JP5083940B2 - Charging roller and manufacturing method thereof - Google Patents

Description

The present invention relates to a charging roller (hereinafter also simply referred to as “roller”) and a method for manufacturing the same , and more particularly to improvement in image quality of the charging roller.

  Conventionally, in an image forming apparatus using an electrophotographic method such as a copying machine, a printer, or a facsimile, first, the surface of the photosensitive member is uniformly charged, and an image is projected onto the photosensitive member from the optical system so as to be exposed to light. An electrostatic latent image is obtained by an electrostatic latent image process in which a latent image is formed by erasing the charged portion, and then the toner image is formed by toner adhesion and the toner image is transferred to a recording medium such as paper. The method of printing is taken.

  In this case, a corona discharge method has been generally employed as an operation for charging the first photoreceptor. However, this corona discharge method requires a high voltage application of 6 to 10 kV, so it is not preferable from the viewpoint of safety maintenance of the machine, and harmful substances such as ozone and NOx are generated during corona discharge. There was also an environmental problem.

  For this reason, efforts have been made to charge systems that can be charged at a lower applied voltage than corona discharge and that can suppress the generation of harmful substances such as ozone. There has been proposed a charging method using a contact method in which a charging member to which a voltage is applied is brought into contact with a charged body such as a photosensitive body at a predetermined pressure to charge the charged body.

  As a charging member used in this contact charging method, for example, a conductive elastic layer (base layer) made of rubber, urethane foam or the like is formed on the outer periphery of a core metal (shaft), and further, surface smoothness is ensured or toner is used. In order to prevent adhesion, a multilayer with a coating layer formed by applying a resin solution in which a resin such as urethane or nylon is dissolved in an organic solvent or a resin solution in which water is dissolved or dispersed in water is applied by dipping or spraying. A charging roller having a structure is known. In addition, in order to improve the adhesion between the base layer and the coating layer, a technique of providing an adhesive layer between these layers is also well known.

On the other hand, in order to obtain good charging performance in the charging roller, it is important to adjust the resistance value. Therefore, in the charging roller having such a multilayer film, a different resistance area is set for each layer, and the desired performance is obtained. Techniques to obtain are also known. For example, in the present applicant, in the charging roller in which at least two coating layers are provided on the base layer via the adhesive layer, the resistance value of the base layer and the adhesive layer is set within a predetermined range, respectively. In a charging roller in which a base layer, at least one lower layer, and a surface layer are sequentially provided on the outer peripheral surface of the core metal or a technique for realizing performance, at least one high resistance layer having a predetermined high resistance value is provided as the lower layer. Providing a technique for improving the pressure resistance performance and durability performance while maintaining good charging performance is provided (Patent Documents 1 and 2).
JP 2002-229305 A (Claims etc.) JP 2004-245933 A (Claims etc.)

  Known methods for solving the problems such as the occurrence of defective charging streaks in the image and obtaining a good image include increasing the product resistance of the charging roller and controlling the surface roughness. Yes. However, the method of increasing the roller resistance has a problem that unevenness of resistance is likely to occur, and in the method of controlling the surface roughness, if Rz is large, the toner contamination is worsened. In either case, the image quality could not be improved without causing other problems.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a charging roller capable of obtaining a good image by solving the problems in the prior art and suppressing occurrence of defective charging lines without causing other problems, and a method for manufacturing the same. There is.

  As a result of intensive studies, the inventors of the present invention have improved charging failure lines by adjusting the ratio of the resistance values of each coating layer within a predetermined range in a charging roller composed of a plurality of coating layers. As a result, the present invention has been completed.

That is, the charging roller of the present invention is a charging roller that contacts a member to be charged and charges the member to be charged by applying a voltage to the member to be charged. In a charging roller comprising a urethane foam layer, a lower layer, and a surface layer in sequence,
The lower layer is formed using a urethane resin, the surface layer is formed using a fluororesin,
The ratio R2 / R1 of the resistance value R1 in the state where the lower layer is formed on the outer periphery of the shaft and the surface resistance value R2 in the state where the surface layer is formed on the outer periphery of the shaft is 2.5 to 15 It is characterized by being within the range.
In the charging roller of the present invention, R2 / R1 is more preferably in the range of 8.6 to 15, and the resistance of the lower layer is preferably adjusted using an ionic conductive agent. it can.

