Rubber Member for Paper Feed Device

1. Field of the Invention

The present invention relates to a rubber member for a paper feed device, more particularly to a rubber member which is outstandingly effective when used as a 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.

2. Prior Art

In a paper feed device for a 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 a 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.

where .mu.F is the friction coefficient between feed roller 2 and paper 1, .mu.R is the friction coefficient between duplicate feed preventive rubber member 3 and paper 1, and .mu.P 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 .mu.F and .mu.P in actually used members, .mu.F was 1.5 to 2.5 and .mu.F was 0.3 to 0.6, and hence .mu.R is desired to be somewhere between 0.7 and 1.2. In the case of a film for an OHP (overhead projector), .mu.F is 2.5 to 3.0 and .mu.P is 0.3 to 1.5, and hence .mu.R 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. 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. 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.degree. to 200.degree. C.). On the other hand, generally, when the paper 1 onto 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.

The present inventors intensively investigated and studied in order to solve the above problems of the prior art and reached the invention by discovering that it would be better to consider a method to charge the paper electrostatically, instead of preventing electric charge of paper by making the duplicate feed preventive rubber member conductive. That is, the invention is characterized by the rubber member 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 which repels against 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.

FIG. 1 is an explanatory diagram showing the paper separating mechanism of a roller/pad separating system.

FIG. 2 is an explanatory diagram showing the paper separating mechanism of a 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 the 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 against 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 onto 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, the rubber member 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. By sliding onto 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 onto 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.). This blend is crosslinked and formed, and by sliding onto 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 onto 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.

The attached Table 1 shows the results of an 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 onto 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 an 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; any other substance to be charged positively when sliding on the paper may be blended, and two or more substances may be also blended.

The above embodiments relate to the duplicate feed preventive rubber member for a 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 onto the paper and preventing electrostatic image disturbance in the transfer step during the electrophotographic process.