JPH04177377A - Contact charger and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it manufactureble inexpensively besides less n the number of processes by installing a surface layer so as to cover the lower layer and setting the film thickness to more than ten times over the maximum value of a parting line uneven difference. CONSTITUTION:When a roller type contact charger member 5 is formed, there is a method that a thermosetting elastomer is pressed in a die and heated and bridged for forming a lower 5b being installed on an outer circumference of a core bar 5a, but in consideration of easiness or the like at time of separating a product from the die, a parting line 9 is made so as to go in the longitudinal direction in the case of a columnar form, for example, such a method as dividing the into two parts is adopted. A step difference produced in the result is solved by means of covering a surface layer 10. In addition, this surface layer 10 is covered so as to make the film thickness have thickness of more than ten times over the step difference (unevenness)6. With this constitution, its forming can be done so easily.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a charging device used in an electrophotographic image forming apparatus and a method for manufacturing the same, and in particular, the present invention relates to a charging device used in an electrophotographic image forming apparatus and a method for manufacturing the same. The present invention relates to a contact charging device for charging by pressing the object, and a method for manufacturing the same.

[Prior Art] Recently, a contact charging device that charges a photoreceptor by directly contacting it has been proposed as described in Japanese Patent Application Laid-Open No. 63-167380, etc., and a conventional corona charging method has been proposed. It has been recognized that this method has advantages such as being able to use a lower applied voltage and generating less ozone.

In this contact charging method, for example, as shown in FIG. 1, a charging roller 5, which is a charging member, is caused to contact and follow an electrophotographic photosensitive drum 1, and an AC voltage V AC and a DC voltage V Do are applied to the electrophotographic photosensitive drum 1 by applying means. By applying 3,
A photosensitive drum 1 is uniformly charged. Therefore, the charging roller 5 needs to maintain conductivity, and the base layer 5b provided around the core bar 58 needs to be made of an elastic material in order to keep the contact area uniform. Conventionally, as such means, the conductivity is adjusted by adding a conductive substance such as conductive carbon black into the base layer 5b, and the elasticity is adjusted by adding a conductive substance such as conductive carbon black into the base layer 5b.
It is adjusted by additives such as process oil and plasticizer added to b.

In this method, the charged surface is a surface in the circumferential direction (hereinafter referred to as the circumferential surface).
It is known that the uniformity of this surface affects the charging characteristics. On the other hand, usually a cylindrical mold is used to prevent parting lines from forming on the circumferential surface, or a mating mold is used to form the mold and then the circumferential surface is made uniform by polishing etc. It is being said. When such a cylindrical mold is used, although the uniformity of the circumferential surface is ensured, it is difficult to remove from the mold during demolding, and the number of steps is undesirable. Furthermore, in the case of polishing, the hardness of the object to be polished is lower than the chargeability involved, so the surface of the polished surface tends to be rough and it is difficult to achieve a uniform surface.

Furthermore, in order to prevent overcurrent due to damage to the photoreceptor, etc. at the contact portion, and to prevent the plastic material etc. from bleeding out from the elastic layer, for example,
As described in Publication No. 1, the top of the elastic layer is further
．． A contact charging device coated with a member having a volume resistivity of 0XIO9Ωcm or more has been proposed. According to this, although the effect of unevenness on the elastic layer is alleviated by having a coating on the surface, it is still insufficient and it is difficult to realize a uniform surface.

[Problems to be Solved by the Invention] That is, an object of the present invention is to provide a contact charging device that solves the above-mentioned drawbacks.

Another object of the present invention is to provide a method for manufacturing a contact charging device that can be manufactured at low cost with a small number of steps.

Another object of the present invention is to provide a contact charging device that has a highly smooth charging surface and can perform stable charging, and a method for manufacturing the same.

[Means and operations for solving the problem] The above object is achieved by a contact charging device and a method for manufacturing the same having the following configuration. That is, firstly, it is a contact charging device used in an electrophotographic apparatus that performs charging by bringing it into contact with a photoreceptor and applying an electric field, and the contact portion of the contact charging device charges at least the lower layer and the surface layer. Consisting of two layers, the lower layer has elasticity and is molded using a matching mold so that the parting line is formed on the contact surface side, and the surface layer is provided to cover the lower layer and This is achieved by a contact charging device configured such that the film thickness is 10 times or more the maximum value of the difference in unevenness of the parting line.