Further, the manufacturing method of the charging roller of the present invention, in order to manufacture the charging roller by sequentially forming a urethane foam layer, a lower layer, and a surface layer on the outer periphery of the shaft,
The lower layer is formed by a dipping method using a urethane resin, and the surface layer is formed by a dipping method using a fluororesin,
The ratio R2 / R1 of the resistance value R1 in the state where the lower layer is formed on the outer periphery of the shaft and the surface resistance value R2 in the state where the surface layer is formed on the outer periphery of the shaft is 2.5 to 15 It is characterized by adjusting within the range.

  According to the present invention, with the above-described configuration, it is possible to realize a charging roller capable of suppressing the occurrence of defective charging streaks without causing other problems such as uneven resistance and obtaining a good image. It was.

Hereinafter, preferred embodiments of the present invention will be described in detail.
FIG. 1 is a schematic sectional view of a charging roller according to a preferred embodiment of the present invention. The charging roller 10 of the present invention is to contact a charged body and apply a voltage to the charged body to charge the charged body. As shown in FIG. The urethane foam layer 2, the lower layer 3, and the surface layer 4 are sequentially provided.

  The charging roller 10 of the present invention has a ratio R2 / R1 between the resistance value R1 in the state where the lower layer 3 is formed on the outer periphery of the shaft 1 and the resistance value R2 in the state where the outer layer 4 is formed on the outer periphery of the shaft 1. Is characterized by being in the range of 2.5-15. The resistance ratio of a conventional charging roller having the same multilayer coating film structure is about 0.1 to 2.3. In other words, in the present invention, the lower layer 3 has a lower resistance, the surface layer 4 has a higher resistance, and the resistance ratio of the surface layer / lower layer is increased to suppress the occurrence of defective charging lines and improve the image quality. It has become possible to achieve. The reason for this is presumed to be that by increasing the resistance ratio, the shared voltage to the surface layer portion of the charging roller is increased, the discharge performance is improved, and the charging capability is increased. The resistance value R1 in the present invention can be measured in a state where the surface layer is peeled off by polishing or the like in the product.

  In the present invention, it is only important that the ratio of the resistance values be within the above range by adjusting the volume resistance values of the lower layer 3 and the surface layer 4, whereby a charging roller capable of obtaining a good image can be obtained. This is realized, and the specific configuration, material, and the like of the other rollers can be appropriately selected according to a conventional method, and are not particularly limited.

  The shaft 1 is not particularly limited as long as it has good conductivity. For example, a steel material such as sulfur free-cutting steel plated with nickel or zinc, or a metal such as iron, stainless steel, or aluminum A metal shaft such as a solid body made of metal or a cylindrical body made by hollowing out the inside thereof can be suitably used.

  The polyurethane raw material for forming the urethane foam layer 2 is not particularly limited as long as it contains a urethane bond in the resin. As the polyisocyanate constituting the polyurethane raw material, aromatic isocyanate or a derivative thereof, aliphatic isocyanate or a derivative thereof, alicyclic isocyanate or a derivative thereof is used. Among these, aromatic isocyanate or a derivative thereof is preferable, and tolylene diisocyanate or a derivative thereof, diphenylmethane diisocyanate or a derivative thereof is particularly preferably used. Tolylene diisocyanate or derivatives thereof include crude tolylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, these These are urea-modified products, burette-modified products, carbodiimide-modified products, urethane-modified products modified with polyols, and the like. As diphenylmethane diisocyanate or a derivative thereof, for example, diphenylmethane diisocyanate or a derivative thereof obtained by phosgenating diaminodiphenylmethane or a derivative thereof is used. Examples of the derivatives of diaminodiphenylmethane include polynuclear bodies, and pure diphenylmethane diisocyanate obtained from diaminodiphenylmethane, polymeric diphenylmethane diisocyanate obtained from a polynuclear body of diaminodiphenylmethane, and the like can be used. Regarding the number of functional groups of polymeric diphenylmethane diisocyanate, a mixture of pure diphenylmethane diisocyanate and polymeric diphenylmethane diisocyanate having various functional groups is usually used, and the average number of functional groups is preferably 2.05 to 4.00, more preferably 2. .50 to 3.50 are used. Derivatives obtained by modifying these diphenylmethane diisocyanates or derivatives thereof, such as urethane modified products modified with polyols, dimers formed by uretidione formation, isocyanurate modified products, carbodiimide / uretonimine modified products, allophanate modified products , Urea-modified products, burette-modified products, and the like can also be used. Also, several types of diphenylmethane diisocyanate and derivatives thereof can be blended and used.

