JP2003195597A - Conductive roller, its manufacturing method and image forming apparatus using the conductive roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive roller having such excellent durability that its characteristic does not change even though it is used for a long time in the case of being used for an electrophotographic device such as a copying machine and an LBP. <P>SOLUTION: This conductive roller obtained by forming a conductive elastic body layer on the outer peripheral surface of a shaft center body (core bar) is constituted to have no surface layer by using an elastic body whose resistance at a part near to the core bar of the conductive elastic body layer is high and whose resistance gets lower and lower toward the outside of the conductive elastic body layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying apparatus, a printer, an electrostatic recording apparatus, or other image forming apparatus, which is configured to form an electrostatic latent image on a conductive roller, particularly an electrostatic latent image on the photosensitive element. The present invention relates to a developing roller which is required to have low hardness and low compression set characteristics in order to form a visible image and does not change in characteristics even after long-term use, and an image forming apparatus using the conductive roller.

[0002]

2. Description of the Related Art A conventional electrophotographic recording apparatus will be described below. An image forming unit is installed inside the main body of this apparatus, and an image is formed through cleaning, charging, latent image, development, transfer and fixing processes. The image forming unit includes a photosensitive drum that is an image carrier, and includes a cleaning unit, a charging unit, a latent image forming unit, a developing unit, and a transfer unit. The image formed on the photosensitive drum by the image forming unit is transferred onto a recording material by a transfer member, conveyed, and then heated and pressurized by the fixing unit and discharged as a fixed recording image.

Next, cleaning, charging, latent image, development,
Among the transfer and fixing processes, charging, latent image formation, development and transfer processes will be described. The charging member performs a primary charging process on the surface of the photosensitive drum so that the predetermined polarity and potential are uniform. After being uniformly charged by the charging member, the electrostatic latent image corresponding to the target image is formed on the surface of the photosensitive drum by receiving the exposure of the target image information. This electrostatic latent image is visualized as a toner image by the developing device. This visible toner image is transferred to the recording material by applying a voltage from the back surface of the recording material by the transfer means under the photosensitive drum. After that, the recording material is conveyed to the fixing unit, undergoes image fixing, and is output as an image formed product.

As a means for executing the developing process in the above-described image forming apparatus such as an electrophotographic apparatus, a developing action is performed by applying a voltage, and in general, a roller type conductive elastic body has been widely used in recent years. There is.

In the developing method described above, the developing member has an electric resistance value in a semiconductive region, and the photosensitive drum,
Since it is constantly in pressure contact with the developing blade, the toner supply roller, etc., it is an essential condition for obtaining a good image to be composed of a material having low hardness and low compression set.
Further, it is necessary that the durability is excellent and the characteristics do not change even after long-term use.

Regarding the conductivity, it is required that the uniformity and the electric resistance value be in the semiconductor region.

When a large amount of conductive agent is mixed in the elastic material, the uneven distribution of the conductive agent is small and the electric resistance value is uniform, but the electric resistance value is small, and the electric resistance value is not so uneven. If the amount of the conductive agent is small, the electric resistance value increases, and it is difficult to achieve the electric resistance of 1E4 to 1E7 Ω · cm in the semiconductor region required for the developing roller. If the electric resistance value is smaller than this, a current leak occurs when the charging roller is used and a current flows when the developing roller is used, and a normal amount of toner does not get on the developing roller. On the other hand, if the electric resistance value is larger than this, when the charging roller is used, current does not flow to the roller and proper charging cannot be given to the photosensitive drum. The transfer to the latent image is reduced and the density does not appear.

In order to make the charge uniform, a smaller electric resistance value on the surface side than in the vicinity of the mandrel of the roller has an advantage that charge unevenness is reduced in the circumferential direction and the longitudinal direction of the roller surface. The reason is that when voltage is applied to the entire roller,
This is because the electric current first flows through the surface portion having a small electric resistance value, the electric charges on the surface become uniform, and then the electric current flows uniformly into the conductive elastic body. Conventionally, in order to take such a resistance configuration, an elastic layer having a relatively high electric resistance,
It was necessary to form a surface layer having a low electric resistance.

