JP2004294675A - Developing roller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing roller which substantially prevents image failure, such as spots, density unevenness, and white image fogging, as far as possible, satisfactorily deals with a color image as well, and securely obtains a high quality image. <P>SOLUTION: The developing roller has at least one resin coating layer 3a on the peripheral face of an elastic layer 3. The resin coating layer 3a comprises an ultraviolet curing type resin or an electron beam curing type resin. A voltage of 8 kV is applied to a corona discharger disposed 1 mm away from the surface of the resin coating layer 3a. Thereby corona discharge is generated to electrify the surface of the layer 3a. In this case, the maximum value of the surface potential after 0.35 sec is equal to or lower than 90 V. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００８２】
表１に示した結果から明らかなように、コロナ帯電から０．３５秒後の表面電位の最大値により表面電荷保持能力を適正化した実施例１〜４のローラは、良好な画像を確実に形成し得ることができる。
【００８３】
【発明の効果】
以上説明したように、本発明によれば、斑点などの画像不良や濃度むら、更には白画像かぶりの発生を可及的に防止して、高品位な画像を確実に得ることができる現像ローラ及びこれを用いた画像形成装置が提供される。
【図面の簡単な説明】
【図１】現像ローラの断面図である。
【図２】画像形成装置の構成図である。
【図３】現像ローラの表面電位を測定する装置の一例を示す概略図である。
【図４】実施例，比較例で用いた計測ユニットの形状及び寸法を示す概略平面図である。
【図５】実施例，比較例で用いた回転抵抗測定器を示す概略図である。
【符号の説明】
１ 現像ローラ
２ シャフト
３ 半導電性弾性層
３ａ 樹脂被覆層
６ トナー
１１ チャック
１２ コロトロン放電器（コロナ放電器）
１３ 表面電位計[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a developing roller used for an image forming apparatus such as an electrophotographic apparatus such as a copying machine and a printer and an electrostatic recording apparatus, and an image forming apparatus using the developing roller.
[0002]
[Prior art]
2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine or a printer, a toner (a non-magnetic one-component developer) is supplied to a photosensitive drum holding a latent image, and the developer is attached to the latent image on the photosensitive drum. As a developing method for visualizing a latent image, a pressure developing method is known.
[0003]
In this pressure development method, a developing roller carrying toner is brought into contact with a latent image holding member (image forming member) holding an electrostatic latent image, such as a photosensitive drum, and toner is applied to the latent image on the latent image holding member. The development is performed by attaching the developing roller. Therefore, the developing roller needs to be formed of an elastic body having conductivity.
[0004]
Such a conductive elastic roller is also used in a case where a minute gap is provided between the latent image holding member and the developing roller so that the toner flies, a toner jet method using an aperture electrode, and the like.
[0005]
Taking this pressure development method as an example, as shown in FIG. 2, for example, a toner application roller 4 for supplying toner and a photosensitive drum (image forming body) 5 holding an electrostatic latent image are provided. The developing roller 1, the photosensitive drum 5, and the toner applying roller 4 are respectively rotated in the direction of the arrow in the drawing, so that the toner 6 is developed by the toner applying roller 4. The toner is supplied to the surface of the photosensitive drum 5 and is formed into a uniform thin layer by the stratification blade 7. In this state, the developing roller 1 rotates while being in contact with the photosensitive drum 5. The latent image adheres to the latent image on the photosensitive drum 5 from the roller 1 and is visualized. In the figure, reference numeral 8 denotes a transfer unit, which transfers a toner image to a recording medium such as paper. Reference numeral 9 denotes a cleaning unit which removes toner remaining on the surface of the photosensitive drum 5 after transfer by the cleaning blade 10.
[0006]
In this case, the developing roller 1 must rotate while securely maintaining a state in which the developing roller 1 is in close contact with the photosensitive drum 5, and therefore, as shown in FIG. 2. A semiconductive elastic layer 3 made of a semiconductive elastic body in which carbon black or metal powder is dispersed in an elastomer such as silicone rubber, NBR, EPDM, ECO, or polyurethane, or a foam body formed by foaming them. Is formed. Further, a resin coating layer 3a is formed on the surface for the purpose of controlling the chargeability and adhesion of the toner, controlling the frictional force between the developing roller and the layering blade, and preventing the photosensitive member from being contaminated by the elastic body of the developing roller. In some cases.
[0007]
As a method of providing this resin coating layer, a method of dipping or spraying a roller in a solvent-based or water-based coating and then drying and curing with heat or hot air is performed. However, since drying for a long time is required, mass production is required. Requires a long drying line. In addition, since the solid layer of the roller is required to have delicate conductivity and surface condition depending on the application, there are problems in cost and quality, such as the temperature distribution in the drying line and the variation of the air volume greatly affect the performance. .
