JP3181988B2 - Medium resistance roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medium resistance roll used for an apparatus such as an electrophotographic copying machine or a printer, and more particularly, to a polyurethane elastic layer containing an alkali metal salt and specific conductive particles. The present invention relates to a medium resistance roll provided with:

[0002]

2. Description of the Related Art Conventionally, a corona discharge method has been employed in a charging step or a transfer step in an electrophotographic method or an electrostatic recording method. However, when a corona discharge method is employed, a high voltage power supply is required. And the generation of harmful ozone. Therefore, a contact charging method has attracted attention as an alternative to the corona discharge method.

An electrophotographic copying machine using a contact charging method has a configuration as shown in FIG. 2, for example. That is, a charging roll (1), a developing roll (2), a transfer roll (3), and a cleaning roll (4) are arranged on the photoreceptor surface. Copying is performed by such an electrophotographic copying machine as follows.
The photoreceptor is rotated as shown by the arrow. On the other hand, the charging roll rotating in the same direction as the photoconductor or in the opposite direction uniformly charges the photoconductor surface while being in contact with the photoconductor surface. Exposure is performed by an exposure unit (not shown), and an electrostatic latent image corresponding to information on the document is formed on the surface of the photoconductor. Next, the developer adheres to the latent image by the developing roll, and the developer that adheres to the surface of the photoconductor is transferred to the recording paper by the transfer roll. The recording paper passes through the fixing device (5), and the developer on the recording paper is fixed. The developer remaining on the photoreceptor surface is removed by a cleaning roll.

The above electrophotographic copying machine includes a charging roll,
Many conductive rolls such as image rolls and transfer rolls are used
But the conductive layer that forms the outside of the roll
Is the excellent property of polyurethane rubber,
Excellent abrasion resistance, compression distortion resistance, etc.
Polyurethane rubber with properties such as low contamination
It is being heavily used. However, Polyure
The volume resistivity of tongue rubber is 10^TenΩcm or more,
To obtain good images, the volume resistance of polyurethane rubber
Rate is 10⁶ Or 10 ⁸ Adjusted to be within Ωcm range
There is a need to.

For example, Japanese Patent Application Laid-Open No. 64-73365 discloses that the volume resistivity is 10 ⁴ Ωcm to 10 ⁸ Ω outside the roll.
cm is provided with a charging roller provided with a medium resistance layer,
There is disclosed a technique in which an elastic rubber mixed with conductive particles such as carbon black is used as the resistance layer. A roll having a medium resistance layer using conductive particles such as carbon black is advantageous in that a roll having desired conductivity can be obtained, but the roll has a large fluctuation or variation in electric resistance value and is stable. It is difficult to obtain a roll having a reduced electric resistance value.

Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 2-198470, when an alkali metal salt is blended in an elastic body instead of carbon black, it is clear that the variation in the electric resistance value of the roll is sure. Although the points have been resolved, this time due to changes in the environment where the role is placed,
The present inventors have found that the change in the electric resistance value is remarkable. As described above, the fact that the characteristics fluctuate due to changes in the environment means that it is necessary to change the blending amount of the alkali metal salt in accordance with the use place of the image forming apparatus, and the use place of the image forming apparatus is limited, It was impossible to use it anywhere, which was inconvenient.

[0007]

Accordingly, there has been a demand for a technique for obtaining a roll that can withstand fluctuations in the use environment of the roll and has no variation in electric resistance. The present inventors have intensively studied to obtain a roll in which the above-mentioned conventional disadvantages have been solved, and as a result, have finally reached the present invention. That is, an object of the present invention is to provide a roll in which the change in the electric resistance value is small and the variation in the electric resistance value is small irrespective of the fluctuation of the use environment.

