JPH10319678A - Electrically conductive rubber roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrically conductive rubber roll with a low hardness foamed rubber layer almost free from compressive permanent strain by using an electrically conductive foam rubber compsn. contg. EPDM as a rubber base, ADCA as a blowing agent and sulfur as a vulcanizing agent. SOLUTION: A shaft 1 positioned at the axial center of an electrically conductive rubber roll 4 is made of a metal such as iron, aluminum or stainless steel or an electrically conductive synthetic resin. A foamed rubber layer 2 disposed on the outside of the shaft 1 is formed from a foamed rubber compsn. prepd. by blending an ethylene-propylene-diene terpolymer (EPDM) as a rubber base with an electrically conductive material, azodicarbonamide (ADCA) as a foaming agent and sulfur as a vulcanizing agent. A resistance regulating layer 3 is preferably disposed as the outermost layer of the roll 4. A polymer contg. an electrically conductive material may be used as a material forming the layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber roller used in an image forming apparatus such as an electrophotographic apparatus, and more particularly to a conductive rubber roller used in contact with a photosensitive member.

[0002]

2. Description of the Related Art An electrophotographic apparatus such as a copying machine and a laser beam printer generally includes a drum-shaped photosensitive member (photosensitive drum), and charges and exposes the photosensitive drum.
An electrostatic latent image is formed on a photosensitive drum, toner is adhered to the latent image and developed, and then the toner on the photosensitive drum is transferred to a recording medium such as recording paper for transfer. And the toner remaining on the photosensitive drum is cleaned, and a new charge exposure is started.
The toner carried on the recording medium by the transfer is melted, pressed and fixed on the recording medium, thereby completing a series of recording operations. In order to carry out each of the above steps, a charging roller, a developing roller, a transfer roller, and a charge eliminating (cleaning) roller are arranged around the photosensitive drum. The charging roller applies a predetermined potential to the photosensitive area of the photosensitive drum, the developing roller transports the toner to the photosensitive drum, the transfer roller transfers the toner image to the recording medium transported to the transfer area, and the charge removing roller. Makes the charged area of the photosensitive drum after the transfer uniform at a constant potential and removes residual deposits such as transfer residual toner from the photosensitive drum. However, in recent years, a cleaning blade has been employed in place of the charge eliminating (cleaning) roller. These rollers are usually composed of a conductive shaft and a conductive elastic layer (polymer such as rubber or polyurethane). Alternatively, the elastic layer is used to adjust the electric resistance of the roller and prevent contamination of the photosensitive drum and the recording medium. Some include a resistance adjusting layer to cover.

[0003] Such a conductive roller is usually used in contact with a photosensitive drum. In particular, a charging roller is used.
It is pressed and urged toward the photosensitive drum by a pressure spring or the like, and is pressed against the photosensitive drum surface with a predetermined pressing force.

[0004]

If the conductive roller is kept in contact with or pressed against the photosensitive drum for a long period of time, the roller (especially the nip portion) is subjected to permanent compression (also referred to as settling).
Occurs. This tendency is remarkable when the conductive roller is made of foamed rubber. When the compression set is deteriorated, there arises a problem that image deformation occurs due to deformation of the roller at a set portion.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a conductive roller having a foamed rubber layer having low hardness and low compression set, and a conductive foamed rubber composition capable of forming such a rubber layer The purpose is to provide things.

[0006]

In order to achieve the above object, a conductive roller according to the present invention is provided with a conductive rubber layer concentrically provided on the outer periphery of a shaft, and further comprises a conductive rubber layer. A resistance adjusting layer may be provided on the outer peripheral surface, a conductive rubber roller used in contact with the photoconductor, the conductive rubber layer is made of foamed rubber, EPDM as a rubber base material, as a foaming agent ADCA is obtained by foaming and curing a composition containing sulfur as a vulcanizing agent.

