JP2010204135A - Charging roller for electrophotography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging roller for electrophotography having excellent electric characteristics compatible with high image quality and high durability by uniformly distributing conductive particles without photoreceptor contamination. <P>SOLUTION: In the charging roller for electrophotography having a covering layer on the outer periphery of a conductive elastic layer formed on the outer periphery of a conductive support, the covering layer mainly comprises polyol and isocyanate, contains conductive particles, and contains a copolymer of polycaprolactone and hydroxy octadecanoic acid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic charging roller having a coating layer formed on the outer periphery of a conductive elastic layer formed on the outer periphery 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, the 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, it is preferable because ozone is hardly generated.

  In this method, since the amount of generated corona is small compared to the corona discharge method, the charging roller is required to have very high conductivity uniformity in terms of physical properties. However, it is not easy to achieve the conductivity uniformity. 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 (for example, 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 achieve 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, conductive particles and insulating particles are placed 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. A method of using them in combination has been proposed (Patent Document 2).

  A method of uniformly dispersing the conductive agent by adding a dispersing agent or the like has been proposed, but an effective solution has not yet been achieved due to such problems as contamination of the photoreceptor by bleed and image defects.

  In addition, to form the resistance control layer, a coating solution in which a conductive agent or binder, which is a material necessary for the structure, is dissolved or dispersed in a solvent is applied to the outer periphery of the conductive elastic roller by a dip method or a spray method. The coating method is often used. However, the charging roller is required to more uniformly disperse the conductive agent in 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

  Therefore, the present invention provides a charging roller for electrophotography in which the conductive agent is more uniformly dispersed in the binder, the photosensitive member is not contaminated, the image quality is high, and the durability is high, and the electrical characteristics are good. Let it be an issue.

  The present invention relates to an electrophotographic charging roller having a coating layer on the outer periphery of a conductive elastic layer formed on the outer periphery of a conductive support, wherein the coating layer is mainly composed of polyol and isocyanate. An electrophotographic charging roller comprising conductive particles and a copolymer of polycaprolactone and hydroxyoctadecanoic acid.

  The present invention is also characterized in that the conductive particles are carbon black, the DBP absorption is 50 ml / 100 g or more and 100 ml / 100 g or less, and the volatile content is 0.3% or more and 0.8% or less. The electrophotographic charging roller.

  The present invention also provides the above-described charging roller for electrophotography, wherein the copolymer of polycaprolactone and hydroxyoctadecanoic acid is further a copolymer of polyethyleneimine.

  The present invention also provides the above-described charging roller for electrophotography, wherein the polyol is a lactone-modified acrylic polyol.

  According to the present invention, by using a copolymer of polycaprolactone and hydroxyoctadecanoic acid in the coating layer coating liquid, the coating liquid can be made uniform and the bleed prevention effect can be improved by improving the dispersibility of the conductive particles. Can be improved.

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.

  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, a conductive elastic layer 2 is formed on the outer periphery of a conductive support 1. Further, a coating layer 3 is formed on the outer periphery 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. If it is smaller than 3 mm, the deformation increases due to the load from both ends of the roller, and if it is larger than 30 mm, the cost increases.

(Elastic layer)
In the present invention, at least one layer is formed on the outer periphery of the conductive support 1 as the elastic layer 2 having conductivity obtained by adding a conductive material to an elastic material such as rubber and mixing it uniformly. Has been. 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. If the angle is less than 20 degrees, the strength of the elastic layer itself is usually weakened. If the angle is greater than 80 degrees, the surface of the photoreceptor to be contacted is likely to be scraped. 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. In addition, when using an elastic material whose electric resistance can be within the above range, for example, epichlorohydrin rubber, NBR or the like, 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 periphery of the conductive support. The elastic layer can be formed by bonding or coating. Moreover, after forming an elastic body layer on the outer periphery 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. If it is smaller than 1 mm, it is difficult to ensure an appropriate nip width in the entire roller area, and if it is larger than 20 mm, an increase in cost becomes a problem.

