JP2009294241A - Charging roller for electrophotography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging roller for electrophotography, which is made for high image quality and high durability, has good electrical property due to improved accuracy for making uniform dispersion and which can be controlled simply and with high accuracy. <P>SOLUTION: In the charging roller for electrophotography with a covered layer which is formed by coating covered layer-coating solution on the outer periphery of a conductive elastic layer formed on the outer periphery of the electrically conductive support, the coating solution contains: carbon black with an aggregate diameter A of 100 nm or more and 300 nm or less; and insulating particles with a primary particle diameter B of 50 nm or less. In this case, the frequency of being measured at particle diameter of 400 nm or more in the particle size distribution which is measured by a laser diffraction/scattering method or a dynamic light scattering method is 3% or more and 50% or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic charging roller having a coating layer formed on the outer peripheral surface of a conductive elastic layer formed on the outer peripheral surface of a conductive support.

  In an electrophotographic apparatus such as a printer / copier, a photosensitive member such as a drum is provided on the surface of the photosensitive drum, and a part of the charged electric charge is removed so that an electrostatic latent image is formed on the surface of the photosensitive member. Is formed. Development is performed by supplying charged toner to the electrostatic latent image. The toner image on the photoreceptor thus obtained is transferred to paper and fixed, whereby the output of the image in the electrophotographic apparatus is completed.

  Conventionally, the uniformity of the density of the output image has been obtained by uniformly charging the surface of the photoreceptor with corona discharge. However, the corona discharge method requires a high voltage of, for example, 6 kV to 10 kV, is not energy efficient, and is not desirable from the viewpoint of safety maintenance. In addition, generation of harmful ozone and NOx is also a problem in environmental health. For this reason, in recent years, switching to a charging method that requires a low applied voltage, in which power consumption is reduced and generation of harmful substances is suppressed as much as possible, has been advanced. One method uses a contact-type charging roller. Since the charging roller can corona discharge in the vicinity of the portion in contact with the photoconductor to charge the photoconductor, only a slight amount of ozone is generated.

  In this method, the amount of generated corona is small compared to the corona discharge method, and therefore the charging roller is required to have very high conductivity and uniform conductivity in terms of physical properties. However, it is not easy to achieve the conductivity uniformity required for the charging roller. Therefore, even if the uniformity of conductivity is not sufficient as the required level, attempts have been made to devise the power supply unit so that the photoreceptor can be charged uniformly, and the superimposed voltage of AC and DC is used. A charging method has been put into practical use.

  In this charging method, in order to ensure the uniformity of charging, an AC voltage having a peak-to-peak voltage more than twice the charging start voltage when a DC voltage is applied is added (superposed) to the DC voltage. As a result, the uniformity of the electrical conductivity required for the charging roller is considerably reduced. However, an extra cost is required for providing an AC power source in the electrophotographic apparatus as compared with a DC charging method in which only a DC voltage is applied. In particular, since there is a strong demand for cost reduction recently, many proposals for a better DC charging method have been made (see Patent Document 1).

  In addition, recent electrophotographic apparatuses are required to have higher image quality at higher speeds, and the charging roller must be able to charge the photoreceptor uniformly even with a very slight fluctuation in discharge amount. However, it is very difficult to obtain high charging uniformity that satisfies such a required level with the current charging roller.

  Therefore, in order to compensate for the lack of charging performance, a mechanism called pre-exposure has been proposed to irradiate the laser beam before charging the photoconductor to completely remove the remaining charge in the previous image output. It takes extra time to output the image. Eventually, the charging ability of the charging roller must be sufficient and uniform. To that end, uniform electrical characteristics among the many characteristics are essential. In order to obtain such uniformity of electrical characteristics, it is necessary that the conductive agent is dispersed as uniformly as possible on at least the surface of the charging roller.

  Therefore, in order to easily adjust the resistance of the charging roller, a conductive filler and an insulating filler are used together in a resistance control layer (also referred to as “coating layer” or “surface layer” in this specification) provided on the outer periphery of the roller. Has been proposed (see Patent Document 2).

In addition, this resistance control layer is prepared by preparing a coating liquid in which a conductive agent or a binder, which is a material necessary for the structure, is dissolved or dispersed in a solvent, and using a dip method or a spray method. A method of coating the outer periphery of the conductive elastic roller is often employed. However, the charging roller is required to more uniformly disperse the conductive agent and the binder in order to cope with higher image quality and higher durability.
Japanese Patent Laid-Open No. 5-341627 Japanese Patent Laid-Open No. 7-20585

  Accordingly, the present invention provides a charging roller for electrophotography having a coating layer containing carbon black and insulating particles and having good electrical characteristics corresponding to high image quality and high durability. Let it be an issue.

