JP2003307896A - Conductive roller and method for manufacturing sponge rubber used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive roller capable of well electrostatically charging a body to be electrostatically charged and a method capable of manufacturing sponge rubber used for the conductive roller with high productivity. <P>SOLUTION: The conductive roller consists of a conductive member for electrostatically charging the body to be electrostatically charged in contact therewith, in which the conductive member has a roller shape comprising a shaft body having an electrical conductivity and the sponge rubber formed on the outer periphery thereof and the foam cells on the surface of the elastic foam are smaller than the foam cells on the shaft body side. The method for manufacturing the sponge rubber comprises forming unvulcanized rubber compounded to make the rate of vulcanization lower than that of unvulcanized rubber and to make the density of crosslinking lower on the layer on the outer side of the unvulzanized rubber compounded to initiate the decomposition of a foaming agent after the vulcanization initiation of at least the unvulcanized rubber so as to coat this layer and subjecting the rubber to vulcanization foaming. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to charging, transfer, paper conveyance, and image forming apparatus using an electrophotographic process.
The present invention relates to a method for producing sponge rubber used for developing and cleaning members and the like.

[0002]

2. Description of the Related Art In a conventional electrophotographic apparatus, a charging device for uniformly charging the surface of a photoconductor or a transferable toner image formed on the surface of the photoconductor is statically transferred onto a sheet-shaped transfer material composed mainly of paper. As a transfer device for electrically transferring, a corotron charger using a corona discharge generated by applying a high voltage to a thin wire such as tungsten and the like is generally used. However, the method using corona discharge has drawbacks such as requiring a high-voltage power source and causing adverse effects such as deterioration of the photoconductor due to strong oxidizing action of generated ozone. Therefore, many ozoneless charging and ozoneless transfer methods have been conventionally proposed. They mainly reduce the discharge current as much as possible by directly supplying an electric charge from a conductive charging member or a transfer member to the photoconductor, which is the member to be charged, and as a result, reduce the amount of ozone generated during discharge. is there. Such a conductive member is required to have appropriate conductivity and low hardness in order to ensure uniform contact with the photosensitive member, and a conductive sponge rubber roller is often used. In addition, in recent years, JP-A-6-3921 and JP-A-11-652.
As disclosed in Japanese Patent No. 31, etc., a mechanism for charging the surface of the body to be charged by directly injecting an electric charge from the contact charging member to the body to be charged has been proposed. The contact charging member having a medium resistance comes into contact with the surface of the body to be charged, and the charge is directly injected to the surface of the body to be charged without interposing the discharge phenomenon, that is, basically without using the discharge mechanism. As the contact charging member, a porous roller such as a sponge roller coated with conductive particles for improving the contact charging property is used to close the contact between the contact charging member and the body to be charged. It is possible to improve the charging property. As the required sponge roller, Japanese Patent Application Laid-Open No. 20
As disclosed in 01-188404, as a charging member in injection charging, the cell diameter is appropriately small, and the cell wall is thin from the viewpoint of the retention of conductive particles and the contact efficiency, and the contact efficiency is also improved. It is a conductive sponge rubber roller having a low hardness so that the nip width can be increased.

In order to achieve both low hardness and fine foam cells on the roller surface, ideally, the cells inside the roller should be large and the roller surface cell diameter should be small. . If the internal cells are large, the hardness of the roller as a whole is reduced, and the nip width with the body to be charged can be increased.

As a method for producing sponge rubber, a free foaming method and a mold are used as a method of forming a sponge by generating a gas in the rubber by mixing a rubber with a thermally decomposable chemical foaming agent and heating it. There is an in-mold foaming method performed in-house. Other methods include a method of mixing and dispersing microcapsules or the like in rubber as in JP 2001-97594 A, or a method of dispersing a soluble material in rubber as in JP 11-198250 A or the like. After that, there is a method of obtaining a sponge rubber by eluting with a solvent. However, in the microcapsule method, although the size and shape of the cell itself can be obtained stably, it is difficult to highly fill it, it is difficult to obtain a sponge body with a thin cell wall, and the material cost is higher than that of a chemical foaming agent. Is expensive. Since the elution method requires a very long elution time as compared with the chemical foaming, it is very difficult to produce at a low cost.

