JPH10254217A - Electrifying roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrifying roll excellent in releasability with respect to the surface of a photoreceptor and toner, capable of preventing the contamination of the surface of the photoreceptor and capable of stable uniform electrification. SOLUTION: This electrifying roll 201 has an elastic layer 2 and surface layer 3 coating the elastic layer 2. The elastic layer 2 is made to epichlorohydrin rubber and the surface layer 3 contains a tin oxide-contg. electrically conductive agent having <=10<4> Ω.cm specific resistance and <=0.5μm primary particle diameter. A binder resin forming the surface layer 3 is preferably nylon or polyvinyl butyral. Electrically conductive particles subjected to silane coupling treatment are desirably used as the electrically conductive agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller constituting a charger in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a corona discharger using a tungsten wire has been employed as a means for uniformly charging the surface of a photoreceptor in an electrophotographic image forming apparatus. There is a problem in terms of cost, environment, and mechanical performance, such as the necessity of a power source, and a large amount of ozone and NOx generated by the discharge of the tungsten wire by the high-voltage power source adversely affecting the human body and the photoconductor.

In order to solve the above-mentioned problems of the corona discharger, a contact charging system characterized by a low-voltage power supply (1-2 kV) and low ozone generation has recently attracted attention. Among the contact charging methods, the charging roller is an important point for uniform charging by the contact charging method, because uniform contact with the photoreceptor is made by two rotating cylinders,
It is easier to realize than other contact charging methods such as brush charging and blade charging, and is being adopted.

[0004] Since the charging roller charges the contact with the photosensitive member as described above, if the charging roller has electrical non-uniformity, the charging density reflects the electrical non-uniformity. Causes unevenness. Therefore, the charging roller is required to have a predetermined resistance and to be electrically uniform.

Further, since the charging roller is in contact with the photoreceptor, it is required that the releasability from the surface of the photoreceptor and the releasability from the toner be good. The term "releasability" as used herein means a relationship in which a phenomenon such as adhesion, adhesion or sticking does not occur between two material surfaces and the interaction is small.

[0006] Further, the charging roller is required not to damage the photoconductor when contacting the photoconductor, and to maintain a uniform nip width for uniform charging. Therefore, the surface of the charging roller is appropriately hardened. And have flexibility. Therefore, the surface of the charging roller is generally composed mainly of a polymer. However, since the roller surface is made of a polymer, there are fundamental problems that the charging potential is apt to change due to a change in the environment and that the photoconductor is easily contaminated by the transferred matter from the roller. This migration may result from the polymer on the roller surface or from the polymer inside. In addition, the charging roller is required to have many other characteristics, such as good durability such as damage resistance of the roller surface.

Here, the electric non-uniformity of the charging roller, which causes the above-described non-uniform charging, is caused by the vicinity of the surface of the roller and, in the case of a two or more-layer roller structure, the roller layer or the base layer serving as a base portion. Occurs in the elastic layer. It has been found that when the elastic layer constituting the conventional charging roller is made of synthetic rubber and a conductive agent for adjusting its resistance, uneven charging is likely to occur. In other words, even though the electrical resistance of the roller as a whole can be adjusted with a resistance adjusting agent such as carbon, it is difficult to uniformly disperse carbon and the like. Often impaired the withstand voltage.

On the other hand, as means effective for uniformity of charging, for example, Japanese Patent Application Laid-Open No. 63-149668 describes
It is disclosed that a voltage applied to a charger is a DC voltage on which an AC voltage is superimposed.

Similarly, Japanese Patent Application Laid-Open No. 7-64378 discloses a charger using a power supply for superimposing an AC voltage on a DC voltage. In the charging roller of this charger, an intermediate layer is provided on a rubber roller made of EPDM rubber (ethylene-propylene-diene rubber) in which carbon particles are dispersed, and a nylon surface layer containing a conductive agent is formed thereon. Thus, the charging roller has provided good results in the functions of improving durability and resistance stability and preventing photoreceptor defect leakage and photoreceptor contamination.

