JPH07295332A - Charging member and electrophotographic apparatus having the same - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the applied voltage is only DC voltage and the oscillating voltage is superimposed on DC voltage, uniform charging characteristics and excellent output image quality can be obtained. (EN) Provided are a charging member that causes little decrease in image density due to charge-up and does not cause bleedout, and an electrophotographic apparatus including the charging member. In a charging member for applying a voltage to a charging member to charge a surface of an object to be charged, the charging member has at least a conductive elastic layer, and an elastic material forming the conductive elastic layer has a Mooney viscosity of In the range of 25-60M, and
When the nitrogen adsorption specific surface area of the conductive agent is 45 to 300 m ² / g, D
A charging member having a BP oil absorption of 50 to 250 ml / 100 g and an electrophotographic apparatus having the charging member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member and an electrophotographic apparatus having the charging member.

[0002]

2. Description of the Related Art Electrophotographic devices such as copying machines and printers are
It includes a step of uniformly charging the body to be charged. The corona charging method is generally used as the charging method, but the corona charging method often generates ozone and other harmful substances to the human body, and requires an additional means or mechanism for coping with it. However, there is a problem that it is easy to increase the size and cost.

Therefore, recently, a contact charging method has been studied as a new charging method replacing the corona charging method, and has been partially put into practical use.

According to the contact charging method, a charging member to which a voltage is applied is brought into contact with a member to be charged with a predetermined pressing force to charge the member to be charged. Since ozone generation is greatly reduced as compared with the corona charging method, the corona charging method has an advantage that an additional means or mechanism essential to the corona charging method is unnecessary. In many cases, the applied voltage is a superposed voltage of a DC voltage and an AC voltage having a peak-to-peak voltage that is about twice the charging start voltage of the body to be charged. However, in this case, since an oscillating electric field called an AC voltage is applied, charging noise is generated.

The charging member is required to have a function of holding the member to be charged at a predetermined potential. Therefore, it is important to provide the charging member with appropriate conductivity and regulate the electric resistance within a certain range. Further, in order to ensure uniform adhesion between the charging member and the body to be charged, it is necessary for the charging member to have appropriate elasticity. The conductive elastic layer in the charging member often has these conductivity and elasticity.

For the conductive elastic layer, rubber or resin which is an elastic material is used to give elasticity, and a conductive pigment or the like is added to give conductivity. Since a large amount of conductive pigment is required for the conductive elastic layer, carbon black is usually used in terms of cost. Powder resistance is 10 ^-2 ~10 ⁰ Ωcm, primary particle size is of the order of 0.03μm widely used for carbon black.

[0007]

However, the charging device using the above charging member has the following problems.

The main constituent materials of the charging member are rubber or resin and pigment. Rubber is often used as the elastic material and carbon black is used as the conductive pigment in the conductive elastic layer in the charging member, and the volume resistivity of the rubber used as the elastic material of the conductive elastic layer is very high. Even the low one is 10 ¹⁰ Ωcm. In order to impart conductivity to rubber exhibiting such a high volume resistivity, a conductive pigment having a very low volume resistivity as compared with rubber is contained,
By containing the conductive pigment, the viscosity of the elastic body is inevitably increased. When the conductive pigment is contained, the viscosity of the unvulcanized rubber increases, the fluidity decreases, and the moldability deteriorates. As a result, there arises a problem that the resistance value variation of the charging member after vulcanization molding increases. As a method of ensuring sufficient fluidity, there is a method of lowering the viscosity by adding a softening agent such as oil or a plasticizer to the compound. The addition of a softening agent such as oil or a plasticizer is also necessary for the purpose of making the charging member have an appropriate low hardness so that the charging member and the member to be charged are sufficiently brought into contact with each other.

Softeners such as these oils and plasticizers generally have migration properties, and when they bleed out to the surface of the charging member (bleed-out), they pose a problem of contaminating the photoconductor. It is desired that the added amount be suppressed as small as possible. Therefore, usually, a highly conductive carbon black capable of reducing the resistance by adding a small amount is used, and the addition amount of the conductive pigment is suppressed as much as possible to keep the addition amount of the softening agent small.