  Polyol components constituting the polyurethane raw material include polyether polyols obtained by addition polymerization of ethylene oxide and propylene oxide, polytetramethylene ether glycol, polyester polyols obtained by condensing acid components and glycol components, polyester polyols obtained by ring-opening polymerization of caprolactone, Polycarbonate diol or the like can be used. Polyether polyols obtained by addition polymerization of ethylene oxide and propylene oxide are, for example, water, propylene glycol, ethylene glycol, glycerin, trimethylolpropane, hexanetriol, triethanolamine, diglycerin, pentaerythritol, ethylenediamine, methylglucotite, Examples include aromatic diamines, sorbitol, sucrose, phosphoric acid and the like as starting materials, and addition polymerization of ethylene oxide and propylene oxide. Particularly, water, propylene glycol, ethylene glycol, glycerin, trimethylolpropane, Those starting from hexanetriol are preferred. Regarding the ratio of ethylene oxide and propylene oxide to be added and the microstructure, the ratio of ethylene oxide is preferably 2 to 95% by weight, more preferably 5 to 90% by weight. In particular, those having ethylene oxide added to the terminal are preferably used. Further, the arrangement of ethylene oxide and propylene oxide in the molecular chain is preferably random. The molecular weight of the polyether polyol is bifunctional when water, propylene glycol, or ethylene glycol is used as a starting material, and preferably has a weight average molecular weight in the range of 300 to 6000, particularly in the range of 400 to 3000. preferable. Further, when glycerin, trimethylolpropane, and hexanetriol are used as starting materials, they are trifunctional and preferably have a weight average molecular weight in the range of 900 to 9000, particularly preferably in the range of 1500 to 6000. Further, a bifunctional polyol and a trifunctional polyol can be appropriately blended and used.

  Polytetramethylene ether glycol is obtained, for example, by cationic polymerization of tetrahydrofuran, and those having a weight average molecular weight of 400 to 4000, particularly 650 to 3000 are preferably used. It is also preferable to blend polytetramethylene ether glycols having different molecular weights. Furthermore, polytetramethylene ether glycol obtained by copolymerizing alkylene oxide such as ethylene oxide or propylene oxide can also be used. It is also preferable to use a blend of polytetramethylene ether glycol and a polyether polyol obtained by addition polymerization of ethylene oxide and propylene oxide. In this case, polytetramethylene ether glycol, addition polymerization of ethylene oxide and propylene oxide was performed. It is preferably used so that the ratio with the polyether polyol is in the range of 95: 5 to 20:80, particularly in the range of 90:10 to 50:50. In addition to the polyol component, a polymer polyol obtained by modifying the polyol with acrylonitrile, a polyol obtained by adding melamine to the polyol, a diol such as butanediol, a polyol such as trimethylolpropane, or a derivative thereof can be used in combination.

