JPH10161390A - Electrostatic charging member and electrostatic charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging member which is capable of solving the image defect by the unequal electrostatic charging in the longitudinal direction of the electrostatic charging member by the deficiency of a crown quantity without increasing a cost and an electrostatic charging device having this electrostatic charging member. SOLUTION: This electrostatic charging member is formed to a crown shape by coating a laminar elastic layer consisting of an elastic material with seamless tubes to one or plural layers. This electrostatic charging device has the electrostatic charging member which is obtd. by forming the elastic material described above to the crown shape, forming the seamless tubes to a straight shape and making the previously applied crown quantity of the elastic material large than the crown quantity necessary as the electrostatic charging member after the coating with the seamless tubes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member mainly used in an electrophotographic image forming apparatus and a charging device having the charging member.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus such as an electrophotographic copying machine, a printer and an electrostatic recording apparatus includes a primary charging means for charging an image carrier, and a transfer for attracting a developer on the image carrier to a printing material. It includes means for uniformly charging the object to be charged, such as means.

[0003] As a charging method used at that time, a contact-type charging method which generates much less ozone than a conventional corona charging method has been studied and has been put to practical use in some parts.

FIG. 1 is a sectional view of an example of a contact-type charging member.
FIG. 2 shows a cross-sectional view of an example of the elastic body. FIG. 3 is a schematic configuration diagram of an image forming apparatus (copier) using a contact-type charging device.

The charging member 2 comprises a conductive metal core 2a for applying a vibration voltage such as a DC voltage or a superposition of a DC voltage and an AC voltage from a power supply 3, and a conductive elastic layer 2b for providing elasticity. If necessary, a resistance control layer 2c for controlling the resistance of the charging member, a coating layer 2d as a surface layer in contact with the member to be charged, and the like are provided outside the elastic layer 2b. The charging member 2 is in contact with the member to be charged 1 with a predetermined contact force by pressing means (not shown). In the image forming apparatus shown in FIG. 3, the charging member 2 and the member to be charged 1 rotate in the directions of the arrows, and the photosensitive layer 1b of the member to be charged with which the charging member 2 contacts is charged by the voltage applied by the power source 3, It becomes an image on the photosensitive layer 1b through the exposure step 4 and the development step 5, and forms an image transferred on the printing substrate 7 in the transfer step 6. Reference numeral 8 denotes a step of cleaning the photosensitive layer 1b. 1a
Is a conductive support.

In the contact charging method, the charging member 2 to which the voltage is applied is brought into contact with the charging member 1 to charge the charging member 1, so that the charging member 2 and the charging member 2 are charged over the charging area. It is important that the abutments 1 abut uniformly.

Further, since the charging member 2 is in contact with the drum-shaped or belt-shaped moving body 1 to be charged, if the charging member 2 is fixed, abrasion or damage may occur at the contact portion. There is. In order to solve this problem, it is general that the charging member 2 is formed into a columnar or cylindrical roller shape and is rotatable so as to be driven by the member 1 to be charged.

Here, ideally, the pressing force for bringing the charging member 2 into contact with the member to be charged 1 is applied uniformly on the line of contact or on the contact band. Is rotatable, a pressing force is applied only to both ends of the tangent line or the tangent band, and a pressing force cannot be applied to the central portion in many cases.

When the pressing force is applied only to both ends as described above, the contact force at the center becomes weaker than at both ends due to the deflection of the charging member 2, and the charge amount differs at the center and both ends. 2 has a disadvantage that image defects occur due to uneven charging in the longitudinal direction. Therefore, the diameter 11 at the center of the charging member is reduced by the diameter 1 at the end by an amount corresponding to the amount of deflection.
A so-called crown shape, which is made thicker than 2, has been studied and is partially implemented.

The structure of the rotatable charging member 2 includes a core 2
a, elastic layer 2b for giving elasticity to charging member 2, elastic layer 2b
No bleed-out of a plasticizer or the like from the surface, a resistance control layer 2c that governs the electrical properties of the electrode layer or the charging member 2, and a member 1 to be charged such as a photoreceptor are not damaged or contaminated. It is common to use a plurality of functionally separated layers such as a surface layer 2d provided as necessary.