[0010]

However, when the AC voltage is superimposed on the DC voltage, there arises a problem that the ozone reduction effect is reduced and the power consumption is increased by the AC superposition as compared with the case where only the DC voltage is used. Also, when an AC voltage is superimposed on a DC voltage, the photoconductor and the charging roller tend to vibrate and come into contact with each other, thereby generating noise called charging noise and generation of a transition from the charging roller to the photoconductor. (I.e., contamination of the photoreceptor). Furthermore, since an AC voltage is applied, it is necessary to prevent an increase in electric capacity and a decrease in withstand voltage due to a thin resistive layer.

Here, it is difficult to simultaneously prevent the charging noise, prevent the transfer from the roller from being generated, and improve the withstand voltage with a roller having a single-layer or two-layer structure (excluding the support). . Therefore, when an AC voltage is superimposed on a DC voltage, it often has a multilayer structure of three or more layers,
There is a problem that the number of roller manufacturing steps increases, that is, the cost increases.

Accordingly, an object of the present invention is to prevent charging unevenness from occurring even when only a DC voltage is applied, as described later. For this purpose, it is necessary that the rollers have a predetermined electric resistance and that there is no electric non-uniformity, and that the withstand voltage, which is a problem in the case of DC voltage alone, is good.

According to the study of the present inventor, in response to the above requirement, the elastic layer itself is semiconductive (10 ⁷ to 10 ⁸ Ω ·
cm), a medium resistance required for the charging roller can be obtained, and electric non-uniformity, which is common in the conductive agent dispersion system, does not occur. It has been confirmed that it is possible to obtain a charging roller which does not deteriorate in withstand voltage as in the case of an agent dispersion system.

On the other hand, as described above, the charging roller is required to be excellent in releasability from the surface of the photoreceptor and releasability from toner, and to be free from contamination of the photoreceptor. On the other hand, the present inventor has clarified that good results can be obtained when nylon or polyvinyl butyral is used for the surface layer of the charging member. However, both nylon and polyvinyl butyral alone cannot provide a sufficient charging potential because of their high electric resistance and have low image density. Further, when the electric resistance is further high, there is a problem that the resistance changes due to the environment, that is, the charging potential fluctuates.

Here, as a method of adjusting the resistance of the surface layer, there is a method using a conductive additive. However, carbon generally used as conductive particles tends to agglomerate and thus has a structure in which primary particles are developed and entangled. In addition, since the resistance of carbon is low, even with the same addition amount, the electrical uniformity changes significantly depending on the dispersion conditions, and even the resistance of the film itself changes. As a specific problem, the entanglement of the structure due to agglomeration of carbon particles in the roller generates an electric conduction portion, which tends to cause unevenness in image density in a sandy state, and a contact portion with a photoconductor defect. There was a problem that leaks easily occurred.

On the other hand, the present inventors have studied means for adjusting the resistance of the surface layer by using a conductive agent containing tin oxide as a constituent. As a result, it has been confirmed that the conductive agent containing tin oxide as a component has an advantage that the electrical characteristics of the roller are not relatively changed by dispersion because the conductive agent does not have a structural structure due to large aggregation like carbon.

In the case of tin oxide alone, the resistance is 1
0 ⁴ ~10 ⁸ Ω · cm and for a medium resistance, generate electrical heterogeneity in particular dispersed state, has the advantage that it by not cause problems abnormal image like. On the other hand, in the case of tin oxide alone, in order to obtain a desired resistance as a charging roller, it is necessary to add about 50 wt%, thereby deteriorating the flexibility of the film. There is also a disadvantage that it is not suitable for a certain charging roller.

The present invention has been made in view of the above points, and has as its object to excel the surface of the charging roller from the surface of the photosensitive member, from the toner, and from contamination of the photosensitive member. Another object of the present invention is to provide a charging roller capable of performing stable and uniform charging by forming a surface layer that does not generate minute electrical conduction portions due to the dispersed state of conductive particles.

[0019]

A charging roller according to claim 1, wherein the charging roller has an elastic layer and a surface layer covering the elastic layer, wherein the elastic layer comprises epichlorohydrin rubber as a component, and Has a specific resistance of 10 ⁴ Ω · c
m or less, and a conductive agent containing tin oxide having a primary particle size of 0.5 μm or less as a component.

