JPH09211932A - Electrostatic charging member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging member which is free from unequal electrostatic charges and which is capable of executing a uniform electrostatic charge treatment on a member to be electrostatically charged by lessening the change in the resistance value of a resistance control layer based on an environmental change as far as possible. SOLUTION: This electrostatic charging member electrostatically charges the surface of the member to be electrostatically charged by impressing voltage on the surface of the member to be electrostatically charged, such as photoreceptor, in the state of pressing the charging member to thereto. This electrostatic charging member 1 consists of a conductive substrate 1a, a conductive elastic material layer 1b fixed to this substrate 1a and the resistance control layer 1c covering this elastic material layer 1b. The resistance control layer 1c is constituted by dispersing conductive carbon black having an oil absorption rate within a range of 30 to 300ml/100g into a urethane resin consisting of diisocyanate and polyol having the average hydroxyl group number per molecule in a range of 2.1 to 2.5 as constituting components.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to a charging member in an image forming apparatus such as an electrophotographic apparatus such as a printer, a facsimile, or a composite OA apparatus thereof, or an electrostatic recording apparatus. More specifically, the present invention relates to a charging member that presses against a surface of a charged body such as a photoreceptor or a dielectric to uniformly charge the surface of the charged body.

[0002]

2. Description of the Related Art In a conventional charging process in an electrophotographic process using, for example, an electrophotographic photosensitive member as a member to be charged, most charging is performed by corona discharge generated by applying a high voltage of 5 to 8 kV DC to a metal wire. The method of doing is adopted. However, with this corona discharge method,
Corona products such as ozone and nitric oxide (NOx) generated at the time of charging react with the photoconductive material and change the surface of the photoconductor, causing deterioration of the photoconductor and image blurring, and wire contamination. Affects the image quality, and there is a problem that white spots and black streaks occur in the image. In addition, the current flowing to the photoconductor is only 5 to 30% of the whole, and most of the current flows to the shield plate, so that there is a drawback that the charging unit has poor power efficiency. In order to eliminate such drawbacks,
A so-called direct charging method, in which a photosensitive member is charged by applying a voltage to a charging member arranged in contact with the photosensitive member, has been noticed and put into practical use. For example, JP-A-57-6475
No. 3, JP-A-58-40566 and JP-A-58-139156, block-shaped contacts using a woven fabric coated with a resin in which conductive particles are dispersed as an electric resistor as a charging member, A roll-shaped charger in which fibrous electrode groups are implanted and a plurality of roll-shaped contacts in which the applied voltage is increased toward the downstream side are disclosed. However, these direct charging methods actually have a problem that spot-shaped image defects due to uneven charging and stripe-shaped or strip-shaped image defects due to dielectric breakdown of the photoconductor occur.

Further, as an elastic layer fixed to the outer periphery of the conductive support, conductive powder such as carbon black is dispersed in an elastomer such as silicone rubber, urethane rubber, ethylene propylene diene rubber (EPDM) and norbonene rubber. 2. Description of the Related Art Conventionally, a charging roll in which a surface layer is coated on the charging roll has been used. For example,
JP-A-64-66674 and JP-A-64-66
No. 676, in order to prevent non-uniform charging of the elastic layer containing conductive powder and contamination of the photoreceptor, it is itself formed of conductive or semi-conductive N-methoxymethylated nylon. A conductive roll coated with a surface layer has been proposed. However, in these charging rolls, the charging ability of the charged body such as the photoconductor greatly changes due to the change of use environment, especially the change of humidity in the atmosphere, and the charging ability is extremely lowered in the low temperature and low humidity environment. There was a problem such as. If the charging ability decreases, the charged body will not be charged uniformly,
The density of the formed image is reduced, and in the reversal development method, a dot-shaped black dot image (black spots) corresponding to uneven charging is formed, and in the regular development method, a white spot image (white spots) is formed. Further, in a high-temperature and high-humidity environment, a leak occurs between the charging member and the body to be charged, and a black belt-shaped image defect occurs. It is difficult to obtain high-quality images under any environment,
There was a problem of poor environmental stability. Further, for example, JP-A-2-49066 and JP-A-2-51562.
The publication discloses a conductive resin composition in which a conductive or semiconductive polypyrrole is itself distributed in a matrix resin, and a film obtained by polymerizing this resin composition is used as a surface layer. Sex rolls have been proposed. However, when these rolls are applied to a charging roll, like the N-methoxymethylated nylon described above,
It was not satisfactory in terms of environmental stability.

