JP4350592B2 - Conductive elastic member and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a conductive elastic member and an image forming apparatus using the same, and is particularly used in an electrophotographic process or the like, and has low hardness and compression set, toner is difficult to agglomerate and fuse, the surface is difficult to scrape, and durability The present invention relates to a conductive elastic member having excellent properties.

  In recent years, color laser printers using toner with a low melting point are increasing as color, speed, image quality, and energy saving of electrophotographic systems increase. Here, when a low-melting toner is used, the low-melting toner is damaged by repeated compression or friction between components, and the toner is aggregated and fused. Since it tends to occur, a low hardness roller is required.

  However, conventionally used rollers made of urethane elastomer have a high Asker C hardness of 65 to 80 degrees, and thus tend to cause aggregation and fusion of low melting point toner. Therefore, an electrophotographic system using a low-melting toner is required to have a roller Asker C hardness of about 40 to 60 degrees.

  On the other hand, when a low-hardness roller is used in an electrophotographic system, pressure contact marks due to a photosensitive drum, blade, supply roller, etc. are likely to be generated on the roller surface. Therefore, it is necessary to use a material having a low compression set for the low-hardness roller. is there. However, since materials with low hardness tend to have large compression set, it has been very difficult to balance both hardness and compression set sufficiently low (see Patent Documents 1 to 3).

JP 2003-252947 A JP-A-9-34216 JP-A-9-114190

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a conductive elastic member that has low hardness and compression set, toner is difficult to agglomerate and fuse, is difficult to scrape, and has excellent durability. There is to do. Another object of the present invention is to provide an image forming apparatus using such a conductive elastic member.

  As a result of diligent studies to achieve the above object, the present inventor made a urethane foam raw material containing a urethane prepolymer synthesized from a polyol and a polyisocyanate, a chain extender comprising a polyol, a catalyst, a foam stabilizer and a conductive agent. In the conductive elastic member made of urethane foam obtained by stirring and foaming, a specific polyol and a specific polyisocyanate are used for the synthesis of the urethane prepolymer, and a specific polyol is used as a chain extender. It has been found that the hardness and compression set can be sufficiently lowered, and that the image quality and durability of the image forming apparatus can be improved by using the conductive elastic member as a developing roller in the image forming apparatus, thereby completing the present invention. It was.

That is, the conductive elastic member of the present invention is obtained by mechanically stirring and foaming a foamed urethane raw material containing a urethane prepolymer synthesized from polyol and polyisocyanate, a chain extender composed of polyol, a catalyst, a foam stabilizer and a conductive agent. In the conductive elastic member made of urethane foam,
The polyol used for the synthesis of the urethane prepolymer and the polyol used as a chain extender have an average functional group number of 2 to 3, and a mass ratio (PO / EO) of propylene oxide (PO) to ethylene oxide (EO) of 100 / Comprising at least one hydrophobic polyol selected from the group consisting of 0 to 93/7 polyether polyol, propylene oxide (PO) modified polybutadiene polyol, polybutadiene polyol and polyisoprene polyol;
The polyisocyanate is tolylene diisocyanate (TDI),
The Asker C hardness is 40-60 degrees with a roller with an outer diameter of φ16mm and a cored bar diameter of φ8mm.
Outer diameter after leaving for 72 hours at 12 ° C and 10% RH temperature, and outside diameter after leaving for 72 hours at 32.5 ° C and 85% humidity on a roller with an outer diameter of φ16mm and cored bar diameter of 8mm The difference from the dimension is 150μm or less,
Place a roller with an outer diameter of φ16mm and a core metal diameter of φ8mm on a flat plate, apply a load of 1000g to each end of the roller, leave it for 3 days in an environment of temperature 40 ℃ and humidity 95% RH, remove the load, and after 30 minutes The amount of surface deformation is 7 μm or less.

  In a preferred example of the conductive elastic member of the present invention, the polyol is composed of the hydrophobic polyol alone or a blend of the hydrophobic polyol and another polyol.

  The conductive elastic member of the present invention is suitable as a developing roller.

  An image forming apparatus according to the present invention uses the conductive elastic member.

  According to the present invention, a urethane urethane conductive material obtained by mechanically foaming a urethane foam raw material containing a urethane prepolymer synthesized from a polyol and a polyisocyanate, a chain extender comprising a polyol, a catalyst, a foam stabilizer, and a conductive agent. In the elastic elastic member, by using a specific polyol and a specific polyisocyanate for the synthesis of the urethane prepolymer and using a specific polyol as the chain extender, a conductive elastic member having sufficiently low hardness and compression set can be obtained. Can be provided. In addition, an image forming apparatus using such a conductive elastic member and having excellent image quality and durability can be provided.

