JPH09244349A - Conductive rubber roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive rubber roller with low hardness and sufficient conductivity by using rubber blended with carbon black in which mean particle size and the oil absorption of di-butyl phthalate(DBP) are prescribed. SOLUTION: In a conductive rubber roller 1, a conductive shaft 3 is inserted in a rubber tube 2. The rubber tube 2 is made of rubber blended with carbon black which is 10-40nm in mean particle size, and 0.4-1.0cm<3> /g in oil absorption of DPB. The oil absorption of DPB of carbon black is one of the indices to judge the size of the structure of carbon black, and the electric conductivity of carbon black is depended on the size of the structure in which the unit particle of carbon black is linked. Usually, the blended amount of carbon black is appropriately set according to the conductivity and hardness required for the rubber roller 1 in the range of 5-60 pts.wt. to rubber of 100 pts.wt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive rubber roller used in electrophotographic copying machines such as electrostatic copying machines, laser printers and facsimiles.

[0002]

2. Description of the Related Art Conventionally, in the above electrophotographic copying apparatus, charging or discharging is performed by bringing the surface of a conductive roller into contact with an object to be charged such as a photoconductor.
Usually, a rubber roller having conductivity is blended with a conductive filler is used as the conductive roller. For example, in Japanese Unexamined Patent Publication (Kokai) No. 5-331307, carbon black as a conductive filler is treated with ethylene-propylene-
A conductive rubber roller compounded with a diene copolymer rubber (EPDM) is disclosed.

[0003]

However, it is necessary to blend a large amount of carbon black with the rubber in order to make the conductive rubber roller have sufficient conductivity. Therefore, the hardness of the rubber roller becomes high, and there is a problem that the surface of the photoconductor or the like is worn or damaged. In order to solve this problem, the hardness is also adjusted by blending a plasticizer. However, since a large amount of plasticizer is required to sufficiently reduce the hardness of the rubber roller, bleeding in which the plasticizer is deposited occurs on the surface of the rubber roller, which causes a new problem of contaminating the surface of the photoconductor.

On the other hand, if the blending amount of carbon black is reduced to prevent the hardness of the rubber roller from increasing, the conductivity of the conductive rubber roller may become insufficient. Therefore, there is a demand for a conductive rubber roller that can realize a low hardness without impairing the conductivity of rubber. An object of the present invention is to provide a conductive rubber roller having low hardness and sufficient conductivity.

[0005]

As a result of intensive studies to solve the above problems, the present inventors have found that the average particle size is 1
When a rubber having a carbon black content of 0 to 40 nm and an oil absorption of dibutyl phthalate (DBP) of 0.4 to 1.0 cm ³ / g is used, low hardness and sufficient conductivity are obtained. The present invention has been completed by discovering a new fact that a conductive rubber roller having the above can be obtained.

That is, according to the present invention, by setting the average particle size of the carbon black and the DBP oil absorption amount within the above ranges, the compounding amount of the carbon black is relatively small, and the high conductivity and the low hardness are obtained. It is possible to obtain a conductive rubber roller which is compatible with the above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive rubber roller of the present invention will be described in detail below. Conductive rubber roller 1 of the present invention
For example, as shown in FIG. 1 as an example, a conductive shaft 3 is inserted into a rubber tube 2 having conductivity. The rubber tube 2 is made by mixing at least carbon black and a vulcanizing agent into raw material rubber, and further, if necessary,
The vulcanization accelerator is formed by mixing and kneading additives such as a vulcanization accelerator, a foaming agent, a filler (reinforcing agent), and an antioxidant, and kneading the mixture.

As the raw material rubber, various kinds of rubber conventionally used for rubber tubes of conductive rubber rollers can be used. Specifically, ethylene-propylene-diene copolymer rubber (EPDM), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (C
R), natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), fluororubber, silicone rubber, epichlorohydrin rubber, NBR hydride, polysulfide rubber, urethane rubber, etc. Alternatively, two or more kinds may be mixed and used.

In the present invention, carbon black is blended to impart conductivity to rubber. The carbon black in the present invention has an average particle size and D
Other than the BP oil absorption, there is no particular limitation, and various conventionally known carbon blacks such as channel black, furnace black, and acetylene black can be used.

