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
1998-12-15
2001-02-20
Lipman, Bernard (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...
C525S332800, C525S333100, C525S366000, C525S367000
Reexamination Certificate
active
06191234
ABSTRACT:
TECHNICAL FIELD
The present invention relates to conjugated diolefin copolymer rubber. More specifically, it relates to conjugated olefin-based copolymer rubber which can provide an auto tire tread having excellent processability and good balance among abrasion resistance, failure characteristics, hysteresis-loss characteristics and wet-skid resistance.
BACKGROUND ART
Due to recent demand for a reduction in the fuel consumption of an automobile, conjugated diolefin-based rubber having low rolling resistance, excellent abrasion resistance and failure characteristics, and steering stability typified by wet skid resistance has been desired as a rubber material for tires.
To reduce the rolling resistance of a tire, the hysteresis-loss of vulcanized rubber may be lowered. As indices for the evaluation of vulcanized rubber are used impact resilience at 50 to 80° C., tan&dgr; at 50 to 80° C., Goodrich heat build-up and the like. A rubber material having either a large impact resilience at 50 to 80° C. or small tan&dgr; at 50 to 80° C. or small Goodrich heat build-up is preferred.
Known rubber materials having a low hysteresis-loss include natural rubber, polyisoprene rubber and polybutadiene rubber. However, they have small wet skid resistance.
As a means of reducing a hysteresis-loss without sacrificing wet skid resistance, there is proposed a method for introducing a functional group to the terminal end of a styrene-butadiene copolymer which is polymerized by an organic lithium initiator in a hydrocarbon solvent and has a variety of structure. There are known a styrene-butadiene copolymer obtained by modifying or coupling the terminal end of a polymer with a tin compound (see JP-A 57-55912) and a styrene-butadiene copolymer obtained by modifying the terminal of a polymer with an isocyanate compound (see JP-A 61-141741). These modified polymers show the effect of reducing a hysteresis-loss and improving abrasion resistance and failure characteristics without sacrificing wet skid resistance, particularly in a compound comprising carbon black as a reinforcement.
Meanwhile, there has recently been proposed a method which uses a rubber compound, comprising silica or a mixture of silica and carbon black as a reinforcement, as a rubber material for tires. A tire tread made from such a rubber composition containing silica or a mixture of silica and carbon black has low rolling resistance and excellent steering stability typified by wet skid resistance, while the vulcanizate of the rubber compound has such problems as low tensile strength and low abrasion resistance. Compounds comprising the above modified styrene-butadiene copolymers and carbon black as a reinforcement may be used as rubber materials for tires having excellent abrasion resistance and failure characteristics, whereas compounds comprising the above modified styrene-butadiene copolymers and silica as a reinforcement have a small effect of improving these properties.
To improve the tensile strength and abrasion resistance of the vulcanizate containing silica or a mixture of silica and carbon black, there is proposed a rubber composition comprising a polymer into which a functional group having affinity for silica has been introduced. JP-B 49-36957 proposes a method for producing a polymer by reacting silicon tetrahalide, trihalosilane or the like. JP-B 52-5071 discloses a method for producing a polymer modified with silane halide compound. Further, JP-A 1-188501 discloses diene-based rubber into which an alkylsilyl group has been introduced and JP-A 5-230286 discloses diene-based rubber into which a silyl halide group has been introduced.
Although the physical properties of a silica or a mixture of silica and carbon black-filled vulcanizate are improved to a certain degree by using these modified polymers, improvements in the tensile strength and abrasion resistance of the vulcanizate thereof are still unsatisfactory. A reduction in hysteresis-loss is also unsatisfactory due to an increase in the proportion of carbon black when a mixture of silica and carbon black is blended. As a silica-containing compound is generally inferior in processability to a carbon black-containing compound, its process costs are high. When a polymer into which a functional group having affinity for silica is introduced is used, its processability is apt to deteriorate disadvantageously.
Conventionally known modified polymers are divided into a type suitable to carbon black-filled compound and a type suitable to silica-filled compound. When a tire is to be produced, rubber to be used must be selected when the type of a reinforcement is changed. When a mixture of silica and carbon black is blended, the effect of either one of the types of the modified polymers increases or reduces relative to the mixing ratio of silica to carbon black.
A polymer to which an amino group is introduced is conceivable as a modified polymer which is effective in blending carbon black or silica. As polymers containing carbon black, there are proposed (1) polymers having an amino group introduced to the terminal using a lithium amide initiator (see JP-A 59-38209, JP-B 5-1298, JP-A 6-279515, JP-A 6-199923 and JP-A 7-53616) and (2) polymers obtained by modifying the terminal of a styrene-butadiene copolymer which is polymerized by an organic lithium initiator and has a variety of structure with an urea compound (see JP A 61-277338) or with a nitrogen-containing compound such as a dialkyl aminobenzophenone compound (see JP-A 58-162604 and JP-A 58-189203) or a lactam compound (see JP-A 61-43402). As a polymer to be blended with silica is proposed diene-based rubber having an introduced amino group as disclosed by JP-A 1-101344, JP-A 64-22940 and JP-A 9-71687.
The polymers obtained by these methods have improved their physical properties to a certain degree by containing carbon black or silica. However, in the above documents, a method for introducing an amino group into a polymer is detailed but as for the relationship between the structure and each property of the polymer itself, only a general description is given.
Problems that the Invention intends to solve
It is an object of the present invention to provide conjugated diolefin copolymer rubber having novel composition and characteristics.
It is another object of the present invention to provide conjugated diolefin-based copolymer rubber having an amino group in the polymer chain, a specific content of polymerization units of an aromatic vinyl compound, a specific content of vinyl bonds in the polymerization unit of a specific conjugated diolefin, and a specific GPC molecular weight distribution.
It is also another object of the present invention to provide conjugated diolefin-based copolymer rubber which has excellent processability when containing carbon black or silica, improves both hysteresis-loss characteristics and wet skid resistance at the same time without sacrificing abrasion resistance and failure characteristics or improves hysteresis-loss characteristics, abrasion resistance and failure characteristics in a well balanced manner at the same time without sacrificing wet skid resistance; and which can be used as a tread material for low fuel consumption tires, large-sized tires and high-performance tires.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, the above objects and advantages of the present invention are attained by copolymer rubber of a conjugated diolefin and an aromatic vinyl compound (may be referred to as “the first copolymer rubber of the present invention” hereinafter), wherein
(1) the content of amino groups bound to the copolymer rubber (nitrogen content value) is 0.0025 to 0.20 mmol/g of copolymer rubber,
(2) the content of the polymerization units of the aromatic vinyl compound is 5 wt % or more and less than 30 wt % based on the copolymer rubber,
(3) the content of vinyl bonds in the polymerization unit of the conjugated diolefin (the total content of a 1,2-bond and a 3,4-bond) is 55 mol % or more b
Akema Hiroshi
Hattori Iwakazu
Nagaoka Tamotsu
Tadaki Toshihiro
JSR Corporation
Lipman Bernard
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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