JP2008026392A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device of a cartridge system made small in size and light in weight and capable of reducing an image defect. <P>SOLUTION: The developing device is equipped with a developing roll 20 having an elastic layer 22 on the periphery of a core bar 21, and a toner supply roll 30 and a developing blade 40 which are made to abut on the developing roll 20, and is also attachably/detachably provided in an electrophotographic image forming apparatus. The elastic layer 22 of the developing roll 20 has a reverse crown shape whose diameter gets larger and larger toward the ends from the center part in a longitudinal direction, and the developing roll 20 is held in such a state that the core bar is bent by pressing force of the toner supply roll 30 and the developing blade 40. The surface position in a radial direction of the center part with reference at the surface positions in the radial direction of both ends in the longitudinal direction of a contact area where the developing roll comes in contact with the photoreceptor is within 0 to +50 μm when a protrusive direction is expressed by +. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device that is detachably mounted on an electrophotographic image forming apparatus such as an electrophotographic copying machine, a facsimile machine, or a printer.

  A developing device of an electrophotographic image forming apparatus such as an electrophotographic copying machine, a facsimile machine, or a printer includes a developing roll, a toner supply member held in contact with the developing roll, and a toner regulating member. Built in and used. In recent years, a developing device that can be replaced as a cartridge has been used. However, the developing device has been reduced in size and weight for ease of handling at the time of replacement. The diameter is reduced and the weight is reduced. However, particularly in a developing device that can be replaced as a cartridge that is reduced in size and weight as described above, if the developing device and the photosensitive drum are pressed against each other, the core of the developing roller is bent, causing a problem of image defects. there were.

  As a technique for solving such image defects when using a developing roller that is reduced in size and weight, a conductive roller having a regular crown shape has been proposed (see Patent Document 1). This technique is intended to improve non-uniformity of the nip region between the conductive roller and the photosensitive drum due to the deflection of the core shaft when the diameter of the core shaft of the conductive roller is reduced.

  However, in the developing device replaceable as the cartridge described above, even when the developing roll has a regular crown shape, the image defect is not eliminated, and it has become clear that a problem different from that of Patent Document 1 occurs.

Japanese Patent Laid-Open No. 10-196637

  In view of the above-described circumstances, an object of the present invention is to provide a developing device that does not cause image defects due to the deflection of the core of the developing roller in a developing device of a cartridge type that is reduced in size and weight.

  As a result of diligent research to solve the above-mentioned problems, the above-mentioned image defect is caused by a core member of a developing roll incorporated in a developing device that can be replaced as a cartridge, particularly a core member having a diameter of 8 mm or less as a toner supply member. This is because the central part of the cored bar is slightly bent so as to protrude toward the photosensitive drum due to the pressing force of the toner supply roll and the developing blade as the toner regulating member. When a developing device incorporating a developing roll in a bent state was used, it was found that the nip width with the photosensitive drum was insufficient at both ends of the developing roll, which resulted in an image defect, and the present invention was completed.

  The first aspect of the present invention includes a developing roll having an elastic layer around a core metal, and at least one of a toner supply member and a toner regulating member that are in contact with the developing roll, and an electrophotographic image. A developing device detachably provided in a forming device, wherein the elastic layer of the developing roll has a reverse crown shape, and the developing roll is bent by a pressing force of the toner supply roll and the developing blade. The surface position in the radial direction of the central portion with respect to the radial surface position of both ends in the longitudinal direction of the contact area of the developing roll with the photosensitive member is expressed as + in the convex direction. The developing device is in the range of 0 μm to +50 μm.

  According to a second aspect of the present invention, in the developing device according to the first aspect, the amount of reverse crown, which is the difference between the diameters at both ends in the longitudinal direction of the elastic layer and the diameter at the center, is less than 55 μm. In the developing device.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, a deflection amount that is a protruding amount in a radial direction of a central portion in the longitudinal direction with respect to the support end portion of the core metal is 8 μm to 130 μm. The developing device is characterized by the above.

  The present invention uses a developing roll having an inverted crown shape whose diameter gradually increases from the longitudinal center to the end of the elastic layer, and uses the developing roll reduced in diameter as the toner supply roll and the developing blade. Since the developing device is held in a state in which the core metal is bent by the pressing force, the device can be downsized by reducing the diameter of the developing roll, and the nip with the photosensitive drum is formed over the entire length of the developing roll. There is an effect that it becomes uniform and a good image can be obtained.

