Rubber member for paper feed device

Abstract: Object: To control charging of the rubber member (3) when sliding on paper (1), and prevent image disturbance in transfer step on electrophotographic process. Constitution: In order to be charged positively when sliding on sheet of paper (1), it is characterized by composing in a blend containing magnesium oxide or barium oxide, nylon short fiber or its powder, or nigrosine compound.

Description: The present invention relates to a rubber member for paper feed device, more particularly to a rubber member which is outstandingly effective when used as duplicate feed preventive rubber pad or rubber roller for separating and feeding sheets of paper smoothly one by one in a paper feed device of copier, facsimile apparatus, printer or other office automating equipment. In paper feed device for copier, facsimile apparatus, printer or other office automating equipment, in order to feed multiple sheets of paper set up in a stack-up state in a cassette or the like by separating one by one, the roller/pad separating method as shown in Fig. 1, the roller/roller separating method as shown in Fig. 2 or other separating mechanism is provided. In Fig. 1 and Fig. 2, numerals 1, 2 and 3 respectively denote sheets of paper, a paper feed roller, and rubber pad or rubber roller as duplicate feed preventive rubber member. Using the paper feed rubber roller 2 and duplicate feed preventive rubber member 3, in order to feed multiple sheets of paper 1, 1... set in a stack-up state in a cassette (not shown) or the like smoothly by separating one by one, it is required that the friction coefficient between members should satisfy the following formula 1. µF > µR > µP where µF is the friction coefficient between feed roller 2 and paper 1, µR is the friction coefficient between duplicate feed preventive rubber member 3 and paper 1, and µP is the friction coefficient between sheets of paper 1, 1. This relation must be maintained even after passing at least 100,000 sheets. As a result of measurement of µF and µP in actually used members, µF was 1.5 to 2.5 and µP was 0.3 to 0.6, and hence µR is desired to be somewhere between 0.7 and 1.2. In the case of a film for an OHP (overhead projector), µF is 2.5 to 3.0 and µP is 0.3 to 1.5, and hence µR should be 1.7 to 2.4. Hitherto, the duplicate feed preventive rubber member 3 is composed of, as a substance excellent in wear resistance, urethane, combination of urethane and cork, natural rubber, chloroprene, or the like. In the conventional duplicate feed preventive rubber member 3 composed of urethane, combination of urethane and cork, natural rubber, chloroprene or the like, when sliding on the paper 1, the paper 1 is electrically charged, and an electrostatic image disturbance occurs in the transfer step in the electrophotographic process. In the electrophotographic progress, generally, for example in the electrophotographic apparatus as shown in Fig. 3, after the surface of a photosensitive drum 4 is uniformly charged by a charger 5, an optical image of the original is projected, and the electric charge disappears in the illuminated portion, thereby forming an electrostatic latent image (an invisible electric image) on the surface of this photosensitive drum 4, and a toner (the developer) is pulled out from a toner tank of a developing roller 6 to deposit on the charged portion of the surface of the photosensitive drum 4, and the toner on the surface of the photosensitive drum 4 is transferred on the paper 1 electrically charged by a transfer charger 7, then the toner image transferred on the paper 1 is passed through two rollers (not shown) to be fixed thermally (about 160 to 200°C). On the other hand, generally, when the paper 1 and rubber member 3 slide on each other, the paper 1 is positively charged, while the rubber member 3 is negatively charged. In this mechanism of electrophotographic apparatus, when using a toner of negative electric charge, if the paper 1 is positively charged, it may attract the toner of negative charge on the surface of the photosensitive drum 4 before transfer as shown in Fig. 4, which may result in image disturbance. It may be therefore considered to make the rubber compositive conductive so as not to charge by blending the polymer with carbon black or conductive zinc white, but if the carbon black is blended sufficiently so as to be conductive, when sliding on the paper 1, the paper 1 may be stained, and it is not suited as the duplicate feed preventive rubber member 2. Or if