JPH09146340A - Electrostatic charging member and electrostatic charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the compatibility of the uniformity of the resistance of an electrostatic charging member and the uniformity of a physical contact state with a member to be electrostatically charged and to improve performance, such as environment dependence and durability, by successively forming a conductive layer and a urethane modified acrylic resin layer on the surface of an elastic layer. SOLUTION: This electrostatic charging member has a structure provided with the conductive layer consisting of an aq. resin on the surface of the elastic layer consisting of a foam and is further provided with the urethane modified acrylic resin layer thereon. The foam is used as the elastic layer, for which a polyurethane foam is more particularly adequate. Carbon, metal oxide, etc., are added to the foam in order to impart electrical conductivity thereto. The compsn. of the acrylic resin component in the urethane modified acrylic resin is preferably 5 to 80wt.% and more particularly preferably 10 to 60wt.%. The surface roughness of the electrostatic charging member is preferably <=4μm in 10-point average roughness Rz scale stipulated in JIS(Japanese Industrial Standards). As a result, the excellent environment dependence is obtd. and the surface smoothness and durability are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member used for charging an object to be charged such as a photoreceptor used in an electrostatic latent image process in a copying machine, a printer and the like, and a charging device using the same. Things.

[0002]

2. Description of the Related Art Conventionally, in electrophotographic processes such as copying machines and printers, first, the surface of a photoconductor is uniformly charged,
A latent image is formed by projecting an image from the optical system onto the photoconductor to erase the electrification of a portion exposed to light, and then a toner image is formed by adhesion of toner, and a latent image is formed on a recording medium such as paper. Printing is performed by transferring a toner image. In this case, a corona discharge method has generally been used for the first operation of charging the photoconductor. However, this corona discharge method requires application of a high voltage of 6 to 10 kV, which is not preferable from the viewpoint of safe maintenance of the machine. Further, there are environmental problems because harmful substances such as ozone are generated during corona discharge.

[0003] For this reason, efforts have been made for a charging method that can perform charging at a lower applied voltage than corona discharge and that can suppress generation of harmful substances such as ozone. As a trial of such a charging method, a method by a contact method has been proposed in which a charging member to which a voltage is applied is brought into contact with an object to be charged such as a photoconductor to charge the object.

As a charging member used in this contact charging system, for example, one in which the surface of an elastic layer is coated with a resin layer is known, and in order to reduce the hardness and to secure a sufficient nip width with the member to be charged. , The elastic layer of the charging member has a foam,
A resin such as urethane or nylon is used for the resin layer. However, although these resins are almost satisfactory in terms of barrier properties and softness, they all have a large effect of moisture, and there is a problem that resistance increases in a low humidity environment and image defects easily occur. Since these resins are organic solvent-soluble type resins, when an organic solvent-soluble type resin is formed on the surface of the elastic layer made of foam by a dipping method, a spray method or the like, the surface is smoothed. There is a problem that it is not possible to obtain sex. This is because the organic solvent swells the foam to form surface irregularities, or the organic solvent that has penetrated into the foam pierces the coating film during drying and forms crater holes on the coating film surface. Of course, in order to prevent this, if the elastic layer is not made of foam, a slight improvement can be seen, but in this case, the hardness of the charging member increases and a sufficient nip width with the charged member can be obtained. The desired physical contact state cannot be maintained.

On the other hand, the present inventors have already proposed a urethane-modified acrylic resin. This resin has barrier properties,
It has certain performance in terms of softness and environmental dependence,
Since it is an organic solvent-soluble resin, it was also difficult to obtain the surface smoothness of the charging member.