[0004]

As described above, in the conventional charging member, the charging ability of the member to be charged is remarkably lowered due to the change in the environment, and the image density is lowered, or the charging member and the member to be charged are changed. There is a problem that an image quality defect such as a leak occurs between them. Therefore, an object of the present invention is to solve the above-mentioned problems, and by minimizing the change in the resistance value of the surface layer due to the change in the environment, there is no charging unevenness and the charged object Another object of the present invention is to provide a charging member that can perform uniform charging processing.

[0005]

The inventors of the present invention have conducted extensive studies to improve the instability of electric characteristics with respect to changes in the environment of a charging member used in an image forming apparatus. As the surface layer for adjusting the electric resistance of the, when the elastic body layer forming the underlayer is covered with the urethane resin having a three-dimensional structure of carbon black dispersion having a predetermined oil absorption amount, the environmental stability of the electric characteristics is significantly increased. It has been found that the present invention is improved and the present invention has been completed.
That is, the charging member of the present invention is a conductive member that applies a voltage to charge the surface of the body to be charged while being pressed against the surface of the body to be charged, and the conductive member is a conductive support, It is composed of a conductive elastic layer fixed to the support and a resistance adjusting layer covering the elastic layer. The resistance adjusting layer has a diisocyanate and an average number of hydroxyl groups per molecule of 2.1 to 2.
It is characterized in that conductive carbon black having an oil absorption of 30 to 300 ml / 100 g is dispersed in a urethane resin having a polyol in the range of 5 as a constituent component.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
When the charging member of the present invention is used as a charging roll,
As shown in FIG. 1, a conductive elastic body layer 1b is fixed to the outer peripheral surface of a cylindrical or hollow cylindrical conductive support body 1a, and the entire surface of the elastic body layer 1b is covered with a resistance adjusting layer 1c. It is composed of a flexible member. Further, a voltage is applied between the conductive support 1a of the charging member 1 and the body to be charged (for example, the photoconductor 11 shown in FIG. 4). The conductive support functions as an electrode and a support member of the charging member, and includes, for example, a metal or alloy such as aluminum, copper alloy, and stainless steel, iron plated with chromium, nickel, or the like, synthetic resin, or the like. It is made of a conductive material. The outer diameter of the conductive support is usually in the range of 4 to 12 mm.

[0007] The conductive elastic layer has a predetermined resistance value and a predetermined hardness so that the charging member can be uniformly charged by pressing the charging member against the surface of the charging member with an appropriate nip width or nip pressure. It is provided to fit in. This elastic layer is formed by dispersing conductive particles in a rubber material. Examples of the rubber material include isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, silicone rubber, fluororubber, SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), EPDM, acrylonitrile-styrene-butadiene rubber, and the like. Blend materials of Among them, silicone rubber and EPDM are preferably used. Examples of the conductive particles include various conductive metals or alloys such as carbon black, graphite, aluminum, and stainless steel, tin oxide, indium oxide, titanium oxide, tin oxide-antimony oxide solid solution, tin oxide-indium oxide solid solution, and the like. Fine powders of various conductive metal oxides can be used. The thickness of the conductive elastic layer is
Usually, it may be in the range of 1 to 5 mm, preferably in the range of 2 to 4 mm. Further, the volume resistance value of the conductive elastic layer is closely related to the volume resistance value of the resistance adjusting layer described later, but it is preferably in the range of 10 ² to 10 ¹⁰ Ωcm. If the volume resistance value is less than 10 ² Ωcm, excess current flows on the surface of the member to be charged, which leads to dielectric breakdown (leakage). On the other hand, when the volume resistance value is larger than 10 ¹⁰ Ωcm, the chargeability is small and image quality defects occur.