As a method of manufacturing the elastic layer 2b, a method of vulcanizing unvulcanized rubber in a mold, a method of foaming and vulcanizing in a vulcanizing can, and the like are known.

As a method for manufacturing the bleeding prevention layer, the electrode layer or the resistance control layer 2c, and the surface layer 2d, a method using a coating liquid such as a dip coating method and a roll coating method is generally used.

However, since the method of coating the coating liquid requires drying, there has been a problem that the cost is high due to the capital investment of the drying furnace and the increase in the number of steps due to the additional drying step.

As the demand for the charging member 2 increases, the number of stacked members tends to increase. When the number of coats is increased, the number of drying steps is required as many as the number of layers.

Therefore, recently, a charging member 2 that does not need to be dried and is obtained by simply covering the elastic member 2b with a seamless tube has been studied.

[0016]

However, when the charging member 2 formed by covering the elastic body 2b with one or a plurality of seamless tubes on the elastic body 2b has a crown shape, there are the following problems.

In the method of forming the tube-covering type charging member 2 into a crown shape, when the elastic body 2b is formed into a crown shape and the seamless tube is formed into a straight shape, the tube-covering type charging member 2 is formed by covering the elastic body with a seamless tube. Since the elastic body 2b is compressed, if the elastic body 2b is formed into a crown shape, the compression ratio differs between the end and the central part, the crown shape given to the elastic body is not maintained, and the crown amount after coating is the crown given to the elastic body. There is a problem that it becomes smaller than the amount. Here, the crown amount refers to a result obtained by subtracting the diameter at the end from the diameter at the center.

An object of the present invention is to provide a charging member and a charging device capable of solving the above-mentioned image defects due to uneven charging in the longitudinal direction of the charging member due to insufficient crown amount without increasing the cost.

[0019]

That is, the present invention relates to a crown-shaped charging member in which one or a plurality of seamless tubes are coated on an elastic layer made of an elastic material.
The elastic body has a crown shape, the seamless tube has a straight shape, and a crown amount of the elastic body applied in advance is larger than a crown amount required as the charging member after the seamless tube is covered. Charging member.

According to the present invention, there is provided a charging device for charging a member to be charged by applying a voltage to the charging member, the charging device having the charging member.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventor has described the charging member 2 described above.
Paying attention to the fact that the uneven charging in the longitudinal direction is caused by the bending of the charging member 2 generated because the pressing force for bringing the charging member 2 into contact with the member 1 to be charged is a load at both ends. Only the diameter 11 at the center of the charging member 2 is changed to the diameter 1 at the end.
It was devised and studied to introduce a so-called crown shape, which is wider than 2, into the charging member 2 of the seamless tube coating type.

The crown amount applied to the charging member 2 depends on the length, hardness and pressing force of the charging member 2, but is generally about one thousandth of the length of the charging member 2. The crown amount here refers to the result of subtracting the diameter of the end from the diameter of the center. As an example, in the case of an A4 size page printer, the length of the charging member 2 is about 200 to 250 mm, so that the crown amount 13 required for the charging member 2 is several hundred μm.
It is generally about m.

The method of forming the charging member 2 of the seamless tube coating type into a crown shape is roughly divided into two methods.
The first is a method in which the elastic body 2b is formed in a straight shape, and the thickness of the seamless tube to be coated is thicker at the center than at the end in the longitudinal direction. The second is a method in which the elastic body 2b according to the present invention has a crown shape, and the seamless tube to be coated has a straight shape.

The seamless tube is generally manufactured by extrusion. Since extrusion molding is continuous molding, it is difficult to continuously and accurately change the wall thickness. Therefore, 1
Adjusting the wall thickness of the second tube is virtually impossible with extrusion. Further, the resistance of the seamless tube used for the resistance control layer 2c depends on the thickness. Therefore, if the thickness is adjusted by several hundred μm at the end and the center, the resistance at the end and the center is greatly increased. However, there is also a problem that is different.

