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
2001-01-05
2003-01-14
Boykin, Terressa 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...
C156S096000, C525S063000
Reexamination Certificate
active
06506849
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a rubber composition and a pneumatic tire, and more particularly to a technique for obtaining a rubber composition having a good workability and a high modulus of elasticity as well as a pneumatic tire.
Prior Art
Recently, it is demanded to develop the steering stability and gripping property higher than the conventional one even in tire performances as power and running speed of automobiles become higher.
In rubber industry, bismaleimide is practically examined as a cross-linking agent. In JP-A-63-99251 is reported that the heat resistance and the high maneuverability are simultaneously established by compounding a bismaleimide compound with a styrene-butadiene copolymer rubber (SBR). And also, the effect of lowering heat build-up through hydrazide as reported in JP-A-10-139934.
Among various road surface conditions, a wet road surface on a rainy day is slippery, so that the running of automobiles is risky. And also, there is recently a tendency to take a regulation to a braking distance and hence wet-skid performances become increasingly important.
As a conventional technique for improving wet-skid performances, there are a method of shifting Tg of a polymer to a higher temperature side to increase tan &dgr; (0° C.), a method of compounding silica to improve wet performances, and so on.
However, in the former method of increasing tan &dgr;, it is difficult to simultaneously establish other performances such as dry-skid performances, low rolling resistance and the like. And also, in the latter method of compounding silica, there are disadvantages that a lock &mgr;, at wet state (frictional coefficient when a tire is fully locked and slipping 100%) is not improved, and the like.
On the other hand, the applicant has discovered that the wet-skid performances can be improved by using N,N′-(1,3-phenylene)bismaleimide and silica together. However, it has been confirmed that when compounding N,N′-(1,3-phenylene)bismaleimide, tan &dgr; at 60° C. is not sufficiently lowered, and the rolling resistance becomes slightly high when being used in a tire tread.
Problems to be solved by the Invention
Recently, the inventors have discovered that when bismaleimide is compounded with rubber containing not less than 50% by weight of SBR together with silica, not only a heat resistance is improved but also a dynamic storage modulus (E′) becomes higher and the steering stability is improved when such a rubber composition using bismaleimide is used in a tread.
However, when a greater amount of bismaleimide is compounded with SBR-containing rubber as mentioned above, vulcanization reaction is obstructed by bismaleimide and hence a long time is taken in the vulcanization and also a blow point (easiness of bubble generation in rubber) at the same vulcanizing degree becomes higher, so that it is necessary to take further longer vulcanization time in order to conduct the vulcanization without leaving bubbles in a rubber article, and the productivity largely lowers and becomes impracticable.
As regards this problem, it can naturally be considered to use an accelerator quickening the start-up of the vulcanization or so-called ultra-accelerator such as guanidines, dithiocarbamates and xanthates. However, these compounds can quicken the start-up of vulcanization to shorten a burning time (scorch time) of an uncured rubber, but fail to largely improve the blow point.
Therefore, the inventors have investigated a cause of obstructing the vulcanization reaction through bismaleimide and confirmed that a reaction between a vulcanization accelerator and a bismaleimide occurs earlier than the vulcanization reaction particularly in SBR compounded system and hence the vulcanization is obstructed are used. This is particularly more remarkable when thiazole-based and thiuram-based vulcanization accelerators are used. Further, it has been confirmed that a part of bismaleimide is decomposed and gasified due to the reaction between a bismaleimide and a vulcanization accelerator and hence an amount of gas larger than in a usual case is generated in rubber to degrade the blow point.
It is, therefore, an object of the invention to solve the above problems and to provide a technique capable of further improving a merit of bismaleimide for the increase in elasticity and avoiding a demerit of productivity due to the delay in vulcanization and to provide a rubber composition capable of providing a pneumatic tire with a remarkable non-slip effect, excellent wet-skid performances and a low rolling resistance on a wet road surface having an extremely low frictional coefficient.
Means for solving the Problems
In order to achieve the above object, the invention is constituted as follows.
The rubber composition according to the invention is characterized by comprising at least one rubber of natural rubber and synthetic diene rubbers as a rubber ingredient, at least one maleimide compound, and at least one nitrogen-containing compound selected from the group consisting of polyanilines, hydrazides and amine compounds. And also, the rubber composition is characterized by comprising at least one rubber of natural rubber and synthetic diene rubbers and at least one maleimide compound selected from the group consisting of bismaleimide, oligomers and polymers of bismaleimide.
Further, the pneumatic tire according to the invention uses the above rubber composition in its tread.
Embodiments of the Invention
The invention will be described in detail below.
In the invention can be used natural rubber and synthetic diene rubbers. As the synthetic diene rubber, mention may be made of cis-1,4-polyisoprene, styrene-butadiene copolymer, polybutadiene, low cis-1,4-polybutadiene, high cis-1,4-polybutadiene, ethylene-propylene-diene terpolymer, chloroprene, halogenated butyl rubber, acrylonitrile-butadiene rubber and so on. The natural rubber and synthetic diene rubbers may be used alone or in a blend thereof.
The natural rubber and at least one of cis-1,4-polyisoprene, styrene-butadiene copolymer and polybutadiene as the diene rubber are preferable because the improving effect by the combination with bismaleimide and hydrazide aiming at the invention is made clear.
And also, it is preferable that the remarkable effect is obtained when at least one of butadiene rubber (BR) and styrene-butadiene copolymer rubber (SBR) is included in the rubber ingredient in an amount of not less than 50% by weight. More preferably, the amount is not less than 80% by weight.
Heretofore, a maleimide compound is applied to a rubber composition containing, for example, natural rubber or isoprene rubber in an amount of not less than 50% by weight of the rubber ingredient. In this case, however, the tensile stress of full region becomes too high due to the compounding of maleimide and the object of the invention can not sufficiently be attained. And also, when butyl rubber is included in an amount of not less than 50% by weight, the increase of tensile stress in a desired region becomes small even in the compounding of the maleimide, so that the object of the invention can not be attained sufficiently likewise the above case.
Comparing BR and SBR with each other, SBR is preferable from a viewpoint of the establishment with dry gripping performance, and further the use of an emulsion polymerized SBR is preferable in view of wear resistance.
As the maleimide compounds used in the invention, a bismaleimide compound represented by the formula [7], or an oligomer or polymer of bismaleimide is preferable.
Moreover, when R
9
or R
20
in the general formula [7] of the bismaleimide compound is an alkylene group, if the carbon number is not less than 4, the molecular weight of the bismaleimide compound becomes large, so that the increasing effect of dynamic storage modulus aimed at the invention is not obtained at the compounding amount thereof.
As the bismaleimide compounds preferably usable in the invention, mention may be made of N,N′-(1,2-phenylene) bismaleimide, N,N′-(1,3-
Ajiro Yukitoshi
Baba Shunji
Fujino Kentaro
Hojo Masahiro
Boykin Terressa M.
Sughrue & Mion, PLLC
LandOfFree
Rubber composition and pneumatic tire does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rubber composition and pneumatic tire, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rubber composition and pneumatic tire will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3017600