JPH09160371A - Conductive roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stabilized conductivity without any fluctuation of electric resistance by making volume resistivity of an adhesive layer smaller than the volume resistivity of a conductive elastic layer. SOLUTION: This conductive roller 4 is composed of a conductive elastic layer 3 whose electric resistance is relatively high by setting the volume resistivity of the adhesive layer 2 smaller than the volume resistivity of the conductive elastic layer 3, and the adhesive layer 2 whose electric resistance is low. Thus, the electric resistance of the whole conductive roller 4 is not influenced by thickness, unevenness or the like of the adhesive layer 2, and the stabilized electric resistance on every part in the length wise direction of the roller can be obtained. In this way, the semiconducting area of the motor-driven roller is controlled, therefore almost constant electric resistance can be obtained on all over the conductive roller regardlessly of thickness of the adhesive layer. Therefore, when this conductive roller is adopted as the developing roller for an electrophotographic device, the occurrence of the image unevenness is prevented since the roller has uniform conductive property.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive roller. In particular, the present invention relates to a conductive roller that can be used in an electrophotographic apparatus or the like and has a stable electric resistance throughout the roller.

[0002]

2. Description of the Related Art An electrophotographic apparatus such as a copying machine, a facsimile or a printer has a conductivity (electrical resistance) suitable for its purpose in order to charge a photoconductor or visualize an electrostatic latent image. Elastic rollers are commonly used. For example,
In a one-component developing type electrophotographic apparatus, a developer (toner) is moved from a developing roller, which is in pressure contact with each other, to a photosensitive member (drum), and an electrostatic latent image is visualized to be developed.
Since such a developing roller is pressed against the photoconductor with a predetermined contact width and carries a developer thinned by a blade or the like, it is required to be easily deformed and have excellent deformation recovery (that is, elasticity). Further, the developing roller is required to have appropriate and uniform conductivity so as not to cause image unevenness. Therefore, in various conductive rollers such as a developing roller, an elastic body (elastomer) or a foam body (foam) containing a conductivity imparting agent having a low hardness is provided on the outer periphery of a rotating shaft (metal core) with a predetermined thickness. A roller having a conductive elastic layer coated on the above is usually used.

Conventionally, as an elastic body containing the above-mentioned conductivity-imparting agent, carbon black, a metal filler, tin oxide or the like conductivity-imparting agent such as silicone rubber, acrylonitrile-butadiene rubber (NBR), polyurethane, ethylene-propylene copolymer Those dispersed in united rubber have been used. These elastic bodies are most suitable for the conductive roller from the viewpoint of environmental stability of electric resistance.

[0004] In the prior art, it has been proposed to interpose an adhesive layer between the conductive elastic layer and the rotating shaft for the purpose of improving the adhesion between the two layers. The electric resistance of fluctuates greatly. Therefore, in order to stabilize the electric resistance, it is necessary to make the thickness of such an adhesive layer uniform. However, it was technically difficult to form an adhesive layer having a uniform thickness in the longitudinal direction of the roller on the rotating shaft (for example, by coating).

[0005]

As described above, although the adhesion between the conductive elastic layer and the rotary shaft is improved by the use of the adhesive layer, the variation in the electric resistance of the conductive roller, that is, each in the roller longitudinal direction. A new problem arose that the electrical resistance at the site was not stable.

In view of the above, it is an object of the present invention to provide a conductive roller which has a stable conductivity without variation in electric resistance even if it has an adhesive layer.

[0007]

According to the present invention, in a conductive roller having a rotating shaft and a conductive elastic layer concentrically provided on the outer periphery thereof, an adhesive layer is formed between the rotating shaft and the conductive elastic layer. The volume resistivity of the adhesive layer is smaller than the volume resistivity of the conductive elastic layer.

