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
2000-02-10
2002-09-24
Wu, David W. (Department: 1713)
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, C152S209160, C152S548000
Reexamination Certificate
active
06455624
ABSTRACT:
BACKGROUND OF THE INVENTION
SPECIFICATION
The present invention relates to the use of rubber compositions intended for the manufacture of tires as elastomeric internal filling compositions, also referred to as “cushion mixes”, in the zones of the shoulder and the crown of a tire.
Radial-carcass tires for motor vehicles bearing heavy loads at greater or lesser speeds, in particular those for heavy vehicles, have a framework formed of reinforcements or plies of metal wires coated with elastomers. Such tires comprise, in the bottom zone, one or more bead wires and carcass reinforcement extending from one bead wire to the other and, at the crown, a crown reinforcement comprising two or more crown plies. This framework is consolidated by elastomeric compositions. Radial-carcass tires, intended to be fitted on vehicles bearing heavy loads at greater or lesser speeds, in particular those for heavy vehicles, are designed to be able to be recapped several times when the tread that is in contact with the ground is worn. This involves having available recappable carcasses which have not been subject to serious damage after wear of one or more treads.
The life of the tire can be shortened due to the appearance of damage within a rubber profiled filling member, for example a break, which may then spread as far as the inner or outer surface of the tire, with the result that the tire cover must be discarded and replaced. Examples of damage are, at the level of the shoulder of the tire, a break in the rubber profiled member of triangular shape, separating the carcass ply reinforcement from the radially inner crown ply, said break resulting from an imposed deformation stress, such as an impact against a curb or an impact against the edge of a roundabout located at a cross roads, because some roundabouts are too cramped for a highway unit With trailer to be able to pass without mounting an edge, the profile of which is frequently harsh.
It is desirable for the cohesion of the rubber internal filler mixes to be as great as possible to avoid or reduce these incipient points for damage.
It is known to the person skilled in the art that elastomeric internal filler compositions undergo deformation upon each rotation of the wheel. Such deformation causes a great amount of heating which is harmful to the life of said compositions because, at operating temperatures which are frequently above 100° C., the mechanical properties and the reinforcement degrade over time by thermochemical and/or thermo-oxidizing aging, with the consequence that the compositions become less resistant to mechanical stress.
In order to eliminate or at the very least minimize as far as possible the risks of breaking of the elastomeric internal filler mixes, i.e., those devoid of reinforcements, it is desirable for these mixes to have high mechanical cohesion as well as hysteresis loss characteristics which are as low as possible at the operating temperature of the tire.
The person skilled in the art, confronted with the problem of balancing minimal heating and high cohesion at high temperature, has proposed a large number of solutions. Thus, it has been proposed to use elastomeric internal filler compositions, i.e., cushion mixes, of relatively low hysteresis, in the form of:
(i) compositions based on natural rubber, pure or in a blend with polybutadiene, the reinforcing filler being a carbon black having a specific surface area preferably less than 110 m
2
/g and used in an amount of 30 to 35 phr (parts by weight per hundred parts of elastomer);
(ii) compositions based on natural rubber, pure or in a blend with polybutadiene, reinforced with a blend of carbon black and silica, the usual amounts of carbon black being from 30 to 35 phr and those of the silica from 10 to 15 phr;
(iii) compositions based on diene rubber and syndiotactic 1,2-polybutadiene as described in Patent Application JP-A-94/092108;
(iv) compositions based on natural rubber, possibly in a blend with another diene elastomer, comprising carbon black and thermoplastic polymer fibers as described in Patent Application JP-A-95/330960.
SUMMARY OF THE INVENTION
The Applicant has discovered that it is possible to obtain a balance between heating and improved cohesion and excellent resistance to the mechanical stresses with high deformation by the use of an elastomeric internal filler composition:
(i) based on natural rubber or synthetic polyisoprene having a majority of cis-1,4 bonds, used pure or in a blend with another diene elastomer,
(ii) reinforced with:
either a carbon black filler used in an amount between 15 phr and 28 phr, and preferably between 20 phr and 25 phr,
or a clear filler selected from among precipitated or pyrogenic silicas comprising SiOH functions at the surface, precipitated aluminas comprising AlOH functions at the surface, a natural or precipitated silicoaluminate comprising at the surface both SiOH and AlOH groups, said clear filler being used in an amount from 15 phr to 40 phr and preferably from 20 phr to 35 phr,
or with a blend of carbon black and clear filler as described above, such that the total amount of filler is between about 15 phr and 50 phr, and that the amount of clear filler in phr is greater than or equal to that of the carbon black in phr minus 5phr.
DETAILED DESCRIPTION
In the case of using clear filler, it is necessary to use a coupling and/or covering agent selected from among the agents known to the person skilled in the art. Preferred coupling agents include, inter alia, sulphur-containing alkoxysilanes of the bis-(3-trialkoxysilylpropyl) polysulphide type, and among these in particular, bis-(3-triethoxysilylpropyl) tetrasulphide sold by DEGUSSA under the names Si69 for the pure liquid product and X50S for the solid product (blend 50/50 by weight with black N330). Covering agents include a fatty alcohol, an alkylalkoxysilane, such as a hexadecyltrimethoxy- or triethoxysilane sold by DEGUSSA under the names Si116 and Si216 respectively, diphenylguanidine, a polyethylene glycol, or a silicone oil possibly modified by means of OH or alkoxy functions. The covering and/or coupling agent is used in a ratio by weight relative to the filler of between 1/100 and 20/100, and preferably of between 2/100 and 15/100, when the clear filler represents the entire reinforcing filler, and between about 1/100 and 20/100 when the reinforcing filler comprises a blend of carbon black and clear filler.
The elastomeric internal filler compositions or cushion mixes according to the invention are, for example, triangular profiled members separating the carcass reinforcement from the radially inner crown ply, the profiled members located between crown reinforcement plies over their entire width and/or the profiled members separating the ends of the crown plies forming the crown reinforcement.
The diene elastomers which may be used in a blend with natural rubber or a synthetic polyisoprene having a majority of cis-1,4 bonds include a polybutadiene (BR), preferably having a majority of cis-1,4 bonds, a solution or emulsion styrene-butadiene copolymer (SBR), a butadiene-isoprene copolymer (BIR) or, alternatively, a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers may be modified during polymerization or after polymerization by means of branching agents, such as divinylbenzene, or starring agents, such as carbonates, tin halides or silicon halides. Alternatively, the elastromers may be modified by means of functionalizing agents resulting in grafting of oxygenated carbonyl or carboxyl functions or, alternatively, an amine function, such as, for example, by the action of dimethyl- or diethylamino-benzophenone on the chain or at the ends of the chain. In the case of blends of natural rubber or of synthetic polyisoprene having a majority of cis-1,4 bonds with one or more of the diene elastomers referred to above, the natural rubber or the synthetic polyisoprene preferably comprises the majority of the blend, and, more preferably, comprises an amount greater than 70 phr.
When carbon black is used as the sole reinforcing filler, the required
Baker & Botts LLP
Harlan R.
Michelin & Recherche et Technique S.A.
Wu David W.
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