  In addition, the polyol may be prepolymerized with polyisocyanate in advance, and as a method thereof, the polyol and polyisocyanate are put in a suitable container and sufficiently stirred, and 30 to 90 ° C., more preferably 40 to 70 ° C., The method of heat-maintaining for 6 to 240 hours, More preferably, 24 to 72 hours is mentioned. In this case, the ratio of the amount of polyol and polyisocyanate is preferably adjusted so that the isocyanate content of the resulting prepolymer is 4 to 30% by weight, more preferably 6 to 15% by weight. If the isocyanate content is less than 4% by weight, the stability of the prepolymer is impaired, and the prepolymer may be cured during storage, making it impossible to use. If the isocyanate content exceeds 30% by weight, the content of non-prepolymerized polyisocyanate increases, and this polyisocyanate reacts with the polyol component used in the subsequent polyurethane curing reaction and the prepolymerization reaction. The effect of using the prepolymer method is diminished because it cures by a reaction mechanism similar to the one-shot manufacturing method that does not pass. In the case of using an isocyanate component in which a polyol is prepolymerized with polyisocyanate in advance, in addition to the above polyol component, diols such as ethylene glycol and butanediol, polyols such as trimethylolpropane and sorbitol, and those Derivatives can also be used.

  Addition of conductive agents such as ionic conductive agents and electronic conductive agents, fillers such as carbon black and inorganic carbonates, antioxidants such as phenol and phenylamine, low friction agents, charge control agents, etc. to polyurethane raw materials be able to. Examples of ionic conductive agents include tetraethylammonium, tetrabutylammonium, dodecyltrimethylammonium (eg, lauryltrimethylammonium), hexadecyltrimethylammonium, octadecyltrimethylammonium (eg, stearyltrimethylammonium), benzyltrimethylammonium, modified fatty acid dimethylethyl. Perchlorates such as ammonium, chlorates, hydrochlorides, bromates, iodates, borofluorides, sulfates, ethyl sulfates, carboxylates, ammonium salts such as sulfonates, lithium, Perchlorate, chlorate, hydrochloride, bromate, iodate, borofluoride, trifluoromethyl of alkali metals and alkaline earth metals such as sodium, potassium, calcium and magnesium Sulfate, and sulfonic acid salts. 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; for ink subjected to oxidation treatment Examples thereof include carbon, pyrolytic carbon, natural graphite, and artificial graphite; conductive metal oxides such as tin oxide, titanium oxide, and zinc oxide; metals such as nickel, copper, silver, and germanium. These conductive agents may be used alone or in combination of two or more. There is no restriction | limiting in particular in the compounding quantity, Although it can select suitably as desired, Usually, the ratio of 0.1-40 weight part with respect to 100 weight part of polyurethane raw materials, Preferably 0.3-20 weight part It is.

  Catalysts used for the curing reaction of polyurethane raw materials include monoamines such as triethylamine and dimethylcyclohexylamine, diamines such as tetramethylethylenediamine, tetramethylpropanediamine, and tetramethylhexanediamine, pentamethyldiethylenetriamine, pentamethyldipropylenetriamine, tetra Triamines such as methylguanidine, triethylenediamine, dimethylpiperazine, methylethylpiperazine, cyclic amines such as methylmorpholine, dimethylaminoethylmorpholine, dimethylimidazole, dimethylaminoethanol, dimethylaminoethoxyethanol, trimethylaminoethylethanolamine, methylhydroxy Alcohol amines such as ethyl piperazine and hydroxyethyl morpholine; (Dimethylaminoethyl) ether, ether amines such as ethylene glycol bis (dimethyl) aminopropyl ether, stannous octoate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin marker peptide, dibutyltin thiocarboxylate, dibutyltin dimaleate, And organic metal compounds such as dioctyltin marker peptide, dioctyltin thiocarboxylate, phenylmercury propionate and lead octenoate. These catalysts may be used alone or in combination of two or more.

  In the present invention, it is preferable to add a silicone foam stabilizer and various surfactants to the polyurethane raw material in order to stabilize the cells of the foam material. As the silicone foam stabilizer, a dimethylpolysiloxane-polyoxyalkylene copolymer or the like is suitably used, and those composed of a dimethylpolysiloxane moiety having a molecular weight of 350 to 15000 and a polyoxyalkylene moiety having a molecular weight of 200 to 4000 are particularly preferable. . The molecular structure of the polyoxyalkylene moiety is preferably an addition polymer of ethylene oxide or a co-addition polymer of ethylene oxide and propylene oxide, and its molecular terminal is preferably ethylene oxide. Examples of the surfactant include cationic surfactants, anionic surfactants, ionic surfactants such as amphoteric, nonionic surfactants such as various polyethers and various polyesters. The blending amount of the silicone foam stabilizer and various surfactants is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the polyurethane raw material. The blending amount of the silicone foam stabilizer and various surfactants is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the polyurethane raw material.

