Patent Application
20070243984
A semiconductive rubber roller 10 of the present invention is described below as one embodiment of the semiconductive rubber member of the present invention.
As shown in
The metal shaft 2 is made of metal such as aluminum, aluminum alloy, SUS or iron, or ceramics.
The sealing portion 3 is made of nonwoven cloth such as Teflon (registered trade mark) or a sheet.
As apparent from a sectional view of the toner-transporting portion 1 shown in
The ratio of the thickness of the base layer 1a to that of the surface layer 1b is set to favorably 5 to 9.5:5 to 0.5 and more favorably 7 to 9:3 to 1.
The electric resistance value of the semiconductive rubber roller 10 is set to the range of 105Ω to 106.5Ω when the electric resistance value thereof is measured by applying a voltage of 100V thereto at a temperature of 10° C. and a relative humidity of 20%.
The electric resistance value of the base layer 1a is set to the range from 103Ω to 105Ω and favorably the range from 104Ω to 105Ω when the electric resistance value thereof is measured by applying the voltage of 100V thereto at the temperature of 10° C. and the relative humidity of 20%. The deflection of the electric resistance value of the base layer 1a is set below 20.
The electric resistance value of the semiconductive rubber roller 10 is set higher than that of the base layer 1a, when the electric resistance values thereof are measured by applying the voltage of 100V thereto at the temperature of 10° C. and the relative humidity of 20%.
As a rubber composition composing the base layer 1a, a rubber composition containing a rubber component and an electro-conductive agent mixed therewith is used.
As the above-described rubber component, it is favorable to use polar rubber such as NBR, chloroprene rubber, and urethane rubber having a high dissolution parameter (SP value) respectively. It is more favorable to use the chloroprene rubber. The chloroprene rubber, of sulfur-unmodified type, which has a low crystallization speed is preferable. It is preferable to use conductive carbon black as the above-described electro-conductive agent. It is preferable to set the mixing amount of the electro-conductive agent to 10 to 25 parts by mass for 100 parts by mass of the rubber component.
As a rubber composition composing the surface layer 1b, a substantially insulating rubber composition or an ionic-conductive rubber composition is used.
As “the substantially insulating rubber composition”, it is favorable to use non-polar rubber such as EPDM, BR, and the like; and the polar rubber such as SBR, NBR, chloroprene rubber, urethane rubber, and the like having a high dissolution parameter (SP value) respectively. It is more favorable to use the EPDM or the chloroprene rubber.
As the EPDM, the unextended type is preferable. As the diene monomer, the EPDM rubber containing ethylidenenorbornene is preferable. The EPDM containing ethylene at 50 to 70 mass % is especially preferable.
As the above-described ionic-conductive rubber composition, a rubber composition containing an epichlorohydrin copolymer, a polyether copolymer, and a chloroprene rubber as its rubber component is especially preferable. Supposing that the entire mass of the rubber components is 100 parts by mass, as the mixing ratio among the three rubber components, the content of the epichlorohydrin copolymer, that of the polyether copolymer, and that of the chloroprene rubber are set to 10 to 40 parts by mass, 5 to 20 parts by mass, and 40 to 85 parts by mass.
As the above-described ionic-conductive rubber composition, a composition containing the epichlorohydrin copolymer, the chloroprene rubber, and NBR is also especially preferable. Supposing that the entire mass of the rubber components is 100 parts by mass, the content of the epichlorohydrin rubber is set to 10 to 50 parts by mass and preferably 10 to 40 parts by mass; the content of the chloroprene rubber is set to 5 to 85 parts by mass and preferably 40 to 85 parts by mass; and the content of the NBR rubber is set to 5 to 65 parts by mass and preferably 5 to 20 parts by mass.
As the epichlorohydrin copolymer, a terpolymer of the ethylene oxide, the epichlorohydrin, and the allyl glycidyl ether is used. The content ratio among the ethylene oxide, the epichlorohydrin, and the allyl glycidyl ether is set to 40 to 70 mol %:20 to 60 mol %:2 to 6 mol %.
As the chloroprene rubber, a sulfur-unmodified type is used.
As the polyether copolymer, a terpolymer of the ethylene oxide, a propylene oxide, and the allyl glycidyl ether is used. The content ratio among the ethylene oxide, the propylene oxide, and the allyl glycidyl ether is set to 80 to 95 mol % 1 to 10 mol %:1 to 10 mol %. The number-average molecular weight Mn of the copolymer is set to favorably not less than 10,000, more favorably not less than 30,000, and most favorably not less than 50,000.