Further, the conductive roller of the present invention may be configured such that a conductive rubber layer is provided concentrically on the outer periphery of a shaft body, and a resistance adjusting layer may be further provided on the outer peripheral surface of the conductive rubber layer. A conductive rubber roller used in contact with a photoreceptor, wherein the conductive rubber layer comprises at least two layers, and an outer layer (photoreceptor side) of the two rubber layers comprises a non-foamed rubber. The inner layer (shaft side) is made of foamed rubber, and the foamed rubber is made of EPDM as a rubber base material, ADCA as a foaming agent,
It is obtained by foaming and curing a composition containing sulfur as a vulcanizing agent.

Further, the conductive foamed rubber composition of the present invention comprises EPDM as a rubber base, ADCA as a foaming agent,
Contains sulfur as a vulcanizing agent.

The present inventors prepared a conductive foamed rubber composition containing EPDM as a rubber base material, ADCA as a foaming agent, and sulfur as a vulcanizing agent in order to obtain a foamed rubber layer free from compression set. Then, when this was foamed and cured to form a foamed rubber layer or a foamed layer in the conductive rubber layer on the outer periphery of the shaft body, it was found that almost no permanent compression set of the roller was generated, and the present invention was reached.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of a conductive rubber roller according to a first embodiment of the present invention. In the figure, 1 is a shaft, 2 is a foamed rubber layer, 3 is a resistance adjusting layer, and 4 is a conductive rubber roller.

The shaft body 1 located at the shaft center of the conductive rubber roller 4 is made of, for example, a metal such as iron, aluminum, or various stainless steels, or a synthetic resin having conductivity.

A foamed rubber layer 2 provided on the outer periphery of a shaft 1
Is formed from a foamed rubber composition in which a conductive material, a foaming agent, and a vulcanizing agent are blended in a rubber base material. Rubber substrate used in the present invention,
Ethylene-propylene-diene terpolymer (EPD
M).

Examples of the conductive material to be added to the foamed rubber composition include conductive powders of carbon black, graphite, metal, and conductive metal oxides (tin oxide and titanium oxide), carbon fibers, and short fibers of metal oxide. And various conductive fibers can be used. The amount of the conductive material is preferably set to 5 to 80 parts with respect to 100 parts by weight (hereinafter, abbreviated as "part") of the rubber base material.

Azodicarbonamide (ADCA) is used as the foaming agent. The amount of the foaming agent is preferably set in the range of 0.5 to 15 parts based on 100 parts of the rubber substrate.

In the present invention, sulfur is used as a vulcanizing agent. In addition to the above materials, additives such as a vulcanization accelerator, a softener, a plasticizer, a reinforcing agent, an antioxidant, and an antistatic agent can be appropriately added to the foamed rubber composition.

A resistance adjusting layer 3 is preferably provided on the outermost periphery of the conductive rubber roller 4 of the present invention. As a material for forming the resistance adjusting layer 3, a polymer material containing a conductive material can be used. Examples of the polymer material include N-methoxymethylated nylon (8-nylon) and urethane.
As the conductive material that can be used, carbon black is particularly preferable among the above-described materials. The resistance adjusting layer 3 controls the electric resistance of the conductive rubber roller 4 within an appropriate range, and gives the roller withstand voltage (leak resistance). Furthermore, the resistance adjustment layer 3
Constitutes the outermost layer of the conductive rubber roller 4 and prevents the softener, the plasticizer and the like from seeping out from the inside of the roller, and prevents the photosensitive drum from abutting.

A feature of the present invention is that the conductive foamed rubber composition comprises a combination of a rubber base material EPDM, a foaming agent ADCA, and a vulcanizing agent sulfur, and in particular, uses ADCA as a foaming agent. When a known foaming agent other than ADCA, for example, OBSH (4,4'-oxybisbenzenesulfonyl hydrazide) is used, the foaming agent inhibits vulcanization when the foamed rubber composition is heated and vulcanized. Therefore,
The crosslink density of the rubber decreases, and the compression set of the foamed rubber layer formed increases. In the present invention, such a problem can be avoided by employing ADCA.