Further, it is necessary to further improve the performance of environmental dependence and durability, and in order to improve the environmental dependence, it is necessary to select a material that is not easily affected by moisture as a coating material. . On the other hand, in order to prevent migration / contamination to the member to be charged, it is also required that the material has a barrier property containing no migration / contaminants. Further, it is required that the material has appropriate softness. In order to improve the durability performance, it is necessary to continue to uniformly supply the charge from the charging member to the charged member. In order to do this satisfactorily, it is necessary to make the resistance of the charging member uniform and further make the physical contact state between the charging member and the member to be charged even more uniform.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in the formation of a latent image in a copying machine, a printer, etc., the uniformity of the resistance of the charging member and the physical contact with the member to be charged are It is an object of the present invention to provide a charging member that achieves both uniformity of contact state and improved performance such as environmental dependency and durability, and a charging device using the charging member.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a charging member for charging a charged body by bringing it into contact with the charged body and applying a voltage between the charged body and the charged body. It is characterized in that a conductive layer made of a water-based resin and a urethane-modified acrylic resin layer are sequentially formed on the surface of the elastic layer.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION That is, although the present invention is a charging member composed of an elastic layer made of foam and a urethane-modified acrylic resin layer, the charging member is excellent in environmental dependency as compared with conventional charging members. As described above, the surface unevenness that seems to be caused by the organic solvent is generated, and it is difficult to obtain the surface smoothness, and attention is paid to the durability, and the surface of the elastic layer made of the foam of the present invention is coated with an aqueous resin. It has been found that when a charging member in which a conductive layer and a urethane-modified acrylic resin layer are sequentially formed is excellent in environmental dependence, surface smoothness is improved, and durability is improved, the present invention is completed. is there.

Hereinafter, the present invention will be described in more detail. Since the charging member of the present invention is of the contact charging type, it is not particularly limited to the shape as long as it contacts the member to be charged. For example, various shapes such as roll shape, plate shape and block shape The thing of what is applicable is a roll shape normally. In the case of a roll, a shaft made of metal or plastic may be provided inside these.

The structure of the charging member provided by the present invention has a structure in which a conductive layer made of an aqueous resin is provided on the surface of an elastic layer made of foam, and a urethane-modified acrylic resin layer is further provided thereon. Foam is used as the elastic layer, and the material is not particularly limited, but polyurethane foam is particularly preferable. Carbon, metal oxides, etc. are added to the foam in order to impart conductivity.
Further, the foam density is 0.05 to 0.9 g / cm ³ ,
Preferably 0.3 to 0.7 g / cm ³ is suitable.
Further, the layer thickness is suitably 0.5 to 10 mm.

The conductive layer is composed of a conductive material and an aqueous resin. The thickness of this layer is 1 to 500 μm, preferably 1 to 200 μm, and more preferably 1 to 100 μm.
Is preferably used. The volume resistivity of this conductive layer is 10 ² to 10 ¹¹ Ωcm, preferably 10 ⁵ to 10 ⁹
It is suitable to adjust to about Ωcm. Here, the water-based resin may be any type as long as it uses water as a solvent, and includes water-soluble type, emulsion type, suspension type, etc., for example, polyester type, acrylic type, urethane type, hot water soluble type, etc. Among them, polyester type and acrylic type are preferable.
Further, if possible, a resin that is difficult to be redissolved in water after drying is preferable.

The conductive substance may be any substance as long as it can impart conductivity. Examples thereof include carbon, graphite, metal oxides, ionic substances, and conductive polymers. Among them, carbon is preferable. In particular, the oxygen content is 6% or more, preferably pH
Carbon with a value of 5 or more is optimal, for example SMP-4
(Orient Chemistry). Furthermore, a thickener, a thixotropy imparting agent, a structural viscosity imparting agent and the like can be added at any time, and either an inorganic type or an organic type may be used. Aqueous resins are often low in viscosity, so it is difficult to increase the thickness of the coating film, but these thickeners, thixotropic agents,
By adding a structural viscosity imparting agent or the like, a coating film having a desired thickness can be easily formed.

The urethane-modified acrylic resin layer is formed on the surface of the conductive layer made of the above-mentioned water-based resin. Here, the urethane-modified acrylic resin is more effective to chemically bond the urethane resin and the acrylic resin component from the viewpoints of compatibility, liquid stability, film flexibility, and the like. As a specific method, β-hydroxyethyl methacrylate or the like is used to react a polymer in which a hydroxyl group is introduced into an acrylic polymer with a urethane prepolymer having an isocyanate group at the molecular end, or at the molecular end as described below (one end or It is synthesized by reacting an acrylic component having hydroxyl groups at both ends) with a urethane prepolymer (A:
Acrylic acid, acrylic acid ester monomer or oligomer). In the polymer thus obtained, the urethane chain and the acrylic chain may be bonded to each other in a block type or a graft type.