The charging roller according to the second aspect is the first aspect of the invention.
Wherein the binder resin of the surface layer is nylon or polyvinyl butyral.

According to a third aspect of the present invention, there is provided the charging roller according to the first aspect.
Wherein the conductive agent in the surface layer is a conductive particle subjected to a silane coupling treatment.

According to a fourth aspect of the present invention, there is provided the charging roller according to the third aspect.
Wherein the conductive particles covered with the silane coupling agent in the surface layer are tin oxide-indium oxide.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram of the charging roller of the present invention. Since the elastic layer 2 is made of epichlorohydrin rubber, unlike the synthetic rubber in which the conductive agent is dispersed in the elastic layer, the charging roller 201 itself has a medium resistance and does not cause electric nonuniformity. Further, a charging roller having higher withstand voltage than a conductive agent / synthetic rubber system can be obtained. Therefore, it is possible to apply the DC voltage alone without causing a problem of uneven charging and a decrease in withstand voltage, thereby making it unnecessary to complicate the layer structure of the charging roller, which is advantageous in terms of the roller manufacturing process. . In FIG. 1, reference numeral 1 denotes a metal core (support).

The surface layer 3 on the elastic layer 2 has a specific resistance of 10 ⁴ Ω · cm or less and a primary particle size of 0.5 μm.
The conductive agent contains the following tin oxide as a constituent.
Since this conductive agent is a conductive particle containing tin oxide having a specific resistance of 10 ⁴ Ω · cm or less, it does not have a developed structure structure like carbon, and is advantageous in terms of electrical uniformity. is there. In addition, since the amount of tin oxide added can be reduced as compared with the case of tin oxide alone, it is advantageous in terms of the flexibility of the surface layer.

Although the conductive agent containing tin oxide as a component does not have a developed structural structure like carbon, the effect of the dispersion state is likely to occur as the resistance becomes lower, and electrical unevenness occurs. However, when the primary particle size of the conductive agent is 0.5 μm or less, the above 10 ⁴ Ω ·
Even if the resistance is less than cm, the influence of the dispersion state is small. Therefore, it was found that no electric conduction portion was generated, and no problems such as unevenness of image density in the form of sand and leak at the contact portion with the photoreceptor defect easily occurred.

Further, by using nylon or polyvinyl butyral as a binder resin for the surface layer 3, the surface layer has excellent releasability from the surface of the photoreceptor and releasability from the toner. It is possible to perform highly stable and stable charging. In addition, since it is effective in preventing contamination of the photoconductor, it is possible to prevent image density unevenness due to contamination of the photoconductor.

[0027] Tin oxide is a constituent component and the specific resistance is 10 ⁴
Examples of the conductive agent having a resistance of Ω · cm or less include tin oxide doped with antimony and tin oxide-indium oxide (mixing of tin oxide and indium oxide). The latter is safe when manufacturing and disposing of rollers. It is advantageous from the viewpoint of gender and pollution prevention.

By the way, since tin oxide is easily oxidized, in the case of a roller using a tin oxide-based conductive agent, the resistance of the roller tends to change depending on the use condition of the roller. In tin oxide-based conductive agents, carriers due to oxygen defects often contribute to the electron conductivity mechanism, and therefore, the carrier concentration is reduced by oxidation, and the resistance of the conductive agent is often changed. is there.

Actually, it has been confirmed that when continuous copying is performed by a roller using a tin oxide-based conductive agent, the resistance changes with time and the charging potential decreases. Ozone is not generated at all even in the case of contact charging, and the main cause is oxidation of the roller surface by ozone during continuous copying.

It has been found that the tin oxide-indium oxide based conductive agent also has a resistance change due to oxidation as described above. Using a tin oxide-indium oxide based conductive agent whose surface is coated with a silane coupling agent,
Since oxidation of the conductive agent by oxygen or moisture did not occur, it was found that the resistance of the roller did not change even when continuous copying was performed, and the potential was stabilized.

