JP4267104B2 - Charging member and charging device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charging member and a charging device using the same. More specifically, the present invention relates to a charging member that has excellent durability and is suitably used for an electrostatic latent image creation process in a copying machine, a printer, and the like, and a charging device formed by mounting the charging member. is there.
[0002]
[Prior art]
Conventionally, in an electrophotographic process such as a copying machine or a printer, first, the surface of the photosensitive member is uniformly charged, and an image is projected onto the photosensitive member from an optical system to erase the charged portion. A latent image is formed, and then printing is performed by forming a toner image by attaching toner and transferring the toner image onto a recording medium such as paper.
In this case, the corona discharge method has generally been adopted for the operation of charging the first photoreceptor. However, since this corona discharge method requires application of a high voltage of 6 to 10 kV, it is not preferable from the viewpoint of safety maintenance of the machine. There is also an environmental problem because harmful substances such as ozone and NOx are generated during corona discharge.
For this reason, efforts have been made to charge systems that can be charged with a lower applied voltage than corona discharge and that can suppress the generation of harmful substances such as ozone. As a trial of such a new charging method, a contact method has been proposed 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.
[0003]
As a charging member used in this contact charging method, for example, a resin solution such as nylon, acrylic or polyurethane is applied to the surface of an elastic layer such as rubber or polyurethane foam by a dipping method or a spray method. For the purpose of ensuring the smoothness of the toner and preventing the adhesion of the toner, those having a coating layer formed thereon are known.
However, in this contact charging method, since the charging member and the member to be charged are always in contact with each other, durability tends to be a problem as compared with a corona method in which the member to be charged is charged without contact from a conventional wire or the like. It is known that the residual toner has a great influence on the durability.
Regarding the influence of the residual toner, a slight amount of toner that arrives at the charging member gradually adheres to the charging member due to transfer failure, cleaning failure, and the like. Originally, it is a fundamental measure to improve transfer efficiency and cleaning efficiency and prevent such residual toner from reaching the charging member, but it is difficult with the current technology.
[0004]
Residual toner does not adversely affect the image to the extent that it slightly adheres to the surface of the charging member. Although the effect is difficult to understand in the initial image, the residual toner adheres to the surface of the charging member as images are repeatedly printed. However, it begins to accumulate and appears as a defective point in the image.
As a method for preventing the adhesion and accumulation of the residual toner, it is considered effective to dispose a fluorine resin having a small friction coefficient and excellent antifouling property on the surface of the charging member.
However, the fluororesin is inferior in dispersibility with the pigment because of its low surface energy. Of course, although there is a method of applying a dispersion stabilizer, in the case of the charging member, since it acts in direct contact with the member to be charged, the dispersion stabilizer or the like tends to contaminate the member to be charged. In addition, it is necessary to add a conductive agent such as carbon black in order to adjust to a desired resistance.
When a charging member adjusted to a desired resistance region is prepared by adding a conductive agent such as carbon black to a fluororesin or a resin obtained by adding another resin to this, a fluororesin and a pigment such as carbon black Therefore, the surface of the charging member becomes uneven and lacks in smoothness. As a result, toner begins to physically accumulate in the recesses, causing image defects in long-term use.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a charging member excellent in durability used in an electrostatic latent image creation process and the like in a copying machine, a printer, and the like, and a charging device using the same. To do.
[0006]
[Means for Solving the Problems]
As a result of earnest research to develop a charging member having excellent durability, the present inventors have found that a charging member having a surface layer containing a fluorine-based resin and carbon black having a specific specific surface area and DBP absorption amount. And found that it can be adapted to the purpose. The present invention has been completed based on such findings.
That is, according to the present invention, in a charging member that charges a member to be charged by contacting the member to be charged and applying a voltage to the member to be charged, the specific surface area of the fluororesin is 100 m ² / g or more and a DBP absorption amount have a surface layer containing carbon black 46~65ml / 100g, surface roughness Rz, it is to provide a charging member, characterized in der Rukoto below 4 [mu] m.