  The present inventors have a particle size distribution of the coating liquid when the particle size distribution of the particles in the coating liquid is measured by a specific particle size measurement method together with the particle diameter of the particles to be blended in the coating liquid. As a result, it was found that a coating layer having uniform electrical characteristics can be easily formed, and finally the present invention has been achieved.

  That is, the present invention is an electrophotographic charging roller having a coating layer formed by coating a coating liquid for coating on the outer periphery of a conductive elastic layer formed on the outer periphery of a conductive support. The coating liquid contains carbon black having an aggregate diameter A of 100 nm or more and 300 nm or less and insulating particles having a primary particle diameter B of 50 nm or less, and also includes a laser diffraction / scattering method or a dynamic light scattering method. The charging roller for electrophotography is characterized in that the frequency of the particle size distribution measured in step (b) measured at a particle size of 400 nm or more is 3% or more and 50% or less.

  In the present invention, the coating liquid has a particle size distribution measured by a laser diffraction / scattering method or a dynamic light scattering method, and an arithmetic average of an aggregate diameter A of carbon black and a primary particle diameter B of insulating particles. The above-described charging roller for electrophotography is characterized in that the frequency measured to a particle size of {(A + B) / 2} or less is 5% or less.

  Furthermore, the present invention is the above-described electrophotographic charging roller, wherein the insulating particles have a refractive index of 1.5 or more.

  According to the present invention, there is provided an electrophotographic charging roller with improved surface uniformity, high image quality, high durability, good electrical characteristics, and less drum leak. In addition, according to the present invention, it is possible to easily monitor whether or not carbon black and insulating particles are uniformly dispersed in the coating layer coating solution. A roller is provided.

  Hereinafter, embodiments of the present invention will be described in detail.

[Electrophotographic charging roller]
FIG. 1 is a schematic cross-sectional view of an example of an electrophotographic charging roller of the present invention. In addition, (a) is sectional drawing orthogonal to a conductive support body, (b) is sectional drawing which follows a conductive support body.

  In FIG. 1, 1 is a conductive support, and a conductive elastic body layer 2 is formed on the outer peripheral surface thereof. Furthermore, a coating layer 3 is formed on the outer peripheral surface of the elastic body layer 2.

[Conductive support]
As a material constituting the conductive support 1, any material can be used as long as the surface is conductive and rigid. For example, metals such as iron, aluminum, titanium, copper and nickel, alloys such as stainless steel, duralumin, brass and bronze, and composite materials in which carbon black and carbon fibers are solidified with plastics can be mentioned. In addition to the columnar shape, a cylindrical shape having a hollow central portion can also be used. In addition, from the viewpoint of conductivity, rigidity, etc., the conductive support preferably has, for example, a surface of a carbon steel cylinder plated with nickel of about 5 μm thickness. The diameter of the conductive support is not particularly limited as long as the strength of the charging roller is maintained, but usually 3 mm to 30 mm, preferably 4 mm to 20 mm is appropriate.

[Elastic layer]
In the present invention, the elastic body layer 2 is made of an elastic material such as rubber having a conductivity obtained by adding a conductive material and mixing uniformly, and at least one layer is formed on the outer peripheral surface of the conductive support 1. Is formed. In addition, in order to adjust electroconductivity, elasticity, etc., the elastic body layer 2 may be formed by overlapping a plurality of layers having respective functions. The hardness of the elastic layer 2 may be the same as that of an elastic layer normally used as a charging roller. For example, a hardness of 20 to 80 degrees is appropriate as a micro rubber hardness. The micro rubber hardness can be measured using a rubber hardness meter such as a micro rubber hardness meter MD-1 (trade name) manufactured by Kobunshi Keiki Co., Ltd.

  As the elastic material used for the elastic layer, those generally used as the elastic layer of the electrophotographic conductive roller can be used without any trouble. Specific examples include the following resins and rubber materials. Resins such as acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, polyvinyl butyral, polyvinyl acetal, polyarylate, polycarbonate, polyester, phenoxy resin, polyvinyl acetate, polyamide, polyvinyl pyridine, and cellulose resin. Rubber materials such as EPDM, polybutadiene, natural rubber, polyisoprene, SBR (styrene butadiene rubber), CR (chloroprene rubber), NBR (nitrile butadiene rubber), silicone rubber, urethane rubber, and epichlorohydrin rubber.

