JPH0772710A - Electrostatic charging member and electrostatic charging device - Google Patents

Abstract

PURPOSE:To obtain an electrostatic charging member whose surface is smooth and by which a body to be electrostatically charged is excellently electrostatically charged by providing a function layer including a water-based high polymer compound in the electrostatic charging member in contact with the body to be electrostatically charged. CONSTITUTION:An electrostatic charging roller having two-layer constitution obtained by coating a middle-resistance elastic sponge roller 4b with one resistance layer 4c is used as the contact electrostatic charging member 4, and a material obtained by doping antimony with water-based urethane resin and uniformly dispersing SnO2 to which conductive processing is performed is used as a coating agent for the resistance layer 4c. The resistance value of the roller 4b must be set within the range of 10<4>-10<8>OMEGAcm in order to prevent a situation that a sponge generates heat and is burnt because an excess current flows when the resistance value of a sponge layer is low in the case a defect such as a pin hole is caused on a photoreceptor, or in order to apply an electrostatic charging current required for the electrostatic charging. A water-based binder which dries comparatively slow is used as the coating agent of the resistance layer 4b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member and a charging device for charging (including discharging) a charged body such as a photoconductor or a dielectric used in an electrophotographic apparatus or an electrostatic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, as a contact charging method for a photosensitive member, there are a method of charging a member to be charged by applying a DC voltage from the outside to a member to be charged (hereinafter referred to as DC charging), and a DC voltage and an AC voltage. Method of charging by applying superposed voltage (hereinafter AC
(Charging) is known.

In these contact charging methods, charging is performed by using a discharge mechanism in a minute air gap formed between the charging roller and the photoconductor, and in DC charging, a discharge start threshold value and a desired discharge threshold value are set. By applying a voltage to the contact charging member, which is the same as the surface potential of the photoconductor of
In C charging, D corresponding to the desired photoreceptor surface potential
Proper charging is performed by superimposing and applying the C voltage and the AC voltage having a peak-to-peak voltage that is twice or more the discharge start threshold voltage.

Although the DC charging method has an advantage that the applied voltage is low, it has disadvantages such as uneven charging, susceptibility to environmental changes, etc., and AC charging is often used from the viewpoint of image stability. .

[0005]

The charging member is, for example, NR in which conductive fine powder such as carbon black or metal oxide is filled on a core metal, silicone rubber, EPDM, S.
A solid type charging roller in which a medium resistance elastic material such as BR or IR is coated to form a roller, and a resistor layer is coated thereon is often used. The resistance layer here is for preventing the charging member and the photoconductor from being damaged by the concentration of the charging current when a defect such as a pinhole occurs on the photoconductor. Specifically, a coating material in which a conductive fine powder such as carbon black or metal oxide (TiO ₂ , SnO _2, etc.) is dispersed is applied to a polymer compound such as acrylic, urethane, or nylon. At this time,
If the conductive fine powder is not evenly dispersed, it may cause a charging failure in a minute area. Therefore, it is necessary to carefully select the paint and the dispersion method.

In order to uniformly charge the surface of the photosensitive member, the surface of the contact charging member must be smooth.
If the surface of the contact charging member has minute irregularities, minute uneven charging occurs, and on the image output by the reversal development type electrophotographic apparatus, a large number of black spots (regular development) In the method, white spots occur, causing image defects.

In particular, when AC charging is performed, an AC voltage is applied to the contact charging member, so that an oscillating electric field is generated between the contact charging member and the photoconductor, and when they are attracted to each other, abnormal noise called a charging sound is generated. This charging sound mainly has a frequency twice as high as the frequency applied to the contact charging member, and the charging sound frequency is several hundreds to several kilohertz at the charging frequency of several hundreds hertz which is usually used, and it feels very annoying. To be

In order to prevent this, it has been considered to reduce the vibration generated between the charging member and the photosensitive member by using the base body of the contact charging member as a foam.