[0008]
As a solution to such a problem, Japanese Patent Application Laid-Open No. 2002-310136 discloses a developing roller in which an ultraviolet curable resin is applied and cured to form a resin coating layer. In paragraph 0018 of the same publication, it is described that a conductive agent may be contained in this resin coating layer.
[0009]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-310136
[Problems to be solved by the invention]
In order to obtain a high-quality image by image formation using the developing roller, the developer held on the developing roller always keeps a constant charge when reaching the image forming body, and is in a uniform charged state. Is required.
[0011]
That is, when high image quality is required for an image forming apparatus such as a printer, or when an attempt is made to cope with a color image, if the electrical characteristics of the developing roller vary over the entire surface of the roller, image defects such as spots and density unevenness will occur. In addition, a problem of fogging of a white image occurs. Also, during continuous printing, the charge amount of the developer held on the developing roller may gradually change, and when a partially solid black image is printed, the developer is newly held at that portion. In some cases, the amount of charge of the developer is different from that of the surroundings, and the resulting uneven charge distribution of the developer may cause a non-uniform image defect. These phenomena tend to occur when the charge applied to the surface of the developing roller hardly escapes.
[0012]
In this case, the charge applied to the developing roller surface is considered to be attenuated mainly by being grounded from the surface through the conductive shaft.For example, in a developing sleeve used for magnetic toner development, the base is made of metal. Because of this, the conductivity is extremely good, the surface charge can easily flow into the ground, and the residual surface charge hardly causes a problem. However, in the case of a developing roller used for non-magnetic one-component toner development using a semiconductive material as a base material, since the resistance of the base material is high, the residual charge is difficult to escape and tends to remain for a long time. Will occur.
[0013]
The present invention has been made in view of the above circumstances, and it is possible to satisfactorily cope with a color image by minimizing the occurrence of image defects such as spots, uneven density, and white image fogging as much as possible. An object of the present invention is to provide a developing roller capable of reliably obtaining a high-quality image and an image forming apparatus including the developing roller.
[0014]
[Means for Solving the Problems]
The developing roller of the present invention is a developing roller having an elastic layer and at least one resin coating layer formed on the outer peripheral surface of the elastic layer, wherein the resin coating layer is made of an ultraviolet curable resin or an electron beam curable resin. Then, a voltage of 8 kV was applied to a corona discharger disposed at a distance of 1 mm from the surface of the resin coating layer to generate a corona discharge and charge the surface, and the surface potential after 0.35 seconds. Is 90V or less.
[0015]
The image forming apparatus of the present invention includes the developing roller.
[0016]
When a voltage of 8 kV is applied to a corona discharger arranged at a distance of 1 mm from the surface of the developing roller to generate corona discharge and charge the surface, the maximum value of the surface potential after 0.35 seconds (hereinafter referred to as By controlling such that the maximum value of the surface potential measured under such conditions (interval, voltage, time) is simply referred to as “maximum surface potential”, is 90 V or less, speckles caused by residual charges are obtained. It is possible to prevent image defects such as image defects and density unevenness, and furthermore the occurrence of white image fog as much as possible, and it is possible to reliably maintain good image quality even during continuous printing or partial image printing, It is possible to reliably and stably obtain a high-quality image that can well cope with a color image.
[0017]
In addition, since the resin coating layer of the developing roller of the present invention is obtained by curing an ultraviolet-curable resin or an electron-beam-curable resin, by optimizing the irradiation amount of the ultraviolet light or the electron beam, the unreacted resin can be obtained. Is prevented from remaining. Further, the crosslink density can be adjusted by adjusting the irradiation amount of ultraviolet rays or electron beams. Therefore, it is possible to prevent the unreacted resin from remaining in the resin coating layer, and to reliably and stably obtain a high-quality image free from the problem of contamination of the photosensitive drum by the unreacted resin.
[0018]
In particular, the resin coating layer obtained by curing the electron beam-curable resin has the following effects. That is, in a resin coating layer formed by applying and curing an ultraviolet-curable resin, for example, when carbon black is blended with the ultraviolet-curable resin to adjust the electric resistance value of the resin coating layer, carbon black is used. Absorbs ultraviolet rays, so that the curing of the ultraviolet curable resin is inhibited, and unreacted resin may remain. On the other hand, since the electron beam is not affected by the carbon black, it can be sufficiently cured even if the carbon black is blended, and the unreacted resin can be prevented from remaining.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0020]
The developing roller of the present invention has a semiconductive elastic layer 3 formed on the outer periphery of a good conductive shaft 2 like the roller 1 shown in FIG. The conductive resin coating layer 3a is formed.
