JPH1122719A - Electro static charge roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a cost by using a thermoplastic elastomer in a semiconductor elastic layer and be stabilized in electro static charge characteristics. SOLUTION: In an electric static charge roller 1 formed such that a semiconductor elastic layer 3 is formed at the circumference of a conductive support 2, the semiconductive elastic layer 3 is formed of a thermoplastic elastomer, and the conductive support 2 is formed of resin Volumetric specified resistance is set to 106 -109 Ω.cm and volumetric specific resistance of a resin material is set to 10 Ω.cm or less. Further a mold release layer 4 is formed on the outside of a semiconductor conductive elastic layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller for charging an object to be charged such as a photoreceptor in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine or a facsimile, a charging roller is used as a means for charging a photosensitive member surface. FIG. 2 schematically shows a configuration of a main part of an image forming apparatus 110 provided with a charging roller. In the figure, reference numeral 101 denotes a drum-shaped photosensitive member on which an electrostatic latent image is formed; A charging roller that performs a charging process by contacting with the photoconductor 103;
Exposure device 10 for irradiating image light B such as reflected light from a document or laser light on the surface of document 01 to write an electrostatic latent image
Reference numeral 4 denotes a developing roller for applying toner to the electrostatic latent image on the surface of the photoreceptor 101 to make it visible, 105 a power supply for applying a DC voltage to the charging roller 102, and 106 a transfer from a paper feed unit (not shown). The recording paper fed to the lower end of the photoconductor 101 as a position, 107 is a transfer roller for transferring the toner image on the photoconductor 101 to the recording paper 107, and 108 is the photoconductor 10
The cleaning device removes and collects toner remaining on one surface. Image forming apparatus 110 configured as described above
Is roughly as follows. First, the charging roller 101 is brought into contact with the surface of the photoconductor 101 rotating in a certain direction, and a DC voltage is supplied from the power supply device 105 to the charging roller 101, so that the surface of the photoconductor 101 and the surface of the charging roller 101 are charged. A discharge is generated to uniformly charge the surface of the photoconductor 101 to a high potential. Next, the image light B is applied to the surface of the photoconductor 101 immediately after the charging. As a result, the potential of only the portion of the surface of the photoconductor 101 irradiated with the image light B decreases. Since the image light B is irradiated according to the distribution of the light and dark portions of the image to be formed, the irradiation of the image light B forms a potential distribution corresponding to the image to be formed on the surface of the photoconductor 101, that is, an electrostatic latent image is formed. Is done. Thereafter, when the portion where the electrostatic latent image is formed by the rotation of the photoconductor 101 passes through the developing position by the developing roller 104, toner adheres to the surface of the photoconductor 101 according to the level of the potential, and the electrostatic latent image can be formed. A visualized toner image is formed. Then, the recording paper 10 is synchronized with the timing when the leading end of the toner image reaches the transfer position.
7 is fed, and the recording paper 107 is
Is transferred to the toner image. Thereafter, the recording paper 107 is separated from the photoreceptor 101, is conveyed to a fixing unit (not shown) through a predetermined conveyance path, and is discharged to the outside of the apparatus after being heat-pressed and fixed. After the transfer is completed, the residual toner is removed from the surface of the photoreceptor 101 by the cleaning device 108, and the residual charge is erased by an unillustrated static eliminator to prepare for the next image forming process.

