JP2001132858A - Developing roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing roller stable in electric resistance while using a foam body, with little increase of driving torque caused by a nip. SOLUTION: In this developing roller with a JIS-A hardness of 5-35 provided with a conductive rubber layer and a surface layer on the outer periphery of a rotating shaft, the conductive rubber layer is formed in two-layer structure comprising a foam rubber layer 2 and a non-foam rubber layer 3 provided on the outer periphery of the foam rubber layer 2 and smaller in electric resistance than the foam rubber layer 2. It is preferable that the volume resistivity of the non-foam rubber layer 3 is 103-1010 Ω.cm and smaller by one order or more than the foam rubber layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roller used in an electrophotographic apparatus or an electrophotographic apparatus, and more particularly, to an integrated image forming unit (a photoreceptor and a peripheral device such as a developing apparatus). (Referred to as an all-in-one cartridge, a process cartridge, etc.).

[0002]

2. Description of the Related Art Conventionally, as an image forming process in an electrophotographic apparatus, as shown in FIG.
A charging unit, a developing unit, a transfer unit, a cleaning unit, and the like have been individually unitized and arranged. In FIG. 3, the photosensitive drum 18 is rotated by a driving means such as a gear in the direction of an arrow while the charging roller 11
, And is exposed at the exposure section by the copy object or the transmission information to form an electrostatic latent image. In the developing section, a toner image is formed on the photosensitive drum 18 by the toner supplied from the developing roller 16, and the transfer section
The image is transferred to a recording paper (not shown) or the like supplied between the image forming unit 7 and the image, and the transferred image is fixed by a fixing unit (not shown), and copying and printing are performed. After the transfer, the toner remaining on the surface of the photosensitive drum 18 is removed by the cleaning blade 19 or the like, the charge is removed, and the photosensitive drum 18 is transferred to the charging unit again, and is used for the next copy.

In recent years, in electrophotographic printers, facsimile machines, and copiers, there has been a keen need for a compact developing device in order to apply to personal courses, desktop publishing, and other applications and to cope with colorization. Attention is paid to the development method in which a developing roller having a conductive elastic layer formed on the outer periphery of a rotating shaft using a magnetic one-component toner is pressed against the photoreceptor because development can be achieved by reducing the diameter of the developing roller and simplifying the device. I'm taking a bath. In particular, in the case of full color, four developing devices for three primary colors and black are required, so that the effect of downsizing is great. In the development of the above-mentioned applications, there has been a strong demand for simplification of maintenance, and various devices that have been conventionally arranged around the photoreceptor have been integrated into one unit. There is a rapidly growing trend to simplify maintenance by replacing each time.

[0004]

When a device around the photosensitive member is integrated, it is important to uniformly and stabilize the contact state between the photosensitive member and the developing roller in order to form a stable toner image. For this reason, it has come to be carried out that both are fixed at a fixed distance between the rotating shafts. Conventionally,
In a developing roller provided with a conductive elastic layer of a rubber solid body on the outer periphery of a rotating shaft used in this type of developing device, when the distance between the shafts is fixed to obtain a necessary contact width with the photoconductor, the rotating shaft is rotated. The torque is greatly increased, and the rotation of the photoconductor and the developing roller becomes unstable, causing image unevenness called jitter, and the problem that the resin gear, which is the driving member of the photoconductor and the developing roller, jumps. I was Also,
In order to obtain the necessary contact width with the photoreceptor and suppress a large increase in rotational torque, it has been attempted to add a large amount of a softening agent (or plasticizer) to the rubber solid body to make it ultra-low in hardness. However, the contamination of the photoreceptor due to the exudation of the softening agent from the developing roller has become a problem more than before.