FIG. 2 is a sectional view showing an example of a conductive rubber roller according to a second embodiment of the present invention. In the figure, 1 is a shaft, 3 is a resistance adjusting layer, 5a is a foamed rubber layer, 5b is a non-foamed rubber layer, and 6 is a conductive rubber roller.

The difference between the conductive rubber roller 6 and the conductive rubber roller 4 shown in FIG.
Is composed of two layers (or more than two layers),
Other than that, both are substantially the same, and the description of each part is omitted. Here, the two layers include both the foamed rubber and the case of the non-foamed rubber and the foamed rubber, and the latter is particularly the inner layer (the shaft body side) of the two rubber layers. It is preferable that the outer layer (photoconductor side) is made of foamed rubber and the outer layer is made of non-foamed rubber. Therefore, in the conductive rubber roller 6 shown in FIG.
a, the outer layer is composed of a non-foamed rubber layer 5b.

The conductive rubber roller 4 according to the first embodiment of the present invention is obtained, for example, from a conductive foamed rubber composition as follows. That is, after the conductive foamed rubber composition is extruded into a tube shape on the outer peripheral surface of the shaft body 1,
The shaft 1 is inserted. Then, it is set in a mold having a cylindrical cavity and heated to foam and vulcanize. Next, the material for forming the resistance adjusting layer 3 is mixed and mixed, and this is dissolved in an organic solvent. This solution is applied to the outer surface of the foam layer by a dipping method, a roller coating method, a spray coating method or the like, and dried to form a resistance adjusting layer 3, thereby producing a conductive rubber roller 4 as shown in FIG. be able to.

The conductive rubber roller 6 according to the second embodiment of the present invention is manufactured by various extrusion molding methods, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 7-295331. Among these, a particularly preferable extrusion molding method is to use an extruder capable of co-extrusion, and to use a foamed rubber composition for forming the inner foamed rubber layer 5a and a rubber composition for forming the outer non-foamed rubber layer 5b. Are simultaneously extruded, and 2
This is a method of obtaining a continuous cylindrical laminate in which a rubber layer is formed. Such a laminate is cut to a predetermined length,
It is placed in a mold having a cylindrical cavity. After that, vulcanization and foaming by heating are performed to integrate the inner foamed rubber layer 5a, the outer non-foamed rubber layer 5b, and the core metal 1 into an object having a shape along the inner peripheral surface of the mold. Obtain a conductive roller. Further, on the outer peripheral surface of the conductive roller,
When the resistance adjusting layer 3 is formed as described above, the conductive rubber roller 6 as shown in FIG. 2 can be manufactured.

As the non-foamed rubber composition used to form the non-foamed rubber layer 5b, the foamed rubber composition not containing the foaming agent ADCA may be used. Can be prepared and used. The rubber base material used for this purpose is not limited to EPDM, and may be a normal rubber or styrene rubber such as nitrile butadiene rubber, chloroprene rubber, isoprene rubber, styrene butadiene rubber, ethylene propylene rubber, isoprene rubber, and polynorbornene rubber. Plastic rubber such as butadiene styrene rubber (SBS) or its water additive (SEBS) can be mentioned.

The conductive rubber roller of the present invention is optimally applied to a charging roller, but can also be used for a developing roller, a transfer roller, a charge removing roller, etc. used in contact with a photosensitive member in an electrophotographic apparatus. It is.

When the rubber rollers 4 and 6 of the present invention are used as a charging roller, the amount of the conductive material to be added to the foamed rubber composition or the non-foamed rubber composition is determined according to the electrical characteristics required for the roller. However, as a desirable charging roller, the resistance value of the roller is 10 ³ to 10 ⁷ Ω, and the volume resistivity of the rubber layer is 10 ¹ to 10 ¹³ Ω · cm.

The embodiments of the present invention will be further described with reference to Examples and Comparative Examples, but these do not limit the scope of the present invention. All parts are by weight unless otherwise indicated.