Therefore, a low electric resistance layer (resin layer) is coated on the outer periphery of a conductive elastic body (a low hardness solid elastic body or a foam body) containing a conductive substance around a metal mandrel. A conductive roller (developing roller) has been proposed.

Conventionally, as the material of the elastic body of the developing roller,
Ethylene propylene rubber (EPDM), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile rubber (NBR), butyl rubber (IIR), silicone rubber (Q), chloroprene rubber (CR), chloro Sulfonated polyethylene (CS
M), acrylic rubber (ACM), hydrin rubber (EC
O), polysulfide rubber (T), fluororubber (FKM), etc. are used.

Further, as the resin layer arranged outside the elastic body in the developing roller, urethane resin, epoxy resin, diallyl phthalate resin, polyethylene resin, polycarbonate resin, fluorine resin, polypropylene resin,
Urea resin, melamine resin, silicon resin, polyester resin, styrene resin, acrylic resin, vinyl acetate resin, phenol resin, polyamide resin, fiber resin,
There are vinyl chloride resin, silicone resin, water-based resin, and the like, and these are used by imparting conductivity.

Japanese Unexamined Patent Publication No. 09-222788 proposes a developing roller in which a resin solution (conductive paint) in which carbon black is dispersed is applied to an elastic body.

[0013]

However, the above-mentioned developing roller has the following problems.

That is, when a two-layer structure is formed by using the combination of the elastic layer material and the resin layer material, a step of applying an adhesive and a step of surface treatment for maintaining the adhesive force are required. Therefore, when a material having a large permanent strain is used for the elastic body, stress concentration may occur and the material may be deformed, resulting in a decrease in adhesion.

The elastic body is required to have a low hardness as described above. However, if a plasticizer is added to reduce the hardness, the plasticizer may seep out of the elastic body during long-term storage, which may lead to a decrease in the adhesive strength over time (long-term storage or paper passing durability). There is.

When a sponge having a low hardness is used as the elastic body, the permanent set becomes large, and the compounding design becomes complicated in order to satisfy the desired characteristics, or the surface smoothness can be obtained by using the sponge. There is a possibility that sex will be impaired.

[0017]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems and provides a conductive roller, particularly a developing roller, which has low hardness, low permanent set and excellent durability. It is provided.

[0018]

The present inventor has completed the present invention as a result of repeated studies for solving the above problems.

That is, the roller of the present invention is a developing roller in which a conductive elastic body is formed on the outer peripheral surface of a mandrel,
The developing roller is characterized in that the electric resistance of the conductive elastic body decreases from the shaft core toward the outside.

Dispersing a conductive substance in the base polymer,
By rotating at high speed around the mandrel during vulcanization, the conductive material is distributed more toward the outside of the elastic body,
A developing roller in which a large amount of conductive material is distributed from the inside to the outside of the elastic body, or the density of rubber gradually increases from the inside to the outside of the elastic body, and the density of the elastic body gradually decreases from the outside to the inside. Developing roller,
In particular, after dispersing the foaming agent in the base polymer, by rotating at high speed around the mandrel during vulcanization, the cell diameter gradually increases from the outside to the inside of the elastic body, and the density of the elastic body goes from the outside to the inside. The developing roller that is gradually becoming smaller, and further the developing roller that disperses the balloon in the base polymer and rotates it around the shaft at a high speed during vulcanization to distribute more of the balloon toward the inside of the elastic body surely causes the above problem. It was found to be effective in solving the point.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

In the conductive roller of the present invention, the electric resistance (volume resistance) value of the conductive elastic body of the roller becomes smaller as it goes outward from the mandrel of the roller. This will be described with reference to the drawings.

FIG. 1 is a sectional view showing a first embodiment of the present invention. In the figure, 3 is a mandrel (core bar) made of metal such as stainless steel, copper, iron, aluminum, etc., around which a conductive substance (black dots in the figure) often goes out from the vicinity of the core bar. The conductive elastic bodies 4 are distributed. Since the conductive material is distributed more on the surface, the electric resistance value is smaller than that in the vicinity of the cored bar.