Specifically, when a charging roller is used as the contact charging member, a sponge roller having a low resistance is formed on a cored bar, and a plurality of resistance layers are provided on the sponge roller, or a sponge roller has a low resistance. Means have been devised, such as forming a tube or the like and coating the resistance layer on it, or forming a sponge roller having a skin layer and providing the resistance layer thereon.

Originally, it is simple and preferable to directly coat the resistance layer on the surface of the sponge (or the surface obtained by polishing the sponge) from the viewpoints of cost, manufacturing, and constitution, but it is generally used. When a binder for coating is dissolved in an organic solvent that is used, and a conductive filler or the like is dispersed in the binder, a sponge surface is coated by a method such as a dipping coating method, a beam coating method, or a roll coating method. There has been a problem that the roller surface after coating is not smooth.

This is because when the binder polymer compound is dissolved in an organic solvent rich in volatility and applied, the coating surface dries quickly, whereas the coating agent that has entered the eyes of the sponge dries. This is because the difference in the degree of dryness causes strain and disturbs the surface shape. When the organic solvent in the eyes of the sponge volatilizes after the coated surface has dried to some extent, the volatilized gas expands like a balloon and breaks through the surface film.
The pimple surface might have a dimple shape or a crater shape.

Therefore, when the photosensitive member is charged by this charging member, the black dot or the white dot image defect as described above occurs.

Further, when a sponge roller having a skin layer is molded, since foaming is generally performed in the mold during molding, unevenness in foaming tends to occur due to temperature distribution, pressure distribution, etc. in the mold. May cause uneven hardness.
Such unevenness in hardness may lead to non-uniform contact between the photosensitive member and the charging member, which may cause a problem that the charging sound is accompanied by the rotation of the charging roller.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a charging member having a smooth surface and a charging device including the charging member.

Another object of the present invention is to provide a charging member and a charging device that charge a body to be charged well.

Another object of the present invention is to provide a charging member and a charging device with reduced charging noise.

[0017]

The present invention is characterized in that the charging member in contact with the member to be charged has a functional layer containing an aqueous polymer compound.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment in which the charging device according to the present invention is mounted on an image forming apparatus such as a copying machine.

The OPC photosensitive drum 1 as the member to be charged is
It is rotatably supported by a pair of bearing members 3 and 3 via a shaft 2. The shaft 2 is electrically connected to a conductive base made of aluminum or the like which holds the photosensitive layer of the photosensitive drum 1,
It is also grounded (E).

A charging roller 4 as a charging member is in contact with the surface (charged surface) of the photosensitive drum 1. The charging roller 4 is rotatably held by a pair of bearing members 6, 6 via a conductive rotating shaft 5 made of metal or the like, and is attached to the photosensitive drum 1 by a coil spring 7 attached to a fixing member 8. It is constantly pressed at a predetermined pressure. Reference numeral 9 is a power source for applying a charging voltage to the charging roller 4 via the conductive rotating shaft 5.

An example in which an image is output by using the charging roller 4 is shown below. FIG. 2 shows a charging roller 4 according to the present invention.
FIG. 3 is a schematic view of a printer equipped with the.

The photosensitive drum 1 is an OPC, and is formed by coating a photo-organic conductive agent on an aluminum drum having a diameter of 30 mm.

A process speed of 2 on the photosensitive drum 1.
Image formation is performed at 4 mm / sec.

As the voltage applied to the charging roller 4, an oscillating voltage obtained by superimposing a DC voltage corresponding to a desired dark portion potential Vd with an AC voltage of 2000V peak-to-peak voltage for uniform charging is used. By performing the AC charging, it is possible to stably charge the surface potential of the photosensitive drum 1 uniformly to Vd irrespective of dirt on the charging roller 4, environmental changes, and the like.

After being uniformly charged by the charging roller 4, the portion of the photosensitive drum 1 which has been image-exposed by the laser beam 17 whose intensity is modulated according to the image signal is discharged. In the developing section, the developing device 21 performs reversal development with the one-component magnetic toner and visualizes the exposed portion with the toner. Here, the jumping development method is used.