Embedded image

Further, the urethane-modified acrylic resin is not limited to the above-mentioned method, and other methods such as a method of adding diisocyanate to an acrylic diol mixed system, an isocyanate monomer having both ends isocyanate polyester,
It can also be obtained by a method of adding a polyether or the like and polymerizing the urethane acrylate. The acrylic resin component used in the synthesis of these has a glass transition temperature Tg as a polymer from room temperature to about 80 ° C.
Those up to the above are preferable, and those containing, for example, ethyl methacrylate, isobutyl methacrylate, glycidyl methacrylate and the like in addition to the above β-hydroxyethyl methacrylate are used. At this time, the composition of the acrylic resin component in the urethane-modified acrylic resin is 5
-80% by weight, particularly 10-60% by weight, and more preferably 20-50% by weight.

Further, from the viewpoint of improving the adhesion to the photoreceptor,
A silicone component may be contained in the urethane-modified acrylic resin. Specifically, for example, a method of synthesizing by reacting a urethane prepolymer using a polyol containing a silicone chain as a raw material with an acrylic component can be considered. In this case, the composition of the silicone component in the urethane prepolymer is 2 to 80% by weight, especially 5 to 50%.
% By weight. The composition of the silicone component in the urethane-modified acrylic resin after the reaction is preferably 1 to 50% by weight, particularly 3 to 30% by weight.

The urethane-modified acrylic resin may be contained alone or in combination of two or more kinds, and other resins may be mixed and used. In this case, examples of the resin other than the urethane-modified acrylic resin include polyester, phenol resin, polyamide, epoxy resin, urea resin, urethane resin and the like.

Further, in the urethane-modified acrylic resin layer whose overall resistance is adjusted with carbon black or the like, in order to partially leak pinholes and improve the adhesion with the photosensitive drum,
So-called silica (white carbon) may be added. Silica is a fine particle silicic acid and a silicate, and usually has a reinforcing property second only to carbon black and improves the strength and elongation of rubber, hardness, abrasion resistance, etc., and is used for transparent or clear products. These are generally ultra-fine, bulky white powders of 10 to 50 μm, and have different manufacturing methods and properties from those of naturally occurring pulverized silicic acid and silicates. When silica is classified according to the manufacturing method, anhydrous silicic acid (such as Aerosil manufactured by Degussa) by a dry method, hydrous silicic acid (burcasil manufactured by Bayer, etc.) by a wet method, synthetic silicate (magnesium silicate, etc.) and the like can be mentioned.

Further, the urethane-modified acrylic resin layer may be crosslinked with a curing agent in order to increase the strength of the coating film. The crosslinking can be carried out by incorporating a hydroxyl group and a reactive group such as an isocyanate group in the main agent and the curing agent. As the curing agent, for example, difunctional diisocyanates or polyisocyanates having more than two functional groups are used, and a group imparting flexibility to the curing agent is introduced to easily increase the strength and elongation, It is possible to improve the durability of the coating film. In addition, the curing agent may contain a silicone component in order to further improve the adhesion.

The urethane-modified acrylic resin of the present invention may be formed by laminating or mixing urethane-modified acrylic resins having different ratios of urethane resin and acrylic resin. Further, the conductive substance may be any substance as long as it can impart conductivity. For example,
Carbon, graphite, metal oxides, ionic substances,
Examples of the conductive polymer include carbon, with carbon being preferred. Further, another coating layer may be provided on the urethane-modified acrylic resin layer.
The layer forming method may be a dipping method or a spraying method in which the elastic layer is dipped to form a coating film in a coating state containing the above.

The surface roughness of the charging member prepared as described above is appropriately adjusted to 4 μm or less, preferably 3 μm or less, more preferably 2 μm or less on the JIS 10-point average roughness Rz scale. is there.