However, when the charging member in which the highly conductive carbon black is dispersed in the charging member is subjected to the charging treatment, minute uneven charging occurs on the potential of the surface of the charging member. When such a charging member is used as a charging member for primary charging for electrophotography, an image defect such as speckled black spots may occur on an image due to minute charging unevenness.
This is particularly noticeable in the halftone image area. This phenomenon is likely to appear when the applied voltage is only the DC voltage, and is unlikely to occur when the oscillating electric field such as the AC voltage is superimposed on the DC voltage and applied. It is considered that this is because there is no "leveling effect" due to an oscillating electric field such as an AC voltage.

As a cause of minute charging unevenness, when the inside of the charging member is viewed microscopically, a portion having a high resistance value such as rubber in the layer and a portion having a low resistance value such as a conductive pigment, that is, the resistance There is unevenness. Therefore, if there is a conductive pigment having a coarse particle diameter due to poor dispersion or the like in the charging member having such a constitutional layer, or if there is a deviation in the distribution of the conductive pigment, resistance unevenness becomes larger, It becomes a problem of charging characteristics.

Highly conductive carbon black, which is often used in the conductive elastic layer, has the effect of imparting conductivity by adding a small amount, but generally has a large specific surface area and oil absorption, and therefore has a strong structure and is uniformly dispersed. It is very difficult to do so, and it is considered that the resistance unevenness described above is likely to occur. On the contrary, since the low-conductivity carbon black has a weak structure, it is relatively easy to disperse it to some extent uniformly. However, in order to obtain the resistance equivalent to that of the highly conductive carbon black, it has to be added in a large amount. Therefore, as described above, adverse effects occur in terms of viscosity and hardness.

Further, the resistance of a charging member containing a small amount of carbon black is likely to increase due to energization. There is a problem that a phenomenon called so-called charge-up is apt to occur, and the charge potential of the surface of the charged body subjected to the charging process is lowered accordingly. Although the mechanism of charge-up is not clear, the larger the amount of the conductive agent added, the better the tendency of preventing charge-up. Here again, although it is desired to add a large amount of the conductive agent, the addition of a large amount increases the hardness of the charging member, which causes an adverse effect that the addition amount of the softening agent must be increased.

[0014]

According to the present invention, the above-mentioned contact charging member has at least a conductive elastic layer, and the rubber forming the conductive elastic layer has a Mooney viscosity in the range of 25 to 60 M, and , Carbon black contained as a conductive agent has a nitrogen adsorption specific surface area and a DBP oil absorption of 45 to 300
It is a charging member characterized by being in the range of [m ² / g] and 50 to 250 [ml / 100g].

The present invention is also an electrophotographic apparatus characterized by using the above charging member as a charging member for primary charging, transfer charging, etc. used in an electrophotographic apparatus.

As the voltage applied to the charging member, a DC voltage, a superimposed voltage of a DC voltage and an AC voltage, or the like can be used.

FIG. 1 is a schematic configuration diagram of an example of an electrophotographic apparatus (copier) in which a contact charging device using a charging member according to the present invention is used as a primary charging means of an image carrier.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a member to be charged, which is rotationally driven at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow. Reference numeral 1a is a conductive drum base such as aluminum of the photosensitive drum 1, and 1b is a photosensitive layer formed on the outer peripheral surface of the drum base 1a.

Reference numeral 2 denotes a contact charging member, and in this embodiment, a roller body (hereinafter, referred to as a charging roller) arranged in parallel with the surface of the photosensitive drum 1 in a direction of a drum bus line and in pressure contact with the photosensitive drum 1.
Then, the photosensitive drum 1 is driven to rotate.

The charging roller 2 of this example is a core metal (2) to which a DC voltage or a superimposed voltage of a DC voltage and an AC voltage is applied.
a), a conductive elastic layer that imparts elasticity and conductivity (2
b), if necessary, a resistance control layer (2d) for controlling the resistance of the charging member is formed on the resistance control layer (2d), and if a resistance control layer is provided outside the conductive elastic layer, the surface may be provided outside the resistance control layer as necessary. A layer (2c) may be provided. The conductive elastic layer 2b, the resistance control layer 2d, and the surface layer 2c of the charging roller 2 of this example will be described later.

