JP6971807B2 - Charging rollers and electrophotographic equipment - Google Patents

Description

The present invention relates to a charging roller used in an electrophotographic apparatus and the like, and an electrophotographic apparatus using the same.

In an electrophotographic apparatus such as a laser beam printer, a charging roller having an elastic layer is used to charge the photoconductor. In recent years, in order to reduce costs, a charging roller (hereinafter referred to as "polishing-less roller") has been manufactured, which eliminates the polishing process for shaping the surface of the elastic layer into a desired shape and reduces the manufacturing man-hours. There is.

However, it is difficult for the polishing-less roller to accurately control the outer diameter of the end portion of the elastic layer in the longitudinal direction. Therefore, when the polishing-less roller is used as the charging roller, the contact state between the polishing-less roller and the photosensitive drum may become unstable.

Patent Document 1 discloses a charging roller in which the hardness of the end portion is smaller than the hardness of the central portion in order to suppress the generation of a gap between the charging roller and the photoconductor in the central portion in the longitudinal direction. ..

Japanese Unexamined Patent Publication No. 2004-361843

The present inventors have studied the use of a polishing-less roller to which the technique according to Patent Document 1 is applied as a charging roller. As a result, it was possible to stabilize the contact state between the polishing-less roller and the photosensitive drum by increasing the contact area between the polishing-less roller and the photosensitive drum at the end in the longitudinal direction. However, when such a polishing-less roller is used as a charging roller for a long period of time, a concentration difference may occur at a position corresponding to the center and the end of the polishing-less roller in the longitudinal direction in the obtained electrophotographic image. rice field.

Therefore, one aspect of the present invention is aimed at providing a charging roller capable of providing a high-quality electrophotographic image for a long period of time and a method for manufacturing the same.

Further, another aspect of the present invention is aimed at providing an electrophotographic image forming apparatus that contributes to the formation of a high-quality electrophotographic image.

According to one aspect of the invention
A charging roller comprising a conductive support and an elastic layer on the conductive support.
The elastic layer is the only elastic layer and is composed of a single layer.
The elastic layer contains a binder resin and holds the elastic particles in an exposed state on the surface of the charged roller, and the surface of the charged roller has a convex portion derived from the elastic particles. death,
When the length of the elastic layer is L, the Martens hardness of the binder resin on the surface at a portion separated from the center of the elastic layer in the longitudinal direction by (3/8) L in the longitudinal direction is H1 (N / mm ² ). ,
The Martens hardness of the binder resin on the surface at the center of the elastic layer in the longitudinal direction is set to H2 (N / mm ² ).
When the Martens hardness of the elastic particles is H3 (N / mm ² ),
A charging roller in which H1, H2 and H3 satisfy the formula (1) is provided:
Equation (1)
H1 <H3 <H2.

According to another aspect of the present invention, an electrophotographic apparatus including the charging roller is provided.

According to still another aspect of the present invention, there is a method for manufacturing the charging roller.
(1) A step of preparing an unvulcanized rubber composition containing the unvulcanized rubber as a raw material of the binder resin and the elastic particles;
(2) A step of extruding the unvulcanized rubber composition on the conductive support while stretching the unvulcanized rubber composition to form a layer of the unvulcanized rubber composition;
(3) It has a vulcanization step of vulcanizing a layer of the unvulcanized rubber composition to obtain the elastic layer.
A method for manufacturing a charged roller is provided, wherein the step (3) includes a step of vulcanizing under different conditions depending on the position in the longitudinal direction of the layer of the unvulcanized rubber composition.

According to still another aspect of the present invention, there is a method for manufacturing the charging roller.
(1) A step of preparing an unvulcanized rubber composition containing the unvulcanized rubber as a raw material of the binder resin and the elastic particles;
(2) A step of extruding the unvulcanized rubber composition on the conductive support while stretching the unvulcanized rubber composition to form a layer of the unvulcanized rubber composition;
(3) A step of vulcanizing the layer of the unvulcanized rubber composition to form a layer of the vulcanized rubber composition, and (4) irradiating the surface of the layer of the vulcanized rubber composition with an electron beam. It has a step of curing to form the elastic layer,
The step (4) provides a method for manufacturing a charged roller, which comprises a step of irradiating an electron beam under different irradiation conditions depending on the position in the longitudinal direction of the layer of the vulcanized rubber composition.

According to one aspect of the present invention, it is possible to obtain a charging roller capable of providing a high-quality electrophotographic image for a long period of time. Further, according to another aspect of the present invention, it is possible to obtain an electrophotographic image forming apparatus that contributes to the formation of a high-quality electrophotographic image.

It is a schematic diagram which shows the cross section in the direction orthogonal to the longitudinal direction of an example of a charging roller. It is a schematic diagram which shows the outer diameter shape of an example of a charging roller. In order to explain the mechanism for suppressing the difference in the central end of the image density, it is a schematic diagram showing the surface state of the contact portion of the charging roller with the photoconductor, and (a) shows the state at the time of non-contact. b) is the state at the time of contact at the end E described later, (c) is the state at the time of contact at the center in the longitudinal direction, and (d) is the state of the elastic layer surface within the contact width at the time of contact. Is shown. (A) is a schematic configuration diagram of an example of a crosshead extruder, and (b) is a partial schematic diagram of the vicinity of the crosshead extrusion port. It is a block diagram which shows typically an example of the electrophotographic apparatus which has a charging roller. It is a schematic diagram for demonstrating a preferable form of a convex part. It is explanatory drawing of the electron beam irradiation apparatus.

As used herein, the term "end" with respect to a charged roller means the longitudinal end of the elastic layer. Further, the longitudinal direction means a direction parallel to the central axis of the conductive support of the charging roller.

FIG. 1 shows a schematic cross-sectional view of an example of a charging roller according to the present invention. The charging roller includes a conductive support 11 and an elastic layer 12 formed on the conductive support, particularly on the outer peripheral surface of the conductive support. In the charging roller, this elastic layer is the only elastic layer and is composed of a single layer. For example, the charging roller can consist of a conductive support and just one elastic layer on top of the conductive support.

The outer diameter shape of the charging roller is shown in FIG. The elastic layer 12 contains a binder resin. The elastic layer holds the elastic particles in an exposed state on the surface of the charging roller, particularly over the entire outer peripheral surface of the elastic layer. The surface of the charged roller has a protrusion 21 derived from elastic particles.

Martens hardnesses H1, H2 and H3 are defined as follows. The length of the elastic layer in the longitudinal direction is L.
H1 (N / mm ² ): Martens hardness of the binder resin on the surface at a portion of the elastic layer 12 separated from the center in the longitudinal direction (part C) by (3/8) L in the longitudinal direction. However, H1 has two portions, a portion E1 separated by (3/8) L from the center of the elastic layer in the longitudinal direction toward one end of the elastic layer, and a portion E2 separated by (3/8) L toward the other end. Each part is defined. H1 defined for E1 is referred to as "H1 (1)", and H1 defined for E2 is referred to as "H1 (2)".
H2 (N / mm ² ): Martens hardness of the binder resin on the surface of the elastic layer 12 at the center in the longitudinal direction.
H3 (N / mm ² ): Martens hardness of elastic particles contained in the elastic layer 12.

Hereinafter, the portions E1 and E2 may be collectively referred to as "end portion E", and H1 may be referred to as "martens hardness of the binder resin of the end portion E". Further, in the following, when the term "central portion" is simply used, it means the central portion in the longitudinal direction of the elastic layer.

The Martens hardness H3 of the elastic particles contained in the elastic layer 12 is larger than the Martens hardness H1 of the binder resin at the end E and smaller than the Martens hardness H2 of the binder resin at the center. That is,
Equation (1)
H1 <H3 <H2
Is satisfied. Equation (1) holds for any of the H1s defined for the portions E1 and E2, i.e., whether H1 is H1 (1) or H1 is H1 (2).

