JPH09146345A - Electrostatic charging roll and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a roll which exhibits adequately low electric resistance and has the excellent enviromnental stability of the electric resistance, adequately low hardness and a small friction coefft. by forming a rubber layer by using a specific rubber compsn. SOLUTION: The rubber layer of the electrostatic charging roll 8 formed by covering the surface of a metallic core material 9 with the rubber layer is formed of the rubber compsn. contg. 40 to 90wt.% epihalohydrin copolymer rubber, 5 to 40wt.% unsatd. rubber and 5 to 20wt.% liquid unsatd. rubber. The epihalohydrin copolymer rubber is preferably the copolymer rubber obtd. by copolymerizing 28 to 70mol% alkylene oxide, 28 to 70mol% epihalohydrin and 2 to 15mol% ethylenic unsatd. epoxide. The electrostatic charging roller 8 which has the smaller dependence of the electric resistance on the environment, the stable semiconductor characteristic and the small dynamic friction, coefft., does not contaminate a photoreceptor drum 1 and prevents the occurrence of fogging by the adhesion of toners is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photosensitive drum (image carrier) in an image forming apparatus such as an electrophotographic copying machine.
More specifically, it relates to a charging roll arranged in contact with a contact roller, and more specifically, it has a small environmental dependency of electric resistance, has stable semi-conductivity, has low hardness, has a small dynamic friction coefficient, and is free from contamination on a photosensitive drum. The present invention relates to a charging roll that does not cause fog due to toner adhesion. The present invention also relates to an image forming apparatus provided with a charging roll having such excellent characteristics.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, image formation is usually carried out by the steps of charging, exposing, developing, transferring, fixing and cleaning. That is, in the image forming apparatus, an electrostatic latent image is formed by a charging step of uniformly and uniformly charging the photosensitive drum, an exposure step of forming an electrostatic latent image on the photosensitive drum by exposure, and a developer (toner). Development process to develop visible image,
A transfer step of transferring the toner on the photosensitive drum to a transfer material,
An image is formed by a fixing step of fixing the toner on the transfer material and a cleaning step of cleaning the toner remaining on the photosensitive drum after the transfer step.

Conventionally, in the process of charging the photosensitive drum, charging is generally performed by corona discharge. However, the charging method using corona discharge has a problem that harmful substances such as ozone are generated in addition to the danger and high cost due to application of high voltage. Ozone not only adversely affects the human body, but also deteriorates the photosensitive drum. Further, the corona charger has poor environmental stability, and when affected by humidity, the charging potential of the photosensitive drum changes, which adversely affects image characteristics.

Therefore, in recent years, a charging method using a charging roll has been proposed (for example, Japanese Patent Laid-Open No. 5-210300).
JP-A-6-266206, JP-A-7-2
8297, JP-A-7-49605, and JP-A-7-72710). In this charging method, a voltage is applied to the charging roll, the charging roll is brought into contact with the photosensitive drum, and the photosensitive drum is directly charged to be charged. Therefore, according to this charging method, ozone is not generated. Also in the transfer step, a transfer roll is used without using corona discharge, a voltage having a polarity opposite to that of the toner is applied to the transfer roll to generate an electric field, and the toner is transferred to the transfer material by the electrostatic force of the electric field. A scheme has been proposed.

On the other hand, after the transfer step, the toner remaining on the photosensitive drum is usually removed by a cleaning device such as a cleaning blade, but recently, a cleanerless system (or a cleaningless process) in which the cleaning step is omitted. ) Has been proposed (for example,
JP-A-5-210300 and JP-A-6-35301
No.). In this method, for example, the toner remaining on the photoconductor drum is collected by passing through a charging process and then electrostatically attracted to the developing device by the difference between the surface potential of the charged photoconductor drum and the developing bias. That is. As the developing device, one having a structure in which the developing roll contacts the photosensitive drum is used. According to this method, the image forming apparatus can be downsized and the toner can be collected in the developing process, so that it is not necessary to discard the toner. An image forming method in which an ozone-free process using a charging roll or a transfer roll as described above and a cleaningless process are combined has also been proposed (for example, Japanese Patent Laid-Open No. 5-210300). In such an image forming system, a non-magnetic one-component developer that does not require a carrier is usually used, and in addition to downsizing of the apparatus, cost reduction and colorization can be achieved.