As a conductive material added to this elastic material, there are conductive particles having an electron conduction mechanism such as carbon black, graphite, metal powder, conductive insulating particles, and ion conduction mechanisms such as alkali metal salts and quaternary ammonium salts. The conductive material which has can be mentioned. These conductive materials can be used alone or in combination of two or more. The electric resistance of the elastic layer is preferably adjusted to less than 10 ¹⁰ Ω · cm. The blending amount of these conductive materials is preferably 0.1 to 100 parts by mass with respect to 100 parts by mass of the elastic material. When an elastic material whose electric resistance can be in the above range, such as epichlorohydrin rubber or NBR, is used, it is not necessary to add a conductive material again.

  Also for these elastic materials, vulcanizing agents, vulcanization accelerators, fillers such as calcium carbonate, plasticizers, flame retardants, anti-aging agents, foaming agents, silane coupling agents, polymeric dispersants, pigments Derivatives, surfactants and the like can be appropriately blended. The blending amount varies depending on the blending component. For example, in the case of a plasticizer or a surfactant, it is usually preferable to set the blending amount to 20 parts by mass or less with respect to 100 parts by mass of the elastic material in order to prevent contamination of the photoreceptor due to bleeding.

  In order to uniformly mix these materials, for example, it is preferable to use a mixer or kneader such as a planetary mixer, a kneader, or a two roll.

  The material obtained by mixing and uniformly dispersing using the mixer or kneader is formed into a sheet shape or tube shape formed in advance to a predetermined film thickness, and this is formed on the outer peripheral surface of the conductive support. An elastic body layer can be formed by adhering to or covering the substrate. Moreover, after forming an elastic body layer on the outer peripheral surface of an electroconductive support body by an extrusion molding method, the method of adjusting a shape by grinding | polishing etc. may be used. A method of injecting a material for forming the elastic body layer into a roller mold having the conductive support disposed thereon and curing it may be used. Further, the elastic layer may be formed by mixing a material used for the elastic layer with a solvent, coating the conductive support as a coating liquid, and then drying. In this case, it may be performed by a coating method such as spray coating or dip coating. In addition, when making an elastic body layer into a multilayer, the above-mentioned method can be combined suitably. The thickness of the elastic layer is suitably in the range of 1 mm to 20 mm.

  The elastic body layer is bonded to the conductive support through an adhesive as necessary. In this case, the adhesive is preferably conductive. In order to make it conductive, the adhesive may contain a known conductive material. Examples of the binder of the adhesive include resins such as thermosetting resins and thermoplastic resins, and known binders such as urethane, acrylic, polyester, polyether, and epoxy can be used. The adhesive layer is suitably about 5 to 10 μm.

[Surface layer]
After forming an elastic layer on the outer periphery of the conductive support and forming a roller, a surface layer is applied as a coating liquid on the outer periphery by dip coating, spray coating, roll coating, ring coating, etc. Processed, dried and cured.

  By forming this surface layer, the conductivity and surface roughness of the electrophotographic charging roller are adjusted to improve the charging performance and prevent the photoreceptor contaminants contained in the elastic layer from bleeding to the surface of the photoreceptor. Is done.

  In the present invention, the coating liquid contains carbon black and insulating particles.

  Carbon black, which has good conductivity, is useful because it can impart conductivity to the charging roller with a small amount of addition. Further, by adding insulating particles, the charging performance can be improved by improving the durability of the surface layer and adjusting the conductivity.

  For that purpose, it is necessary that carbon black and insulating particles are uniformly dispersed in the coating liquid, and it is good to evaluate the dispersibility of these components in the coating liquid, particularly carbon black. This is preferable for forming the surface layer. However, in the coating liquid containing carbon black and insulating particles, the distribution area of carbon black and insulating particles overlaps even when measured with an existing particle size distribution analyzer, and carbon black is the most important for conductivity control. It is difficult to measure the degree of dispersion.

  By using a combination of carbon black having a particle size in a specific range and specific insulating particles, the present inventors can clearly grasp the dispersion state of carbon black by measuring the particle size distribution of the coating liquid by the laser diffraction / scattering method. And found that dispersibility control is possible. That is, it has been found that the conductivity control of the surface layer can be easily performed. The particle size distribution measurement of the coating liquid may be performed by a dynamic light scattering method other than the laser diffraction / scattering method.

  Here, the mechanism that makes it easy to control the conductivity by observing the particle size distribution by the laser diffraction / scattering method or dynamic light scattering method by combining carbon black having a particle size in a specific range and specific insulating particles is not clear. It is not, but I guess as follows.