The present inventors estimated the mechanism for suppressing the difference in the central edge of the image density due to the increase in the stain on the edge by the charging roller according to the present invention as follows.
FIG. 3 schematically shows the surface state when the charging roller comes into contact with the photoconductor. FIG. 3A is a schematic view of a state in which the charged roller is not in contact with the photoconductor 31 when observed from a direction orthogonal to the longitudinal direction of the charged roller. FIGS. (B) and (c) are schematic views when the surface state when the end portion E and the central portion of the charging roller are in contact with the photoconductor 31 is observed from the same direction, respectively. Further, FIG. 3D is a schematic view showing the state of the surface of the elastic layer within the contact width when the charging roller comes into contact with the photoconductor.

At the end E of the charging roller, the maltens hardness H3 of the elastic particles 32 is larger than the maltens hardness H1 of the binder resin 33. Therefore, as shown in FIG. 3B, the binder resin 33 is deformed and the elastic particles 32 sink into the binder resin at the time of contact with the photoconductor 31, so that the contact area of each elastic particle with the photoconductor is small. ..

At the central portion of the charging roller, the maltens hardness H3 of the elastic particles 32 is smaller than the maltens hardness H2 of the binder resin 33. Therefore, as shown in FIG. 3C, the elastic particles 32 are deformed, and the contact area of each elastic particle with the photoconductor becomes large.

On the other hand, the contact width formed by the charging roller is wider at the end portion E than at the central portion as shown in FIG. 3 (d). This is because the Martens hardness H1 of the binder resin at the end E is smaller than the Martens hardness H2 of the binder resin at the center, and the amount of deformation of the elastic layer is larger at the end E than at the center. Therefore, the number of elastic particles in contact with the photoconductor is larger at the end E than at the center.

As described above, in the contact portion 34 of the end portion E, the contact area of the individual elastic particles is small because the elastic particles sink into the binder resin, but the contact width is wide, so that the number of particles in contact is large. many. Further, in the contact portion 35 in the central portion, the contact area of the individual elastic particles is large because the elastic particles are deformed, but the contact width is narrow, so that the number of particles in contact is small. In such a contact state, the difference in the center end of the contact area within the contact width with the photoconductor becomes small, so that the difference in the center end of stains caused by toner, external additives, etc. also becomes small, and the image It is presumed that the difference in the central end of the concentration can be suppressed.

The Martens hardness of the binder resin on the surface of the elastic layer decreases or is constant (does not increase) from the center C to each end in the longitudinal direction of the elastic layer as the distance from the center C increases.

In order to reduce the difference at the central end of the contact area, it is necessary to form a convex portion where the elastic particles are exposed. Since the particles are elastic, when they come into contact with the photoconductor, the elastic particles sink into the binder resin at the end E and can be deformed at the center. The exposed elastic particles allow the elastic particles to be deformed. Since the convex portion formed by the elastic particles is formed, the elastic particles can be deformed and the elastic particles can be submerged in the binder resin when they come into contact with the photoconductor.

The Martens hardness H1 of the binder resin at the end E of the charging roller (when H1 is either H1 (1) or H1 (2)), the Martens hardness H2 of the binder resin at the center, and the Martens hardness H3 of the elastic particles are , It is preferable to satisfy the formulas (2) and (3).
Equation (2)
5 ≦ H3-H1.
Equation (3)
5 ≦ H2-H3.

When the formula (2) is satisfied, the difference between the Martens hardness H3 of the elastic particles and the Martens hardness H1 of the binder resin at the end E is ^{smaller than 5 N / mm 2, and} when it comes into contact with the photoconductor, At the end E, the elastic particles sink more into the binder resin. Therefore, the contact area of the end E with the individual elastic particles is further reduced, and the difference in the center end of the contact area can be reduced, so that the difference in the center end of the image density can be suppressed more effectively.

If the formula (3) is satisfied, the difference between the Martens hardness H2 of the binder resin in the central portion and the Martens hardness H3 of the elastic particles is ^{smaller than 5 N / mm 2} , and the center at the time of contact with the photoconductor. The elastic particles come into contact with the photoconductor in the portion and are further deformed. Therefore, the contact area of the individual elastic particles in the central portion is further increased, and the difference in the central end portion of the contact area can be reduced, so that the difference in the central end portion of the image density can be suppressed more effectively.

Further, the Martens hardness H1 of the binder resin at the end E of the charging roller (when H1 is either H1 (1) or H1 (2)) and the Martens hardness H2 of the binder resin at the center are given by the formula (4). It is preferable to satisfy (5).
Equation (4)
2 ≦ H1.
Equation (5)
H2 ≦ 60.

If H1 (and therefore H2) is 2 N / mm ² or more, toner, an external additive, etc. are embedded in the binder resin at the end E to increase stains, which causes a stepped image adverse effect at the end. , It is easy to effectively suppress the difference in the central end of the image density. If H2 (and therefore H1 is also) 60 N / mm ² or less, the toner is cracked and adheres to the periphery of the deformed elastic particles, resulting in a circular image (hereinafter referred to as “potty”). Is easy to effectively suppress.

Further, the Martens hardness H3 of the elastic particles preferably satisfies the formula (6).
Equation (6)
10 ≦ H3 ≦ 50.

When the Martens hardness H3 of the elastic particles is 10 N / mm ² or more, it is possible to easily prevent toner, an external additive, or the like from being embedded in the elastic particles to increase stains. Therefore, it is possible to more effectively suppress the image adverse effect of step unevenness caused by this stain. Further, since the end portion E has a wide contact width and the end portion E having many apparent elastic particles within the contact width is particularly reduced in stains, the difference in the central end portion of the image density can be suppressed more effectively. When the Martens hardness H3 of the elastic particles is 50 N / mm ² or less, the toner stains due to the toner cracked by the elastic particles at the time of contact with the photoconductor can be reduced, and the harmful effects of the pot-shaped image can be suppressed more effectively. .. In addition, the amount of toner embedded in the elastic layer is reduced, and dirt is reduced especially at the end portion having a wide contact width, so that the difference in the central end portion of the image density can be suppressed more effectively.

Hereinafter, preferred embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

The charging roller of the present invention is suitable as a polishing-less roller, but is not limited to this, and may be a charging roller in which the elastic layer is polished. In either case, the above mechanism can work effectively. Further, the charging roller of the present invention may or may not have a crown shape (crown amount is zero), and may further have an inverted crown shape.

<Charging roller>
The charging roller typically consists of a conductive support and a conductive elastic layer formed on the conductive support. Hereinafter, each element constituting the charging roller will be described in order.

(Conductive support)
The conductive support may be any as long as it has conductivity, can support the elastic layer, and can maintain the strength as a charging roller. The conductivity of the conductive support can be appropriately set, and can be appropriately set within a range known as the conductivity of the conductive support of the charging roller for electrophotographic.

(Elastic layer)
The elastic layer contains a binder resin and holds the elastic particles in an exposed state on the surface of the charged roller. The elastic layer is typically conductive. The conductivity of the elastic layer can be appropriately set, and can be appropriately set within a range known as the conductivity of the elastic layer of the charging roller for electrophotographic.

(Observation method of elastic particles)
Elastic particles are exposed on the surface of the charging roller. The presence or absence of exposure of elastic particles can be confirmed by observing the surface of the charged roller using a confocal microscope (product name: OPTELICS HYBRID, manufactured by Lasertec Co., Ltd.). At this time, measurement conditions of 20 times the objective lens, 1024 pixels of pixels, and a height resolution of 0.1 μm can be adopted. It suffices if it can be confirmed that at least one elastic particle is not covered with the binder resin on the surface of the elastic layer in the field of view when the elastic layer is observed under the above-mentioned measurement conditions. In this field of view, it is preferable that five or more exposed elastic particles are present.