The toner image is transferred to the transfer roller 22 of the next transfer portion.
At the transfer material P. In the printer of this embodiment, the transfer roller 22 to which a voltage of 3 KV is applied is used as the transfer charging device.

After the transfer, the residual toner on the photosensitive drum 1 is removed by a cleaner 23 having a counter blade made of urethane rubber.

After that, the toner image on the transfer material P is fixed by the thermal fixing device 25 and discharged to the outside of the apparatus main body.

In the above structure, when the photosensitive drum 1 of FIG. 1 is rotationally driven in the direction of arrow a in FIG. 1 by a driving means (not shown), the charging roller 4 contacts the photosensitive drum 1 at a predetermined pressure in the direction of arrow b. The surface of the photosensitive drum 1 is uniformly and uniformly charged by being driven to rotate and applying a voltage from the power source 9 to the charging roller 4. As the applied voltage, for example, by applying an oscillating voltage in which a DC voltage of −700 V is superimposed with an AC voltage of 1500 to 2500 V (peak-to-peak voltage) and a frequency of 500 Hz, the surface of the photosensitive drum 1 becomes −7.
It is charged to about 00V. The oscillating voltage is a voltage that periodically changes, and the waveform of the oscillating voltage can be a sine wave, a triangular wave, a rectangular wave, or the like. Further, the oscillating voltage may be a rectangular wave formed by repeating ON / OFF of the DC power supply.

The peak-to-peak voltage of the oscillating voltage is at least twice as large as the charging start voltage value (the applied DC voltage value at which the charging of the member to be charged starts by applying the DC voltage to the charging member). It is desirable because the effect of leveling the potential of the body to be charged can be obtained. The charging start voltage of the OPC photosensitive drum of this embodiment was about -600V.

In this embodiment, the process cartridge 12 detachable from the image forming apparatus comprises the photosensitive drum 1, the charging roller 4, the developing device 21, and the cleaner 23, but at least the photosensitive drum 1 and the charging roller 4. I'm good.

Example 1 In this example, as a contact charging member, an elastic sponge roller of medium resistance was coated with a resistance layer to form a two-layer charging roller, and a water-based urethane resin was doped with antimony as a coating agent for the resistance layer. The material is characterized in that SnO ₂ which has been subjected to the conductivity treatment and uniformly dispersed is used as the material.

As the contact charging member, there are other blade-shaped charging blades, charging brushes, charging cloths, sponges, and charging portions having non-uniform surface properties such as sponges. When coating the surface, it is possible to use the coating material prepared by the above-mentioned method, and the following invention is not limited to the case of being applied to the charging roller.

FIG. 3 shows the structure of the sponge charging roller of this embodiment.

A medium resistance sponge roller 4b is formed on a core metal 4a having a diameter of 6 mm. When defects such as pinholes occur on the photoconductor, excessive current will flow if the resistance value of the sponge layer is low, preventing the sponge from generating heat and burning, and also the charging required for charging. Since it is necessary to pass an electric current, the resistance value of the sponge roller is 10 ⁴ to 10 ⁸ Ω.
It must be in the cm range.

The material of the sponge is EPDM. 5 to 15 parts by weight of Ketjen black is added to give conductivity to the sponge, and AD is used as a foaming agent for foaming during vulcanization.
5 to 10 parts by weight of CA is added. This rubber is extruded into a tube shape, and is subjected to primary vulcanization by a steam vulcanization method to form a foam, and then subjected to secondary vulcanization.

The tube thus formed has a non-uniform surface, and the foaming in the vicinity of the surface is unstable, and there are many foaming irregularities and hardness irregularities, so the surface is polished to obtain a sponge roller having a diameter of 12 mm.

The resulting sponge roll has a physical property value of a foaming diameter of 100 μm and an ASKERC hardness of 35.
It became °.