  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.

(Coating layer)
When a coating layer is formed on the outer periphery of the elastic layer, the conductivity and surface roughness of the electrophotographic charging roller are adjusted, and charging performance is improved and the photosensitive material contamination contained in the elastic layer is reduced to the photosensitive material. Bleed to the surface can be prevented.

  The coating layer is formed by forming an elastic body layer on the outer periphery of the conductive support and forming a roller, and then dip coating, spray coating, and roll on the outer periphery using the material constituting the coating layer as a coating liquid. It is formed by coating, ring coating, etc., drying and curing.

  In the present invention, this coating layer is mainly composed of polyol and isocyanate, and is characterized by containing conductive particles and a copolymer of polycaprolactone and hydroxyoctadecanoic acid.

-About polyol The polyol which can be normally used for a polyurethane is used for the polyol used by this invention. Examples include polyether polyols, polyester polyols, silicone glycols, polybutadiene glycols, castor oil, acrylic polyols, fluorine-containing polyols, polyol polymers, and mixtures thereof.

  Examples of the polyether polyol include compounds having a structure in which an alkylene oxide is added to a compound having at least 2 (preferably 2 to 8) active hydrogen atoms, and mixtures thereof. Examples of the compound having an active hydrogen atom include polyhydric alcohol, polyhydric phenol, amines, polycarboxylic acid, phosphoric acid and the like.

  The following can be mentioned as said polyhydric alcohol. Alkylene glycol such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol; diol having a cyclic group (for example, Japanese Examined Patent Publication No. 45-1474) Dihydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, hexanetriol and triethanolamine; tetrahydric alcohols such as pentaerythritol, methylglycoside and diglycerin; Sugar alcohols having the number of functional groups (for example, pentitol such as adonitol, arabitol, xylitol, etc., hexitol such as sorbitol, mannitol, iditol, tallitol, dulcitol, etc.); Monosaccharides such as glucose, mannose, fructose and sorbose, oligosaccharides such as sucrose, trehalose, lactose and raffinose; glycosides {eg glycols (eg glycols such as ethylene glycol, propylene glycol, glycerin, trimethylolpropane, hexanetriol) A polyalkane polyol such as triglycerin and tetraglycerin; a polypentaerythritol such as dipentaerythritol and tripentaerythritol; a cycloalkane polyol such as tetrakis (hydroxymethyl) cyclohexanol} Such.

  The following are mentioned as said polyhydric phenol. Monocyclic polyphenols such as pyrogallol, hydroquinone, and phloroglucin; bisphenols such as bisphenol A and bisphenolsulfone; condensates (novolacs) of phenol and formaldehyde (for example, polyphenols described in US Pat. No. 3,266,641) and the like.

  Moreover, the following are mentioned as said amines. Ammonia; alkanolamines such as mono-, di- and tri-ethanolamine, isopropanolamine, aminoethylethanolamine; C1-C20 alkylamines; C2-C6 alkylenediamine {eg, ethylenediamine, propylenediamine, hexamethylenediamine, Polyalkylene polyamines (for example, aliphatic amines such as diethylenetriamine and triethylenetetramine)}; aromatic amines such as aniline, phenylenediamine, diaminotoluene, xylylenediamine, methylenedianiline, diphenyletherdiamine; isophoronediamine, cyclohexylene Cycloaliphatic amines such as amine and dicyclohexylmethanediamine; aminoethylpiperazine, and other heterocyclic amino acids described in JP-B No. 55-21044 And Louis.

  Two or more compounds containing these active hydrogen atoms may be used in combination.

  Examples of the alkylene oxide added to the compound containing the active hydrogen atom include ethylene oxide, propylene oxide, 1,2-, 1,3-, 1,4- and 2,3-butylene oxide, styrene oxide, and the like. The mixture of 2 or more types of these is mentioned. In addition, when used together, the addition form of alkylene oxide may be a block or random.

