Patent Application
20070254792
A semiconductive rubber roller 10 of the present invention is described below as one embodiment of the 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
An oxide film 1c is formed on the surface of the toner-transporting portion 1.
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 hardness of the base layer 1a of the semiconductive rubber roller 10 is set to 50 to 60 degrees in JIS A hardness. The hardness of the surface layer 1b of the semiconductive rubber roller 10 is set to 65 to 75 degrees in JIS A hardness. The hardness of the entire rubber roller 10 is set to 52 to 70 degrees in JIS A hardness. The hardness of the surface layer 1b is set higher than that of the base layer 1a. The electric resistance value of the rubber roller 10 is set to the range of 105Ω to 107Ω, when the electric resistance value thereof is measured by applying a voltage of 100V thereto at a temperature of 23° C. and a relative humidity of 55%.
The hardness of the base layer of the semiconductive rubber roller 10, that of the surface layer thereof and that of the laminate thereof are measured by a method described in the example of the present invention which will be described later.
The electric resistance value of the base layer 1a is set to the range from 103Ω to 106Ω and favorably the range from 104Ω to 105.5Ω, when the electric resistance value thereof is measured by applying a voltage of 100V thereto at a temperature of 23° C. and a relative humidity of 55%. 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 to the range of 105Ω to 107Ω, when the electric resistance value thereof is measured by applying the voltage of 100V thereto in the condition of the low temperature of 10° C. and the low relative humidity of 20%. The electric resistance value of the semiconductive rubber roller 10 is set to the range of 103Ω to 106.8Ω, when the electric resistance value thereof is measured by applying the voltage of 100V thereto in the condition of a high temperature of 30° C. and a high relative humidity of 80%. Both of the electric resistance values of the-semiconductive rubber roller 10 measured by applying the voltage of 100V thereto in the condition of the low temperature and the low relative humidity described above and the condition of the high temperature and the high relative humidity described above are not more than 107Ω.
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); and ionic-conductive rubbers such as epichlorohydrin copolymers having a polyether bond. It is more favorable to use the chloroprene rubber or/and the ionic-conductive rubbers such as the epichlorohydrin copolymers having the polyether bond. 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 for 100 parts by mass of the rubber component to 12 to 25 parts by mass.
As the rubber composition composing the base layer, an ionic-conductive rubber composition is also preferably used. It shows sufficient performance in a printer having the print speed of approximately 25 sheets/min. In this case, the ion-conductive composition to set the mixing amount of the weakly conductive carbon black to 10 to 25 parts by mass for 100 parts by mass of the ion-conductive rubber is preferably used.
As a rubber composition composing the surface layer 1b, a substantially insulating rubber composition or an ionic-conductive rubber composition is used.
The above-described “substantially insulating rubber composition” means rubbers, each of which has a volume resistivity set to the range of 1010 Ω·cm to 1015 Ω·cm so that they have a substantially insulating property, when the volume resistivity thereof is measured by applying a voltage of 100V thereto at the temperature of 10° C. and the relative humidity of 20%. As the rubbers, 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). 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 and the chloroprene rubber, a composition containing the epichlorohydrin copolymer and NBR, or 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 24% 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 favorable to mix the sulfur and the ethylene thiourea with each other at (sulfur:ethylene thiourea)=1:0.2 to 8 and more favorable to mix them at (sulfur:ethylene thiourea)=1:1.5 to 4.
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 5 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, more favorably 5 to 50 parts by mass, and most favorably 10 to 45 parts by mass for 100 parts by mass of the rubber component. By mixing the amount of the weakly conductive carbon black described above 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.
To allow the rubber roller to have a lower hardness, it is preferable to use the ionic-conductive rubber containing a slight amount of the weakly conductive carbon black therein as the base layer and use the ionic-conductive rubber containing the weakly conductive carbon black therein or the insulating rubber as the surface layer.
To allow the rubber to have little fluctuations in the electric resistance value thereof, it is preferable to use the electro-conductive rubber containing the weakly conductive carbon black therein as the base layer and use the ionic-conductive rubber containing the weakly conductive carbon black therein or the insulating rubber as the surface layer.
In adding oil to the rubber composition composing the base layer, it is preferable that the rubber composition contains oil, plasticizer, wax, and the like and that the ionic-conductive rubber containing the weakly conductive carbon black therein or the insulating rubber is used as the surface layer and as necessary, form an oil-shielding layer between the base layer and the surface layer.
The semiconductive rubber roller 10 is produced in the following procedure.
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 to make it easier to mold later. 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 sequentially 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. It is preferable to integrate the adjacent two layers with each other without interposing an adhesive agent therebetween. 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, Curelast meter). The vulcanization temperature may be set around 160° C. in dependence on necessity. To prevent the 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 10 is capable of imparting 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 (tanδ)=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 in the image-forming apparatus by the semiconductive rubber roller 10 is set to 0.01 to 1.0 mg/cm2.
By mixing at least 20 parts by mass of chloroprene rubber with 100 parts by mass of the entire rubber component of the surface layer 1b such that the chloroprene rubber is contained in the rubber component in a larger amount than the NBR rubber or the polyether copolymer, the semiconductive rubber roller 10 can be suitably used as the developing roller for use in the image-forming apparatus in which the unmagnetic one-component toner to be positively charged is used.
In a print test of the semiconductive rubber roller 10 described in the examples of the present invention, 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. 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 favorably less than 2.2. When it is not less than 2.2, there is a fear that a variation in the print density occurs owing to the large amount of the toner consumption. 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 tables 1 and 2, the rubber component and the carbon black (the conductive carbon black or the weakly 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 tables 1 and 2, 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 an 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 tables 1 and 2.
