Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-05-23
2002-11-05
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S213000, C525S222000, C525S232000, C525S238000, C525S241000, C425S223000, C425S263000
Reexamination Certificate
active
06476140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermoplastic elastomer composition in which dynamically cross-linked rubber is dispersed. More particularly, the present invention relates to a thermoplastic elastomer composition which is preferably used to form a rubber roller having a high degree of flexibility and wear resistance so that the rubber roller can be used as a paper-feeding roller, for an ink jet printer or the like, required to be compatible with a recording liquid.
2. Description of the Related Art
The rubber roller is used in the paper-feeding mechanism of an ink jet printer, a laser printer, an electrostatic copying apparatus, a facsimile apparatus, an automatic deposit payment machine (ATM), and the like. The rubber roller is required to feed paper after picking up a sheet of paper or a film one by one from sheets of paper piled up. Therefore, it is necessary to provide the rubber roller with a high degree of flexibility and wear resistance.
Of the paper-feeding roller, the paper-feeding rubber roller for use in the ink jet printer is required to have favorable affinity (compatibility) for a recording liquid (aqueous ink). The recording liquid for the ink jet printer contains much polar components such as water and multivalent alcohol. If the rubber roller has unfavorable affinity for the recording liquid (polar), the recording liquid does not spread favorably on a portion of paper which contacted the rubber roller during feeding of the paper. As a result, a roller mark is formed on the paper.
The present applicant proposed the rubber roller composed of the thermoplastic elastomer composition formed by mixing the rubber component, the hydrogenated styrene thermoplastic elastomer, and the thermoplastic resin with one another; and dynamically cross-linking the rubber component with the resinous cross-linking agent and dispersing it in the mixture of the hydrogenated styrene thermoplastic elastomer and the thermoplastic resin.
In forming the thermoplastic elastomer composition, dynamic cross-linking speed is controlled by setting the addition amount of halogen serving as the resinous cross-linking agent to the range of 0.25-1.5 wt % or using both a halogen-added resinous cross-linking agent and a halogen-unadded resinous cross-linking agent. Cross-linking of the rubber component is completed when the mixing of the rubber and the resin has progressed in a certain extent. By doing so, the moldability and the dispersibility of the rubber can be secured, and the amount of the rubber component with respect to the resin can be increased.
As described above, by increasing the dispersibility of the rubber, it is possible to increase the flexibility of the rubber without deteriorating the durability of the molded rubber roller, enhance the paper-feeding performance of the rubber roller, and improve the wear resistance of the rubber roller. Further, by increasing the amount of the rubber component, the paper-feeding performance and durability of the rubber roller are enhanced further and reduction of worn powder is achieved.
In the thermoplastic elastomer composition disclosed in U.S. Pat. No. 2,837,741, rubber is dynamically cross-linked in not less than two kinds of thermoplastic elastomers. More specifically, the thermoplastic elastomer composition contains ethylene-&agr; olefin copolymer rubber, a crystalline ethylene-propylene block copolymer resin, a low-molecular-weight propylene homo-polimerized resin having a number-average molecular weight of 2000-20000, and a softener consisting of mineral oil.
However, according to the thermoplastic elastomer composition proposed by the present applicant, the cross-linking speed is controlled slowly to increase the dispersibility of the rubber. Thus, the cross-linking density is low.
Accordingly, the mechanical property of the thermoplastic elastomer composition is low. In particular, the thermoplastic elastomer composition has a low degree of durability. Thus, a paper-feeding roller composed of the thermoplastic elastomer composition has low degree of paper-passing performance. Because there is a limit in the increase of the rubber component, it is impossible to greatly reduce generation of worn powder and improve the durability of the paper-feeding roller.
If the cross-linking density is increased by making the cross-linking speed high to solve the problem, the rubber component has a low degree of dispersibility. Consequently, the rubber component has a low degree of flexibility.
In the thermoplastic elastomer composition disclosed in U.S. Pat. No. 2,837,741, the low-molecular-weight propylene is used. Because polypropylene is not an elastomer, it deteriorates the mechanical property of the thermoplastic elastomer composition, especially flexibility.
The thermoplastic elastomer composition of this kind has a high flexibility in the case where the mixing amount of the rubber component is increased. Consequently, the paper-feeding roller composed of the thermoplastic elastomer composition has improved paper-feeding force and wear resistance, whereas the thermoplastic elastomer composition has deteriorated processability and moldability. To disperse cross-linked rubber particles uniformly in the thermoplastic elastomer, it is necessary to keep the mixing ratio of the rubber component constant. According to the conventional method, the maximum mixing ratio of the rubber component is 65-80 wt % with respect to the entire weight of a polymer (oil is excluded).
As the mixing ratio of a rubber-dispersing high-molecular-weight resin becomes more, the mechanical property of the thermoplastic elastomer composition is improved increasingly, the paper-feeding roller composed of the thermoplastic elastomer composition has paper-feeding performance increasingly, and generation of worn powder is suppressed increasingly. Therefore, in the conventional art, a styrene thermoplastic elastomer and thermoplastic resin having a high molecular weight are used.
However, the use of the high-molecular-weight styrene thermoplastic elastomer and thermoplastic resin causes the processability of the thermoplastic elastomer composition to deteriorate and the dispersibility of the rubber component of a mixture of resin and rubber oil to deteriorate in dynamically cross-linking the rubber. Thereby the paper-feeding roller composed of the thermoplastic elastomer composition deteriorates in its wear resistance and paper-feeding performance.
It is difficult for the conventional art to form the thermoplastic elastomer composition in which flexibility is compatible with wear resistance as well as durability. Thus there is a demand for the development of a thermoplastic elastomer having superior performance. It is ideal to develop a thermoplastic elastomer composition similar to rubber in it flexibility and similar to resin it its moldability and mechanical strength.
Any of the above-described thermoplastic elastomer compositions contains a non-polar material such as thermoplastic resin not in consideration of compatibility with a recording liquid such as aqueous ink (polar) . Thus in the case where printing is made on super-fine glossy paper, photo-printing paper, color OHP paper or the like by using a rubber roller as the paper-feeding roller for an ink jet printer, the recording liquid does not spread on a portion of paper which has contacted the rubber roller during paper feeding. As a result, a roller mark is formed on the portion of the paper. That is, an irregular image is formed thereon.
Therefore, there is a growing demand for the development of the rubber roller, composed of the thermoplastic elastomer composition, having favorable affinity for an aqueous recording liquid (polar).
SUMMARY OF THE INVENTION
The present invention has been made in view of the problem. Thus, it is a first object of the present invention to provide a thermoplastic elastomer composition superior in flexibility and wear resistance as well as durability, and in addition moldability and superior as the material for a rubber roller.
It is
Hattori Takayuki
Mizoguchi Tetsuo
Mizumoto Yoshihisa
Okuyama Hideyuki
Nutter Nathan M.
Sumitomo Rubber Industries Ltd.
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