The urethane foam used in the present invention preferably has a density of 0.2 to 0.8 g / cm ³ , more preferably 0.3 to 0.6 g / cm ³ . Further, the Asker C hardness of the urethane foam is preferably 20 to 65 °, more preferably 25 to 45 °. In the present invention, as a method for foaming the polyurethane raw material in advance, a conventionally used method such as a mechanical floss method, a water foam method, a foaming agent floss method, etc. can be used, but the density is 0.2 to 0. From the viewpoint of obtaining a polyurethane foam having an closed cell structure with an .8 g / cm ³ and Asker C hardness of 20 to 65 °, it is preferable to use a mechanical floss method in which foaming is performed by mechanical stirring while mixing an inert gas. Here, the inert gas used in the mechanical froth method may be an inert gas in the polyurethane reaction, and in addition to inert gases in a narrow sense such as helium, argon, xenon, radon, krypton, nitrogen, carbon dioxide, drying Examples thereof include gases that do not react with polyurethane raw materials such as air. A polyurethane foam in which a self-skin layer (thin layered film) is formed on a portion in contact with the metal mold can be obtained by casting the foamed polyurethane raw material into a metal mold or the like and curing it. At that time, the moldability can be imparted to the metal mold by a method such as coating the inner surface of the metal mold with a fluororesin or the like.

  Moreover, there is no restriction | limiting in particular about the molding conditions of the urethane foam layer 2, It can follow a normal condition, for example, starts foaming of a polyurethane raw material in the temperature of 15-80 degreeC, Preferably it is the range of 20-65 degreeC, The urethane foam layer 2 can be obtained by performing curing at a temperature of about 70 to 120 ° C. after the completion of pouring into the metal mold in which the shaft 1 is disposed, and then removing the mold.

The resistance value of the urethane foam layer 2 is not particularly limited, but can usually be within a range of 10 ⁰ to 10 ⁸ Ω, particularly 10 ² to 10 ⁵ Ω.

  The lower layer 3 can be formed of an appropriate resin as desired. Examples of such a resin include nylon, polyester, urethane-modified acrylic resin, phenol resin, acrylic resin, epoxy resin, urethane resin, urea resin, and fluorine resin. Etc. In particular, it is preferably formed using a urethane resin. Moreover, desired conductivity can be provided in the lower layer 3 by appropriately containing the above-described ionic conductive agent or electronic conductive agent as a conductive agent. In the present invention, it is preferable to adjust the resistance of the lower layer 3 using an ionic conductive agent that is highly stable and easy to adjust the resistance value, and the blending amount is improved by improving the bleed resistance performance of the ionic conductive agent. Thus, the resistance can be reduced.

The resistance value of the lower layer 3 is not particularly limited as long as it satisfies the above-described resistance ratio according to the present invention, and is usually within a range of 10 ³ to 10 ⁸ Ω, particularly 10 ⁴ to 10 ⁵ Ω. And

  Further, the thickness of the lower layer 3 is not particularly limited, but can be usually in the range of 50 to 300 μm, particularly 80 to 180 μm.

  The surface layer 4 can be formed by appropriately using the same resin as that of the lower layer 3, but preferably has a material structure suitable for the purpose of preventing toner adhesion and ensuring surface smoothness, and in particular, the surface smoothness of the charging roller. Fluorine resin is preferably used from the viewpoints of adhesion and low adhesion to the photoreceptor. Examples of the fluororesin include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, poly Examples include chlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride, etc., and those obtained by polymerizing these in a solution or a resin obtained by dissolving a polymerized resin in an organic solvent. Fluorine resin or the like is used. Also for the surface layer 4, desired conductivity can be imparted by appropriately containing the above-described ionic conductive agent or electronic conductive agent as the conductive agent. For the surface layer 4, it is considered that by using carbon black as a conductive agent and making carbon black highly dispersed, it is possible to achieve high resistance and uniform resistance.