The resistance adjusting layer is provided to adjust the charging member to a predetermined resistance value, and is formed of a thin film in which conductive carbon black is dispersed in a polymer of a diisocyanate component and a polyol component. Examples of the diisocyanate component include hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tridiene. Diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-
Diphenyl diisocyanate, 4,4'-diphenyl diisocyanate, o-tolidine diisocyanate, m-
Examples thereof include trisine diisocyanate, 3,3′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, and a prepolymer of a diisocyanate compound having an isocyanate group at the terminal and a polyol. These diisocyanate components can be used alone or in combination of two or more.

As the polyol component, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol,
Dipropylene glycol, tripropylene glycol,
Cyclohexanediol, dimethylolcyclohexane, hydrogenated bisphenol A, hydrogenated bisphenol F, and other diols, glycerin, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, and other triols, pentaerythritol, sorbitol, and other tetravalents The above polyols and the like can be mentioned. In addition, polyalkylene glycol such as tetramer or more polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc., polyether polyol such as polyalkylene glycol copolymer such as poly (oxyethylene-oxypropylene) glycol, terminal or side chain To 2
Examples thereof include saturated polyesters having one or more hydroxyl groups, ε-caprolactone ring-opening polymers having hydroxyl groups at the ends, and polyester polyols such as polycarbonate polyols obtained from ethylene carbonate and hexamethylene glycol.

These polyol components have an average number of hydroxyl groups per molecule in the range of 2.1 to 2.5, and a mixture of a divalent polyol and a trivalent or higher polyol is used at an appropriate ratio. To be For example, divalent polyol and 3
When a mixture with a divalent polyol is used, about 0.11 to 1 of the trivalent polyol is added to 1 mol of the divalent polyol.
When mixed in a molar range, the average number of hydroxyl groups per molecule is adjusted to a polyol component of 2.1 to 2.5. Since the proportion of the urethane resin having a three-dimensional structure is small in the polyol component having an average number of hydroxyl groups of less than 2.1,
The conductive carbon black cannot be dispersed sufficiently uniformly. As a result, uneven charging may occur on the charged body to be charged, and the resistance value of the resistance adjusting layer greatly changes with environmental changes. In particular, it is preferable to use a polyol component having an average number of hydroxyl groups of 2.2 or more because the charging unevenness and the environmental dependence of the resistance value are significantly improved as compared with the conventional ones. When the average number of hydroxyl groups in the polyol component is more than 2.5, the affinity between the ketone-based or ether-based solvent generally used as a solvent for urethane resin and carbon black becomes too strong, resulting in dispersion of carbon black. In addition to deteriorating the properties, a one-component urethane resin, which lacks paint suitability as a coating liquid for forming the resistance adjusting layer, cannot be used.

The conductive carbon black dispersed in the resistance adjusting layer has an oil absorption of 30 to 300 ml / 100 g. That is, with carbon black having an oil absorption of less than 30 ml / 100 g, it is difficult to impart a predetermined conductivity to the resistance adjusting layer because of its short structure length. Also,
In the case of carbon black having an oil absorption of more than 300 ml / 100 g, the amount of compounding required to give a predetermined resistance value is small, so that the resistance value of the resistance adjusting layer varies widely. In addition,
The oil absorption of carbon black in the present invention is determined by ASTM
The value determined according to the measuring method shown in D1510. The volume resistance value of the resistance adjusting layer is 10 ⁵ to 10 ¹¹ Ω
It is preferably in the range of cm. Volume resistance value is 10 ⁵ Ω
If it is less than cm, an excessive current flows on the surface of the member to be charged, and if a pinhole is present on the surface of the member to be charged, leakage is likely to occur. On the other hand, when the volume resistance value is larger than 10 ¹¹ Ωcm, it becomes difficult to charge the body to be charged at a low voltage, and an image quality defect occurs due to insufficient charge amount.