[0031]

[Comparative Example] and

EXAMPLE First, (1) an apparatus and method for evaluating the charging characteristics (charging potential and charging uniformity) of the charging roller, (2) releasability from the photoreceptor surface and toner, and durability (resistance) of the charging roller An apparatus and method for evaluating voltage characteristics and film strength of the surface layer will be described. (1) Apparatus and method for evaluating charging characteristics of charging roller FIG. 2 shows an apparatus for evaluating charging characteristics. 201 is a charging roller to be evaluated; 202 is a power supply for applying a DC voltage Va to the cored bar 1; 203 is a photosensitive drum; 204 is a neutralization lamp; 205 is the surface potential (charging potential) Vs of the photosensitive drum 203; It is an electrometer for measuring.

The method of evaluating the charging roller by the charging characteristic evaluation apparatus will be described below. The charging roller 201 which rotates in contact with and follows the photosensitive drum 203 rotating at a linear velocity v.
DC voltage Va is applied to the surface of the photosensitive drum 203, which has been neutralized by the neutralization lamp 204, to a charging potential Vs.
The charging potential Vs of the photosensitive drum 203 by the electrometer 205
Is measured. It is a measurement result by this electrometer 205.
The uniformity of the charging potential Vs can be evaluated from the charging characteristic chart.

(2) Image Forming Apparatus for Evaluating Charging Roller and Evaluation Method Therewith FIG. 3 shows an image forming apparatus for evaluating charging roller. 303
Denotes a photosensitive drum, 304 denotes a discharge lamp, 306 denotes a laser beam as exposure information, 307 denotes a developing device, 308 denotes a cleaner for the photoconductive drum, and 309 denotes a transfer belt. This image forming apparatus is for investigating practical problems of the charging roller.

Specifically, the releasability and non-staining property of the charging roller from the photoreceptor were evaluated from the horizontal streak image due to the roller trace on the photoreceptor, and the image was stained after a 10,000-time running test. The releasability of the roller from the toner was evaluated from the state of toner adhesion to the toner. Further, the voltage resistance and the surface layer strength of the roller were evaluated based on the abnormal image and the damage state of the roller. Leakage due to a defect of the photoreceptor was similarly evaluated by image evaluation. In addition, apart from the initial evaluation, a severe running test of 200,000 times was continuously performed.

Next, comparative examples and examples will be described. Comparative Example 1 As shown in FIG. 1, a charging roller 201 including a cored bar (support) 1, an elastic layer 2, and a surface layer 3 was manufactured. Core 1 is S
US303, the elastic layer 2 was made of carbon-dispersed chloroprene rubber (rubber thickness 3 mm). The surface layer 3 was coated with N-methoxymethylated nylon (Toresin EF-30T, manufactured by Teikoku Chemical Industry Co., Ltd.) according to the following formulation and coating conditions, and then 100 ° C.
To form a film.

[Preparation conditions]-N-methoxymethylated nylon 2.4 wt%-Methanol 24.4 wt%-2-ethoxyethanol 73.2 wt% [Coating conditions]-Spray gun TABI-951 made by Devilbis-Spray gun moving speed 30mm / sec ・ Spray gun / roller distance 93mm ・ Atomization air flow rate 50l / min ・ Roller rotation speed 400rpm

As shown in [Table 1], the uniformity of charging,
There were problems with the withstand voltage and the film strength (surface layer). However, the uniformity of the chargeability was improved by applying the DC + AC voltage.

[0038]

[Table 1] [Evaluation order] ○: Good or no problem △: Slightly poor or slightly problematic ×: Bad or problematic

Comparative Example 2 As shown in FIG. 1, a charging roller 201 including a cored bar 1, an elastic layer 2, and a surface layer 3 was prepared. Core 1 is SUS30
3. The elastic layer 2 is made of epichlorohydrin rubber (rubber thickness 3 m
m). The surface layer is made of fluorine paint (Lumiflon LF6
01C, manufactured by Asahi Glass Co., Ltd.) under the following mixing and coating conditions, followed by baking at 150 ° C. to form a film.