  The present invention is described in detail below. The conductive elastic member of the present invention is a urethane foam obtained by mechanically stirring and foaming a urethane prepolymer synthesized from a polyol and a polyisocyanate, a chain extender comprising a polyol, a catalyst, a foam stabilizer, and a conductive agent. A conductive elastic member made of the above-described urethane prepolymer and a polyol used as a chain extender having an average functional group number of 2 to 3, and comprising propylene oxide (PO) and ethylene oxide (EO) Including at least one hydrophobic polyol selected from the group consisting of polyether polyols having a mass ratio (PO / EO) of 100/0 to 93/7, propylene oxide (PO) -modified polybutadiene polyols, polybutadiene polyols and polyisoprene polyols The polyisocyanate is tolylene diene It characterized in that it is a cyanate (TDI). In addition, another well-known additive can be used for the said foaming urethane raw material as needed.

  The polyol used for the synthesis of the urethane prepolymer is a poly having an average functional group number of 2 to 3 and a mass ratio (PO / EO) of propylene oxide (PO) to ethylene oxide (EO) of 100/0 to 93/7. It contains at least one hydrophobic polyol selected from the group consisting of ether polyols, propylene oxide (PO) modified polybutadiene polyols, polybutadiene polyols and polyisoprene polyols, and may contain other polyols. These polyols may be used alone or in a blend of two or more. In the present invention, the polyol used for the synthesis of the urethane prepolymer preferably has a hydroxyl value in the range of 10 to 120 mgKOH / g.

  The polyisocyanate used for the synthesis of the urethane prepolymer is tolylene diisocyanate (TDI). The TDI has a plurality of isomers, among which 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate are preferable. The TDI used in the present invention is more preferably 2,4-tolylene diisocyanate / 2,6-tolylene diisocyanate in a mass ratio of 65/35 to 100/0.

  In the synthesis of the urethane prepolymer, the urethane prepolymer preferably has an NCO (isocyanate group) content of 1 to 10%.

  The chain extender used as the urethane foam raw material is a compound that connects the urethane prepolymers, has an average functional group number of 2 to 3, and a mass ratio of propylene oxide (PO) and ethylene oxide (EO). (PO / EO) 100/0 to 93/7 polyether polyol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, polytetramethylene glycol, propylene oxide (PO) modified polybutadiene polyol, polybutadiene polyol and It contains at least one hydrophobic polyol selected from the group consisting of polyisoprene polyols, and may contain other polyols. These polyols may be used alone or in a blend of two or more. In the present invention, the polyol used as the chain extender preferably has a hydroxyl value in the range of 10 to 1300 mgKOH / g. The chain extender is used in a molar ratio (NCO / OH) between the isocyanate group (NCO) of the urethane prepolymer and the hydroxyl group (OH) of the chain extender in the range of 90/100 to 120/100. It is preferable to select as appropriate.

  The catalyst used for the urethane foam raw material is a catalyst for urethanization reaction, for example, organic tin such as dibutyltin dilaurate, dibutyltin diacetate, dibutyltin thiocarboxylate, dibutyltin dimaleate, dioctyltin thiocarboxylate, tin octenoate, etc. Compounds; Organic lead compounds such as lead octenoate; Monoamines such as triethylamine and dimethylcyclohexylamine; Diamines such as tetramethylethylenediamine, tetramethylpropanediamine, and tetramethylhexanediamine; Pentamethyldiethylenetriamine, Pentamethyldipropylenetriamine, Tetra Triamines such as methylguanidine; triethylenediamine, dimethylpiperazine, methylethylpiperazine, methylmorpholine, dimethylaminoethyl Cyclic amines such as morpholine and dimethylimidazole; Alcohol amines such as dimethylaminoethanol, dimethylaminoethoxyethanol, trimethylaminoethylethanolamine, methylhydroxyethylpiperazine, and hydroxyethylmorpholine; bis (dimethylaminoethyl) ether, ethylene glycol bis And ether amines such as (dimethyl) aminopropyl ether. Of these catalysts, organotin compounds are preferred. These catalysts may be used individually by 1 type, and may be used in combination of 2 or more type. The amount of the catalyst used is preferably in the range of 0.001 to 2.0 parts by mass with respect to 100 parts by mass of the urethane prepolymer.