As a solution to these problems, a developing roller using a foamed rubber which is easily deformed by using a small amount of a softening agent and has excellent deformation restoring property for the conductive elastic layer has been used. However, in the case of a developing roller using foamed rubber, there has been a problem that electric resistance and surface hardness vary due to variations in foam cell diameter and cell density, resulting in uneven development. Also, in order to carry and transport the toner on the outer peripheral surface, when foaming is performed using a cylindrical mold having a roughened mold surface for the purpose of roughening the outer diameter surface, the outer peripheral surface of the foamed rubber has an inner diameter of the cylindrical mold. If it is foamed using a split mold, the burrs on the split surface of the mold will occur if the part is chipped when the mold is removed, or a peeling part will be formed on the outer diameter surface. Thus, there is a problem that the developing roller cannot be used as it is. Further, even if an attempt is made to polish the outer peripheral surface of the obtained foamed rubber, it is difficult to polish it to a uniform and necessary roughness over the entire length and the entire circumference because of low hardness. The present invention solves the above-mentioned problem of the developing roller, in which the roller is a roller using a foam, has a stable electric resistance, and is fixed to a photosensitive member and a shaft. An object of the present invention is to provide a developing roller which does not cause unevenness or damage to a driving gear and has a surface roughness necessary for carrying toner.

[0006]

SUMMARY OF THE INVENTION The present inventor has solved the above-mentioned problems in the case where a conductive foam is used for a developing roller which is deeply involved in forming a clear and stable copy image in an electrophotographic apparatus or the like. In order to solve the problem, the present inventors have made intensive studies on the material, structure, function, and the like of the foamed roller, and in the course of the process, have come up with the present invention. The above problem is solved by a developing roller having a JIS-A hardness of 5 to 35 in which a conductive rubber layer and a surface layer are concentrically laminated on the outer periphery of a rotating shaft, wherein the conductive rubber layer is formed on the outer periphery of the foamed rubber (inside) by the foamed rubber layer. The inventor of the present invention has conceived that the problem can be solved by providing a non-foamed rubber layer having a small electric resistance. This configuration is a basic feature of the present invention. That is, in the present invention, since the conductive rubber layer has a two-layer structure in which a thin layer of non-foamed rubber having a smaller electric resistance than the foamed rubber layer is provided on the outer periphery of the foamed rubber layer, the developing roller is in contact with the photosensitive member. Even if a necessary contact width (nip width) is obtained, the foamed rubber layer is easily deformed and the deformation resistance is small, so that the driving torque of the photosensitive drum and the developing roller is rarely increased. The image is stabilized without unevenness (jitter), gear jump, and gear damage. In addition, since a non-foamed rubber material is arranged on the outer periphery of the foamed rubber material and foamed and vulcanized to form an integral body, variations in the diameter and density of the cells of the foamed rubber layer can be reduced,
Variations in the electrical resistance and surface hardness of the foam can be reduced, and as a result, the electrical resistance between the outer peripheral surface of the developing roller and the rotating shaft is stabilized, and accordingly, the image is stabilized.
Furthermore, stable and uniform development can be achieved even when a small particle size toner is used in response to high resolution.

According to a second aspect of the present invention, in the developing roller according to the first aspect, the non-foamed rubber thin layer has a volume resistivity of 10 ³ to 10 ¹⁰ Ω · cm and is at least one order of magnitude smaller than the foamed rubber layer. By doing so, it is possible to remove static electricity in the semiconductive region and improve development stability. A third aspect of the present invention is the developing roller according to the first and second aspects, wherein the thickness of the non-foamed rubber layer is 0.05 to 1.0.
It is 00 mm, and if it becomes thinner than 0.05 mm,
Since the thickness of the non-foamed layer is too thin, the non-uniformity of the outer peripheral surface of the foamed layer remains unchanged, and the uniformity of hardness, pressure distribution, and electric resistance is lacking, and the uniformity of development is impaired. Also,
As the thickness exceeds 1.00 mm, the hardness of the entire roller increases due to the surrounding of the non-foamed layer, and the deformability peculiar to the foamed rubber layer deteriorates. Therefore, the thickness is preferably in the above range, particularly preferably 0.2 to 0.5 mm.

[Embodiment] The developing roller of the present invention has the structure shown in FIG.
As shown in the sectional view of FIG. 1, a developing roller 10 is provided with a foamed rubber layer 2 on the outer periphery of a rotating shaft 1, a non-foamed rubber layer 3 on the outer periphery, and a surface coating layer 4 concentrically provided on the outer periphery. In the present invention, the rotating shaft may be made of a material such as metal, ceramic or rigid plastic, and may be made of aluminum, stainless steel, or a rust-proofed (plated) steel material from the viewpoint of strength, durability, and conductivity. Are preferred. The shape is an elongated rod or a cylinder, with an outer diameter of 4-8 mm and a length of 200-700 mm
It is about.