[Preparation conditions]-Fluorine paint (base) 10.3 wt%-Fluorine paint (curing agent) 2.1 wt%-Toluene 43.8 wt%-Xylene 43.8 wt% [Coating conditions] Same as Comparative Example 1.

As shown in Table 1, the charged potential and
There is a problem in contamination of the photoreceptor (the contact position between the roller and the photoreceptor is streaked on the image).

Comparative Example 3 Using the same core metal and elastic layer (epichlorohydrin rubber) as in Comparative Example 2, a surface layer was formed using alcohol-soluble nylon (CM8000, manufactured by Toray) containing carbon (Denka Black, manufactured by Denka). The evaluation was performed using the formed charging roller. The preparation and coating conditions of the paint for forming the surface layer were as follows.

[Formulation conditions]-Carbon 0.36 wt%-Nylon 3.24 wt% (solid content: 3.6 wt%)-Ethanol 64.3 wt%-Xylene 32.1 wt% [Coating conditions]-Same as Comparative Example 1・ Dispersion conditions at the time of preparation: 13 with a 300 W ultrasonic cleaner.
0 minutes ・ Drying temperature: 150 ℃

As shown in Table 1, there was no contamination on the photoreceptor. However, the electrical resistance of carbon is low,
Since conductive portions were formed between the carbon fine particles, there was a problem in the uniformity of charging, and therefore, sand-like unevenness occurred in the image. Also, for the same reason, a leak occurred at a photoconductor defect.

Comparative Example 4 Using the same core metal and elastic layer (epichlorohydrin rubber) as in Comparative Example 2, tin oxide (primary particle size: 0.02 μm, specific resistance: 10 ⁶ Ω · cm) was used as a surface layer forming material. The evaluation was performed using a charging roller using the contained alcohol-soluble nylon (Daiamide T171, manufactured by Daicel Huls). In this case, the surface layer was formed under the following mixing and coating conditions. In addition, the mixing ratio of tin oxide and the above nylon was calculated so that the tin oxide content of the surface layer was 65 wt%.

[Preparation conditions]-Tin oxide 2.16 wt%-Nylon 1.44 wt% (solid content: 3.6 wt%)-Ethanol 64.3 wt%-Xylene 32.1 wt% [Coating conditions]-Comparative example 1 Same ・ Dispersion condition at the time of preparation: 15 with a 300 W ultrasonic cleaner
・ Drying temperature: 150 ℃

As shown in Table 1, there was no contamination on the photoreceptor, and the charging potential, that is, the image density was good.
However, slight cracks were observed in the surface layer, and the film strength was insufficient.

Comparative Example 5 A charging roller having the same structure as that of Comparative Example 4, using antimony-doped tin oxide (core material: barium sulfate) having a primary particle diameter of 0.7 μm and a specific resistance of 10 Ω · cm as a conductive agent for the surface layer. ,
The addition amount was 30 wt%. [Table 1]
As shown in the figure, the film strength was improved as compared with Comparative Example 4, but the uniformity of the image was impaired.

Example 1 Evaluation was performed using the charging roller of the present invention. Antimony-doped tin oxide (primary particle size 0.0
2 μm, specific resistance 10 Ω · cm), and the configuration of the charging roller was the same as that of Comparative Example 4. The addition amount of the tin oxide in the surface layer was 30 wt%. The surface layer was formed under the following mixing and coating conditions.

[Preparation conditions]-Antimony-doped tin oxide 1.08 wt%-Nylon 2.52 wt% (Diamid T171, manufactured by Daicel Huls: solid content 3.6 wt%)-Ethanol 64.3 wt%-Xylene 32.1 wt% [Coating conditions] ・ Same as Comparative Example 1 ・ Dispersion condition at the time of preparation: 15 with a 300 W ultrasonic cleaner
・ Drying temperature: 150 ℃

As a result of the evaluation, as shown in [Table 1], the uniformity and the film strength of the image were good, the charging potential was good, and there was no problem in the image density.

Example 2 A charging roller having the same structure as in Example 1 was used, and polyvinyl butyral (Denka butyral 3) was used as a binder in the surface layer.
000-k, manufactured by Denka Co., Ltd., and tin oxide-indium oxide (primary particle size 0.02 μm, specific resistance 10
Ω · cm). The amount of antimony-doped tin oxide added to the surface layer was 30 wt%. The surface layer was formed under the following mixing and coating conditions.