The average particle size of the carbon black used in the present invention is 10 to 40 nm, preferably 20 to 35 nm.
It is suitable to be in the range of. When the average particle size of carbon black exceeds the above range, the effect of imparting conductivity to rubber becomes low. Therefore, the amount of carbon black compounded to give sufficient conductivity increases, and the hardness of the conductive rubber roller increases. On the other hand, when the average particle diameter of carbon black is less than the above range, it is considered that sufficient conductivity can be imparted with a smaller blending amount. However, it is difficult to produce carbon black having an average particle size below the above range.

The DBP oil absorption of carbon black indicates the amount of DBP absorbed per 1 g of carbon black, and is one of the indexes for judging the size of the structure of carbon black. The structure of carbon black is formed by connecting unit particles of carbon black in a chain shape, and its size influences the electrical conductivity of carbon black. In the present invention, the DBP oil absorption is measured according to JIS K6221.

D of carbon black used in the present invention
The BP oil absorption is suitably 0.4 to 1.0 cm ³ / g, preferably 0.6 to 0.8 cm ³ / g. When the DBP oil absorption of carbon black is below the above range, the effect of imparting conductivity to rubber becomes low. Therefore, the amount of carbon black compounded to give sufficient conductivity increases, and the hardness of the conductive rubber roller increases. Further, even when the DBP oil absorption of carbon black exceeds the above range, the hardness of the conductive rubber roller becomes high. The reason for this is not known in detail, but it is presumed that it is due to the structure structure of carbon black.

The amount of carbon black blended is not particularly limited because it varies depending on the type of carbon black used, but it is usually 5 to 60 parts by weight, preferably 20 to 40 parts by weight per 100 parts by weight of rubber. , Is appropriately set according to the conductivity and hardness required for the conductive rubber roller. If the blending amount of carbon black exceeds the above range, the conductivity of the rubber roller may become too high, or the hardness of the rubber roller may become too high.
On the other hand, when the blending amount of carbon black is less than the above range, the conductivity of the rubber roller may be insufficient.

Further, in the present invention, in order to adjust the conductivity of the rubber, metal oxide, graphite or the like may be blended in addition to the above carbon black. The conductivity of the conductive rubber roller is represented by the electric resistance R from the conductive shaft to the outer surface of the roller. The electric resistance R is obtained as shown in FIG. That is, the conductive rubber roller 1
2 is installed on the aluminum plate 4 as shown in FIG. 2, a load W of 500 g is applied to both ends of the conductive shaft 3, and then a current value (A) when a voltage of 1000 V is applied to the conductive shaft 3. And the electrical resistance (Ω) according to Ohm's law
Is calculated.

Electric resistance R of the conductive rubber roller of the present invention
Is usually 10 ³ to 10 ¹⁰ Ω, preferably 10 ⁶ to 10
^A good value is in the ⁹ Ω range. When the electric resistance R is below the above range, leaks, paper stains, etc. occur, and the quality of the formed image deteriorates. On the other hand, when the electric resistance R exceeds the above range, the charging or discharging efficiency becomes poor and it becomes unsuitable for practical use.

The hardness of the conductive rubber roller of the present invention is usually in the range of 20-40, preferably 25-40, in Asker C. When the hardness (Asker C) is less than the above range, the roller is liable to be worn or worn, and the durability of the conductive roller is deteriorated. on the other hand,
When the hardness exceeds the above range, a sufficient contact state cannot be obtained on a charged body such as a photoconductor, and the quality of the formed image may deteriorate, such as occurrence of hollow characters in the characters in the formed image. .

Other additives to be added to the raw rubber include a vulcanizing agent, a foaming agent, a vulcanization accelerator, an antiaging agent, a reinforcing agent and a filler, but other than the vulcanizing agent. The additive may be added if necessary. As the vulcanizing agent, for example, sulfur, organic sulfur-containing compounds, and organic peroxides can be used. Examples of the organic sulfur-containing compound include tetramethylthiuram disulfide, N, N'-dithiobismorpholine and the like. Examples of the organic peroxide include benzoyl peroxide and the like. The compounding amount of the vulcanizing agent is 0.
Appropriately 3 to 4 parts by weight, preferably 0.5 to 3 parts by weight.

Examples of the vulcanization accelerator include inorganic accelerators such as slaked lime, magnesia (MgO) and litharge (PbO), and thiurams such as tetramethylthiuram disulfide and tetraethylthiuram disulfide; zinc dibutyldithiocarbamate and diethyldithiocarbamine. Dithiocarbamic acids such as zinc acid; thiazoles such as 2-mercaptobenzothiazole and N-cyclohexyl-2-benzothiazolesulfenamide; trimethylthiouric acid; organic promoters such as thioureas such as N, N′-diethylthiourea can give.