Conventionally, as a charging roll, for example, polyurethane, SBR, EVA, SBS, SEB is provided on a core metal.
S, SIS, TPO, EPDM, EPM, NBR, I
A coating layer made of a composition in which a conductive filler such as carbon black, carbon fiber, metal oxide or metal powder is mixed with a resin or rubber such as R, BR, NR, silicon rubber or epichlorohydrin rubber is provided. Things are known. A conductive coating is applied on the conductive elastic layer, which is further coated with a non-adhesive coating made of conductive fluororesin, or on a medium resistance elastic layer formed of rubber filled with a conductive filler. The one in which a resistor layer is formed by coating (Japanese Patent Laid-Open No. 7-72710) has been proposed. Further, a conductive roll is known in which a core metal is mixed with a fluororesin or an amide resin in epichlorohydrin and a coating layer formed of a material containing a conductive filler is formed.

However, in these charging rolls,
A relatively large amount of conductive filler must be dispersed in order to reduce the electric resistance of the charging roll to an appropriate range. Such a charging roll has a problem that the hardness is high, the contact with the photosensitive drum is not sufficient, and the charging is not uniform. A charging roll in which a non-adhesive layer made of a fluorine-containing cross-linked copolymer is provided on an elastic layer having a medium electric resistance such as epichlorohydrin rubber (Japanese Patent Laid-Open No. 6-2662).
No. 06), or a fluororesin or a polyamide resin that may contain various inorganic fillers or conductive particles on an elastic layer having an electrical medium resistance, such as epichlorohydrin rubber having a hardness (JISA) of 40. A charging roll provided with a surface layer such as an acrylic resin (Japanese Patent Laid-Open No. 7-49605) has also been proposed, but all of them have high hardness.

A low-hardness electrifying roll in which EPDM is impregnated with process oil is known. However, the impregnating process oil is released to contaminate the photoconductor and cause unevenness in the visible image, so that a nylon sheet is formed on the roll surface. Is wrapped around.
However, it cannot be sufficiently prevented with a nylon sheet, and it is made multi-layered or thickened. Therefore, it is not possible to obtain a sufficient charge imparting effect.

Further, the conventional charging roll has a problem that the toner remaining on the photosensitive drum tends to adhere to the charging roll when mounted on a cleanerless type image forming apparatus.
That is, in the cleanerless method, the photosensitive drum is charged by the charging roll in a state where the untransferred residual toner exists on the photosensitive drum. Therefore, the toner tends to adhere to the charging roll. When the toner adheres to the charging roll, the toner adheres to the charging roll aggravated as the total number of printed sheets increases, and it becomes impossible to uniformly charge the photosensitive drum, which causes fog. To reduce the adhesion, reduce the tackiness of the surface of the charging roll,
It is necessary to keep the dynamic friction coefficient small.

In order to impart good chargeability to the photosensitive drum, it is necessary to increase the contact area between the charging roll and the photosensitive drum, and for that purpose, it is required to reduce the surface hardness of the charging roll. . On the other hand, in order to apply a bias voltage to the charging roll, the electric resistance of the charging roll must be lowered. The charging roll is deformed by contact with the photosensitive drum, but must not be permanently deformed by it. In this way, the charging roll has
Many characteristics are required. Further, in an image forming apparatus having a structure in which the charging roll and the photoconductor drum are in contact with each other, they are always in contact with each other. Therefore, it is necessary to prevent the photoconductor drum from being contaminated by the charging roll. Particularly, as organic photoconductors (OPC photoconductors), which are easily polluted, have been used with the downsizing of devices, prevention of pollution has become a more important issue.

[0011]

DISCLOSURE OF THE INVENTION The object of the present invention is to have a stable semiconductivity, which has a small environmental dependence of electric resistance,
An object of the present invention is to provide a charging roll having a low hardness, a small dynamic friction coefficient, no contamination on a photosensitive drum, and no fog caused by toner adhesion. Another object of the present invention is to provide a charging roll suitable for a so-called cleanerless type image forming apparatus, which is a non-magnetic one-component contact developing system and does not require a device for cleaning the photosensitive drum.

The inventors of the present invention have conducted extensive studies in order to overcome the above-mentioned problems of the prior art. As a result, in a charging roll in which the surface of a metal core material (core metal) is covered with a rubber layer, an epihalohydrin copolymer rubber is used. When a rubber layer was formed using a rubber composition in which a unsaturated rubber solid at room temperature and a liquid unsaturated rubber liquid at room temperature were blended in a specific ratio, a moderate amount of conductive filler was not required. It was found that a roll having low electric resistance, excellent environmental stability of electric resistance, moderately low hardness, and small dynamic friction coefficient can be obtained. When this roll is used as a charging roll, it has good adhesion to the photoconductor drum and can be uniformly charged, and even if it comes in contact with the toner remaining on the photoconductor drum, the toner does not adhere. , Does not contaminate the photosensitive drum. Of course, there is no problem such as the release of oil. The present invention has been completed based on these findings.