  In a particle size distribution analyzer that detects the diffraction / scattering state of light by dispersed particles by the laser diffraction / scattering method or the dynamic light scattering method, light scattering (Mie scattering) increases as the diameter of the dispersed particles decreases. That is, when ultraviolet light or laser light in the visible light region is used as light used for measurement, the light scattering intensity by dispersed particles having a particle diameter of 100 nm to 300 nm, which is about ½ of the wavelength, becomes the highest. However, when the particle diameter is further reduced from 100 nm, a Rayleigh scattering region is formed, light scattering by the fine particles is weakened, and information based on the particle diameter is difficult to obtain.

  Such fluctuations in the light scattering state due to the particle size are usually corrected when the volume frequency is converted, and calculated as an appropriate volume particle size distribution. However, in a coating liquid in which dispersed particles of different materials are mixed as used in the present invention, volume frequency conversion is difficult to be corrected appropriately.

  Therefore, carbon black having an aggregate diameter A (Stokes mode diameter, which will be described later) of 30 nm to 300 nm, having a wavelength sensitivity of 100 nm or more and 300 nm or less, that is, having strong Mie scattering. Select and use. On the other hand, as the insulating particles, those having a primary particle diameter of 50 nm or less at which the Mie scattering intensity based on the insulating particles decreases with the progress of dispersion in the coating liquid are used. Thereby, even in the combined use of carbon black and insulating particles, it is possible to discriminate and measure the degree of dispersion caused by carbon black as the dispersion progresses.

  Insulating particles having a primary particle size exceeding 50 nm may generate particles having a particle size exceeding 300 nm when not dispersed, and Mie scattering of the insulating particles themselves may not be uniquely reduced with the progress of dispersion.

  Here, when the dispersion treatment is performed so that the frequency of coarse particles of 400 nm or more due to carbon black in the coating liquid is 3% to 50%, preferably 10% to 30%, The performance of the charging roller formed from the coating liquid is improved. When the frequency of coarse particles of 400 nm or more is more than 50%, black streaky image defects (so-called pinhole leaks) are caused in the printed image due to defects such as pinholes on the surface of the photoreceptor during contact charging. It tends to occur. On the other hand, if the frequency of coarse particles of 400 nm or more is less than 3%, the resistance value of the charging roller becomes too high, the photosensitive member becomes poorly charged, and a white streak-like image defect may occur.

  Furthermore, when the particle size distribution of the particles in the coating liquid is measured, the particle size is not more than the arithmetic average value ((A + B) / 2) of the aggregate diameter A of the carbon black and the primary particle size B of the insulating particles. When the measured frequency is 5% or less, the performance of the charging roller formed from the coating liquid is improved. This is because the carbon black is uniformly dispersed in the coating liquid, and the insulating particles are uniformly dispersed, and the particle size is not more than measurable by Mie scattering.

  Further, since the scattering efficiency of the insulating particles is high when the refractive index is 1.5 or more, this effect can be effectively verified.

(Carbon black and aggregate diameter)
The carbon black used in the present invention is preferably acetylene black by an acetylene method, furnace black by a furnace method, special carbon black by a gasification furnace by a shell method, or conductive carbon black such as ketjen black. The blending amount is preferably 1 to 80% by mass, more preferably 5 to 60% by mass, based on the solid content of the surface layer raw material, because the conductivity of the surface layer can be made appropriate.

  The aggregate diameter of carbon black is also called a so-called aggregate diameter or Stokes mode diameter, which is obtained by the following method. This corresponds to a particle size when a carbon black aggregate composed of a plurality of primary particles is regarded as one particle. Usually, when carbon black is dispersed in a coating solution, this aggregate diameter is the ideal minimum dispersion particle diameter of carbon black.

  In the present invention, the aggregate diameter of carbon black is measured as the Stokes mode diameter by centrifugal sedimentation. For example, when a centrifugal sedimentation type particle size distribution measuring device manufactured by Brookhaven Instruments is used as the measuring device, the measurement conditions are as follows.

  10 mg of carbon black is dispersed ultrasonically in 50 ml of a 10 vol% ethanol aqueous solution containing a small amount of a surfactant. After adding 10 ml of spin solution (pure water) at a rotation speed of 8000 rpm, 1 ml of buffer solution (10 solution% ethanol aqueous solution) is injected. Thereafter, 0.5 ml of carbon black dispersion is added with a syringe and centrifuged to measure the Stokes mode diameter.

