JP4286343B2 - Charging member and charging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charging member and a charging device that are preferably used when a charged object such as a photoconductor is charged in an electrostatic latent image process in a copying machine, a printer, or the like.
[0002]
[Prior art]
In an electrophotographic apparatus such as a copying machine or a printer, first, the surface of the photoconductor is uniformly charged, and an image is projected onto the photoconductor from the optical system to erase the charged portion of the light. An electrostatic latent image is obtained by an electrostatic latent image process for forming a latent image, and then printing is performed by forming a toner image by adhesion of toner and transferring the toner image to a recording medium such as paper. .
In this case, conventionally, a corona discharge method has been generally employed for the operation of charging the photoreceptor. However, the corona discharge method requires application of a high voltage of 6 to 10 kV, which is not preferable from the viewpoint of safety maintenance of the machine. In addition, since harmful substances such as ozone and NOx are generated during corona discharge, there is also an environmental problem.
[0003]
For this reason, efforts have been made to charge systems that can be charged at a lower applied voltage than corona discharge and that can suppress the generation of harmful substances such as ozone. There has been proposed a contact-type method in which a charging member to which a voltage is applied is brought into contact with a member to be charged such as a photosensitive member at a predetermined pressure to charge the member to be charged.
As a charging member used in this contact charging method, for example, a resin solution obtained by dissolving a resin such as acrylic, urethane or nylon in an organic solvent on the surface of an elastic layer made of rubber, urethane foam or the like is a dipping method or the like. It is known to apply a spray method or the like to form a coating film layer of these resins to ensure surface smoothness and prevent toner adhesion.・
[0004]
[Problems to be solved by the invention]
However, when a resin solution in which the resin is dissolved in an organic solvent is applied to form the coating layer, an elastic body such as rubber or urethane foam that forms the elastic layer is swollen by the organic solvent, causing irregularities on the surface, It becomes difficult to ensure the smoothness of the surface. As a means for preventing this, there is a method of forming a coating film layer using a water-based paint, but in this method, the coating film layer becomes hydrophilic and easily wetted with water. Below, the coating layer swells or partially dissolves due to moisture, and the surface becomes non-uniform, resulting in a problem of image defects.
The present invention has been made in view of the above circumstances. That is, the present invention is a charging member that is excellent in surface smoothness even when used in an electrostatic latent image process in a copying machine, a printer, etc., and does not cause image defects even under high temperature and high humidity, and a charging device using the charging member The purpose is to provide.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the elastic layer swells due to the charging member in which a coating layer having a specific property using a water-based resin is formed outside the elastic layer. The present invention was completed by discovering that the surface smoothness was excellent, the water resistance of the coating film was improved, the coating film did not dissolve even under high temperature and high humidity, and a charging member that did not cause image defects was obtained. Is.
[0006]
That is, according to the present invention, in a charging member that charges a charged body by contacting the charged body and applying a voltage between the charged body, an elastic layer and an outer side of the elastic layer. And a coating member formed directly or via another layer, the coating layer being formed of a water-based resin, and a contact angle with water exceeding 100 °, and a coated member A charging device comprising: a charging member that contacts a charging body and charges the object to be charged; and a voltage applying unit that applies a voltage between the charging object and the charging member. The present invention relates to a charging device using the charging member.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
As described above, the charging member of the present invention has an elastic layer and a coating layer formed outside the elastic layer. As the form, any form can be used as long as it can stably come into contact with the member to be charged and can uniformly charge the layer to be charged by applying a voltage. Shape, plate shape, block shape, spherical shape, brush shape, and the like, but in general, a roll shape is preferable. In the case of forming in a roll shape, for example, as shown in FIG. 1, the charging member 1 in which the elastic layer 3 is formed on the outer periphery of the shaft 2 and the coating layer 4 is formed outside the elastic layer 3 is exemplified. be able to. In this case, the shaft 2 can be a metal or plastic shaft, and the shaft 2 can be omitted depending on the form of the charging member and the mechanism of the charging device using the charging member.
[0008]
The elastic layer 3 is not particularly limited, and can be formed of rubber or resin, or a foam thereof (hereinafter referred to as “foam”). Specifically, polyurethane, silicone rubber, butadiene rubber, Examples of rubber compositions using isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, epichlorohydrin rubber, etc. as the base rubber, Polyurethane is particularly preferable, and a polyurethane foam having an expansion ratio of 1.5 to 50 times is more preferable. In this case, the foam density is suitably about 0.05 to 0.9 g / cm ³ .