  Examples of the polyester polyol include condensation type, lactone type and polycarbonate type described in "Polyurethane Resin Handbook", Keiji Iwata, Nikkan Kogyo Shimbun, pages 108 to 111.

  As said silicone glycol, the reactive silicone oil which contains active hydrogen in a molecule | numerator is mentioned.

  Examples of the polybutadiene glycol include those described in pages 112 to 113 of the “Polyurethane Resin Handbook”.

  Examples of the acrylic polyol include those described in page 112 of the “Polyurethane Resin Handbook”.

  Examples of the fluorine-containing polyol include 4,4 ′-(hexafluoroisopropylidene) -diphenol and 3-perfluorooctylpropanediol.

  Examples of the polyol polymer include those obtained by polymerizing an ethylenically unsaturated monomer in a polyol in the presence of a polymerization initiator.

  Among these polyols, preferred are polyether polyol, polyester polyol, acrylic polyol and silicone glycol, and more preferred is lactone-modified acrylic polyol.

  The OH value (mgKOH / g) of the polyol used in the present invention is not particularly limited, but is preferably 10 to 2000, and particularly preferably 20 to 1000. If it is less than 10, it is difficult to obtain the effect of preventing seepage of contaminants such as a plasticizer contained in the conductive elastic layer, and if it is more than 2000, the hardness of the coating layer increases.

-Isocyanate As the isocyanate used in the present invention, an isocyanate having a molecular weight of 100 to 300 is preferably used, and specific examples thereof include the following. Isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), triresin diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI) and the like. Further, these isocyanates may be used as polymer isocyanate (molecular weight 1000 or more) polymerized by polymerization. In addition, it is preferable to use an isocyanate and a polyol as a one-pack type mixture, and it is preferable to use a blocked isocyanate for that purpose.

  The amount of isocyanate used is preferably 5 to 1000 parts by mass with respect to 100 parts by mass of polyol. If the amount is less than 5 parts by mass, it is difficult to obtain the effect of preventing the contamination of the photoreceptor contaminants such as a plasticizer contained in the conductive elastic layer, and if it exceeds 1000 parts by mass, the hardness of the coating layer increases.

-About electroconductive particle The electroconductive particle used for this invention is used in order to provide electroconductivity to a coating layer.

  As the conductive particles, those generally used for imparting conductivity to the conductive rubber roller can be used, and examples thereof include the following. Carbon black, graphite, metal powder, metal oxide powder such as titanium oxide, tin oxide, zinc oxide, tin oxide, antimony oxide, indium oxide, molybdenum oxide, zinc, aluminum, gold, silver on the surface of suitable powder , Copper, iron, chromium, cobalt, lead, platinum, rhodium, etc. deposited by electrolytic treatment, spray coating, mixed shaking.

  As the conductive particles used here, it is preferable to use carbon black having the following physical properties from the viewpoint of control of conductivity and affinity with a copolymer of polycaprolactone and hydroxyoctadecanoic acid. The DBP absorption amount is 50 ml / 100 g or more and 100 ml / 100 g or less, and the volatile content is 0.3 mass% or more and 0.8 mass% or less. If the DBP absorption amount is 50 ml / 100 g or more, good conductivity can be secured, and if it is 100 ml / 100 g or less, the physical properties of the coating liquid are easily stabilized. Further, when the volatile content is 0.3% by mass or more, dispersion uniformity is good due to the strong affinity with the copolymer of polycaprolactone and hydroxyoctadecanoic acid, and when 0.8% by mass or less, the conductivity is good.

  As the conductive particles used in the present invention, composite conductive particles in which insulating particles and carbon black or graphite are bound can also be used. The composite conductive particles are obtained by binding the conductive particles to the core particles, which are insulating particles, with an adhesive, preferably by thin film coating. Thus, the coating layer can obtain excellent resistance uniformity.

  Examples of the conductive material used for the composite conductive particles include carbon black and graphite. There is no restriction | limiting in particular as carbon black, Generally what is used for electroconductivity provision to a conductive roller is mentioned. Examples of the conductive carbon black include acetylene black by an acetylene method, furnace black by a furnace method, and special carbon black by a shell method gasification furnace.