(Insulating particles)
In the present invention, as the insulating particles, titanium oxide, aluminum oxide, silica, zinc oxide, magnesium oxide, iron oxide, strontium titanate, magnesium titanate, barium titanate, potassium zirconate, aluminum hydroxide, calcium carbonate, etc. Can be used.

  The primary particle size of the insulating particles was determined by observing only 100 primary particles excluding the secondary agglomerated particles with a transmission electron microscope (TEM), obtaining the projected area, and calculating the equivalent circle diameter of the obtained area. This is calculated and converted into volume to obtain a volume distribution, which is obtained from the average.

  The blending amount of the insulating particles is preferably 1 to 50% by mass, and more preferably 5 to 30% by mass with respect to the mass of the surface layer, because the conductivity can be adjusted well.

  In the coating liquid used in the present invention, a solvent and a binder for forming a coating film are appropriately used.

  Specific examples of the solvent include the following. Alcohols such as methanol, ethanol and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone; sulfoxides such as dimethyl sulfoxide; Ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; aliphatic halogenated hydrocarbons such as chloroform, ethylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene; benzene, toluene, Aromatic compounds such as xylene, ligroin, chlorobenzene and dichlorobenzene.

  Specific examples of the binder include the following. Resins such as acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, polyvinyl butyral, polyvinyl acetal, polyarylate, polycarbonate, polyester, phenoxy resin, polyvinyl acetate, polyamide, polyvinyl pyridine, and cellulose resin; EPDM, polybutadiene, natural Rubber materials such as rubber, polyisoprene, SBR (styrene butadiene rubber), CR (chloroprene rubber), NBR (nitrile butadiene rubber), silicone rubber, urethane rubber and epichlorohydrin rubber.

(Particle size distribution meter)
The particle size distribution meter used in the present invention is based on a laser diffraction / scattering method or a dynamic light scattering method, and any existing one can be used as long as it can be measured with a division number of 30 or more within a measurement region of 10 to 5000 nm. Can be used without hindrance. Specifically, the following are commercially available.
By laser diffraction / scattering method: Shimadzu laser diffraction particle size distribution analyzer SALD-2200 (trade name, Shimadzu Corporation), laser diffraction / scattering particle size distribution analyzer Partica LA-950, 920, 750 ( All are trade names, HORIBA, Ltd.), Microtrac particle size distribution analyzer MT3000, HRA (both trade names, Nikkiso Co., Ltd.), Laser diffraction scattering particle size distribution analyzer LS13 320 (trade name, Beckman Coulter) Co., Ltd.), laser diffraction type particle size distribution measuring apparatus Mastersizer 2000 (trade name, Sysmex Corporation), etc.
Also, by dynamic light scattering method: Shimadzu nanoparticle size distribution measuring device SALD-7100 (trade name, Shimadzu Corporation), dynamic light scattering particle size distribution measuring device LB-550 (trade name, Horiba, Ltd.) ), Microtrac particle size distribution measuring device UPA, Nanotrack particle size distribution measuring device UPA (all trade names, Nikkiso Co., Ltd.), Submicron particle analyzer DelsaNano (trade name, Beckman Coulter, Inc.), Dynamic light scattering particle size distribution Total Zetasizer Nano (trade name, Sysmex Corporation), dynamic light scattering particle size distribution analyzer ELS-Z2 (trade name, Otsuka Electronics Co., Ltd.), etc.

(Formation of surface layer)
The raw material for the surface layer is put in a solvent and subjected to a dispersion treatment using, for example, a mill using beads. In the middle of this dispersion treatment, the dispersion state of the carbon black is appropriately measured with the particle size distribution meter. When the dispersion state reaches a predetermined dispersion state, the beads are filtered to obtain a coating solution. The obtained coating liquid is applied on the outer peripheral surface of the elastic layer of the roller on which the elastic layer is formed on the outer peripheral surface of the conductive support, by the dip coating method, spray coating method, roll coating method, ring coating method. Then, the surface layer is formed by drying or further curing to obtain the electrophotographic charging roller of the present invention.

  When the charging roller for electrophotography of the present invention is used for charging a photoconductor of an electrophotographic image forming apparatus (electrophotographic apparatus) such as a printer and a copying machine, the photoconductor is uniformly charged. Even if there is a pinhole, there is no problem and it is good.

  FIG. 2 shows a schematic configuration diagram of an example of an image forming apparatus incorporating the electrophotographic charging roller of the present invention.