Next, the surface property of the contact charging member is made uniform to prevent discharge unevenness, and further, a resistance layer 4c is coated in order to prevent leakage to pinholes on the photosensitive member. The volume resistivity of the resistance layer 4c is preferably 10 ⁵ to 10 ⁹ Ωcm.

Before coating, a primer treatment was performed with a silane coupling agent in order to ensure the adhesion between the sponge surface layer and the coating layer.

When a conventional general solid type charging roller is prepared, various polymer compounds such as nylon, polyester and urethane dissolved in an organic solvent are used as binders for the coating material. However, when this is applied to a substrate with a sponge-like surface and dried with hot air, distortion due to the difference in the drying speed of the paint that entered the surface layer of the sponge and foaming eyes, and paint that entered the eyes The problem that the coated surface is not smooth due to the generation of bubbles when the solvent is vaporized.

In order to solve such a problem, the present embodiment is characterized in that a water-based binder, which is relatively slow to dry, is used as a coating agent for the resistance layer. Specifically, the water-based urethane paint Adekabon Titer HUX-232 manufactured by Asahi Denka Co., Ltd. was used.

Further, conductive fine particles are dispersed in the binder in order to adjust the coating material to a suitable volume resistance value as a resistance layer. In the present embodiment, tin oxide fine particles which are antimony-doped and subjected to a conductive treatment are used as the conductive fine particles. This is because when conductive particles having a low volume resistance value of about 10 ⁰ to 10 ¹ Ωcm, such as carbon black, are used, the volume resistance value of the coating material largely fluctuates with respect to the added amount, which affects stability of resistance control. This is because it is preferable to use a powder having a relatively high volume resistance value of about 10 ¹ Ωcm.

When the dispersibility of the conductive fine particles in the paint is poor, a minute insulating region is formed on the surface of the charging member, which may cause defective charging of the photoconductor at a position corresponding to this. In the examples, a paint shaker was used as a disperser to perform dispersion for 12 hours. The amount of tin oxide dispersed in the coating liquid is 60% by weight.

At this point, the viscosity of the solution is 200-300C.
It is PS.

The paint thus prepared is applied to the surface of the sponge roller. In this embodiment, the dipping coating method was used as the coating method, but other than this, a roll coating method, a beam coating method or the like can be appropriately used.

The conditions for the dipping coating were as follows: the sponge roller was pulled up in the above-mentioned solution at a speed of 30 mm / sec, and the roller was turned upside down to obtain a coating film thickness of about 80 μm. I applied it again. It is possible to reduce the difference in coating film thickness between the upper and lower sides of the roller by performing the coating by reversing in this manner.

The coated roller was dried in a hot air drying oven at 120 ° C. for 1 hour.

The roller thus produced had a uniform surface property, and there were no surface defects that caused a sand image.

When the image was formed by the AC charging method (applied voltage DC: -700 V, AC: 500 Hz, 2000 Vpp sine wave) with the sponge charging roller thus prepared, a high temperature and high humidity environment, a low temperature and low humidity environment, etc. were obtained. It was confirmed that the photoreceptor can be uniformly charged to −700 V under all the environments including the above, and that the charging performance can be obtained which is completely equivalent to that of the solid type charging roller.

As a comparative example, an example in which a sponge roller prepared by the same method as described above is coated with a solvent-based paint will be briefly described.

As the binder of the coating agent, toluene and IPA are used as a solvent, and trade name Sampren IB-104 is used. Tin oxide is dispersed in the same dispersion method as above to coat, and hot air is applied at 120 ° C. for 1 hour. A sponge charging roller was dried to produce a sponge charging roller, which had good surface properties at the time of coating, but the surface condition deteriorated due to the drying process, resulting in a rough surface with Rz of 20 μm or more. The generated crater-shaped dimples became a significant surface defect.

An image was formed by the AC charging method using such a charging roller, but even if the bias condition for the AC charging was optimized, it was not possible to eliminate the sand image under the normal environment.