  The insulating particles as the core particles used for the composite conductive particles are not particularly limited as long as the volume resistance is larger than that of the coating layer, but are preferably inorganic compounds that can easily obtain a small particle size, such as silica, alumina, titania titanium oxide, etc. Oxides, double oxides, nitrides, carbides, ceramics, and the like can be used, and silica, alumina, and titania are particularly preferable.

-Adhesive in composite conductive particles Examples of the adhesive include organosilane compounds generated from alkoxysilanes, polysiloxanes, modified polysiloxanes, terminal-modified polysiloxanes, and mixtures thereof. Specific examples of the alkoxysilane include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane. Examples include methoxysilane and decyltrimethoxysilane.

  The adhesive is attached to the surface of the core particle by a known powder surface treatment method. Known adhesion methods include dry methods and wet methods, and examples of wet methods include aqueous solution methods, organic solvent methods, and spray methods.

  Silica coated with composite conductive particles such as carbon black can be produced by shearing carbon black and silica with powder using a wheel-type kneader. As kneading conditions, kneading time and the number of wheel rotations are set as appropriate, and kneading is performed until most of the carbon black adheres to silica. The carbon black bonded to the surface of the composite conductive particles obtained by adhering carbon black while applying shear in this way has a small structure structure and a structure reflecting the shape and particle size of silica. .

  The blending amount of the conductive particles used in the present invention is preferably 1% by mass to 80% by mass, more preferably 5% by mass to 60% by mass with respect to the mass composition of the coating layer. If it is less than 5% by mass, it is difficult to ensure conductivity, and if it exceeds 60% by mass, the hardness of the coating layer will increase.

  Those having a primary average particle diameter (measured by observation with a differential scanning electron microscope) of 1 to 100 nm are preferably used, and those having a diameter of 5 to 60 nm are more preferable. If the thickness is smaller than 1 nm, the change in physical properties when the coating liquid is used becomes large, and if it is larger than 100 nm, it becomes difficult to obtain sufficient conductivity.

-Copolymer of polycaprolactone and hydroxyoctadecanoic acid The copolymer of polycaprolactone and hydroxyoctadecanoic acid used in the present invention is dissolved in the coating solution and adsorbed on the surface of the conductive particles, so that the conductive particles Maintain uniform dispersion. Further, since the hydroxyl group can be polymerized by a curing reaction with isocyanate at the time of forming the coating layer, contamination on the surface of the photoreceptor is reduced.

  When the polyol used here is a lactone-modified acrylic polyol, the compatibility between the polycaprolactone used and the copolymer of hydroxyoctadecanoic acid is particularly good, so that the effects of the present invention can be maximized. Can do.

  The copolymer of polycaprolactone and hydroxyoctadecanoic acid used in the present invention may be a copolymer with a polyalkyleneimine such as polyethyleneimine. A copolymer of polycaprolactone, hydroxyoctadecanoic acid and polyethyleneimine copolymerized with polyalkyleneimine can adjust the amine value, and is suitable for adsorption according to the surface properties of the conductive particles used.

  The blending amount of the copolymer of polycaprolactone and hydroxyoctadecanoic acid is preferably 0.1% by mass to 10% by mass with respect to the mass composition of the coating layer. If it is less than 0.1% by mass, it will be difficult to obtain the effect of uniform dispersion of the conductive particles expected in the present invention. If it is more than 10% by mass, the conductive particles will be overdispersed, resulting in high resistance. This makes it difficult to adjust to a conductive region.

  In order to uniformly mix and disperse these materials and obtain a coating liquid, the above raw material for the surface layer is put in a solvent and, for example, a dispersion treatment is performed by a mill using beads. In the middle of this dispersion treatment, the dispersion state of carbon black is appropriately measured with a 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 to the outer periphery of the elastic layer of the roller on which the elastic layer is formed on the outer periphery of the conductive support by dip coating, spray coating, roll coating, ring coating, etc. It is coated and then dried or further cured to form a surface layer to obtain the electrophotographic charging roller of the present invention.

