JPH06324554A - Electrostatic charging member and electrostatic charging device using same - Google Patents

Abstract

PURPOSE:To enable uniform electrostatic charge by forming a resist layer from a base material containing a sulfonate. CONSTITUTION:An elastic layer 202 of polar rubber (epichlorohydrine rubber, nitrile rubber, urethane rubber, chloroprene rubber, acrylic rubber and the like) 1 to 5mm in thickness and containing a sulfonate is formed over a core 201. The volume resistivity of the elastic layer 202 is in the range of 10<6> to 10<8>OMEGA.cm. Further, a surface layer 203 which is 5 to 50mum in thickness and made from a non-sticking resin is formed thereover. The surface layer 203 is formed from a material having medium resistance and composed chiefly of at least a solvent- soluble fluororesin, to prevent toners and paper powder from sticking to the surface of an electrostatic charging roller so as to maintain the uniformity of electrostatic charge over a long period of time. Thereby the uniformity of the electrostatic charge by application of DC voltage and environmental stability can both be enhanced.

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 in an image forming apparatus such as a copying machine, a facsimile, a printer and the like, and a charging device using the charging member. The present invention relates to an improvement for uniform charging by contacting with.

[0002]

2. Description of the Related Art Heretofore, various types have been known for charging a charging member by contacting it with an object to be charged. For example, Japanese Patent Application Laid-Open No. 56-132356 discloses that a constant current type power source is used to apply a voltage to a roller-shaped charging member. In addition, JP-A-63
In Japanese Patent Publication No. 149668, in order to make the charging uniform,
As the voltage applied to the charging roller, the charging start voltage (V
It is disclosed that an AC voltage having a peak-to-peak voltage that is at least twice that of th) is applied. In addition, JP-A-3-15647
Japanese Unexamined Patent Publication (Kokai) No. 6 discloses that a voltage obtained by superimposing a DC voltage on an AC voltage is used to apply a voltage to the charging roller, and AC constant current control is performed. Although not a charging member, JP-A-63-189976 discloses a developing roller having a urethane rubber developing roll with a low resistance by adding an alkali metal salt to the medium resistance. It is disclosed.

[0003]

Conventionally, in an electrophotographic image forming apparatus, a corona discharger has been widely used as a charging means for uniformly charging the entire surface of the photoconductor. This corona discharger is effective as a means for uniformly charging the photoconductor to a certain constant potential, but on the other hand, the charging process by corona discharge requires a high voltage power source and ozone Occurs. Not only will the environment be adversely affected if a large amount of ozone is generated,
There is also a problem that ozone deteriorates the charging member and the photoconductor.

Therefore, as described above, instead of the corona discharger, for example, a charging roller 100 as shown in FIG. 1A is brought into contact with the photosensitive drum 101 and driven to rotate,
A charging roller 100 that applies a voltage from a power source 103 to a core metal 102 of the charging roller 100 to charge the surface of the photosensitive drum 101 has been proposed and put into practical use. According to this, it is possible to reduce the voltage of the power supply 103 of the charging roller 100 as the charging means, and there is an advantage that the amount of ozone generated due to the charging process is small.

However, at present, the uniformity of charging is considerably inferior to that of the charging process using a corona discharger. The "contact charging method" of JP-A-63-149668 is intended to improve the uniformity of the charging, but the charging start voltage (Vth) of 2 when a DC voltage is applied is set.
To apply an AC voltage with a peak-to-peak voltage more than double,
In addition to the DC power supply, an AC power supply is required, which leads to an increase in the cost of the apparatus itself, and also consumes a large amount of useless AC current that hardly contributes to the charged position of the photoconductor, which not only increases the power supply cost. However, a large amount of ozone is generated, which may result in deterioration of the charging member and the photoconductor.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a charging member that enables more uniform charging as compared with the conventional case, and a charging device using the charging member. It is to be.

[0007]

In order to achieve the above object, the invention of claim 1 comprises a resistance layer having a predetermined electric resistance on a conductive support, and the predetermined electric resistance layer is provided on the resistance layer. A charging member having a surface layer, wherein the resistance layer is formed of a material containing a sulfonate in a base material.

The invention according to claim 2 is the charging member according to claim 1, wherein the base material is a polar rubber.

According to a third aspect of the present invention, in the charging member according to the first aspect, the surface layer is mainly composed of a solvent-soluble fluororesin.