As described above, in the case of using the sponge type base layer, the occurrence of surface defects due to drying can be prevented only by using an aqueous binder as the material of the coating agent.

This is because when a surface of a contact charging member having a sponge surface is coated with a water-based paint, the water as a dispersion medium dries more slowly than when an organic solvent is used. This is because the uniform surface property of the contact charging member can be obtained without disturbing.

Furthermore, it is possible to coat with a high-viscosity coating liquid when coating with a water-based paint, and since overcoating is easy, the coating film thickness can be increased. It also has advantages such as easy control of the film thickness.

Although it is usually difficult to uniformly disperse the fine powder particles in the binder, in the present invention, a water-based binder is used, and a conductive oxide is added to an aqueous dispersion medium whose pH value is adjusted. By mixing and coating a dispersion liquid in which a metal oxide such as tin is uniformly dispersed, it becomes possible to easily prepare a coating material in which conductive particles are uniformly dispersed, as compared with the conventional case. In this method, the conductive fine particles are uniformly dispersed in the paint, which makes it possible to eliminate the charging failure in the minute area, which was apt to occur due to the uneven dispersion in the conventional method. .

Example 2 In this example, the same charging roller as in Example 1 was used as the contact charging member except for the coating agent, and an aqueous binder was used as the coating agent and water was previously dispersed as the conductive filler in water. It is characterized in that a tin oxide slurry is mixed and used.

In the first embodiment, a mechanical dispersion method such as a paint shaker or a ball mill was used as a method for dispersing tin oxide in a water-based binder as a coating agent. However, when such a method is used, dispersion is performed. However, it is difficult to ensure the stability of the dispersion, and it is inevitable that the dispersion state changes depending on the storage, transportation, manufacturing conditions of the tin oxide powder, the temperature of the solvent during dispersion, and the like.

Further, since the aqueous binder stabilizes the binder in an emulsion state in water with an emulsifier or the like, when the dispersion is carried out with a high shearing force, the solution is gelated during the dispersion. There was a possibility that it would end up.

In order to solve these problems, in this embodiment, a liquid in which tin oxide is stably dispersed in water whose pH value has been adjusted beforehand is used as a conductive filler, and this is mixed with an aqueous binder. It is characterized in that a coating agent is prepared by.

As such a slurry and sol, tin oxide sol and titanium oxide sol manufactured by Taki Chemical Co., Ltd. are known, but in addition to this, a conductive filler is stabilized in a dispersion medium that can be mixed with water by the same method. It is possible to use dispersed ones.

A specific example is shown below.

The binder of the coating agent is the water-based urethane paint HUX-232 manufactured by Asahi Denka Kogyo Co., Ltd. used in the first embodiment. A slurry in which tin oxide, which has been made conductive by doping treatment with antimony, is stably dispersed in water whose pH is adjusted to 4 to 6 with an alkali such as ammonia or sodium hydroxide is mixed as a conductive filler.

The mixing ratio of the urethane paint and the conductive filler is
The conductive fillers are mixed with each other in a weight ratio of 60% with respect to the solid content of the urethane paint. As a mixing method, the conductive filler can be uniformly dispersed in the urethane resin by simply mixing them with a stirrer or the like, but an appropriate disperser can also be used appropriately.

Under the conditions used in this example, the viscosity of the mixed solution became 200 cps.

The coating liquid thus prepared is coated on a medium resistance sponge roller by the same method as in the first embodiment to prepare a charging roller. Since the concentration of the mixed liquid is different from that of the first embodiment, the pulling speed was 20 mm / sec by the dipping coating method to apply the resistance layer with the same coating thickness of about 80 μm, and the roller was turned upside down twice. Coating was performed.

As described above, in the method of preparing the coating liquid by mixing the materials having water as a solvent and dispersion medium, it is possible to uniformly disperse the conductive filler without using shearing force.
It is also possible to mix and use a plurality of binders having different physical and chemical properties.