  FIG. 1 is a diagram schematically showing a cross section of a developing device according to an embodiment of the present invention. As shown in FIG. 1, the developing device 1 of the present embodiment is of a cartridge type that incorporates toner, and includes a developing roll 20 in an opening 11 of the cartridge body 10. Inside, a toner supply roll 30 as a toner supply member and a development blade 40 as a toner regulating member are incorporated in contact with the development roll 20. In addition to the toner supply roll, the toner supply member includes a toner supply blade and a toner supply belt. The toner control member includes a development blade and a toner control roll, and is not particularly limited. In some cases, only one of the toner supply member and the toner regulating member is provided.

  The developing roll 20 basically has a cylindrical conductive roll main body (core metal) 21 made of a metal such as iron or stainless steel, and a substantially entire outer peripheral surface of the long surface portion of the core metal 21. And an elastic layer 22 provided so as to cover it.

The elastic layer 22 is formed of a conductive elastic polymer material in which an elastic polymer material is used as a base and a conductivity-imparting agent such as carbon black or metal powder is blended therein. As the base elastic polymer material, a synthetic rubber material such as silicone rubber, acrylonitrile butadiene rubber, silicone-modified ethylene propylene rubber, urethane rubber, or thermoplastic elastomer such as thermoplastic urethane resin can be used. A preferred base polymer material in the present invention is a synthetic rubber material. Moreover, it is preferable to mix | blend a electroconductivity imparting agent with a base polymer material in the quantitative ratio that the elastic layer 21 shows the volume resistance value of ¹⁰ < ² > -10 < ¹⁰ > (omega | ohm) * cm. Furthermore, the elastic layer 22 preferably has a JIS A hardness of 20 ° to 60 °.

  Further, since the developing roll 20 is in contact with the photosensitive drum and the toner regulating member by forming a nip portion, if the elastic layer 22 has a large compressive strain, the nip mark remains on the developing roll 20 and adversely affects the image. . Therefore, it is most preferable that the material constituting the elastic layer 22 exhibits a compression set of 5% or less after being placed at 70 ° C. for 22 hours under a 25% compression load. If the strain is 10% or less, it can be used without any trouble.

  Note that a coating layer (not shown) may be provided on the surface of the elastic layer 22. Such a coating layer is formed from, for example, urethane silicone obtained by reacting an isocyanate compound, a reactive silicone oil, and a polyol. The coating layer preferably has an elongation at break of 100% or more, preferably 130% or more. When the coating layer has an elongation at break of 100% or more, the coating layer can follow the deformation of the underlying elastic layer 22 even when used at a medium speed or higher, effectively preventing toner leakage. This is because it can be prevented.

  Here, as shown in FIG. 2, the elastic layer 22 of the developing roll 20 of the present invention has an inverted crown shape in which the diameter gradually increases from the central portion in the longitudinal direction toward the end portion. That is, the elastic layer 22 has a so-called reverse crown shape in which the diameter of the central portion D2 in the longitudinal direction is the smallest, the diameter gradually increases as the distance from the central portion to the end portion increases, and D1 and D3 at both ends become maximum.

  Further, in the developing roll 20 of the present invention, the core metal 21 has a diameter of, for example, 8.0 mm or less, preferably about 6.5 mm to 7.5 mm, and the toner supply roll 30 and the developing blade 40 described above are included. Since it is incorporated in the cartridge main body 10 while being pressed against the developing roll 20 by a considerable force, the developing roll 20 is held in a state where the cored bar 21 is bent by the pressing force of the toner supply roll 30 and the developing blade 40. Has been.

  This state is schematically shown in FIG. FIG. 3 shows the developing roll 20 and the toner supply roll 30, but shows a state where the cored bar 21 of the developing roll 20 is bent so as to protrude in the opposite direction to the toner supply roll 30. ing.

  As described above, since the developing roll 20 is incorporated in the cartridge body 10 with the core 21 bent, the outer peripheral surface of the elastic layer 22 exposed from the opening 11 of the cartridge body 10 is substantially linear in the longitudinal direction. It has become. That is, the opening 11 of the cartridge main body 10 is a contact area between the developing roll 20 and the photoconductor 50, and the surface position in the radial direction of the outer peripheral surface of this area is substantially linear in the longitudinal direction.

  Here, the state in which the surface position in the contact area of the developing roll 20 with the photoreceptor 50 is substantially linear in the longitudinal direction is the radial direction of the central portion with reference to the radial surface positions of both ends in the longitudinal direction. The surface position is preferably in the range of 0 μm to +50 μm when the convex direction is represented by +. This is because the nip amount with respect to the photoconductor 50 can be made uniform in the longitudinal direction, and the nip defect that causes the image defect can be prevented. When the surface position of the central portion is-, nip failure is likely to occur at the central portion, whereas when the surface position of the central portion exceeds +50 μm, nip failure is likely to occur at both ends.