According to a fourth aspect of the invention, in the charging member according to the third aspect, the solvent-soluble fluororesin is obtained by crosslinking a fluorocopolymer having fluoroolefin and vinyl ether having a hydroxyl group as constituent components with isocyanate. It is characterized by being a fluorine-containing cross-linked copolymer.

According to a fifth aspect of the present invention, in a charging device for applying a voltage to the charging member while the charging member is in contact with the image carrier, the charging member according to the first aspect is used as the charging member. In addition, a direct current voltage is used as the voltage applied to the conductive support.

[0012]

The present inventor has examined why the conventional charging roller (generally having a resin overcoat layer on the surface of the conductive elastic layer) causes charging unevenness only by applying a DC voltage. As a result, they found that the conductive elastic layer was a dispersion system of synthetic rubber and carbon black. This fact is demonstrated by using a charging roller in which the conductive elastic layer (dispersion system of synthetic rubber and carbon black) of a conventional charging roller is replaced with a polar rubber material containing no conductive particles such as carbon black. It turned out as a result.

Here, the polar rubber (or polar rubber) means a rubber having a polar group in a polymer. For example, epichlorohydrin rubber, nitrile rubber, urethane rubber, chloroprene rubber, and acrylic rubber are --Cl, --CN, --NH.
It has a polar group of -COO. On the other hand, natural rubber,
Rubbers containing no polar groups such as styrene-butadiene rubber and butyl rubber are called non-polar rubbers.

That is, the charging unevenness of the conventional charging roller is due to electrical non-uniformity of the conductive elastic layer due to poor dispersion of carbon black / synthetic rubber, and the use of polar rubber eliminates the charging unevenness. Further, even under low temperature and low humidity, the increase in volume resistance of the roller layer is small and a stable charging potential can be obtained. Then, the present inventor, when the desired resistance cannot be obtained only by the base material such as polar rubber,
As a result of various studies on substances such as carbon black for lowering resistance that does not cause problems, it has been found that inclusion of a sulfonate is effective. When the base material containing the sulfonate is used, uneven charging does not occur. Sulfonate, like carbon black, does not chemically react in the base material such as polar rubber. It exists in the form of being dispersed in the base material, but each of the dispersing units is remarkably smaller than carbon black. Therefore, the base material is not limited to the above-mentioned polar rubber, and non-polar rubber or the like can also eliminate the charging unevenness. However, when non-polar rubber is used as the base material, a relatively large amount of sulfonate is contained in order to achieve the desired layer resistance. It may be necessary to take measures against contamination of the surface of the object.

[0015]

EXAMPLE An example in which the present invention is applied to a charging device for uniformly charging a photosensitive drum as an image carrier in an image forming apparatus will be described. FIG. 1B is a schematic configuration of a charging roller that can perform uniform charging only by applying a DC voltage, that is, without superimposing an AC voltage (DC + AC), and can reduce fluctuations in charging potential even at low temperature and low humidity. Is shown. In the figure, the thickness of 1
An elastic layer 202 containing a sulfonate in a polar rubber (epichlorohydrin rubber, nitrile rubber, urethane rubber, chloroprene rubber, acrylic rubber, etc.) of 5 mm is formed. The volume resistance of the elastic layer 202 is 10 ⁶
The range of 10 ⁸ Ω · cm is preferable. On top of that, a thickness of 5
A surface layer 203 made of non-adhesive resin having a thickness of 50 μm is formed. The surface layer 203 is formed to prevent toner, paper powder, etc. from adhering to the surface of the charging roller and maintain the charging uniformity for a long period of time. It is formed by the substance. The volume resistance of the surface layer 203 is preferably in the range of 10 ⁸ to 10 ¹⁰ Ω · cm.

The sulfonates used in the present invention include aromatic sulfonate-based bezene sulfonates, P-toluene sulfonates, naphthalene-β-sulfonates, and the like.
Further, aliphatic sulfonate-based ethane sulfonate, allyl sulfonate, and the like can be mentioned. Note that examples of the element that forms a salt include potassium, sodium, lithium, and the like.

The solvent-soluble fluororesin used for the surface layer is an amorphous polymer obtained by a copolymerization reaction of fluoroolefin and hydrocarbon vinyl ether. This resin has a relatively low fluorine content of 25 to 32 wt%, but is an alternating polymer having a chain structure in which fluoroolefins and hydrocarbon vinyl ethers are alternately arranged, and is chemically stable and excellent in durability. In addition, since this polymer is soluble in organic solvents, it is necessary to crosslink the polymer after coating to impart solvent resistance to the coating film.For this purpose, a highly reactive hydroxyl group-containing vinyl ether is copolymerized to produce an isocyanate. It is preferable to use a resin that can be easily cross-linked by.