[0021]
As the shaft 2, any material having good conductivity can be used, but usually, a metal core such as iron, stainless steel, or aluminum, or a hollow metal inside is used. A metal shaft such as a hollow metal cylinder is used.
[0022]
The semiconductive elastic layer 3 formed on the outer periphery of the shaft 2 is formed by blending an electronic conductive agent such as carbon black or an ionic conductive agent such as sodium perchlorate into a single elastomer or a foam obtained by foaming the elastomer. It is formed of a semiconductive elastic body in which is adjusted.
[0023]
In the present invention, a reaction injection molding method (RIM molding method) may be used in a molding step for integrating the shaft 2 and the elastic layer 3. That is, the two types of monomer components constituting the raw material components of the elastic layer 3 are mixed and injected into a cylindrical mold, and a polymerization reaction is performed, whereby the shaft 2 and the elastic layer 3 are integrated. As a result, the molding process can be performed in a required time of about 60 seconds from the injection of the raw material to the demolding, so that the production cost can be significantly reduced.
[0024]
Examples of the elastomer constituting the semiconductive elastic layer 3 include silicone rubber, EPDM, NBR, natural rubber, SBR, butyl rubber, chloroprene rubber, acrylic rubber, epichlorohydrin rubber, EVA, polyurethane, and mixtures thereof. Of these, silicone rubber, EPDM, epichlorohydrin rubber and polyurethane are particularly preferably used. In addition, these elastomers can also be used as a foam body that is chemically foamed by using a foaming agent, or foamed by mechanically entrapped air, such as a polyurethane foam.
[0025]
In addition, as the conductive agent to be mixed into the semiconductive elastic layer 3, an electronic conductive agent, an ionic conductive agent, or the like is used.
[0026]
Examples of the electronic conductive agent include conductive carbon such as Ketjen black and acetylene black, carbon for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT; Ink) carbon, pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, germanium and other metals and metal oxides, polyaniline, polypyrrole, polyacetylene, etc. Whiskers such as conductive polymers, carbon whiskers, graphite whiskers, titanium carbide whiskers, conductive potassium titanate whiskers, conductive barium titanate whiskers, conductive titanium oxide whiskers, and conductive zinc oxide whiskers. The compounding amount of these electronic conductive agents is preferably 1 to 50 parts by weight, especially 5 to 40 parts by weight, based on 100 parts by weight of the elastomer.
[0027]
Examples of ionic conductive agents include perchlorates, chlorates, hydrochlorides, bromine salts such as tetraethylammonium, tetrabutylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, benzyltrimethylammonium and modified fatty acid dimethylethylammonium. Ammonium salts such as acid salts, iodate salts, borofluoride salts, sulfate salts, ethyl sulfate salts, carboxylate salts, and sulfonates; alkali metals such as lithium, sodium, potassium, calcium, and magnesium; and alkaline earth salts Metal perchlorates, chlorates, hydrochlorides, bromates, iodates, borofluorides, sulfates, trifluoromethyl sulfates, sulfonates and the like can be mentioned. The compounding amount of these ionic conductive agents is usually suitably used in the range of 0.01 to 5 parts by weight, particularly 0.05 to 2 parts by weight based on 100 parts by weight of the elastomer.
[0028]
The conductive agent may be used alone or in combination of two or more. In this case, an electronic conductive agent and an ionic conductive agent may be combined.
[0029]
The semiconductive elastic layer 3 is not particularly limited, but preferably has a resistance value of 10 ³ to 10 ¹⁰ Ωcm, particularly 10 ⁴ to 10 ⁸ Ωcm, depending on the composition of the conductive agent. If the resistance value is less than 10 ³ Ωcm, electric charges may leak to the photosensitive drum or the like, or the developing roller itself may be damaged by a voltage. On the other hand, if the resistance value exceeds 10 ¹⁰ Ωcm, fogging tends to occur.
[0030]
If necessary, a crosslinking agent and a vulcanizing agent can be added to the semiconductive elastic layer 3 in order to convert the elastomer into a rubbery substance. In this case, a vulcanization aid, a vulcanization accelerator, a vulcanization acceleration aid, a vulcanization retarder and the like can be used in both cases of organic peroxide crosslinking and sulfur crosslinking. Furthermore, peptizing agents, foaming agents, plasticizers, softeners, tackifiers, antiblocking agents, separating agents, mold release agents, extenders, coloring agents that are commonly used as rubber compounding agents other than those described above. Etc. can be added.