As the components of the semiconductive rubber roller of each of the examples and the comparison examples, the following substances were used:
The following properties of the semiconductive rubber roller of each of the examples and the comparison examples were measured. The coefficient of friction of the semiconductive rubber roller were measured by a method described in the embodiment of the invention.
Hardness of Laminate and Base Layer
As shown in
A rubber roller having an outer diameter of φ20 mm was made of only the rubber composition composing the surface layer. Thereafter the hardness of the surface layer was measured by using the same method as that described above.
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 tables 1 and 2. The electric resistance value of each of the rubber rollers was measured at a constant temperature of 23° C. and a constant humidity relative humidity of 55%.
The surface layer of each roller was abraded to form a one-layer construction 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 tables 1 and 2 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 tables 1 and 2 as the electric resistance deflection.
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 an obtained sheet 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.
By using the rubber roller made of only the rubber composition composing surface layer measured the hardness of the surface layer, the electric resistance value R thereof was measured by using the same method as that described above.
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 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.
In the print test, a printer used in the examples 1 through 4, 6 and the comparison examples 1 through 6 was of the type of using the unmagnetic one-component toner to be positively charged, whereas a printer used in the example 5 and the comparison example 7 was of the type of using the unmagnetic one-component toner to be negatively charged.
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 tables 1 and 2).
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 tables 1 and 2) 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 print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was computed. Tables 1 and 2 show the results.
In the above-described print test, the print density of the image at the initial stage and the print density after the image is printed on 2,000 sheets of paper are favorably not less than 1.6 and more favorably not less than 1.8. Further, the print density of the image at the initial stage and the print density after the image is printed on 2,000 sheets of paper are favorably less than 2.2.
The difference between the print density of the image at the initial stage and the print density after the image is printed on 2,000 sheets of paper is favorably not more than 0.2 and more favorably not more than 0.1.
As printing proceeds, toner deteriorates. Hence it becomes difficult to electrically charge the toner. As a result, it is difficult to hold the toner on the developing roller, which causes the toner to flow to the sealing portion. Consequently the toner caught between the developing roller and the sealing portion wears the developing roller and the sealing portion. As the wear of the developing roller and the sealing portion proceeds, the toner leaks from worn portions thereof. Thus the leak of the toner from the sealing portion can be utilized as an index for synthetically examining the deterioration of the toner and the durability of the developing roller including the wear resistance thereof.
More specifically, after the print test finished, the image was printed on 5,000 sheets of paper in the same condition as that of the print test to observe the degree of the leak of the toner from the sealing portion. The commercially available laser printer used in the test for examining the toner leak ensures print of 6,500 sheets of paper when the image was printed at 5%.
The following synthetic evaluation was made based on the results of the print test and the toner leak-examining test:
In the semiconductive rubber rollers to which the mark of ⊚ was given, toner did not leak, the print density at the initial stage and the print density after the image was printed on 2,000 sheets of paper were not less than 1.8 and less than 2.2; and the difference between the print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was not more than 0.1.
In the semiconductive rubber rollers to which the mark of ◯ was given, toner did not leak, the print density at the initial stage and the print density after the image was printed on 2,000 sheets of paper were not less than 1.8 and less than 2.2; and the difference between the print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was not less than 0.1 nor more than 0.2.
In the semiconductive rubber rollers to which the mark of Δ was given, toner leaked a little; or either the print density at the initial stage or the print density after the image was printed on 2,000 sheets of paper were less than 1.8 or not less than 2.2; or the difference between the print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was more than 0.2.
In the semiconductive rubber rollers to which the mark of × was given, the toner leaked.
In the tests conducted on the semiconductive rubber roller of the comparison examples 1, 4 and 7, the difference between the print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was small. That is, the print density did not drop. But the print density at the initial stage was not less than 2.2. That is, the print density of the initial stage was too large. Further the wear of the rubber roller caused the toner to leak from the sealing portion thereof. In addition a portion where an image was not to be formed was fogged with the toner. That is, the semiconductive rubber roller of the comparison examples 1, 4 and 7 had a problem in its durability.
As described above, in the semiconductive rubber roller of the comparison examples 1 and 7, the print density after the image was printed on 2,000 sheets of paper was higher than that of the image at the-initial stage. The reason is as follows: Because the toner deteriorated greatly after the image was printed on 2,000 sheets of paper, the toner was electrically charged in a considerable amount. Thereby the print density became higher.
In the tests conducted on the semiconductive rubber roller of the comparison examples 2, 3, 5 and 6, the print density after the image was printed on 2,000 sheets of paper was not more than 1.75. That is, the rubber roller did not provide a sufficient print density. The difference between the print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was more than 0.2. That is, the print density dropped a little. In addition, the toner leaked in a small amount and thus had a problem in its durability.
On the other hand, in the tests conducted on the semiconductive rubber rollers of the examples 1 through 6, both the print density at the initial stage and the print density after the image was printed on 2,000 sheets of paper were not less than 1.85 and less than 2.20. The difference between the print density of the image at the initial stage and the print density after the image was printed on 2,000 sheets of paper was not more than 0.15. In addition, the sealing portion of each rubber roller did not wear, and the toner did not leak.
As apparent from the above-described description, the rubber member of the present invention provides a sufficient print density even in the low temperature and humidity condition. Further the print density hardly deteriorates. In addition, the sealing portion of the developing roller does not wear and hence the toner does not leak. That is, the rubber member is durable. Consequently the developing roller composed of the rubber member provides a high-quality image for a long time.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-124716 | Apr 2006 | JP | national |
| 2007-103526 | Apr 2007 | JP | national |