In the composition of the elastic layer of the present invention, the amount of the sulfonate added is 100 parts by weight based on 100 parts by weight of the polar rubber.
A range of 2 to 2.0 parts by weight is preferable. If the amount of sulfonate added is 0.2 parts by weight or less, it is difficult to obtain the desired volume resistance, and if it exceeds 2.0 parts by weight, the bleed-out phenomenon of sulfonate comes to be observed. Contamination of the surface of the photoconductor (OPC, etc.) may cause an abnormal image or lose the rubber moldability.

A conventional charging roller which leaves the above charging roller and charging uniformity to AC superimposition (Japanese Patent Laid-Open No. 64-7336).
4 and 64-73367), the electric characteristics (R, C) and the roller layer structure are largely different. That is, the AC superposition type is composed of a conductive elastic layer (a rubber layer in which conductive particles such as carbon black are dispersed) and a surface resistance layer. Since the surface resistance layer functions as a capacitor, the capacitance is large and AC superposition The effect of uniformizing the charge is great. On the other hand, in the DC type of the present invention, the roller layer functions as a resistor (small electrostatic capacity), and therefore AC superposition does not contribute much to charging uniformity.

The embodiment will be described in more detail below. Examples 1 and 2, Comparative Example 1 First, Examples 1 and 2 and Comparative Example 1 will be described with reference to Table 1. This table 1
The type and amount (unit: parts by weight) of the compound of the material forming the elastic layer of the elastic roller, the volume resistance value of the elastic roller by the measurement method described below, and the charging roller completed by forming the surface layer are described below. The results of the image test are shown (the same applies to Tables 2 to 5). (Hereafter, margin)

[Table 1]

In each of the examples shown in Table 1, first, a mixture of epichlorohydrin rubber [trade name: Epichroma CG (manufactured by Daiso Co.)] and a sulfonate is kneaded with an 8-inch two-roll for about 15 minutes (kneading). The surface temperature of the two rollers at this time is 90 in the case of sodium P-toluenesulfonate.
C., 50.degree. C. for sodium allyl sulfonate, and 50.degree. C. if no sulfonate is added)
170 on φ8 × 340mm stainless steel core 201
Molded to have a diameter of 14 × 305 mm under vulcanization conditions of 15 ° C. for 15 minutes, and a medium resistance elastic layer 202 for roller-shaped charging member is formed.
Was set up. On the other hand, also in the comparative example, an elastic layer was provided in the same manner except for the composition. In all Examples and Comparative Examples, 30 parts by weight of calcium carbonate [Whiten SO (manufactured by Shiraishi Calcium Co.)], a vulcanization accelerator [NOXCERA TT (large Uchi Shinko Chemical Co., Ltd.)] 1.0 part by weight, [Noxera DM (Ouchi Shinko Chemical Co., Ltd.)] 1.5 parts by weight, and vulcanizing agent [Salfax PMC (Tsurumi Chemical Co., Ltd.)] 0.25 Parts by weight were compounded.

Next, a surface layer was formed on this elastic roller by the following method. That is, as a surface layer material, 100 g of a terpolymer of epichlorohydrin rubber [trade name: Epichroma CG, manufactured by Daiso Co., Ltd.] was kneaded with an 8-inch two-roller for about 15 minutes, and then 2.5 weight of this epichlorohydrin rubber was used. Parts to an organic solvent (toluene / 4-methyl-2-
Pentanone) = 1 to dissolve in 97.5 parts by weight to prepare an epichlorohydrin rubber solution. In addition, as a solvent-soluble fluororesin [Product name: Lumiflon LF60 / C main agent, manufactured by Asahi Glass Co., Ltd.] 22.0 parts by weight, isocyanate-based curing agent [Product name: Coronate HX, manufactured by Nippon Polyurethane Industry Co., Ltd.]
2.0 parts by weight was dissolved in 76.0 parts by weight of an organic solvent (toluene / xylene) = 1 to prepare a fluororesin solution. Then, as a surface layer coating material, 100 parts by weight of the epichlorohydrin rubber solution and 60 parts by weight of the fluororesin solution were mixed and made. After coating the surface layer coating material on each of the above elastic rollers by the dipping method, 100
It was dried at 30 ° C. for 30 minutes to form a surface layer having a thickness of 20 μm. The volume resistance of this surface layer was 6 × 10 ⁸ Ω · cm.