As the NBR, low-nitrile NBR containing acrylonitrile at not more than 25% is used.
Both the rubber composition composing the base layer 1a and the rubber composition composing the surface layer 1b contain a vulcanizing agent for vulcanizing the rubber component.
As the vulcanizing agent, sulfur and ethylene thiourea are used in combination. The mixing amount of the vulcanizing agent is set to not less than one part by mass nor more than three parts by mass for 100 parts by mass of the rubber component. It is preferable to mix the sulfur and the ethylene thiourea at (sulfur:ethylene thiourea)=1:0.05 to 8. The reason the lower limit of the ratio of the part by mass of the ethylene thiourea to that of the sulfur is set to 0.05 is because when the sulfur and the ethylene thiourea are used in combination, the ethylene thiourea is effective for vulcanizing the rubber component, even though a small amount of the ethylene thiourea is used. The reason the upper limit of the ratio the part by mass of the ethylene thiourea to that of the sulfur is set to 8 is as follow: If the ratio exceeds 8, the rubber component scorches in a short period of time, and hence it is liable to burn. Therefore processability is low when a plurality of layers is formed.
It is more favorable to set the mixing mass ratio between the sulfur and the ethylene thiourea to (sulfur ethylene thiourea)=1:1.5 to 4. To decrease the compression set, it is preferable to set the mixing ratio between the sulfur and the ethylene thiourea to (sulfur:ethylene thiourea)=1:1.5.
The rubber composition composing the base layer 1a and the rubber composition composing the surface layer 1b may contain other components in addition to the rubber component and the vulcanizing agent.
A filler is used as one of the other components. Zinc oxide is used as the filler. Conductive carbon black which is an electro-conductive agent and weakly conductive carbon black which is described below also serve as the filler. The addition amount of the filler is set to 10 to 70 parts by mass and preferably 10 to 50 parts by mass for 100 parts by mass of the rubber component.
An acid-accepting agent is contained in the rubber composition containing halogen-containing rubber represented by the epichlorohydrin copolymer. As the acid-accepting agent, hydrotalcite is used. The mixing amount of the acid-accepting agent is set to not less than 1 part by mass nor more than 10 parts by mass for 100 parts by mass of the rubber component.
The rubber composition composing the surface layer 1b contains the weakly conductive carbon black as a dielectric loss tangent-adjusting agent.
The weakly conductive carbon black used in the present invention has an average primary diameter of 100 to 250 nm and is spherical or has a configuration similar to the spherical shape. The mixing amount of the weakly conductive carbon black is set to favorably 5 to 70 parts by mass and more favorably 5 to 30 parts by mass for 100 parts by mass of the rubber component. By mixing the weakly conductive carbon black with the rubber component, it is possible to decrease the dielectric loss tangent of the semiconductive rubber roller of the present invention and decrease a tacky feeling of the surface of the rubber roller and further separate toner therefrom favorably.
The method of producing the semiconductive rubber roller 10 is described below.
Initially the rubber composition composing the base layer 1a and the rubber composition composing the surface layer 1b are formed.
For example, components of the rubber composition are mixed with one another by using a known kneader such as a Banbury mixer, a kneader, an open roll or the like. A mixture obtained by kneading the components one another may be pellet-shaped, sheet-shaped or ribbon-shaped. A temperature at a kneading time and a kneading period of time are appropriately selected. The mixing order is not specifically limited either. All the components may be mixed with one another. Alternatively after a part of all the components is mixed with one another, other components may be mixed with an obtained mixture.
More specifically, after the rubber component, the conductive carbon black or the weakly conductive carbon black, and the zinc oxide are supplied to the kneader, these components are kneaded at a discharge temperature of 80 to 150° C. After the vulcanizing agent and other additives such as the acid-accepting agent are added to the kneaded components, the components are kneaded by using a roller for 1 to 30 minutes and preferably 1 to 15 minutes. The acid-accepting agent is used as desired. The obtained kneaded material is formed into a ribbon-shaped compound.
Using the rubber composition composing the base layer 1a and the rubber composition composing the surface layer 1b, the rubber is extruded in two layers at a collet temperature of 40 to 80° C. to obtain a tubular roller having the base layer 1a and the surface layer 1b. The thickness of each of the two layers can be arbitrarily set by altering the configuration of a collet and the collet temperature at the time of extrusion in consideration of the design and abrasion area of a final product and a vulcanization-caused volume change of the rubber.
The preform is vulcanized at 160° C. for 15 to 120 minutes.