  As the foam stabilizer used for the urethane foam raw material, an ionic surfactant, a nonionic surfactant, or the like can be used in addition to a silicone-based foam stabilizer such as polyether-modified silicone oil. The amount of the foam stabilizer used is preferably in the range of 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the urethane prepolymer.

  Examples of the conductive agent used for the urethane foam raw material include conductive carbon, ionic conductive agent, metal oxide powder, and metal powder. These electrically conductive agents may be used individually by 1 type, and may be used in combination of 2 or more type. The amount of the conductive agent used is preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the urethane prepolymer.

  The conductive elastic member of the present invention has an Asker C hardness of 40 to 60 degrees in a roller shape having an outer diameter of φ16 mm and a core metal diameter of φ8 mm. When the Asker C hardness in the roller shape satisfies the above range, aggregation and fusion of the low melting point toner can be prevented while securing sufficient hardness as an elastic member such as a developing roller.

  The conductive elastic member of the present invention is a roller having an outer diameter of φ16 mm and a cored bar diameter of φ8 mm. The outer diameter after leaving for 72 hours at a temperature of 12 ° C. and a humidity of 10% RH, and a temperature of 32.5 ° C. and a humidity of 85% RH The difference from the outer diameter after being left for 72 hours is 150 μm or less. Since the conductive elastic member of the present invention has high dimensional stability against differences in storage environments, it is suitable as a precision part such as a developing roller.

  The conductive elastic member of the present invention is mounted on a flat plate as a roller having an outer diameter of φ16 mm and a cored bar diameter of φ8 mm, a load of 1000 g is applied to both ends of the roller, and left for 3 days in an environment of a temperature of 40 ° C. and a humidity of 95% RH. After that, the amount of deformation of the roller surface 30 minutes after removing the load is 7 μm or less. Even if the conductive elastic member of the present invention is pressed against another member for a long period of time, it is easy to return to its original shape by releasing from the pressed contact state. That is, since the compression set is small, as a precision component such as a developing roller. Is preferred.

  The urethane foam constituting the conductive elastic member of the present invention is a prepolymer / mechanical floss obtained by mechanically agitating and foaming a foamed urethane raw material containing the urethane prepolymer, chain extender, catalyst, foam stabilizer and conductive agent. It is a process foamed urethane. The foamed urethane is foamed by a method in which a urethane raw material is mechanically stirred and bubbles are mixed without using a foaming agent. Moreover, a conductive elastic member having a desired shape can be manufactured by forming the urethane foam in a mold having a desired shape.

  The conductive elastic member of the present invention is suitable as a developing roller for an image forming apparatus. In this case, the developing roller may include other materials such as a metal shaft in addition to the urethane foam. The developing roller can be produced, for example, by mixing and injecting the urethane raw material into a mold having a desired shape in which a metal shaft is disposed at the center, and curing the mixture.

  The image forming apparatus of the present invention uses the above-described conductive elastic member, and preferably includes the conductive elastic member as a developing roller. The image forming apparatus of the present invention is not particularly limited except that the conductive elastic member is used, and can be manufactured by a known method.

  The image forming apparatus of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a partial cross-sectional view of an example of the image forming apparatus of the present invention. The image forming apparatus of the illustrated example includes a toner supply roller 2 for supplying toner 1, a photosensitive drum 3 holding an electrostatic latent image, and a developing roller disposed between the toner supply roller 2 and the photosensitive drum 3. 4, a developing blade 5 provided above the developing roller 4, a transfer unit 6 located below the photosensitive drum 3, and a cleaning unit 7 provided adjacent to the photosensitive drum 3. The image forming apparatus of the present invention can further include known components (not shown) that are normally used in the image forming apparatus.