The surface of the charged roller has protrusions derived from elastic particles. Therefore, the exposed elastic particles form convex portions on the roller surface. The height of the convex portion is not particularly limited. The presence or absence of the convex portion can be confirmed with a confocal microscope (product name: OPTELICS HYBRID, manufactured by Lasertec Co., Ltd.). At this time, measurement conditions of 20 times the objective lens, 1024 pixels of pixels, and a height resolution of 0.1 μm can be adopted. A preferred form of the convex portion, particularly a preferred height, will be described with reference to FIG. First, a razor is put on the surface of the elastic layer in which the elastic particles 32 forming the convex portion are present, and the rubber piece 60 containing the elastic particles is cut out. Then, the rubber pieces are cut with a razor so that the elastic particles are cut from the normal direction of the surface of the elastic layer. The cut surface (cross section along the normal direction of the surface of the elastic layer) is schematically shown in FIG. In such a cut surface, a straight line 62 is drawn which is a point belonging to the surface of the elastic layer formed of the binder resin and passes through two points 61a and 61b in contact with the elastic particle. The straight line 63 is extended vertically from the straight line 62, and the longest distance from the straight line 62 to the contour line when the straight line 63 intersects the contour line of the elastic body particle is set to the height h. can. It is preferable that the average value of the height h of all the exposed elastic particles is 1.0 μm or more in the visual field when observed under the above-mentioned measurement conditions.

From the viewpoint of cost reduction by simplifying the production process, there is only one elastic layer, and it is necessary to consist of a single layer. The thickness of the elastic layer is preferably 0.8 mm or more and 4.0 mm or less, particularly preferably 1.2 mm or more and 3.0 mm or less in order to secure the contact width with the photoconductor.

(Measurement method of Martens hardness of binder resin)
The Martens hardness of the binder resin can be measured in a 23 ° C. and 55% RH (relative humidity) environment using a micro-hardness measuring device (trade name: Picodenter HM500, manufactured by Fisher Instruments Co., Ltd.). As the indenter for measurement, a square pyramidal diamond may be used. The pushing speed is a condition of the equation (7).
Equation (7)
dF / dt = 0.1mN / 10s
(F represents force and t represents time).

A rubber piece in the shape of a kamaboko (the curved surface of which corresponds to the outer peripheral surface of the elastic layer) is cut from the elastic layer, and the rubber piece is cut from the normal direction with respect to the surface of the elastic layer to create a thin piece. The portion of the elastic layer forming the flakes is defined as a region between two planes orthogonal to the axis of rotation of the roller, respectively, in a position in the direction of the axis of rotation of the roller. Then, the portion of the elastic layer forming the flakes is surrounded by the following elements in each of these two planes. That is, an arc forming the outer circumference of the elastic layer; a string corresponding to the arc; and two straight lines orthogonal to the string. However, the two intersections where these two straight lines intersect with the chord are at the target positions with the midpoint of the chord as the boundary.

Using the microscope attached to the micro-hardness measuring device, confirm that there are no elastic particles on the cross-sectional portion of the elastic layer surface (peripheral surface) of the thin section. After that, an indenter was applied to the binder resin forming the elastic layer surface from the normal direction of the elastic layer surface, and the hardness when the indenter was pushed in with a force of 0.04 mN (the pushing force and the indenter were embedded). Extract the surface area ratio of the part, N / mm ² ).

At each of the end portions E (parts E1 and E2), the values measured at 6 points (6 points at intervals of 60 ° in the circumferential direction) are averaged so that the positions in the circumferential direction are not biased. Even in the central portion (C), measurements are made at 6 points so that the positions in the circumferential direction are not biased, and the values are averaged. As a result, the Martens hardness H1 (1) of the binder resin of the portion E1, the Martens hardness H1 (2) of the binder resin of the portion E2, and the Martens hardness H2 of the binder resin in the central portion are obtained.

(Measurement method of Martens hardness of elastic particles)
The Martens hardness of the elastic particles is measured by applying an indenter to the exposed elastic particles present on the surface of the charging roller using the same equipment and measurement conditions as the Martens hardness of the binder resin. However, the step of confirming that the elastic particles are not present on the cross-sectional portion of the elastic layer surface (peripheral surface) by using the microscope provided in the micro-hardness measuring device is unnecessary.
This is performed for 10 elastic particles exposed in each of the partial E1 and E2 and the central portion, and the obtained values (30 points in total) are averaged to obtain the Martens hardness of the elastic particles. be able to.

(Internal hardness of elastic layer)
The MD-1 hardness, which indicates the internal hardness of the elastic layer, is not particularly limited, but may be about 60 ° to 80 °. The measurement can be performed in the peak hold mode at 23 ° C. and 55% RH environment using a micro hardness tester MD-1 type (product name: MD-1 capa, manufactured by Polymer Meter Co., Ltd.). More specifically, the charging roller is placed on a metal plate, and a metal block is placed to easily fix the charging roller so that it does not roll. Then, the measurement terminal is accurately pressed against the center of the elastic layer from the normal direction with respect to the metal plate (the center in the direction orthogonal to the longitudinal direction of the elastic layer when viewed from the normal direction), and the peak is measured for 5 seconds. Read the value. This was measured at 6 points each at the end E (parts E1 and E2) of the elastic layer and at the center so that there was no bias in the circumferential position, and the average value of the obtained measured values was measured at the end E (part E1). And E2) and MD-1 hardness at the center.

(Binder resin)
As the binder resin of the elastic layer, for example, an elastomer composition can be used. The elastomer composition is a composition obtained by appropriately blending a raw material elastomer (an elastomer that has not been vulcanized) with a compounding agent such as a conductive agent and a cross-linking agent, and appropriately vulcanizing the composition.

A conductive elastomer composition can be used to obtain a conductive elastic layer. The conductive mechanism of the conductive elastomer composition is roughly classified into an ionic conductive mechanism and an electronic conductive mechanism. The conductive elastomer composition of the ionic conductivity mechanism generally contains a polar rubber typified by chloroprene rubber and acrylonitrile-butadiene rubber, and an ionic conductive agent. This ion conductive agent is an ion conductive agent that is ionized in the polar rubber and has a high mobility of the ionized ions.

As the conductive elastomer composition by the electron conductive mechanism, a composite in which conductive particles are dispersed in the elastomer is used. Examples of conductive particles include Ketjen Black EC (trade name: manufactured by Lion Specialty Chemicals Co., Ltd.) and conductive carbon black such as acetylene black; SAF (Super Abrasion Furnace), ISAF (Intermediate SAF), HAF. (High Abrasion Furnace), FEF (Fast Extruding Furnace), GPF (General Purpose Furnace), SRF (Semi-Reinforcing Furnace), FT (Fine Thermal), MT (Medium Thermal) carbon black for rubber; Examples include carbon black for color (ink), pyrolysis carbon black, natural graphite, artificial graphite; metals and metal oxides such as tin oxide, titanium oxide, zinc oxide, copper and silver, and mixtures thereof.

The blending amount of these conductive particles can be appropriately selected depending on the type of the raw material elastomer, the conductive particles, and other blending agents so that the conductive elastic layer has a desired electric resistance. For example, the amount may be 0.5 parts by mass or more, 100 parts by mass or less, preferably 2 parts by mass or more, 60 parts by mass or less, etc. with respect to 100 parts by mass of the polymer (raw material elastomer).

It is preferable that the conductive particles do not have large convex portions, and it is preferable to use particles having an average particle diameter of 10 nm to 300 nm. The average particle size of the conductive particles is the "length average particle size" obtained by the following method. First, the cross section of the conductive particles was observed with a scanning electron microscope (product name: JEOL LV5910, manufactured by JEOL Ltd.), an image was taken, and the photographed image was image analysis software (product name: Image-Pro Plus, Planetron). Analyze using (manufactured by the company). The analysis calibrates the number of pixels per unit length from the micron bar at the time of photography, measures the directional diameter from the number of pixels on the image for 100 particles randomly selected from the photograph, and arithmetically average particles. Obtain the diameter and use it as the average particle diameter of the conductive particles.