The foamed rubber layer of the present invention may be made of EPDM (ethylene propylene diene rubber), CR (chloroprene rubber), NBR (nitrile butadiene rubber), PU
A rubber such as (polyurethane) is preferably used. As the foaming agent, for example, azodicarbanamide or diazoaminobenzene is used. Carbon black is generally used as the conductivity-imparting agent for imparting conductivity to the foamed rubber layer, but carbon fibers, graphite powder, metal particles and the like may also be used. The use of foamed rubber as the rubber layer requires a large amount of a softener (plasticizer) in order to ensure a JIS-A hardness of the roller of 5 to 35 without foaming, thereby deteriorating the physical properties. In addition, the exudation of the softening agent may increase and the photosensitive drum may be contaminated. On the other hand, in the case of foamed rubber, the JIS-A hardness in the above range can be obtained with a small amount of the softening agent, resulting in deterioration of physical properties and contamination. This is because the problem becomes a negligible level. The shape of the foamed rubber layer is cylindrical, the thickness is 3 to 8 mm, and the length is 2
It is about 00 to 600 mm, and is usually vulcanized and bonded to the rotating shaft.

In the present invention, the provision of the non-foamed rubber layer on the outer periphery of the foamed rubber layer makes the distance from the foamed rubber layer to the surface constant, stabilizes the electric resistance, and reduces the pressure distribution during pressure welding. This is because there is an effect of being made uniform. By laminating a material for non-foamed rubber to a material for foamed rubber in an unvulcanized state, and foaming and vulcanizing, the non-foamed rubber acts as a cushion between the mold and the cell, so that the cells are sealed.
It is considered that the above-mentioned effects are exhibited. Thereby, the foamed cell is exposed on the surface, the difference in the surface potential is suppressed by the cell portion and the cell wall portion, and the variation in the electric resistance between the roller surface and the conductive axis is reduced, As a result, it is considered that a uniform image without a cell pattern can be obtained even when a small particle diameter toner is used in response to high resolution.

EPDM, C
Rubber having a JIS-A hardness of 40 to 65, such as R, NBR, and PU, is preferably used. As the conductivity imparting agent, carbon fibers, graphite powder, metal particles, or the like may be used in addition to carbon black. In addition, a softener (plasticizer) such as dioctyl phthalate (DOP) or rapeseed oil, a filler such as zinc oxide, a vulcanizing agent such as oil sulfur, and the like may be appropriately blended. The electric resistance of the non-foamed rubber layer is 10 ³ to 10 ¹⁰ Ω · cm in volume resistivity. As the volume resistivity is higher than 10 ¹⁰ Ω · cm, sparks due to static electricity are more likely to occur. If the volume resistivity is lower than 10 ³ Ω · cm, leakage may occur in the development area and serious image defects may occur. Is preferred. When the volume resistivity of the non-foamed rubber layer is in the above range and lower than the volume resistivity of the foamed rubber layer by at least one order, it is possible to impart necessary electric characteristics to the toner carried on the outer periphery. As a result, a desired toner charge can be obtained. Preferably, it is reduced by 1 to 3 orders. The volume resistivity of the foamed rubber layer and the non-foamed rubber layer may be measured separately by preparing a sheet-shaped sample and using the SRIS method or the like.