The surface of the photosensitive member 101 is charged by the charging roller 102 with the charging roller 102 and the photosensitive member 1.
It is known that this is performed by corona discharge in accordance with Paschen's law in a small space between 01 and 01. According to Paschen's law, the firing voltage V is determined by the pressure of the atmosphere and the distance d between the electrodes, that is, the charging roller 10 in this case.
2 is a function of the product P · d of the size of the minute space between the surface of the photoconductor 101 and the surface of the photoreceptor 101 in the vicinity of the contact portion.
V increases both in the decreasing direction and in the increasing direction of P · d, and P
• Take the minimum value at the value of d. Therefore, when the charging roller 102 rotating in contact with the surface of the photosensitive member 101 does not have sufficient flexibility, a gap is generated between the photosensitive member 101 and the above-described minute Variations in the shape and size of the space cause poor charging. Therefore, as shown in FIG. 3, the charging roller 102 has a dual inner / outer structure, and a flexible semiconductive elastic layer 20 is provided on the outer side of the inner hard conductive support 201.
2, the photosensitive member 101 and the charging roller 1
In this case, the occurrence of charging failure due to poor contact with 02 is prevented. Conventionally, as the conductive support 201, a metal such as SUS or SUM which is formed into a columnar or cylindrical shape and whose surface is plated with nickel has been used. The semiconductive elastic layer 202 is made of epichlorohydrin rubber, EP
DM rubber, nitrile rubber and the like have been used.

[0004]

However, the conventional charging roller uses a metal for the conductive support 201 and a rubber (resin) for the semiconductive elastic layer 202, so that the conductive support 201 and the semiconductive elastic layer 202 need to be bonded with an adhesive, which complicates the manufacturing process.
There are many problems such as peeling easily due to insufficient adhesive film thickness and difficulty in selecting an adhesive. There is also a rubber tube used for the semiconductive elastic layer 202, into which a metal conductive support 201 is press-fitted. However, the rubber tube is easily deformed over time after press-fitting, which causes image unevenness. Easy to be. In addition, rubber materials are manufactured through a number of processes such as rubber kneading, pre-molding, vulcanization, and post-processing, so that the manufacturing process is complicated. Due to the difficulty, once the vulcanization process fails, rework is impossible. Therefore, there are limits to stabilization of quality and cost reduction. Further, the rubber material has a problem that the photoconductor is easily contaminated by bloom (reaction residue), bleed (excess liquid), or the like generated due to a change in hardness over time, a processing state, a material mixing condition, and the like. . Further, as a material of the semiconductive elastic layer 202, there is a material using a thermoplastic elastomer instead of a rubber material. According to the thermoplastic elastomer, it is not necessary to go through a number of steps as in the case of rubber, and the thermoplastic elastomer can be reworked, so that the cost can be reduced. In addition, since parts can be collected and recycled, waste can be reduced and the environment can be protected. However, when the conductive support 201, that is, the core metal, is press-fitted into a thermoplastic elastomer molded into a tubular shape, the semiconductive elastic layer 202 is deformed with time after press-fitting as in the case of using a rubber material. There is.

Further, when the semiconductive elastic layer 202 is formed by extrusion or injection molding of a thermoplastic elastomer on the outside of the conductive support 201, the metal which is the material of the conductive support 201 and the semiconductive elastic layer 202 are formed. Conductive elastic layer 2
02, there is a large difference in thermal conductivity with the thermoplastic elastomer, which is the material of No. 02, so that a difference occurs in the thermal history at the time of molding between the inside and the outside of the semiconductive elastic layer 202, The most important property, semiconductivity (10 ⁶ to
(10 ⁹ Ω · cm). It was also found that the structure was greatly affected by the structure of the mold used for injection molding. That is, the conductive support 201
Large difference in thermal conductivity between the metal of the material and the thermoplastic elastomer of the material of the semiconductive elastic layer 202,
This has a very bad effect on the semiconductivity of the semiconductive elastic layer 202, and causes a variation in resistance within each charging roller and between charging rollers. Such a variation in the resistance of the charging roller becomes remarkable when a plurality of charging rollers are simultaneously formed using a large-sized mold in order to improve productivity. As a result, variations occur in the charging characteristics within each charging roller and between the charging rollers, causing uneven potential on the surface of the photoconductor after the charging process, thereby causing image unevenness. Accordingly, attempts have been made to take measures such as pre-drying the thermoplastic elastomer used for the semiconductive elastic layer 202 at the time of molding, but no significant effect was obtained. Also, the conductive support 201
The difference in the thermal expansion coefficient (shrinkage rate) between the conductive support 201 and the semiconductive elastic layer 202 causes a difference in the amount of shrinkage of the conductive support 201 and the semiconductive elastic layer 202 due to a decrease in temperature after molding. This has the disadvantage that the air is easily entrapped between the conductive support 201 and the semiconductive elastic layer 202 because the property tends to decrease. The problem to be solved by the present invention is to provide a charging roller having a stable charging characteristic while reducing costs by using a thermoplastic elastomer for the semiconductive elastic layer.