  The photosensitive drum 5 as an image carrier is primarily charged by the charging roller 6 while rotating in the direction of the arrow, and then exposed to exposure 11 by the exposure means to form an electrostatic latent image. The toner in the thin layer on the developing roller 4 as developing means comes into contact with the surface of the photosensitive drum 5, whereby the electrostatic latent image is developed and a visualized toner image is formed. In this figure, a toner charging roller 29 is used to make the charge amount of the toner on the developing roller 4 appropriate.

  The developed toner image is transferred from the photosensitive drum 5 to a transfer member 77 such as paper at a transfer portion between the transfer roller 8 and the photosensitive drum 5, and then fixed by heat and pressure at the fixing portion 9. It becomes a permanent image. If necessary, the charge remaining on the photosensitive drum is erased by exposure or the like, and the photosensitive drum is returned to the ground potential. Thereafter, the transfer residual toner on the photosensitive drum that has not been transferred is removed by the cleaning blade 10.

  A voltage is applied to the developing roller 4, the toner charging roller 29, the charging roller 6 and the transfer roller 8 from the power sources 18, 19, 20 and 22 of the image forming apparatus, respectively, to ensure a predetermined operation. Reference numeral 28 denotes a toner conveying roller that supplies toner to the developing roller 4, and 30 denotes an elastic regulating blade that applies frictional charging to the toner on the developing roller 4 and regulates the amount of toner carried. Reference numeral 31 denotes a toner container.

  Here, a voltage is applied to the charging roller 6 from the power source 20. In addition, since the charging roller for electrophotography of the present invention is used, if the applied voltage is a DC voltage, the cost of the power source can be kept low, and the advantage that the generated charging noise does not occur when the AC voltage is used. There is.

  When the direct current voltage is applied, the absolute value thereof is preferably the sum of the discharge start voltage of air and the primary charging potential of the surface of the member to be charged (photosensitive member surface). Usually, the discharge start voltage of air is about 600 to 700 V, and the primary charging potential of the photoreceptor surface is about 300 to 800 V. Therefore, the specific primary charging voltage is set to 900 to 1500 V.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these. Moreover, unless otherwise indicated, "part" in an Example shows a mass part.

Production Example 1 (Manufacture of a raw material roller having an elastic layer)
To 100 parts of epichlorohydrin rubber, 2 parts of quaternary ammonium salt, 30 parts of calcium carbonate, 5 parts of zinc oxide and 5 parts of fatty acid were added and kneaded for 10 minutes in a closed mixer adjusted to 60 ° C. Into this, 15 parts of an ether ester plasticizer was added, and the mixture was further kneaded for 20 minutes in a closed mixer cooled to 20 ° C. to prepare a compound. To this compound, 1 part of sulfur (vulcanizing agent), 1 part of Noxeller DM (trade name, manufactured by Ouchi Shinsei Chemical Co., Ltd.) and Noxeller TS (trade name, Ouchi Shinsei Chemical Industry Co., Ltd.) as a vulcanization accelerator (Made) 0.5 part was added and it knead | mixed for 10 minutes with the 2 roll cooled to 20 degreeC.

  The obtained raw material compound was extruded together with a metal conductive support having a diameter of 6 mm and a length of 252.5 mm by an extruder, and an uncured elastic layer was formed on the outer peripheral surface of the conductive support. Next, it is vulcanized by heating at 160 ° C. for 1 hour in an electric oven, and then, unnecessary elastic layers at both ends of the conductive support are cut off and further polished to a diameter of 8.5 mm to obtain a conductive material. A raw material roller having an elastic layer on the outer peripheral surface of the support was obtained.

Example 1
・ Acrylic polyol solution (active ingredient 70% by mass, xylene 30% by weight contained as diluent solvent) 100 parts ・ Isocyanate A (isophorone diisocyanate (IPDI), active ingredient 60% by mass, n-butyl acetate 15% by mass and xylene as diluent solvent) 40 parts ・ Isocyanate B (hexamethylene diisocyanate (HDI), active ingredient 80 mass%, containing 20 mass% ethyl acetate as a diluent solvent) 30 parts ・ Carbon black (aggregate diameter 150 nm) 30 parts ・ SH28PA ( Silicone oil, manufactured by Toray Dow Corning Silicone Co., Ltd.) 0.1 parts ・ Alumina ・ Zirconia surface-treated titanium oxide (primary particle size 20 nm, refractive index 2.7) 25 parts ・ Methyl isobutyl ketone 200 parts Stir and mix for 30 minutes , It was dispersed by the φ0.8mm glass beads dispersion media and the horizontal bead mill dispersing machine. A part of the dispersion treatment liquid during the dispersion treatment was sampled, diluted with methyl isobutyl ketone so as to have an appropriate concentration, and particle size distribution measurement was performed. At this time, when the dispersion treatment time was controlled so that the frequency measured when the particle diameter was 400 nm or more was 10% to 30%, the frequency was 20% in 20 hours. Moreover, the frequency measured to a particle diameter of 85 nm or less, which is an arithmetic average of the aggregate diameter of carbon black of 150 nm and the primary particle diameter of insulating particles of 20 nm, was 2%. For the particle size distribution measurement, a dynamic light scattering type particle size distribution meter (Microtrac UPA (trade name)) was used for measurement for a measurement time of 5 minutes, and measurements obtained from the obtained particle size distributions, respectively. The results were averaged and used as data for the sample.