A predetermined resistance value can be imparted to the elastic layer 3 by adding a conductive agent.
[0009]
The conductive agent is not particularly limited. For example, lauryltrimethylammonium, stearyltrimethylammonium, octadodecyltrimethylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, modified fatty acid / dimethylethylammonium perchlorate, chloric acid Cationic surfactants such as quaternary ammonium salts such as salts, borohydrofluoric acid salts, sulfate salts, etosulphate salts, benzyl bromide salts, benzyl chloride salts, and the like, aliphatic sulfonates Anionic surfactants such as higher alcohol sulfate, higher alcohol ethylene oxide addition sulfate, higher alcohol phosphate, higher alcohol ethylene oxide addition phosphate, and amphoteric ions such as various betaines Surfactants, higher alcohol ethylene oxide, polyethylene glycol fatty acid esters, polyhydric alcohol fatty acid ester of a non-ionic antistatic agents antistatic agents such _{as, LiCF 3 SO 3, NaClO 4} , LiAsF 6, LiBF 4, NaSCN, KSCN Li ⁺ such as NaCl, Na ⁺ , metal salts of Group 1 of the periodic table such as K ⁺ , electrolytes such as NH ₄ ⁺ salts, and Ca ²⁺ and Ba ²⁺ such as Ca (ClO ₄ ) ₂ A metal salt of Group 2 of the periodic table, and the like, and those having a group having an active hydrogen that reacts with an isocyanate such as at least one hydroxyl group, carboxyl group, primary or secondary amine group, 4-butanediol, ethylene glycol, polyethylene glycol, propylene glycol, polyethylene glycol and other polyhydric alcohols Complexes such as derivatives, or ion conductive agents such as complexes with monools such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, or conductive carbon such as ketjen black EC and acetylene black, SAF, ISAF, HAF, FEF, Carbon for rubber such as GPF, SRF, FT, MT, carbon for color (ink) subjected to oxidation treatment, pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, Examples thereof include metals such as copper, silver, and germanium and metal oxides, and conductive polymers such as polyaniline, polypyrrole, and polyacetylene.
[0010]
The blending amount of the conductive agent is appropriately selected according to the type of the composition. Usually, the volume resistivity of the elastic layer 3 is 1 × 10 ⁰ to 1 × 10 ⁸ Ω · cm, preferably 1 × 10 ^2. It is adjusted to be ˜1 × 10 ⁶ Ω · cm.
In the present invention, the coating layer 4 formed on the outside of the elastic layer 3 is formed of a water-based resin and is formed of a coating film having a contact angle with water exceeding 100 ° or more.
[0011]
Here, the water-based resin is not limited as long as the solvent is water, and can be used in any form such as a water-soluble type, an emulsion type, and a suspension type. However, the molecular weight of the resin can be increased without increasing the viscosity of the paint. The emulsion type is preferably used in that the strength of the formed coating film is excellent.
As a method of emulsifying the resin, a method of emulsifying by adding a surfactant (forced emulsification type) and a method of emulsifying by introducing a hydrophilic functional group such as a carboxyl group or a hydroxyl group into the resin (self-emulsification) However, if the surfactant is present in the coating layer, there are problems such as a decrease in contact angle and contamination of the photoreceptor. Used.
[0012]
As the water-based resin for forming the coating layer 4, a water-based fluororesin is preferably used from the viewpoints of water repellency and low friction. Examples of water-based fluororesins include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, fluoroethylene-vinyl ether copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polychlorotrifluoroethylene, polyfluorinated ethylene Examples include vinylidene, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, etc., but fluoroethylene-vinyl ether copolymer due to film-forming properties at low temperatures and affinity with pigments. The emulsion is preferably used.
[0013]
Further, in the present invention, a dispersion type water-based fluororesin in which fluororesin fine particles are dispersed in water can be used in order to ensure the smoothness of the coating film and decrease the toner adhesion, and in particular, tetrafluoroethylene A dispersion type water-based fluororesin in which fine particles are dispersed in water is preferably used. The particle diameter of the fluororesin fine particles used is not particularly limited, but is preferably 5 μm or less, and particularly preferably 0.05 to 1 μm from the viewpoint of smoothness.
[0014]
The total amount of the water-based fluororesin and fluororesin fine particles contained in the coating layer 4 is preferably 50% by weight or more, particularly 60% by weight or more in the total resin, and if it is less than this, the contact angle is It becomes less than 100 °, and the purpose of the present invention, that is, the water resistance of the coating film is improved, and a coating film that is difficult to dissolve even under high temperature and high humidity can be obtained and image defects can be prevented. End up.