Examples of the vulcanization accelerating aid include metal oxides such as zinc white, fatty acids such as stearic acid, oleic acid and cottonseed fatty acid, and various conventionally known vulcanization accelerating aids. Examples of the filler (reinforcing agent) include carbon black, calcium carbonate, silica, clay, talc, barium sulfate and diatomaceous earth.

The compounding amount of the filler is usually 100 times as much as the base rubber.
The amount is set to 35 parts by weight or less, preferably 5 to 20 parts by weight with respect to parts by weight. When the compounding amount of the filler exceeds 35 parts by weight, problems such as increased hardness of rubber occur, which is not preferable. Among the fillers (reinforcing agents) exemplified above, carbon black is used as a conductive filler, and the compounding amount thereof is set within the above-specified range.

As the plasticizer, for example, phthalic acid type compounds, adipic acid type compounds, sebacic acid type compounds, benzoic acid type compounds and the like are used. Specific examples thereof include dibutyl phthalate, dioctyl phthalate and tricresyl phosphate. The amount of the plasticizer compounded is preferably 20 parts by weight or less with respect to 100 parts by weight of rubber. When the compounding amount of the plasticizer exceeds the above range, the plasticizer may precipitate on the surface of the foamed rubber member obtained, which is not preferable.

Examples of the antiaging agent include imidazoles such as 2-mercaptobenzimidazole, phenyl- and the like.
α-naphthylamine, N, N′-di-β-naphthyl-p
Amines such as -phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, di-t-
Examples thereof include phenols such as butyl-p-cresol and styrenated phenol.

As the conductive shaft in the conductive rubber roller of the present invention, any of those conventionally used can be used. Specifically, copper, aluminum,
Examples include metal shafts such as carbon steel and stainless steel. Next, a method for manufacturing the conductive roller of the present invention will be described. The conductive rubber tube constituting the conductive roller is, for example, carbon black in the above-exemplified rubber, a vulcanizing agent and various additives as necessary are mixed and kneaded, and further extruded into a cylindrical shape for vulcanization and It is produced by performing secondary vulcanization as needed.

Can vulcanization is preferable as the above vulcanization method, but other vulcanization methods may be used. The vulcanization conditions are
Depending on the type and composition of rubber used, it is usually
It is preferable to carry out at 140 to 170 ° C. for about 0.5 to 6 hours.
In addition, the secondary vulcanization is performed in, for example, a hot air oven at about 140-
It is good to carry out at 200 ° C. for about 0.5 to 4 hours. The electrically conductive rubber roller of the present invention is obtained by inserting the electrically conductive shaft into the rubber tube obtained by the above method, cutting it into a predetermined length, and polishing the surface if necessary.

[0025]

EXAMPLES Next, the conductive rubber roller of the present invention will be described with reference to Examples and Comparative Examples. Preparation of Conductive Rubber Roller Examples 1-3, Comparative Examples 1-7 The following components and 100 parts by weight of ethylene-propylene-diene copolymer rubber (trade name "EPT4010" manufactured by Mitsui Petrochemical Co., Ltd.) were used. The carbon black shown in Table 1 was blended.

(Components) (parts by weight) ZnO 5 Stearic acid 1 PEG # 4000 1 Sulfur 2 Noxceller TT 0.7 Noxcellor BZ 2 Noxceller M 2 Noxceller TTTE 0.5 Vinylhol AC # 3 4 Cellpaste 101 4 Neocellbon N # 5000 12 Of the above components, PEG # 4000 has a molecular weight of 4,000.
Of polyethylene glycol. NOXCELLER TT (Tetramethylthiuram disulfide), NOXCELLER BZ
(Zinc dibutyldithiocarbamate), Nocceller M
(2-mercaptobenzothiazole) and noxceller TTTE (tellurium diethyldithiocarbamate) are both trade names of vulcanization accelerators manufactured by Ouchi Shinko Chemical Co., Ltd.
Vinyl Hall AC # 3 and Neocerbon N # 5000
Is the trade name of the foaming agent manufactured by Eiwa Chemical Co., Ltd., and the cell paste 101 is the trade name of the foaming aid manufactured by the same company.