Reference numeral 3 denotes a voltage application power source for the charging roller 2. By applying a predetermined voltage from the power source to the core metal 2a of the charging roller 2, the surface of the rotating photosensitive drum 1 is of a contact charging type. Is charged.

The voltage applied to the charging roller 2 may be a DC voltage alone or a DC voltage may be superposed with an oscillating electric field such as an AC voltage. In terms of uniform charging, it is more advantageous to superpose an oscillating electric field, but the problem of charging noise has been mentioned above.

Around the surface of the photosensitive drum 1 which has been uniformly primary-charged to a predetermined potential by the charging roller 2, an exposing means 4 (not shown) for exposing according to the image information of the original to form an electrostatic latent image, A developing device 5 for forming a toner image by attaching toner to the electrostatic latent image, a transfer charger 7 for transferring the toner image on the photosensitive drum onto a transfer material P supplied from a paper feed cassette 6,
A cleaning device 9 that removes residual toner on the photosensitive drum 1 after transfer and a pre-exposure device 10 (not shown) that removes charges on the photosensitive drum 1 in preparation for the next primary charging are arranged. Further, on the downstream side of the transfer charger 7, a fixing device 8 that fixes the toner image transferred on the transfer material P to the transfer material P is arranged.

In the charging roller 2, the conductive elastic layer 2b
Has suitable conductivity and elasticity in order to secure power supply to the photosensitive drum 1 as the member to be charged and good uniform adhesion of the charging roller 2 to the photosensitive drum 1. Further, in order to ensure uniform adhesion between the charging roller 2 and the photosensitive drum 1, the conductive elastic layer 2b may be formed into a so-called crown shape by polishing the central portion to have the largest thickness at the central portion and become thinner toward both ends. Many. Since the charging roller 2 that is generally used is in contact with the photosensitive drum 1 by applying a predetermined pressing force to both ends of the cored bar 2a, the pressing force at the central portion is small and becomes large at both ends. Moreover, there is no problem if the straightness of the charging roller 2 is sufficient, but if it is not sufficient, density unevenness may occur in the image corresponding to the central portion and both end portions. The crown shape is formed to prevent this.

The conductivity of the conductive elastic layer 2b is adjusted by adding a conductive agent such as carbon black to an elastic material such as rubber. The elasticity is adjusted by adding process oil, plasticizer and the like. Specific elastic materials for the conductive elastic layer 2b include, for example, natural rubber, EPDM, SBR, silicon rubber, urethane rubber, synthetic rubber such as IR, BR, NBR, and CR, as well as polyamide resin, polyurethane resin, and silicone resin. Resins such as are also mentioned.

The surface layer 2c is often provided to prevent bleed-out of the plasticizer or the like in the conductive elastic layer 2b to the surface of the charging roller. Specific materials for the surface layer 2c include polyamide resin, polyurethane resin, fluororesin,
Resins such as silicone resin, and epichlorohydrin,
Examples thereof include urethane rubber, chloroprene, acrylonitrile rubber and the like. A conductive agent such as carbon black, tin oxide, or titanium oxide is often dispersed in order to provide the surface layer 2c with appropriate conductivity.

The resistance control layer 2d is often provided to control the resistance of the charging member. Specific materials for the resistance control layer 2d include resins such as polyamide resin, polyurethane resin, fluororesin, silicone resin, and the like. Examples include epichlorohydrin, urethane rubber, chloroprene, and acrylonitrile rubber. Conductive agents such as carbon black, tin oxide, and titanium oxide are often dispersed in the resistance control layer 2d.

Using carbon black under the conditions as in the present invention as a conductive agent in the conductive elastic layer 2b of the charging roller 2,
If kneading and dispersing are sufficiently performed, uneven distribution of the pigment is unlikely to occur. In particular, carbon black under the conditions as in the present invention has a relatively weak structure structure and is easy to obtain a uniformly dispersed state. Therefore, the uneven resistance in the layer due to the uneven distribution of the pigment can be reduced to such an extent that there is no problem in charging characteristics. Further, the charging member using carbon black under the conditions as in the present invention has a small charge-up due to long-term energization. This is because the carbon black under the conditions as in the present invention needs to be added in a relatively large amount in order to obtain the desired conductivity, so that the ratio of the conductive agent (here, carbon black) in the charging member is increased and the charge-up is increased. It is considered to be superior to the prevention of However, the mechanism of charge-up is not clear.