For example, HUX-232 has the characteristics that it is less likely to contaminate the photoconductor and has a strong film strength.
On the contrary, there is a problem that the hardness of the film is high and the hardness of the roller becomes high when molded as a roller, and the charging noise becomes large. On the other hand, the same water-based urethane paint HUX-290H has the characteristic that the film is soft but a flexible coat film can be formed, although it has some stains on the photoreceptor.

As a result of repeated experiments, the present inventor found that HUX-2
A mixture of 32 and HUX-290H in a weight ratio of 3: 7 can achieve both the flexibility of the film and the stain resistance to the photoconductor, suppresses the generation of charging noise, and has no adverse effect. I found that you can create.

In addition to the above, there are other water-based binders such as ACRYSET manufactured by Nippon Shokubai Co., Ltd. and BYRON manufactured by TOYOBO. Each of them is mixed alone or in order to effectively use each characteristic. Can be used.

As described above, in this example, the aqueous binder polymer compound was mixed with the conductive filler which was previously stably dispersed in water to prepare the coating liquid for the resistance layer of the contact charging member. Can be easily and uniformly dispersed in the coating liquid. Further, since the conductive filler can be dispersed without using a shearing force, a coating liquid can be stably prepared without changing the emulsion state of the binder solution.

Example 3 This example is characterized in that when a functional layer is coated on an elastic sponge type contact charging member, an aqueous ion conductive material is used as the coating material.

In the first and second embodiments, a water-based insulating binder in which a conductive filler is dispersed to adjust the resistance value is used as the coating material.

These materials are advantageous in that there is wide room for selection of the material because the electric resistance value of the binder may be insulating and there is little environmental change in the resistance value after the resistance value is adjusted by the conductive filler. There is.

However, since the conductive filler is dispersed in the coating material, there are problems that the resistance value may fluctuate due to the manufacturing conditions, the hardness of the film becomes high due to the reinforcing effect of the filler, and the dispersion takes time. Was.

As a method of solving this, in the present embodiment, an ion conductive polymer compound having a specific resistance of a substance suitable as a resistance layer is used as a coating material. Specifically, the characteristic of the coating material is that it is water-based in order to coat the sponge substrate uniformly, and its volume resistivity value is 10
^{It is 6} to 10 ⁹ Ωcm, and the film must be soft.
The volume resistivity of the sponge layer is 10 ⁴ to 10 ⁸ Ωcm.

Generally, in order to satisfy such characteristics, a functional group having a strong cathodic property is introduced into a polymer compound,
Alternatively, urethane, acrylic resin or the like having a polyether bond is used, and in addition, Nal, LiClO ₄ , K
An alkali metal salt such as SCN or NaSCN is added to give conductivity.

In the present embodiment, the contact charging member was constructed by using Reolex ASE-720 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as such a material, but this material does not limit the scope of the present invention. It is also possible to use a polymer compound similar to the above.

ASE-720 has a resin volume resistance value of 10
It is about ⁸ Ωcm, and by coating the roller of the sponge substrate, it becomes possible to obtain an appropriate resistance value as a contact charging member. Specifically, the medium resistance sponge roller used in the first embodiment was coated by a roll coating method to form a resistance layer having a thickness of 100 μm. The test was carried out by drying this with hot air drying at 120 ° C. for 1 hour.

The roller thus prepared had a hardness of 35 °, a roller resistance value of 10 ⁶ Ωcm in a normal environment, and a surface roughness of Rz.
The value was about 5 μm, and the surface of the roller was smooth without unevenness or dimples. This is due to the effect of coating with a water-based material. As a comparative example, when coating with a solvent-based urethane resin, epichlorohydrin rubber, etc., surface defects occur during drying and a good charging member is obtained. It was difficult to secure the surface property.