Second, there is a method for manufacturing a contact charging device used in an electrophotographic apparatus, in which the contact charging device is brought into contact with a photoreceptor and charged by applying an electric field, and the contact portion of the contact charging device is connected to at least a lower layer and a surface layer. When forming two layers, the lower layer is molded using an elastic material using a matching mold, and the parting line is formed on the contact surface side, and the surface layer is formed so that its film thickness is the maximum of the difference in unevenness of the parting line. This is achieved by a method for manufacturing a contact charging device, in which the lower layer is coated so as to have a value of 10 times or more.

Hereinafter, the configuration of the present invention will be explained in detail.

First, the first feature of the contact charging device of the present invention is that
Its structure consists of at least two layers: a lower layer that controls elasticity (hereinafter referred to as the elastic layer) and a surface layer that adjusts the surface (hereinafter referred to as the coating layer). The reason for having such a two-layer structure is to obtain a structure that has conductivity to perform the charging action as in the conventional case, and also has elasticity to provide flexibility in contact so that charging is performed uniformly. .

Here, the material for the elastic layer is a material selected based on its properties such as elasticity and resistance, such as ethylene propylene diene polymer (EPDM).

Dimethyl silicone rubber (Q-Me), butadiene rubber (
Examples include materials in which conductive pigments are added to resin elastomers such as BR) and natural rubber (NR).

Further, as the surface layer material of the photoconductor contacting part, a material that is flexible at room temperature is preferable in view of the stability of the contact state in the charged part and wear of the photoconductor, such as polyamide, polyimide, and polyurethane.

Examples include polyvinyl alcohol, Teflon, silicone, polyester, and the like.

Next, with the characteristics of the cylinder 1 mentioned above as a prerequisite, the second feature of the present invention is to inject the lower elastic layer using a mating mold so that the parting line is formed on the side of the contact surface with the photoreceptor. It lies in shaping.

For example, when forming a roller-type contact charging device member as shown in FIG. A method of press-fitting into a mold and heat crosslinking, a method of injecting a thermoplastic elastomer into a mold under heating and molding, a method of injecting a thermoplastic resin into a mold under heating and molding, etc. were used. Mold forming is preferable, and the problem is where to set the parting line.

Originally, it is better to eliminate the level difference at the parting line that occurs in the molded product due to misalignment of the mating surfaces of the mold (
However, there are limitations on accuracy due to manufacturing technology.
It is not possible to eliminate the gap.

Normally, when molding is performed using the split mold method, the surface is polished to eliminate parting lines, but in the case of contact charging devices, JIS K63
Since the hardness specified by 01-A must be 20 to 90° and the object to be polished is soft, it is difficult to achieve a surface smoothness equivalent to that produced by a mold by polishing.

Therefore, in consideration of the ease of removing the product from the mold, for example, in the case of a cylindrical (roller) shape as shown in Figure 2, the mold is divided into upper and lower halves so that the parting line is in the elongated direction. This method attempts to solve the resulting step difference by covering it with a surface layer (coating layer), which will be described later.

The above-mentioned "parting line should be formed on the side of the contact surface with the photoconductor" is intended to make it easier (to shorten the time) when removing the forming field from the mold. This is a configuration requirement that occurs in

Note that, as understood from the above, it is preferable that the gate opening for mold forming according to the present invention is not arranged on the parting line. At the gate opening, the unevenness is thicker than the parting line (this is because it is difficult to achieve surface uniformity even if a coating layer is provided. Therefore, the preferred form of the gate opening is as shown in Figure 2. If it is cylindrical, it is preferable that the compound material is injected in the axial direction by placing it on both longitudinal ends and on the surface that does not come into contact with the photoreceptor.In this case, the resistance of the charging device will fluctuate in the axial direction. The resistance tends to increase, especially at both ends.This can be countered by methods to keep strain on the compound material low, such as by keeping the vulcanization temperature low and the pressure during injection. be able to.