[0031]
When the elastic layer 3 is formed using polyurethane or EPDM as a base material, for example, various charge controls such as nigrosine, triaminophenylmethane, and a cationic dye are used in order to control the amount of toner charge on the surface when used as a developing roller. Agents, silicone resin, silicone rubber, and fine powder of nylon and the like can be added. In this case, the amount of these additives is preferably 1 to 5 parts by weight of the charge control agent and 1 to 10 parts by weight of the fine powder, based on 100 parts by weight of the polyurethane or EPDM.
[0032]
The hardness of the semiconductive elastic layer 3 is not particularly limited, but is preferably 80 degrees or less, particularly 40 to 70 degrees in Asker C hardness. In this case, if the hardness exceeds 80 degrees, the contact area between the developing roller and the photosensitive drum or the like becomes small, and good development may not be performed. Further, the toner is damaged, and the toner adheres to the photoreceptor or the layered blade, and the image is likely to be defective. Conversely, if the hardness is too low, the frictional force between the photoconductor and the stratification blade becomes large, and image defects such as jitter may occur.
[0033]
Since the semiconductive elastic layer 3 is used in contact with a photoreceptor, a laminating blade, or the like, it is preferable that the compression set be as small as possible even when the hardness is set to a low hardness. % Is preferable.
[0034]
The surface roughness of the semiconductive elastic layer 3 is not particularly limited, but is preferably 15 μmRz or less, particularly preferably 1 to 10 μmRz in terms of JIS 10-point average roughness. When the surface roughness exceeds 15 μmRz, the thickness of the toner layer of the one-component developer (toner) and the uniformity of charging may be impaired. However, by adjusting the surface roughness to 15 μmRz or less, the adhesion of the toner can be improved. It is possible to more reliably prevent image deterioration due to abrasion of the roller during long-term use.
[0035]
The roller surface may be polished in order to obtain an appropriate roughness, but providing a polishing step greatly deteriorates productivity and causes an increase in cost. Therefore, it is preferable to optimize the surface roughness of the mold at the time of molding the elastic body and use it as it is.
[0036]
In the developing roller of the present invention, as shown in FIG. 1, an electron beam-curable resin is cured on the semiconductive elastic layer 3 in order to adjust the resistance and control the amount of toner charge and the amount of conveyance. A resin coating layer 3a is formed.
[0037]
As shown in FIG. 1, the developing roller of the present invention has a UV curable resin or an electron beam curable resin on the semiconductive elastic layer 3 in order to adjust the resistance and control the amount of toner charge and the amount of conveyance. The resin coating layer 3a formed by curing the resin is formed. Examples of the ultraviolet curable resin or the electron beam curable resin forming the resin coating layer 3a include polyester resin, polyether resin, fluorine resin, epoxy resin, amino resin, polyamide resin, acrylic resin, acrylic urethane resin, urethane resin, and alkyd. Examples thereof include a resin, a phenol resin, a melamine resin, a urea resin, a silicone resin, and a polyvinyl butyral resin, and one or more of these can be used as a mixture. Further, modified resins in which a specific functional group is introduced into these resins can also be used.
[0038]
Further, it is preferable to introduce a crosslinked structure in order to improve the mechanical strength and environmental resistance of the resin coating layer 3a.
[0039]
The ultraviolet curable resin or the electron beam curable resin is not particularly limited, but a (meth) acrylate-based resin composition containing a (meth) acrylate oligomer is preferable.
[0040]
Examples of such (meth) acrylate oligomer include urethane (meth) acrylate oligomer, epoxy (meth) acrylate oligomer, ether (meth) acrylate oligomer, ester (meth) acrylate oligomer, and polycarbonate (meth) acrylate oligomer. And fluorine-based and silicone-based acrylic oligomers.
[0041]
The (meth) acrylate oligomer includes compounds such as polyethylene glycol, polyoxypropylene glycol, polytetramethylene ether glycol, bisphenol A type epoxy resin, phenol novolak type epoxy resin, and adduct of polyhydric alcohol and ε-caprolactone; It can be synthesized by reaction with (meth) acrylic acid or by urethane-forming a polyisocyanate compound and a (meth) acrylate compound having a hydroxyl group.
[0042]
The urethane-based (meth) acrylate oligomer is obtained by urethane-forming a polyol, an isocyanate compound, and a (meth) acrylate compound having a hydroxyl group.