The present invention also relates to a charging device comprising: a charging member that abuts on 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. The present invention also provides a charging device using the charging member as the charging member.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The charging member of the present invention is of a contact charging type, but the shape thereof is not particularly limited as long as it can contact the member to be charged. For example, various shapes such as a roll shape, a plate shape, and a block shape are available. However, it is usually preferable to use a roll shape. In the case of a roll, a metal or plastic shaft may be provided.
The charging member of the present invention has at least a part of a surface layer containing a fluororesin and carbon black, and the surface layer is made of a fluororesin or another resin added to the fluororesin. a resin, a specific surface area of 100 m ² / g or more, preferably 100 to 300 m ² / g, more preferably by adding carbon black in the range of 120~300m ² / g, it is controlled to a desired resistance. As described above, when carbon black having a large specific surface area, that is, a small particle size is used, even a fluororesin can be adjusted to a system having excellent dispersibility, and as a result, surface smoothness can be improved. A rich charging member can be obtained. However, if the particle size is too small, it takes time for the dispersion work, and the above-described range is preferable.
[0008]
The carbon black is not particularly limited as long as it satisfies the above specific surface area. However, in order to keep the resistance increase during energization relatively low, the DBP (dibutyl phthalate) absorption amount is 100 ml / 100 g. preferably the following, Ri is preferably der the following 80 ml / 100 g Furthermore, it is preferred that the particular 46~65ml / 100g.
Since carbon black with such a small DBP absorption amount does not develop a structure, the amount of addition for adjusting to a desired resistance is slightly increased, but conversely, the number of conduction paths is increased, so that the resistance rises during energization. Can be kept low.
Examples of the carbon black having a specific surface area in the above range and satisfying the DBP absorption amount described above include # 2300 (manufactured by Mitsubishi Chemical Corporation), # 2400 (manufactured by Mitsubishi Chemical Corporation), Printex55 (manufactured by Degussa) ), # 40 [Mitsubishi Chemical Corporation], # 44 [Mitsubishi Chemical Corporation], # 45 [Mitsubishi Chemical Corporation], # 52 [Mitsubishi Chemical Corporation], and SAF, ISAF, SRF, etc. are mentioned. These carbon blacks may be used alone or in combination of two or more.
[0009]
On the other hand, examples of the fluorine resin include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-ethylene copolymer. , Polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, polyvinylidene fluoride, and polyvinyl fluoride. These fluorine-based resins include water-based resin types and organic solvent-based resin types, but are particularly excellent in water resistance and are not dependent on the environment, especially organic solvent-based resin types, especially polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl. Organic solvent resin types such as vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-ethylene copolymer are suitable. These fluororesins may be used alone or in combination of two or more.
The aqueous resin type means a resin that can be dissolved or dispersed in water using water as a solvent. The organic solvent resin type means a resin that can be dissolved or dispersed in an organic solvent using the solvent as an organic solvent.
[0010]
Moreover, in this invention, another resin can be added to the said fluororesin as needed. In this case, examples of other resins used include acrylic resins, polyurethane resins, nylon resins, silicone resins, polyester resins, epoxy resins, celluloses, melamine resins, and the like. From the viewpoint of improving dispersibility, acrylic resins and polyurethanes are used. Resin and nylon resin are preferred. These may be added alone or in appropriate combination.
[0011]
The resistance of the surface layer in the charging member of the present invention is a volume specific resistance value, usually 10 ³ to 10 ¹² Ω · cm, preferably 10 ⁵ to 10 ¹⁰ Ω · cm. Based on the total amount of the surface layer, it is usually added in a proportion of 0.01 to 40% by weight, preferably 5 to 20% by weight.
The thickness of the surface area is not particularly limited, but is preferably 50 μm or less, particularly preferably 1 to 30 μm, and if it exceeds 50 μm, it may become hard and the flexibility of the surface layer may be impaired.
Further, it is possible to form a plurality of layers. In this case, the outermost surface layer only needs to contain at least the fluororesin and carbon black having a specific surface area of 100 m ² / g or more. May be composed of any resin. Here, as the resin and conductive agent used in the lower layer, the resin and conductive agent exemplified in the surface layer can be exemplified.