Next, the third characteristic point of the present invention is that from above the lower layer (elastic layer) 5b obtained as described above, which has a step (irregularity) due to a parting line on the surface (abutting side surface),
Furthermore, a surface layer (coating layer) 10 as shown in FIG. 3 is formed so that the thickness thereof is ten times or more that of the steps (irregularities). This results in a uniform contact surface.

That is, in the contact type charging action, it is possible to perform charging with a uniform distribution.

Here, the level difference (unevenness) due to the parting line may be measured using either a contact method or a non-contact method.
The maximum value among the amounts of unevenness obtained from this is taken as the representative value.

In addition, the thickness of the surface layer 10 is required to be at least 10 times as thick as the unevenness of the parting line, but if it is less than 10 times, the effect of the unevenness cannot be fully alleviated and the parting line This is undesirable because it causes poor charging of the pitch. - On the other hand, the upper limit of the film thickness is determined by the volume resistance of the surface layer material used. Note that the resistance value in the present invention is measured as follows. As shown in FIG. 4, a metal foil 12 with a width of 1 cm is wrapped around the contact charging device 11, and the core metal portion 5a is
250V is applied using the and metal foil 12 as electrodes, part 1
Measure the current value after minutes and calculate the resistance value from it. According to this measuring method, the resistances of the elastic layer 5b and the surface layer 10 are determined so that the resistance value is 10' to 109Ω. As a preferable combination, the resistance of the elastic layer 5b is 1.
0"~10'Ω, and on top of this 106~1010Ωc
A surface layer 10 having a volume resistivity of m is formed to have a thickness of 100 μm or more. Normally, the unevenness of the parting line is limited to 10 μm even if the mold precision is improved, and from this, the thickness of the surface layer 10 is required to be 100 μm or more.

If the resistance of the elastic layer 10 is less than 10<3 >[Omega], if a defect such as a pinhole occurs on the photoreceptor, the applied voltage will concentrate on the surface layer, causing dielectric breakdown, etc., which is undesirable. On the other hand, if it exceeds 10'Ω, it is unfavorable because it is susceptible to the effects of molding and non-uniformity appears in the resistance.

If the volume resistivity of the surface layer 10 is less than 10 6 Ωcm, it is not preferable because the film thickness to obtain a proper resistance becomes thick and the surface hardness of the charger increases. On the other hand, if it is 10IOΩcm or more, the film thickness cannot be increased, which is not preferable.

Furthermore, since the elastic layer 5b according to the present invention is used to support the electrode, it is preferably flame retardant, and particularly preferably has a flame retardance of 94HB or higher according to the UL-94 standard. preferable.

[Example] Examples of the present invention will be specifically shown below.

The above materials are mixed for 30 minutes on two rolls cooled to 20° C. to prepare a raw material compound. Above 10 raw materials
0 parts by weight of dicumyl peroxide 2 as a vulcanizing agent
Add parts by weight and mix on a roll for 2 hours. Using this compound, an elastic layer 5b is vulcanized and molded around a φ6 stainless steel core metal 5a so as to have an outer diameter of φ12.

At this time, the inner diameter of the mold is φ12, which is divided into two in the longitudinal direction.
After vulcanization, the cylindrical mold is disassembled and the elastic layer for the charging device is taken out. The unevenness of the parting line on this elastic layer was measured using a laser microscope and was found to be 10 μm. Further, the resistance was measured and found to be 1 o''Ω. In order to provide the surface layer 10 on the elastic layer 5b, a coating material was prepared by dissolving in a mixed solvent of methanol/toluene. Using this coating material, A contact charging device 11 was prepared by forming a 200 μm surface layer on the above elastic layer by roll coating.

The unevenness of the parting line trace on the surface layer of the charging device is
When measured using a laser microscope, it was 2 μ or less. Further, when the resistance was measured, it was 106Ω. This charging device was attached to the charging device position of the cartridge used in LBP-811 (manufactured by Canon), and a bias was applied to the core bar 5a to perform charging. We evaluated the following.