[0043]
Examples of the epoxy-based (meth) acrylate oligomer include any compound as long as it is a reaction product of a compound having a glycidyl group and (meth) acrylic acid. Among them, a benzene ring, a naphthalene ring, a spiro ring, dicyclopentadiene, A reaction product of a compound having a cyclic structure such as tricyclodecane and having a glycidyl group and (meth) acrylic acid is preferred.
[0044]
Further, ether (meth) acrylate oligomer, ester (meth) acrylate oligomer and polycarbonate (meth) acrylate oligomer are obtained by reacting polyol (polyether polyol, polyester polyol and polycarbonate polyol) with (meth) acrylic acid. Can be obtained by
[0045]
A reactive diluent having a polymerizable double bond is added to the resin composition for viscosity adjustment as needed. Examples of such a reactive diluent include a monofunctional, bifunctional or polyfunctional polymerizable compound having a structure in which (meth) acrylic acid is bonded to a compound containing an amino acid or a hydroxyl group by an esterification reaction and an amidation reaction. Etc. can be used. These diluents are preferably used in an amount of usually 10 to 200 parts by weight per 100 parts by weight of the (meth) acrylate oligomer.
[0046]
The resin coating layer 3a may be mixed with a conductive agent for the purpose of controlling its conductivity. As the conductive agent, those similar to those exemplified as the conductive agent used in the semiconductive elastic layer 3 are used. Can be exemplified.
[0047]
The compounding amount of the conductive agent in the resin coating layer 3a is preferably 20 parts by weight or less, more preferably 0.01 to 20 parts by weight, particularly preferably 1 to 10 parts by weight, based on 100 parts by weight of the resin.
[0048]
When the conductive agent is a transparent conductive agent such as a metal such as tin oxide, titanium oxide, zinc oxide, potassium titanate, barium and nickel, and copper, and a metal oxide, the ultraviolet ray is easily transmitted, and the ultraviolet ray is hardened. The effect of not hindering the polymerization of the mold resin is obtained. The amount of the transparent conductive agent is preferably 100 parts by weight or less, more preferably 1 to 80 parts by weight, particularly preferably 10 to 50 parts by weight, based on 100 parts by weight of the resin.
[0049]
When carbon black is blended as a conductive agent in the electron beam-curable resin coating layer, the amount is preferably 100 parts by weight or less, more preferably 1 to 80 parts by weight, and particularly preferably 1 to 50 parts by weight, per 100 parts by weight of the resin.
[0050]
When the resin of the resin coating layer is an ultraviolet curable resin, it preferably contains a polymerization initiator. As the UV polymerization initiator, known ones can be used. For example, 4-dimethylaminobenzoic acid, 4-dimethylaminobenzoic acid ester, 2,2-dimethoxy-2-phenylacetophenone, acetophenone diethylketal, alkoxy Benzophenone derivatives such as acetophenone, benzyldimethylketal, benzophenone and 3,3-dimethyl-4-methoxybenzophenone, 4,4-dimethoxybenzophenone, 4,4-diaminobenzophenone, alkyl benzoylbenzoate, bis (4-dialkylaminophenyl) Ketones, benzyl derivatives such as benzyl and benzyl methyl ketal, benzoin derivatives such as benzoin and benzoin isobutyl ether, benzoin isopropyl ether, 2-hydroxy-2-meth Lepropiophenone, 1-hydroxycyclohexylphenyl ketone, xanthone, thioxanthone and thioxanthone derivatives, fluorene, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl Pentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1,2-benzyl-2-dimethylamino -1- (morpholinophenyl) -butanone-1 and the like. These may be used alone or in combination of two or more.
[0051]
The amount of the ultraviolet polymerization initiator is preferably 0.1 to 10 parts by weight per 100 parts by weight of the (meth) acrylate oligomer.
[0052]
In the present invention, in addition to the above essential components, a tertiary amine such as triethylamine and triethanolamine, and an alkyl phosphine such as triphenylphosphine may be used, if necessary, to promote a photopolymerization reaction using the above photopolymerization initiator. A thioether-based photopolymerization accelerator such as a p-thiodiglycol and the like may be added. The addition amount of these compounds is usually preferably in the range of 0.01 to 10 parts by weight per 100 parts by weight of the (meth) acrylate oligomer.
[0053]
It should be noted that various other additives can be added to the resin coating layer 3a as needed.
[0054]
As a method for forming the resin coating layer 3 a on the semiconductive elastic layer 3, a coating liquid comprising a composition containing the resin component and the additive is applied to the surface of the semiconductive elastic layer 3. Irradiation with ultraviolet rays or electron beams is preferably employed. This coating liquid preferably does not contain a solvent.
[0055]
As a method of applying the coating liquid, a spray method, a roll coater method, a dipping method, or the like can be used.