Further, the elastomer composition may contain other conductive agents, fillers, processing aids, antiaging agents, cross-linking aids, cross-linking accelerators, cross-linking accelerators, cross-linking retarders, dispersants and the like. can.

A thermoplastic elastomer can be used as the elastomer composition, but in particular, a rubber composition containing isoprene rubber, chloroprene rubber, butadiene rubber, acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber, styrene-butadiene-styrene rubber and the like. The thing is preferably used. These rubbers (unvulcanized state) have a double bond derived from the butadiene skeleton, and when vulcanizing the binder resin using the above rubber, vulcanization is effective with the cleavage of the double bond. You can proceed to. Therefore, it is preferable to use the above rubber because when the vicinity of the central portion of the elastic layer is selectively vulcanized, the Martens hardness at that portion can be easily increased selectively.

(Elastic body particles)
Examples of the elastic particles include resin particles made of at least one resin selected from phenol resin, nylon resin, acrylic resin, urethane resin, silicone resin, polyacrylonitrile, polypropylene and the like. In particular, elastic particles made of urethane resin or silicone resin, which have high heat resistance and whose Martens hardness does not easily change even after heat treatment, are preferable.

The blending amount of the elastic particles can be 2 parts by mass or more, 70 parts by mass or less, preferably 5 parts by mass or more, 50 parts by mass or less, etc. with respect to 100 parts by mass of the raw material elastomer (raw material rubber).

The average particle size of the elastic particles is not particularly limited, but is preferably about 6 μm or more and 30 μm or less. When the average particle size is 6 μm or more, the elastic particles are exposed on the surface of the charged roller to form a convex portion, the difference in the central end of the contact area is reduced, and the difference in image density between the end and the central portion is reduced. Is easy. Further, when the average particle size is 30 μm or less, it is easy to reduce the spot-like stains due to the accumulation of toner around the elastic particles.

The average particle size of the elastic particles is the “length average particle size” and can be measured in the same manner as the average particle size of the conductive particles.

<Manufacturing method of charging roller>
It is preferable to use the surface of the elastic layer formed by crosshead extrusion as it is as the surface of the elastic layer having the convex portion where the elastic particles are exposed, in order to simplify the production process. No polishing step is required to polish the elastic layer. Specifically, using a crosshead extrusion molding machine, the unvulcanized rubber composition can be molded while being pressed by a core metal as a conductive support. The unvulcanized rubber composition contains unvulcanized rubber as a raw material for a binder resin and elastic particles, and may appropriately contain a compounding agent such as a conductive agent and a cross-linking agent. The unvulcanized rubber composition and the core metal having a predetermined length are simultaneously fed into the cross-head extruder, and the unvulcanized rubber composition having a predetermined thickness is evenly coated on the outer peripheral surface of the core metal. The unvulcanized rubber roller is extruded from the outlet of the crosshead.

FIG. 4A is a schematic configuration diagram of the crosshead extruder 4. The crosshead extruder 4 is an apparatus for manufacturing an unvulcanized rubber roller 43 having a core metal 41 in the center by evenly covering the core metal 41 with the unvulcanized rubber composition 42 over the entire circumference thereof. be.

The crosshead extruder 4 has a crosshead 44 to which a core metal 41 and an unvulcanized rubber composition 42 are fed, a transport roller 45 to feed the core metal 41 to the crosshead 44, and an unvulcanized rubber to the crosshead 44. A cylinder 46 for feeding the composition 42 and a cylinder 46 are provided.

The transport roller 45 continuously feeds a plurality of core metal 41s into the crosshead 44 in the axial direction. The cylinder 46 is provided with a screw 47 inside, and the unvulcanized rubber composition 42 is fed into the crosshead 44 by the rotation of the screw 47.

When the core metal 41 is fed into the crosshead 44, the entire circumference is covered with the unvulcanized rubber composition 42 fed into the crosshead from the cylinder 46. Then, the core metal 41 is sent out from the die 48 at the outlet of the crosshead 44 as an unvulcanized rubber roller 43 whose surface is coated with the unvulcanized rubber composition 42. By molding the unvulcanized rubber composition so that the thickness is thinner than the gap of the extrusion port of the cross head, that is, by extruding the unvulcanized rubber composition while stretching it, the elastic particles are formed into an elastic layer. It is exposed to the surface and then to the surface of the charged roller, forming a protrusion.

FIG. 4B shows a partial schematic diagram near the crosshead extrusion port. The inner diameter of the die of the crosshead extrusion port D, and the outer diameter of the longitudinal center of the unvulcanized rubber roller d, the outer diameter of the core upon the d _0, "(longitudinal center of the unvulcanized rubber composition _{(D-d 0} ) / (D-d ₀ ) corresponding to "thickness of) ÷ (gap of extrusion port)" is defined as the take-back rate (%). When this value is 100%, it means that the gap between the extrusion ports and the thickness of the unvulcanized rubber composition are the same. The smaller the take-up rate, the more the molding is performed while stretching, and the convex portion due to the exposed elastic particles is likely to be formed. As the take-back rate, for example, 95% or less and 85% or more can be exemplified as a value at which the elastic particles can be appropriately exposed to form a convex portion.

The crown amount CR indicating the crown shape is given by the formula (8) when the outer diameter of the central portion of the elastic layer is D2 (μm) and the outer diameters of both ends are D1 (μm) and D3 (μm), respectively. It is a value calculated in.
Equation (8)
CR = D2- (D1 + D3) / 2.
The amount of crown is not particularly limited, but can be exemplified to be about 60 μm or more and 280 μm or less.

The take-up rate can be adjusted by changing the relative ratio between the core metal feed rate by the transport roller 45 and the unvulcanized rubber composition feed rate from the cylinder 46. For example, the feed rate of the unvulcanized rubber composition 42 from the cylinder 46 to the crosshead 44 is constant. Then, by adjusting the core metal feed rate, the wall thickness of the unvulcanized rubber composition 42 is determined according to the ratio of the feed rate of the core metal 41 to the feed rate of the unvulcanized rubber composition unit 42. By molding while changing the wall thickness, the unvulcanized rubber composition can be molded into a crown shape. In this way, the unvulcanized rubber roller 43 can be obtained.

Next, the unvulcanized rubber roller is vulcanized to obtain a vulcanized rubber roller. At that time, by devising a heating method, it is possible to make a difference in hardness in the longitudinal direction of the elastic layer. Further, after obtaining the vulcanized rubber roller, it is possible to make a difference in hardness in the longitudinal direction of the elastic layer by devising the surface treatment. Examples of such a heat treatment method or a surface treatment method include the following methods (1), (2), and (3).

(1) The rubber layer of the unvulcanized rubber roller (the layer of the unvulcanized rubber composition corresponding to the elastic layer) is vulcanized under different conditions depending on its position in the longitudinal direction. Here, the layer of the unvulcanized rubber composition is vulcanized by heating it in two stages. In the first stage of heating, the entire rubber layer of the unvulcanized rubber roller is heated. In the second step of heating, the heating conditions of the central portion of the rubber layer (the portion corresponding to the central portion C of the elastic layer) and the heating conditions of the portions corresponding to the portions E1 and E2 are different. By further advancing the vulcanization of the central portion, the hardness of the central portion is further increased.

Specifically, for example, the following is performed. That is, the unvulcanized rubber roller is placed in a hot air furnace, vulcanized for about 1 hour to 1 hour and 30 minutes, and the vulcanized rubber roller is taken out from the hot air furnace. After that, while rotating the vulcanization rubber roller at 60 rpm, hot air is blown from a position about 10 cm away to the center of the rubber layer (the part corresponding to the center C of the elastic layer) for about 15 to 45 minutes for additional sulfur. I do. At this time, the heat propagation by the heat gun proceeds from the central portion to the end portion. Therefore, the Martens hardness distribution of the rubber layer is highest in the central part and becomes smaller toward the end part. The temperature of the hot air is measured at a position 10 cm away from the heat gun using a thermocouple.