The "conductive elastic layer" used in the present specification is not limited to a single layer having an electric resistance of 10 ³ to 10 ¹⁰ Ω · cm and imparting environmental stability,
Including a multi-layer structure in which a conductive resin liquid is applied to improve the surface characteristics and a surface coating layer is provided. Hereinafter, the present invention will be described in more detail with reference to the drawings.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a conductive roller which is an embodiment of the present invention, and FIG. 2 is a sectional view thereof. In the figure, 1 is a rotating shaft, 2 is an adhesive layer, and 3 is a conductive elastic layer. Further, 4 represents a conductive roller.

In the present invention, silicone rubber, acrylonitrile butadiene rubber, polyurethane, ethylene propylene copolymer rubber, etc. can be used as the member constituting the conductive elastic layer 3. Of these, conductive polyurethane elastomers are preferable from the viewpoints of environmental stability of conductivity and low compression set.

A suitable polyurethane elastomer is obtained by reacting a polyisocyanate, a polyol, and optionally a chain extender, a cross-linking agent and the like. As the polyisocyanate, either aliphatic or aromatic polyisocyanate may be used. For example, phenylene, 4,4′-diphenylmethane diisocyanate (p-MDI), polymethylene polyphenyl isocyanate (polymeric MDI), dicyclohexylmethane diisocyanate (hydrogenated MD
I), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), tolylene diisocyanate (TDI), tolidine diisocyanate (TODI), xylylene diisocyanate (XD)
I), naphthalene-1,5-diisocyanate (ND
I), paraphenylene diisocyanate (PPDI),
And dimers, trimers or modified forms thereof such as urea and burette. These polyisocyanates can be used alone or as a mixture of two or more kinds.

In the present invention, the polyisocyanate to be used is preferably liquid at around room temperature (10 to 40 ° C.), and particularly HDI trimer (trimer), HDI burette (burette body), IPDI, cooled MDI, carbodiimide. Modified MDI, TDI and the like are preferable.

Polyols that can be used in the present invention include polyester polyols having two or more functional groups, polyether polyols, polycarbonate polyols, polyether carbonate polyols and the like.

Examples of the conductivity imparting agent that imparts conductivity to the elastomer forming the conductive elastic layer 3 include conductive fillers such as carbon black, metal filler (copper) and tin oxide. In addition to these, an ionic conductive agent such as a quaternary ammonium salt can also be used. Carbon black is the most suitable from the viewpoint of dispersion stability in elastomer. When a polyurethane elastomer is used as an elastomer, these conductivity-imparting agents are usually added and kneaded in advance in an amount of 0.3 to 5.0 parts by weight with respect to 100 parts by weight of the polyol, so that uniform dispersion is achieved.

In order to adjust the reaction rate of the polyisocyanate and the polyol, a tin-based catalyst (trimethyltin laurate, dibutyltin dilaurate, etc.) or an amine-based catalyst (triethylenediamine, diazabicycloamine salt, etc.) is usually used as the polyol 100. 0.1 to 0.5 relative to parts by weight
Used by adding parts by weight.

A feature of the present invention is that the adhesive layer 2 is formed between the rotating shaft 1 and the conductive elastic layer 3, and in particular, the volume resistivity of the adhesive layer 2 is specific to the volume of the conductive elastic layer 3. It is smaller than resistance.

The adhesive that can be used in the present invention as the adhesive layer 2 can bond the rotating shaft 1 and the conductive elastic layer 3 and the volume resistivity thereof is lower than that of the conductive elastic layer 3. Any known adhesive can be used as long as it is a small adhesive. A suitable adhesive may be selected in consideration of the elastomer used for the conductive elastic layer 3,
As an example, an adhesive containing epoxy resin, phenol resin, polyurethane resin, chlorinated rubber, chloroprene rubber or the like as a main component can be mentioned. According to the present invention, an appropriate amount of the conductivity-imparting agent used for the conductive elastic layer is mixed and dispersed in these adhesives to prepare an adhesive composition, and the volume of the adhesive layer 2 to which the adhesive composition is applied. The specific resistance is adjusted to be smaller than the volume specific resistance of the conductive elastic layer 3.