Further, in the in-mold foaming method, Japanese Unexamined Patent Publication No. 2001-19
A method using a split mold like 1349 has been proposed, and it is said that a highly foamed sponge rubber having a high cell density can be obtained. However, variations in hardness depending on the charged amount and in the partition part of the split mold. Since the variation in electric resistance is a problem and the die needs to be processed with extremely high precision, the die manufacturing cost is high, and thus it is difficult to produce at low cost.

On the other hand, the free foaming method has a high productivity because a continuous vulcanizing device can be used, and since it does not require mold handling and mold manufacturing cost, it can be manufactured at low cost. Is advantageous to. However, it is not easy to produce a highly foamed sponge rubber by free foaming under normal pressure. As in JP-A-8-169974, by pre-vulcanizing only the surface portion, it is possible to increase the expansion ratio of the sponge rubber by preventing the gas generated by the foaming of the foaming agent from escaping to the outside. However, it is difficult to obtain a sponge rubber having a small cell diameter and a thin cell wall because the surface portion is insufficiently vulcanized.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention provides a conductive roller which can favorably charge an object to be charged,
Another object of the present invention is to provide a method capable of manufacturing the conductive roller with high productivity.

[0008]

That is, according to the present invention, in a conductive member for contact-charging an object to be charged, the conductive member has a conductive shaft and a roller-shaped outer periphery made of sponge rubber. The conductive roller is characterized in that the foam cells on the surface of the elastic foam are smaller than the foam cells on the shaft side.

Further, according to the present invention, the vulcanization rate is higher than that of the unvulcanized rubber in the outer layer of the unvulcanized rubber compounded so that the decomposition of the foaming agent is started at least after the vulcanization of the unvulcanized rubber is started. The method for producing a sponge rubber is characterized in that an unvulcanized rubber compounded so as to have a low viscosity and a low crosslink density is formed by coating and vulcanized and foamed.

[0010] At least when the unvulcanized rubber compounded so that the decomposition of the foaming agent starts after the unvulcanized rubber starts to be vulcanized and foamed, the crosslinking of the rubber proceeds during the foaming. Since the viscosity of the rubber is much higher than that of unvulcanized rubber, the escape of the foaming gas of the foaming agent can be reduced and a sponge rubber with a high expansion ratio can be manufactured. In order to maintain such a balance between vulcanization and foaming, it is preferable to use a thiuram compound and / or a carbamate compound having a high accelerating vulcanization effect as compared with a commercially available thermally decomposable foaming agent. It is possible by combining azodicarbonamide (hereinafter referred to as ADCA), which has a high decomposition temperature, and by blending it in excess of a general blending amount so that foaming occurs even in a state where vulcanization proceeds. In addition, by using a foaming agent with a high decomposition temperature, vulcanization of the rubber surface can proceed more than before, so the foam cells near the surface of the sponge rubber are small and the foam cells gradually increase inward. It is possible to

Here, when vulcanizing and foaming an unvulcanized rubber compound, a highly foamed sponge rubber having a fine cell diameter and a thin cell wall is produced by a heating device for heating from the surface of rubber such as normal hot air. However, since vulcanization of the surface has proceeded excessively, cracks and the like will occur on the surface during the process of foaming and expansion of the rubber. Therefore, the present inventors have formulated a non-vulcanized rubber compound on the outer surface of the non-vulcanized rubber compound in such a manner that the vulcanization rate is slower and the crosslink density is lower than that of the unvulcanized rubber compound, in order to prevent cracking during molding. It has been found that it is possible to stably produce a sponge rubber having the above-mentioned properties by forming a layer of a vulcanized rubber compound and vulcanizing and foaming. That is, it is necessary to prevent the modulus of the rubber surface from increasing so much as to cause cracks when the rubber expands due to foaming, and the foaming cells are inclined near and inside the sponge rubber surface as shown in FIG. It is possible to produce sponge rubber that is distributed in a distributed manner.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