[0013]

Thus, according to the present invention, there is provided a charging roll having a surface of a metal core material coated with a rubber layer, wherein the rubber layer comprises (A) epihalohydrin copolymer rubbers 40 to 90. A charging roll comprising a rubber composition containing 5% by weight of (B) 5 to 40% by weight of unsaturated rubber, and (C) 5 to 20% by weight of liquid unsaturated rubber. To be done. The epihalohydrin copolymer rubber (A) is a copolymer rubber obtained by copolymerizing 28 to 70 mol% of alkylene oxide, 28 to 70 mol% of epihalohydrin, and 2 to 15 mol% of ethylenically unsaturated epoxide. It is preferable.

Further, according to the present invention, at least the photosensitive drum, the exposing means, the developing roll, and the charging roll are provided, and (1) the charging roll contacts the photosensitive drum to charge the surface of the photosensitive drum, 2) An electrostatic latent image is formed on the surface of the photosensitive drum charged by being exposed by the exposing means, and (3) a developing roll coated with a developer contacts the photosensitive drum to develop the electrostatic latent image. An image forming apparatus configured to be developed into a visible image with an agent, wherein the charging roll is the above-mentioned charging roll.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. (A) Epihalohydrin Copolymer Rubber The epihalohydrin copolymer rubber of the component (A) used in the present invention is a copolymer rubber obtained by copolymerizing a monomer mixture containing epihalohydrin as an essential monomer. Is. Examples of epihalohydrin include epichlorohydrin, epibromohydrin, epifluorohydrin and the like. Among these, epichlorohydrin is preferable in terms of availability and price. As the comonomer that is copolymerized with epihalohydrin, alkylene oxide and ethylenically unsaturated epoxide are preferable.
As the epihalohydrin copolymer rubber, alkylene oxide 28 to 70 mol% and epihalohydrin 28 to 7 are used.
A copolymer rubber obtained by copolymerizing 0 mol% and ethylenically unsaturated epoxide 2 to 15 mol% is preferable.

As the alkylene oxide, for example,
Examples thereof include ethylene oxide, propylene oxide, butylene oxide, and these can be used alone or in combination of two or more kinds. When used alone, ethylene oxide (EO) is preferred. When used in combination, ethylene oxide (EO) and propylene oxide (PO)
It is preferable to use both and, and the usage ratio of both (EO:
PO) is usually used in a ratio of 10:90 to 90:10 (molar ratio).

The copolymerization ratio of alkylene oxide is usually 28 to 70 mol%, preferably 35 to 65 mol%.
More preferably, it is 40 to 60 mol%. When the copolymerization ratio of the alkylene oxide in the epihalohydrin copolymer rubber exceeds 70 mol%, the hygroscopicity becomes high, or the environmental resistance of the electric resistance becomes large. On the contrary, this ratio is less than 28 mol%. And electrical resistance becomes high, which is not preferable. The copolymerization ratio of epihalohydrin is usually 28 to 70 mol%, preferably 30 to 65 mol%, more preferably 35 to 60 mol%. If the copolymerization ratio of epihalohydrin in the epihalohydrin copolymer rubber exceeds 70 mol%, the electric resistance becomes high, and conversely, if this ratio is less than 28 mol%, the hygroscopicity becomes high, or the environment of the electric resistance becomes high. Dependency becomes large and neither is preferable.

Examples of the ethylenically unsaturated epoxide include allyl glycidyl ether, glycidyl methacrylate, glycidyl acrylate and butadiene monooxide. By copolymerizing an ethylenically unsaturated epoxide, vulcanization by a sulfur vulcanization system (sulfur or a sulfur donor) or a peroxide becomes possible, and thermal softening deterioration resistance and dynamic ozone resistance are improved. The copolymerization ratio of the ethylenically unsaturated epoxide is usually 2 to 15 mol%, preferably 3 to 10 mol%. If the copolymerization ratio of the ethylenically unsaturated epoxide in the epihalohydrin copolymer rubber exceeds 15 mol%, curing deterioration due to heat tends to occur and the rubber elasticity tends to be lost, resulting in brittleness. On the contrary, this ratio is less than 2 mol%. If so, it is difficult to obtain a smooth rubber sheet.