An optimum vulcanizing time period should be set by using a vulcanization testing rheometer (for example, Curelastmeter). The vulcanization temperature may be set around 160° C. in dependence on necessity. To prevent the semiconductive rubber member from contaminating the electrophotographic photoreceptor and the like and reduce the degree of the compression set thereof, it is preferable to set conditions in which the preform is vulcanized so that a possible largest vulcanization amount is obtained. A conductive foamed roller may be formed by adding a foaming agent to the rubber component.
After the metal shaft 2 is inserted into the roller and bonded thereto, the surface thereof is polished and cut to a necessary dimension. The metal shaft 2 may be inserted into the roller before it is vulcanized.
The surface of the roller is irradiated with ultraviolet rays to form the oxide film 1c on the surface thereof. More specifically, after the roller is washed with water by using an ultraviolet ray irradiator, the surface of the roller is irradiated with ultraviolet rays (wavelength: 184.9 nm and 253.7 nm) at intervals of 90 degrees in its circumferential direction of the roller for three to eight minutes and with the ultraviolet ray irradiation lamp spaced at 10 cm from the roller. The roller is rotated by 90 degrees four times to form the oxide film on its entire peripheral surface (360 degrees).
The dielectric loss tangent of the semiconductive rubber roller 10 is set to 0.1 to 1.5 and preferably 0.2 to 1.0, when an alternating voltage of 5V is applied thereto at a frequency of 100 Hz. The semiconductive rubber roller imparts a high electrostatic property to toner to a high extent and keeps the electrostatic charge imparted thereto.
The dielectric loss tangent is measured as follows:
As shown in
Dielectric loss tangent (tan δ)=G/(ωC), G=1/R
The dielectric loss tangent is found as G/ωC, when the electrical characteristic of one roller is modeled as a parallel equivalent circuit of the electric resistance component of the roller and the capacitor component thereof.
The coefficient of friction of the semiconductive rubber roller 10 is set to 0.1 to 1.5 and preferably 0.25 to 0.8.
With reference to
The amount of toner which can be transported by the semiconductive rubber roller 10 is set to 0.01 to 1.0 mg/cm2.
In a print test of the semiconductive rubber roller 10 of each of examples and comparison examples, printing is carried out by using a cartridge allowing 5%-printing to be accomplished on 7000 sheets of paper. The print density of a printed solid black image at an initial stage and the print density thereof after the solid black image is printed on 2,000 sheets of paper are set to not less than 1.6 and favorably not less than 1.8. Further the difference between the print density of the printed solid black image at the initial stage and the print density thereof after the solid black image is printed on 2,000 sheets of paper is set to not more than 0.2 and favorably not more than 0.1.
The examples of the present invention and comparison examples are described below. Needless to say, the present invention is not limited to the examples.
In accordance with the mixing ratio shown in table 1, the rubber component and the conductive carbon black were sequentially supplied to a 10 L kneader. After 5 parts by mass of zinc white (“two kinds of zinc oxide” produced by Mitsui Mining and Smelting Co., Ltd.) was added to 100 parts by mass of the rubber component, the components were kneaded at a discharge temperature of 110° C. After a vulcanizing agent was added to an obtained mixture, the mixture and the vulcanizing agent were kneaded for five minutes by a roller to obtain a ribbon-shaped compound.
As the vulcanizing agent, 0.5 parts by mass of powder sulfur and 1.4 parts by mass of ethylene thiourea (“Accel 22-S” produced by KAWAGUCHI CHEMICAL INDUSTRY CO., LTD.) were used for 100 parts by mass of the rubber component.
In accordance with the mixing ratio shown in table 1, the rubber component, the weakly conductive carbon black, and zinc oxide were sequentially supplied to the 10 L kneader. The vulcanizing agent was added to the obtained mixture. When the epichlorohydrin rubber and the chloroprene rubber were used as the rubber component, the acid-accepting agent was added to the obtained mixture. Thereafter all the components were kneaded for five minutes by the roller to obtain a ribbon-shaped compound.
When the epichlorohydrin rubber was used as the rubber component, three parts by mass of hydrotalcite (“DHT-4A-2” produced by Kyowa Chemical Industry Co., Ltd.) was used as the acid-accepting agent for 100 parts by mass of the epichlorohydrin rubber. When the chloroprene rubber was used as the rubber component, five parts by mass of hydrotalcite was used as the acid-accepting agent for 100 parts by mass of the chloroprene rubber. The kind and mixing amount of the zinc oxide and the vulcanizing agent are identical to those of the rubber composition composing the base layer.