In the method for producing a sponge rubber of the present invention, as shown in the step of FIG. 1, first, an unvulcanized rubber is appropriately kneaded by a rubber kneading device such as an ordinary kneader, Banbury mixer and open roll. Obtain the formulation.
Next, it is molded into a desired shape, but the device to be used is not particularly limited, and if it is molded into a tube shape, for example,
It may be extruded using a two-layer extruder as shown in FIG.
The tube extruded in two layers is continuously conveyed into a heating furnace by a belt conveyor or a roll conveyor, and is passed through the heating furnace to form a sponge rubber tube, and then the outer layer is peeled off. Further, the obtained sponge tube may be subjected to secondary vulcanization if necessary. When manufacturing a conductive sponge roller, an unvulcanized rubber compound having conductivity is used, and a sponge rubber tube manufactured by the above process is coated with a conductive shaft, for example, an adhesive agent. After press-fitting the cored bar and applying adhesion,
It can be manufactured by forming a desired shape by a polishing process. Further, by adjusting the polishing allowance in the polishing step, large cells on the sponge rubber surface are removed, and as shown in FIG. 4, a roller having fine cells on the roller surface and large cells on the shaft side is manufactured. it can.

The method of laminating is not particularly limited to the above-mentioned method, and it may be formed integrally with the conductive shaft body by incorporating a crosshead die in the extrusion head instead of the tubular shape. After integrally molding the core metal and the unvulcanized rubber, the unvulcanized rubber compounded such that the vulcanization rate is slower and the crosslink density is lower than the unvulcanized rubber is used as a mold injection method or a sheet. You may wind things around.

The unvulcanized rubber (raw polymer) used in the unvulcanized rubber compound which is the material of the sponge rubber of the present invention is selected according to the intended use of the roller.
For example, butadiene rubber, styrene butadiene rubber (SB
R), nitrile rubber (acrylonitrile-butadiene rubber), ethylene-propylene rubber (EPDM: ethylene-propylene-diene terpolymer), ethylene-propylene rubber (EPM) and nitrile-butadiene rubber (N).
BR) and the like. In the present invention, the Mooney viscosity (ML ₁₊₎ is preferable for obtaining a highly foamed sponge rubber because a foaming gas is more difficult to escape as the unvulcanized rubber compound has a higher viscosity and a higher vulcanization rate. ₄ ) A raw material polymer having 40 or more is used.

The unvulcanized rubber compound is suitable as a vulcanizing agent from sulfur or non-sulfur vulcanizing agents such as metal oxides and organic peroxides under the conditions such as a heating device and vulcanization rate. Add things. When sulfur is used as a vulcanizing agent in the present invention, it is important to obtain a high vulcanization rate. Therefore, it is desirable to use a super accelerator such as a thiuram compound or a carbamate compound alone or in combination. It is possible to get speed.

A foaming agent is added to the unvulcanized rubber compound, and the amount of addition and the kind of the foaming agent are selected according to the vulcanization conditions, the vulcanization temperature, etc. In the present invention, it is desirable that the decomposition of the foaming agent starts after the vulcanization has progressed to a certain extent, so that the foaming agent having a relatively high decomposition temperature is preferable. For example, as an organic foaming agent,
ADCA (azodicarbonamide) type and DPT (dinitrosopentamethylene tetraamine) type are preferable,
ADCA which is not colored and has a small odor of decomposed gas is particularly preferable. Inorganic foaming agents and OBS with relatively low decomposition temperature
H and TSH have high cell diameters and thin cell walls because decomposition starts at the same time as vulcanization at 140 ° C, which is a general vulcanization temperature, regardless of whether or not a foaming aid is used together. It is difficult to obtain foamed sponge rubber. Similarly AD
When CA, DPT, or the like is used, it is preferable to use it alone while keeping the decomposition temperature higher than using it by combining it with a foaming auxiliary to lower the decomposition temperature. Further, in the present invention, since it is preferable to produce a highly foamed sponge rubber having an expansion ratio of 2 to 10, it is preferable to add a relatively large amount of a foaming agent, and to obtain a desired expansion ratio, It is preferable to add 15 to 30 parts by weight to 100 parts by weight of unvulcanized rubber. If the amount is less than 15 parts by weight, the amount of foaming gas generated is insufficient and the expansion ratio tends to be low.
When the amount is more than 0 parts by weight, the expansion ratio is too high because the amount of the foaming gas is excessive, and the size of the foam cells is apt to increase.