(2) The entire rubber layer of the unvulcanized rubber roller is heated to obtain a vulcanized rubber roller. Next, the rubber layer of the vulcanized rubber roller is surface-treated (electron beam irradiation or the like) under different conditions depending on its position in the longitudinal direction to be cured. As a result, the degree of curing treatment of a part of the rubber layer (including the portion corresponding to the central portion C) is made higher than the degree of curing treatment of the remaining portion (including the portions corresponding to the portions E1 and E2).

For example, when the surface treatment of the layer of the vulcanized rubber composition is performed by irradiating the electron beam, the electron beam is irradiated under different irradiation conditions depending on the position in the longitudinal direction of the layer of the vulcanized rubber composition. The method can be mentioned. Specifically, for example, the dose of the electron beam received by the surface of the layer of the vulcanized rubber composition is smaller on the end side than the central portion in the longitudinal direction of the layer of the vulcanized rubber composition. Irradiate the line.

More specifically, for example, the following surface treatment methods can be mentioned. That is, the unvulcanized rubber roller is placed in a hot air furnace and vulcanized for about 1 hour to obtain a vulcanized rubber roller. Next, the surface of the layer of the vulcanized rubber composition of the vulcanized rubber roller is irradiated with an electron beam to perform surface treatment.

First, an electron beam irradiation device used for surface treatment with an electron beam will be described with reference to FIG. 7. The electron beam irradiation device shown in FIG. 7 has a filament 71 as an electron beam source for generating an electron beam in the electron beam generating unit 70. In order to prevent the electrons 73 generated in the filament 71 from colliding with gas molecules and losing energy, the electron beam generating unit 70 is usually 1 × 10 ^-6 Pa to ^{1 × 10 − by a vacuum pump (not shown). The} degree of vacuum is maintained at 7 Pa. Further, the electron beam irradiation device has an acceleration tube 72 for accelerating the electron 73 generated in the filament 71 in the electron beam generation unit 70. Further, the electron beam irradiation device is provided with a chamber 78 for processing the vulcanized rubber roller 75, which is an object to be processed. The vulcanized rubber roller 75 to be processed is conveyed in the chamber 78 in the direction of arrow 76 at a predetermined speed and while rotating in the direction of arrow 77.

A foil 74 emitted from the filament 71 and accelerating by the electron beam generating unit 70 is provided between the chamber 78 and the electron beam generating unit 70. The foil 74 separates the vacuum atmosphere of the electron beam generating portion 70 from the atmosphere inside the chamber 78. Therefore, the foil 74 needs to be made of a material that has airtightness and mechanical strength that can secure the vacuum state of the electron beam generating portion 70 and that allows the electron beam to pass through. Examples of the foil that can satisfy such characteristics include aluminum foil, titanium foil and beryllium foil. Examples of the electron beam irradiation device having such a configuration include "EC150 / 45/40 mA" (trade name, manufactured by Iwasaki Electronics Co., Ltd.). The length of the foil portion in the direction along the direction of the arrow 76 is, for example, 20 mm.

A method for obtaining a charged roller according to this embodiment by using such an electron beam irradiation device will be described below.

In order to make the Martens hardness H2 of the binder resin in the central portion larger than the Martens hardness H1 of the binder resin in the end portion E, the number of electron beam irradiations in the central portion is increased more than the number of electron beam irradiations in the end portion E.

First, the elastic layer is conveyed in the chamber 78 in the direction of arrow 76 at a predetermined speed, for example, 10 mm / sec while rotating the vulcanizing rubber roller 75 in the direction of arrow 77 at a predetermined speed, for example, 100 rpm. The electron beam is irradiated over the entire longitudinal direction of the paper, that is, the entire depth direction of the paper surface in FIG. 7 (first surface treatment step).

Next, for the vulcanized rubber roller that has undergone the first surface treatment step, the regions from both ends to (1/8) L are each covered with aluminum foil to prevent the electron beam from hitting the vulcanized rubber roller, and then the first surface treatment step. The surface treatment is performed in the same manner as above (second surface treatment step).

Further, for the vulcanized rubber roller that has undergone the second surface treatment step, the region from both ends to (2/8) L is covered with aluminum foil to prevent the electron beam from hitting the vulcanized rubber roller, and then the first surface treatment step is performed. Surface treatment is performed in the same manner (third surface treatment step).

Furthermore, for the vulcanized rubber roller that has undergone the third surface treatment step, the region from both ends to (3/8) L is covered with aluminum foil to prevent the electron beam from hitting the vulcanized rubber roller, and then the first surface treatment step. The surface treatment is performed in the same manner as in the above to obtain a charged roller according to this embodiment (fourth surface treatment step).

When the electron beam irradiation condition is an acceleration voltage of 80 kV and the electron current is 40 mA using the electron beam irradiation device as described above, the dose of the electron beam received by the surface of the central portion in the longitudinal direction of the layer of the vulture rubber composition is measured. It can be 1350 kGy.

(3) The rubber layer of the unvulcanized rubber roller is heated and vulcanized under different conditions depending on its position in the longitudinal direction. At this time, the rubber layer is heated so that the temperature of a part (including the portion corresponding to the central portion C) is higher than the temperature of the remaining portion (including the portions corresponding to the portions E1 and E2).

Specifically, for example, the following is performed. That is, the unvulcanized rubber roller is put into the infrared heating device. In the infrared device, 14 infrared heating lamps (product name: HYL25, manufactured by Hi-Beck Co., Ltd.) are installed at equal intervals along the longitudinal direction of the elastic layer. The infrared heating lamp is installed so that the unvulcanized rubber roller can be irradiated with infrared rays from a direction orthogonal to the axis thereof. Further, the distance between the surface of the elastic layer and the infrared heating lamp is constant at 60 mm. The output of this infrared lamp is reduced from the center to the end, and infrared irradiation is performed for about 10 minutes to 1 hour while rotating the unvulcanized rubber roller at 60 rpm.

Among these methods, the method (1), particularly vulcanization using a hot air furnace, is preferable because the manufacturing process is simple.

According to the above method, it is possible to obtain an elastic layer in which the maltens hardness H2 of the binder resin in the central portion is larger than the maltens hardness H1 of the binder resin in the end portion E. Further, the Martens hardness of the binder resin on the surface of the elastic layer can be reduced (may be partially constant) from the central portion C to each end portion in the longitudinal direction of the elastic layer as the distance from the central portion C increases.

Examples of the binder resin that can be suitably used for the above method include the above-mentioned isoprene rubber, chloroprene rubber, butadiene rubber, acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber, styrene-butadiene-styrene rubber and the like. A rubber composition containing rubber can be mentioned.

<Electrographer>
Subsequently, a block diagram (FIG. 5) of an example of an electrophotographic apparatus having a charging roller of the present invention will be used to explain an electrophotographic image forming process. The photosensitive member 51 as a charged body has a conductive support 51b and a photosensitive layer 51a formed on the support 51b, and has a cylindrical shape. Then, it is driven at a predetermined peripheral speed around the axis 51c in a clockwise direction on the paper.

The charging roller 52 is arranged in contact with the photoconductor 51 to charge the photoconductor to a predetermined potential. The charging roller 52 includes a conductive support 11 and an elastic layer 12 formed on the conductive support 11. Both ends of the conductive support 11 are pressed against the photoconductor 51 by a pressing means (not shown). By applying a predetermined DC voltage from the power source 53 to the conductive support 11 via the rubbing electrode 53a, the photoconductor 51 is charged to a predetermined potential.