[0022]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following. "Example 1" On a conductive polyurethane foam roller, Conductive layer A having a thickness of 30 μm and further having a thickness of 1
A urethane modified acrylic resin layer B having a thickness of 00 μm was formed.
The conductive layer A uses a paint A1 in which SMP-4 is mixed with a water-dispersible polyester resin as carbon, and the urethane-modified acrylic resin layer B uses carbon as a urethane-modified acrylic resin (urethane resin / acrylic resin = 5/5). The mixed paint B1 was used and applied by the dip method. The volume resistivity of the conductive layer A was adjusted to about 10 ⁷ Ωcm, and the volume resistivity of the urethane-modified acrylic resin layer B was adjusted to about 10 ⁸ Ωcm. In addition, SMP-4 has an oxygen content of 10%, p
H is carbon of 7.33. The roller surface roughness is J
IS 10-point average roughness Rz scale is 1.6 μm,
The micro hardness was 62 degrees. When the resistance of this roller was measured, it was 2.5 at a temperature of 15 ° C and a humidity of 10% RH.
× 10 ⁶ Ω, temperature 35 ° C / humidity 1.0% under 85% RH
It was 10 ⁶ Ω. Attach this roller to the printer,
Even if 6000 consecutive images are output, the image deterioration is
Almost never.

[Example 2] A conductive layer A having a thickness of 30 µm was formed on a conductive polyurethane foam roller, and a urethane-modified acrylic resin layer C having a thickness of 110 µm was further formed thereon. The conductive layer A uses a paint A1 in which SMP-4 is mixed with a water-dispersible polyester resin as carbon, and the urethane-modified acrylic resin layer C uses carbon as a urethane-modified acrylic resin (urethane resin / acrylic resin = 6 /
The coating material C1 mixed in 4) and the coating material C2 in which carbon was mixed with a urethane-modified acrylic resin (urethane resin / acrylic resin = 4/6) were applied by the dipping method. Here, the urethane-modified acrylic resin layer C was formed by continuous dipping using two kinds of paints having different ratios of urethane resin and acrylic resin. The volume resistivity of the conductive layer A is about 10 ⁷ Ωcm, and the urethane-modified acrylic resin layer C is
The volume resistivity was adjusted to about 10 ⁸ Ωcm. Note that S
MP-4 is carbon with an oxygen content of 10% and a pH of 7.33. The roughness of the roller surface is 1.9 μm on the JIS 10-point average roughness Rz scale, and the micro hardness is 67.
Degree. The resistance of this roller was measured and found to be 3.5 × 10 ⁶ Ω at a temperature of 15 ° C. and a humidity of 10% RH and a temperature of 3
It was 1.5 × 10 ⁶ Ω at 5 ° C./85% RH.
Even when this roller was mounted on a printer and images were continuously printed on 6000 sheets, there was almost no deterioration in the images.

Comparative Example 1 A 100 μm thick urethane-modified acrylic resin layer B was formed on a conductive polyurethane foam roller. Urethane modified acrylic resin layer B
Was applied by a dipping method using a coating material B1 in which carbon was mixed with urethane-modified acrylic resin (urethane resin / acrylic resin = 5/5). The volume resistivity of the urethane-modified acrylic resin layer B was adjusted to about 10 ⁸ Ωcm. The roughness of the roller surface was severely varied between 5 and 60 μm on the JIS 10-point average roughness Rz scale, and the micro hardness was 70 degrees. The resistance of this roller was measured and found to be 2.2 × 10 ⁶ at a temperature of 15 ° C. and a humidity of 10% RH.
Ω, temperature 35 ° C / humidity 85%, 1.0 × 10 ⁶ Ω under RH
Met. This roller is installed in the printer and continuous 60
When 00 images were printed, the image had some black spots that seemed to be due to the unevenness of the surface from the beginning, and the image became even worse as the number of images increased.