The thickness of the resistance adjusting layer is preferably in the range of 5 to 100 μm, more preferably 20 to 50 μm. When the film thickness is thinner than 5 μm, not only the function as the resistance adjusting layer cannot be sufficiently exhibited, but also the surface of the body to be charged easily leaks. On the other hand, the film thickness is 100 μm
If it is thicker, the resistance value and hardness of the charging member increase more than necessary. The volume resistance value of the charging member is preferably in the range of 10 ⁵ to 10 ¹⁰ Ωcm so that the above-mentioned inconvenience does not occur. This can be adjusted within the above range by appropriately combining the volume resistance value of the conductive elastic layer and the volume resistance value and film thickness of the resistance adjusting layer.

The charging member of the present invention is manufactured, for example, as follows. First, a rubber material, conductive particles, and an appropriately mixed compounding agent such as a softening agent, a cross-linking agent (including a vulcanizing agent and a vulcanization accelerator), a non-conductive filler, etc. are kneaded to obtain an elastic body. A rubber composition for forming a layer is prepared. Then, the above rubber composition is injected into a mold supported mainly by the conductive support (1a) by an extrusion molding method, an injection molding method, or the like, and generally 100 depending on the type of the rubber material and the compounding agent. ~ 2
Heat at 00 ° C. for 5-90 minutes. During this time, the crosslinking reaction of the rubber material proceeds. Then, the conductive elastic body layer (1b) containing the conductive particles is taken out from the mold while being fixed to the outer periphery of the support (1a). Conductive elastic layer (1b)
The surface may be subjected to polishing treatment, if necessary. Next, a urethane resin raw material of the diisocyanate component and the polyol component, conductive carbon black, an additive such as an amine-based curing agent that is appropriately blended is added to 2-butanone, cyclohexanone, methyl cellosolve, an organic solvent such as dioxane, A resistance adjusting layer forming coating liquid is prepared by thoroughly mixing. Then, the coating solution is applied to the surface of the conductive elastic layer (1b) by an appropriate coating method such as a dipping method, an air spray method, or a roll coating method, and then dried at room temperature or by heating to form a urethane resin. A resistance adjusting layer (1c) in which carbon black is dispersed is formed. When forming the resistance adjusting layer (1c), it is preferable to use the coating liquid as a one-component urethane resin. That is, the two-component urethane resin is a functional group (isocyanate group) that is free even after curing.
There are a large number of particles in the resin, and these react with water in the air, so the charging member (1) manufactured as described above
Greatly depends on the environment. On the other hand, the one-pack type urethane resin has an advantage that it has a long molecular length and a small number of free functional groups, and thus has little environmental dependence.

As described above, the roll-shaped charging member (charging roll)
Has been described, the form of the charging member of the present invention,
It may be block-shaped or blade-shaped. As shown in FIG. 2, the block-shaped or blade-shaped charging member has a conductive elastic layer 2 whose surface is covered with resistance adjusting layers 2c and 3c.
b and 3b are fixed to the plate-like conductive supports 2a and 3a on the surface opposite to the charged body on which the charging members 2 and 3 are pressed and arranged in the thickness direction. Such a charging member is manufactured, for example, as follows. That is, the rubber material in the rubber composition is crosslinked, and the obtained conductive elastic body is cut into a desired size to form a conductive elastic body layer. Next, after a conductive support is bonded to one surface of the conductive elastic layer, the coating liquid is applied to a surface other than the bonding surface,
The resistance adjustment layer may be formed by drying. Further, the adhesion of the support and the formation of the resistance adjusting layer may be performed in the reverse order.
The charging member of the present invention can be applied to a transfer device, a static eliminator, and the like in addition to the charger. When used as a charging member in a transfer device, the charging member is pressed against a charged body such as a photoconductor through a transfer material such as paper, and its volume resistance value is 1
It is adjusted to a range of 0 ⁷ ~10 ¹⁰ Ωcm. When used as a charging member in a static eliminator, the charging member is in direct contact with the body to be charged and its volume resistance value is 10 ² to 10 ⁴ Ωcm.
It may be adjusted within the range.