(B) Unsaturated Rubber The unsaturated rubber of the component (B) used in the present invention is a rubber in a solid state at room temperature. As such unsaturated rubber,
For example, acrylonitrile-butadiene copolymer rubber (NBR), styrene-butadiene copolymer rubber (SB
R), polybutadiene rubber (BR), ethylene / propylene / diene copolymer rubber (EPDM), chloroprene rubber, acrylonitrile / isoprene copolymer rubber, acrylonitrile / butadiene / isoprene copolymer rubber (NBIR), polyurethane, and these. And a partial hydrogenation product of rubber. Among these, NBR
Also, partially hydrogenated NBR is preferable because it has good compatibility with the epihalohydrin copolymer rubber.

(C) Liquid unsaturated rubber The liquid unsaturated rubber of the component (C) used in the present invention is an unsaturated rubber in a liquid state at room temperature. Examples of such liquid unsaturated rubber include liquid polybutadiene and liquid NB.
R, liquid chloroprene and the like can be mentioned. Among these, liquid NBR is epihalohydrin copolymer rubber and NB.
It is preferable because it has good compatibility with R and partially hydrogenated NBR.

Rubber Composition In the present invention, in a charging roll in which the surface of a metal core material is coated with a rubber layer, the rubber layer comprises (A) epihalohydrin copolymer rubber 40 to 90% by weight, and (B) unsaturated rubber. 5-4
It is formed from a rubber composition containing 0% by weight and (C) 5 to 20% by weight of a liquid unsaturated rubber. In the rubber composition,
The epihalohydrin copolymer rubber of the component (A) has a content of 40-
90% by weight, preferably 50 to 90% by weight, more preferably 55 to 85% by weight. If the proportion of the component (A) exceeds 90% by weight, the hardness and the coefficient of dynamic friction become high, and further, problems such as contamination of the photoreceptor and adhesion of toner occur. When the proportion of the component (A) is less than 40% by weight, it becomes difficult to appropriately reduce the electric resistance.

In the rubber composition, the proportion of the unsaturated rubber as the component (B) is 5 to 40% by weight, preferably 5 to 35% by weight,
More preferably, it is 5 to 30% by weight. If the proportion of the component (B) is too large, it becomes difficult to obtain an appropriately low electric resistance, and conversely, if it is too small, the workability is lowered, and the hardness and the dynamic friction coefficient are increased. The proportion of the liquid unsaturated rubber as the component (C) in the rubber composition is 5 to 40% by weight, preferably 5 to 35% by weight, more preferably 5 to 30% by weight. If the proportion of the component (C) is too large, the dynamic friction coefficient becomes high, and the toner adheres to the charging roll.
If the amount is too small, the hardness becomes high, the contact with the photosensitive drum is insufficient, and the charging becomes uneven.

In the present invention, a vulcanizing agent is added to the rubber composition to shape it into a roll shape and then vulcanized. As the vulcanizing agent, a sulfur-based vulcanizing agent or peroxide is usually used.
Metal oxides can be used, but they are not preferable because they may contaminate the photosensitive drum. As a sulfur-based vulcanizing agent,
Sulfur and sulfur donors commonly used for vulcanizing diene rubber can be used. As a sulfur donor,
Examples thereof include thiuram compounds such as morpholine disulfide and tetramethylthiuram disulfide. Examples of peroxides include dicumyl peroxide, di (t-butylperoxy) diisopropylbenzene, and 2,5-di-t-butylperoxy-2,5.
-Dimethylhexane, benzoyl peroxide, etc. can be mentioned.

A vulcanization accelerator may be used in combination in order to increase the vulcanization efficiency of the sulfur-based vulcanizing agent and the peroxide. When sulfur is used as the vulcanizing agent, a sulfur donor such as tetramethylthiuram disulfide may be used together as a vulcanization accelerator. Further, maleimide compounds such as maleimide and phenyl bismaleimide are also suitable as the vulcanization accelerator. When a peroxide is used as the vulcanizing agent, an acrylate-based or methacrylate-based polyfunctional monomer can be used together as a crosslinking aid.

A thiourea-based vulcanizing agent and an amine-based vulcanizing agent are not preferable because they may contaminate the photosensitive drum. The vulcanizing agent is usually used in a proportion of 0.1 to 5 parts by weight, preferably 0.2 to 3 parts by weight, based on 100 parts by weight of the rubber composition. The rubber composition of the present invention can be appropriately blended with a conductive filler such as conductive carbon black, a reinforcing agent, a filler, and a rubber additive such as an antiaging agent, if necessary.