The conductive roller 4 of the present invention can be manufactured, for example, as follows. That is, first, the outer peripheral portion of the rotating shaft 1 is degreased and washed, and the adhesive composition is applied,
dry. As the rotary shaft 1, a pipe or rod made of metal, which has been processed to support both ends of the pipe, is used.
From the viewpoint of rust prevention, a rotating shaft made of stainless steel or surface-treated steel is preferably used. Next, the rotary shaft 1 is positioned and installed in a molding die having a molding space (cavity), and preheated to 80 to 110 ° C. When a reaction mixture of polyisocyanate and a polyol containing a conductivity-imparting agent is filled in the mold and cured by heating, an adhesive layer 2 and a conductive elastic layer 3 made of polyurethane elastomer are formed on the outer periphery of the rotary shaft 1. To obtain a molded body. Subsequently, this molded body is taken out from the molding die together with the rotary shaft 1.

When a rubber-based elastomer other than polyurethane is used as the conductive elastic layer 3, a conventional method is used.
The rotary shaft 1 treated with the adhesive composition is positioned and installed in a molding die, filled with a rubber composition, and then heat-vulcanized and molded to obtain a desired conductive elastic layer 3.

In the conductive roller of the present invention, the volume resistivity of the adhesive layer 2 is set smaller than the volume resistivity of the conductive elastic layer 3, so that the conductive elastic layer 3 having a relatively high electrical resistance and the electrical resistance. Since the adhesive layer 2 and the adhesive layer 2 are low in electric resistance, the electric resistance of the conductive roller 4 as a whole is not affected by the thickness and unevenness of the adhesive layer 2, and the electrical stability of each part in the longitudinal direction of the roller is stabilized. Resistance is obtained.

As described above, the conductive roller of the present invention is useful as a conductive roller for an electrophotographic apparatus, but it can also be used as a conductive roller for various other purposes.

[0022]

The embodiments of the present invention will be further described below with reference to Examples and Comparative Examples, but these do not limit the scope of the present invention. All parts are parts by weight. MW represents a molecular weight.

Example 1 99 parts of polypropylene polyol (MW = 3000, manufactured by Sumitomo Bayer Urethane Co.) and 1 part of polypropylene polyol (MW = 400, manufactured by Sumitomo Bayer Urethane Co.)
Conductive carbon black (manufactured by Lion Akzo) 0.5
After thoroughly stirring and mixing the parts and the like, the mixture was kneaded with a roll. DBN (1,5-diazabicyclo (4,3,0) was added to this mixture.
0.5 part of nonene-5) phenol salt was added and mixed and stirred. After the mixture became uniform, vacuum dehydration was performed at 35 ° C. and a pressure of 3 Torr or less for 5 hours.

An appropriate amount of HDI trimer (Sumitomo Bayer Urethane Co., Ltd.) was weighed and added to the polyol mixture thus prepared so that the isocyanate index was 110. The liquid temperature of the polyol component and the HDI trimmer at the time of addition was 35 ° C. After addition of the HDI trimmer, the mixture was stirred at the agitator for about 2 minutes to form the reaction mixture.

5 parts of conductive carbon black (manufactured by Lion Akzo) was added to 100 parts of the adhesive Chemlok 218 (manufactured by Road Far East Co., Ltd.), and the thickness was about 20 μm along the outer circumference of the metallic cored bar. Was applied. The core metal was set in a roller mold heated to 80 ° C. The reaction mixture was poured into a mold and cured for about 10 minutes. Then, the mold was cooled to room temperature, the molded body roller was taken out, and the roller surface was washed with a solvent. This was dried at room temperature to obtain the conductive roller of the present invention.

Example 2 A conductive roller of the present invention was manufactured in the same manner as in Example 1 except that an adhesive (including carbon black) was applied to the outer peripheral portion of the cored bar to a thickness of about 60 μm.