The sponge rubber has a volume resistance of 10³-10¹²Ω
・ When making it conductive with an electric resistance of about cm,
The conductive powder is dispersed in the vulcanized rubber compound. For example,
Conductive powders often used include carbon black and conductive powder.
Carbons such as electric carbon, graphite, TiO
₂, SnO₂Conductive metal oxides such as ZnO and ZnO, SnO ₂
And Sb₂O₃Solid solution of ZnO and Al₂O₃As a solid solution of
Complex oxides with the above metal oxides, metals such as Cu and Ag
Etc., and conductive fibers can also be used.
Wear. Depending on the desired conductivity, the conductive powder used
Conductivity to 100 parts by weight of unvulcanized rubber depending on specific gravity
It is preferable to add 5 to 200 parts by weight of powder. Well
It also has ionic conductivity like quaternary ammonium salt
Materials may be added.

In addition, inorganic fillers such as carbon black, talc and clay may be added to the unvulcanized rubber compound, and the unvulcanized rubber compound may be kneaded or extruded thereafter. If necessary, a process oil, a softening agent or the like, which is advantageous in forming a cylindrical shape, is appropriately added.

In the present invention, on the outer surface of the "unvulcanized rubber composition in which the decomposition of the foaming agent starts later,""compounded so that the vulcanization rate is slower and the crosslink density is lower than that of the unvulcanized rubber. It is preferable that the outer layer does not contain a foaming agent and a vulcanizing agent. Materials differing only in the absence of a foaming agent and a vulcanizing agent are preferred for the formulation of the "vulcanized rubber compound". Of course, it is also possible to use other raw material polymers.

The vulcanization conditions vary depending on the temperature at which the foaming agent of the rubber added to the unvulcanized rubber compound used decomposes and the type of vulcanization accelerator or vulcanizing agent, but the foaming agent decomposes. Since the temperature can be controlled by selecting the foaming agent, it may be a temperature that is sufficient for the vulcanization of the rubber to proceed and a temperature at which the foaming agent starts to decompose after a fixed time from the start of heating,
The vulcanization temperature of the rubber is preferably 120 to 250 ° C. Since the higher the vulcanization rate, the more preferable, the vulcanization temperature is more preferably 160 ° C to 200 ° C.

As the heating means, the HAV method for heating with hot air which has been conventionally used as a continuous heating device, the LCM method for heating in a bath in which a metal salt having a low melting point is melted, and the minute glass beads are heated with hot air. Then, the PCM method used as a heat medium, and other heating means using UHF or far infrared rays can be used.

The sponge rubber produced under such conditions has a foaming ratio of 3 to 10 times and a cell diameter of 20 to 200 μm.
The cell diameter such as m is dense and has low hardness, and defects such as cracks do not occur during vulcanization foam molding, and stable manufacturing is possible.

The expansion ratio of sponge rubber is as shown below.
Specific gravity before and after foaming (g / cm ³)
To calculate.

Expansion ratio = (specific gravity before vulcanization foaming) / (specific gravity after vulcanization foaming)

The cell diameter was measured as follows.