The charged photoconductor 51 is then subjected to an electrostatic latent image corresponding to the target image information on its peripheral surface by the exposure apparatus 54. The electrostatic latent image is then sequentially visualized as a toner image by the developing device 55. This toner image is sequentially transferred to the transfer material 57. The transfer material 57 is conveyed from a paper feeding means unit (not shown) to a transfer unit between the photoconductor 51 and the transfer means 56 at an appropriate timing in synchronization with the rotation of the photoconductor 51. The transfer means 56 is a transfer roller, and the toner image on the photoconductor 51 side is transferred to the transfer material 57 by charging the transfer material 57 with the opposite polarity to the toner. The transfer material 57, which has received the transfer of the toner image on the surface, is separated from the photoconductor 51 and conveyed to a fixing means (not shown) to fix the toner and output as an image forming product. On the peripheral surface of the photoconductor 51 after image transfer, toner and the like remaining on the surface of the photoconductor 51 are removed by a cleaning device 58 provided with a cleaning member typified by an elastic blade. The peripheral surface of the cleaned photoconductor 51 moves to the electrophotographic image forming process in the next cycle.

Hereinafter, the present invention will be described in more detail by way of examples, but these are not limited to the present invention. In the following, unless otherwise specified, commercially available high-purity products were used as reagents and the like not specified. In each example, a polishing-less roller was manufactured as a charging roller.

<Preparation of particles>
Particles 1 to 10 to be contained in the elastic layer of the charging roller according to the examples and comparative examples were prepared.

<Preparation of particle 1>
As the particles 1, polyurethane resin particles were prepared by the following procedure. To 100 parts by mass of polydiethylene / butylene adipate having a hydroxyl value of 45, 10 parts by mass of polyisocyanate (trade name: Duranate 24A, manufactured by Asahi Kasei Kogyo Co., Ltd.) with NCO% = 49.2 was added and mixed uniformly. A dispersion in which 5 parts by mass of fluorine-treated silica (trade name: WACKER HDK, manufactured by Dainichiseika Kogyo Co., Ltd.) is dispersed in 300 parts by mass of fluorine oil (trade name: Garden HT135, manufactured by Monte Cartini Co., Ltd.). In addition to. The obtained mixture was subjected to ultrasonic treatment for 20 minutes to obtain an emulsion. The temperature of this emulsion was raised to 90 ° C., and the mixture was stirred at 400 rpm for 8 hours to obtain a dispersion of polyurethane gel particles. By vacuum drying this dispersion, polyurethane particles (average particle diameter 15 μm, Martens hardness 6.5 N / mm ² ) were prepared.

<Preparation of particle 2>
^{Polyurethane particles (average particle diameter 15 μm, martens hardness 8 N / mm 2} ) as particles 2 were prepared in the same manner as in the above-mentioned production method for particles 1 except that the amount of polyisocyanate was changed to 12.5 parts by mass.

<Preparation of particle 3>
Urethane resin particles (trade name: U400-T, manufactured by Negami Kogyo Co., Ltd.) were prepared as the particles 3.

<Preparation of particle 4>
As the particles 4, silicone particles were prepared by the following procedure. Methylvinylpolysiloxane with kinematic viscosity of 600 mm ² / s 600 g and methylhydrogen polysiloxane with kinematic viscosity of 30 mm ² / s (with 0.90 hydroxyl groups for each olefinically unsaturated group) ) 24 g was mixed. The kinematic viscosity is a value at 25 ° C. To this end, these components were stirred at 2000 rpm using a homomixer. Then, add 6 g of polyoxyethylene octylphenyl ether (trade name: polyoxyethylene (10) octylphenyl ether, manufactured by Wako Pure Chemical Industries, Ltd.) and 180 g of water, stir at 5000 rpm, and after confirming the increase in viscosity, further. Stirring was continued for 10 minutes. Then, 400 g of water was added while stirring at 2000 rpm to obtain an emulsion. This emulsion is transferred to a glass flask, the temperature is adjusted to 20 ° C., and then 0.8 g of a toluene solution of platinum chloride acid-olefin complex (platinum content 0.05%) and 1 g of polyoxyethylene octylphenyl ether are added under stirring. A mixed solution was added. This was stirred at the same temperature for 12 hours to obtain an aqueous dispersion of silicone elastomer fine particles. To 700 g of the dispersion, 2500 g of water, 70 g of 28 mass% ammonia water, and 4 g of a 40 mass% dimethyldiallyl ammonium chloride polymerization aqueous solution (trade name: ME Polymer H40W, manufactured by Toyo Kagaku Kogyo Co., Ltd.) were added. The temperature of the obtained liquid was adjusted to 10 ° C., 50 g of methyltrimethoxysilane was added over 20 minutes, and the mixture was further stirred for 1 hour. After that, in order to complete the hydrolysis and condensation reaction, the mixture was heated to 60 ° C. and stirred for 1 hour. The solution was dehydrated by about 30% by mass using a pressure filter. After adding water to the dehydrated product and dehydrating it again, it was dried at a temperature of 105 ° C. to prepare ^{silicone resin particles (average particle diameter 15 μm, Martens hardness 54 N / mm 2).}

<Preparation of particles 5 to 10>
The following particles were prepared as particles 5 to 10.

The average particle size and maltens hardness of the particles 1 to 10 are shown in Table 2 below.

[Example 1]
(Preparation of unvulcanized rubber composition for elastic layer)
The materials shown in Table 3 below were mixed to obtain an A kneaded rubber composition. As the mixer, a 6-liter pressurized kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.

Then, the materials shown in Table 4 were mixed to obtain an unvulcanized rubber composition-1. As the mixer, an open roll (product name: 12 × 30 test roll, manufactured by Kansai Roll) having a roll diameter of 12 inches (0.30 m) was used. The mixing conditions were a front roll rotation speed of 10 rpm and a rear roll rotation speed of 8 rpm, and after turning left and right 20 times in total with a roll gap of 2 mm, thinning was performed 10 times with a roll gap of 0.5 mm.

(Molding of vulcanized rubber layer)
First, in order to obtain a core metal having an adhesive layer for adhering the vulcanized rubber layer, the following operation was performed. That is, a conductive vulcanizing adhesive (trade name: Metalloc U-20, Toyo Kagaku) is attached to the axially central portion 236 mm of a cylindrical conductive core metal (steel, surface is nickel-plated) having a diameter of 5 mm and a length of 249 mm. (Made in the laboratory) was applied and dried at 80 ° C. for 30 minutes.

Using a crosshead extruder having the configuration shown in FIG. 4, the core metal having the adhesive layer was coated with the unvulcanized rubber composition-1 for the surface layer to obtain a crown-shaped unvulcanized rubber roller. .. At this time, the molding temperature was 100 ° C. and the screw rotation speed was 10 rpm, and molding was performed while changing the feed rate of the core metal. The take-back rate of the unvulcanized rubber rollers averaged in the axial direction was 92%. The inner diameter of the die of the crosshead extruder is Φ (diameter) 7.8 mm, the outer diameter of the rubber layer of the unvulcanized rubber roller is 7.6 mm in the center in the axial direction, and the outer diameter of the end in the axial direction is 7.5 mm. Met. Further, the deviation of the outer diameter dimension at the center in the axial direction was 10 μm, and the deflection of the outer diameter dimension at the end portion in the axial direction was 50 μm.

After extrusion molding, the unvulcanized rubber roller was placed in a hot air furnace, vulcanized at 195 ° C. for 80 minutes, and the vulcanized rubber roller was taken out from the hot air furnace. Then, hot air at 210 ° C. was blown toward the center of the rubber layer in the longitudinal direction with a heat gun (product name: HAKKO882, manufactured by Hakko Co., Ltd.) from a position 10 cm away from the vulcanized rubber roller for 15 minutes to perform additional sulfurization. Then, both ends of the vulcanized rubber layer were cut to obtain an elastic layer having an axial length of 223 mm.

(Observation of elastic particles)
The surface of the elastic layer of the charging roller was observed according to the above-mentioned observation method of elastic particles.

(Measurement of Martens hardness of binder resin)
According to the above-mentioned method for measuring the maltens hardness of the binder resin, the maltens hardnesses H1 (1), H1 (2), and H2 of the binder resin at the end portions E (parts E1 and E2) and the central portion were measured, respectively.