  In order to manufacture such a developing device, it is necessary to set the deflection amount of the core metal 21 of the developing roll 20 and the reverse crown amount of the elastic layer 22 within a predetermined range.

  The amount of deflection of the core 21 of the developing roll 20 depends on the thickness and material of the core 21 and the pressing force of the toner supply roll 30 and the developing blade 40, but the developing roll 20 receives from the toner supply roll 30 and the developing blade 40. The pressing force is normally about 500 to 1000 g, and the amount of deflection that is the amount of protrusion in the radial direction of the central portion in the longitudinal direction with respect to the support end when the A4 size cored bar 21 is made of a SUM material having an outer diameter of 10 to 6 mm. If it calculates with the formula of a uniform load, it will be about 8 micrometers-130 micrometers.

  On the other hand, the reverse crown amount, which is the difference between the diameters at both ends in the longitudinal direction of the elastic layer 22 of the developing roll 20 and the diameter at the center, is preferably less than 55 μm. This is because if it is larger than this, an image defect occurs. Further, an image defect occurs even when there is no reverse crown. Therefore, the reverse crown amount needs to be at least about 2 μm, preferably about 5 μm.

  Therefore, in a developing device using such an inverted crown-shaped developing roll 20 and incorporating the cored bar 21 in a bent state, the radial surface positions at both ends in the longitudinal direction of the elastic layer 22 of the developing roll 20 are used as a reference. The surface position in the radial direction of the center portion is preferably in the range of 0 μm to +50 μm when the convex direction is represented by +.

  In addition, the manufacturing method of the image development roll 20 which has such an inverted crown-shaped elastic layer 22 is not specifically limited. For example, a cylindrical body that becomes an elastic layer is extruded and cut into a predetermined length, and then a core metal is press-fitted into the cylindrical body, and then polished into an inverted crown shape to form an elastic layer. The layer may be molded with a mold and then polished into an inverted crown shape, or an inverted crown shaped elastic layer may be molded with a mold. In any case, after forming a crown-shaped elastic layer, a coating layer can be provided as necessary.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these Examples.

<Examples 1-3>
(Manufacture of developing roll)
Using an uncured silicone rubber material (DY32-4036 manufactured by Toray Dow Corning Co., Ltd.) containing carbon black as a silicone rubber, this was extruded into a tube shape and cured at 400 ° C. for 2 minutes (primary curing). The tube was cut to a predetermined length and cured (secondary curing) at 200 ° C. for 4 hours to produce a tube having an inner diameter of 6.5 mm and an outer diameter of 20 mm.

  This tube was press-fitted into a metal core made of SUM22 having a diameter of 7.5 mm using compressed air, and the tube surface was polished into a predetermined reverse crown shape as shown in the following table to obtain a roll having a surface length of 234 mm.

  On the other hand, 100 parts by weight of a fluorine-containing polyol (Daikin Kogyo Zeffle), 5 parts by weight of conductive carbon black (Cabot) and 300 parts by weight of butyl acetate are dispersed by a disperser, and volatile silicone oil (Shin-Etsu Chemical Co., Ltd.) is dispersed therein. 5 parts by weight of KF96L manufactured by Kogyo Co., Ltd. is used as a main agent, and this main agent and urethane-modified hexamethylene diisocyanate (manufactured by Asahi Kasei Kogyo Co., Ltd.) as a curing agent The coating material was prepared by blending so that the equivalent weight was 1: 1.

  This coating material was spray-coated on the roll surface to a thickness of 10 μm, air-dried, and then heated at 160 ° C. for 40 minutes to obtain developing rolls having coating layers of Examples 1 to 3.

<Comparative Examples 1-5>
The tube surface produced in the same manner as in the examples was polished into a predetermined reverse crown shape as shown in the following table to form a roll, and a coating layer was formed in the same manner as in the examples to obtain development rolls of Comparative Examples 1 to 5. .

<Test Example 1> (Development roll outer diameter measurement)
Using a laser length measuring device (RSV15100 manufactured by Tokyo Kodenshi Co., Ltd.), 19 locations including the position of 27 mm and the central portion from both ends were measured (mm), and the reverse crown amount C was measured. The results are shown in FIGS. The reverse crown amount is as follows.