Furthermore, it is preferable to add another aqueous resin to the coating layer 4 in order to improve the film formability of the coating and prevent cracks and cracks from occurring during drying. Preferred examples of the water-based resin include polyvinyl acetal resin, vinylidene chloride resin, urethane resin, acrylic resin, polyester resin, and the like, and one or more of these resins can be used in combination.
[0015]
According to the present invention, a coating film having excellent water repellency and water resistance can be formed. However, in order to further improve water resistance and mechanical properties, the coating layer 4 is crosslinked with the aqueous resin. Therefore, a crosslinking agent can be added. In this case, the cross-linking agent is appropriately selected according to the type of resin used and the like, and any may be used as long as a desired cross-linking effect can be obtained. Usually, an oxazoline-based, epoxy-based, Melamine-based, guanamine-based, isocyanate-based and phenol-based crosslinking agents are preferably used. The addition amount of the crosslinking agent is usually in the range of 0.1 to 50 parts by weight with respect to 100 parts by weight of the resin. There is nothing to do.
[0016]
The coating layer 4 can be imparted or adjusted by adding a conductive agent, and usually has a volume resistivity of 1 × 10 ³ to 1 × 10 ¹² Ω · cm, particularly 1 × 10. It is preferable to adjust to ⁵ to 1 × 10 ¹⁰ Ω · cm. In this case, as the conductive agent, the same conductive agent as exemplified in the elastic layer 3 can be exemplified, but carbon is particularly preferably used. The addition amount of the conductive agent is appropriately selected according to the kind of the conductive agent and the like so as to have the above volume resistivity, and is not particularly limited. However, when carbon is used as the conductive agent, it is usually 0.01. -40% by weight, especially 5-20% by weight.
[0017]
The carbon used as the conductive agent in the coating layer 4 is not particularly limited, but the oxygen content is preferably 5% or more, more preferably 7% or more, and the pH is 5 or more. Further, it is preferably 6 or more, particularly 7 or more. That is, the oxygen content of normal carbon is about 0.1 to 3%, and some of the carbon has undergone oxidation treatment, but the carbon that has undergone this oxidation treatment has increased as the oxygen content increases. There is a tendency that the pH shifts to the acidic side. When carbon becomes acidic as described above, when it is added to an aqueous resin (specifically, an aqueous fluororesin), the stability may be lowered.
[0018]
On the other hand, the carbon having the above oxygen content and pH that is preferably used in the present invention maintains neutrality or alkalinity despite the high oxygen content, and is a stable water-based fluororesin. Can be added. Although the detailed structure of carbon having such an oxygen content and pH is not clear, in the present invention, a functional group such as a carboxyl group, a hydroxyl group, or a ketone group is attached to the carbon surface, and the hydrogen contained in these functional groups. Those obtained by substituting a part of them with an alkali metal such as sodium are preferably used.
[0019]
The coating layer 4 may be any coating film that contains the water-based resin and has a contact angle with water exceeding 100 °, and other than the water-based resin, as long as it does not depart from the object of the present invention. These resins can also be contained. Moreover, the coating-film layer 4 can also be comprised from multiple layers as needed.
Further, the coating layer 4 is appropriately added with a film-forming aid, a pigment dispersant, a thickener, a leveling agent, a thixotropic property-imparting agent, a structural viscosity-imparting agent, and the like without departing from the object of the present invention. An appropriate amount of an agent can be added as necessary.
[0020]
The coating layer 4 is an outermost layer of the charging member of the present invention, that is, a layer that forms the surface of the charging member, and the surface roughness of the coating layer 4 is the surface roughness of the member. In the present invention, the surface roughness of the coating layer 4, that is, the surface roughness of the member is 4 μm or less, further 3 μm or less, particularly 2 μm or less in terms of JIS 10-point average roughness Rz from the viewpoint of preventing image defects and the like. It is preferable that Such surface roughness can be easily achieved by forming the coating layer 4 using the water-based resin as described above.
[0021]
In addition, about the thickness of the coating film layer 4, although it does not restrict | limit in particular, It is preferable to set it as 30 micrometers or less, especially 1-15 micrometers. If the thickness of the coating film layer 4 exceeds 30 μm, the film may become too hard and the flexibility of the coating film layer 4 may be impaired.
The method for forming the coating film layer 4 is not particularly limited, but a method of preparing a coating material containing each of the above components constituting the coating film layer 4 and applying the coating material by dipping or spraying is preferable. Used.
