12: Conductive shaft core 13: Conductive resin layer 14: Conductive elastic layer 30: Charging roller 32 : Development roller 34: Transfer roller

Claims (6)

An electrophotographic roller having a conductive shaft core and a conductive resin layer as a surface layer on the shaft core.
The conductive resin layer contains a binder and a plurality of solid resin particles.
A bowl-shaped resin particle having an opening is held in a state where the opening is exposed on the surface of the electrophotographic roller.
The surface of the electrophotographic roller has a concave portion derived from the opening of the bowl-shaped resin particles and a convex portion derived from the edge of the opening of the bowl-shaped resin particles.
At least two of the solid resin particles are in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles.
When the bowl-shaped resin particles are orthographically projected onto the surface of the shaft core, the projection circle formed on the surface of the shaft core is defined as the first projection circle.
The solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are formed on the surface of the shaft core when the solid resin particles are projected onto the surface of the shaft core. When the projection circles are the second projection circle and the third projection circle, respectively.
The bowl-shaped resin particles and the solid resin particles in contact with the outer wall surface of the shell forming the recesses of the bowl-shaped resin particles are
At least a part of the second projection circle overlaps with the first projection circle, and at least a part of the third projection circle overlaps with the first projection circle, and
A line segment passing through the center of gravity of the second projection circle and the center of gravity of the third projection circle extends parallel to the axial direction of the axis, and intersects with a straight line passing through the center of gravity of the first projection circle. Positioned to have,
When the compressive elastic modulus of the conductive resin layer is G and the compressive elastic modulus of the solid resin particles is J, the following mathematical formulas (1) and (2) are satisfied.
Formula (1)
G <J
Formula (2)
0.1 MPa ≤ G ≤ 10 MPa. The roller for electrophotograph according to claim 1, wherein the average particle diameter of the bowl-shaped resin particles by spherical approximation is 10 μm or more and 100 μm or less. The electrophotographic roller according to claim 1 or 2, wherein the average particle diameter of the solid resin particles by spherical approximation is 1 μm or more and 50 μm or less. The roller for electrophotograph according to any one of claims 1 to 3, wherein the solid resin particles contain a resin selected from a polyethylene resin and an acrylic resin. A process cartridge having the electrophotographic roller according to any one of claims 1 to 4, and the process cartridge being detachably attached to and detachable from the main body of the electrophotographic image forming apparatus. An electrophotographic image forming apparatus comprising the roller for electrophotographic according to any one of claims 1 to 4.

Images