FIG. 2 is a sectional view showing a second embodiment of the present invention. In the figure, 3 is a mandrel (core bar) made of metal such as stainless steel, copper, iron, aluminum, around which fine bubbles 7 are dispersed, and the diameter of the bubbles 7 is The conductive elastic body 4 is larger in the vicinity and smaller in the surface layer. This bubble 7
Since the diameter of is smaller on the surface, the electric resistance value is smaller than that near the core metal.

FIG. 3 is a sectional view showing a third embodiment of the present invention. In the figure, 3 is a mandrel (core metal) made of a metal such as stainless steel, copper, iron, aluminum, etc., and a conductive material in which the minute balloons 8 are distributed around the core metal from the vicinity of the core metal to the outside. It is a flexible elastic body 4. Since the balloon 8 is less on the surface, the electric resistance value is smaller than that in the vicinity of the cored bar.

Materials used for the elastic body used in the present invention include ethylene propylene rubber (EPDM), isoprene rubber (IR), and styrene butadiene rubber (SB).
R), butadiene rubber (BR), nitrile rubber (NB
R), butyl rubber (IIR), silicone rubber (Q),
Examples thereof include chloroprene rubber (CR), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM), hydrin rubber (ECO), polysulfide rubber (T), urethane rubber (U) and fluororubber (FKM). However, in terms of processing, the silicone, which is a liquid material, is used to move the conductive material, foam such as balloons, foaming agent, etc. by utilizing the centrifugal force by rotating at high speed around the mandrel during vulcanization. It is desirable to use rubber or urethane rubber.

As the silicone rubber used here,
Examples thereof include polydimethyl siloxane, polymethyl vinyl siloxane, polymethyl phenyl vinyl siloxane, polymethyl p-vinyl phenyl siloxane, polymethyl trifluoropropyl vinyl siloxane, and modified silicone rubbers thereof. These silicone raw rubbers may be used alone or in a mixture thereof.

Further, it is necessary to select a vulcanizing agent depending on the kind of rubber used, and a sulfur vulcanizing agent, an organic peroxide, a quinoid vulcanizing agent, a resin crosslinking agent, a metal oxide crosslinking agent, an amine crosslinking agent. Agents, triazine-based crosslinking agents, polyol crosslinking agents, metal soap crosslinking agents, maleimide-based crosslinking agents, and the like.

Examples of organic peroxide-based vulcanizing agents include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di (tert-butylperoxy). ) Hexane, parachlorobenzoyl peroxide, ditertiary butyl peroxide, dialkyl peroxide, tertiary butyl perbenzoate, 1,1-di (tertiary butyl peroxy) -3,3,5-trimethylcyclohexane, etc. . These organic peroxides may be used alone or as a mixture thereof.

The urethane rubber used here is obtained from an isocyanate compound and a polyol.

As the isocyanate compound, diphenylmethane-4,4'-diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, p -Phenylene diisocyanate, isophorone diisocyanate, carbodiimide-modified MDI, xylylene diisocyanate, trimethylhexamethylene diisocyanate, tolylene diisocyanate, naphthylene diisocyanate, paraphenylene diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl polyisocyanate and the like can be used. Also, a mixture of these may be used, and the mixing ratio may be any ratio.

As the polyol used here,
As the divalent polyol (diol), ethylene glycol, diethylene glycol, propylene glycol,
Dipropylene glycol, 1,4-butanediol, hexanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, xylene glycol, triethylene glycol, etc. can be mentioned, and trivalent Examples of the above polyols include 1,1,1-trimethylolpropane, glycerin, pentaerythritol, and sorbitol. Further, polyols such as high molecular weight polyethylene glycols, polypropylene glycols, ethylene oxide-propylene oxide block glycols obtained by adding ethylene oxide or propylene oxide to diols or triols can also be used. Also, a mixture of these may be used, and the mixing ratio may be any ratio.