the conductive zinc white is blended enough to be conductive, the wear resistance is impaired, and it is not suited as the duplicate feed preventive rubber member used in severe abrasive condition of sliding against the paper 1. It is an object of the present invention to provide apparatus for feeding paper sheets in which the described problems of the prior art are alleviated. According to one aspect of the present invention, there is provided an apparatus for feeding paper sheets, which comprises a paper feed roller and a plate-like rubber pad adjacent to said paper feed roller for preventing duplicate feed of paper sheets, which rubber pad comprises a polymer, vulcanizer, vulcanization aid and filler; characterised in that the rubber pad also comprises at least one component selected from the group consisting of magnesium oxide, barium oxide, nylon short fibers, powder of nylon short fibers and nigrosine compound and in that said component is present in an amount of 1 to 100 parts by weight to 100 parts by weight of the polymer whereby, in use, a paper sheet is identically charged in polarity with toner when sliding on said rubber pad. According to another aspect of the present invention, there is provided an apparatus for feeding paper sheets, which comprises a paper feed roller and a rubber roller adjacent to said paper feed roller for preventing duplicate feed of paper sheets, which rubber roller comprises a polymer, vulcanizer, vulcanization aid and filler; characterised in that the rubber roller also comprises at least one component selected from the group consisting of magnesium oxide, barium oxide, nylon short fibers, powder of nylon short fibers and nigrosine compound and in that said component is present in an amount of 1 to 100 parts by weight of the polymer whereby, in use, a paper sheet is identically charged in polarity with toner when sliding on said rubber roller. The invention employs a rubber member (pad or roller) which is composed in such a blend as to be charged positively when sliding on the paper. By using the rubber member of the invention, when sliding on the paper, it is positively charged, and the paper is negatively charged, and the paper repels the toner of negative charge before the transfer step, and therefore the toner is not attracted to the paper, so that image disturbance does not occur. The drawings, which have already been discussed, are as follows:- Fig. 1 is an explanatory diagram showing the paper separating mechanism of roller/pad separating system. Fig. 2 is an explanatory diagram showing the paper separating mechanism of roller/roller separating system. Fig. 3 is an explanatory diagram showing the peripheral parts of the photosensitive unit of an electronic copier. Fig. 4 is an explanatory diagram showing the image disturbance occurring when the paper is positively charged. Some of the embodiments of the rubber member for paper feed device of the invention are described in detail below. In a first embodiment of the rubber member of the invention, it is composed of a blend of a polymer containing proper amounts of ordinary vulcanizer, vulcanization aid, and filler [for example, NBR (acrylonitrile-butadiene copolymer rubber), NR (natural rubber), urethane, etc.] with magnesium oxide or barium oxide, and this blend is formed in a desired shape by crosslinking through the process of transfer forming, injection forming, press forming or extrusion forming. Since this rubber member contains magnesium oxide or barium oxide, it decreases the quantity of negative electric charge applied when sliding on the paper, and is positively charged to the contrary. As a result, the paper is negatively charged, and it repels the toner of negative charge, and therefore the toner will not be attracted to the paper before the transfer step. Here, in order to be charged positively when sliding on the paper, a proper content of the magnesium oxide or barium oxide should be 1 to 100 parts by weight to 100 parts by weight of the polymer. In a second embodiment of the invention, it is composed of a blend of the same polymer as in the first embodiment with nylon short fiber or its powder, and this blend is crosslinked and formed, and by sliding on the paper, it was also positively charged and the paper was negatively charged, as confirmed in the experiment by the applicant. In order to be charged positively when sliding on the paper, a proper content of the nylon short fiber or its powder should be 1 to 100 parts by weight to 100 parts by weight of the