  The toner supply roller 2, the developing roller 4, and the photosensitive drum 3 rotate in the direction of the arrow in the drawing, so that the toner 1 on the toner supply roller 2 is sent to the photosensitive drum 3 through the developing roller 4. The toner 1 is adjusted to a uniform thin layer by the developing blade 5 on the developing roller 4 and further rotated while the developing roller 4 and the photosensitive drum 3 are in contact with each other. It adheres to the image and the latent image becomes visible. The toner 1 attached to the latent image is transferred to a recording medium such as paper by the transfer unit 6, and the toner 1 remaining on the photosensitive drum 3 after the transfer is removed by the cleaning blade 8 of the cleaning unit 7. In the image forming apparatus of the present invention, for example, by using a conductive elastic member having the above-described hardness and compression set low and a small outside diameter variation in the developing roller 4, the melting point of the toner 1 is lower than usual. However, aggregation and fusion of the toner 1 can be suppressed, and a good image can be formed over a long period of time.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Example 1)
Mass ratio of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (100 parts by weight) of tri-functional polyether polyol having a molecular weight of 5,000 and a hydroxyl value of 42 mgKOH / g added with glycerin and propylene oxide (2,4-tolylene diisocyanate) The urethane prepolymer was synthesized by reacting 23.4 parts by mass of tolylene diisocyanate (TDI-80) having an isomer / 2,6-isomer of 80/20 with stirring at 60 ° C. for 48 hours. The obtained urethane prepolymer had an NCO content of 6.6%. 100 parts by mass of this urethane prepolymer and 2.0 parts by mass of conductive carbon black [Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.] were mixed and stirred under reduced pressure to prepare a urethane prepolymer in which conductive carbon was dispersed. Was designated as component A.

  On the other hand, 20.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 2.0 and a molecular weight of 400, 6.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 3.0 and a molecular weight of 430, and 4.0 parts by mass of a polyether-modified silicone oil (foam stabilizer) Then, 0.2 part by mass of dibutyltin dilaurate (DBTDL) was mixed and stirred to prepare a mixture, which was used as component B.

  The above A component and B component are stirred, mixed, and foamed with a mechanical floss foaming machine so that the flow rate ratio (A / B) between the A component and B component is 102.0 / 31.2. The inner diameter of the coated inner diameter was 16.0 mm, and the core was poured into a core having an outer diameter of φ8 mm set in the center. Next, both ends of the cylindrical mold are sealed, and after being heated and cured in a hot air circulating oven at 110 ° C. for 30 minutes, the molded product is taken out from the cylindrical mold, and a thermosetting coating liquid is applied to the surface of the molded product. Then, it was heated and dried at 60 ° C. for 1 hour to obtain a conductive roller having an outer diameter of φ16.0 mm.

The obtained conductive roller had a resistance value of 10 ^4.4 Ω at room temperature, an Asker C hardness of 51 degrees, and a foam density of 0.52 g / cm ³ . In addition, the conductive roller after being left for 72 hours at a temperature of 12 ° C and humidity of 10% RH (L / L environment) and after being left for 72 hours at a temperature of 32.5 ° C and humidity of 85% RH (H / H environment) The difference in outer diameter was 146 μm. Furthermore, the conductive roller is placed on a flat plate, a load of 1000 g is applied to both ends of the roller, and after standing for 3 days in an environment of a temperature of 40 ° C. and a humidity of 95% RH, the load is removed and the roller surface is deformed after 30 minutes. The amount (dent amount) was 5.7 μm.

  This conductive roller is incorporated into a dry electrophotographic apparatus as a developing roller and left for 2 weeks in an environment of temperature 40 ° C and humidity 95% RH. After printing a gray (8% density) image, a good image is obtained. Obtained. Next, this dry electrophotographic apparatus was allowed to stand for 48 hours in an environment of a temperature of 20 ° C. and a humidity of 50% RH, and a gray image (density 8%) was printed. As a result, a good image was obtained. Further, after continuous printing of 10,000 sheets, a gray image was printed. As a result, there was no image defect such as white streaks due to toner aggregation and fusion, and a good image was obtained. Further, when the used toner cartridge was disassembled and the surface of the developing roller was observed, it was found that the surface of the developing roller was free from scratches or scratches due to a photosensitive drum, a developing blade, a toner supply roller, or the like. Further, when the toner near the developing roller was observed with a microscope, the toner maintained the initial state and no aggregation or fusion was observed.

(Example 2)
50 parts by mass of a polyether polyol having a trifunctional molecular weight of 5,000 and a hydroxyl value of 42 mgKOH / g, which is obtained by adding propylene oxide to glycerin, and an average functional group number of 2.3 modified with propylene oxide (PO) at the end of the polybutadiene polyol, a molecular weight of 4,800, and a hydroxyl value 50 parts by mass of propylene oxide (PO) modified polybutadiene polyol of 27 mg KOH / g and mass ratio of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (2,4-isomer / 2,6-6-isomer) Was reacted with 22.0 parts by mass of 80/20 tolylene diisocyanate (TDI-80) in an airtight container at 60 ° C. for 48 hours with stirring to synthesize a urethane prepolymer. The obtained urethane prepolymer had an NCO content of 6.6%. 100 parts by mass of this urethane prepolymer and 2.0 parts by mass of conductive carbon black [Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.] were mixed and stirred under reduced pressure to prepare a urethane prepolymer in which conductive carbon was dispersed. Was designated as component A.