Comparative Example 1 Adhesive Chemlock 218 (manufactured by Road Far East Co.)
Was applied to a metallic cored bar with a thickness of about 20 μm on its outer peripheral surface. The core metal was set in a roller mold heated to 80 ° C., and the reaction mixture of the polyol component and the polyisocyanate component used in Example 1 was injected into this mold,
It was cured for about 10 minutes. The conductive roller of this example thus obtained does not contain a conductivity imparting agent (carbon black) in the adhesive layer.

Comparative Example 2 A conductive roller was manufactured in the same manner as in Comparative Example 1 except that the adhesive Chemlock 218 was applied to a metallic cored bar to a thickness of about 60 μm. Therefore, the conductive roller of this example also
The adhesive layer does not contain a conductivity imparting agent (carbon black).

Electric Resistance Test of Roller The electric resistance (volume specific resistance) of each conductive roller obtained from the above-mentioned Examples and Comparative Examples was measured.
Table 1 shows the measurement results.

[0030]

[Table 1]

The volume resistivity was measured as follows. Sample pieces (predetermined thickness) of the conductive elastic layer and the adhesive layer of the conductive roller to be measured were manufactured according to the manufacturing method described in Examples and Comparative Examples.

Each sample piece was placed between the electrodes according to the standard measuring method of volume resistivity, a voltage of 100 V was applied, the current value after 30 seconds was measured, and the resistance value was calculated. The volume resistivity of each sample piece can be calculated from the measured resistance value (R), the cross-sectional area of the sample piece electrode grounding portion (S), and the thickness of the sample piece (t) according to the following equation.

[0033]

[Equation 1]

Further, the electric resistance of each conductive roller was measured at different portions in the longitudinal direction of the roller. For this reason 30
The electrode loaded with 0 gf load was pressed against the conductive roller, and the electric resistance at each part of the roller was determined. See FIG. In the figure, 1
Is a rotating shaft, 3 is a conductive elastic layer, 5 is an ammeter, and 6 is an electrode. The electrode was pressed against the roller, a voltage of 100 V was applied, the current value was read after 30 seconds, and the resistance value was calculated. FIG. 4 shows a graph in which the electric resistance value of each part of the conductive roller thus measured is plotted with respect to the part where the measurement is performed. In FIG. 4, A is a roller of Example 1, B is a roller of Example 2, C is a roller of Comparative Example 1, and D is a roller of Comparative Example 2.

From the graph of the electric resistance value of FIG. 4, the electric conductive roller of the present invention has a constant electric resistance value at both ends and the central portion and shows a stabilized electric resistance. It can be seen that the electric resistance values of the end portions and the central portion vary, and the electric resistance of the roller as a whole is not stabilized.

[0036]

As described above, according to the present invention, the semiconductive region of the electrically conductive roller is controlled, and a substantially constant electric resistance can be obtained in the entire electrically conductive roller regardless of the thickness of the adhesive layer.

Therefore, when the conductive roller of the present invention is used as a developing roller of an electrophotographic apparatus, it has uniform conductivity and therefore image unevenness does not occur.

[Brief description of the drawings]

FIG. 1 is an overall perspective view of a conductive roller that is an embodiment of the present invention.

2 is a vertical cross-sectional view of the conductive roller of FIG.

FIG. 3 is a schematic view illustrating an electric resistance measurement test at each part (left end, center, right end) of the conductive roller.

FIG. 4 is a graph in which electric resistance values at measurement sites of the conductive roller of the present invention and a comparative example are plotted in relation to the site.

[Explanation of symbols]

 1 Rotating shaft 2 Adhesive layer 3 Conductive elastic layer 4 Conductive roller 5 Ammeter 6 Electrode

Claims (1)

[Claims] 1. A conductive roller having a rotating shaft and a conductive elastic layer concentrically provided on the outer periphery of the rotating shaft, wherein an adhesive layer is formed between the rotating shaft and the conductive elastic layer, and the volume of the adhesive layer is large. A conductive roller having a specific resistance smaller than a volume specific resistance of the conductive elastic layer.