JP2000162848A - Electrifying member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the energy used in the manufacturing process smaller, thereby to make recycling possible, to eliminate the generation of image void, etc., and also to eliminate image failures due to soiling and sticking of toner to a photoreceptor drum by forming a protective layer on a surface of a semiconductive elastic layer and providing graphite dispersed inside the protective layer. SOLUTION: In this electrifying device, an electrifying roll 2 is constituted to have a conductive support body 21 covered by a semiconductive elastic layer 22. This semiconductive elastic layer 22 is formed with a thermoplastic elastomer with an ion conductive material dispersed in it. In this case, a protective layer 23 is provided in the periphery of the semiconductive elastic layer 22. Then graphite, which is provided with lubricity and also excels in corrosion resistance, is dispersed inside the protective layer 23. The general characteristics of this graphite are known to be superior in heat resistance, corrosion resistance and lubricity. In this case, the good lubricity is utilized. Furthermore, graphite is of crystallized carbon, and its crystal structure is a lamination of the carbon layer of six ring net of planar shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
In an image forming apparatus such as a laser printer or a facsimile, the present invention relates to a charging member such as a charging roller for performing a charging process on a photosensitive member.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine, a laser printer, and a facsimile, a charging roller is generally used as a charging member for performing a charging process on a photosensitive member. FIG. 2 is an explanatory diagram of such a conventional charging roller type image forming apparatus. FIG.
FIG. 9 is a cross-sectional view of a conventional charging roller.

In FIG. 2, reference numeral 110 denotes a conventional charging roller type image forming apparatus. A conventional charging roller type image forming apparatus 110 includes a photosensitive drum 101 on which an electrostatic latent image is formed, a charging roller 102 that contacts the photosensitive drum 101 and performs a charging process, a laser beam, reflected light of a document, and the like. Exposure means 103, developing roller 104 for attaching toner to the electrostatic latent image on photoreceptor drum 101, and charging roller 102
A power pack 105 for applying a C voltage, a transfer roller 106 for transferring a toner image on the photosensitive drum 101 to a recording sheet 107, a cleaning device 108 for cleaning the photosensitive drum 101 after the transfer processing, and The photosensitive drum 101 includes a surface voltmeter 109 for measuring the surface potential. In FIG. 2, functional units normally required in other electrophotographic processes are omitted because they are not required in this specification.

Next, a basic image forming operation in such a conventional charging roller type image forming apparatus 110 will be described.

When a DC voltage is supplied from the power pack 105 to the charging roller 102 in contact with the photosensitive drum 101, the surface of the photosensitive drum 101 is uniformly charged to a high potential. Immediately thereafter, the image light is applied to the photosensitive drum 101.
When the surface of the photosensitive drum 101 is irradiated with the exposure means 103, the potential of the irradiated part of the photosensitive drum 101 decreases.
The photosensitive drum 101 by such a charging roller 102
It is known that the mechanism for charging the surface of the surface is a discharge in accordance with Paschen's law in a minute space between the charging roller 102 and the photosensitive drum 101.

Since the image light has a light amount distribution corresponding to the white / black of the image, when the image light is irradiated, the potential distribution corresponding to the recorded image is formed on the surface of the photosensitive drum 101 by the irradiation of the image light. That is, an electrostatic latent image is formed. When the portion of the photosensitive drum 101 on which the electrostatic latent image is formed passes through the developing roller 104, toner adheres according to the level of the potential, and a toner image is formed by visualizing the electrostatic image. Is done. Photoconductor drum 10 on which such a toner image is formed
The recording paper 107 is conveyed to a portion 1 by a registration roller (not shown) at a predetermined timing, and overlaps the toner image. Then, after the toner image is transferred onto the recording paper by the transfer roller 106, the recording paper 107 is separated from the photosensitive drum 101. Separated recording paper 107
Is conveyed through a conveyance path, is heated and fixed by a fixing unit (not shown), and is then discharged out of the apparatus.
When the transfer is completed in this manner, the photosensitive drum 101
The surface is cleaned by a cleaning device 108, and the remaining charge is removed by a quenching lamp (not shown) to prepare for the next image forming process.

