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
1995-04-07
2003-02-18
Henderson, Christopher (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...
C525S342000
Reexamination Certificate
active
06521713
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to a vulcanizable rubber composition containing an ethylene-propylene-nonconjugated diene copolymer rubber (EPDM) excellent in thermal resistance, fatigue resistance, and also in dynamic characteristics, low in tan &dgr; value and suitable for applications such as automobile tires and vibration-proof rubber. The present invention also relates to a vulcanized rubber prepared by vulcanizing the above-described rubber composition.
Diene rubbers such as natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR) are known as rubbers excellent in dynamic fatigue resistance and dynamic characteristics, and have been used as raw materials for automobile tires and vibration-proof rubber. However, the environment for the application of these rubber products has been largely changed recently to require improvements in thermal resistance and weather resistance of rubber products.
In automobile tires, tread and tire side walls especially require weather resistance. However, no rubber has been available which maintains the excellent fatigue resistance and dynamic characteristics of the existing diene rubber as well as having good weather resistance.
Thus various blended rubber compositions of diene rubber (which is excellent in dynamic fatigue resistance and dynamic characteristics) with EPT ((EPDM) which is excellent in thermal resistance and weather resistance) have been investigated. However, since the level of the dynamic characteristics of EPT is different from that of diene rubber, no blended rubber composition showing uniform properties could be prepared so far.
The dynamic characteristics of automobile tires are evaluated on the basis of whether the material increases fuel cost or not and its index tan &dgr; (loss tangent) value. The lower the tan&dgr; value, the better are the dynamic characteristics.
On the other hand, in the vibration-proof rubber products for automobiles, the existing vibration-proof rubber products based on natural rubber (which is a diene rubber) cannot provide sufficient fatigue resistance capable of withstanding practical use with the range of temperature increases in the engine compartment.
Therefore, there is a strong desire for a new rubber material having excellent thermal resistance, as well as dynamic characteristics and fatigue resistance, equal to or higher than those of diene rubber. Generally, in order to improve fatigue resistance, the rubber material is required to have a force relaxing mechanism. For this purpose, it is required to have the crosslinked form of the polysulfur bond in the rubber rather than a monosulfur bond. A proper crosslinking density is also required.
On the other hand, it is required to increase crosslinking density in order to improve dynamic characteristics. However, attempts to bring the dynamic characteristics of EPT in conformity with those of a diene rubber such as NR has resulted in too high a crosslinking density with the resultant deterioration of fatigue resistance; it was impossible to make dynamic characteristics compatible with fatigue resistance.
The dynamic characteristics in the vibration-proof rubber are evaluated on the basis of whether it has a low dynamic magnification. Since the dynamic magnification is approximately proportional to the tan &dgr; value, tan &dgr; can be used as its index.
The present invention discloses that the dynamic characteristics and the fatigue resistance, which are in opposite relation with respect to each other, can be unexpectedly improved at the same time by using (1) an ethylene-propylene-nonconjugated diene copolymer rubber (which is excellent in thermal resistance), (2) a specific alkoxysilane compound, and (3) a specific amorphous silica powder, to enhance the interaction between the amorphous silica powder and the polymer, that is, the ethylene-propylene-nonconjugated diene copolymer rubber through the alkoxysilane compound.
SUMMARY OF THE INVENTION
One object of the present invention is to solve the above-mentioned problems accompanying the conventional technology and to provide a rubber composition which has fatigue resistance and dynamic characteristics equal to those of a diene rubber (such as natural rubber) and which is also excellent in thermal resistance and weather resistance.
Another object of the present invention is to provide a vulcanized rubber comprising the above-mentioned rubber composition.
The vulcanizable rubber composition according to the present invention is characterized in that it contains an ethylene-propylene-nonconjugated diene copolymer rubber (EPDM), a crosslinking system as commonly used as well as at least one of the alkoxysilane compounds expressed by the following general formula (I) or (II), and silica and/or silicate powder having a specific surface area of 50 to 100 m
2
/g (BET adsorption: ISO 5794/1, Annex D).
The alkoxysilane has the general formula I:
where R is an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms; R
1
is an alkyl group having 1 to 4 carbon atoms or phenyl groups; n is 0, 1 or 2; R
2
is a divalent straight-chained or branched hydrocarbon radical (alkylene) having 1 to 6 carbon atoms; R
3
is an arylene group having 6 to 12 carbon atoms; m and p are respectively 0 or 1 but not 0 at the same time; q is 1 or 2; and B is —SCN or —SH when q is 1 and —Sx—(where x is an integer of 2 to 8) when q is 2.
Alternatively, the alkoxysilane has the general formula
where R is an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms; R
1
is an alkyl group having 1 to 4 carbon atoms or phenyl group; n is 0, 1 or 2; and R
4
is a monovalent straight-chained or branched unsaturated hydrocarbon radical having 2 to 20 carbon atoms.
In the rubber composition according to the present invention, an ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber having a Mooney viscosity (MS
1+4
, 160° C.) of 40 to 80 is preferred as the above-mentioned ethylene-propylene-nonconjugated diene copolymer rubber.
The vulcanized rubber according to the present invention is characterized in that it is prepared by vulcanizing the rubber composition described above.
The rubber composition according to the present invention, and the vulcanized rubber prepared from the rubber composition, unexpectedly have fatigue resistances and dynamic characteristics equal to those of diene rubber (such as NR) and also are excellent in thermal resistances and weather resistances.
DETAILED DESCRIPTION OF THE INVENTION
The rubber composition according to the present invention, and the vulcanized rubber prepared from the rubber composition, will be illustrated as follows:
First, the rubber composition according to the present invention will be described. The rubber composition according to the present invention contains (1) an ethylene-propylene-nonconjugated diene copolymer rubber, (2) a specific alkoxysilane compound, and (3) a specific amorphous silica and/or silicate powder.
Ethylene-Propylene-Nonconjugated Diene Copolymer Rubber
The ethylene-propylene-nonconjugated diene copolymer rubber used in the present invention contains usually 50 to 83 mol % (preferably 50 to 73 mol %) of ethylene and usually 50 to 17 mol % (preferably 50 to 27 mol %) of propylene.
The above-mentioned nonconjugated dienes include, for example, (a) chain nonconjugated dienes such as 1,4-hexadiene; 1,6-octadiene; 2-methyl-1,5-hexadiene; 6-methyl-1,5-heptadiene; and 7-methyl-1,6-octadiene; (b) cyclic nonconjugated dienes such as cyclohexadiene; dicyclopentadiene; methyltetrahydroindene; 5-vinylnorbornene; 5-ethylidene-2-norbornene; 5-methylene-2-norbornene; 5-isopropylidene-2-norbornene; and 6-chlormethyl-5-isopropenyl-2-norbornene; and (c) trienes such as 2,3-diisopropylidene-5-norbornene; 2-ethylidene-3-isopropylidene-5-norbornene; 2-propenyl-2,2-norbornadiene; 1,3,7-octatriene; and 1,4,9-decatriene. Among them, preferably used are 1,4-hexadiene and cyclic nonconjugated dienes, particularly 5-ethylidene-2-norbornene. When 5-ethylidene-2-nor
Haddeman Marinus
Nakahama Hidenari
Panenka Rainer
Wolff Siegfried
Degussa - AG
Henderson Christopher
Smith , Gambrell & Russell, LLP
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