(Measurement of Martens hardness of elastic particles)
The Martens hardness H3 of the urethane particles was measured according to the above-mentioned method for measuring the Martens hardness of elastic particles. The row "H3-H1 (1)" in Table 3-1 shows the value of the difference between the hardness H3 and the hardness H1 (1), and the row "H3-H1 (2)" shows the hardness. The value of the difference between H3 and hardness H1 (2) is shown.

(Image Evaluation 1) Evaluation of Difference in Central Edge of Image Density The produced charging roller was attached to a black cartridge of an electrophotographic apparatus (trade name: LBP7600C, manufactured by Canon Inc., for vertical output of A4 paper). The image was output by this electrophotographic apparatus in an environment of 15 ° C./10% RH.

Specifically, first, an image randomly printed in 1 area% of the image forming area of A4 paper is used, and when one image is output, the electrophotographic apparatus is stopped and the image forming operation is restarted after 10 seconds. The operation was repeated and an image output durability test of 30,000 images was performed.

Then, as an evaluation image after the durability of 30,000 sheets, one halftone image (an image having an intermediate density in which a horizontal line having a width of 1 dot and an interval of 2 dots is drawn in a direction orthogonal to the rotation direction of the photoconductor) was output. This image was placed vertically, and the edges and the center in the horizontal direction (short side direction of A4 paper) were visually observed and evaluated according to the following criteria. When a difference in image density occurred between the two image edges, the image density was observed at the edge and the center of the image, and the evaluation was performed.

Here, the edge of the image is a position 50 mm from each edge of the image forming region of A4 paper. The central portion of the image is a position from 80 mm to 130 mm from the edge of the image forming region of A4 paper.
Rank A: There was no difference in the central edge of the image density.
Rank B: There was a slight difference in the image density at the center edge.
Rank C: There was a slight difference in the image density at the center edge.
Rank D: There was a difference in the central edge of the image density.

(Image evaluation 2) Evaluation of step unevenness-like image unevenness The evaluation image created in evaluation 1 was visually observed, and the step unevenness-like image unevenness was evaluated based on the following criteria.
Rank A: No step unevenness was observed in the image.
Rank B: Very slight unevenness in the image was observed.
Rank C: A slight step-like unevenness in the image was observed.
Rank D: Significant step unevenness-like image unevenness was observed.

(Image evaluation 3) Evaluation of spot-shaped image unevenness The produced charging roller was attached to a black cartridge of an electrophotographic apparatus (trade name: LBP7600C, manufactured by Canon Inc., for vertical output of A4 paper). At this time, the cleaner blade equipped on the black cartridge was replaced with a cleaner blade having an international rubber hardness of 65 °. As a result, the contact pressure of the cleaner blade with respect to the photoconductor was reduced, and the toner easily slipped between the cleaner blade and the photoconductor. The image was output by this modified machine in an environment of 15 ° C./10% RH (relative humidity).

Specifically, an image randomly printed in 1 area% of the image forming area of A4 paper is used, and when one image is output, the electrophotographic apparatus is stopped and the image forming operation is restarted after 10 seconds. Was repeated to output 30,000 images.

Next, as an evaluation image, one halftone image (an intermediate density image in which a horizontal line having a width of 1 dot and an interval of 2 dots is drawn in a direction orthogonal to the rotation direction of the photoconductor) was output. The obtained evaluation image was visually observed, and the spot-shaped image unevenness was evaluated based on the following criteria.
Rank A: No spot-like image unevenness was observed.
Rank B: Very slight spot-like image unevenness was observed.
Rank C: A slight spot-like image unevenness was observed.
Rank D: Significant spot-like image unevenness was observed.

[Examples 2 to 16]
A charging roller was prepared in the same manner as in Example 1 except that the particles and vulcanization conditions were changed as shown in Table 5-1.

[Example 17]
A charged roller was prepared by the same operation as in Example 14 except that the vulcanization condition of the hot air furnace was changed to 85 minutes at 230 ° C. and electron beam irradiation treatment was performed instead of vulcanization by a heat gun, and the same evaluation was performed. rice field.

The electron beam irradiation treatment was performed by performing the electron beam treatment step four times as described above. The electron beam irradiation conditions were an acceleration voltage of 80 kV and an electron current of 40 mA. Further, in FIG. 7 of the vulcanized rubber roller, the transport speed in the direction of arrow 76 was 10 mm / sec, and the rotation speed in the direction of arrow 77 was 100 rpm. Further, the shortest distance between the surface of the foil 74 on the chamber 78 side and the surface to be treated was set to be 10 mm. As a result, the dose of the electron beam received by the surface of the central portion in the longitudinal direction of the layer of the vulcanized rubber composition, that is, the surface not covered with the aluminum foil, became 1350 kGy.

[Example 18]
A charging roller was produced in the same manner as in Example 15. Next, the E2 near the end of the charging roller was further vulcanized using a heat gun at a vulcanization temperature of 160 ° C. and a vulcanization time of 5 minutes to prepare a charging roller according to this embodiment.

[Comparative Example 1]
A charged roller was produced in the same manner as in Example 1 except that no particles were added and the vulcanization conditions were as shown in Table 5-2.

[Comparative Examples 2-5, 7]
A charged roller was produced in the same manner as in Example 1 except that the particles and vulcanization conditions were as shown in Table 5-2.

[Comparative Example 6]
The position of the heat gun was changed from the central part to both ends, and vulcanization with the heat gun was applied only to both ends. The vulcanization conditions using the heat guns at both ends were the same as in Example 14 except that the vulcanization temperature was changed to 170 ° C. for 15 minutes.

[Comparative Example 8]
A charged roller was produced by the same operation as in Example 1 except that the NBR was changed to ethylene propylene diene rubber (EPDM) (trade name: JSR EP33, manufactured by JSR Corporation).

The charged rollers according to Examples 1 to 18 and Comparative Examples 1 to 8 were subjected to the evaluation described in Example 1. The results are shown in Tables 6-1 and 6-2. In addition, when "Yes" is described in the row of "Exposure of particles" in Tables 6-1 and 6-2, it means that the particles are exposed on the surface of the charged roller according to the above-mentioned observation method of elastic particles. Means confirmed. In addition, when "Yes" is described in the line of "Convex part due to exposed particles (average height 1 μm or more)", the existence of the convex part is confirmed and all exposed in the field of view at the time of observation. It means that the average value of the height h of the particles was 1.0 μm or more.

Since the charged roller according to Comparative Example 1 does not contain particles in the elastic layer, no convex portion is formed. Therefore, the evaluation result of "convex portion due to exposed particles (average height 1 μm or more)" was described as "none".

In Examples 1 to 18, the difference at the central end of the image density was evaluated as A to C. This is because the martens hardness H1 of the binder resin at the end E is smaller than the maltens hardness H3 of the elastic particles, and the maltens hardness H2 of the binder resin at the center is larger than the maltens hardness H3 of the elastic particles, so that the center of the contact area. This is because the edge difference can be reduced.

In Examples 1 to 18, the step-like image unevenness was evaluated as A to C. This is because the martence hardness H2 of the binder resin in the central portion is larger than the martence hardness H1 of the binder resin in the end portion E, and the contact width of the end portion E can be made larger than that in the central portion. Further, when the maltens hardness H3 of the elastic particles is 10 N / mm ² or more and the martens hardness H1 and H2 of the binder resin at the end E and the central portion are 2 N / mm ² or more, the toner, the external additive, etc. are the elastic layer. It is preferable because it is easy to suppress the embedding in the material.

In Examples 1 to 18, the spot-shaped image unevenness was evaluated as A to C. The maltens hardness H3 of the elastic particles was 50 N / mm ² or less, or the martens hardness H1 and H2 of the binder resin at the end E and the binder resin at the center were 60 N / mm ² or less, so that toner cracking could be suppressed. Is. It is more preferable that both of these conditions are satisfied.