In addition, a crosslinking agent, a thickener, a thixotropy imparting agent, a structural viscosity imparting agent, and the like can be appropriately added to any layer as necessary.
The thickener, thixotropic agent, and structural viscosity agent are appropriately selected from inorganic and organic materials.
The surface layer may be formed by any method as long as the surface layer that satisfies the above-mentioned conditions is formed from a fluororesin and carbon black, and is not particularly limited. For example, a dipping method, a spray method, An extrusion method or the like can be used.
[0012]
In the charging member of the present invention, an elastic layer may be provided in the lowermost layer in order to ensure the contact between the charging member and the member to be charged. There is no restriction | limiting in particular as this elastic layer, It can form with the rubber | gum and resin conventionally used as the elastic layer of a charging member, or these foams (foam). Specifically, rubbers using base rubbers such as polyurethane, silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, epichlorohydrin rubber, etc. Examples of the composition include polyurethane, and polyurethane foam having a foaming 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 .
Predetermined conductivity can be imparted to the elastic layer by adding a conductive agent such as an ionic conductive agent or an electronic conductive agent.
[0013]
Here, examples of the ion conductive agent include tetraethylammonium, tetrabutylammonium, dodecyltrimethylammonium such as lauryltrimethylammonium, octadecyltrimethylammonium such as stearyltrimethylammonium, hexadecyltrimethylammonium, benzyltrimethylammonium, modified aliphatic dimethylethyl. Perchlorates such as ammonium, chlorates, hydrochlorides, bromates, iodates, borofluorides, sulfates, alkyl sulfates, carboxylates, sulfonates, ammonium salts; lithium, Perchlorates, chlorates, hydrochlorides, bromates, iodates, borofluorides, trifluoromethyl sulfates of alkali metals or alkaline earth metals such as sodium, calcium, magnesium, Such as sulfonic acid salts, and the like.
[0014]
On the other hand, examples of the electronic conductive agent include conductive carbon black such as ketjen black and acetylene black; carbon black for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT and MT; Examples include carbon black for ink, pyrolytic carbon black, graphite; conductive metal oxides such as tin oxide, titanium oxide, and zinc oxide; metals such as nickel and copper.
These conductive agents may be used alone or in combination of two or more. Moreover, there is no restriction | limiting in particular as addition amount of these electrically conductive agents, Although it selects suitably according to various situations, in the case of an ionic electrically conductive agent, 0.01-5 normally with respect to 100 weight part of rubber materials. Parts by weight, preferably 0.05 to 2 parts by weight. Moreover, in the case of an electronic conductive agent, it is 0.5-50 weight part normally, Preferably it is the range of 1-40 weight part. Thereby, it is preferable to adjust the volume resistivity value of the elastic layer to 10 ³ to 10 ¹⁰ Ω · cm, particularly 10 ⁴ to 10 ⁸ Ω · cm.
[0015]
In addition to the conductive agent, other additives for rubber such as known fillers and crosslinking agents can be appropriately added to the elastic layer as necessary.
Further, as described above, if the charging member has irregularities on its surface, toner may be clogged in the concave portion as described above, which may cause image defects. Therefore, the surface of the member is preferably as smooth as possible. In the present invention, although not particularly limited, the JIS 10-point average roughness Rz is preferably 4 μm or less, particularly 3 μm or less, and more preferably 2 μm or less.
In order to stably form an image in various environments, it is preferable to use a charging member that absorbs less water. In the present invention, the contact angle with respect to water is 90 degrees or more, although not particularly limited. In particular, it is preferably 95 ° or more, particularly preferably 100 ° or more.
Further, the surface hardness of the charging member is preferably 10 N / mm ² or less in terms of universal hardness at a depth of 7 μm. By optimizing the universal hardness, it is possible to perform a stable charging operation over a long period of time without causing performance deterioration due to deformation of the charging member due to the mixing of residual toner, and it is possible to further improve durability. .
[0016]
The universal hardness is obtained by pushing the indenter into the object to be measured while applying a load.