The carbon black used in each of the examples and comparative examples had the average particle size (nm), DBP oil absorption (c)
m ³ / g) and the blending amount (parts by weight) are shown in Table 1.

[0028]

[Table 1]

The above-mentioned compound was kneaded and extruded into a tube shape, then vulcanized by can vulcanization at 160 ° C. for 30 minutes, and then secondary vulcanization (200 ° C., 1 hour) by a hot air oven. A conductive rubber tube was obtained. A conductive shaft was inserted into the conductive rubber tube, the length of the rubber tube was further cut to 216 mm, and the conductive rubber roller was obtained by polishing and finishing so that the outer diameter was 17 mm. Comparative Example 8 A compound having the same composition as in Comparative Example 4 except that the amount of carbon black was 25 parts by weight, and a plasticizer (trade name "Dyna Process Oil PW90" manufactured by Idemitsu Kosan Co., Ltd.) was added.
20 parts by weight were compounded.

This formulation was then used to prepare Example 1 above.
.About.3 and Comparative Examples 1 to 7, conductive rubber rollers were produced. Evaluation of Conductive Rubber Roller For the conductive rubber rollers of the above Examples and Comparative Examples,
The electrical resistance R (Ω) and the hardness of the roller surface (Asker C) were measured.

The electric resistance R was measured according to the above-mentioned method, and the measurement result is shown as a logarithmic value (log R). Also,
The Asker hardness was measured using a rubber hardness meter "DD2 type C" manufactured by Kobunshi Keiki Co., Ltd. Furthermore, the conductive rubber rollers of the above-described examples and comparative examples are each manufactured by a laser beam printer (model PC manufactured by NEC Corporation).
PR1000 / 4), and a solid black image was formed.

Image formation was carried out continuously on five sheets, and the presence or absence of the void phenomenon in the formed image and the presence or absence of contamination of the charged body (photoreceptor) were visually evaluated. When the hollowing-out phenomenon and contamination of the body to be charged did not occur, it was rated as ◯, and when it occurred, was rated as x. Also,
From the results of the electric resistance, the hardness of the roller surface, the presence / absence of a hollow defect, and the presence / absence of contamination of the body to be charged, a comprehensive evaluation was carried out when the conductive rubber rollers of each Example and Comparative Example were actually used. .

Table 2 shows the above measurement results and evaluation results.

[0034]

[Table 2]

As is clear from Table 2, the conductive rubber rollers of Examples 1 to 3 all have an average particle size of 10 to 40 n.
m, and carbon black having a DBP oil absorption of 0.4 to 1.0 cm ³ / g is used. In each of the conductive rubber rollers, the hardness is reduced without impairing the conductivity. In addition, image defects such as hollow defects do not occur, and the problem of contamination of the charged body does not occur.

On the other hand, the conductive rubber rollers of Comparative Examples 1 to 7 use carbon black whose average particle diameter or DBP oil absorption amount is out of the range of the present invention. When the value is set to the same value as in Examples 1 to 3, there is a problem that the hardness of the rubber roller becomes high. In particular, in Comparative Examples 1 to 4, since the particle size of carbon black is small, the amount of carbon black compounded to obtain the same electrical resistance value as in Examples 1 to 3 can be reduced, but such carbon blacks are used. In both cases, since the DBP oil absorption amount exceeds 1.0 cm ³ / g, the hardness of the rubber roller becomes high.

Further, the conductive rubber roller of Comparative Example 8 has a small hardness because it is mixed with a large amount of process oil (plasticizer), but has a problem that the surface of the body to be charged is contaminated. occured.

[0038]

According to the present invention, the hardness of the conductive rubber roller can be lowered without impairing the conductivity.
Further, the amount of the plasticizer used can be reduced, and the risk of contaminating the body to be charged can be eliminated. Therefore, the conductive rubber roller of the present invention is suitably used for applications such as electrophotographic copying machines.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a conductive rubber roller of the present invention.

FIG. 2 is a schematic view showing a method for measuring the electric resistance of a conductive rubber roller.

[Explanation of symbols]

 1 Conductive rubber roller

Claims (1)

[Claims] 1. An average particle size of 10 to 40 nm and an oil absorption of dibutyl phthalate (DBP) of 0.4 to 1.0 cm ^3.
A conductive rubber roller characterized by using a rubber compounded with carbon black of 10 g / g.