Further, by using the raw material rubber under the conditions as in the present invention as the elastic material of the conductive elastic layer 2b, even if a relatively large amount of carbon black is added, the addition amount of the softening agent is suppressed as much as possible. The viscosity of the vulcanized rubber can be kept low. As a result, it is possible to obtain a charging member that is less likely to be contaminated by the photosensitive drum, has an excellent molding process, and has a small variation in resistance. Preferably, the variation in resistance value of the charging member in the longitudinal direction is within one digit.

Injection molding as a method of molding the conductive elastic layer,
Although there are extrusion molding, transfer molding, compression molding, and the like, the present invention can obtain a charging member having a small resistance value variation even in transfer molding in which molding conditions are difficult to control by a simple method.

On the other hand, when carbon black which is out of the conditions of the present invention is used, the nitrogen adsorption specific surface area is 45 [m.
² / g] and DBP oil absorption is 50 [ml /
If it is less than 100 g] or if either one is less than the condition, it is difficult to obtain conductivity even if a large amount is contained. If the pigment is contained in a too large amount, the hardness of the conductive elastic layer increases and the elasticity is lost.
Furthermore, the nitrogen adsorption specific surface area exceeds 300 [m ² / g],
If the DBP oil absorption exceeds 250 [ml / 100 g] or if either one exceeds, image defects such as speckled black spots occur on the image.

If a raw material rubber having a higher Mooney viscosity than the conditions of the present invention is used and carbon black of the conditions of the present invention is used, the unvulcanized rubber has a high viscosity, so that the molding processability is deteriorated and the resistance of the charging member is reduced. The variation in value becomes large. On the contrary, if a raw material rubber having a lower Mooney viscosity than the conditions of the present invention is used, the shearing force at the time of dispersing the pigment is reduced, and the dispersibility of the pigment may be reduced.

The charging roller 2 as a charging member that contacts the photosensitive drum 1 as the member to be charged may be non-driven, or may be driven to rotate. Further, the charging member 2 is not limited to the roller type, but may have an appropriate shape or form such as a blade type or a block type as shown in FIGS. 3 (a) and 3 (b). The raw rubber forming the electroconductive elastic layer 2b has a Mooney viscosity of 25 to 6
Carbon black having a nitrogen adsorption specific surface area of 45 to 300 [m ² / g] and a DBP oil absorption amount of 50 to 250 [ml / g] as a conductive agent. By doing so, the same effect as that of the roller type charging member can be obtained.

The Mooney viscosity of the rubber used in the present invention is measured according to JIS K6300.

The nitrogen adsorption specific surface area of the carbon black in the present invention is measured by the BET method utilizing nitrogen adsorption.

The DBP oil absorption of the carbon black in the present invention is 100 g per 100 g obtained from 70% of the maximum torque when DBP (dibutyl phthalate) is added to the carbon black using an absorption meter. It is a value showing the DBP oil absorption.

[0037]

EXAMPLES Examples of the present invention will be described below. (Example 1) A charging roller 2 as a charging member according to the present invention was prepared in the following manner.

SBR 100 parts by weight Carbon black 30 parts by weight Zinc oxide 5 parts by weight Fatty acid 2 parts by weight The following materials are mixed in a closed type mixer adjusted to 60 ° C.
After kneading for 20 minutes, 20 parts by weight of naphthenic oil is added to 100 parts by weight of SBR, and the mixture is kneaded for 20 minutes in a closed mixer cooled to 20 ° C. to prepare a raw material compound. Further, 0.5 parts by weight of sulfur as a vulcanizing agent, 1 part by weight of thiazole type and 1 part by weight of thiuram type as a vulcanization accelerator were added to 100% by weight of SBR of the raw material rubber, and the mixture was cooled to 20 ° C. Knead for 10 minutes on a roll machine. Using this compound, a conductive elastic layer 2b was vulcanized by transfer molding around a φ9 stainless steel cored bar in a roller shape so as to have an outer diameter of φ16.