A contact type charging roller 102 used in such a charging roller type image forming apparatus 110.
Is in contact with the photosensitive drum 101 made of a metal base with a predetermined pressing force and rotates in contact with the rotation of the photosensitive drum 101 made of a metal base, so that the charging roller 102 does not have sufficient flexibility. However, even if there are slight depressions on the surface, floating occurs between these depressions and the photosensitive drum 101, and the above-mentioned minute space between the charging roller 102 and the photosensitive drum 101 varies, so Failure will occur. Therefore, as shown in FIG. 3, in the charging roller 102, the conductive support 121
A photoconductive drum 10 on which a semiconductive elastic layer 122 is provided.
Prevents the floating of 1

The semiconductive elastic layer 122 is made of a rubber material. As such a rubber material, vulcanized rubber such as ethylene-propylene-diene rubber (EPDM), urethane rubber, silicone rubber, epichlorohydrin rubber and the like is generally used. It is used for

In recent years, environmental protection activities have been increasing worldwide, and companies are also demanding environmentally conscious activities such as reduction of energy consumption during manufacturing and reduction of waste materials.

However, vulcanized rubber consumes energy in the vulcanization process during production and, once vulcanized, cannot be recycled by re-molding. It is undeniable that it is a disadvantageous material.

Therefore, recently, from the viewpoint of environmental protection, attention has been paid to the substitution of a thermoplastic elastomer material. In this way, thermoplastic elastomers attract attention because they can be molded in the same way as thermoplastic resins,
This is because there is an advantage that the energy consumption in the manufacturing process is reduced by eliminating the need for the vulcanization process, and the waste is reduced by recycling.

The characteristics required when the thermoplastic elastomer is applied to the charging member include roller hardness and compression set, and low sound and high sound characteristics that can withstand the general storage environment including the temperature in the actual machine. It is required to be good. When such a thermoplastic elastomer is applied to a charging member, it is important to make the thermoplastic elastomer semiconductive. In order to solve such a technical problem, a charging member using a thermoplastic elastomer in which a conductive pigment such as carbon black is dispersed has been proposed (JP-A-7-121006).

However, when the conductive pigment is dispersed,
The charging member is placed in a semiconductive region (about 10 ⁵ to 10 ⁹ Ωcm).
If this is set, the variation in resistance value is large, and image defects such as partial charging failure occur. this is,
It is difficult to uniformly disperse the conductive pigment in the thermoplastic elastomer, which is caused by poor dispersion.

Apart from this, there is an elastomer in which an ion conductive material is dispersed. This type of elastomer has a small variation in the resistance value as in the above-described conductive pigment dispersion type, and partial charging failure does not cause a problem in image quality.

[0015]

However, the ionic conductive material dispersion type has a problem that bleeding occurs on the surface of the ionic conductive material due to pressing against the photosensitive drum and leaving for a long time. This bleed causes contamination of the photosensitive drum, causing deterioration of the photosensitive drum and image defects. In addition, since toner adheres to the charging member, there is a problem that poor charging due to the accumulation of toner also occurs at the same time.

Accordingly, the present invention has the advantage that the energy can be reduced in the manufacturing process and that recycling is possible, and the above-mentioned problems such as image defects do not occur. It is an object of the present invention to provide a charging member free from image defects due to contamination of the toner and adhesion of toner.

[0017]

Means for Solving the Problems The inventors of the present invention have conducted experiments to solve the above-mentioned problems, and have used a thermoplastic elastomer material in which an ionic conductive material is dispersed in an elastic layer and a graphite dispersed in the surface thereof. By forming the protective layer formed on the photosensitive drum, there is an advantage that energy can be reduced in a manufacturing process and recycling is possible, and the above-mentioned problems such as image defects do not occur. The present invention was completed by finding that there was no image defect due to contamination of toner and adhesion of toner.

That is, the invention according to claim 1 is a charging member in which a semiconductive elastic layer made of a thermoplastic elastomer in which an ionic conductive material is dispersed is formed on a conductive support. A charging layer, wherein a protective layer is formed on the protective layer, and graphite is dispersed in the protective layer.