[0006]

According to a first aspect of the present invention, there is provided a charging roller comprising a semiconductive elastic layer provided around a conductive support. The conductive elastic layer is made of a thermoplastic elastomer, and the conductive support is made of a resin. According to a second aspect of the present invention, in the charging roller according to the first aspect, the thermoplastic elastomer material has a volume resistivity of 10 ⁶ to 10 ⁹ Ωcm, and the resin material has a volume resistivity of 10 ⁶ to 10 ⁹ Ωcm. It is characterized by being 10 Ωcm or less. According to a third aspect of the present invention, in the charging roller according to the first or second aspect, the conductive support and the semiconductive elastic layer are made of a thermoplastic elastomer material and a resin material. It is characterized by being obtained by injection molding simultaneously with a color molding method. According to a fourth aspect of the present invention, in the charging roller according to any one of the first to third aspects, a release layer is provided on an outer peripheral surface of the semiconductive elastic layer.

[0007]

Next, an embodiment of the present invention will be described. FIG. 1 is a sectional view showing an example of an embodiment of the charging roller according to the present invention. This charging roller 1 is provided with a semi-conductive elastic layer 3 of a uniform thickness made of a thermoplastic elastomer around a cylindrical resin-made conductive support 2, and around the semi-conductive elastic layer 3. A release layer 4 is provided. Various resins such as polyamide (PA), polycarbonate (PC), and acrylonitrile-butadiene styrene (ABS) resin can be used as the resin used for the conductive support 2. When slidability is required for other members that come into contact with the conductive support 2, a crystalline resin such as PA may be selected. When straightness is required, an amorphous resin such as PC may be selected. When a resin is used for the conductive support 2, it can be molded by a gas molding method in which a gas is injected into the resin when the shaft diameter is large, though it depends on its shape. Further, when there is a degree of freedom in shape change, it is also possible to form a lightened shape. Further, the resin used for the conductive support 2 is required to have high conductivity (low resistance), and it is desirable that its volume specific resistance is 10 Ω · cm or less. When the volume specific resistance of the conductive support 2 exceeds 10 Ω · cm, the power supply to the semiconductive elastic layer 3 becomes unstable, and a state in which insufficient charging easily occurs. In order to make resins such as PA, PC, and ABS conductive, it is effective to add carbon or the like to them. As the elastomer used for the semiconductive elastic layer 3, an olefin type, a styrene type, or a composite type thereof is suitable. Further, the volume resistivity of the elastomer used is desirably 10 ⁶ to 10 ⁹ Ωcm. If the resistance is higher than 10 ⁹ Ωcm, the charge amount is insufficient, so that a sufficiently high potential cannot be obtained and an image defect occurs.
On the other hand, when the resistance is lower than 10 ⁶ Ωcm, the charging current flows intensively and intensively at a defective portion such as a pinhole on the surface of the photoreceptor. (Normal development) and black spots (reversal development) are likely to occur.