(Operation of the Invention) Charging member (1-3) of the present invention
In the above, as the resin constituting the resistance adjusting layer, diisocyanate and the average number of hydroxyl groups per molecule are 2.1 to 2.5.
The urethane resin obtained from the polyol in the range of is used. Since this urethane resin partially has a three-dimensional structure, the dispersibility of the conductive carbon black is improved, and the uneven electrical resistance of the charging member is eliminated. Further, since the oil absorption of carbon black dispersed in the resistance adjusting layer is within a predetermined range, the electric resistance of the charging member can be easily adjusted. Therefore, when a voltage is applied between the charging member and the member to be charged and the member is charged while pressing the charging member against the surface of the member to be charged, uneven charging of the member to be charged does not occur. At the same time, the environmental dependence of the electric resistance of the charging member is reduced, and a good image can be stably obtained. In particular, when a one-pack type urethane resin having a small number of free functional groups is used, the environmental dependency can be significantly reduced.

[0016]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples. (Image Forming Apparatus) FIG. 3 is an overall explanatory view of an image forming apparatus incorporating the roll-shaped charging member of the present invention shown in FIG. In FIG.
Inside the main body of the image forming apparatus U, a cylindrical photosensitive member (drum) 11 rotating in the arrow direction is arranged and functions as an electrostatic latent image carrier. A laser writing device 12 that writes an electrostatic latent image on the surface of the photoconductor 11 is arranged on one side inside the image forming apparatus U main body. Around the cylindrical photoconductor 11, along the rotation direction thereof, a charger 13 for uniformly charging the surface of the photoconductor 11 in sequence, a developing device 14 for visualizing the electrostatic latent image, and a visualizing device. A transfer device 15 that transfers the formed toner image to a sheet (transfer material) and a cleaning device 16 that removes residual toner on the photoconductor 11 are arranged. The developing device 14 is a container 14 for storing toner.
a. In the container 14a, there are provided stirring members 14b, 14b for stirring toner, a rotatable developer carrier 14c, and a toner supply roller 14d for supplying toner to the carrier 14c. Developer carrier 14
c faces the opening of the container 14a and is supported by the container 14a with a slight gap from the surface of the photoconductor 11.
The cleaning device 16 has a casing 16a. A metal blade holder 16b is fixed to the casing 16a, and a sheet-like cleaning blade 16c is fixed to a tip of the blade holder 16b.
The edge of the tip of the cleaning blade 16c is in contact with the surface of the photoconductor 11.

At the lower part of the main body of the image forming apparatus U, a paper feed tray 17 for accommodating paper is arranged. Paper tray 1
A paper take-out roller 18 for taking out paper one by one from a paper feed tray 17 is arranged at an upper end portion of the upper surface 7. A pair of paper transport rollers 19 is provided above the side of the paper take-out roller 18.
A pair of paper guides 20 for guiding the paper conveyed by the printer are arranged. A heating roller 21a and a pressure roller 21b are provided on the upper side of the other side inside the image forming apparatus U body.
Is provided, and the fixing device 21
A transfer path 22 for transferring the sheet on which the toner image has been transferred is provided between the transfer device 15 and the transfer device 15. Above the fixing device 21, a pair of discharge rollers 23 and a transport path 24 for guiding the sheet on which the toner image is fixed from the fixing device 21 to the discharge rollers 23 are provided. A discharge tray 25 on which sheets discharged from the discharge roller 23 are placed is formed on the upper surface of the image forming apparatus U main body.