  When the charging roller for electrophotography of the present invention is used to charge a photoconductor of an electrophotographic image forming apparatus (electrophotographic apparatus) such as a printer / copier, 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.

  A photosensitive drum (photosensitive member) 5 serving as an image carrier is primarily charged by a charging roller 6 while rotating in the direction of an arrow, and then exposed to exposure 11 by an exposure unit 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 600V to 700V, and the primary charging potential of the photoreceptor surface is about 300V to 800V. Therefore, the specific primary charging voltage is set to 900V to 1500V.

  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 base layer 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 extrusion molding machine to form an uncured elastic body layer on the outer periphery of the conductive support. Next, vulcanize by heating at 160 ° C. for 1 hour in an electric oven, then cut off unnecessary elastic layers at both ends of the conductive support, and further polish to an outer diameter of 8.5 mm, A base layer roller having an elastic layer on the outer periphery of the conductive support was obtained.

Example 1
The following raw materials were stirred and mixed with a mixer for 30 minutes, and then subjected to a dispersion treatment in a horizontal bead mill disperser using φ0.8 mm glass beads as a dispersion medium.
・ Polyol (trade name: DC2009, lactone-modified acrylic polyol, active ingredient 70 mass%, diluting solvent (xylene) 30 mass%, manufactured by Daicel Chemical Industries, Ltd.) 100 parts ・ Isocyanate A (isophorone diisocyanate (IPDI), active ingredient 60) 40% by weight, diluted solvent (15% by weight of n-butyl acetate and 25% by weight of xylene)) Isocyanate B (hexamethylene diisocyanate (HDI), active ingredient 80% by weight, diluted solvent (ethyl acetate) 20% by weight) 30 Parts / conductive particles (carbon black “# 33” (trade name, DBP absorption 76 ml / 100 g, volatile content 0.6%, manufactured by Mitsubishi Chemical Corporation)) 30 parts / silicone oil (SH28PA (trade name), Toray・ Made by Dow Corning Co., Ltd. 1 part ・ Copolymer of polycaprolactone and hydroxyoctadecanoic acid (trade name: Hinoact T-8000, copolymer of polycaprolactone, hydroxyoctadecanoic acid and polyethyleneimine, manufactured by Kawaken Fine Chemical Co., Ltd.) 5 parts ・ Methyl isobutyl ketone 200 copies

  Glass beads were filtered off from the coating solution dispersed for an appropriate time, and 300 ml thereof was taken in a graduated cylinder. In that, the base layer roller produced 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 liquid was applied was subjected to a curing reaction 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 15.2 μm was formed.

Example 2
An electrophotography was performed in the same manner as in Example 1 except that carbon black “MA100” (trade name, DBP absorption amount 100 ml / 100 g, volatile content 1.5%, manufactured by Mitsubishi Chemical Corporation) was used as the conductive particles. A charging roller was obtained.

Example 3
As the conductive particles, carbon black “# 30” (trade name, DBP absorption amount 113 ml / 100 g, volatile content 0.6%, manufactured by Mitsubishi Chemical Corporation) was used. As a copolymer of polycaprolactone and hydroxyoctadecanoic acid, Hinoact T-8000 (trade name, copolymer of polycaprolactone, hydroxyoctadecanoic acid and polyethyleneimine, manufactured by Kawaken Fine Chemical Co., Ltd.) was used. Except for these, an electrophotographic charging roller was obtained in the same manner as in Example 1.

Example 4
In the same manner as in Example 3, except that carbon black “# 990” (trade name, DBP absorption 112 ml / 100 g, volatile content 1.5%, manufactured by Mitsubishi Chemical Corporation) was used as the conductive particles, A photographic charging roller was obtained.