[0056]
The thickness of the resin coating layer 3a is not particularly limited, but is usually preferably about 1 to 100 μm, particularly about 3 to 100 μm, and particularly preferably about 5 to 100 μm. When the thickness is less than 1 μm, the charging performance of the surface layer may not be sufficiently secured due to friction during durability. On the other hand, when the thickness is more than 100 μm, the surface of the developing roller becomes hard and damages the toner. As a result, the toner may adhere to an image forming body such as a photoreceptor or a layered blade, resulting in an image defect.
[0057]
The developing roller of the present invention is not particularly limited, but preferably has an electric resistance value of 10 ⁴ Ω to 10 ¹⁰ Ω, particularly preferably 10 ⁵ Ω to 10 ⁹ Ω when 100 V is applied. If the resistance is less than 10 ⁴ Ω, gradation control may become extremely difficult in some cases, and a bias leak may occur when an image forming member such as a photoreceptor has a defect. On the other hand, if the resistance value exceeds 10 ¹⁰ Ω, for example, when developing the toner on a latent image holding member such as a photoconductor, the developing bias causes a voltage drop due to the high resistance of the developing roller itself, and the developing bias is insufficient. In some cases, a sufficient image density cannot be obtained because the developing bias cannot be secured. The resistance value can be measured from a current value obtained by applying a voltage of 100 V between the shaft and the counter electrode by pressing the developing roller against a flat or cylindrical counter electrode at a predetermined pressure, for example. .
[0058]
As described above, it is important to properly and uniformly control the resistance value of the developing roller in order to keep the electric field strength for toner movement appropriate and uniform. It is important to control the charge holding ability of the toner and keep it uniform, in order to make the charge amount of the toner proper and uniform. In this case, the surface charge holding ability is examined by measuring the surface resistance by arranging a pair of electrodes on the surface of the developing roller and applying a constant voltage between the two electrodes. Does not flow, but also flows inside the developing roller, so that accurate evaluation of the surface of the developing roller cannot be performed. In addition, although improvement in accuracy by the four-terminal method has been proposed, especially in the case of a stacked developing roller, the surface layer is quite thin, and it is difficult to characterize only the surface in this method. . Therefore, the characteristic values obtained by these conventional measurement methods cannot accurately represent the surface charge holding ability.
[0059]
Therefore, in the present invention, in a constant temperature environment of 22 ° C. and 50% RH, a voltage of 8 kV is applied to a corona discharger arranged at a distance of 1 mm from the surface of the developing roller to generate corona discharge and charge the surface. The surface charge retention ability is evaluated based on the maximum value of the surface potential 0.35 seconds after the application, and the maximum value is set to 90 V or less, preferably 50 V or less. In this case, if the maximum value exceeds 90 V, the toner is supplied to the image forming body, and when the toner is removed from the surface of the developing roller, the charge in that portion stays there without escaping. Next, the charge amount of the toner charged in the same portion is low. Further, when the toner is continuously rotated without being supplied to the image forming body, the toner charge gradually increases, and in some cases, the electric field generated by the toner charging exceeds the maximum value, so that the image forming body such as a photoreceptor is formed. Discharge may occur between the two, and image defects may occur.
[0060]
Here, the reason why the surface potential was measured 0.35 seconds after charging due to the occurrence of corona discharge is as follows. That is, it is difficult to measure the surface potential immediately after charging by corona discharge, and since the initial surface potential is unstable, it is not preferable to control the characteristic value in this portion. When an actual process in image formation such as development is considered, for example, when the developing roller has a roller shape, the rotation speed is usually 0.35 sec / 1 rotation, and the control of residual charges on the surface may be performed in this time.
[0061]
The measurement of the maximum surface potential of the developing roller can be performed by, for example, the apparatus shown in FIG. That is, both ends of the shaft 2 of the developing roller 1 are gripped by the chuck 11 to support the developing roller 1, and a small corotron discharger (corona discharger) 12 and a surface voltmeter 13 are juxtaposed at a predetermined interval. The measuring unit thus arranged is opposed to the surface of the developing roller 1 with a gap of 1 mm, and the measuring units 12 and 13 are moved at a constant speed from one end to the other end of the developing roller 1 while the developing roller 1 is kept stationary. The method of measuring the surface potential 0.35 seconds after the surface charge is applied while applying the surface charge is preferably adopted.