(Charger) FIG. 4 is an enlarged view of the main part of FIG. 3 and shows the structure of the charger. Referring to FIG.
Is provided with the roll-shaped charging member 1. Charging member 1
Is a support member 31 in which both ends of the conductive support 1a are fixed to the casing 16a of the cleaning device 16.
Supported by The charging member 1 is pressed against and contacts the surface of the photoconductor 11 by the urging forces of two pressure springs 32, one end of which is fixed to the support member 31 and the other end of which is fixed to the end of the support 1a. A metal pad holder 33 is fixed to the support member 31, and a sheet-like cleaning pad 34 fixed to the end of the metal pad holder 33 removes the toner even if it adheres to the surface of the charging member 1 very slightly. It is designed to be removed. Further, the charging member 1
A superimposed oscillating voltage is applied to the support 1a from a DC power supply 35 and an AC power supply 36 connected in series. Therefore, the surface of the photoconductor 11 rotating in a predetermined direction while being in contact with the resistance adjusting layer 1c of the surface layer is uniformly charged by the conductive elastic layer 1b and the resistance adjusting layer 1c via the support 1a. You can

The operation of the image forming apparatus U in the present invention is as follows.
It is the same as the conventional one, and will be briefly described as follows. As described above, the surface of the photoconductor 11 rotating in the direction of the arrow is uniformly charged by the charging member 1 to which the superimposed oscillation voltage is applied. Photoreceptor 11 uniformly charged
Is written with an electrostatic latent image by the laser writing device 12.
The electrostatic latent image on the photoconductor 11 is developed into a toner image by the developing device 14. The toner image is transferred to the paper feed tray 1 by the transfer device 15.
7 is transferred to a sheet conveyed from the printer 7. After the transferred toner image is fixed by the fixing device 21, the paper is discharged onto the discharge tray 25 by the discharge roller 23.
After the toner image is transferred to the paper, the photosensitive member 11
The toner remaining on the surface is removed by the blade 16c of the cleaning device to prepare for the next electrophotographic process.

Example 1 A rubber composition containing 100 parts by weight of liquid silicone rubber and 30 parts by weight of carbon black was sufficiently kneaded with an open roll. Next, SUS with an outer diameter of 8 mm
(Stainless steel) support (1a) is supported at 150 ℃
Inject the above kneaded material into a mold having an inner diameter of 14 mm preheated to
Support (1a) excluding both ends by keeping at the same temperature for 15 minutes
A roll-shaped conductive elastic layer (1b) having a thickness of 3 mm was formed on the outer periphery of the. This elastic layer (1b) is kept at normal temperature and humidity (temperature 25
When the volume resistance value was measured under the environment of (° C., 50% RH), it was 7 × 10 ⁵ Ωcm. Next, the following compositions were mixed by a ball mill to prepare a coating liquid in which carbon black was uniformly dispersed in the resin solution. The elastic layer (1b) is immersed in the obtained coating liquid, and then heated and dried to obtain a film thickness of 30 μm.
A resistance adjusting layer (1c) of m was formed. The volume resistance value of the formed resistance adjusting layer (1c) was 9.5 × 10 ⁷ Ωcm at room temperature and normal humidity. One-pack type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.3 (Barnock DF-407: manufactured by Dainippon Ink and Chemicals, Inc.) Carbon black; Oil absorption 65 ml / 100 g 5 parts by weight (Regal 660R: Cabot) 100 parts by weight of 2-butanone

Example 2 The following compositions were mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 5.2 × 10 ⁸ Ωcm. One-part type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.5 (Samprene C-810-40: manufactured by Sanyo Chemical Industry Co., Ltd.) Carbon black; Oil absorption 65 ml / 100 g 5 parts by weight (Regal 660R: Cabot) 100 parts by weight of 2-butanone