[0026] In order to form a charging roller using a charging roll the rubber composition as a metal core roll-shaped substrate, such as a metal rotation axis, placed in a roll mold, there was placed a rubber composition Then, it may be formed into a roll shape around the cored bar, and then heated and vulcanized. The vulcanization temperature is usually 100 to 250 ° C. After the vulcanization and molding, the obtained rubber roll is preferably subjected to a surface treatment so as to reduce the frictional resistance of the surface or reduce the adhesive force in order to use it as a charging roll. When the surface treatment of the rubber roll is performed, it is usually preferable to appropriately polish the surface with an abrasive and then perform various surface treatments described below.

The surface treatment method of the charging roll includes, for example, ultraviolet irradiation, ozone exposure, coating of a reactive silicone compound, coating of a reactive fluorine compound, and the like. By these surface treatments, it is possible to reduce the frictional resistance of the surface of the charging roll and reduce the adhesive force to the photosensitive drum, and as a result, it is possible to effectively prevent the contamination of the photosensitive drum. Further, when the frictional resistance on the surface of the charging roll is reduced, it is possible to prevent toner from adhering, and it is possible to prevent the occurrence of fog due to toner adhering.

Examples of the surface treatment method by ultraviolet irradiation include a method in which a charging roll to be processed is rotated around an ultraviolet lamp having a wavelength of 200 to 450 nm and the ultraviolet rays are irradiated for 1 to 10 minutes. As an ultraviolet lamp, for example, an output of 80 W / cm and a rated power of 4000 W
Are preferred. As a surface treatment method by exposure to ozone, for example, the ozone concentration is 10 to 30 pphm (× 1
0 ^8), under an atmosphere of temperature 35 to 45 ° C., and a method of leaving the charging roller 0.5 to 2 hours.

As the surface treatment method by coating the reactive silicone compound, for example, a silicone compound having an isocyanate introduced at the terminal is used, and the silicone compound is dissolved in a solvent such as ethyl acetate at a concentration of about 1 to 10% by weight. After coating the solution on the surface of the charging roll, it is air-dried and then heat-treated at about 80 to 120 ° C. for about 30 minutes to 2 hours. Among these surface treatment methods, surface treatment by UV irradiation is easy to operate,
It is particularly preferable because desired physical properties are easily obtained.

The charging roll of the present invention has an electric resistance (volume specific resistance) of LL conditions of low temperature and low humidity (10 ° C. × 20% R).
Under H), it is usually about 1 × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm, preferably about 1 × 10 ⁶ to 1 × 10 ⁹ Ω · cm. The electric resistance value (b) measured under high temperature and high humidity HH conditions (35 ° C. × 80% RH) is smaller than the electric resistance value (a) measured under LL conditions, but with the charging roll of the present invention ,
The ratio (a / b) of both is usually within 10 (within one digit), and the environmental dependence of electrical resistance is small. In order to adjust the electric resistance value of the charging roll within an appropriate range, it is preferable to add a small amount of a conductive filler of about 0.1 to 5 parts by weight to 100 parts by weight of the rubber composition.

The charging roll of the present invention has hardness (JIS A)
Is usually about 30 to 40, which is appropriately small, and it can be brought into close contact with the photosensitive drum to provide sufficient charging property. If the hardness of the charging roll is too high, uniform charging cannot be imparted.
The charging roll of the present invention has a small hardness,
The coefficient of kinetic friction is usually as small as 0.5 or less, and it is possible to rotate smoothly in contact with the photosensitive drum. The charging roll of the present invention does not contaminate the photoconductor drum even when it is used in contact with the photoconductor drum, and even when it is used in a cleanerless image forming apparatus, the toner does not adhere to it. No fogging occurs.

Image Forming Apparatus The charging roll of the present invention comprises at least a photosensitive drum, an exposing means, a developing roll, and a charging roll. (1) The charging roll contacts the photosensitive drum to charge the surface of the photosensitive drum. , (2) an electrostatic latent image is formed on the surface of the photoconductor drum charged by being exposed by the exposing means, and (3) the developing roll coated with the developer is brought into contact with the photoconductor drum to form the electrostatic latent image. Is used in an image forming apparatus configured to be developed into a visible image by a developer.