As the conductive material used in the present invention, carbonaceous materials such as carbon black and graphite, fine powder of metal such as aluminum, silver, gold, tin-lead alloy, copper-nickel alloy, zinc oxide and titanium oxide. Examples thereof include metal oxides such as aluminum oxide, tin oxide, antimony oxide, indium oxide, and silver oxide, and various fillers plated with a conductive metal such as copper, nickel, and silver. These electroconductivity imparting agents based on the electronic conduction mechanism can be used alone or in a mixture of two or more in a powdery or fibrous form, and any one having a higher specific gravity than the base polymer may be used.

The types of balloons include natural shirasu balloons, artificially made inorganic borosilicate inorganic fine hollow bodies such as glass balloons, resin balloons, vinylidene chloride and acrylic, or a combination thereof. Microballoons made of polymers can be used. As synthetic resin balloons, hollow microspheres of acrylonitrile-vinylidene chloride copolymer and phenolic resin balloon "UCAR" (manufactured by Union Carbide Co.,
The product name) may be used.

The hardness of the conductive roller of the present invention is preferably 50 degrees or less, and more preferably 50 to 10 degrees, in Asker C hardness defined by the Japan Rubber Association standard SRIS0101. .

FIG. 4 shows a side view of an example in which the conductive roller of the present invention is used as a developing roller. The conductive roller 9 of the present invention, which is composed of the conductive elastic body 4 and the core metal 3 on the photosensitive drum 1.
The toner charging roller 2 is provided in contact with the conductive roller 9 so as to rotate the photosensitive drum 1, and the toner supplied from the toner supply roller 6 on the conductive roller 9 is charged with static electricity. Further, a developing blade 5 is provided between the toner charge roller 2 and the toner supply roller 6 to make the toner uniform on the conductive roller 9.

Thereafter, the toner on the conductive roller 9 is transferred to the latent image formed on the photosensitive drum 1, and an image is formed on the photosensitive drum 1. This image is transferred to a medium such as paper (not shown), passed through a hot roll pair (not shown),
Fix the image on the medium.

[0038]

The roller of the present invention is a conductive roller in which a conductive elastic body is formed on the outer peripheral surface of a mandrel, and the electric resistance of the conductive elastic body becomes smaller as it goes outward from the mandrel. By doing so, it is not necessary to form a complicated structure such as providing a high resistance elastic body on the outer periphery of a mandrel such as a conventional conductive roller and further providing a surface layer of a low resistance layer.

Further, since the surface layer is not formed, there is no problem such as a decrease in adhesion between the base layer and the surface layer due to aging (long-term storage, paper passing durability, etc.), or deterioration of image quality due to peeling of the surface layer.

The roller of the present invention disperses a conductive substance in a base polymer and rotates at a high speed around a mandrel during vulcanization, so that the conductive substance having a specific gravity higher than that of the base polymer is made into an elastic substance by centrifugal force. The conductive elastic roller can be distributed more toward the outside, and the conductive material is gradually distributed from the inside to the outside of the elastic body, so that the resistance decreases as it goes to the outside of the elastic body. can get. Further, by increasing the rotation speed or using a conductive material having a higher specific gravity, it is possible to obtain an elastic body in which the base layer has a high-resistance elastic body and the surface layer has a low-resistance layer, which is substantially similar to a two-layer structure. .

That is, since it is possible to form the function of the surface layer which is conventionally required at the same time as the vulcanization, only the elastic body can be formed. There is no problem such as deterioration of the adhesion of the surface layer or deterioration of image quality due to peeling of the surface layer.

In the roller of the present invention, the density of the rubber is gradually increased from the inside to the outside of the elastic body, and the density of the elastic body is gradually decreased from the outside to the inside, particularly foamed on the base polymer. After dispersing the agent, by rotating at high speed around the shaft during vulcanization, the cell diameter gradually increases from the outside to the inside of the elastic body, and the density of the elastic body gradually decreases from the outside to the inside. A conductive roller is obtained.