The conductive support 2 and the semiconductive elastic layer 3
Is formed by simultaneously extruding and molding a thermoplastic elastomer material to be the semiconductive elastic layer 3 and a resin material to be the conductive support 2 by a double extrusion method, or by injection molding by a two-color molding method. can do. However, 2
In consideration of the influence of the melting point difference of the materials, two-color molding is more preferable than double extrusion. That is, it is desirable to first form the conductive support 2 and then form the semiconductive elastic layer 3. The reason is that the semiconductive material generates resistance unevenness even if there is a slight unevenness in the heat distribution in the process of heating and cooling at the time of molding, but the conductive support 2 is formed first, and This is because a heat history can be prevented from being left by injection molding a semiconductive material. The surface of the semiconductive elastic layer 3 obtained as described above has tackiness as it is, but since the release layer 4 is formed around the semiconductive elastic layer 3, the charging roller 1 Adhesion of toner to the surface can be prevented. The material of the release layer 4 is preferably a material having good releasability for a toner of 10 ⁹ to 10 ¹² Ωcm. In addition, if a thermoplastic resin can be selected as a material of the release layer 4, the release layer 4 can be simultaneously formed with the conductive support 2 and the semiconductive elastic layer 3. In the above-described embodiment, the case where the entire conductive support 2 is formed of a resin has been described as an example. However, if no problem occurs due to the difference in heat shrinkage from the semiconductive elastic layer 3, the conductive support 2 may be formed. Some, for example, metal can also be used in the center.

[0009]

EXAMPLES Table 1 below shows Examples and Comparative Examples of the present invention.

[0010]

Table 1 shows that the conductive support has a volume resistivity of 1Ω.
In the case of using SUS303 of cm and using a material having a volume resistivity of 10 ⁷ Ωcm by adding carbon to an olefin elastomer for the semiconductive elastic layer (Comparative Example 1, Conventional Example), conductive support A resin material having a volume resistivity of 2 Ω · cm by adding carbon to polycarbonate is used as a body, and a volume resistivity of 1 is obtained by adding carbon to an olefinic elastomer as a semiconductive elastic layer.
In the case of using a material having a resistivity of 0 ⁷ Ω · cm (Example 1), a resin material having a volume resistivity of 2 Ω · cm by adding carbon to polycarbonate was used as a conductive support,
When a material having a volume resistivity of 10 ⁸ Ω · cm by adding carbon to a styrene-based elastomer is used as the semiconductive elastic layer (Example 2), carbon is added to polycarbonate as a conductive support. Volume resistivity is 1
When a resin material having a resistivity of 1 Ω · cm was used, and a material having a volume resistivity of 10 ⁸ Ω · cm by adding carbon to a styrene-based elastomer as a semiconductive elastic layer (Comparative Example 2), A resin material having a volume resistivity of 2 Ω · cm by adding carbon to polycarbonate as a conductive support, and a volume resistivity of 3 × by adding carbon to a styrene elastomer as a semiconductive elastic layer.
In the case of using a material with 10 ⁹ Ω · cm (Comparative Example 3),
And a resin material having a volume resistivity of 2 Ω · cm by adding carbon to polycarbonate as a conductive support, and a volume resistivity of 8 × by adding carbon to a styrene elastomer as a semiconductive elastic layer. 10 ⁵ Ω
The results of evaluation in the case of using a material having a cm (Comparative Example 4) are shown.

The following can be understood from the above evaluation results. When the comparative example 1 is compared with the examples 1 and 2, the examples 1 and 2 have a larger volume resistivity of the conductive support than the comparative example 1 but have a larger volume resistivity than the comparative example 1. In Examples 1 and 2, better evaluation results were obtained. In particular,
In Comparative Example 1, the variation in the volume resistivity of the rollers between lots was one order (measured volume resistivity of a predetermined number (for example, 100) of rollers).
It means that it was about ¹ Ω · cm. However, in Examples 1 and 2, it was reduced to the order of 0.2, and air entrainment between the semiconductive elastic layer and the conductive support was also
In Comparative Example 1, about 20% occurred, but in Examples 1 and 2, no occurrence occurred. This is better than Examples 1 and 2 than SUS303 used for the conductive support in Comparative Example 1.
The resin material used for the conductive support has a smaller thermal conductivity difference with the elastomer forming the semiconductive elastic layer, so that the characteristics of the semiconductive elastic layer are improved. This is because the difference in the coefficient of thermal expansion (shrinkage) between the semiconductive elastic layer and the semiconductive elastic layer is small, and the adhesion between the conductive support and the semiconductive elastic layer is improved.