Example 5
An electrophotographic charging roller was obtained in the same manner as in Example 3 except that 90 parts of conductive tin oxide “SN-100P” (trade name, manufactured by Ishihara Sangyo Co., Ltd.) was used as the conductive particles.

Example 6
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that the polyester polyol “Nipporan N5033” (trade name, manufactured by Nippon Polyurethane Co., Ltd.) was used as the polyol.

Comparative Example 1
For electrophotography, as in Example 1, except that a fatty acid-modified polyester dispersant “EFKA6225” (trade name, manufactured by Ciba Specialty Chemicals Co., Ltd.) was used as a copolymer of polycaprolactone and hydroxyoctadecanoic acid. A charging roller was obtained.

Comparative Example 2
An electrophotographic charging roller was obtained in the same manner as in Example 1 except that the copolymer of polycaprolactone and hydroxyoctadecanoic acid was not added.

  With respect to the electrophotographic charging roller obtained above, the resistance value and its peripheral unevenness, the performance as a charging roller (image evaluation) and the photoreceptor contamination were evaluated as follows. The results are shown in Table 1.

(Charging roller resistance and circumferential unevenness)
FIG. 3 shows an 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 each end of the conductive support with a load of 500 g (4.9 N). 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, a value obtained by dividing the circuit voltage value (−200 V) by the current value is regarded as the resistance value of the electrophotographic charging roller 6. By this method, one round is calculated as the resistance value of the electrophotographic charging roller 6, and the average value is used as the resistance value of the electrophotographic charging roller. Further, Log (maximum value / minimum value) is calculated from the maximum value and the minimum value, and this value is defined as circumferential unevenness. The circumferential unevenness is an index of roller resistance uniformity, and the closer this value is to 1, the more uniform it can be considered. The value of the circumferential unevenness is preferably 1 or more and 1.4 or less, and more preferably 1 or more and 1.2 or less.

(Image evaluation)
The electrophotographic charging roller obtained above is attached as a charging roller to an image forming apparatus “Laser Beam Printer LBP-5400” (trade name, manufactured by Canon Inc.), and is a standard chart in an environment of 15 ° C./10% RH. And evaluated the image.

The output image obtained on the 10,000th sheet (endurance) from the output is visually observed, and the following criteria regarding the occurrence of image defects (streak-like defects) due to the resistance value of the charging roller and image density unevenness due to resistance unevenness Based on the image evaluation.
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 streak-like defects exist in the halftone image area.

(Evaluation of photoconductor contamination)
The charging roller for electrophotography obtained above is incorporated as a charging roller in the image forming apparatus and stored for one month in a 40 ° C. and 95% relative humidity environment, and then a monochrome standard pattern is output to confirm image output. And the photoreceptor contamination was evaluated according to the following criteria.
○: No image defect was observed.
X: An image defect that appears to be a photoreceptor contamination was observed.

DESCRIPTION OF SYMBOLS 1 Conductive support body 2 Elastic body layer (conductive elastic body layer)
3 Surface layer (resistance adjustment layer, coating layer)
4 Developing roller 5 Photosensitive drum (photosensitive member)
6 Charging roller 7 Recording medium 8 Transfer roller 9 Fixing section 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 measuring 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 (4)

  In an electrophotographic charging roller having a coating layer on the outer periphery of a conductive elastic layer formed on the outer periphery of a conductive support, the coating layer is mainly composed of polyol and isocyanate, and has conductive particles. And an electrophotographic charging roller characterized by containing a copolymer of polycaprolactone and hydroxyoctadecanoic acid.   The conductive particles are carbon black, the DBP absorption amount is 50 ml / 100 g or more and 100 ml / 100 g or less, and the volatile content is 0.3 mass% or more and 0.8 mass% or less. Electrophotographic charging roller.   The charging roller for electrophotography according to claim 1 or 2, wherein the polyol is a lactone-modified acrylic polyol.   4. The electrophotographic charging roller according to claim 1, wherein the copolymer of polycaprolactone and hydroxyoctadecanoic acid is a copolymer of polyethyleneimine.

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