(Embodiment 1) For 100 parts of EPDM,
60 parts of carbon black, 15 parts of blowing agent azodicarbonamide (ADCA), and other additives such as vulcanizing agent sulfur were appropriately blended and kneaded with an open roll to prepare a foamed rubber composition. The foamed rubber composition was extruded using a die to prepare a cylindrical roller material. Add a metal core (diameter 6)
A stainless steel round bar with a length of 250 mm and a length of 250 mm) is passed through a cylindrical mold, heated (200 ° C., 20 minutes), foamed and vulcanized, and a conductive foamed rubber layer is formed on the outer periphery of the cored bar. The conductive rubber roller of the invention was obtained. The dimensions of the foam rubber layer 2 were 3 mm in thickness and 230 mm in length. The charged amount of the rubber composition was 30% by volume when the volume of the core metal and the mold was 100. The hardness of the conductive foamed rubber layer is Asker C
30 °, and the volume resistance of the conductive rubber roller of this example was 10 ⁵ Ω · cm.

Example 2 The surface of the roller obtained in Example 1 was washed with a solvent. This was further diluted with a urethane coating solution (100 parts of Resamine ME-3119; 40 parts of carbon black ATL8794; methyl ethyl ketone 9).
1 part; dimethylformamide 49 parts), and after immersion, dried at room temperature.
The resistance adjusting layer 3 having a thickness of 0 μm was formed to obtain the conductive rubber roller of the present invention.

(Embodiment 3) For 100 parts of EPDM,
60 parts of carbon black, 15 parts of a blowing agent azodicarbonamide (ADCA), and other additives such as a vulcanizing agent sulfur were appropriately blended and kneaded with an open roll to prepare a foamed rubber composition for an inner layer. Subsequently, a non-foamed rubber composition for the outer layer in which the foaming agent ADCA was not blended in the composition was prepared. The prepared two types of rubber compositions are integrally extruded by a two-color extruder, and a metal core (a stainless steel round bar having a diameter of 6 mm and a length of 250 mm) is sent out from a substantially central portion of a die of the molding machine. Then, a molded article comprising two layers, an inner layer and an outer layer, and a metal core was obtained.

In a cylindrical mold, a heat treatment (2
(00 ° C., 1 hour), foamed and vulcanized, and a rubber layer was integrally formed with a core metal to obtain a roller. Thereafter, the mold was cooled to room temperature, the molded body roller was taken out, and the roller surface was washed with a solvent. This is further immersed in the urethane coating solution used in Example 2 containing a predetermined amount of carbon black, and after immersion, dried at room temperature, and has a resistance of about 100 μm on the outer peripheral surface of the non-foamed rubber layer 5b. The adjustment layer 3 was formed to obtain the conductive rubber roller of the present invention.

(Comparative Example 1) For 100 parts of natural rubber,
60 parts of carbon black, 15 parts of a blowing agent OBSH, and other additives such as a vulcanizing agent and sulfur were appropriately mixed and kneaded with an open roll to prepare a foamed rubber composition. Using this composition, a conductive rubber roller was manufactured in the same manner as in Example 1.

Comparative Example 2 For 100 parts of EPDM,
60 parts of carbon black, 15 parts of a blowing agent OBSH, and other additives such as a vulcanizing agent and sulfur were appropriately mixed and kneaded with an open roll to prepare a foamed rubber composition. Using this composition, a conductive rubber roller was manufactured in the same manner as in Example 1.

Comparative Example 3 For 100 parts of EPDM,
60 parts of carbon black, 15 parts of blowing agent dinitrosopentamethylenetetramine (DPT), other additives such as a vulcanizing agent and sulfur are appropriately blended and kneaded with an open roll.
A foam rubber composition was prepared. Using this composition, a conductive rubber roller was manufactured in the same manner as in Example 1.

