Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-11-05
2001-04-03
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S493000
Reexamination Certificate
active
06211278
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to rubber compositions and, in particular, rubber compositions intended for the manufacture of tire casings and elastic bearings for vehicle suspension systems, and particularly to rubber compositions used in the tread of tire casings for trucks, construction and farm vehicles or airplanes.
The compositions of treads for tire casings are generally made by incorporating a reinforcing filler, such as carbon black, in one or more elastomers. In the case of tire casings which must withstand heavy loads or roll at high speed, there is an intense release of heat and the tire casings are subjected to high temperatures. This temperature rise is accompanied by high rolling resistance and fuel consumption and can be the source of damage to the tire. It is therefore desirable to obtain mixtures which generate less heat under these difficult operating conditions in order to avoid premature ageing of the carcass, which must be capable of retread after tread wear. Obtaining such slightly hysteretic mixtures must not, however, be accompanied by deterioration on wear and traction.
By partially or totally replacing the carbon black with silica in a natural rubber-base composition, it is known to the expert that mixtures less hysteretic than those reinforced with carbon black can be obtained and that the use of a coupling agent between the silica and the elastomer makes it possible to limit the interactions between the silica particles which are the source of hysteresis loss (that is, hysteresis) and to improve the reinforcement, in particular, of wear resistance, as described in EP-A-0,501,227.
As silica-elastomer coupling agents of mixtures vulcanizable with sulfur, which are known to the expert, it is possible to mention the alkoxysilanes reactive at one end with silica (silane part) and at the other end with the carbon-carbon double bonds of the diene elastomer, for example, by means of a polysulfide or mercapto group. Such coupling agents can be premixed with silica and possibly grafted on the silica or added during preparation of the mixture, the coupling agents being combined in situ with the silica. Among the coupling agents of this type most used, Si69 can be mentioned, which is the bis-(3-triethoxysilylpropyl) tetrasulfide marketed by Degussa (
Rubber Chem. Technol.,
1977, Vol. 50, p. 447) or X50S, also marketed by Degussa, which is a 50/50 mixture by weight of Si69 and N330 black.
It is also known to the expert that silanes having an aminoalkyl group are mentioned under the same heading as silanes having methyl or vinyl groups as being not active coupling agents with the diene elastomers (Wagner,
Rubber Chem. and Technol.,
1976, pp. 703 to 794), for there is no predictable reaction between the amino group and the double bonds of the elastomer. However, in some patents disclosing (i) diene elastomer, (ii) silica and (iii) coupling agent base compositions, it is possible to find cited under the same heading as the sulfo, mercapto or poly-sulfide groups active with the elastomers possessing double bonds, the vinyl, amino and epoxy groups, as, for example, in EP 0,738,613 A1 or U.S. Pat. No. 5,225,011, in which the amino or epoxy alkoxysilanes are described as coupling agents for natural rubber-base compositions possessing as filler a carbon black and silica mix under the same heading as a mercaptoalkoyxysilane and a bisalkoxysilane polysulfide, such as Si69, but obviously not used in the examples given. In fact, it is known to the expert that a vinyl or amino or epoxy group cannot be reactive with the double bonds of a diene elastomer.
However, if an aminoalkyltrialkoxysilane is used, even at very low levels in a composition with majority natural rubber base and a majority silica-type filler, the composition cannot be used, for the scorching mixture (vulcanization lag time almost nil) starts reticulating in the course of the mixing and shaping stages; the use of that mixture, which becomes very hard, and notably its extrudability, is rendered almost impossible on the industrial scale.
On the other hand, the use of alkylalkoxysilanes is known, such as, for example, the hexadecyltrimethoxy and triethoxy silanes, Si 116 and Si216 respectively, marketed by DEGUSSA, free of groups reactive with unsaturated elastomers, but reactive by their alkoxy groups with silica-type fillers, that is, possessing Si—OH groups on the surface, which make it possible to reduce viscosity, improve proccessability and activate the vulcanization of compositions containing one or more polysulfide silanes like Si69 (Technical Information, DEGUSSA AG No. 6000.1 of June 1994). Consequently, an alkyltrialkoxysilane-aminoalkyltrialkoxysilane combination is not therefore envisaged by the expert to increase the almost nil lag time due to the use of aminoalkyltrialkoxysilane.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a rubber composition at least partially reinforced with silica, which can be used on an industrial scale without particular difficulty and which presents an hysteresis less than that of the known compositions containing the most widely used coupling agents, such as Si69 and X50S, while imparting, in the case of a tire casing application, notably in the tread, wear resistance and traction characteristics practically as good or even better than those of the known compositions reinforced with silica or carbon black, a reduction of hysteresis and, consequently, a fuel saving and a prolonged carcass lifetime, because the internal temperature of the tire during rolling remains relatively low.
This object has been obtained, surprisingly, by using in the rubber composition both an aminoalkylalkoxysilane and an alkylalkoxysilane free of any group capable of reacting with the elastomer.
The rubber composition according to the invention is characterized in that it contains:
a) at least one diene elastomer having oxygenated functions;
b) a filler consisting, at least in part, of at least one so-called “silica-type” material chosen in the group formed by the silicas and the materials other than silicas possessing on the surface oxygenated functions of silicon;
c) at least one coupling agent chosen in the group formed by aminoalkyalkoxysilanes, aminoarylalkoxysilanes and aminoaralkyalkoxysilanes, the alkyl, aryl or aralkyl groups can optionally, be substituted by functional groups;
d) at least one coating agent chosen in the group formed by alkylalkoxysilanes, arylalkoxysilanes and aralkylalkoxysilanes, alkyl, aryl or aralkyl groups which can, optionally be substituted by functional groups, except amino or sulfo groups.
The invention also concerns articles containing the composition according to the invention, those articles being, for example, semifinished articles, notably treads for tire casings or finished products, notably, elastic bearings for vehicle suspension systems, such as for connecting the shock absorbers, the rods, arms and struts in suspenion systems, the frames, etc. . . . , and tire casings.
The oxygenated functions of the elastomer can, notably, be carbonyl (aldehyde, ketone), carboxyl (acid) or epoxy functions.
The elastomer with oxygenated functions can be a synthetic diene elastomer, the oxygenated functions being introduced in the polymer on synthesis of the latter or by a subsequent treatment performed on the polymer in order to introduce those functions.
Examples of such synthetic diene elastomers with oxygenated functions include the polyisoprenes, polybutadienes, butadiene-isoprene copolymers (BIR), butadiene-styrene copolymers (SBR) or butadiene-isoprene-styrene terpolymers (SBIR), which are modified:
in the course of synthesis by incorporation, in an emulsion process, of a monomer, like, for example, an alkyl acrylate or methyacrylate converted by subsequent acidification into a carboxyl group or else a glycidyl acrylate or methacrylate which supplies a polymer with epoxy functions along the chain;
or at the end of the chain, on finishing synthesis in organic solution, with, for example, an organolith
BakerBotts L.L.P.
Cain Edward J.
Compagnie Generale des Etablissements Michelin--Michelin & Cie
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