Using this roller, the photoreceptor was charged by the CD charging method. When a charging roller was pressed against the photosensitive drum having a photosensitive layer with a thickness of 25 μm with a total weight of 500 g and a DC voltage of −1300 V was applied, the surface of the photosensitive member was uniformly charged to −700 V, and reversal development was performed. As a result, no charging defects such as black spots and sand were observed, and no image defects due to abnormal charging occurred.

In addition to this, when an ion conductive material is used for the surface of the contact charging member, ions, polymer compounds, etc. may be deposited and exude on the surface in a high temperature and high humidity environment to cause contamination of the photoreceptor. However, in the structure of this example, since the water-based coating is previously performed on the sponge substrate to form a uniform surface, it is possible to apply another coating as a protective layer thereon.

Specifically, the above-mentioned A of the ion conductive system is used.
By coating the SE-720 coat with about 10 μm of methoxymethylated nylon (trade name: resin resin manufactured by Teikoku Kagaku), a contact charging member capable of obtaining stable characteristics in all environments can be constructed. I can do it now.

At this time, even if the sponge substrate is directly coated with methoxymethylated nylon to form a charging roller, methoxymethylated nylon is a solvent-based coating material in which the solvent is methyl alcohol, so that a uniform coating is obtained. Needless to say, the surface property cannot be obtained, and it is necessary to once coat the sponge substrate with a water-based binder to ensure a uniform surface property.

As described above, the method of coating a material having an aqueous binder on the coating layer in contact with the sponge to obtain a smooth surface and then coating another functional layer is described in this embodiment. The material is not limited to such an ion conductive material, and it is also possible to use a dispersion material in which the conductive filler as described in the first and second embodiments is dispersed.

As described above, in this embodiment, by using the material which is water-based and has ion conductivity, the resistance value at the time of production is suppressed from varying and the contact charging is performed by a single material which does not disperse the conductive filler. Members can now be constructed.

Embodiment 4 This embodiment is characterized in that an elastic sponge-like transfer roller of an electrophotographic apparatus as a contact charging member is coated with an aqueous material.

The transfer roller of the electrophotographic apparatus is a member for transferring a toner image on an image bearing member such as a photoconductor, an intermediate transfer member, or a transfer drum onto a transfer paper, and electrostatically applying a voltage. Transfer.

The required characteristic is a resistance value (medium resistance, 1
0 ⁵ to 10 ⁹ Ω), low hardness to prevent image dropout that occurs when transfer pressure is high, and high separation to easily clean excess toner adhered to the transfer roller surface. Moldability is required.

In order to satisfy such characteristics, particularly low hardness, it is general to use a sponge roller having a medium resistance, and carbon, zinc oxide or the like is dispersed in EPDM, CR, urethane or the like to be foamed. A sponge roller is used.

However, such a rubber material is not basically said to have good releasability from the toner, and it is difficult to completely remove the toner once attached to the roller even if cleaning by an electric field is performed. Occasionally, the back surface of the transfer material was stained.

Especially when a transfer roller is applied to a copying machine, toner may be directly transferred onto the transfer roller without passing through the transfer material when the size of the copy original is different from that of the transfer material. It was necessary to enhance the cleaning property of the transfer roller in order to prevent the backside of the transfer material from being smeared during the image formation.

Therefore, in this embodiment, while using a sponge roller having a low hardness, the surface of the transfer roller is coated with an aqueous material in order to improve the toner cleaning property.

In order to improve the cleaning property with respect to the toner, there are means such as smoothing the surface of the sponge and coating with a material having a good releasability. However, in order to realize the former, in the above-mentioned embodiments. As mentioned above, coating with an aqueous material is a necessary condition. For this reason, in this embodiment, the water-based urethane paint HUX-232 described in the first embodiment is used as the coating material, and tin oxide is dispersed therein to adjust the resistance value, and Teflon particles are dispersed to further improve the releasability. Let

A method of manufacturing the transfer roller in this embodiment will be specifically described.