[0022]
For example, as described above, the charging member of the present invention forms the coating layer 4 on the outer side of the elastic layer 3 as the outermost layer, but between the elastic layer 3 and the coating layer 4 as necessary. In addition, another coating layer can be formed as an intermediate layer. For example, when the elastic layer 3 is formed using polyurethane foam, in order to reduce noise during voltage application and improve the surface smoothness of the elastic layer 3, acrylic resin, polyester resin, polyurethane resin, A coating film obtained by adding a conductive agent to a base resin such as nylon resin, epoxy resin, urethane-modified acrylic resin, butyral resin, phenol resin, vinylidene chloride copolymer, or polyvinyl acetal resin can be provided as an intermediate layer. In addition, although resin which forms the coating film provided as this intermediate | middle layer is not specifically limited, In this invention, it is preferable to use water-based resin.
[0023]
As described above, the charging member of the present invention uses a water-based resin for the coating layer 4 to form a coating layer on the elastic layer 3 or the intermediate layer by a dip method or a spray method. A smooth member surface is obtained without swelling of the elastic layer 3 and the intermediate layer, thereby effectively preventing the residual toner from adhering. Furthermore, by adjusting the contact angle of the coating film layer 4 with water to be 100 ° or more, the water resistance of the coating film is improved, and a coating film that is difficult to dissolve even under high temperature and high humidity is obtained, resulting in poor image quality. Can be prevented. When only the organic solvent-based resin is used as the coating layer 4, first, good surface smoothness cannot be obtained, and residual toner adheres from the beginning of use. If the contact angle with water is less than 100 °, it is easy to get wet with water and image defects will occur under high temperature and high humidity.
[0024]
In the present invention, as shown in FIG. 2, the contact angle is an angle θ formed between the surface of the solid S and the liquid surface when a liquid L such as water is dropped on the surface of the solid S to be measured. Good, a large θ means that it is difficult to get wet with water. The contact angle θ can be measured by using a goniometer or other angle measuring device. In the present invention, the contact angle when water is dropped on the charging roller is measured using an image processing contact angle meter (for example, Kyowa). Measured using Interface Science Co., Ltd. (CA-X type), and the obtained value is used.
[0025]
The charging member of the present invention is disposed in contact with a member to be charged such as a photosensitive drum, and charges the member to be charged by applying a voltage between the member and the member to be charged. In this case, however, the voltage applied between the charging member and the member to be charged may be a DC voltage or an AC voltage, and is not particularly limited, but the AC voltage is superimposed on the DC voltage. It is preferable to perform charging by applying a voltage to the object to be charged, whereby the object to be charged can be more uniformly charged. Further, the contact pressure between the charging member of the present invention and the member to be charged is not particularly limited, but is preferably 50 to 2000 g, particularly preferably 100 to 1000 g, and this ensures reliable charging. it can.
[0026]
As for a charging device using the charging member of the present invention, for example, as shown in FIG. 3, the charging member 1 of the present invention is brought into contact with a member to be charged 5 such as a photosensitive drum with a predetermined pressure, and voltage applying means 6 is applied. A charging device configured to apply a voltage between the charging member 5 and the member 5 to be charged can be exemplified, but the present invention is not limited to this. The voltage application method according to 6 may be changed as appropriate.
[0027]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these examples.
Example 1
An elastic layer A having a thickness of 3000 μm is formed on the outer periphery of the metallic shaft, a coating layer A having a thickness of 300 μm is formed on the elastic layer A, and a coating having a thickness of 10 μm is further formed on the coating layer A. Each film layer B was formed by using a dipping method to produce a charging roller. The configurations of the elastic layer A, the coating layer A, and the coating layer B are as follows. The surface roughness of the obtained charging roller was JlS 10-point average roughness Rz of 0.5 μm, and the contact angle of the charging roller surface with water was 110 °. The contact angle was measured using the method described above.
[0028]
Elastic layer A
A polyester-based polyol and a polyurethane foam (density 0.48 g / cm ³ ) prepared by adding carbon to isocyanate.
Coating layer A
It was formed by applying a paint in which carbon was added to a water-based acrylic resin, and the volume resistivity was adjusted to 5 × 10 ⁷ Ω · cm.
Coating layer B
Polytetrafluoroethylene fine particle dispersion (particle size: 0.15 μm, 20% by weight), fluoroethylene-vinyl ether copolymer water-based fluororesin (55% by weight), and water-based urethane resin (25% by weight) are blended to form carbon. The volume resistivity was adjusted to 5 × 10 ⁷ Ω · cm. Carbon having an oxygen content of 10% and a pH of 7.3 was used.