Example 3 The following compositions were mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 6.3 × 10 ⁷ Ωcm. One-pack type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.3 (Barnock DF-407: manufactured by Dainippon Ink and Chemicals, Inc.) Carbon black; Oil absorption 112 ml / 100 g 5 parts by weight (Monarch 880: Cabot) 100 parts by weight of 2-butanone

Example 4 The following compositions were mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 1.0 × 10 ⁸ Ωcm. One-pack type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.5 (Samprene C-810-40: manufactured by Sanyo Chemical Industry Co., Ltd.) Carbon black; Oil absorption 112 ml / 100 g 5 parts by weight (Monarch 880: Cabot) 100 parts by weight of 2-butanone

Comparative Example 1 The following composition was mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in a resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 2.5 × 10 ⁷ Ωcm. One-component urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.0 (Nipporan 5128: manufactured by Nippon Polyurethane Co.) Carbon black; Oil absorption 65 ml / 100 g 5 parts by weight (Regal 660R: manufactured by Cabot) 2- Butanone 100 parts by weight

Comparative Example 2 The following compositions were mixed by a ball mill to sufficiently disperse carbon black in the resin. Next, the molar ratio of hydroxyl groups to isocyanate groups in the urethane resin raw material is 1: 1.
Polyisocyanate (Barnock D75
(0: Dainippon Ink and Chemicals, Inc.) 4 parts by weight was added and sufficiently stirred to prepare a coating solution. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 3.8 × 10 ⁷ Ωcm. Urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.2 (Bernock DF-30-55: manufactured by Dainippon Ink and Chemicals, Inc.) Carbon black; Oil absorption 65 ml / 100 g 5 parts by weight (Regal 660R: Cabot) Made) 2-butanone 100 parts by weight

Comparative Example 3 The following composition was mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in a resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 2.6 × 10 ⁷ Ωcm. One-component urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.3 (Barnock DF-407: manufactured by Dainippon Ink and Chemicals, Inc.) Carbon black; Oil absorption 350 ml / 100g 5 parts by weight (Ketjen Black EC : Made in Japan EC) 2-butanone 100 parts by weight

Comparative Example 4 The following composition was mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in a resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 5.8 × 10 ⁸ Ωcm. One-pack type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.3 (Barnock DF-407: manufactured by Dainippon Ink and Chemicals, Inc.) Carbon black; Oil absorption 26 ml / 100 g 10 parts by weight (Asahi Thermal: Asahi Thermal Carbon Co., Ltd.) 2-butanone 100 parts by weight

Comparative Example 5 The following compositions were mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 7.4 × 10 ⁷ Ωcm. One-part type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.0 (Nipporan 5128: made by Nippon Polyurethane Co.) Carbon black; Oil absorption amount 350 ml / 100 g 5 parts by weight (Ketjen Black EC: made by EEC Japan) ) 2-butanone 100 parts by weight

Comparative Example 6 The following composition was mixed by a ball mill to prepare a coating liquid in which carbon black was dispersed in resin. The elastic layer formed in Example 1 was immersed in the obtained coating liquid, and then heated and dried to form a resistance adjusting layer having a film thickness of 30 μm. When the volume resistance value of this resistance adjusting layer was measured in the same manner as in Example 1, it was 6.9 × 10 ⁸ Ωcm. One-pack type urethane resin 100 parts by weight Polyol component; Polyester polyol having an average number of hydroxyl groups of 2.0 (Nipporan 5128: manufactured by Nippon Polyurethane Company) Carbon black; Oil absorption amount 26 ml / 100 g 10 parts by weight (Asahi Thermal: manufactured by Asahi Carbon Co., Ltd.) 2 -Butanone 100 parts by weight