[0008]

According to the present invention, a polyurethane elastic body is used for a resistance layer of a roll, and an alkali metal salt, carbon black, and carbon black are used as the polyurethane elastic body.
Consisting of porous fibers, copper particles, silver particles and nickel particles
The technical feature of the present invention is to use together with more selected conductive particles. That is, when the above-mentioned specific conductive particles are added to the polyurethane elastic body having an alkali metal salt , as shown in the examples described later , the fluctuation of the electric resistance value due to the environment, which is a disadvantage of the alkali metal salt, is completely suppressed. the fact that not seen is found, and, of viscosity
Since no rise is observed, it has excellent moldability and is used as a medium resistance roll.
Not also seen variation in electrical resistance value, which is the suitability of Te is also the in. This phenomenon occurs when the alkali metal salt
It means a synergistic effect due to the combined use of conductive particles
There is .

[0009]

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below. Hereinafter, the present invention will be described focusing on a charging roll, which is a typical example of the medium resistance roll of the present invention. As shown in FIG. 1, for example, the charging roll as an example of the medium resistance roll of the present invention has a polyurethane elastic layer (12) formed on the surface of a core shaft (11). The surface of the elastic layer may be formed with a resin film or may be treated with a surface treatment liquid.

The polyurethane elastic material of the present invention is composed of a known material prepared from a polyol and a polyisocyanate. Examples of the polyol include a polyester polyol and a polyether polyol. As the polyether polyol, polyethylene glycol, polypropylene glycol, polyalkylene glycol known as polypropylene glycol-ethylene glycol or blends thereof, polytetramethylene ether glycol, copolymerized polyol of tetrahydrofuran and alkylene oxide, Various modified products thereof, blends thereof, and the like can be given.

Examples of the polyester polyol include a condensed polyester polyol, a lactone-based polyester polyol, a polycarbonate polyol obtained by condensing a dicarboxylic acid such as adipic acid and a polyol such as ethylene glycol, or a blend thereof.

The polyisocyanate may be any of those commonly used in the preparation of polyurethanes known per se. Examples thereof include diphenylmethane diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, tolidine diisocyanate, and the like.
Examples thereof include paraphenylene diisocyanate, isophorone diisocyanate, prepolymers or modified products thereof, and blends thereof.

These polyurethane elastomers can be prepared in the presence of known additives. Examples of the additive include a chain extender and a crosslinking agent. Specific examples include glycols, hexanetriol, trimethylolpropane, and amines.

As the alkali metal salt, a sodium salt, a potassium salt, a lithium salt and the like can be used, and a lithium salt is particularly preferable. Specific examples thereof include a halogen oxyacid salt, a perhalogen oxyacid salt, a thiocyanate, a phosphate and the like, but a perhalogen chloroxylate is particularly preferable, and lithium perchlorate is more preferable.

The amount of the alkali metal salt is 0.001 to 3.0 parts by weight, preferably 0.05 to 1.0 part by weight, based on 100 parts by weight of the polyurethane elastic body.

Conductivity used in combination with the alkali metal salt
Are selected from carbon black, carbonaceous fiber, copper particles, silver particles, and nickel particles . Among them, conductive carbon black is preferably used.

The amount of the conductive particles to be added varies depending on the particles used. In the case of conductive carbon black, the amount is usually 0.05 to 5.0 parts by weight, preferably 0.5 to 2.0 parts by weight, based on 100 parts by weight of the polyurethane elastomer. Parts are preferred. If the amount of the conductive particles exceeds the above range, the resulting medium resistance layer will have a large variation in electric resistance, not only making it impossible to obtain a good-quality copy, but also increasing the viscosity of the polyurethane-forming raw material. There is a drawback that the moldability deteriorates too much.

These two types of additives are blended in a raw material for producing polyurethane, and after sufficiently kneading, a roll can be produced by a conventional method. In addition to the above additives, other known additives can be added.

[0020]

According to the present invention, it is possible to obtain an excellent roll which is a medium-resistance roll, has no variation in electric resistance value, eliminates environmental dependency of the roll, and has good formability. did it. In particular, since the charging roll of the present invention can uniformly charge the surface of the photoreceptor, the density of an image based on the variation in the amount of charge is not observed,
This enabled stable, high-quality images to be obtained.