On the other hand, in the second method, the elastic member 2b
Is formed into a crown shape, so that the seamless tube may be kept in a straight shape, and can be manufactured by extrusion molding. Examples of a method for forming the elastic body 2b into a crown shape include a method in which a mold is previously formed in a crown shape, a method in which a crown shape is formed by polishing, and the like. Here, if the crown amount given to the elastic body 2b is set to be larger than the crown amount desired as the charging member, the end portion and the center portion are compressed by the individual compression ratios by the seamless tube coating, and as a result, A desired crown shape as the charging member 2 is obtained.

Among the charging members 2 applicable to the present invention, as the elastic body 2b provided on the core metal 2a, a conductive elastic body in which conductive carbon is dispersed in silicone rubber or the like can be used. The conductive elastic body is a rubber and a thermoplastic elastomer such as isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, chloroprene rubber, butyl rubber, acrylic rubber, urethane rubber, fluorine rubber, ethylene propylene rubber and epichlorohydrin rubber, graphite, It may be prepared by adding an appropriate amount of a conductive substance such as metal fine powder and metal oxide.

The elastic body 2b can be formed by using an injection molding machine and vulcanizing simultaneously with molding in a crown-shaped mold. As another method, a foaming agent is added to form a sponge formed by foaming simultaneously with vulcanization in a vulcanization can, or a thermoplastic elastomer is extruded into a tube shape and pressed into a cored bar 2a to form a sponge. It may be formed into a crown shape by polishing.

On the elastic layer 2b made of the elastic body, a resistance control layer 2c made of a seamless tube and a surface layer 2d are provided as necessary. The seamless tube is roughly classified into a heat-shrinkable tube and a non-heat-shrinkable tube according to a coating method, and the present invention can be applied to any of them.

When a heat-shrinkable tube is used, a heat-shrinkable tube is formed with an inner diameter larger than the maximum outer diameter of the object to be coated, and the object to be coated is inserted inside the tube and heat is applied to shrink the tube. Integrate with the object to be coated.

When a non-heat-shrinkable tube is used, thermoplastic elastomer tubes such as thermoplastic styrene elastomers, thermoplastic urethane elastomers, thermoplastic olefin elastomers, thermoplastic amide elastomers and thermoplastic polyester elastomers, and polymer alloys thereof. Is used as a base resin, and additives such as a conductive agent are blended according to the purpose of use. The compound thus obtained is extruded by extrusion into a tube having an inner diameter smaller than the minimum outer diameter of the object to be coated to obtain a non-heat-shrinkable tube. When coating the tube with the object to be coated, air or the like is blown into the inside of the tube to expand the tube until the inner diameter becomes larger than the maximum outer diameter of the object to be coated. Is inserted to shut off the widening means such as air pressure, the elasticity of the tube attempts to return to the initial inner diameter, and the tube and the object to be coated come into close contact with each other to be integrated.

The charging member 2 obtained by covering the crown-shaped elastic body 2b with the straight seamless tube on the crown-shaped elastic body 2b thus obtained has the crown shape even after the tube is covered. Although it does not always coincide with the later crown amount and depends on the hardness of the tube to be coated and the coating method, since it is smaller than the crown amount given to the elastic body 2b, the charging member 2
It is necessary to apply a crown amount larger than the desired crown amount to the elastic body 2b in advance. [Embodiment] The effect will be described in detail with reference to the following embodiments. Although the embodiment has been described using a contact-type charging roller, the present invention is not limited to this embodiment. [Example 1] (Preparation of elastic body) A vulcanizing agent and a foaming agent were mixed with EPDM rubber in which conductive carbon was dispersed by two rolls, and formed into a tube by extrusion. When this tube-shaped molded product was foamed in a vulcanizing can, the length was 24
A sponge tube having a diameter of 0 mm, an inner diameter of 5 mm, and an outer diameter of 15 mm was obtained.

(Adhesion of Core Metal and Elastic Body) A core metal having a length of 240 mm and an outer diameter of 6 mm coated with an adhesive is inserted into the inside of the sponge tube, and the core metal and the elastic body are bonded in a heat oven. An elastic layer was formed.