Here, the volume resistance of the elastic roller is measured at 20 ° C. and 60% R. After discharging in an H environment for 16 hours, an electrometer 610C manufactured by Keithre Co. was used. The measuring electrode was a 10 mm wide copper foil tape [No. 1245] is wound around the circumference of the roller. The volume resistance of the surface layer only was measured by applying a coating for the surface layer on a thin aluminum plate (thickness 0.2 mm) to a thickness of about 20 μm at 20 ° C and 60% at 20 ° C.
R. After left in the H environment for 16 hours, the resistance measurement cell [Y
HP 16008A] with a Keithre Electrometer 610C.

FIG. 1C shows a part of the image forming apparatus used for image evaluation of the charging roller. Photoconductor drum 10
1 is an OPC with a tourist layer thickness of 30 μm (OPC drum linear velocity: 1
00 mm / sec), the power source 103 is a DC power source, the quenching lamp 104 is an LED, and the cleaner 105 is a blade cleaning unit for removing the residual toner on the OPC drum. The image evaluation of each charging roller under the three environments shown in Table 1 of this apparatus was performed. The results are shown in the table as presence / absence of “image defect”.

From the results of Examples 1 and 2 and Comparative Example 1, by incorporating a sulfonate in the epichlorohydrin rubber, the conductivity is improved, the charging uniformity and the image stability under low temperature and low humidity are improved. I understand that.

Examples 3, 4 and Comparative Example 2 Next, Tables 2 will be used to describe Examples 3, 4 and Comparative Example 2. (Hereafter, margin)

[Table 2]

In each of the examples shown in Table 2, first, a mixture of nitrile rubber [NBR: N215SL (manufactured by Nippon Synthetic Rubber Co., Ltd.)] and a sulfonate was kneaded for about 15 minutes using an 8-inch two-roller. (The surface temperature of the two rollers during kneading is maintained at 65 ° C. for sodium benzene sulfonate, 50 ° C. for sodium allyl sulfonate, and 50 ° C. for the case where no nullphonate is added). Three
It was molded on a 40 mm stainless steel cored bar under a vulcanization condition of 170 ° C. for 15 minutes so as to be φ14 × 305 mm, and a medium resistance elastic layer of a roller-shaped charging member was provided. On the other hand, also in the comparative example, an elastic layer was provided in the same manner except for the composition. In addition, in any of the Examples and Comparative Examples, Table 2
5 parts by weight of Zinc Hua No. 1 as a "other" compound in
1.5 parts by weight of stearic acid and 1.0 part by weight of sulfur were blended. Next, a surface layer was formed on the elastic roller by using the same paint and method as in Example 1 above. Examples 3 and 4,
From the results of Comparative Example 2, it can be seen that the inclusion of the sulfonate in the nitrile rubber improves the conductivity and improves the charging potential and its uniformity.

Examples 5, 6 and Comparative Examples 3-5 Next, Tables 3 will be used to explain Examples 5, 6 and Comparative Examples 3-5. (Hereafter, margin)

[Table 3]

In each of the examples shown in Table 3, first, a mixture of urethane rubber [Miracene E-34 (manufactured by TSE Co.)] and a sulfonate was used in an amount of about 1 by using an 8-inch double roller.
Kneading for 5 minutes (The surface temperature of the two rollers at the time of kneading is maintained at 95 ° C for lithium P-toluenesulfonate, 65 ° C for sodium allylsulfonate, and 60 ° C for the case where no sulfonate is added. After that, it was molded on a stainless cored bar of φ8 × 340 mm so as to have a diameter of φ14 × 305 mm under vulcanization conditions of 150 ° C. for 10 minutes, and a medium resistance elastic layer of a roller-shaped charging member was provided. On the other hand, in the comparative example,
An elastic layer was provided as in the example, except for the formulation. In addition, in all Examples and Comparative Examples, Table 3
As the composition of "other" in, zinc stearate 0.
5 parts by weight and 5 parts by weight of dicumyl peroxide are blended. Next, the surface layer was formed on this elastic roller by the same paint and method as in Example 1 above. From the results of Examples 5 and 6 and Comparative Examples 3 to 5, it can be seen that the incorporation of the sulfonate in the urethane rubber improves the conductivity and improves the charging potential and its uniformity.
If the amount of sulfonate added is 0.1 parts by weight, it is difficult to obtain the conductive effect, and the image density becomes insufficient due to the insufficient charging potential. On the other hand, if the amount of sulfonate is 2.3 parts by weight, the bleed-out phenomenon of sulfonate causes the OPC surface. A horizontal streak occurred due to the migration.