[0062]
In the present invention, the ultraviolet-curable resin composition or the electron beam-curable resin composition for forming the resin coating layer may be formed on one surface of a metal plate such as a copper plate or SUS so that the thickness after curing is 30 μm. It is preferable that the maximum surface potential measured in the same manner as described above is 150 V or less, particularly 90 V or less, for the resin layer formed by coating and curing by irradiating an ultraviolet ray or an electron beam. In order for the maximum surface potential of the resin layer to be 150 V or less as described above, for example, an appropriate amount of an appropriate conductive agent may be blended into the ultraviolet curable resin or the electron beam curable resin composition.
[0063]
In order to realize a developing roller having a maximum surface potential of 90 V or less, the resin layer formed as described above preferably has a maximum surface potential of 150 V or less. Even if the maximum surface potential exceeds 150 V, a developing roller having a maximum surface potential of 90 V or less can be realized by reducing the thickness of the resin coating layer to, for example, 3 to 10 μm.
[0064]
The developing roller of the present invention can be incorporated in an image forming apparatus using toner. Specifically, as shown in FIG. 2, a toner applying roller 4 for supplying toner and a photosensitive roller holding an electrostatic latent image are provided. The developing roller 1 of the present invention is disposed between and in contact with the photosensitive drum 5, the toner 6 is supplied to the developing roller 1 by the toner coating roller 4, and the developing roller 1 is Thus, the toner can be supplied to the photosensitive drum 5 from the thin layer, and the toner can be attached to the electrostatic latent image on the photosensitive drum 5 to visualize the latent image. Since the details of FIG. 2 have been described in the related art, the description thereof will be omitted.
[0065]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.
[0066]
[Example 1]
Propylene oxide and ethylene oxide are added to glycerin, and 100 parts (parts by weight, hereinafter the same) of polyether polyol (OH value: 33) having a molecular weight of 5000, 1.0 part of 1,4-butanediol, a silicone surfactant 1.5 parts, 0.5 parts of nickel acetylacetonate, 0.01 parts of dibutyltin dilaurate and 0.01 parts of sodium perchlorate were added and mixed with a mixer to prepare a polyol composition. After stirring and defoaming the polyol composition under reduced pressure, 17.5 parts of urethane-modified MDI was added, stirred for 2 minutes, then poured into a mold heated to 110 ° C., and cured for 2 hours. Thus, a roller body having an elastic layer having an outer diameter of 12 mm and a total length of the elastic layer portion of 210 mm was obtained.
[0067]
As shown in Table 1, on the outer peripheral surface of the roller body manufactured as described above, a urethane-based ultraviolet-curable resin composition containing 2 PHR of sodium perchlorate as an ion conductive agent was applied with a roll coater so as to have a thickness of 30 μm. After application, the roller was rotated using a Unicure UVH-0252C device manufactured by Ushio Inc. while irradiating with ultraviolet light at an illuminance of 300 mW and an integrated light amount of 1000 mJ / cm ² . A resin coating layer having a certain thickness was formed.
[0068]
With respect to the obtained developing roller, the resistance value when a voltage of 100 V was applied between the developing roller and the counter electrode (metal drum) was measured using the rotational resistance measuring device shown in FIG.
[0069]
Further, using the apparatus shown in FIG. 3, a voltage of 8 kV is applied to the roller to charge the roller surface by corona discharge, and the measuring units 12 and 13 are moved at a speed of 200 mm / sec. After 35 seconds, the surface potential was measured. The shape and dimensions of the measuring unit are as shown in FIG. By this method, the entire roller surface was measured, and the maximum value was measured as the surface potential value. The measurement environment was controlled at a temperature of 22 ° C. and a humidity of 50%.
[0070]
Further, with respect to the ultraviolet-curable resin composition used for forming the resin coating layer, a 30-μm-thick resin layer was formed on a copper plate under the same conditions as when the resin coating layer was formed. Similarly, the maximum surface potential was measured.
[0071]
Next, an image was formed by attaching the produced developing roller to the image forming apparatus shown in FIG. 2, and the obtained image was evaluated.
[0072]
Table 1 shows the results.
[0073]
[Example 2]
A developing roller was manufactured in the same manner as in Example 1, except that sodium perchlorate was not used in forming the resin coating layer, and the thickness of the resin coating layer was changed to 5 μm. It was shown to.
[0074]
[Example 3]
A developing roller was manufactured in the same manner as in Example 1 except that the roller body was formed as follows, and the evaluation was performed in the same manner. The results are shown in Table 1.
[0075]
1. Sannics FA952 (Sanyo Kasei Kogyo Co., Ltd., polyether polyol, OH value = 37) 100 parts, SRX274C (Toray Dow Corning Silicone Co., Ltd. foaming agent) 1 part, TOYOCAT NP (Tosoh Corporation amine catalyst) Eight parts, 1.5 parts of TOYOCAT EP (amine catalyst manufactured by Tosoh Corporation) and 59 parts of Sunform IC-716 (tolylene diisocyanate manufactured by Sanyo Chemical Industries, Ltd.) were mechanically stirred and foamed.