According to a second aspect of the present invention, there is provided the charging member according to the first aspect, wherein a polyether chain or a polyester chain is contained as a component of the thermoplastic elastomer. is there.

According to a third aspect of the present invention, there is provided the charging member according to any one of the first to second aspects, wherein conductive particles are dispersed in the resin of the protective layer. .

According to a fourth aspect of the present invention, in the charging member according to any one of the first to third aspects, the resistance of the protective layer is made larger than the resistance of the semiconductive elastic layer. Charging member.

According to a fifth aspect of the present invention, in the charging member according to any one of the first to fourth aspects, the protective layer is made of a polyvinyl butyral resin or a polyamide resin.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the charging roller according to the present invention. The charging roller 2 includes a conductive support 2
1 is covered with a semiconductive elastic layer 22. The semiconductive elastic layer 22 is formed of a thermoplastic elastomer in which an ionic conductive material is dispersed.

The ionic conductive agent can be easily dispersed in the thermoplastic elastomer by using a biaxial kneader, a kneader or the like. Further, the coating of the conductive support 21 with the thermoplastic elastomer composition can be formed into an arbitrary shape by means of an extruder, injection molding or the like without obtaining a vulcanizing step required for the rubber composition.

Examples of the ionic conductive agent include alkali metal peroxides such as lithium peroxide, perchlorates such as lithium perchlorate, quaternary ammonium salts such as tetrabutylammonium salt, and phosphate salts. Regarding the compounding amount of the ion conductive agent, the resistance value is set in a predetermined range (10 ⁵ to 10 ^9).
Ωcm), the base material 10
It is preferable to add 0.1 to 10 parts by weight to 0 part by weight.

Since the ionic conductive agent forms a kind of coordination bond with an atom having an unpaired electron in the thermoplastic elastomer, it is uniformly dispersed in the elastomer at a molecular level. Therefore, the resistance value does not vary due to poor dispersion as seen in the elastomer in which the conductive pigment is dispersed, and image defects due to partial charging failure and the like do not occur.

The thermoplastic elastomer used as the semiconductive elastic layer 22 is not particularly limited as long as it has the flexibility required for the charging roller. Alternatively, an elastomer containing a polyester chain allows ions to move more easily, so that a variation in resistance value is smaller and a charging member exhibiting stable conductivity can be obtained.

As shown in FIG. 3, the semiconductive elastic layer 122
When only the charging roller 102 is used, the uniformity of charging may be poor due to poor surface properties. In this case, as shown in FIG.
3 can be improved. In addition, although mentioned as a problem for the purpose of the present invention, the thermoplastic elastomer used for the semiconductive elastic layer 22 of the present invention has a problem due to bleeding of the ionic conductive material. The protective layer 23 needs to exert a barrier effect on the bleed.

A resin material is generally used in order to improve the surface properties, obtain a barrier property against bleed, and follow the underlying elastic layer. However, since these resins have an electrical insulating property, if the protective layer 23 is formed alone, the characteristics as a charging member cannot be obtained. Therefore, the resistance of the protective layer 23 is reduced by blending various conductive agents with the resin. Commonly used conductive agents include carbon black and metal oxides.

It is not always necessary that the resistance of the protective layer 23 be low. Although the charging member is in contact with the photosensitive drum 101, the photosensitive drum 101 has a pinhole,
When a defect or the like is present, when the resistance of the charging member, particularly the resistance of the surface is low, a current leaks to the pinhole and the like, and charging is not performed in the vicinity thereof.
Further, when the concentration is severe, a large current causes damage to the charging member and the photosensitive drum 101. For this reason, the protective layer 23 allows the charging current to flow in the direction with respect to the photosensitive drum 101 (that is, the radial direction of the charging roller in FIG. 1), but does not allow the charging current to flow in the circumferential direction and axial direction. It is necessary to have anisotropy in resistance.
In other words, the protective layer 23 needs to have a configuration in which the volume resistance (resistance in the film thickness direction) is low and the surface resistance is high.