Comparative Example 4 For 100 parts of EPDM,
60 parts of carbon black, 15 parts of blowing agent OBSH, other vulcanizing agents, appropriately blending additives such as peroxides,
The mixture was kneaded with an open roll to prepare a foamed rubber composition.
Using this composition, a conductive rubber roller was manufactured in the same manner as in Example 1.

Evaluation of Compression Permanent Set A load of 500 g was applied to both ends of each of the conductive rubber rollers obtained from the above Examples and Comparative Examples, and they were pressed against a photoreceptor having an outer diameter of 30 mm. (3 days), and the amount of settling was measured.

FIG. 3 schematically shows such an evaluation test of compression set. In the figure, 10 is a conductive rubber roller, 11
Represents a photosensitive drum. The set amount is, as shown in FIG. 4, a value obtained by measuring the dent on the outer peripheral portion of the roller as compared with before the test.

Table 1 shows the results of the above evaluation tests.

[0038]

[Table 1]

REFERENCE EXAMPLE For each of the foamed rubber composition containing ADCA used in Example 1 and the foamed rubber composition containing OBSH used in Comparative Example 1, a rheometer (M
DR2000), a vulcanization test (160 ° C.) was performed and a torque-time curve (vulcanization curve) was recorded. As a result, a vulcanization curve as shown in FIG. 5 was obtained. In the foamed rubber composition of Comparative Example 1 using OBSH as a foaming agent, the maximum torque was recorded after 10 minutes of the vulcanization time, and the vulcanization did not proceed any further.
On the other hand, in the foamed rubber composition of Example 1 using ADCA as a foaming agent, the maximum torque was recorded after elapse of 20 minutes, and this maximum value was much larger than the maximum torque value of the foamed rubber composition of Comparative Example 1. Therefore, in the foamed rubber composition of Comparative Example 1, the foaming of OBSH significantly inhibited the progress of vulcanization, and the degree of vulcanization was not sufficiently increased.

[0040]

As described above, according to the present invention, since the conductive rubber layer is foamed from the foamed rubber composition containing the foaming agent ADCA, the rubber base EPDM, and the sulfur vulcanizing agent, the amount of settling is small. An excellent roller material is obtained in compression set. Therefore, when an image is formed using the conductive rubber roller of the present invention, image unevenness does not occur.

Further, since the conductive rubber roller of the present invention has a small compression set, it has good vibration absorption characteristics, and can suppress generation of charging noise during use. Further, a good image can be obtained without impurities bleeding out (bleed out) from the inside of the roller.

[Brief description of the drawings]

FIG. 1 is a sectional view of a conductive rubber roller according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a conductive rubber roller according to a second embodiment of the present invention.

FIG. 3 is a schematic perspective view for explaining a compression set measurement test.

FIG. 4 is a schematic diagram illustrating a definition of a set amount.

FIG. 5 is a graph showing a vulcanization curve obtained using a rheometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shaft 2,5a Foam rubber layer 3 Resistance adjustment layer 4,6,10 Conductive rubber roller 5b Non-foam rubber layer 11 Photosensitive drum

Claims (2)

[Claims] An electroconductive rubber layer is provided concentrically on the outer periphery of a shaft body, and a resistance adjusting layer may be further provided on the outer peripheral surface of the conductive rubber layer. The conductive rubber layer is made of foamed rubber, EPDM is used as a rubber base material, and ADC is used as a foaming agent.
A. A conductive rubber roller obtained by foaming and curing a composition containing sulfur as a vulcanizing agent. 2. A method in which a conductive rubber layer is provided concentrically on the outer periphery of a shaft body, and a resistance adjusting layer may be further provided on the outer peripheral surface of the conductive rubber layer. The conductive rubber layer comprises at least two layers, of which the outer layer (photoconductor side) is made of non-foamed rubber and the inner layer (shaft side) is foamed rubber. The foamed rubber, EPDM as a rubber substrate,
A conductive rubber roller obtained by foaming and curing a composition containing ADCA as a foaming agent and sulfur as a vulcanizing agent.