(Image Evaluation Test) The roll-shaped charging member (1) manufactured as described above is used as a copying machine (Able 322).
1: Mounted on the charger (13) of Fuji Xerox Co., Ltd. DC power supply (35) and AC power supply (36) connected in series
Apply the superposed oscillating voltage of and to the support (1a) of the charging member,
The surface of the photoreceptor (11) having an outer diameter of 30 mm which comes into contact with the charging member (1) was uniformly charged to -420V. The superimposition oscillating voltage is a DC component and a peak-to-peak voltage (V _PP) AC component of 1.5kV of -420V. Further, in the process after the charging treatment, an image was formed on the paper according to a conventional method. Such an image evaluation test is performed at low temperature and low humidity (10 ° C, 30
% RH), normal temperature and normal humidity and high temperature and high humidity (28 ° C, 90%
% RH), good image quality was obtained after printing 30,000 images in each of the three environments in each example. On the other hand, in Comparative Example 1, sandy fog was caused due to the non-uniformity of the nip after the image was printed on 10,000 (10,000) sheets under low temperature and low humidity.
White spots caused by a leak occurred after printing 8,000 sheets under high temperature and high humidity. In Comparative Example 2, sandy fog was generated due to an increase in resistance after printing 12,000 sheets under low temperature and low humidity.
White spots due to leakage occurred after printing 6,000 sheets under high temperature and high humidity. In Comparative Example 3, white spots due to leakage occurred after printing 6,000 sheets under high temperature and high humidity. Comparative Example 4
In, in the low temperature and low humidity, after the printing of 8,000 sheets, the sandy fog occurred due to the increase in resistance. In Comparative Example 5, white spots due to leakage occurred after printing 4,000 sheets under high temperature and high humidity. In Comparative Example 6, sandy soil fogging caused by non-uniformity of the nip occurred after printing 6,000 sheets under low temperature and low humidity.

The volume resistance value of the resistance adjusting layer in each environment and the above-mentioned image evaluation results are summarized in Table 1 below.

[Table 1] The "image" evaluation results in Table 1 are as follows. ◯: The image was good after outputting 30,000 sheets * ¹⁾ : Sandy fog occurred while outputting 30,000 sheets * ²⁾ : Leak occurred during outputting 30,000 sheets

[0032]

According to the charging member of the present invention, since the urethane resin constituting the resistance adjusting layer partially has a three-dimensional structure, the conductive carbon black having an oil absorption amount within a predetermined range is the above urethane. Disperse evenly in the resin. As described above, since the dispersibility of carbon black is excellent, it is possible to perform the charging process without causing uneven charging on the body to be charged. Further, it becomes possible to remarkably reduce the environmental dependency of the volume resistance value, and it is possible to uniformly charge the charged body in both low temperature and low humidity and high temperature and high humidity environments.

[Brief description of drawings]

FIG. 1 is an explanatory view of a charging member shown as an example of the present invention, FIG. 1A is a perspective view thereof, and FIG. 1B is a sectional view thereof.

FIG. 2 is an explanatory view of a charging member shown as another example of the present invention, and FIGS. 2A and 2B are cross-sectional views of different charging members.

FIG. 3 is an overall explanatory view of an image forming apparatus incorporating the charging member of the present invention.

FIG. 4 is an enlarged view of a main part of FIG. 3, showing a structure of a charger.

[Explanation of symbols]

1 to 3 ... Charging member, 1a to 3a ... Conductive support, 1b to
3b ... Conductive elastic layer, 1c to 3c ... Resistance adjusting layer, 11
... Charged object (photoreceptor).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29K 307: 04

Claims (2)

[Claims] 1. A conductive member that charges a surface of an object to be charged by applying a voltage while being pressed against the surface of the object to be charged,
The conductive member comprises a conductive support, a conductive elastic layer fixed to the support, and a resistance adjusting layer covering the elastic layer, and the resistance adjusting layer includes diisocyanate and one molecule. Charging, characterized in that conductive carbon black having an oil absorption of 30 to 300 ml / 100 g is dispersed in a urethane resin containing a polyol having an average number of hydroxyl groups of 2.1 to 2.5 as a constituent component. Element. 2. The charging member according to claim 1, wherein the resin forming the resistance adjusting layer is obtained from a one-component polyurethane resin.