Two vacuum-type rubber extruder of φ60 were arranged in parallel. The rubber composition composing the base layer and the rubber composition composing the surface layer were supplied to the two vacuum-type rubber extruders respectively. Each extruder was provided with a specific layering portion. The two kinds of the rubber compositions were successively extruded in layers at the collet temperature of 60° C. through a collet so devised that the base layer and the surface layer can be layered. Thereby a tubular laminated roller having a inner diameter of φ8.5 mm and a outer diameter of φ20.5 mm was obtained.
The thickness of each of the two layers can be arbitrarily set by altering the configuration of the collet and the collet temperature at the time of extrusion in consideration of the design of an end product, an abrasion area of the roller, and a vulcanization-caused volume change of the rubber. In this process, it is possible to remove water other than water adsorbed by bubbles and molecules of the rubber.
A metal shaft having a diameter of φ8 mm at a normal pressure was inserted into the obtained roller. The roller was heated at 160° C. for 60 minutes to vulcanize the rubber.
After the surface of each of the rollers was washed with water, the surface thereof was irradiated with ultraviolet rays to form an oxidized layer thereon. By using an ultraviolet ray irradiator (“PL21-200” produced by Sen Tokushu Kogen Inc), the surface of each roller was irradiated with ultraviolet rays (wavelength: 184.9 nm and 253.7 nm) at intervals of 90 degrees in its circumferential direction for five minutes and with the ultraviolet ray irradiation lamp spaced at 10 cm from the roller. Each semiconductive roller was rotated by 90 degrees four times to form an oxide film on its entire peripheral surface (360 degrees). ¼ (corresponding to 90 degrees) of the entire surface of each roller was irradiated for the period of time shown in table 1.
As the components of the semiconductive rubber roller of each of the examples and the comparison examples, the following substances were used:
Epichlorohydrin rubber (ECO): “Epichroma D” produced by DAISO CO., LTD.
Chloroprene rubber: “Shoprene WRT” produced by Showa Denko K.K.
Epichlorohidrin rubber (GECO): “Epichroma CG102” produced by DAISO CO., LTD.
[ethylene oxide (EO)/epichlorohidrin (EP)/allyl glycidyl ether (AGE)=56 mol %/40 mol %/4 mol %]
Polyether copolymer: “Zeospan ZSN8030” produced by Zeon Corporation.
[ethylene oxide (EO)/propylene oxide (PO)/allyl glycidyl ether (AGE)=90 mol %/4 mol %/6 mol %]
Acrylonitrile-butadiene rubber (NBR): “Nippol 401LL” (low-nitrile NBR containing acrylonitrile at 18%) produced by Zeon Corporation
Ethylene-propylene-diene copolymer (EPDM): “Esprene 505A” (oil-unextended type) produced by Sumitomo Chemical Co., Ltd.
Conductive carbon black: “Denka black” produced by Denki Chemical Industry Co., Ltd.
Weakly conductive carbon black: “Asahi #15 (average primary particle diameter: 122 nm) produced by Asahi carbon Co., Ltd.
The following properties of the semiconductive rubber roller of each of the examples and the comparison examples were measured.
Measurement of Electric Resistance of Semiconductive Rubber Roller
To measure the electric resistance of each roller, as shown in
A voltage V applied to the internal electric resistance r of the conductor wire was detected. Supposing that a voltage applied to the apparatus is E, the electric resistance R of the roller is: R=r×E/(V−r). Because the term −r is regarded as being extremely small, R=r×E/V. A load F of 500 g was applied to both ends of the metal shaft 2. A voltage E of 100V was applied to the roller, while it was being rotated at 30 rpm. The detected voltage V was measured at 100 times during four seconds. The electric resistance value R was computed by using the above equation. The electric resistance value of each roller obtained by computing the average value of obtained values is shown as a logarithmic value in table 1. The measurement was conducted after the rollers were left for not less than 24 hours at a low temperature 23° C. and a low relative humidity of 20%.
Measurement of Electric Resistance of Base Layer
The surface layer of each roller was abraded to form a one-layer construction of the base layer so that the electric resistance value R thereof was measured by using the same method as that described above. An average value of obtained values is shown in table 1 as the electric resistance value of the base layer. (The maximum electric resistance value)/(the minimum electric resistance value) was computed from the obtained maximum and minimum electric resistance values. The obtained value is shown in table 1 as the electric resistance deflection.