  Reverse crown amount C (μm) = [(D1 + D3) / 2−D2] × 1000

<Test Example 2> (Measurement of deflection of developing roll incorporated in developing device)
The developing rolls of Examples 1 to 3 and Comparative Examples 1 to 5 were incorporated into a toner unit (developing device): TN-350 (for Brother HL-2040 printer) to form a developing device.

  Then, the surface position of the unloaded developing roll and the developing roll incorporated in the developing device was measured as follows to measure the deflection.

  Deflection measurement: The surface length was measured with a surface roughness meter (Surfcom 1400D manufactured by Tokyo Seimitsu Co., Ltd.), the measurement length was 180 mm, and the cross section was measured according to JIS 82 standard, and the measurement was performed at 6 mm / sec and 500 times.

  The results are shown in FIGS.

  Further, the deflection was calculated from the displacement at both ends (displacements A and C) and the displacement at the center (displacement B) by the following equation. In addition, each displacement AC was taken as the average value measured at five places where circumferential directions differ, respectively.

  Deflection (μm) = (Displacement A + Displacement C) / 2−Displacement B

<Test Example 3> (Image Evaluation Test)
The developing device was incorporated into a printer HL-2040 manufactured by Brother Industries, Ltd., 10 halftone images were printed in A4 size, the images were visually confirmed, and the following evaluation was performed.

Evaluation criteria: ○ No difference in density, good
△ There is a difference in concentration, but there is no problem in use.
× NG due to concentration difference

(Test results)
As a result of Test Examples 1 and 2, in the developing device using the developing rolls of Examples 1 to 3 whose reverse crown amounts are 5, 25, and 50 μm, the deflections are 45, 28, and 5 μm, respectively. The image evaluation was good. On the other hand, in the developing device using the developing roll of Comparative Example 1 whose surface was polished straight, the deflection was 50 μm, and the density was particularly low at both ends in the width direction, resulting in an image defect. Further, in the developing device using the developing rolls of Comparative Examples 2 and 3 having a crown shape, the deflection was increased to 53 and 60 μm, and the images at both ends in the width direction were further deteriorated. On the other hand, in the developing devices using the developing rolls of Comparative Examples 4 and 5 in which the reverse crown amounts were 55 μm and 60 μm, the deflection was 0 and −2 μm, which was almost flat, but the density at the center in the width direction was There was a tendency to be thin and the image was defective.

  From the above results, the developing device that holds the core metal in a bent state using the reverse-crown-shaped developing roll in a predetermined range can achieve a light weight and a small size without sacrificing the image. It became clear.

1 is a diagram schematically showing a cross section of a developing device according to an embodiment of the present invention. It is a figure which shows roughly the cross section of the image development roll which concerns on one Embodiment of this invention. FIG. 3 is a diagram schematically showing a cross section of a developing roll and a toner supply roll of a developing device according to an embodiment of the present invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on Example 1 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on Example 2 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on Example 3 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on the comparative example 1 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on the comparative example 2 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on the comparative example 3 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on the comparative example 4 of this invention. It is a figure which shows the outer diameter curve of the image development roll which concerns on the comparative example 5 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on Example 1 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on Example 2 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on Example 3 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on the comparative example 1 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on the comparative example 2 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on the comparative example 3 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on the comparative example 4 of this invention. It is a figure which shows the cross-sectional curve of the image development roll which concerns on the comparative example 5 of this invention.

Explanation of symbols

10 Cartridge body 20 Developing roll 21 Conductive roll body (core metal)
22 Elastic layer 30 Toner supply roll 40 Developing blade

Claims (3)

A developing device comprising a developing roll having an elastic layer around a core metal, and at least one of a toner supply member and a toner regulating member in contact with the developing roll, and is detachably provided in the electrophotographic image forming apparatus The developing roll has an inverted crown shape, and the developing roll is held in a state where the core metal is bent by the pressing force of the toner supply roll and the developing blade. The radial surface position of the central portion with respect to the radial surface positions of both end portions in the longitudinal direction of the contact area with the photosensitive member is in the range of 0 μm to +50 μm when the convex direction is represented by +. A developing device. 2. The developing device according to claim 1, wherein a reverse crown amount, which is a difference between a diameter of both end portions in the longitudinal direction of the elastic layer and a diameter of the central portion thereof, is less than 55 μm. 3. The developing device according to claim 1, wherein a deflection amount which is a protruding amount in a radial direction of a central portion in a longitudinal direction with respect to a support end portion of the core metal is 8 μm to 130 μm.

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