In the present invention, the material itself of the protective layer 23 does not have such anisotropic characteristics, but the volume resistivity of the protective layer 23 is about 10 ¹⁰ Ω · cm and the film thickness is about 10 μm. As a result, a sufficient current flows in the radial direction, but hardly flows in the circumferential direction and the axial direction. Therefore, it is possible to prevent the leakage of the charging current to the pinhole of the photosensitive drum 101 described above.

The protective layer 23 needs to have excellent releasability from the toner and the photosensitive drum 101. Generally, carbon black, metal oxide, and the like are dispersed in a resin having excellent releasability from the toner and the photosensitive drum 101, and the above-described electrical characteristics and releasability are measured. It is difficult to maintain the cleaning performance for a long period of time due to the fact that there is no resin exhibiting the releasability in all of the various mixtures such as the toner and the deterioration of the resin with the passage of time. In the present invention, by dispersing graphite having excellent lubricity and excellent corrosion resistance in the protective layer 23, it is possible to avoid the problem of toner sticking for a long period of time.

The graphite has the following general properties:
It is known to have excellent heat resistance, corrosion resistance, and lubricity.
In the present invention, the good lubricity is used. Graphite is a crystal of carbon, and its crystal structure is formed by laminating carbon layers having a six-membered ring network plane. The layers are weakly bonded by Van der Waals forces and are easily cleaved, but the six-membered network is a covalent bond as strong as diamond. Due to this layered structure, the shear strength is low, the coefficient of friction is low, and lubrication is provided. Recycling in the case where the protective layer 23 is provided can be performed by removing the protective layer 23 with a solvent or removing it by polishing.

Comparative Example 1 A thermoplastic elastomer containing a polyester component (Elastage ES5) as a semiconductive elastic layer was formed on a core shaft (diameter 6 mm) made of stainless steel.
000A, manufactured by Tosoh Corporation) and a composition in which 0.5 part by weight of lithium perchlorate was blended with 100 parts by weight by extrusion molding to obtain a charging roller having a diameter of 14 mm (same configuration as in FIG. 3). When the surface hardness (JIS-A) and electric resistance of the charging roller thus obtained were measured, the surface hardness was 50 ° and the electric resistance was 4 × 10 ⁸ Ωcm.

(Comparative Example 2) An olefin-based thermoplastic elastomer (Millastomer 5030N, manufactured by Mitsui Petrochemical Co., Ltd.) and conductive carbon black (Ketjen) as a semiconductive elastic layer were formed on a core shaft (diameter 6 mm) made of stainless steel. Composition containing 12% by weight of Black EC (Ketjen Black International) (surface hardness JIS)
-A; 60 °, resistance 4 × 10 7 Ωcm) by extrusion molding to obtain a charging roller 14 mm in diameter (same configuration as in FIG. 3).

(Comparative Example 3) Carbon black (total solid content) was added as a protective layer on a semiconductive elastic layer of a charging roller prepared in the same manner as in Comparative Example 1 in polyvinyl butyral resin (manufactured by Denki Kagaku Kogyo KK). The mixture (resistance: 3 × 10 ¹⁰ Ωcm) to which 10 wt% was added was coated to a thickness of about 7 μm to obtain a charging roller (same configuration as in FIG. 1).

(Example 1) Carbon black (total solid content) was added as a protective layer on a polyvinyl butyral resin (manufactured by Denki Kagaku Kogyo Co., Ltd.) on the semiconductive elastic layer of the charging roller produced in the same manner as in Comparative Example 1. And a mixture of graphite powder (8 wt% with respect to the total solid content) (resistance: 3 × 10 ¹⁰ Ωcm) was coated to a film thickness of about 7 μm to form a charging roller (see FIG. 1). The same configuration was obtained.

(Example 2) Carbon black (based on the total solid content) was formed as a protective layer on a semiconductive elastic layer of a charging roller manufactured in the same manner as in Comparative Example 1 as a protective layer in a polyamide resin (manufactured by Daicel Huls). A mixture of 7 wt%) and graphite powder (8 wt% based on the total solid content) (resistance: 3 × 10 ¹⁰ Ωcm) was coated to a film thickness of about 7 μm, and a charging roller (similar to FIG. 1) Is obtained.