  On the other hand, 20.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 2.0 and a molecular weight of 400, 6.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 3.0 and a molecular weight of 430, and 4.0 parts by mass of a polyether-modified silicone oil (foam stabilizer) Then, 0.2 part by mass of dibutyltin dilaurate (DBTDL) was mixed and stirred to prepare a mixture, which was used as component B.

  The above A component and B component are stirred, mixed, and foamed with a mechanical floss foaming machine so that the flow rate ratio (A / B) between the A component and B component is 102.0 / 31.2. The inner diameter of the coated inner diameter was 16.0 mm, and the core was poured into a core having an outer diameter of φ8 mm set in the center. Next, both ends of the cylindrical mold are sealed, and after being heated and cured in a hot air circulating oven at 110 ° C. for 30 minutes, the molded product is taken out from the cylindrical mold, and a thermosetting coating liquid is applied to the surface of the molded product. Then, it was heated and dried at 60 ° C. for 1 hour to obtain a conductive roller having an outer diameter of φ16.0 mm.

The obtained conductive roller had a resistance value of 10 ^4.6 Ω at room temperature, an Asker C hardness of 53 degrees, and a foam density of 0.55 g / cm ³ . In addition, the conductive roller after being left for 72 hours at a temperature of 12 ° C and humidity of 10% RH (L / L environment) and after being left for 72 hours at a temperature of 32.5 ° C and humidity of 85% RH (H / H environment) The difference in outer diameter was 132 μm. Furthermore, the conductive roller is placed on a flat plate, a load of 1000 g is applied to both ends of the roller, and after standing for 3 days in an environment of a temperature of 40 ° C. and a humidity of 95% RH, the load is removed and the roller surface is deformed after 30 minutes. The amount (dent amount) was 4.9 μm.

  This conductive roller is incorporated into a dry electrophotographic apparatus as a developing roller and left for 2 weeks in an environment of temperature 40 ° C and humidity 95% RH. After printing a gray (8% density) image, a good image is obtained. Obtained. Next, this dry electrophotographic apparatus was allowed to stand for 48 hours in an environment of a temperature of 20 ° C. and a humidity of 50% RH, and a gray image (density 8%) was printed. As a result, a good image was obtained. Further, after continuous printing of 10,000 sheets, a gray image was printed. As a result, there was no image defect such as white streaks due to toner aggregation and fusion, and a good image was obtained. Further, when the used toner cartridge was disassembled and the surface of the developing roller was observed, it was found that the surface of the developing roller was free from scratches or scratches due to a photosensitive drum, a developing blade, a toner supply roller, or the like. Further, when the toner near the developing roller was observed with a microscope, the toner maintained the initial state and no aggregation or fusion was observed.

(Example 3)
70 parts by mass of a polyether polyol having a trifunctional molecular weight of 5,000 and a hydroxyl value of 42 mgKOH / g obtained by adding propylene oxide to glycerin, 30 parts by mass of a polybutadiene polyol having an average functional group number of 2.3 and a molecular weight of 2,800 and a hydroxyl value of 47 mgKOH / g, , 4-tolylene diisocyanate and 2,6-tolylene diisocyanate by mass ratio (2,4-isomer / 2,6-isomer) of 80/20 tolylene diisocyanate (TDI-80) 23.6 parts by mass A urethane prepolymer was synthesized by reacting in an airtight container at 60 ° C. with stirring for 48 hours. The obtained urethane prepolymer had an NCO content of 6.6%. 100 parts by mass of this urethane prepolymer and 2.0 parts by mass of conductive carbon black [Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.] were mixed and stirred under reduced pressure to prepare a urethane prepolymer in which conductive carbon was dispersed. Was designated as component A.

  On the other hand, 20.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 2.0 and a molecular weight of 400, 6.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 3.0 and a molecular weight of 430, and 4.0 parts by mass of a polyether-modified silicone oil (foam stabilizer) Then, 0.2 part by mass of dibutyltin dilaurate (DBTDL) was mixed and stirred to prepare a mixture, which was used as component B.