Measurement of Electric Resistance of Surface Layer
The surface layer of each roller was shaven off to obtain a one-layer construction of the surface layer so that the volume resistivity of the surface layer was measured, when a voltage of 100V was applied thereto by using a Highrester UR-SS probe (MCP-HTP15) manufactured by Dia Instrument Inc. Because the spot diameter of the probe was φ3 mm, the electric resistance value of a small sample like the above-described surface layer can be measured.
Print Test
The semiconductive rubber roller of each of the examples and the comparison examples was mounted on a laser printer (commercially available printer in which unmagnetic one-component toner to be positively charged is used) as a developing roller to evaluate the performance of each roller. A change of the amount of toner outputted as an image, namely, a change of the amount of the toner which deposited on printed sheets was used as the index in the evaluation. The measurement of the deposited amount of the toner on the sheets on which the solid black image was printed can be substituted by measurement of a transmission density described below.
More specifically, the solid black image was printed at the temperature of 10° C. and the relative humidity of 20%. The transmission density was measured by a reflection transmission densitometer (“Tecikon densitometer RT120/Light table LP20” produced by TECHKON Co., Ltd.) at given five points on each obtained sheet on which the solid black image was printed. The average of the transmission densities was set as an initial print density (shown as “C0” in table 1).
Thereafter an image to be printed at 5% was printed on 1,999 sheets of paper at the temperature of 10° C. and the relative humidity of 20%. After the operation of the printer was suspended for 12 hours, the solid black image was printed on 2000th sheet. In a manner similar to the above-described manner, the transmission density was measured for the 2000th sheet on which the solid black image was printed. The average of measured transmission densities was set as the print density (shown as “C2000” in table 1) after the image was printed on 2,000 sheets of paper. The reason the transmission density after the image was printed on 2,000 sheets of paper was measured is because normally a break-in finishes when an image is printed on about 2,000 sheets of paper.
From obtained values, the difference (indicated by C0-C2000) between the initial print density and the print density after the image was printed on 2,000 sheets of paper was computed. Table 1 shows the results.
In the above-described print test, the print density of the solid black image at the initial stage and the print density thereof after it is printed on 2,000 sheets of paper are favorably not less than 1.6 and more favorably not less than 1.8.
The difference between the print density of the solid black image at the initial stage and the print density thereof after it is printed on 2,000 sheets of paper is favorably not more than 0.2 and more favorably not more than 0.1.
Evaluation of Image
The semiconductive rubber roller of each of the examples and the comparison examples was mounted on a commercially available laser printer (commercially available printer in which unmagnetic one-component toner to be positively charged is used) as a developing roller. After an image to be printed at 5% was printed on 100 sheets of paper, a halftone image to be printed at 25% was printed to observe whether the image was evenly printed. Rollers which did not cause uneven print were marked by ◯. Rollers which caused uneven print to a slight extent were marked by Δ. Rollers which caused uneven print to a high extent were marked by X. The decrease of the print density caused by the rotation of the roller was also observed.
In the tests conducted on the semiconductive rubber roller of the comparison example 1, both the print density of the solid black image at the initial stage and the print density thereof after it was printed on 2,000 sheets of paper were low. There was a big difference between the print density of the solid black image at the initial stage and the print density thereof after it was printed on 2,000 sheets of paper. In the tests conducted on the semiconductive rubber roller of the comparison example 2, there was also a big difference between the print density thereof at the initial stage and the print density thereof after it was printed on 2,000 sheets of paper. The results indicate that in the semiconductive rubber roller of each of the comparison examples 1 and 2, the print density was low in the low temperature and humidity condition.
In the tests conducted on the semiconductive rubber roller of the comparison example 3, the print density of the printed image at the initial stage was so low that the semiconductive rubber roller cannot be put into practical use.
In addition, the semiconductive rubber roller of each of the comparison examples 1 through 3 caused uneven print and the print density to drop owing to the rotation thereof.
On the other hand, in the tests conducted on the semiconductive rubber rollers of the examples 1 through 4, the print density of the solid black image at the initial stage and the print density thereof after it was printed on 2,000 sheets of paper were more than 1.7. The difference between the print density thereof at the initial stage and the print density thereof after it was printed on 2,000 sheets of paper was not more than 0.1. The results indicate that the semiconductive rubber roller of the present invention prevent the print density from decreasing in the low temperature and humidity condition.
The semiconductive rubber roller of each of the examples 1 through 4 did not cause uneven print nor caused the print density to drop owing to the rotation thereof. These results indicate that the semiconductive rubber roller of the present invention maintains a high-quality image for a long time.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-111969 | Apr 2006 | JP | national |