(Adjustment of the length of the elastic layer)
The sponge elastic layer was adjusted to a length of 220 mm so that both ends of the core remained 10 mm each.

(Preparation of Crown of Elastic Layer) The elastic layer with the cored bar was finished by polishing to have an outer diameter at the end of 10.70 mm and an outer diameter at the center of 11.35 mm to prepare an elastic layer with a crown. The crown amount of the elastic layer is 650 μm.

(Preparation of Resistance Control Layer) A thermoplastic urethane elastomer in which conductive carbon was dispersed was extruded into a seamless tube having an inner diameter of 10.2 mm and a thickness of 400 μm to obtain a seamless tube to be a resistance control layer.

(Formation of Surface Layer) A thermoplastic styrene elastomer having conductive carbon dispersed therein was extruded into a seamless tube having an inner diameter of 10.5 mm and a thickness of 250 μm to obtain a seamless tube serving as a surface layer.

(Coating of Resistance Control Layer and Surface Layer) The inner diameter of the resistance control layer was widened with air, the elastic layer was inserted inside the layer, the air was shut off, and the elastic layer was coated with the resistance control layer. . Similarly, the surface layer was coated on the resistance control layer.

A charging member having a three-layer structure was prepared as described above, and its outer diameter was measured.
m and 11.95 mm at the center, and the crown amount was 200 μm.

The contact-type charging member is brought into contact with a photoreceptor,
A contact-type charging device was obtained in which a pressing force of 500 g was applied to both ends of the cored bar.

When this contact-type charging device was incorporated into an image forming apparatus and image evaluation was performed, the image was good over the entire charging area. Furthermore, when the image evaluation was continued,
Even when printing 10,000 sheets of A4 size, the image was very good without any deterioration.

Example 2 (Preparation of Elastic Body) Same as Example 1.

(Adhesion of core metal and elastic body) Same as in Example 1.

(Adjustment of Length of Elastic Layer) Same as in the first embodiment.

(Preparation of Crown of Elastic Layer) The elastic layer with the cored bar was polished to an outer diameter of 11.10 mm at the end and an outer diameter of 11.35 mm at the center to prepare an elastic layer with a crown. The crown amount of the elastic layer is 250 μm.

(Formation of Resistance Control Layer) Same as in the first embodiment.

(Formation of Surface Layer) Same as Example 1.

(Coating of Resistance Control Layer and Surface Layer) Same as in Example 1.

A charging member having a three-layer structure was prepared as described above, and its outer diameter was measured.
m, the central portion was 11.95 mm, and the crown amount was 100 μm.

The contact-type charging member is brought into contact with a photoreceptor,
A contact-type charging device was obtained in which a pressing force of 500 g was applied to both ends of the cored bar.

When this contact type charging device was incorporated into an image forming apparatus and the image was evaluated, the image was good over the entire length of the charged area. Furthermore, when the image evaluation was continued,
From the time when 8,000 sheets of A4 size passed, slight image defects due to defective charging occurred in a low temperature (15 ° C.) and low humidity (10% RH) environment. When the charging member was observed, the developer was deposited only at the center of the charging member. Although there is no problem in practical use, the reason is that the crown amount was slightly insufficient.

Comparative Example 1 (Preparation of Elastic Body) Same as in Example 1.

(Adhesion of core metal and elastic body) Same as in Example 1.

(Adjustment of Length of Elastic Layer) Same as in the first embodiment.

(Preparation of Elastic Layer Crown) The cored elastic layer was polished to an outer diameter of 11.25 mm at the end and an outer diameter of 11.35 mm at the center to prepare an elastic layer with a crown. The crown amount of the elastic layer is 100 μm.

(Formation of Resistance Control Layer) Same as in the first embodiment.

(Formation of Surface Layer) Same as Example 1.

(Coating of Resistance Control Layer and Surface Layer) Same as in Example 1.

A charging member having a three-layer structure was prepared as described above, and its outer diameter was measured.
m and 11.95 mm at the center, and the crown amount was 30 μm.