  The above A component and B component are stirred, mixed, and foamed with a mechanical floss foaming machine so that the flow rate ratio (A / B) between the A component and B component is 102.0 / 31.2. The inner diameter of the coated inner diameter was 16.0 mm, and the core was poured into a core having an outer diameter of φ8 mm set in the center. Next, both ends of the cylindrical mold are sealed, and after being heated and cured in a hot air circulating oven at 110 ° C. for 30 minutes, the molded product is taken out from the cylindrical mold, and a thermosetting coating liquid is applied to the surface of the molded product. Then, it was heated and dried at 60 ° C. for 1 hour to obtain a conductive roller having an outer diameter of φ16.0 mm.

Obtained conductive roller, the resistance value at room temperature in 10 ^4.8 Omega, Asker C hardness of 55 degrees, foam density was 0.54 g / cm ^3. In addition, the conductive roller after being left for 72 hours at a temperature of 12 ° C and humidity of 10% RH (L / L environment) and after being left for 72 hours at a temperature of 32.5 ° C and humidity of 85% RH (H / H environment) The difference in outer diameter was 138 μm. Furthermore, the conductive roller is placed on a flat plate, a load of 1000 g is applied to both ends of the roller, and after standing for 3 days in an environment of a temperature of 40 ° C. and a humidity of 95% RH, the load is removed and the roller surface is deformed after 30 minutes. The amount (dent amount) was 5.4 μm.

  This conductive roller is incorporated into a dry electrophotographic apparatus as a developing roller and left for 2 weeks in an environment of temperature 40 ° C and humidity 95% RH. After printing a gray (8% density) image, a good image is obtained. Obtained. Next, this dry electrophotographic apparatus was allowed to stand for 48 hours in an environment of a temperature of 20 ° C. and a humidity of 50% RH, and a gray image (density 8%) was printed. As a result, a good image was obtained. Further, after continuous printing of 10,000 sheets, a gray image was printed. As a result, there was no image defect such as white streaks due to toner aggregation and fusion, and a good image was obtained. Further, when the used toner cartridge was disassembled and the surface of the developing roller was observed, it was found that the surface of the developing roller was free from scratches or scratches due to a photosensitive drum, a developing blade, a toner supply roller, or the like. Further, when the toner near the developing roller was observed with a microscope, the toner maintained the initial state and no aggregation or fusion was observed.

(Comparative Example 1)
100 parts by mass of a trifunctional polyether polyol (mass ratio of PO / EO = 86/14) having a molecular weight of 5,000 and a hydroxyl value of 42 mgKOH / g obtained by adding propylene oxide (PO) and ethylene oxide (EO) to glycerin; , 4-tolylene diisocyanate and 2,6-tolylene diisocyanate by mass ratio (2,4-isomer / 2,6-isomer) of 80/20 tolylene diisocyanate (TDI-80) 21.9 parts by mass A urethane prepolymer was synthesized by reacting in an airtight container at 60 ° C. with stirring for 48 hours. The obtained urethane prepolymer had an NCO content of 6.6%. 100 parts by mass of this urethane prepolymer and 2.0 parts by mass of conductive carbon black [Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.] were mixed and stirred under reduced pressure to prepare a urethane prepolymer in which conductive carbon was dispersed. Was designated as component A.

  On the other hand, 20.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 2.0 and a molecular weight of 400, 6.0 parts by mass of a propylene oxide addition polyol having an average functional group number of 3.0 and a molecular weight of 430, and 4.0 parts by mass of a polyether-modified silicone oil (foam stabilizer) Then, 0.2 part by mass of dibutyltin dilaurate (DBTDL) was mixed and stirred to prepare a mixture, which was used as component B.

  The above A component and B component are stirred, mixed, and foamed with a mechanical floss foaming machine so that the flow rate ratio (A / B) between the A component and B component is 102.0 / 31.2. The inner diameter of the coated inner diameter was 16.0 mm, and the core was poured into a core having an outer diameter of φ8 mm set in the center. Next, both ends of the cylindrical mold are sealed, and after being heated and cured in a hot air circulating oven at 110 ° C. for 30 minutes, the molded product is taken out from the cylindrical mold, and a thermosetting coating liquid is applied to the surface of the molded product. Then, it was heated and dried at 60 ° C. for 1 hour to obtain a conductive roller having an outer diameter of φ16.0 mm.