  Glass beads were filtered off from the coating solution in which the dispersion state became appropriate, and 300 ml thereof was taken in a graduated cylinder. In that, the raw material roller created in the said manufacture example 1 was hold | maintained in the perpendicular | vertical state with respect to the surface of the said coating liquid, and it immersed in the coating liquid, and dip-coated. Then, it was left to stand at room temperature (23 ° C.) for 30 minutes to evaporate the solvent. Next, the roller to which the coating solution was applied was cured for 1 hour in a drier adjusted to 160 ° C. to obtain an electrophotographic charging roller on which a surface layer having a film thickness of 18.5 μm was formed.

Example 2
Except for carbon black having an aggregate diameter of 100 nm, using colloidal silica (primary particle size 40 nm, refractive index 1.4) as insulating particles, and setting the dispersion treatment time in a bead disperser to 18 hours, In the same manner as in Example 1, an electrophotographic charging roller was obtained. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 22%, and the particle size is 70 nm or less, which is an arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The frequency measured was 3%.

Example 3
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that carbon black having an aggregate diameter of 300 nm was used and the dispersion treatment time in the bead disperser was 35 hours. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 23%, and is measured at a particle size of 160 nm or less, which is an arithmetic average of the aggregate diameter of carbon black and the primary particle diameter of the insulating particles. The frequency of being done was 5%.

Example 4
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that alumina-silica surface-treated titanium oxide having a primary particle size of 50 nm and a refractive index of 2.7 was used as the insulating particles. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in particle size distribution is 18%, and the particle size is 100 nm or less, which is an arithmetic average of the aggregate diameter of carbon black and the primary particle diameter of insulating particles. The frequency measured was 5%.

Example 5
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that the dispersion time of the bead disperser was 40 hours. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 3%, and the particle diameter is 85 nm or less, which is an arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The frequency measured was 1%.

Example 6
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that the dispersion time of the bead disperser was 9 hours. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 3%, and the particle diameter is 85 nm or less, which is an arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The frequency measured was 7%.

Comparative Example 1
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that carbon black having an aggregate diameter of 60 nm was used and the dispersion time of the bead disperser was 12 hours. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 20%, and the cumulative volume frequency of 40 nm or less, which is the arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The value was 7%.

Comparative Example 2
For electrophotography, similar to Example 1, except that alumina surface-treated titanium oxide having a primary particle size of 180 nm and a refractive index of 2.7 is used as insulating particles, and the dispersion time of the bead disperser is 62 hours. A charging roller was obtained. In addition, the frequency with which the coating liquid is measured to have a particle size distribution of 400 nm or more in the particle size distribution is 21%, and the particle size is 165 nm or less, which is an arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The frequency measured was 33%.

Comparative Example 3
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that the dispersion time of the bead disperser was 60 hours. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 1%, and the particle size is 85 nm or less, which is an arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The frequency measured was 0%.

Comparative Example 4
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that the dispersion time of the bead disperser was 4 hours. In addition, the frequency with which the coating liquid is measured at a particle size distribution of 400 nm or more in the particle size distribution is 57%, and the particle size is 85 nm or less, which is an arithmetic average of the aggregate diameter of the carbon black and the primary particle diameter of the insulating particles. The frequency measured was 16%.

(Charging roller resistance and circumferential unevenness)
For the electrophotographic charging roller prepared in the above Examples and Comparative Examples, the resistance value and the circumferential unevenness thereof were measured for the conductivity of the roller by using the resistance measuring device shown in FIG. The results are shown in Table 1.