The resistance value of the surface layer 4 is not particularly limited as long as it satisfies the above-described resistance ratio according to the present invention, and is usually in the range of 10 ⁵ to 10 ¹¹ Ω, particularly 10 ⁹ to 10 ¹⁰ Ω. It can be.

  The thickness of the surface layer 4 is not particularly limited, but is usually in the range of 1 to 20 μm, particularly 5 to 15 μm. If the surface of the charging roller is uneven, toner may be clogged in the recess and cause image defects. Therefore, the surface of the member is preferably as smooth as possible. Therefore, the surface roughness of the surface layer 4 is preferably JIS ten-point average roughness Rz, usually 10 μm or less, particularly 6 μm or less.

  In the roller 10 of the present invention, an adhesive layer 5 can be provided between the urethane foam layer 2 and the lower layer 3 as shown in the figure. The adhesive layer 5 is not essential in the present invention, and is appropriately provided as necessary in order to fulfill the function of improving the adhesion between the urethane foam layer 2 and the lower layer 3, and its forming material Examples include nylon, polyester, urethane-modified acrylic resin, phenol resin, acrylic resin, urethane resin, epoxy resin, urea resin, and the like. The resistance value can be adjusted similarly to the case of the surface layer 4.

The resistance value of the adhesive layer 5 is not particularly limited, and can usually be in the range of 10 ⁰ to 10 ⁸ Ω, particularly 10 ² to 10 ⁵ Ω. The thickness of the adhesive layer 5 is preferably about 1 to 100 μm, more preferably about 10 to 30 μm, in order to ensure adhesion between the urethane foam layer 2 and the lower layer 3.

  Appropriate additives such as thickeners, thixotropy imparting agents, structural viscosity imparting agents and the like can be appropriately added to the lower layer 3 and the surface layer 4 as desired. In this case, the additives may be inorganic or organic. Either may be sufficient.

  The total thickness of the lower layer 3, the surface layer 4 and the adhesive layer 5 is not particularly limited, but is preferably a thin layer so as not to impair the flexibility of the urethane foam layer 2. It is about 450 μm.

  In addition, there is no restriction | limiting in particular as a formation method of each layer of the adhesive layer 5, the lower layer 3, and the surface layer 4, The coating material containing each component which forms these each layer is prepared, and this coating material is apply | coated by the dipping method or the spray method. The method can be preferably used.

  As described above, the charging roller 10 of the present invention is disposed in contact with a charged body such as a transfer body, and a voltage is applied between the charged body and the charging roller of the present invention. The object to be charged is charged. In this case, the voltage applied between the charging roller and the member to be charged may be a DC voltage or an AC voltage, and is not particularly limited. However, a voltage obtained by superimposing the AC voltage on the DC voltage is applied. It is preferable to perform charging, whereby the object to be charged can be more uniformly charged. In addition, the contact pressure between the charging roller of the present invention and the member to be charged is preferably 50 to 2000 g, particularly 100 to 1000 g, whereby good charging can be reliably obtained.

  As for a charging device using the charging roller 10 of the present invention, for example, as shown in FIG. 2, the charging roller 10 of the present invention is brought into contact with a charged body 11 such as a transfer body and charged from the voltage applying means 12. A charging device configured to apply a voltage between the body 11 and the body 11 can be exemplified, but is not limited thereto, and the form of the charged body 11 and the charging roller 10 and the voltage applied by the voltage applying unit 12 are not limited thereto. The application method and the like can be changed as appropriate.

Hereinafter, the present invention will be described in more detail with reference to examples.
First, a polyurethane foam was supported on the outer periphery of a core metal 1 (φ8 mm, length 260 mm, material: sulfur free-cutting steel) by a mechanical floss method to form a urethane foam layer 2.