Since the transfer roller has a higher resistance value than the charging roller, the resistance value of the base layer sponge roller is set to 10 ⁸ Ω. This is prepared by dispersing Ketjen black, which is carbon, and zinc oxide in EPDM to adjust the resistance value and foaming them.

The coating material is HUX-232, tin oxide, and Teflon particles in a solid content weight ratio of 100: 60:
It was mixed at a ratio of 10 and dispersed for 12 hours with a paint shaker.

The coating material thus obtained was actually applied in the form of a sheet by the barcode coating method, and the volume resistance value was measured and found to be about 10 ⁸ Ωcm.

This was coated on a sponge roller under the same conditions as in the first embodiment and dried to form a transfer roller. The completed transfer roller has a smooth surface property with a surface roughness Rz value of 10 μm or less, and since Teflon particles are further mixed therein, high releasability can be secured.

As a comparative example, Table 1 below shows an example in which a transfer material and a cleaning property are compared by using a sponge roller coated with a coating material prepared from a solvent type binder and a sponge roller alone.

[0103]

[Table 1]

As described above, it can be seen that the cleaning property is improved as the uniform coating is performed, as compared with the sponge alone. Further, when coating is performed using a solvent-based binder as a material, large surface defects in the form of craters and dimples that occur during drying cause transfer defects, resulting in defective images.

As described above, in this embodiment, the transfer roller surface is uniformly coated to improve the cleaning property of the transfer roller, and by using the water-based material, the uniform roller surface can be easily realized. As a result, it is possible to configure a transfer roller having high cleaning performance without any adverse effect such as transfer omission.

[0106]

As described above, by using the functional layer containing the water-based polymer compound in the charging member of the present invention, uniform coating can be performed.

As the material for this functional layer, an aqueous polymer compound and a slurry in which a conductive filler such as tin oxide is stably dispersed in a dispersion medium such as water in advance are mixed to obtain a conductive filler. It has become possible to prepare a coating liquid that is uniformly dispersed.

As a result, it becomes possible to easily produce a softer contact charging member in which the conductive filler is uniformly dispersed and the resistance value is uniform and the surface property is uniform.

[Brief description of drawings]

FIG. 1 is a perspective view of a charging device of the present invention.

FIG. 2 is a schematic sectional view of an image forming apparatus to which a charging device can be applied.

FIG. 3 is a sectional view of a charging member.

[Explanation of symbols]

 1 Photoreceptor 4 Charging Member 4a Core Bar 4b Foam 4c Coating Layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Jun Murata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (14)

[Claims] 1. A charging member capable of contacting a charged body and charging the charged body, comprising a functional layer containing an aqueous polymer compound. 2. The charging member according to claim 1, wherein the charging member has a foam layer inside the functional layer. 3. A charging device having a charging member that can be contacted with a member to be charged and to which a voltage is applied to charge the member to be charged, wherein the charging member includes a functional layer containing an aqueous polymer compound. A charging device characterized by the above. 4. The charging device according to claim 3, wherein the charging member has a foam layer inside the functional layer. 5. The charging device according to claim 4, wherein the foam layer is an elastic body. 6. The charging device according to claim 3, wherein the functional layer has a conductive filler dispersed therein. 7. The functional layer comprises a mixture of a liquid in which a conductive filler is dispersed in water or a dispersion medium which can be mixed with water in advance, and the polymer compound. Charging device. 8. The charging device according to claim 6, wherein the conductive filler is a metal oxide. 9. The charging device according to claim 8, wherein the conductive filler is tin oxide. 10. The charging device according to claim 3, wherein the charging member has a roller shape. 11. The charging device according to claim 3, wherein the voltage is an oscillating voltage. 12. The charging device according to claim 3, wherein the member to be charged is an image carrier. 13. The charging device according to claim 3, wherein the member to be charged is a transfer material, and the charging member transfers the image of the image carrier to the transfer material. 14. The charging device according to claim 12, wherein the charging member and the image carrier are provided in a process cartridge that can be attached to and detached from the image forming apparatus.