In the present invention, a surface layer made of polyurethane or the like is further provided on the outer periphery of the non-foamed layer in consideration of abrasion resistance against rubbing with the photoreceptor. As a surface layer, it is easy to form a tough coating layer with excellent wear resistance, and it is easy to follow deformation due to pressure contact with the photoreceptor.
(Thermoplastic polyurethane) is preferably used. In addition, the TPU
It is preferable to add particles such as a silicone-acrylic copolymer and a fluororesin to (the thermoplastic polyurethane resin). The particle size of the silicon-acrylic copolymer and fluororesin particles is preferably about 0.1 to 10 μm, and TP
About 0.1 to 10% by weight of U is mixed. This is preferable because pinholes are not generated when the outermost layer is formed, the releasability from the photoreceptor is improved, and the slip stick property is improved. The production of the developing roller of the present invention comprises:
The method described in JP-A-6-182784, which was previously proposed by the present applicant, may be followed, and as schematically shown in FIG. 2, a foaming material rubber and a non-foaming material kneaded with a compounding agent. The rubber forms a two-layer cylindrical material whose inner diameter is the same as or slightly larger than the outer diameter of the rotating shaft 1, whose outer diameter is smaller than the outer diameter of the roller, foaming rubber inside and non-foaming rubber outside. And a cylindrical outer mold 6 having an inner diameter substantially equal to the outer diameter of the roller.
And a seal mold 5 fitted to both ends thereof and holding a rotating shaft, a mold in which a rotating shaft is inserted through a cylindrical material is arranged, and both ends of the rotating shaft are fixed to the seal mold to form a mold. Then, by heating the entire mold, the cylindrical material is foamed and vulcanized simultaneously with foaming, thereby forming a conductive foamed rubber layer having a two-layer structure composed of a foamed rubber layer and a non-foamed rubber on the outer periphery thereof. As a result, unlike the case of using the split type, no protrusion (burr) occurs at the roller portion at the roller portion, and variations in electrical resistance in the circumferential direction due to the flash can be prevented, and a uniform thin toner layer can be obtained. It becomes easy to be. Usually, a surface layer is further formed on the non-foamed rubber layer obtained as described above by a dipping method or a coating method to form a developing roller.

As the surface layer, a thermoplastic polyurethane resin having a JIS-A hardness of about 80 is dissolved in a solvent such as tetrahydrofuran (THF), a conductivity imparting agent such as carbon black, a silicone acrylic copolymer resin and a fluororesin. A system particle is added and mixed to prepare a coating solution for forming a surface layer. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (P
VDF) and polyvinyl fluoride (PVF). A roller having a foamed rubber layer and a non-foamed rubber layer is immersed in this coating solution, pulled up and dried to form a surface layer, thereby obtaining a developing roller of the present invention. The JIS-A rubber hardness of the rubber layer of the developing roller of the present invention is 5 to 35 or less. JI
When the SA hardness exceeds 35 degrees, in order to obtain a required contact width by fixing the distance between the photoconductor drum and the shaft, the torque increases, and it becomes easy to generate judge due to uneven rotation. Also,
When the value is smaller than 5, problems in physical properties and form retention tend to occur, so the above range is preferable. Particularly preferably, 15 to
25. The JIS-A hardness of the roller in the present invention is a hardness measured by applying a JIS-A type hardness meter to the outer periphery of the rubber layer of the roller under a load of 1 kg. Roller J
The IS-A hardness can be controlled in the range of 5 to 35 by controlling the foaming conditions to control the size of the foam cells or by selecting a rubber material as appropriate. Further, the electric resistance of the developing roller of the present invention is, between the outer peripheral surface of the roller and the end of the rotating shaft,
It can be measured by applying a predetermined voltage. The image forming unit in which the developing device incorporating the developing roller of the present invention and other peripheral devices of the photosensitive member are integrated with the photosensitive member is called an all-in-one cartridge type, and the contact width between the photosensitive member and the developing roller is 0. The shaft is fixed at a distance of 1 to 7 mm, preferably 1 to 3 mm. This ensures that the developing roller contacts the photoreceptor reliably and uniformly, and does not cause rotational unevenness due to an increase in rotational torque, so that no jitter or damage to the drive gear occurs and a slip stick with the photoreceptor occurs. It is difficult
The tearing of the outermost layer is less likely to occur.