polymer. In a third embodiment of the invention, it is composed of a blend of the same polymer as in the first embodiment with nigrosines compound (made by Orient Chemical Industrial Co.), and this blend is crosslinked and formed, and by sliding on the paper, it was also positively-charged and the paper was negatively charged, as confirmed in the experiment by the applicant. In order to be charged positively when sliding on the paper, a proper content of the nigrosine compound should be 1 to 100 parts by weight to 100 parts by weight of the polymer. Attached Table 1 shows the results of experiment conducted to prove positive electric charging of the rubber member blending magnesium oxide or barium oxide, nylon short fiber or its powder, and nigrosine compound, when sliding on the paper. However, in test (A) the above substances were not blended in the NBR, in tests (B), (C) the NBR was blended with nylon short fiber or its powder, in test (D) the above substances were not blended in the NR, in tests (E), (F) magnesium oxide or barium oxide was mixed in the NR, in test (C) the above substances were not blended in the urethane, and in test (H) the urethane was blended with nigrosine compound. As is clear from the results of experiment in Table 1, it is known that the materials were positively charged when sliding on the paper in tests (B), (C), (E), (F), (H). It is hence evident that when blended with magnesium oxide or barium oxide, nylon short fiber or its powder, or nigrosine compound, the paper is negatively charged and the toner is not attracted before the transfer step. Meanwhile, the foregoing embodiments are about the rubber member blending magnesium oxide or barium oxide, nylon short fiber or its powder, and nigrosine compound, but the invention is not limited to these embodiments alone, and two or more substances may be also blended. The above embodiments relate to the duplicate feed preventive rubber member for paper feed device used in office automating equipment, but the invention is not limited to this, and may be applied to any rubber member sliding on the paper. According to the invention as described herein, it is possible to present a rubber member capable of controlling the electric charging of the paper when sliding on the paper, and preventing electrostatic image disturbance in the transfer step in the electrophotographic process.

Claims: An apparatus for feeding paper sheets, which comprises a paper feed roller (2) and a plate-like rubber pad (3) adjacent to said paper feed roller (2) for preventing duplicate feed of paper sheets, which rubber pad (3) comprises a polymer, vulcanizer, vulcanization aid and filler; characterised in that the rubber pad also comprises at least one component selected from the group consisting of magnesium oxide, barium oxide, nylon short fibers, powder of nylon short fibers and nigrosine compound and in that said component is present in an amount of 1 to 100 parts by weight to 100 parts by weight of the polymer whereby, in use, a paper sheet (1) is identically charged in polarity with toner when sliding on said rubber pad (3). Apparatus according to claim 1 characterised in that said polymer is selected from the group consisting of acrylonitrilebutadiene copolymer rubber (NBR), natural rubber (NR), and urethane. An apparatus for feeding paper sheets, which comprises a paper feed roller (2) and a rubber roller (3) adjacent to said paper feed roller (2) for preventing duplicate feed of paper sheets (1), which rubber roller (3) comprises a polymer, vulcanizer, vulcanization aid and filler; characterised in that the rubber roller (3) also comprises at least one component selected from the group consisting of magnesium oxide, barium oxide, nylon short fibers, powder of nylon short fibers and nigrosine compound and in that said component is present in an amount of 1 to 100 parts by weight of the polymer whereby, in use, a paper sheet is identically charged in polarity with toner when sliding on said rubber roller (3). Apparatus according to claim 3, characterised in that said polymer is selected from the group consisting of acrylonitrile-butadiene copolymer rubber (NBR), natural rubber(NR), and urethane.

Inventors: ITANI HITOSHI, MURAKAMI HIROTOSHI, TANAKA HIROAKI C O SUMITOMO GO, ITANI, HITOSHI, MURAKAMI, HIROTOSHI, TANAKA, HIROAKI, TANAKA, HIROAKI, C/O SUMITOMO GOMU KOGYO K.K.
Applicants: SUMITOMO RUBBER IND, SUMITOMO GOMU KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: B65H3
IPC codes: G03G15, B65H3, B41J13, H04N1