Examples 7 and 8 and Comparative Example 6 Next, Tables 4 will be used to describe Examples 7 and 8 and Comparative Example 6. (Hereafter, margin)

[Table 4]

In each of the examples shown in Table 4, first, a mixture of chloroprene rubber [Neoprene GS (manufactured by Showa Denko KK)] and a sulfonate was used for about 15 minutes using an 8-inch two-roller. (The surface temperature of the two rollers during kneading is maintained at 70 ° C. for sodium benzene sulfonate and 65 ° C. for sodium allyl sulfonate) and then 160 ° C. on a φ8 × 340 mm stainless steel cored bar.
It was molded to have a diameter of 14 × 305 mm under a vulcanization condition for 10 minutes, and a medium resistance elastic layer of a roller-shaped charging member was provided. On the other hand, in the comparative example, the elastic layer was provided in the same manner as in the example except that the composition was used. In addition, in any of Examples and Comparative Examples, as the compound of "other" in Table 4,
Magnesia 4.0 parts by weight, stearic acid 0.5 parts by weight,
And 10 parts by weight of Zinc Hua No. 1 were blended. Next, a surface layer was formed on the elastic roller with the same paint and method as in Example 1 above. From the results of Examples 7 and 8 and Comparative Example 6, it can be seen that the inclusion of the sulfonate in the chloroprene rubber improves the conductivity and improves the charging potential and its uniformity.

[Comparative Examples 7 to 10] Next, using Table 5,
Comparative examples 7 to 10 will be described. (Hereafter, margin)

[Table 5]

Each comparative example shown in Table 5 shows the results when carbon black [Ketjen Black EC (manufactured by Lion Akzo Co.)] was dispersed as a conductivity adjusting agent for a rubber polymer. The coating material for the surface layer and the method of making the same are the same as in Example 1 above. In any case, the resistance variation width in the medium resistance region of the elastic roller is large, and as a result, uneven charging occurs in any of the comparative examples.

[0034]

According to the first aspect of the present invention, since the non-dispersed medium resistance material is used for the predetermined resistance layer, it is possible to improve the uniformity of charging and the environmental stability when DC is applied.

According to the invention of claim 2, the polar rubber is
Since this polymer itself has a relatively low resistance, it is possible to control a predetermined resistance layer to a medium resistance region by adding a small amount of a resistance adjusting agent.

According to the third aspect of the present invention, since a fluorine-based coating having high non-adhesiveness can be easily formed (air spray method, dipping method, etc.), the life of the charging member can be improved. it can.

According to the invention of claim 4, since the solvent-soluble fluororesin can be formed into a film at a relatively low temperature (room temperature to 100 ° C.), the non-adhesive layer (surface layer) can be formed on the elastic rubber. I can do it now.

According to the fifth aspect of the present invention, uniform charging can be performed only by applying DC, and the amount of ozone generated can be greatly reduced (1/30 to 1/40) as compared with DC + AC, and power source cost can be further reduced. Can also be lowered.

[Brief description of drawings]

FIG. 1A is a schematic configuration diagram of a charging device according to an embodiment. FIG. 2B is a schematic configuration diagram of a charging roller for the charging device according to the embodiment. (C) Explanatory drawing of the charging roller evaluation device.

[Explanation of reference numerals] 100 charging roller 101 photoconductor drum 102 core metal 103 power supply 201 core metal 202 elastic layer 203 surface layer

Claims (5)

[Claims] 1. A charging member comprising a conductive support and a resistance layer having a predetermined electric resistance, and a surface layer on the predetermined electric resistance layer, wherein the resistance layer has a base material of sulfonic acid. A charging member, which is formed of a material containing salt. 2. The charging member according to claim 1, wherein the base material is a polar rubber. 3. The charging member according to claim 1, wherein the surface layer is mainly composed of a solvent-soluble fluororesin. 4. The solvent-soluble fluororesin is a fluorine-containing crosslinked copolymer obtained by crosslinking a fluorine-containing copolymer having fluoroolefin and vinyl ether having a hydroxyl group as constituent components with isocyanate. 3 charging member. 5. A charging device, wherein a direct current voltage is used as a voltage applied to the conductive support in a state where the charging member of claim 1 is in contact with the image carrier.