Visible light (halogen lamp) was applied to an arbitrary cross section of the sponge rubber and observed with an optical microscope (DMR HC metallographic microscope manufactured by Leica Microsystem Co., Ltd.) at a magnification of 200. The obtained cell and cell wall The sponge structure composed of 2 is binarized, and from the area of each cell, each cell is converted into a true circle equivalent diameter, and the average is taken as the cell diameter. However, the cell diameter is calculated excluding cells of 10 μm or less.

[0028]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 Using the materials shown below, FIG.
A sponge rubber was prepared by the manufacturing method shown in FIG.

[0030]   <Unvulcanized rubber compound for inner layer>   Ethylene propylene diene rubber 100 parts by weight   [Product name: EPT8075E, manufactured by Mitsui Chemicals, Inc.]   Zinc white 5 parts by weight   Stearic acid 2 parts by weight   Carbon black 50 parts by weight   20 parts by weight of calcium carbonate   Paraffin oil 50 parts by weight   [Product name: PW-380, manufactured by Idemitsu Kosan Co., Ltd.]   2 parts by weight of mercaptobenzothiazole (vulcanization accelerator)   Zinc dibutylcarbamate (vulcanization accelerator) 1 part by weight   Diethyl thiuram disulfide (vulcanization accelerator) 2 parts by weight   2 parts by weight of sulfur (vulcanizing agent)   ADCA (foaming agent) 25 parts by weight   [Product name: Vinyl Hall AC # 3, manufactured by Eiwa Kasei Co., Ltd.]

<Unvulcanized rubber compound for outer layer> A compound containing no vulcanizing agent, vulcanization accelerator and blowing agent from the above-mentioned unvulcanized rubber compound for inner layer, that is, ethylene propylene diene rubber 100. Parts by weight [Product name: EPT8075E, manufactured by Mitsui Chemicals, Inc.] Zinc white 5 parts by weight Stearic acid 2 parts by weight Carbon black 50 parts by weight Calcium carbonate 20 parts by weight Paraffinic oil 50 parts by weight [Product name: PW-380, Idemitsu Kosan Co., Ltd.]

HAV (heating device using heated air) was used as the heating device, the temperature of the heating furnace was 170 ° C., and the heating time was 30 minutes.

Table 1 shows the presence / absence of cracks in the obtained sponge rubber and the results of measuring the expansion ratio and cell diameter by the above method.

Example 2 A sponge rubber was formed in the same manner as in Example 1 using the following materials.

<Unvulcanized Rubber Compound for Inner Layer> The same material as the unvulcanized rubber compound for inner layer of Example 1 was used.

[0036]   <Unvulcanized rubber compound for outer layer>   Ethylene propylene diene rubber 100 parts by weight   [Product name: EPT8075E, manufactured by Mitsui Chemicals, Inc.]   Zinc white 5 parts by weight   Stearic acid 2 parts by weight   Carbon black 50 parts by weight   20 parts by weight of calcium carbonate   Paraffin oil 50 parts by weight   [Product name: PW-380, manufactured by Idemitsu Kosan Co., Ltd.]   Mercaptobenzothiazole (vulcanization accelerator) 1 part by weight   Sulfur (vulcanizing agent) 0.1 part by weight

The same results as in Example 1 are shown in Table 1.

Comparative Example 1 A sponge rubber was formed in the same manner as in Example 1 using the following materials.

<Unvulcanized Rubber Composition for Inner Layer> The same material as the unvulcanized rubber composition for inner layer of Example 1 was used.

[0040]   <Unvulcanized rubber compound for outer layer>   Ethylene propylene diene rubber 100 parts by weight   [Product name: EPT8075E, manufactured by Mitsui Chemicals, Inc.]   Zinc white 5 parts by weight   Stearic acid 2 parts by weight   Carbon black 50 parts by weight   20 parts by weight of calcium carbonate   Paraffin oil 50 parts by weight   [Product name: PW-380, manufactured by Idemitsu Kosan Co., Ltd.]   2 parts by weight of mercaptobenzothiazole (vulcanization accelerator)   Sulfur (vulcanizing agent) 1 part by weight

The same results as in Example 1 are shown in Table 1.