Mooney of SBR used for the conductive elastic layer
Viscosity (ML_{1 + 4} 100 ° C) is 35 and is a carbon bra
Nitrogen adsorption specific surface area and DBP oil absorption are 250
[M ² / G] and 170 [ml / 100g].

As the material for the surface layer 2c, 100 parts by weight of methylolated nylon and 30 parts by weight of titanium oxide are dispersed and dissolved in a mixed solvent of methanol / toluene to prepare a coating material for the surface layer. This coating material was applied on the conductive elastic layer 2b by a dipping method to form a surface layer 2c having a thickness of 30 .mu.m to form a roller-shaped contact charging member 2 (charging roller). The resistance value of the obtained charging roller 2 is set at a temperature of 23.5 ° C. and a humidity of 50% (environment 1).
The aluminum foil is closely attached to the outer periphery of the coil and wound, and a DC voltage (250v) is applied between the support and the aluminum foil to measure the resistance of the resistance meter "HI".
OKI 3119 DEGITALMΩ HI TES
TER (Hioki Electric Co., Ltd.) was used to measure three locations (end 1, center, end 2) in the longitudinal direction of the charging roller. The results are shown in Table 1.

This charging roller 2 is used as the charging roller 2 at the position of the primary charger of the copying machine "NP6030 (Canon Co., Ltd.)" shown in FIG. 1, and the core metal 2a of the charging roller 2 is- A direct current voltage of 1500 V was applied to charge the photosensitive drum 1, and a durability test was performed on a plurality of 50,000 sheets of images. Initial and 50,000
The image was evaluated by visually observing the image obtained after running 0 sheets. The results are shown in Table 2. In the table, ◯ indicates that the obtained image is good, Δ indicates that the image is acceptable, and x indicates that it is not acceptable.

Further, the photosensitive drum 1 at the initial stage of the image output durability test of 50,000 sheets and after the durability test of 50,000 sheets.
The potential of the surface of the central portion in the longitudinal direction is measured by an electrometer "MODEL34".
4 (TREK, INC.) ”. The results are shown in Table 2.
Shown in. Although the surface potential of the photosensitive drum is decreased by several tens of volts, it is at a level where there is no problem in practical use.

The above-mentioned image output and potential measurement are as follows.
Temperature 23.5 ° C, humidity 50% (environment 1) and temperature 2
It was performed at 3.5 ° C. and a humidity of 5% (environment 2).

In addition, the cartridge of the copying machine is set to 10
After harshly standing for 2 months in an environment of temperature 40 ° C. and humidity 90%, the surface of the photosensitive drum 1 is observed with a microscope, and the photosensitive drum is caused by bleed-out of oil, plasticizer, etc. contained in the charging member. Checked for pollution. The results are shown in Table 2.
In the table, ○ indicates no abnormality, and × indicates contamination of the photosensitive drum. If even one of the ten drums was contaminated with the drum, it was evaluated as x.

Example 2 The raw material rubber and carbon black used in the conductive elastic layer 2b in Example 1 were EPDM 100 parts by weight and carbon black 40 parts by weight, and paraffinic oil 25 parts by weight instead of naphthenic oil. Evaluation was performed in the same manner as in Example 1 except that the parts were used. The results are shown in Tables 1 and 2.

EPDM film used in the conductive elastic layer
Knee viscosity (ML_{1 + 4} 100 ° C) is 57 and carbon
The nitrogen adsorption specific surface area and DBP oil absorption of the rack are 50
[M ² / G] and 180 [ml / 100g].

Example 3 The raw rubber and carbon black used in the conductive elastic layer 2b in Example 1 were NBR 100 parts by weight and carbon black 26 parts by weight, and dioctyl phthalate (DOP) 17 was used in place of the naphthene-based oil. Evaluation was performed in the same manner as in Example 1 except that the parts by weight were used. The results are shown in Tables 1 and 2.