Universal hardness = [Test load] / [Surface area of contact of the indenter with the test object under the test load] (I)
And the unit is expressed in N / mm ² .
The universal hardness can be measured using a commercially available hardness measuring device, and can be measured using, for example, an ultra micro hardness meter H-100V (manufactured by Fischer). In this measuring device, a quadrangular pyramid or triangular pyramid shaped indenter is pushed into the object to be measured while applying a test load, and when the desired depth is reached, the indenter comes into contact with the object to be measured. The surface area is calculated, and the universal hardness is calculated from the above formula (I).
[0017]
In addition, there is no restriction | limiting in particular about the measurement conditions of this universal hardness, Any conditions may be sufficient if the universal hardness by the said indentation depth is calculated | required. For example, in the case of measuring universal hardness using the above micro hardness meter H-100V (manufactured by Fischer), the following conditions can be exemplified, and the indenter is gradually increased to a predetermined indentation depth under the following conditions. The universal hardness can be obtained from the load and the contact area of the indenter when the indentation depth reaches a desired depth.
Example of measurement conditions Indenter: Square pyramid diamond indenter with a face-to-face angle of 136 degrees Initial load: 0.02 mN
Maximum load: 5-400mN
Load increase time from initial load to maximum load: 10 to 60 seconds
The charging member of the present invention is disposed in contact with a charged body such as a photosensitive drum, and the charged body is charged by applying a voltage between the charged body and the charging member of the present invention. In this case, 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. It is preferable to perform charging by applying a voltage on which an alternating voltage is superimposed, whereby the object to be charged can be more uniformly charged. Further, although not particularly limited, the contact pressure between the charging member of the present invention and the member to be charged is preferably 50 to 2000 g, particularly 100 to 1000 g, so that good charging can be reliably obtained. Can do.
The present invention also provides a charging device using the above-described charging member of the present invention.
The charging device of the present invention is exemplified by a charging device configured such that a charging member is brought into contact with a member to be charged such as a photosensitive drum at a predetermined pressure and a voltage is applied between the voltage applying unit and the member to be charged. However, the present invention is not limited to this, and the form of the member to be charged and the charging member, the voltage application method using the voltage application means, and the like may be changed as appropriate.
[0019]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, 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 a metal shaft, a coating layer A having a thickness of 120 μm is formed thereon, and a coating layer B having a thickness of 5 μm is formed thereon (outermost layer). Thus, a charging roller was produced. The elastic layer A, coating layer A and coating layer B (outermost layer) are as follows. The obtained charging roller had a universal hardness of 8.1 N / mm ² at a depth of 7 μm from the surface, a JIS 10-point average roughness Rz of 2.7 μm, and a contact angle with water of 101 degrees.
When the roller was mounted on a printer and an image was taken out, a good image was obtained. Furthermore, there was no image abnormality even when 8000 images were continuously displayed.
Elastic layer A
This is a polyurethane foam having a density of 0.55 g / cm ³ and produced by adding carbon black to a polyester polyol and a polyisocyanate compound.
Coating A
A coating film formed by applying a paint containing carbon black to urethane acrylic resin (trade name: EAU77B, manufactured by Asia Industries Co., Ltd.) and adjusting the volume resistivity to 6.3 × 10 ⁷ Ω · cm Is a layer.
Coating film B
A paint obtained by adding a fluorine-based resin [trade name: Kyner 7200P (copolymer of tetrafluoroethylene and vinylidene fluoride), manufactured by Elfatechem] and carbon black (trade name: Printex 55, manufactured by Degussa) to a methyl ethyl ketone solvent. It is a coating layer formed by coating and having a volume solid resistance value adjusted to 3.3 × 10 ⁷ Ω · cm. Carbon black (Printex55) has a specific surface area of 110 m ² / g and a DBP absorption of 46 ml / 100 g.
[0020]
Example 2
A charging roller was prepared in the same manner as in Example 1 except that the coating layer B was changed to the coating layer C.
The obtained charging roller had a universal hardness of 7.4 N / mm ² at a depth of 7 μm from the surface, a JIS 10-point average roughness Rz of 2.9 μm, and a contact angle with water of 103 degrees.