Furthermore, by dispersing the balloon in the base polymer and rotating it at a high speed around the shaft during vulcanization, the balloon can be distributed more toward the inner side of the elastic body by centrifugal force, and the rubber density is higher than that of the elastic body. It is possible to obtain a conductive elastic body roller in which the density of the elastic body gradually increases from the inner side to the outer side and gradually decreases from the outer side to the inner side. Further, by increasing the rotation speed or using a balloon having a lower specific gravity, an elastic body having a high electrical resistance layer having a sponge elastic body as a base layer and a low electrical resistance layer as a surface layer can be obtained in an almost similar state to an elastic body. be able to. Since the smaller the density in the elastic body, the higher the electric resistance, it is possible to obtain the elastic roller whose resistance becomes lower toward the outside of the elastic body. In other words, it is possible to form the surface layer function that was conventionally required at the same time as vulcanization with only the elastic body, so the coating process for forming the surface layer can be omitted and at the same time the adhesion between the base layer and the surface layer over time. There is no problem such as deterioration in image quality due to peeling of the surface or peeling of the surface.

[0044]

EXAMPLES The present invention will be described in detail below with reference to examples. Although only the developing roller is described in this embodiment, the conductive roller having the same configuration is not limited to this embodiment. In addition, unless otherwise specified, parts represent parts by weight.

Measurement of electric resistance (volume resistance value): The electric resistance was measured as follows. Roller elastic layer thickness 1
Peel it off to a mm, press it on the surface of a flat plate with a 1 cm square electrode, and convert the voltage applied to a resistance of 1 kΩ into a current value using an apparatus (circuit) as shown in Fig. 5 at an applied voltage of 100 V. Then, the resistance value of the sample was calculated.

Roller Asker C hardness measurement: Using an Asker C type spring type rubber hardness meter (manufactured by Kobunshi Keisoku Co., Ltd.) conforming to the Japan Rubber Association standard SRIS0101, in an environment of 23 ° C. and 55% RH. The value was obtained after 30 seconds from the contact of the terminal with a force of 10 N against the roller that had been allowed to stand for 12 hours or more.

Example 1 100 parts of vinyl-terminated polydimethylsiloxane (manufactured by Toray Dow Corning Silicone Co.) was added to carbon black (manufactured by Mitsubishi Chemical Corporation, Ketjen Black EC600JD).
(Brand name)) 30 parts, 100 parts of polydimethylsiloxane having a silicon atom-bonded hydrogen atom (manufactured by Toray Dow Corning Silicone Co., Ltd.) are kneaded until uniformly dispersed by a roll, and a core metal (diameter 8 mm) coated with a primer is used. It was injected by transfer molding into a pipe-shaped mold in which was set. Then, at a high speed (800
(100 RPM) for vulcanization at 100 ° C. for 30 minutes, after cooling, the pipe mold is demolded, and secondary vulcanization is carried out at 200 ° C. for 4 hours using a hot air drying furnace to produce a conductive roller having a diameter of 16 mm ( Figure 1) was obtained. When the electric resistance of the conductive roller (developing roller) obtained here was measured, the volume resistance value of the inner peripheral side (1 mm from the core metal) was 3E7Ω, the volume resistance value of the intermediate portion (2 mm from the core metal) was 4E6Ω, and the outer peripheral side. The volume resistance value (0.5 mm from the skin) was 2E5Ω. The Asker C hardness of this roller was as good as 45 degrees.

As a result of halftone image evaluation using this developing roller, a good image could be obtained. Also, using an LBP that incorporates this developing roller,
When the image was evaluated after 000 sheets were passed, it was possible to obtain the same good image as before the running.

Example 2 100 parts of a polyol having a molecular weight of 2500 and an average number of functional groups of 2.5 (manufactured by Nippon Polyurethane Co., Ltd.) and 1 part of carbon black (Ketjenblack EC600JD (trade name) manufactured by Mitsubishi Chemical Co., Ltd.) in a three-roll system Kneading, molecular weight 330,
8 parts of MDI isocyanate (manufactured by Nippon Polyurethane Co., Ltd.) having an average number of functional groups of 2.2 and an NCO content of 28% and 2 parts of water were added, mixed and stirred, and defoamed under reduced pressure using a vacuum pump.