Comparative Example 2 A sponge rubber was prepared using the unvulcanized rubber compound for the inner layer of Example 1. However, the unvulcanized rubber compound for the outer layer was not used, and it was formed by a single layer extruder. The same results as in Example 1 are shown in Table 1.

[0043]

[Table 1]

From the results shown in Table 1, at least the outer surface of the unvulcanized rubber compounded so that the decomposition of the foaming agent is started after the vulcanization of the unvulcanized rubber is vulcanized rather than the unvulcanized rubber. Stabilizes conductive sponge rubber with a fine cell diameter and a high expansion ratio by forming a layer of unvulcanized rubber compound that is compounded so that the speed is slow and the crosslink density is low, and vulcanized and foamed. It can be manufactured without defects. On the other hand, when the coating is not performed, there is no problem with respect to the expansion ratio and the cell diameter, but cracks occur and good results cannot be obtained.

[0045]

As described above, according to the present invention,
At least on the outer surface of the unvulcanized rubber compounded such that decomposition of the foaming agent starts after vulcanization of the unvulcanized rubber, the vulcanization rate is slower than that of the unvulcanized rubber, and the crosslink density is low. By forming a layer of the unvulcanized rubber compounded as described above and vulcanizing and foaming, a sponge rubber having a fine cell diameter and high foaming and low hardness can be produced. The present invention can easily produce a low-hardness conductive sponge member used in an electrophotographic apparatus, for example, a conductive sponge rubber roller such as a charging roller for injection charging at low cost.

[Brief description of drawings]

FIG. 1 is a schematic chart of steps in a manufacturing method of the present invention.

FIG. 2 is a schematic view of a manufacturing apparatus in the manufacturing method of the present invention.

FIG. 3 is an image view of a sponge rubber tube of the present invention.

FIG. 4 is an image view of a conductive member of the present invention.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 501 G03G 15/16 103 4F212 15/16 103 21/00 312 21/10 B29C 67/22 (72) Invention Atsushi Murata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yoshiaki Nishimura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Noriyuki Nagata, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F-term (reference) 2H077 AC04 AD06 FA12 FA22 FA25 2H134 GA01 GB02 HA01 HA03 HA05 KH10 KH15 2H171 FA07 FA11 FA13 FA15 FA17 FA30 PA08 QB03 QB07 QB35 QB47 QC03 QC14 QC14QC QC25 UA03 UA12 UA22 XA02 XA12 XA14 XA16 2H200 FA13 HA03 HA28 HB12 HB22 HB45 HB46 HB47 JA02 JA25 JA26 JA27 LC09 MA01 MA03 MA08 MA13 MA14 MA17 MA20 MB01 MB04 MC01 3J103 AA02 BA41 FA15 GA02 GA45 GA58 GA02 GA57 GA58 GA60 GA58 GA58 GA58 GA60 GA58 GA58 GA60 GA60 UB01 UB22 UG05 UG07 UN02 UN21

Claims (5)

[Claims] 1. A conductive member for contact-charging an object to be charged, wherein the conductive member has a shaft body having conductivity and a roller shape formed of sponge rubber on the outer periphery of the shaft body. The conductive roller is characterized in that the foam cells of are smaller than the foam cells on the shaft side. 2. The diameter of foam cells on the surface of sponge rubber is 20 to.
The conductive roller according to claim 1, which has a thickness of 200 μm. 3. The conductive roller according to claim 1, wherein the foaming ratio of the sponge rubber is 3 to 10 times. 4. A vulcanization rate is slower than that of the unvulcanized rubber in an outer layer of the unvulcanized rubber blended so that decomposition of the foaming agent starts at least after the vulcanization of the unvulcanized rubber starts. A method for producing a sponge rubber, which comprises coating and forming an unvulcanized rubber compounded to have a low crosslink density and vulcanizing and foaming. 5. The method for producing sponge rubber according to claim 4, wherein the heating temperature in the heating furnace is 120 ° C. or higher and 250 ° C. or lower.