When the roller was mounted on a printer and an image was taken out, a good image was obtained. Furthermore, there was no image abnormality even when 8000 images were continuously displayed.
Coating layer C
It is formed by coating a methyl ethyl ketone solvent with a fluorine resin (trade name: Kyner 7200P) and carbon black (# 2300, manufactured by Mitsubishi Chemical Corporation), and has a volume resistivity of 3.3 × 10. It is a coating layer adjusted to ⁷ Ω · cm. Carbon black (# 2300) has a specific surface area of 260 m ² / g and a DBP absorption of 65 ml / 100 g.
[0021]
Comparative Example 1
A charging roller was produced in the same manner as in Example 1 except that the coating layer B was changed to the coating layer D.
The obtained charging roller had a universal hardness of 9.4 N / mm ² at a depth of 7 μm from the surface, a JIS 10-point average roughness Rz of 6.9 μm, and a contact angle with water of 95 degrees.
When the above roller was mounted on a printer and an image was output, a good image was obtained at the beginning, but when a continuous image was output, a black spot image defect occurred from 5500 sheets. When the charging roller was taken out and observed, toner was deposited in the concave portion of the roller.
Coating layer D
It is formed by applying a coating material in which a fluorine-based resin (trade name: Kyner 7200P) and carbon black (# 3050, manufactured by Mitsubishi Chemical Corporation) is added to a methyl ethyl ketone solvent, and the volume resistivity value is 4.1 × 10. It is a coating layer adjusted to ⁷ Ω · cm. Carbon black (# 3050) has a specific surface area of 50 m ² / g and a DBP absorption of 180 ml / 100 g.
[0022]
Comparative Example 2
A charging roller was produced in the same manner as in Example 1 except that the coating layer B was changed to the coating layer E.
The obtained charging roller had a universal hardness of 9.9 N / mm ² at a depth of 7 μm from the surface, a JIS 10-point average roughness Rz of 4.6 μm, and a contact angle with water of 71 degrees.
When the above roller was mounted on a printer and an image was output, a good image was obtained at the beginning, but when continuous images were output, fog and black spot image defects occurred from 4500 sheets. When the charging roller was taken out and observed, the toner adhered to the roller surface, and the toner was deposited particularly on the concave portion.
Coating layer E
It is formed by applying a paint in which a nylon resin (trade name: EF30T, manufactured by Teikoku Chemical Industry Co., Ltd.) and carbon black (# 2300, manufactured by Mitsubishi Chemical Co., Ltd.) is added to a methanol solvent. Is a coating layer adjusted to 4.8 × 10 ⁷ Ω · cm. The specific surface area of carbon black (# 2300) is 260m ² / g, D B P uptake 65 ml / 100 g.
[0023]
【The invention's effect】
The charging member of the present invention has at least a surface layer containing a fluorine-based resin and carbon black having a specific surface area, and has excellent durability. In a copying machine, a printer, etc., an electrostatic latent image It is suitably used for the creation process.

Claims (6)

In a charging member for charging a member to be charged by contacting the member to be charged and applying a voltage to the member to be charged, the fluororesin has a specific surface area of 100 m ² / g or more and a DBP absorption amount. Has a surface layer containing 46 to 65 ml / 100 g of carbon black, and has a surface roughness Rz of 4 μm or less.  The fluororesin is polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, polychlorotriethylene. The charging member according to claim 1, wherein the charging member is at least one selected from fluoroethylene, chlorotrifluoroethylene-ethylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, polyvinylidene fluoride, and polyvinyl fluoride.  The charging member according to claim 1 or 2, wherein the fluororesin is of an organic solvent resin type.  The charging member according to claim 1, wherein a contact angle of water on the surface is 90 degrees or more. The charging member according to claim 1, wherein the surface hardness is 10 N / mm ² or less in terms of universal hardness at a depth of 7 μm.  A charging device comprising: a charging member that contacts a charged body and charges the charged body; and a voltage applying unit that applies a voltage between the charged body and the charging member. Item 6. A charging device using the charging member according to any one of Items 1 to 5.