This contact type charging member is brought into contact with a photosensitive member,
A contact-type charging device was obtained in which a pressing force of 500 g was applied to both ends of the cored bar.

When this contact-type charging device was incorporated into an image forming apparatus and image evaluation was performed, the image was good over the entire charging area. When the image evaluation was further continued, A
After 2,000 sheets of 4 sizes had passed, slight image defects due to charging failure occurred in a low-temperature (15 ° C.) low-humidity (10% RH) environment. . Observation of the charging member revealed that the developer was heavily deposited at the center of the charging member. This is a level that cannot be put to practical use.

Comparative Example 2 (Preparation of Elastic Body) Same as in Example 1.

(Adhesion of core metal and elastic body) Same as in Example 1.

(Adjustment of Length of Elastic Layer) Same as in the first embodiment.

(Formation of Crown of Elastic Layer) The elastic layer with the cored bar was polished by polishing so that both the outer diameter at the end and the outer diameter at the center were both 1 mm.
Finished to 1.35 mm, a straight elastic layer without crown was created.

(Formation of Resistance Control Layer) Same as in the first embodiment.

(Formation of Surface Layer) Same as in Example 1.

(Coating of Resistance Control Layer and Surface Layer) Same as in Example 1.

A charging member having a three-layer structure was prepared as described above, and the outer diameter of the charging member was measured to be 11.95 mm at both the end and the center. The charging member also had a straight shape.

The contact-type charging member is brought into contact with the photosensitive member,
A contact-type charging device was obtained in which a pressing force of 500 g was applied to both ends of the cored bar.

When this contact-type charging device was incorporated into an image forming apparatus and image evaluation was performed, an image defect due to poor charging occurred even in a normal temperature and normal humidity environment from the initial stage. However, it was found that the central portion of the charging member was floating over about 30 mm, and was not charged normally.

From the above, it is clear that the crown amount as the charging member having the configuration shown in the embodiment is required to be 100 μm or more in the second embodiment, and preferably 200 μm in the first embodiment. Further, in the tube-coated type charging member, as shown in Comparative Example 1, even when the minimum necessary amount of 100 μm crown as the charging member is applied to the elastic layer, the crown is compressed to about 30 μm after the tube coating, It has been clarified that this causes image failure due to insufficient crown.

[0072]

As described above, a crown-shaped charging member in which one or more seamless tubes are coated on an elastic layer made of an elastic material, wherein the elastic material has a crown shape, The tube has a straight shape, and the crown amount of the elastic body to be applied in advance is set larger than the crown amount required as the charging member after the seamless tube is coated, so that the crown amount desired as the charging member is reduced. Thus, image defects due to uneven charging in the longitudinal direction of the charging member can be solved at low cost without increasing the cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a contact-type charging member of the present invention.

FIG. 2 is a sectional view showing an example of an elastic layer of the charging member according to the present invention.

FIG. 3 is a schematic configuration diagram showing an example of an image forming apparatus using a contact-type charging device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 charged body (image carrier) 1 a conductive support 1 b photosensitive layer 2 charging member 2 a rigid body (core metal) 2 b elastic body (elastic layer) 2 c resistance control layer 2 d coating layer 3 power supply 4 exposure step 5 development step 6 transfer Step 7 Printed material 8 Cleaning step 11 Central outside diameter of charging member 12 End outside diameter of charging member 21 Center outside diameter of elastic body 22 End outside diameter of elastic body

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroyoshi Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Naoki Fuui 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroyuki Nagata 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (3)

[Claims] 1. A crown-shaped charging member in which one or more seamless tubes are coated on a layer made of an elastic body, wherein the elastic body has a crown shape and the seamless tube has a straight shape. A charging member, wherein a crown amount of the elastic body to be applied in advance is larger than a crown amount necessary for the charging member after the seamless tube is covered. 2. The charging member according to claim 1, wherein the seamless tube is a thermoplastic elastomer tube. 3. A charging device for charging a member to be charged by applying a voltage to the charging member, wherein the charging member is the charging member according to claim 1 or 2.