FIG. 1 shows a sectional view of an example of such an image forming apparatus. FIG. 1 is a specific example of an image forming apparatus used in a non-magnetic one-component developing method. The photoconductor drum 1 for forming an electrostatic latent image and the charging roll 8 are arranged in contact with each other, and a voltage is applied from a power source 10 through a core metal 9 of the charging roll. Charge the surface of the drum. The electrostatic latent image is formed on the surface of the photoconductor drum 1 which is charged by exposure by the exposure means 7 using a laser light source or the like. The photosensitive drum 1 is arranged so as to also contact the developing roll 2. In the development process,
The non-magnetic one-component developer (toner) 4 is applied to the surface of the adjacent developing roll 2 by the supply roll 6. The developing blade 3 uniformly controls the thickness of the toner applied on the surface of the developing roll. The toner uniformly and evenly applied to the surface of the developing roll visualizes the electrostatic latent image formed on the surface of the photosensitive drum. The toner image on the photosensitive drum is transferred onto a transfer material 15 such as transfer paper. In FIG. 1, a transfer roll 11 is used, and a power source 13 is used to transfer a transfer roll core 12
There is disclosed a method in which a voltage having a polarity opposite to that of the toner is applied via an electric field to generate an electric field, and the electrostatic force of the electric field transfers the toner on the photosensitive drum to a transfer material.

After the transfer step, the toner remaining on the surface of the photosensitive drum may be removed by a cleaning device such as a cleaning blade. In FIG. 1, a so-called cleanerless system without such a cleaning device is used. An image forming apparatus is shown. Therefore, the toner remaining on the surface of the photosensitive drum comes into contact with the charging roll. In the cleanerless method, after passing through the charging step, the toner is attracted to the developing device by electrostatic force and collected due to the difference between the surface potential of the charged photosensitive drum and the developing bias. That is, after the charging process is completed and before the transfer process is started, for example, the residual toner is collected by the electrostatic force generated in the developing process. In addition,
The core metal of the developing roll 2 is usually configured so that a bias voltage can be applied. In the case of the reversal developing method, a bias voltage having the same polarity as that of the electrostatic latent image on the photosensitive drum is applied to the core metal of the developing roll. The transfer material is, for example, paper or an OHP sheet.

Developer (Toner) The toner that can be used in the image forming apparatus of the present invention is not particularly limited, but a non-magnetic one-component developer is usually used, and the toners shown below are particularly preferable. used. That is, the preferable toner has a volume average particle diameter (Dv) of usually 3 to 15 μm, preferably 5 to 10
and the ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) is usually 1.0 to 1.4.
Is a substantially spherical non-magnetic one-component developer within the range of. It is preferable to use such a substantially spherical toner because the transferability is good, and when the cleanerless method is used, the amount of toner remaining on the photoconductor is small and the adhesion to the charging roll is small. .

A preferable spherical toner has a value (Sc / Sr) of 1.0 to 1 obtained by dividing the area (Sc) of a circle having the diameter of the absolute maximum length of the particle by the substantial projected area (Sr) of the particle. .3
And the specific surface area (S) by the BET method [unit:
m ² / g], number average particle diameter (dn) [unit: μm], and true specific gravity (d) product (S × dn × d) are 5 to 10. Toner charge amount (Q) [Unit: μc
/ G] and specific surface area (S) ratio (Q / S) [unit: μc
/ M ² ] is preferably in the range of 80 to 150.

Such a non-magnetic one-component developer can be obtained by polymerizing a homogeneous mixed solution containing a vinyl monomer and a colorant by a suspension polymerization method. In particular,
For example, a mixture containing a vinyl-based monomer, a colorant, a polymerization initiator, and optionally various additives is uniformly dispersed in a ball mill or the like to prepare a mixed solution, and the mixed solution is then subjected to high shear stirring in water. After atomizing into droplet particles,
A method of suspension polymerization at 30 to 200 ° C. is exemplified.

Various additives may be added internally or externally to the non-magnetic one-component developer in order to control chargeability, conductivity, fluidity, or adhesion to the photosensitive drum or fixing roll. You can Such additives include low molecular weight polypropylene, low molecular weight polyethylene, various waxes, release agents such as silicone oil; carbon black, silica, alumina, titanium oxide, zinc oxide, inorganic fine powder such as cerium oxide and calcium carbonate. And the like.