  Specifically, a polyurethane raw material consisting of 100 parts by weight of prepolymerized isocyanate (TDI + polyol), 20 parts by weight of polyether polyol, and 2 parts by weight of acetylene black is prepared, and this polyurethane raw material is mechanically stirred by a mixer. Then, dry air was mixed and foamed. This polyurethane foam raw material was cast into a metal cylindrical split mold in which a hole for penetrating the shaft was provided at the end, and a metal cap for supporting the shaft was installed. Inside the mold, the core metal 1 was disposed in a state where an adhesive was applied to the outer periphery. Next, the mold in which the foamed polyurethane raw material was cast was left in a hot air oven adjusted to 90 ° C. for 4 hours to cure the foamed polyurethane raw material.

  Next, the cured polyurethane foam was removed from the mold, and the constituent material of the lower layer 3 shown in Table 1 below was mixed with 100 parts by weight of the resin in an amount (parts by weight) shown in Tables 2 and 3 below. The lower layer 3 having a film thickness of 100 μm was formed on the outer periphery by dip-coating the paint. Further, a surface layer 4 having a film thickness of 5 μm was formed on the outer periphery in the same manner according to the following Tables 1 to 3 to produce a charging roller having a roller body of φ16 mm and a length of 240 mm. The surface roughness of the obtained roller was 5 μm in terms of JIS ten-point average roughness Rz.

<Measurement of resistance value>
The resistance value of the central portion in the longitudinal direction of each test roller was measured circumferentially with a high resistance meter (manufactured by HIOKI). The measurement was performed twice, that is, the stage (lower layer resistance R1) formed up to the lower layer 3 and the stage (product resistance R2) formed up to the surface layer 4, and the resistance ratio (R2 / R1) was obtained from the result.

<Evaluation of image quality>
Each test roller is incorporated into a commercially available printer and evaluated for the presence or absence of streaks due to poor charging. “○” indicates no streaks, and “△” indicates slight streaks. " Similarly, image unevenness was also evaluated. The case where there was no density unevenness was indicated as “◯”, and the case where there was density unevenness was indicated as “x”.
These results are also shown in Tables 2 and 3 below.

  As shown in Tables 2 and 3 above, in the charging roller of the example satisfying the resistance ratio R2 / R1 in the range of 2.5 to 15, it is possible to satisfactorily prevent occurrence of defective charging streaks and image unevenness. It was confirmed that it could be done.

It is sectional drawing which shows the charging roller which concerns on one suitable embodiment of this invention. It is a schematic explanatory drawing which shows the structure of a charging device.

Explanation of symbols

1 Axis 2 Urethane foam layer 3 Lower layer 4 Surface layer 5 Adhesive layer 10 Charging roller 11 Charged body 12 Voltage application means

Claims (4)

A charging roller for contacting a charged body and charging the charged body by applying a voltage between the charged body and a urethane foam layer, a lower layer, and a surface layer on an outer periphery of a shaft In a charging roller comprising
The lower layer is formed using a urethane resin, the surface layer is formed using a fluororesin,
The ratio R2 / R1 of the resistance value R1 in the state where the lower layer is formed on the outer periphery of the shaft and the surface resistance value R2 in the state where the surface layer is formed on the outer periphery of the shaft is 2.5 to 15 A charging roller characterized by being in the range of. The charging roller according to claim 1 , wherein R2 / R1 is in a range of 8.6 to 15 . Said lower layer, according to claim 1 or 2 charging roller according containing ion conductive agent. In producing a charging roller by sequentially forming a urethane foam layer, a lower layer, and a surface layer on the outer periphery of the shaft,
The lower layer is formed by a dipping method using a urethane resin, and the surface layer is formed by a dipping method using a fluororesin,
The ratio R2 / R1 of the resistance value R1 in the state where the lower layer is formed on the outer periphery of the shaft and the surface resistance value R2 in the state where the surface layer is formed on the outer periphery of the shaft is 2.5 to 15 The method for manufacturing a charging roller is characterized in that the adjustment is performed within the above range.

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