Next, a cored bar coated with an adhesive (diameter 8 mm)
Is set in a roller mold heated to 120 ° C., the above mixed material is injected, and the core metal is rotated at a high speed (50000).
RPM) to cure reaction under heating conditions of 120 ° C. and 1 hr, and after removing from the mold, further complete curing reaction under heating conditions of 120 ° C. and 2 hr, Asker C hardness 30
A conductive foam roller having a diameter of 16 mm was obtained (FIG. 2).
Cut the conductive roller (developing roller) obtained here,
Observation of the cross section revealed that the cell diameter gradually decreased from the core metal side to the outside of the elastic body. Moreover, when the electric resistance of the elastic body obtained here was measured, a volume resistance value of 4E8Ω on the inner peripheral side (1 mm from the core metal), a volume resistance value of 8E6Ω on the middle portion (2 mm from the core metal), and an outer peripheral side (from the skin) The volume resistance value of 0.5 mm was 9E4Ω.

As a result of halftone image evaluation using this developing roller, a good image could be obtained. Also, using an LBP that incorporates this developing roller,
When the image was evaluated after 000 sheets were passed, it was possible to obtain the same good image as before the running.

Example 3 A resin balloon hollow resin powder (vinylidene chloride-acrylonitrile copolymer resin, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), Microsphere (100 parts of vinyl-terminated polydimethylsiloxane (manufactured by Toray Dow Corning Silicone)) (Trade name)) 15 parts, carbon black (manufactured by Mitsubishi Chemical Corporation, Ketjen Black EC600JD (trade name)) 30 parts,
100 parts of polydimethylsiloxane having hydrogen atoms bonded to silicon (manufactured by Toray Dow Corning Silicone Co., Ltd.) is kneaded until it is uniformly dispersed by a roll, and a pipe-shaped gold having a core metal (diameter 8 mm) coated with a primer is set. It was poured into the mold by transfer molding. After that, the cored bar is rotated at a high speed (20,000 RPM) for vulcanization at 170 ° C. for 30 minutes, the pipe mold is demolded after cooling, and the hot air drying furnace is used at 200 ° C. for 4 hours.
Conductive roller with a diameter of 16 mm by subsequent vulcanization (Fig. 3)
Got The conductive elastic roller (developing roller) obtained here was cut, and the distribution of the resin balloons in the cross section was observed. As a result, the number of balloons at the center of the elastic body was larger than that at the outside of the elastic body. . Moreover, when the electric resistance of the elastic body obtained here was measured, the inner peripheral side (1 m from the core bar
m) volume resistance value 4E8Ω, middle part (2 mm from core)
So the volume resistance value is 3E7Ω, the outer peripheral side (0.5m from the skin)
The volume resistance value of m) was 9E4Ω. The Asker C hardness of this roller was 38 degrees.

As a result of halftone image evaluation using this developing roller, a good image could be obtained. Also, using an LBP that incorporates this developing roller,
When the image was evaluated after 000 sheets were passed, it was possible to obtain the same good image as before the running.

[0054]

As described above, according to the roller of the present invention, in the conductive roller in which the conductive elastic body is formed on the outer peripheral surface of the shaft core, the portion of the conductive elastic body close to the core bar is opposed. The conductive roller has a high resistance and a low resistance as it goes to the outside of the conductive elastic body.

Specifically, (1) a conductive roller in which the distribution density of the conductive material is gradually decreased from the roller surface toward the mandrel, and the conductive material is dispersed in the base polymer to form the mandrel. It can be easily manufactured by distributing a large amount of a conductive substance having a specific gravity higher than that of the base polymer toward the outside of the elastic body by a centrifugal force by rotating at high speed during vulcanization.