[0021]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Comparative Examples and Examples, but it goes without saying that the present invention is not limited to these Examples.

Example 1 0.05 parts by weight of lithium perchlorate and 2 parts by weight of Ketjen Black EC (lion fat) were added to 100 parts by weight of a polyester polyol (Kurapole P-2010: manufactured by Kuraray Co., Ltd.), stirred and dissolved. After that, the temperature was adjusted to 100 ° C., and then 40 parts by weight of Coronate HX (manufactured by Nippon Polyurethane Industries, Ltd.) was added and stirred to obtain a mixture. This mixture was previously placed on a shaft (φ: 8 mm, l: 270 mm).
The mixture was poured into a mold preheated to 0 ° C. and heated at 120 ° C. for 60 minutes to obtain a roll having a conductive polyurethane elastic layer formed on the shaft surface excluding both ends. The hardness of this roll is
41 ° (JIS A) and the roll resistance is 2 × 10 ⁸
Ω. Table 1 shows the roll measurement results.

Example 2 A conductive polyurethane elastic material was prepared in the same manner as in Example 1 except that 0.05 parts by weight of lithium perchlorate and 0.5 parts by weight of Ketjen Black EC (lion fat) were added as conductive particles. A roll on which a layer was formed was obtained. The hardness of this roll is 40 ° (JIS A) and the roll resistance is 2
× 10 ⁸ Ω. Table 1 shows the roll measurement results.

Comparative Example 1 A roll having a conductive polyurethane elastic layer was obtained in the same manner as in Example 1, except that 0.05 parts by weight of lithium perchlorate was added as the conductive particles. The hardness of this roll is
40 ° (JIS A) and the roll resistance is 3 × 10 ⁸
Ω. Table 1 shows the roll measurement results.

Comparative Example 2 Ketjen Black EC instead of Lithium Perchlorate
(Lion fat) A roll having a conductive polyurethane elastic layer formed thereon was obtained in the same manner as in Comparative Example 1 except that 3.5 parts by weight was added. The hardness of this roll is 42 ° (JIS
A), and the roll resistance was 1 × 10 ⁸ Ω. Table 1 shows the roll measurement results.

[0026]

* The change of the electric resistance value due to the environment was measured by the following method. That is, a charging roll left at a desired temperature and humidity was placed on a brass plate. Then, a load is applied to the roll to bring the stainless steel plate and the charging roll into close contact with each other,
One of the brass plates and one of the metal cores of the charging roll were connected via a power supply. From the measured current value, the electric resistance value of the charging roll was found. The electric resistance of the charging roll left at different temperatures and humidity was determined, and the change in the electric resistance due to the environment was determined. In addition, in the evaluation of Table 1, "large" means electric
Change and roses luck of physical properties such as resistance value is large, medium resistance low
Means that it is unsuitable as Le, "small" is, above Symbol properties
Small variation and suitable for medium resistance roll
It means that is.

[Brief description of the drawings]

FIG. 1 is a sectional view of a charging roll as a typical example of a medium resistance roll of the present invention.

FIG. 2 is a schematic sectional view of a main part of an electrophotographic copying machine using a contact charging method.

[Explanation of symbols]

 1. Charging roll 2. Development roll 3. Transfer roll 4. Cleaning roll 5. Photoconductor 11. Core shaft 12. Polyurethane elastic layer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-50-150438 (JP, A) JP-A-64-73365 (JP, A) JP-A-2-198470 (JP, A) JP-A-2- 230267 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 101 G03G 15/16 103 G03G 15/08 501 F16C 13/00

Claims (2)

(57) [Claims] 1. A medium-resistance roll in which a polyurethane elastic layer is formed on a surface of a core metal, wherein the polyurethane elastic body is composed of an alkali metal salt, carbon black, and carbonaceous fiber.
From the group consisting of fiber, copper particles, silver particles and nickel particles
A medium resistance roll comprising: selected conductive particles. 2. The medium resistance roll according to claim 1, wherein the alkali metal salt and the conductive particles are a lithium salt and carbon black, respectively.