With respect to the above charging roller, image evaluation was performed using the image forming apparatus shown in FIG. On this occasion,
The voltage applied to the charging roller was DC-1600V.
Table 1 shows the evaluation results. The following ranking was used to evaluate abnormal images caused by voltage concentration on the photoconductor pinholes and abnormal discharge. Rank 1: No white spots occur on the image due to abnormal discharge, or the diameter of the crossing is within 2 mm. Rank 2: White spots are 2 mm or more, but are not streaked. Rank 3: Streaks are formed on the image and white spots occur.

[0040]

[Table 1]

The advantages of the present invention are as follows. Since the material forming the semiconductive elastic layer is a thermoplastic elastomer in which an ionic conductive material is dispersed, there is no variation in resistance due to poor dispersion of the conductive agent, and image defects due to partial charging failure and the like occur. There is no
It has the advantage of being able to reduce the energy in the manufacturing process and the amount of wastes due to recycling. Furthermore,
Since graphite is dispersed in the protective layer provided on the semiconductive elastic layer, it is possible to obtain a charging member free from contamination of the photosensitive drum and charging failure due to toner fixation.

Since the thermoplastic elastomer forming the semiconductive elastic layer contains a polyether chain or a polyester chain as a constituent component, the movement of ions is facilitated, and the variation in resistance value is reduced. A charging member exhibiting stable conductivity without causing image defects due to partial charging failure or the like can be obtained.

Since the resin used as the material of the protective layer is insulative, sufficient charging efficiency cannot be obtained as it is.
Therefore, since a mixture of conductive particles dispersed in a resin is used as a material for the protective layer, a charging member having good charging efficiency can be obtained.

Since the resistance value of the protective layer is made larger than the resistance value of the semiconductive elastic layer, it is possible to provide a charging member which can avoid both voltage concentration on the photoconductor pinhole and abnormal discharge.

The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the gist of the present invention.

[0046]

As described above, according to the present invention, according to the present invention, a protective layer in which graphite is dispersed is formed on the surface of a thermoplastic elastomer material in which an ion conductive material is dispersed in an elastic layer. It has the advantage of reducing energy in the manufacturing process and being recyclable,
In addition, there is no problem such as the above image defect,
Further, it is possible to provide a charging member free from image defects due to contamination on the photosensitive drum and adhesion of toner.

[Brief description of the drawings]

FIG. 1 is a diagram showing a charging roller of the present invention.

FIG. 2 is a diagram schematically illustrating an image forming apparatus using a charging roller.

FIG. 3 is a diagram illustrating a conventional charging roller.

[Explanation of symbols]

 Reference Signs List 21 conductive support 22 semiconductive elastic layer 23 protective layer 101 photoreceptor drum 102 charging roll 103 exposing means 104 developing roll 105 power pack 106 transfer roll 107 recording paper 108 cleaning device 109 surface electrometer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Kamiya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Yutaka Narita 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) Inventor Hiroyuki Kitano 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H003 AA12 BB11 CC05 DD03 EE11 3J103 FA07 FA15 FA20 FA30 GA02 GA52 GA57 GA58 GA60 HA03 HA12 HA20 HA41 HA44 HA52

Claims (5)

[Claims] 1. A charging member in which a semiconductive elastic layer made of a thermoplastic elastomer having an ion conductive material dispersed thereon is formed on a conductive support, wherein a protective layer is formed on the surface of the semiconductive elastic layer. A charging member, wherein graphite is dispersed in the protective layer. 2. The charging member according to claim 1, wherein a component of the thermoplastic elastomer contains a polyether chain or a polyester chain. 3. The charging member according to claim 1, wherein conductive particles are dispersed in the resin of the protective layer. 4. The semiconductor device according to claim 1, wherein the resistance value of the protective layer is larger than the resistance value of the semiconductive elastic layer.
4. The charging member according to any one of claims 1 to 3. 5. The method according to claim 1, wherein the protective layer is a polyvinyl butyral resin or a polyamide resin.
5. The charging member according to any one of 4.