[0014]

Example 1 Medium and high nitrile NBR1 with a nitrile content of 33%
00 parts by weight is used as a base rubber, and carbon black, zinc oxide, stearic acid, a vulcanizing agent (including a vulcanization accelerator), a foaming agent (including a foaming aid), and the like are blended as in Formulation 1 of Table 1. The mixture was kneaded with an open roll to obtain a foaming material rubber. Similarly, excluding the foaming agent, the mixture was blended and kneaded as in Formulation 2 in Table 1 to obtain a non-foaming material rubber. These two types of material rubbers are 2 ′ for foaming inside and 3 ′ for non-foaming outside using a screw-type two-layer extruder, 12 mm in outer diameter and 7.5 in inner diameter.
It was extruded into a tube of mm and cut into a length of about 275 mm to obtain a cylindrical roll material. Outer diameter 7mm, length 320m
An adhesive was applied to a stainless-steel rotating shaft 1 which was D-shaped so that both ends were pivotally supported and one end was fitted with a driving gear at m, and was prepared and inserted into a cylindrical roll material. 16 inside diameter
A roll material having a rotating shaft inserted into a medium die 6 made of a steel cylinder having a diameter of 1 mm is inserted. Both ends of the rotating shaft are passed through holes in the center of the seal die 5, and the seal die is taperedly fitted to both ends of the medium die. Complete the patterning. By heating the entire mold at 150 ° C. × min, the inner layer is foamed and vulcanized and integrated with the outer non-foamed layer. After cooling, the molded body is taken out of the mold, and the foamed rubber layer 2 A conductive elastic rubber layer composed of the non-foamed rubber layer 3 was formed. Separately, a vulcanized rubber sheet (foamed and non-foamed) for measuring volume resistivity of 150 mm square and 2 mm thick was prepared using foamed material rubber and non-foamed material rubber, and inserted into a copper plate electrode. The current value at 5 V was read to determine the resistance (SRIS method). JIS-A hardness 8
0 degree caprolactone ester type thermoplastic polyurethane is dissolved in about 4 times weight of THF solvent, carbon black, silicone acrylic resin and DV having an average particle diameter of 10 μm.
DF powder was added and dispersed in the amount shown in Table 2 to prepare a coating solution for the surface layer.

The roller body having the conductive elastic rubber layer is immersed in the coating liquid, pulled up, dried, and the solvent is blown off.
A surface layer was formed. Both ends of the elastic portion were cut by about 2 mm to obtain a developing roller of the present invention having an outer diameter of 16 mm and a length of the elastic portion of 270 mm. Electrodes were applied to the center of the obtained developing roller in the outer peripheral length direction and the shaft end of the rotating shaft, and the electric resistance of the roller was determined from the current value at a voltage of 10 V. A resin-made roller between the shafts is attached to both end shafts of the obtained developing roller so that the nip width becomes 1.5 mm in an integrated image forming unit in which a photoconductor, a developing device, a cleaning device, and the like are integrated. And the shaft support was fixed. This integrated image forming unit was attached to a laser beam printer, and an initial image was output, an image was output after 30,000 copies were run, and damage to the drive gears and contamination of the photoreceptor were evaluated by visual inspection. The results are shown in Table 2.

[0016]

Example 2 The same procedure as in Example 1 was carried out except that the amount of the raw rubber was adjusted so that the thickness of the non-foamed rubber layer became 1.00 mm.
A developing roller having an IS-A hardness of 25 degrees was obtained, incorporated in an integrated image forming unit, and ran for 30,000 sheets. Table 2 shows the results.

[0017]

Example 3 A developing roller having a JIS-A hardness of 18 degrees was obtained in the same manner as in Example 1 except that the amount of the raw rubber was adjusted so that the thickness of the non-foamed rubber layer was 0.07 mm. It was assembled in an image forming unit and 30,000 copies were run. Table 2 shows the evaluation results.

[0018]

Example 4 As in Formulation 3 in Table 1, JIS was carried out in the same manner as in Example 1 except that the amount of carbon black in the non-foamed rubber was reduced and the volume resistivity of the non-foamed rubber layer was increased by about one digit. A developing roller having a -A hardness of 18 degrees was obtained, assembled into an integrated image forming unit, and 30,000 sheets were run. Table 2 shows the evaluation results.

[0019]

Example 5 A developing roller having a JIS-A hardness of 10 degrees was obtained in the same manner as in Example 1 except that the expansion ratio was changed, and the developing roller was assembled into an integrated image forming unit, and 30,000 sheets were run. Table 1 shows the results of each evaluation.