Comparative Example 2 A conductive polyurethane foam roller was provided with a conductive layer A having a thickness of 30 μm, a coating layer D having a thickness of 100 μm, and a thickness of 1 on the coating layer D.
A coating layer E having a thickness of 0 μm was formed. Coating layer A is SMP-4
Is used as a coating material A1 in which a carbon is mixed with a water-dispersible polyester resin, coating layer D is a coating material D1 in which carbon is mixed with a urethane resin, and coating layer E is made of conductive titanium oxide in an alcohol-soluble nylon resin. Mixed paint E
1 was applied by the dip method. The volume resistivity of the conductive layer A was adjusted to about 10 ⁷ Ωcm, and the volume resistivity of the coating layers D and E was adjusted to about 10 ⁸ Ωcm. In addition, SMP-
No. 4 is carbon having an oxygen content of 10% and a pH of 7.33. The roughness of the roller surface is JIS 10 point average roughness Rz.
The scale was 2.3 μm, and the micro hardness was 66 degrees. When the resistance of this roller was measured, the temperature was 15
8.5 × 10 ⁶ Ω at a temperature of 10% RH and a temperature of 35 ° C
/1.0% 10 ⁶ Ω under a humidity of 85% RH. Even when this roller was mounted on a printer and images were continuously printed on 6000 sheets, there was almost no deterioration in the images.

COMPARATIVE EXAMPLE 3 A conductive layer A having a thickness of 30 μm was formed on a conductive polyurethane foam roller, and a coating layer F having a thickness of 100 μm was further formed thereon. Conductive layer A
Is a paint A1 in which SMP-4 is mixed with a water-dispersible polyester resin as carbon, and the coating layer F is a mixture of carbon with a urethane-modified acrylic resin (urethane resin / acrylic resin = 9.6 / 0.4). The coating material F1 prepared above was applied by the dip method. The volume resistivity of the conductive layer A is about 10 ⁷ Ωcm, and the volume resistivity of the coating layer F is 10 ⁸ Ωcm.
It was adjusted to about cm. SMP-4 is carbon having an oxygen content of 10% and a pH of 7.33. The roughness of the roller surface is 1.6μ on the JIS 10-point average roughness Rz scale.
m, and the micro hardness was 53 degrees. When this roller was attached to the printer, it caused severe contact with the photoconductor.

Comparative Example 4 A conductive layer A having a thickness of 30 μm and a coating layer G having a thickness of 100 μm were formed on a conductive polyurethane foam roller. Conductive layer A
Is a coating material A1 in which SMP-4 is mixed with a water-dispersible polyester resin as carbon, and the coating layer G is a coating material G1 in which carbon is mixed with a urethane-modified acrylic resin (urethane resin / acrylic resin = 1/9). Each of them was applied by the dip method. The volume resistivity of the conductive layer A is 10 ⁷ Ω
cm, and the volume resistivity of the coating layer F was adjusted to about 10 ⁸ Ωcm. In addition, SMP-4 has an oxygen content of 10%,
Carbon with a pH of 7.33. The roller had cracks on its surface during handling.

[0028]

As described above, according to the charging member of the present invention, in forming a latent image in a copying machine, a printer or the like,
To provide a charging member that has both resistance uniformity of a charging member and physical contact state with a member to be charged, and has improved performance such as environmental dependency and durability, and a charging device using the same. Is possible.

Claims (5)

[Claims] 1. A charging member for charging a charged body by bringing it into contact with the charged body and applying a voltage between the charged body and the charged body, wherein an aqueous resin is formed on the surface of an elastic layer made of foam. 1. A charging member comprising a conductive layer made of and a urethane-modified acrylic resin layer sequentially formed. 2. The charging member according to claim 1, wherein the acrylic resin component of the urethane-modified acrylic resin layer is 5 to 80% by weight. 3. The charging member according to claim 1, wherein the main material of the elastic layer is polyurethane. 4. The charging member according to claim 1, wherein the surface of the charging member has a JIS 10-point average roughness Rz scale of 4 μm or less. 5. A charging device comprising: a charging member that is in contact with an object to be charged and charges the object to be charged; and a voltage applying unit that applies a voltage between the object to be charged and the charging member. A charging device comprising the charging member according to any one of claims 1 to 4 as a charging member.