[0029]
When the obtained charging roller was mounted on a printer and imaged at room temperature and normal humidity (20 ° C./50% RH), a good image was obtained. Moreover, even when an image was printed at high temperature and high humidity (32 ° C./85% RH), a good image was obtained. Furthermore, there was no deterioration of the image even when 6000 images were continuously displayed.
Comparative Example 1
A charging roller similar to that of Example 1 was prepared except that the coating layer B was replaced with the following coating layer C. The surface roughness of the obtained charging roller was JIS 10-point average roughness Rz, 0.5 μm, and the contact angle of the charging roller surface with water was 67 °.
[0030]
Coating layer C
Polytetrafluoroethylene fine particle dispersion (particle size: 0.15 μm, 50% by weight), aqueous vinylidene chloride resin (30% by weight), and aqueous butyral resin (20% by weight) are blended and coated with carbon. The volume resistivity was adjusted to 5 × 10 ⁷ Ω · cm. Carbon having an oxygen content of 10% and a pH of 7.3 was used.
When the obtained charging roller was mounted on a printer and imaged at high temperature and high humidity (32 ° C./85% RH), defects such as thread pulling on the image occurred from the beginning. Layer C was dissolved in some places.
[0031]
Comparative Example 2
A charging roller was prepared in the same manner as in Example 1 except that the coating layer A was replaced with the following coating layer D and the coating layer B was replaced with the following coating layer E. The surface roughness of the obtained charging roller was 9.2 μm in terms of JIS10 point average roughness Rz, and the contact angle of the charging roller with water was 76 °.
Coating layer D
It was formed by applying a paint in which ketjen black carbon was added to urethane dissolved in toluene, and the volume resistivity was adjusted to 5 × 10 ⁷ Ω · cm.
Coating layer E
It was formed by applying a paint in which ketjen black carbon was added to nylon dissolved in methanol, and the volume resistivity was adjusted to 5 × 10 ⁷ Ω · cm.
When the obtained charging roller was imaged in the same manner as in Example 1, a dot defect occurred in the image when 500 images were printed, and when the roller was observed, toner adhered to the concave and convex portions on the surface. Was.
[0032]
【The invention's effect】
According to the charging member of the present invention, even when used in an electrostatic latent image process in a copying machine, a printer, etc., the charging member can exhibit stable charging performance over a long period of time without causing deterioration in performance due to toner adhesion or the like. it can.
Therefore, according to the charging device using the charging member of the present invention, a good charging operation can be stably performed over a long period of time without causing deterioration in charging performance due to long-term use.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a configuration of a charging member of the present invention.
FIG. 2 is a cross-sectional view for explaining a contact angle in the present invention.
FIG. 3 is a cross-sectional view showing an example of the configuration of the charging device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Charging member 2 Shaft 3 Elastic layer 4 Coating layer 5 Charged body 6 Voltage application means

Claims (8)

In the charging member for charging the object to be charged by bringing the object into contact with the object to be charged and applying a voltage between the object and the object to be charged, an elastic layer and another layer directly or outside the elastic layer are provided. A coating layer formed through a dispersion-type fluororesin fine particle formed by dispersing an aqueous fluororesin and a polytetrafluoroethylene resin in water and an aqueous urethane resin , A charging member having a contact angle with water exceeding 100 °. The charging member according to claim 1 , wherein the water-based fluororesin is a fluoroethylene-vinyl ether copolymer. The charging member according to claim 1 or 2 , wherein the total amount of the water-based fluororesin and the fluororesin fine particles contained in the coating layer is 50% by weight or more based on the total coating layer resin. Coating layer, the charging member according to any one of claims 1 to 3, wherein the pH in oxygen content 5% or more is one that contains carbon is 5 or more. Elastic layer, the charging member according to claim 1, characterized in that the urethane foam having a density of 0.05~0.9g / cm ^3. Surface, the charging member according to any one of claims 1 to 5, characterized in that a 4μm or less in average roughness Rz scale JIS10 points. The charging member according to claim 1, wherein the particle diameter of the fluororesin fine particles is 0.05 to 1 μm. A charging device comprising: a charging member that contacts a member to be charged and charges the member to be charged; and a voltage applying unit that applies a voltage between the member to be charged and the charging member. A charging device using the charging member according to any one of 1 to 7 .

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