[0039]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The electrical characteristics,
The properties relating to hardness, coefficient of dynamic friction, photoreceptor contamination, and toner adhesion were measured by the following methods. (1) Electric resistance The charging roll is fixed by the metal core material, a brass electrode having a width of 2 mm and a weight of 500 g is placed on the surface of the charging roll, and the metal core material of the charging roll and the brass electrode are placed between them. 500V
DC voltage is applied to measure the electric resistance of the charging roll.
The measured electric resistance is R (Ω) and the contact area of the electrode is S
(Cm ² ) and the distance between the metal core and the electrode is L (cm), the volume specific resistance ρ (Ω · cm) can be calculated by the following equation. ρ = (R · S) / L The environmental conditions for measurement are low temperature and low humidity LL (10 ° C × 2
0% RH) and high temperature / high humidity conditions HH (35 ° C x 80% R
It carried out on 2 conditions of H).

(2) Hardness The hardness is 2 mm in accordance with JIS K-6253.
A thick rubber sheet was measured as a sample. (3) Dynamic friction coefficient Fixed to a moving body so that the charging roll does not move, 20 mm
The width of the polyester sheet was brought into contact with the charging roll so that the contact angle was 90 degrees, the load was changed from 50 g to 200 g, the moving body was pulled at a pulling speed of 100 mm / min, and the tension at this time was measured. Calculate using a formula. μ = 2 / π × Ln (W2 / W1) Here, μ is a dynamic friction coefficient, W1 is a load lowered during measurement, and W2 is an average value of measured tension. FIG. 2 shows a schematic view of a dynamic friction coefficient measuring device.

(4) Contamination of OPC photoconductor A commercially available OPC photoconductor is fixed, and 1K from above the charging roll.
A charging roll was placed on the OPC photosensitive member so that a load of g was applied and left for 2 weeks in an environment of 50 ° C. × 80% RH, and the presence or absence of contamination of the OPC photosensitive member was visually evaluated. ◯: No contamination is observed. X: Contamination is recognized. (5) Adhesion of Toner on Charging Roll The electrophotographic printer (image forming apparatus) shown in FIG. 1 is equipped with the charging roll thus prepared, and continuous printing is performed on 10,000 sheets. The presence or absence of fogging on the printing paper caused by the above was examined, and the toner adhesion on the charging roll was evaluated. A: No fogging due to toner adhesion is observed. ◯: Fogging due to toner adhesion is slightly observed, but there is no problem. X: Fogging due to toner adhesion is recognized and the image is unclear.

[Examples 1 to 4 and Comparative Examples 1 to 3] Ethylene oxide and propylene oxide were used as the alkylene oxide, epichlorohydrin was used as the epihalohydrin, and allyl glycidyl ether was used as the ethylenically unsaturated epoxide. Each epihalohydrin copolymer rubber having the copolymer composition shown was produced. In addition to these epihalohydrin copolymer rubbers, acrylonitrile-butadiene copolymer rubber (NBR) as an unsaturated rubber that is solid at room temperature, and liquid acrylonitrile-butadiene copolymer rubber (liquid NBR) as a liquid unsaturated rubber that is liquid at room temperature In the proportion shown in Table 1, and further, with respect to 100 parts by weight of these rubber components, the vulcanization system shown in Table 1,
And other additives were added to prepare a rubber composition.

Table 1 shows the composition of the epihalohydrin copolymer rubber and the compounding ratio of each component. In Table 1, the composition of the epihalohydrin copolymer rubber is shown by mol% of each copolymer component, and the mixing ratio of the copolymer rubber, the unsaturated rubber and the liquid unsaturated rubber is by weight% of each rubber component. The mixing ratio of the vulcanization system and other additives is 100
It is expressed in parts by weight relative to parts by weight. The rubber compositions obtained in each of the above Examples and Comparative Examples were kneaded with a roll, molded into a sheet and vulcanized at 155 ° C. for 30 minutes to obtain a vulcanized rubber sheet having a thickness of 2 mm. The hardness of each of the obtained vulcanized rubber sheets was evaluated by the above method. Molding of the charging roll is performed by placing a roll-shaped base material such as a metal rotating shaft in a roll mold as a core metal, putting the rubber composition therein, and shaping it into a roll shape around the core metal, followed by heating. And then vulcanized.

After vulcanization and molding, the surface of the obtained charging roll was polished with an abrasive to reduce the surface roughness to 10 μm or less. Then, the surface of the charging roll was irradiated with ultraviolet rays. The UV irradiation method was a method of using a UV lamp having a lamp output of 80 W / cm, a rated power of 4000 W and a wavelength of 200 to 450 nm, and irradiating for 1 to 3 minutes while rotating the charging roll at a distance of 10 cm from the UV lamp. With respect to the charging roll thus obtained, the dynamic friction coefficient, O
The fogging of the printing paper due to the PC photoconductor contamination and toner adhesion was evaluated. Table 1 shows the results.