[0076]
A metal shaft having an outer diameter of 6.0 mm and a length of 240 mm is arranged from one side opening of a metal cylindrical type having an inner diameter of 16 mm and a length of 250 mm and having a fluorine-processed surface, and the above-mentioned foamed polyurethane material is foamed for RIM molding. Injected from machine.
[0077]
Next, the mold into which the foamed polyurethane raw material was injected was cured in an oven at 80 ° C. for 20 minutes, and then demolded to obtain a roller body having an elastic layer having an outer diameter of 12 mm and a total length of an elastic layer portion of 210 mm.
[0078]
[Example 4]
In forming the resin coating layer, carbon black was blended with 20 PHR instead of sodium perchlorate, and the roller was rotated using a Min-EB device manufactured by Ushio Inc. instead of ultraviolet rays, while accelerating voltage was 30 kV and tube current was A developing roller was manufactured in the same manner as in Example 1 except that the electron beam was irradiated under the conditions of 300 μA, an irradiation distance of 100 mm, an atmosphere of 1 Torr, and an irradiation time of 1 minute. The developing roller was evaluated in the same manner, and the results are shown in Table 1. Was.
[0079]
[Comparative Example 1]
A developing roller was manufactured in the same manner as in Example 1, except that sodium perchlorate was not used in forming the resin coating layer, and the thickness of the resin coating layer was set to 120 μm. 1 is shown.
[0080]
[Comparative Example 2]
A developing roller was manufactured in the same manner as in Example 4 except that carbon black was not used in forming the resin coating layer, and the thickness of the resin coating layer was set to 120 μm. It was shown to.
[0081]
[Table 1]

[0082]
As is clear from the results shown in Table 1, the rollers of Examples 1 to 4 in which the surface charge holding ability was optimized by the maximum value of the surface potential 0.35 seconds after corona charging ensured a good image. Can be formed.
[0083]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the occurrence of image defects such as spots and density unevenness, as well as the occurrence of white image fog as much as possible, and to reliably obtain a high-quality image. And an image forming apparatus using the same.
[Brief description of the drawings]
FIG. 1 is a sectional view of a developing roller.
FIG. 2 is a configuration diagram of an image forming apparatus.
FIG. 3 is a schematic diagram illustrating an example of an apparatus for measuring a surface potential of a developing roller.
FIG. 4 is a schematic plan view showing shapes and dimensions of measurement units used in Examples and Comparative Examples.
FIG. 5 is a schematic diagram showing a rotational resistance measuring instrument used in Examples and Comparative Examples.
[Explanation of symbols]
Reference Signs List 1 developing roller 2 shaft 3 semiconductive elastic layer 3a resin coating layer 6 toner 11 chuck 12 corotron discharger (corona discharger)
13 Surface electrometer

Claims (6)

In a developing roller having an elastic layer and at least one resin coating layer formed on an outer peripheral surface of the elastic layer,
The resin coating layer is made of an ultraviolet curable resin or an electron beam curable resin,
When a voltage of 8 kV is applied to a corona discharger arranged at a distance of 1 mm from the surface of the resin coating layer to generate a corona discharge and charge the surface, the maximum surface potential after 0.35 seconds. A developing roller having a value of 90 V or less. 2. The developing roller according to claim 1, wherein an electric resistance value when 100 V is applied is 10 < ⁴ > to ¹⁰ < ¹⁰ > [Omega]. The thickness according to claim 1 or 2, wherein the ultraviolet-curable resin composition or the electron beam-curable resin composition forming the resin coating layer is applied to one surface of a metal plate and cured by ultraviolet light or an electron beam. When a voltage of 8 kV is applied to a corona discharger disposed at a distance of 1 mm from the surface of the resin layer of 30 μm to generate a corona discharge and charge the surface, the maximum surface potential after 0.35 seconds is obtained. A developing roller having a value of 150 V or less. The developing roller according to claim 1, wherein the resin coating layer contains a conductive agent. The resin coating layer according to any one of claims 1 to 4, wherein the resin coating layer is coated with a coating liquid comprising a solvent-free ultraviolet curable resin composition or an electron beam curable resin composition, and cured by ultraviolet irradiation or electron beam irradiation. A developing roller, wherein An image forming apparatus having a developing roller, wherein the developing roller is the developing roller according to any one of claims 1 to 5.

Images