In Comparative Example 2, the volume specific resistance of the conductive support was increased despite the use of a resin material for the polycarbonate as the conductive support and the use of a styrene elastomer for the semiconductive elastic layer. Was too large to form an image. Further, in Comparative Examples 3 and 4, although the resin material was used for the polycarbonate as the conductive support and the styrene elastomer was used for the semiconductive elastic layer, the styrene elastomer was used for the semiconductive elastic layer. Despite using,
Because the value of the volume resistivity of the semiconductive elastic layer was too large,
An image could not be formed. In Example 1, the cylinder temperature during the formation of the semiconductive elastic layer was 220 ° C., a water-cooled mold was used, and the cooling time was 40 seconds. Further, in Example 2, the cylinder temperature at the time of forming the semiconductive elastic layer was set to 200 ° C., and a mold maintained at about 40 ° C. was used.
The cooling time was 50 seconds.

[0013]

As described above, according to the present invention, the following excellent effects can be exhibited. According to the first aspect of the present invention, it is possible to obtain a semiconductive elastic layer that is hardly affected by heat history due to heating and cooling during molding, to obtain uniform semiconductivity, and to obtain image unevenness due to potential unevenness. , No defects. In addition, it is possible to prevent air from entering between the conductive support and the semiconductive elastic layer. Furthermore, the simplification of the injection molding die manufacturing process and the possibility of rework enable reduction in cost and stabilization of quality. In addition, since parts can be collected and recycled, waste can be reduced and the environment can be protected. According to the invention described in claim 2, the volume resistivity of the thermoplastic elastomer material is set to 1
0 ⁶ to 10 ⁹ Ωcm, and the volume resistivity of the resin material is 1
By setting the resistance to 0 Ω · cm or less, insufficient charging potential can be prevented, and the occurrence of leakage to the pinhole of the photoconductor can be suppressed, and a high-quality image can be obtained. According to the third aspect of the present invention, it is possible to simultaneously form the conductive support and the semiconductive elastic layer by the two-color molding, and it is possible to obtain not only a cost reduction but also a charging roller having a stable thermal history. Image quality is also stable. According to the fourth aspect of the present invention, a release layer is further provided outside the semiconductive elastic layer to prevent migration from the semiconductive elastic layer to the photoreceptor. And the durability of the charging roller can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an embodiment of a charging roller according to the present invention.

FIG. 2 is a diagram schematically illustrating a configuration of a main part of an image forming apparatus including a charging roller.

FIG. 3 is a cross-sectional view illustrating an example of a conventional charging roller.

[Explanation of symbols]

1 charging roller, 2 conductive support, 3 semiconductive elastic layer, 4 release layer

Claims (4)

[Claims] 1. A charging roller in which a semiconductive elastic layer is provided around a conductive support, wherein the semiconductive elastic layer is made of a thermoplastic elastomer, and the conductive support is made of a resin. A charging roller characterized by the following. 2. The volume resistivity of the thermoplastic elastomer material is 10 ⁶ Ω · cm to 10 ⁹ Ω · cm, and the volume resistivity of the resin material is 10 Ω · cm or less. Charging roller. 3. The conductive support and the semiconductive elastic layer are obtained by injection molding the thermoplastic elastomer material and the resin material by a two-color molding method. Item 3. The charging roller according to Item 1 or 2. 4. The charging roller according to claim 1, wherein a release layer is provided on an outer peripheral surface of said semiconductive elastic layer.