[0045]

[Table 1]

(Footnote) (* 1) NBR: Acrylonitrile-butadiene copolymer with an acrylonitrile content of 33% by weight (* 2) Liquid NBR: Liquid acrylonitrile-butadiene copolymer with an acrylonitrile content of 33% by weight (* 3) TT: Tetramethylthiuram disulfide ・ The unit of volume resistivity MΩ ・ cm is 10 ⁶ Ω ・
cm.

Each of the charging rolls obtained by using the rubber compositions of Examples 1 to 4 had an electric resistance change of less than one digit under the LL condition and the HH condition, and had an appropriate electric resistance. The environmental resistance of the electrical resistance is small. The vulcanized sheet of each example has low hardness, and the dynamic friction coefficient of the charging roll is small in spite of the low hardness, and the physical properties of the charging roll are well balanced. Further, each charging roll of these examples had no contamination of the photoconductor. Further, in each of the charging rolls of these examples, toner adhered to the surface of the charging roll, and as a result, the charge on the OPC photosensitive member was insufficient, and printing defects such as fogging on the printing paper were not observed.

On the other hand, when the rubber composition does not contain unsaturated rubber (Comparative Example 1) or when the amount of liquid unsaturated rubber used is out of the usable range (Comparative Examples 2 and 3), charging is performed. It turned out to be impractical as a roll. That is, in Comparative Example 1 in which the rubber composition did not contain unsaturated rubber and liquid unsaturated rubber, the dynamic friction coefficient was large, and the OPC photoreceptor contamination and the toner adhesion were severe, which was not practical. When the amount of liquid unsaturated rubber used is too low (Comparative Example 2), the hardness becomes too high, and when it is too high (Comparative Example 3), the dynamic friction coefficient increases and toner adhesion is observed in all cases. Was given.

[0049]

According to the present invention, the environmental dependence of the electric resistance is small, the electric resistance is stable, the hardness is low, the dynamic friction coefficient is small, and the photosensitive drum is not contaminated.
Provided is a charging roll that is free from contamination due to toner adhesion. INDUSTRIAL APPLICABILITY The charging roll of the present invention is a non-magnetic one-component contact developing system and is suitable for a cleanerless system image forming apparatus which does not require a device for cleaning the photosensitive drum. When the rubber layer of the charging roll is the one of the present invention, the toner is less attached to the roll surface and the contact portion with the photoconductor becomes uniform, so that the photoconductor is uniformly charged. as a result,
Toner easily adheres evenly, causing uneven printing, fading,
Fog will not occur. Further, according to the present invention, an image forming apparatus provided with a charging roll having such excellent characteristics is provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an image forming apparatus used in the present invention.

FIG. 2 is a schematic diagram showing a method for measuring a dynamic friction coefficient.

[Explanation of symbols]

 1: Photoconductor drum 2: Development roll 3: Development blade 4: Developer (toner) 5: Developer container 6: Supply roll 7: Exposure device 8: Charging roll 9: Core metal of charging roll 10: Power supply 11: Transfer Roll 12: Core bar 13: Power supply 14: Fixing roll 15: Transfer material (paper, OHP sheet, etc.)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C08L 21:00)

Claims (3)

[Claims] 1. A charging roll having a surface of a metal core material coated with a rubber layer, wherein the rubber layer comprises (A) epihalohydrin copolymer rubber 40 to 90% by weight, and (B) unsaturated rubber 5 to
40% by weight, and (C) 5 to 20% by weight of liquid unsaturated rubber
A charging roll, which is formed from a rubber composition containing. 2. An epihalohydrin copolymer rubber (A)
The charging roll according to claim 1, wherein is a copolymer rubber obtained by copolymerizing 28 to 70 mol% of alkylene oxide, 28 to 70 mol% of epihalohydrin, and 2 to 15 mol% of ethylenically unsaturated epoxide. 3. A photosensitive drum, an exposure means, a developing roll, and a charging roll are provided at least, and (1) the charging roll contacts the photosensitive drum to charge the surface of the photosensitive drum,
(2) An electrostatic latent image is formed on the surface of the photoconductor drum charged by being exposed by the exposure means, and (3) the developing roller coated with the developer is brought into contact with the photoconductor drum to form an electrostatic latent image. An image forming apparatus configured to be developed into a visible image with a developer, wherein the charging roll is a charging roll.
An image forming apparatus, which is the charging roll described above.