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
2001-04-30
2003-11-25
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C052S524000, C052S521000, C052S523000, C052S525000, C052S426000, C052S515000
Reexamination Certificate
active
06653404
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition comprising a crosslinked rubber particle and a conjugated diene/aromatic vinyl copolymeric rubber as essential components. A rubber composition of the invention exhibits an excellent processability, and also exhibits excellent handling performance and dimension stability, and the like especially when combined with a silica as a reinforcing agent. A vulcanized rubber obtained by vulcanizing a rubber composition of the invention has excellent tensile strength and wearing resistance, and the like.
2. Description of the Related Art
A starting rubber employed frequently for a rubber product is a conjugated diene rubber such as a polybutadiene rubber, a polyisoprene rubber, a natural rubber, a styrene-butadiene copolymeric rubber, an acrylonitrile-butadiene copolymeric rubber, and the like.
Any of these starting rubbers, when combined with a silica as a reinforcing agent, can provide a colored rubber product except for a black colored product. However, unlike to a carbon black, a silica may lead to a problematic reduction in the tensile strength and the wearing resistance of a vulcanized rubber, and the like. Additional problems associated with the incorporation of a silica include {circle around (1)} a reduction in the processability and the compound consistency upon kneading, {circle around (2)} an insufficient smoothness of the surface of a sheet made from a compound using a roll and an irregular sheet edge accompanied with a substantial shrinkage upon cooling, and the like.
Such problems may be due to an aggregation of a silica instead of a sufficient dispersion. A rubber composition in which a silica is not dispersed sufficiently poses a difficulty in obtaining a certain reinforcing effect of the incorporation of a reinforcing agent and undergoes a heat generation attributable to the interaction between poorly dispersed silica particles, resulting in a substantial reduction in the processability. Such poor dispersion of a silica occurs possibly because of the reasons that a silica has a high self-interacting effect when compared with a carbon black and tends to aggregate easily and that a starting rubber usually consists of carbon and hydrogen and has a lower polarity when compared with a silica which leads to a low affinity with the silica.
For the purpose of increasing the affinity of a silica with a hydrocarbon-based rubber, the use of a conjugated diene-based rubber to which a functional group having an affinity with the silica is introduced has been investigated. For example, a conjugated diene-based rubber to which a hydroxyl group is introduced (WO96/23027), a conjugated diene-based rubber to which an alkoxysilyl group is introduced (JP-A 9-208623) and a conjugated diene-based rubber to which an alkoxysilyl group and an amino group or a hydroxyl group are introduced (JP-A 9-208633) have been proposed. However, such conjugated diene-based rubber to which a functional group described above is introduced mostly exhibits problematically poor dispersion, excessive heat generation upon processing and poor processability, and the like since it undergoes an extensive aggregation with a silica when the silica is admixed.
On the other hand, a silane coupling agent is incorporated usually for the purpose of preventing an aggregation of a silica and achieving a uniform dispersion. This results in an improvement in the dispersibility of a silica to some extent and a substantial improvement in the processability of a rubber composition and the tensile strength and the wearing resistance of a vulcanized rubber and the like. Nevertheless, the smoothness of the surface and the edge of a sheet or the problematic shrinkage of a sheet upon cooling or the like has not adequately been improved. Furthermore, a sufficient improvement in the processability, the tensile strength or the wearing strength or the like requires the incorporation of a silane coupling agent in an amount as high as about 8 to 15% by weight based on a silica, but such silane coupling agent is expensive and increases the cost for a rubber composition.
SUMMARY OF THE INVENTION
The present invention overcomes the problems experienced conventionally as described above, and is intended to provide a rubber composition having excellent processability and handling performance, which are experienced as a satisfactory processability upon kneading, a smooth sheet surface, a regular sheet edge and a less shrinkage upon cooling, and the like. A vulcanized rubber obtained by vulcanizing a rubber composition described above has excellent tensile strength and wearing resistance, and the like.
We made an effort to solve the problems mentioned above and discovered that by incorporating a crosslinked rubber particle having a certain composition and a conjugated diene/aromatic vinyl copolymeric rubber into a rubber composition it is possible to obtain a rubber composition which exhibits a satisfactory processability upon kneading and which achieves a satisfactory smoothness of the sheet surface and the sheet edge and a less sheet shrinkage upon cooling. It was also discovered that by using this rubber composition it is possible to obtain a vulcanized rubber having sufficient tensile strength and wearing resistance, and the like. In addition, even when a silane coupling agent is used only in a reduced amount or is not used, the processability and the tensile strength, and the like were revealed to be improved sufficiently to the levels at which no practical problems are experienced. Furthermore, it was also revealed that even when a carbon black is incorporated a rubber composition having an excellent processability and a satisfactory dimension stability can be obtained and a vulcanized rubber having an excellent wearing resistance and the like can be obtained.
The present invention is based on the findings described above and can be described as follows.
1. A rubber composition comprising (1) a crosslinked rubber particle containing as repeating units (a) 39.89 to 79.89% by weight of a conjugated diene unit, (b) 20 to 60% by weight of an aromatic vinyl unit, (c) 0.01 to 10% by weight of a monomer unit having at least two polymerizable unsaturated group and (d) 0.1 to 30% by weight of a monomer unit having one polymerizable unsaturated group and an amino group [the total amount of (a), (b), (c) and (d) is 100% by weight], and (2) a conjugated diene/aromatic vinyl copolymeric rubber whose conjugated diene unit has a 1,2-vinyl content of 10 to 30% and a 1,4-trans content exceeding 55%.
2. A rubber composition according to 1 above, further comprising at least one selected from a silica and a carbon black.
3. A rubber composition according to 2 above, wherein the total amount of said silica and said carbon black, when said silica and said carbon black are employed in combination, is 10 to 120 parts by weight based on 100 parts by weight as the total amount of said crosslinked rubber particle and said conjugated diene/aromatic vinyl copolymeric rubber.
4. A rubber composition according to 1 above, wherein at least a part of said conjugated diene/aromatic vinyl copolymeric rubber comprises 0.1 to 30% by weight of a monomer unit having one polymerizable unsaturated group and at least one functional group selected from a carboxylic group (CO
2
H and/or CO
2
−
), an amino group, a hydroxyl group, an epoxy group and an alkoxysilyl group.
5. A rubber composition according to 4 above, further comprising at least one selected from a silica and a carbon black.
6. A rubber composition according to 5 above, wherein the total amount of said silica and said carbon black, when said silica and said carbon black are employed in combination, is 10 to 120 parts by weight based on 100 parts by weight as the total amount of said crosslinked rubber particle and said conjugated diene/aromatic vinyl copolymeric rubber.
7. A rubber composition according to 1 above, wherein
said conjugated diene forming said conjugated diene unit (a) and said conjug
Akema Hiroshi
Konno Tomohisa
Tadaki Toshihiro
Udagawa Yoshiyuki
Hu Henry S.
JSR Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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