The obtained conductive roller had a resistance value of 10 ^4.6 Ω at room temperature, an Asker C hardness of 53 degrees, and a foam density of 0.51 g / cm ³ . In addition, the conductive roller after being left for 72 hours at a temperature of 12 ° C and humidity of 10% RH (L / L environment) and after being left for 72 hours at a temperature of 32.5 ° C and humidity of 85% RH (H / H environment) The difference in outer diameter was 210 μm. Furthermore, the conductive roller is placed on a flat plate, a load of 1000 g is applied to both ends of the roller, and after standing for 3 days in an environment of a temperature of 40 ° C. and a humidity of 95% RH, the load is removed and the roller surface is deformed after 30 minutes. The amount (dent amount) was 8.1 μm.

  This conductive roller was incorporated into a dry electrophotographic apparatus as a developing roller, left in an environment of temperature 40 ° C and humidity 95% RH for 2 weeks, and after printing a gray image (density 8%), the length of the developing roller A streak-like image defect in the same direction as the vertical direction was confirmed. Further, the used toner cartridge was disassembled and the surface of the developing roller was observed. As a result, pressure contact marks between the developing blade and the photosensitive drum were observed on the surface of the developing roller. Next, this dry electrophotographic device was left for 48 hours in an environment of temperature 20 ° C and humidity 50% RH, and after printing a gray (density 8%) image, streaky defects were confirmed in the image as well. It was done. Furthermore, after printing 10,000 sheets continuously, when a gray image was printed, a streak-like image defect in the same direction as the length direction of the developing roller and a streak-like image defect perpendicular to the length direction of the developing roller occurred. confirmed. Also, when the used toner cartridge was disassembled and the surface of the developing roller was observed, white streaks in the direction perpendicular to the length direction of the developing roller were generated in addition to the previously observed pressure contact marks between the developing blade and the photosensitive drum. It was found that the surface of the developing roller corresponding to the position was scraped. Further, when the toner near the shaved portion was observed with a microscope, the toner was agglomerated and fused.

  As is clear from Table 1, the urethane foam conductive roller obtained by using a specific polyol and polyisocyanate for the synthesis of the urethane prepolymer and using a specific polyol as a chain extender has a hardness and a compression set. The image forming apparatus using the roller as a developing roller can form a good image even at high temperature and high humidity and has excellent durability.

1 is a partial cross-sectional view of an example of an image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Toner 2 Toner supply roller 3 Photosensitive drum 4 Developing roller 5 Developing blade 6 Transfer part 7 Cleaning part 8 Cleaning blade

Claims (4)

In the conductive elastic member made of urethane foam obtained by mechanically stirring and foaming urethane foam raw material containing urethane prepolymer synthesized from polyol and polyisocyanate, chain extender consisting of polyol, catalyst, foam stabilizer and conductive agent,
The polyol used for the synthesis of the urethane prepolymer and the polyol used as a chain extender have an average number of functional groups of 2 to 3, and a mass ratio (PO / EO) of propylene oxide (PO) to ethylene oxide (EO) of 100 / Comprising at least one hydrophobic polyol selected from the group consisting of 0 to 93/7 polyether polyol, propylene oxide (PO) modified polybutadiene polyol, polybutadiene polyol and polyisoprene polyol;
The polyisocyanate is tolylene diisocyanate (TDI),
Asker C hardness with a roller with an outer diameter of φ16mm and a cored bar diameter of φ8mm is 40-60 degrees,
Outer diameter after leaving for 72 hours at 12 ° C and 10% RH temperature, and outside diameter after leaving for 72 hours at 32.5 ° C and 85% humidity on a roller with an outer diameter of φ16mm and cored bar diameter of 8mm The difference between the dimensions is 150 μm or less,
Place a roller with an outer diameter of φ16mm and a cored bar diameter of φ8mm on a flat plate, apply a load of 1000g to each end of the roller, leave it under an environment of temperature 40 ℃ and humidity 95% RH for 3 days, then remove the load and after 30 minutes A conductive elastic member having a surface deformation amount of 7 μm or less.   2. The conductive elastic member according to claim 1, wherein the polyol is composed of the hydrophobic polyol alone or a blend of the hydrophobic polyol and another polyol.   The conductive elastic member according to claim 1, wherein the conductive elastic member is a developing roller.   An image forming apparatus using the conductive elastic member according to claim 1.

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