Raw rubber NBR used in the conductive elastic layer
Has a Mooney viscosity (ML _{1 + 4} 100 ° C.) of 42 and the nitrogen adsorption specific surface area and DBP oil absorption of carbon black are 145 [m ² / g] and 120 [ml / 100 g], respectively.

(Example 4) Carbon black used in Example 3 was used as the carbon black used in Example 3, and 40 parts by weight of carbon black was used, and 25 parts by weight of naphthenic oil was used to obtain the conductive elasticity. Evaluation was performed in the same manner as in Example 1 except that the surface of the layer 2b was subjected to polishing treatment to form a crown shape.
The results are shown in Tables 1 and 2.

Example 5 A resistance control layer 2d was formed on the conductive elastic layer 2b formed in Example 1 as follows.

As a material for the resistance control layer 2d, 100 parts by weight of polyurethane resin and 90 parts by weight of titanium oxide are dispersed and dissolved in a solvent of methyl ethyl ketone to prepare a coating material for the resistance control layer. This coating material is applied on the conductive elastic layer 2b by a dipping method to form a resistance control layer 2 having a thickness of 100 μm.
d was formed.

A surface layer 2c similar to that of Example 1 was formed on the resistance control layer 2d to prepare a charging roller 2 as shown in FIG. Using the charging roller 2 obtained, the same evaluation as in Example 1 was performed. The results are shown in Tables 1 and 2.

(Example 6) The raw rubber used for the conductive elastic layer 2b in Example 1 was 100 parts by weight of IR, and only IR was adjusted to 60 ° C before dispersing and kneading additives such as carbon black. 3 with 2 roll machine
Mastication was performed for 0 minutes. The charging roller 2 obtained in the same manner as in Example 1 in the subsequent steps was evaluated in the same manner as in Example 1.
The results are shown in Tables 1 and 2.

The Mooney viscosity (ML _{1 + 4} 100 ° C.) after mastication of IR used in the conductive elastic layer 2b was 45. However, the Mooney viscosity of IR before mastication (ML _{1 +} 41
(00 ° C.) is 80, and it cannot be used as it is as a raw material rubber for the present invention.
(And natural rubber) can be mechanically reduced in Mooney viscosity by mastication. In the case of other synthetic rubbers, the decrease in Mooney viscosity due to this mastication is small.

When the conductive elastic layer 2b is molded by injection molding and extrusion molding, the variation in the resistance value of the charging member is further reduced and a good charging member can be obtained.

Further, the surface layer 2 of the above Examples 1 to 6
Although titanium oxide is used as the conductive pigment for c, tin oxide, indium oxide, or the like may be used instead.

The surface layer 2c may have no pigment.

(Comparative Example 1) A charging roller 2 was prepared in the same manner as in Example 1 except that the raw material rubber used in the conductive elastic layer 2b was 100 parts by weight of EPDM. An evaluation was made. The results are shown in Tables 1 and 2.

As can be seen from Table 1, there is a two-digit variation in the longitudinal resistance value of the charging roller 2 after molding.
This variation in the resistance value caused unevenness in image density.

The EPDM used for the conductive elastic layer had a Mooney viscosity (ML _{1 + 4} 100 ° C.) of 75.

Comparative Example 2 A charging roller was prepared in the same manner as in Example 1 except that the carbon black used in the conductive elastic layer 2b in Example 1 was 5 parts by weight of carbon black and the naphthenic oil was 15 parts by weight. Was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

The carbon black used for the conductive elastic layer 2b has a nitrogen adsorption specific surface area and a DBP oil absorption of 127, respectively.
It is 0 [m ² / g] and 480 [ml / 100 g].

The so-called highly conductive carbon black having a large specific surface area and large oil absorption as used in Comparative Example 2 constitutes a strong structure. With such a structure, a conductive path is formed in the rubber, and it is effective in adding a small amount to high-resistance rubber or the like to give conductivity. However, the highly conductive carbon black has a strong structure and is disadvantageous in obtaining a uniform dispersed state.

Comparative Example 3 The procedure of Example 1 was repeated except that the conductive pigment used in the conductive elastic layer 2b was 80 parts by weight of carbon black, but the charging roller 2 was made conductive. I couldn't get it. It was above the upper limit of measurement (2000 MΩ) of the resistance meter.