[Preparation conditions]-Tin oxide-indium oxide 1.08 wt%-Polyvinyl butyral 2.52 wt% (solid content 3.6 wt%)-Ethanol 38.6 wt%-Xylene 57.8 wt% [Coating conditions]-Comparison Same as Example 1. Dispersion condition at the time of preparation: 15 with a 300 W ultrasonic cleaner.
・ Drying temperature: 150 ℃

As a result of the evaluation, as shown in [Table 1], good results were obtained in all of the initial evaluation items as in Example 1. However, after performing a severe endurance test,
As shown in Table 2, a decrease in the charging potential of 370 V was observed.

[0055]

[Table 2]

Example 3 The same structure as in Example 2 was used, except that tin oxide-indium oxide having a primary particle diameter of 0.36 μm and a specific resistance of 10 Ω · cm (core material was alumina ) Was used. The preparation and coating conditions for the surface layer were the same as in Example 2. As a result of the evaluation, as shown in [Table 1] and [Table 2], good results were obtained in all of the initial evaluation items. In addition, even in a severe endurance test, the decrease in potential was small, and good results were obtained.

[0057]

As is clear from the above description, according to the present invention, the following remarkable functions and effects can be obtained. (1) Claim 1: In a charging roller having an elastic layer and a surface layer covering the elastic layer, a medium resistance epichlorohydrin rubber is used for the elastic layer, and the surface layer has a specific resistance of 10 ⁴ Ω · cm.
Or less, and a conductive particle having a primary particle diameter of 0.5 μm or less as a constituent is included, so that an excessive amount of the conductive agent is not required. And the effect of the conductive agent dispersion state is small, and since no electrically conductive part is generated, image density unevenness in a sandy state,
Leakage at a contact portion with a photoconductor defect can be prevented. (2) Claim 2: Since the binder resin forming the surface layer is made of nylon or polyvinyl butyral, in addition to the function and effect of claim 1, the releasability of the surface layer from the photoreceptor and the toner is improved, and the photoreceptor is improved. Thus, a surface layer having excellent film strength and excellent durability can be formed without contamination. (3) Claim 3: Since the conductive particles forming the surface layer are silane-coupling conductive particles, in addition to the effects of claim 1, there is no deterioration in roller resistance due to oxidation. A stable charged potential can be obtained even when high-speed continuous copying is performed. In addition, a stable charging potential can be obtained over a long period of time and against changes in the environment. (4) Claim 4: Since the conductive particles coated with the silane coupling agent in the surface layer are tin oxide-indium oxide, in addition to the effects of claim 3, they are safe at the time of production and disposal of the roller. The effect is high, which is advantageous in terms of pollution prevention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a charging roller.

FIG. 2 is a schematic explanatory view showing an apparatus for evaluating charging characteristics of a charging roller.

FIG. 3 is a schematic explanatory view showing an image forming apparatus for evaluating a charging roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core metal (support) 2 Elastic layer 3 Surface layer 201 Charging roller 202 Power supply 203 Photoconductor drum 204 Static elimination lamp 205 Electrometer 303 Photoconductor drum 304 Static elimination lamp 306 Laser beam 307 Developing device 308 Cleaner 309 Transfer belt

Claims (4)

[Claims] 1. A charging roller having an elastic layer and a surface layer covering the elastic layer, wherein the elastic layer comprises epichlorohydrin rubber as a component, and the surface layer has a specific resistance of 10 ^4.
A charging roller comprising: a conductive agent containing tin oxide having a primary particle size of 0.5 μm or less, which is Ω · cm or less. 2. The charging roller according to claim 1, wherein the binder resin of the surface layer is nylon or polyvinyl butyral. 3. The charging roller according to claim 1, wherein the conductive agent in the surface layer is a silane-coupled conductive particle. 4. The charging roller according to claim 3, wherein the conductive particles coated with the silane coupling agent in the surface layer are tin oxide-indium oxide.