(1) Potential Stability After neutralizing the photoreceptor, it was charged by applying the above bias, and the surface potential of the photoreceptor was measured with a surface potentiometer, and evaluated by the fluctuation of the charging roller pitch among the potential fluctuations on the chart.

○→Potential fluctuation within 5V 06:00 Same as above 5 to IOV △) Same as above 10 to 20V △ ×) Same as above 20 to 30V Then, pass a pinhole through the charged part 100 times to measure the frequency at which abnormal current flows.

○ Medium current generation occurred within 3 times ○ △ Medium Same as above 3 to 5 times △) Same as above 5 to 10 times △ ×) Same as above 10 to 20 times As shown in the table, both the chargeability and pinhole resistance were abnormal (and stable) up to the negative side.

Note that 0 in the table indicates that the above phenomenon was not observed.

Ratio 1↓ Evaluation was performed in the same manner as in Example 1 except that the thickness of the surface layer 10 was 50 μm.

As shown in Table 1, the results showed that charging defects occurred at the parting pitch from the initial stage, and pinhole resistance tended to deteriorate with durability. The evaluation was performed in the same manner as in Example 1, except that .

The results are shown in Table 1.

Evaluation was carried out in the same manner as in Example 2, except that the blood mold was made into a cylindrical integral type. The results are as shown in Table 1.
Hydrin rubber adhered to the mold, the surface of the elastic layer 5b became non-uniform, and charging defects occurred with severe pitch of the charging device.

Evaluation was carried out in the same manner as in Example 1, except that the precision of the Mitate mold was lowered and the elastic layer 5b with a parting line unevenness of 20 μm was used.

As a result, as shown in Table 1, similar to Example 1, stable charging properties and pinhole resistance were exhibited.

Support I Positive A Evaluation was performed in the same manner as in Example 3 except that the amount of carbon in the elastic layer 5b was 3 parts by weight.

As shown in Table 1, the results showed that the pinhole resistance was significantly improved.

Evaluation was performed in the same manner as in Example 3, except that the amount of titanium oxide in the formulation of Fugotoji surface layer 10 was 100 parts by weight. As shown in Table 1, the results showed sufficient charging properties and pinhole resistance.

Table 1 [Effects of the Invention] As explained above, according to the contact charging device and the manufacturing method thereof of the present invention, molding can be easily performed by using a 00% mold; By coating the parting line with a film that is 10 times or more thicker than the unevenness that occurs, it is possible to remove the effect and obtain a uniform charging effect. It became.

[Brief explanation of drawings]

FIG. 1 shows a part of an electrophotographic image forming apparatus using a conventional contact charging device. FIG. 2 is a diagram showing an example of a method for manufacturing an elastic layer for a contact charging device according to the present invention. The third diagram shows a configuration diagram of the contact charging device of the present invention. FIG. 4 is a diagram showing means for measuring the resistance of the contact charging device of the present invention. 1... Photoreceptor 3... Voltage application means 5
... Contact charging device 5a ... Core metal 5b ...
Lower layer (elastic layer)

Claims (2)

[Claims] (1) A contact charging device used in an electrophotographic device that performs charging by contacting a photoreceptor and applying an electric field, the contact charging device having at least two contact portions, a lower layer and a surface layer.
The lower layer has elasticity and is formed by a matching mold so that the parting line is formed on the contact surface side, and the surface layer is provided to cover the lower layer and the film is A contact charging device characterized in that the thickness is 10 times or more the maximum value of the difference in unevenness of the parting line. (2) A method for manufacturing a contact charging device used in an electrophotographic device, in which the contact charging device is charged by bringing it into contact with a photoreceptor and applying an electric field, the contact charging device having at least two contact portions, a lower layer and a surface layer. When forming layers, the lower layer is molded using an elastic material using a matching mold, and the parting line is formed on the contact surface side, and the surface layer is formed so that its film thickness is the maximum value of the difference in unevenness of the parting line. A method for manufacturing a contact charging device, characterized in that the lower layer is coated to a thickness of 10 times or more.