[0020]

Comparative Example 1 A developing roller was obtained in the same manner as in Example 1 except that the amount of carbon was reduced and the volume resistivity of the non-foamed rubber layer was slightly higher than that of the foamed rubber layer, as shown in Formulation 4 in Table 1. , Built into an integrated image forming unit, 30,000
Ran. Table 2 shows the evaluation results.

[0021]

Comparative Example 2 A developing roller was prepared in the same manner as in Example 1 except that the amount of carbon was reduced and the volume resistivity of the non-foamed rubber layer was increased by at least one digit as compared with the foamed rubber layer, as shown in Formulation 5 in Table 1. And integrated into an integrated image forming unit,
00 sheets were run. Table 2 shows the evaluation results.

[0022]

Comparative Example 3 A developing roller was obtained in the same manner as in Example 1 except that the thickness of the non-foamed rubber layer was changed to 0.03 mm. The developing roller was assembled into an integrated image forming unit, and 30,000 sheets were run. Table 2 shows the evaluation results.

[0023]

Comparative Example 4 A developing roller having a JIS-A hardness of 40 was obtained in the same manner as in Example 1 except that the amount of the raw rubber was adjusted so that the thickness of the non-foamed rubber layer became 1.5 mm. It was assembled in a forming unit and 30,000 copies were run. Table 2 shows the evaluation results.

[0024]

[Table 1] [A]: NBR (medium and high nitrile content, polymer Mooney ML1 + 4 (100 ° C.) = 35) [b]: carbon black 1: MAF carbon [c]: carbon black 2: HAF carbon [d]: oil sulfur [e]: Tellurium diethyldithiocarbamate [f]: N-cyclohexyl-2-benzothiazyl-sulifenamide

[0025]

[Table 2]

From the results shown in Table 2, it can be seen that the developing roller of the present invention is a foaming roller, but a stable image can be obtained without a cell pattern, and image formation is good even after 30,000 sheets of running. However, in the developing rollers of Comparative Examples 1 to 4, the unevenness in the density of the image became severe with the running, the image fluctuated, and the entire image became light, and the stability of the image was lacking.

[0027]

According to the developing roller of the present invention, the conductive rubber layer is formed of a foamed rubber layer and a non-foamed thin rubber layer so as to be easily deformed and to reduce the instability caused by the foamed cells. Therefore, even if the required contact width (nip width) with the photoreceptor is taken, the increase in driving torque is small, the jitter caused by uneven rotation is reduced, and the electric resistance and pressure attributed to the cells of the inner foam layer are reduced. Variation in distribution can be reduced. Therefore, the toner can be stably carried on the outer periphery of the developing roller with a uniform thickness, and it is possible to cope with a case where a small particle size toner corresponding to high resolution is used.

[0028]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a developing roller of the present invention.

FIG. 2 is a schematic sectional view showing a production example of a developing roller of the present invention.

FIG. 3 is a schematic view showing an all-in-one cartridge type electrophotographic apparatus.

[Explanation of symbols]

 1. Rotation axis 2. Foamed rubber layer 2 '. Material rubber for foaming 3. Non-foamed rubber layer 3 '. Non-foaming material rubber 4. Surface layer 5. Seal type 6. Cylindrical outer mold 16. Developing roller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H077 AD06 FA13 FA22 FA25 3J103 AA02 AA14 AA37 AA85 FA18 GA02 GA57 GA58 GA60 HA03 HA12 HA18 HA53 HA54

Claims (3)

[Claims] 1. A JIS-A hardness of 5 to 35, wherein a conductive rubber layer and a surface layer are provided concentrically on the outer periphery of a rotating shaft.
2. The developing roller according to claim 1, wherein said conductive rubber layer has a two-layer volume structure in which a non-foamed rubber thin layer having lower electric resistance than the foamed rubber layer is provided on the outer periphery of the foamed rubber layer. 2. The non-foamed rubber thin layer has a volume resistivity of 10 ³ to 10 ³ .
2. The developing roller according to claim 1, wherein the developing roller has a volume resistivity of 10 ¹⁰ Ω · cm and at least one order of magnitude smaller than the volume resistivity of the foamed rubber layer. 3. The thickness of the non-foamed rubber thin layer is 0.05 to 1.
The developing roller according to claim 1, wherein the diameter of the developing roller is 00 mm.