The carbon black used for the conductive elastic layer has a nitrogen adsorption specific surface area and a DBP oil absorption of 27, respectively.
The values were [m ² / g] and 68 [ml / 100g].

Comparative Example 4 A charging roller was prepared in the same manner as in Example 1 except that the raw rubber used in the conductive elastic layer was 100 parts by weight of SBR in Example 1, and the charging roller was prepared in the same manner as in Example 1. Was evaluated. The results are shown in Tables 1 and 2.
Shown in.

The SBR used for the conductive elastic layer has a Mooney viscosity (ML _{1 + 4} 100 ° C.) of 44, but since it is an oil-extended rubber, it contains 37.5 parts by weight of naphthene oil in advance. There is.

It was 2 out of 10 that the photosensitive drum was contaminated due to severe storage.

[0069]

[Table 1]

[0070]

As described above, according to the present invention, in the charging member for contacting and charging the body to be charged, the Mooney viscosity of the raw material rubber forming the conductive elastic layer of the charging member ( ML _{1 + 4} 100 ° C.) is in the range of 25 to 60, and the nitrogen adsorption specific surface area of the conductive agent is 45 to 300.
It is in the range of [m ² / g] and the DBP oil absorption is 50 to
By containing carbon black in the range of 250 [ml / 100 g], the moldability is excellent, the resistance value variation of the obtained charging member is small, and the voltage applied to the charging member is only DC voltage and DC voltage In both cases where the AC voltage is superposed on, good uniform charging characteristics and output image quality can be secured. Further, since the charging member is less likely to be charged up, even if a plurality of images are continuously printed, the image density is hardly reduced. In addition, since the content of oil and plasticizer can be suppressed as much as possible, the risk of bleeding out of oil or the like in the charging member due to long-term storage is low, and the risk of contamination of the charged body can be reduced accordingly. It can be effectively used as a charging member of a contact charging device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an electrophotographic apparatus in which a contact charging device using a charging member according to the present invention is used as a primary charging unit of an image carrier.

FIG. 2 is a schematic configuration diagram of a contact charging member showing another embodiment.

3 (a) and 3 (b) are diagrams showing another example of the contact charging member according to the present invention.

[Explanation of symbols]

1 Charged Object (Photosensitive Drum) 2 Charging Roller as Charging Member, Charging Blade, Charging Block 2a Core Bar 2b Conductive Elastic Layer 2c Surface Layer 3 Power Supply 4 Exposure Means 5 Developing Device 6 Paper Feed Cassette 7 Transfer Charger 8 Fixing Device 9 Cleaning device 10 Pre-exposure device P Transfer material

Claims (8)

[Claims] 1. A charging member for charging a surface of an object to be charged by applying a voltage to the charging member, wherein the charging member has at least a conductive elastic layer, and a Mooney of an elastic material forming the conductive elastic layer. The viscosity is in the range of 25 to 60 M, and the nitrogen adsorption specific surface area of the conductive agent is 45 to 300 m ² / g.
The DBP oil absorption is in the range of 50 to 250 ml / 100 g. 2. The charging member according to claim 1, wherein the elastic material forming the conductive elastic layer is a non-oil extended system. 3. The volume resistivity of the conductive elastic layer is 1
The charging member according to claim 1, which has a resistance of 0 ² to 10 ¹⁰ Ωcm. 4. The charging member according to claim 1, wherein the voltage applied to the charging member is only a DC voltage. 5. The charging member according to claim 1, wherein the voltage applied to the charging member is a superimposed voltage of a DC voltage and an oscillating voltage. 6. The charging member according to claim 1, wherein the charging member is a primary charging charging member for electrophotography. 7. The charging member according to claim 1, wherein the charging member is a transfer charging charging member for electrophotography. 8. An electrophotographic apparatus having a photoconductor, a latent image forming means, a means for developing the formed latent image, and a means for transferring the developed image to a transfer material. An electrophotographic apparatus, wherein the charging member according to claim 1 is used as a charging member used for a next charging process or a charging member used for a transfer charging process in the transfer means.