In Comparative Example 1, the difference at the central end of the image density was evaluated as D. This is because elastic particles were not added and the difference in contact area between the end E and the center could not be reduced.

In Comparative Example 2, the difference at the central end of the image density was evaluated as D. This is because the martiness hardness H3 of the elastic particles is larger than the martence hardness H2 of the binder resin in the central portion, and when the elastic particles come into contact with the photoconductor, the elastic particles sink into the binder resin at the end E and the central portion, and the contact area is increased. This is because the difference at the central end could not be reduced.

In Comparative Example 3, the difference at the central end of the image density was evaluated as D. This is because the martiness hardness H3 of the elastic particles is smaller than the martence hardness H1 of the binder resin at the end E, and when the elastic particles come into contact with the photoconductor, the elastic particles are crushed by the photoconductor at the end E and the central portion, and the contact area is reached. This is because the difference at the center end of the was not able to be reduced.

In Comparative Example 4, the difference at the central end of the image density was evaluated as D. This is because the Martens hardness H3 of the elastic particles is smaller than the hardnesses H1 and H2 at the end E and the central portion, and when the elastic particles come into contact with the photoconductor, the elastic particles are crushed by the photoconductor at the end E and the central portion and come into contact with each other. This is because the difference at the central end of the area could not be reduced. Further, the image unevenness in the form of step unevenness was evaluated as D. This is because the Martens hardness H2 of the binder resin in the central portion is equal to the Martens hardness H1 of the binder resin in the end E, and the contact unevenness in the central portion could not be suppressed. Further, the maltens hardness of the elastic particles ^{is smaller than 10 N / mm 2} , and the Martens hardness H1 and H2 of the binder resin are ^{smaller than 2} N / mm 2, so that the toner, the external additive, or the like is embedded in the elastic layer.

In Comparative Example 5, the difference at the central end of the image density was evaluated as D. This is because the Martens hardness H3 of the elastic particles is larger than the hardnesses H1 and H2 at the end E and the central portion, and when the elastic particles come into contact with the photoconductor, the elastic particles sink into the binder resin at the end E and the central portion and come into contact with each other. This is because the difference at the central end of the area could not be reduced. Further, the image unevenness in the form of step unevenness was evaluated as D. This is because the Martens hardness H2 of the binder resin in the central portion is equal to the Martens hardness H1 of the binder resin in the end portion E, and the contact unevenness in the central portion cannot be suppressed.

In Comparative Example 6, the difference at the central end of the image density was evaluated as D. This is because the martence hardness H3 of the elastic particles is smaller than the martence hardness H1 of the binder resin at the end E and larger than the martence hardness H2 of the binder resin at the center. This is because the difference in parts has increased. Further, the image unevenness in the form of step unevenness was evaluated as D. This is because the Martens hardness H1 of the binder resin at the end E is larger than the Martens hardness H2 of the binder resin at the center, the contact width of the end E cannot be increased, and the contact unevenness at the center cannot be suppressed. ..

In Comparative Example 7, the difference at the central end of the image density was evaluated as D. This is because the inorganic particles are added instead of the elastic particles, and the inorganic particles are not deformed at the time of contact with the photoconductor, and the difference at the central end of the contact area cannot be reduced.

In Comparative Example 8, the difference at the central end of the image density was evaluated as D. This is because the Martens hardness H3 of the elastic particles is larger than the hardnesses H1 and H2 at the end E and the central portion, and when the elastic particles come into contact with the photoconductor, the elastic particles sink into the binder resin at the end E and the central portion and come into contact with each other. This is because the difference at the central end of the area could not be reduced. Further, the image unevenness in the form of step unevenness was evaluated as D. In this example, even if hot air was blown by a heat gun in the central part, vulcanization did not proceed with EPDM having high heat resistance. Therefore, the Martens hardness H2 of the binder resin in the central portion could not be made larger than the Martens hardness H1 of the binder resin in the end portion E, so that the contact unevenness in the central portion could not be suppressed.

11 Conductive support 12 Elastic layer 21 Convex part L Longitudinal length of elastic layer C Longitudinal center part of elastic layer E1 Longitudinal center part of elastic layer (3/8) L away from one end E2 A portion of the elastic layer separated by (3/8) L from the center in the longitudinal direction toward the other end 31 Photoreceptor 32 Elastic particle 33 Binder resin 34 Contact portion of end E 35 Contact portion of center

Claims (11)

A charging roller comprising a conductive support and an elastic layer on the conductive support.
The elastic layer is the only elastic layer and is composed of a single layer.
The elastic layer contains a binder resin and holds the elastic particles in an exposed state on the surface of the charged roller, and the surface of the charged roller has a convex portion derived from the elastic particles. death,
When the length of the elastic layer is L, the Martens hardness of the binder resin on the surface at a portion separated from the center of the elastic layer in the longitudinal direction by (3/8) L in the longitudinal direction is H1 (N / mm ² ). ,
The Martens hardness of the binder resin on the surface at the center of the elastic layer in the longitudinal direction is set to H2 (N / mm ² ).
When the Martens hardness of the elastic particles is H3 (N / mm ² ),
Charging rollers, characterized in that H1, H2 and H3 satisfy equation (1):
Equation (1)
H1 <H3 <H2. The charging roller according to claim 1, wherein H1, H2 and H3 satisfy the formulas (2) and (3).
Equation (2)
5 ≦ H3-H1;
Equation (3)
5 ≦ H2-H3. The charging roller according to claim 1 or 2, wherein H1 and H2 satisfy the formulas (4) and (5).
Equation (4)
2 ≦ H1;
Equation (5)
H2 ≦ 60. The charging roller according to any one of claims 1 to 3, wherein H3 satisfies the formula (6):
Equation (6)
10 ≦ H3 ≦ 50. The binder resin includes at least one rubber selected from the group consisting of isoprene rubber, chloroprene rubber, butadiene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, and styrene-butadiene-styrene rubber, according to claims 1 to 4. The charging roller according to any one item. The charging roller according to any one of claims 1 to 5, wherein the elastic particles include at least one of a urethane resin and a silicone resin. An electrophotographic apparatus comprising the charging roller according to any one of claims 1 to 6. The method for manufacturing a charging roller according to any one of claims 1 to 6.
(1) A step of preparing an unvulcanized rubber composition containing the unvulcanized rubber as a raw material of the binder resin and the elastic particles;
(2) A step of extruding the unvulcanized rubber composition on the conductive support while stretching the unvulcanized rubber composition to form a layer of the unvulcanized rubber composition;
(3) The step of vulcanizing the layer of the unvulcanized rubber composition to obtain the elastic layer.
A method for manufacturing a charged roller, wherein the step (3) includes a step of vulcanizing under different conditions depending on the position in the longitudinal direction of the layer of the unvulcanized rubber composition. The method for manufacturing a charged roller according to claim 8, wherein the condition is a condition for heating by a heat gun or an infrared heating device for the vulcanization. The method for manufacturing a charging roller according to any one of claims 1 to 6.
(1) A step of preparing an unvulcanized rubber composition containing the unvulcanized rubber as a raw material of the binder resin and the elastic particles;
(2) A step of extruding the unvulcanized rubber composition on the conductive support while stretching the unvulcanized rubber composition to form a layer of the unvulcanized rubber composition;
(3) A step of vulcanizing the layer of the unvulcanized rubber composition to form a layer of the vulcanized rubber composition, and (4) irradiating the surface of the layer of the vulcanized rubber composition with an electron beam. It has a step of curing to form the elastic layer,
The step (4) is a method for manufacturing a charged roller, which comprises a step of irradiating an electron beam under different irradiation conditions depending on the position in the longitudinal direction of the layer of the vulcanized rubber composition. In the step (4), the dose of the electron beam received by the surface of the layer of the vulcanized rubber composition is smaller at the end than at the center in the longitudinal direction of the layer of the vulcanized rubber composition. The method for manufacturing a charged roller according to claim 10, which comprises a step of irradiating a line.

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