(2) A conductive roller in which bubbles are contained in the conductive elastic body and the density of the elastic body is gradually reduced from the roller surface toward the mandrel. This is because by rotating at high speed around the mandrel while foaming during vulcanization,
A conductive roller in which the cell diameter of the generated bubbles gradually increases from the outer side to the inner side of the elastic body and the density of the elastic body gradually decreases from the outer side to the inner side can be easily obtained. Alternatively, by dispersing the balloon in the base polymer and rotating it around the mandrel at a high speed during vulcanization, it is possible to distribute more balloons toward the inside of the elastic body by centrifugal force, and the density of the elastic body changes from the inside to the outside. It is possible to obtain a conductive roller that gradually increases over time.

In any case, by using a balloon having a lower specific gravity, the number of rotations around the mandrel during vulcanization is made higher, or a conductive material having a higher specific gravity is used. In comparison with a conventional conductive roller having a two-layer structure in which a base layer is an elastic high resistance layer and a surface layer is a low resistance layer, a roller having electric properties comparable to those of a conventional conductive roller can be easily manufactured.

Further, in the conductive roller of the present invention, the function of the surface layer which has been conventionally required can be formed simultaneously with the vulcanization only by the elastic body. Therefore, the coating process for forming the surface layer is possible. At the same time, there is no problem that the adhesive strength between the base layer and the surface layer is deteriorated with time, or the image quality is deteriorated due to peeling of the surface layer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a conductive roller showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conductive roller showing a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conductive roller showing a third embodiment of the present invention.

FIG. 4 is a side view of a part of the developing device showing an example in which the conductive roller of the present invention is used as a developing roller.

FIG. 5 is a schematic diagram of an apparatus (circuit) for measuring the resistance value of the elastic body of the present invention.

[Explanation of symbols]

1 photosensitive drum 2 Toner charge roller 3 Shaft core (core) 4 Conductive elastic body 5 Development blade 6 Toner supply roller 7 bubbles 8 balloons 9 Conductive roller

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29K 105: 24 B29K 105: 24 B29L 31:32 B29L 31:32 F term (reference) 2H071 BA43 DA08 2H077 AC04 AD06 AD13 AD17 AE02 FA00 FA12 FA22 FA25 3J103 AA02 AA12 AA32 AA41 EA02 EA11 EA20 GA02 GA57 GA58 HA03 HA12 HA20 4F203 AA45 AB02 AB13 AE03 AG20 AH04 DA11 DC01 DF02

Claims (9)

[Claims] 1. A conductive roller in which a conductive elastic body is formed on an outer peripheral surface of a mandrel, characterized in that the electric resistance of the conductive elastic body becomes smaller toward the outer side from the mandrel. Conductive roller. 2. The conductive roller according to claim 1, wherein a large amount of the conductive substance is distributed outward from the mandrel. 3. The conductive roller according to claim 1, wherein air bubbles are dispersed inside the elastic body, and the density of the elastic body increases toward the outside from the portion near the mandrel. 4. The conductive roller according to claim 3, wherein the cell diameter of the air bubbles dispersed inside the elastic body gradually increases as it approaches the mandrel. 5. The electrically conductive roller according to claim 3, wherein the air bubbles dispersed in the elastic body are balloons, and the balloons are gradually distributed in a larger amount toward the mandrel. 6. A resin raw material in which a conductive material is dispersed is vulcanized around a core metal (mandrel) to produce a conductive roller, which is rotated at a high speed during vulcanization molding around the mandrel. 3. The method of manufacturing a conductive roller according to claim 1, wherein the conductive material is distributed in a larger amount toward the outer side of the elastic body. 7. A resin raw material in which a conductive material is dispersed is vulcanized and molded around a core metal, and when a conductive roller is manufactured, a high speed rotation is performed around a shaft core while foaming during vulcanization molding. The method of manufacturing a conductive roller according to claim 1, 3 or 4. 8. A resin raw material in which a conductive material is dispersed is vulcanized and molded around a core metal, and when a conductive roller is manufactured, a resin raw material containing balloons is used, and a shaft core is formed during vulcanization molding. The method for producing a conductive roller according to claim 1, wherein the high speed rotation is performed as a center. 9. An image forming apparatus using the conductive roller according to claim 1 as a developing roller.