  FIG. 3 is a diagram for explaining the outline of a resistance measuring apparatus used for measuring the resistance value of the electrophotographic charging roller. The electrophotographic charging roller 6 is pressed against the cylindrical electrode 32 made of aluminum at a load of 500 g at both ends of the conductive support. In this state, the cylindrical electrode 32 is rotated, and the electrophotographic charging roller 6 is rotated. A voltage of −200 V is applied from the power source 23 to the conductive support of the rotating electrophotographic charging roller 6, and a voltage value applied to a fixed resistor (1 kΩ) connected in series to the cylindrical electrode 32 is measured by a voltmeter 34. taking measurement. Thereby, the current value (= voltage value / fixed resistor resistance value) flowing through the roller 6 is obtained. Here, since the resistance value of the fixed resistor is sufficiently smaller than the resistance value of the electrophotographic charging roller 6, the value obtained by dividing the circuit voltage value (−200V) by the obtained current value is used for electrophotography. This is regarded as the resistance value of the charging roller 6. By this method, the resistance value of the electrophotographic charging roller 6 is calculated for one round, and the maximum value, minimum value, and average value are obtained. Here, log (maximum value / minimum value) was defined as circumferential unevenness.

(Image evaluation)
Further, the charging roller for electrophotography obtained in the above examples and comparative examples is attached to the image forming apparatus “Laser Beam Printer LBP-5400” (trade name, manufactured by Canon Inc.) as a charging roller, and 15 ° C./10%. A standard chart was output in an RH environment and image evaluation was performed.

The output images obtained on the fifth output (initial) and the 10,000th output (endurance) are visually observed, and the image density due to image defects (streaky defects) and resistance unevenness due to the resistance value of the charging roller. The occurrence of unevenness was evaluated based on the following criteria.
A: There is no defect in the halftone image area (the image is very good)
B: Extremely gentle density unevenness or streaks are observed in the halftone image portion, but the image is good. C: Density unevenness or streaky defects are present in the halftone image portion.

(Pinhole leak)
Furthermore, when there is a pinhole in the photosensitive drum, current concentrates in the pinhole, and an abnormality that occurs in the halftone image of the part other than the pinhole (the density changes on the image and a band with a different density appears. ) Was examined below. The results are shown in Table 1.

The electrophotographic charging roller obtained in Examples and Comparative Examples was used as the charging roller in the same manner as in the above image evaluation except that a pinhole drum having a pinhole was used as the photosensitive drum. The image output was a halftone image in a high-temperature and high-humidity environment of 30 ° C./80% RH where the resistance was reduced. The obtained image was visually evaluated according to the following criteria.
◎: No density unevenness ○: Slight density unevenness occurred, but no problem in practical use ×: Density unevenness due to pinhole leak

It is a schematic sectional drawing of the charging roller for electrophotography. 1 is a schematic configuration diagram of an image forming apparatus. It is a schematic explanatory drawing of the resistance measuring apparatus of a charging roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductive support body 2 Elastic body layer (conductive elastic body layer)
3 Surface layer (resistance adjustment layer, coating layer)
DESCRIPTION OF SYMBOLS 4 Developing roller 5 Electrophotographic photosensitive drum 6 Charging roller 7 Recording medium 8 Transfer roller 9 Fixing part 10 Cleaning blade 11 Exposure light (laser)
18 Developing roller, toner supply roller, and elastic regulating blade bias applying power source 19 toner charging roller bias applying power source 20 charging roller bias applying power source 22 transfer roller bias applying power source 23 resistance measurement bias applying power source 28 toner supplying roller 29 toner Charging roller 30 Elastic regulation blade 31 Toner container 32 Cylindrical electrode (metal roller)
33 Fixed resistor 34 Voltmeter

Claims (3)

An electrophotographic charging roller having a coating layer formed by coating a coating liquid for coating on the outer periphery of a conductive elastic layer formed on the outer periphery of a conductive support,
The coating liquid contains carbon black having an aggregate diameter A of 100 nm or more and 300 nm or less and insulating particles having a primary particle diameter B of 50 nm or less, and is obtained by a laser diffraction / scattering method or a dynamic light scattering method. An electrophotographic charging roller characterized in that the frequency of measurement with a measured particle size distribution with a particle size of 400 nm or more is 3% or more and 50% or less.   The particle size distribution of the coating solution measured by a laser diffraction / scattering method or a dynamic light scattering method, and an arithmetic average value {(A + B) / of the aggregate diameter A of carbon black and the primary particle diameter B of insulating particles 2. The electrophotographic charging roller according to claim 1, wherein the frequency measured for a particle size of 2} or less is 5% or less.   The electrophotographic charging roller according to claim 1, wherein the insulating particles have a refractive index of 1.5 or more.

Images