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...
Utility Patent
1998-07-07
2001-01-02
Hoke, Veronica P. (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...
Utility Patent
active
06169137
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a radial carcass tire having a crown reinforcement of small hysteresis loss, with improved rolling resistance.
Since savings in fuel and the need to protect the environment have become a priority, it is desirable to employ rubber compositions which can be used for the manufacture of various semifinished products entering into the construction of tires, such as, for instance, cushion and calendering rubbers for cord fabric plies or treads in order to obtain tires having reduced resistance to rolling.
It is known to the person skilled in the art that the first and main factor affecting the resistance to rolling of a radial carcass tire resides in the rubber composition forming the tread of the tire.
Significant progress has been achieved in the field of tires having at the same time reduced resistance to rolling, excellent adherence both on dry and on snowy ground, very good resistance to wear, and reduced rolling noise, by the use, as tire tread, of a rubber composition, described in European Patent Application EP 0 501 227, which is vulcanizable by sulfur, obtained by the thermo-mechanical working of a conjugated diene polymer and an aromatic vinyl compound prepared by solution polymerization with 30 to 150 parts by weight of a highly dispersible precipitated silica to 100 parts by weight of elastomer.
It is also known to the person skilled in the art that the second factor which exerts a dominant influence with respect to the rolling resistance of a radial carcass tire is the crown reinforcement.
The crown reinforcement is generally formed of two plies of cord fabric having non-stretchable cords parallel to each other in one ply and crossed from one ply to the next, forming equal or different angles of between 10° and 45 ° with the circumferential direction. The cords are either metal cables, in particular of steel, or synthetic textile cords, in particular of aramids. These plies which are inclined with respect to the circumferential direction are referred to as “working” plies.
Particularly in the case of tires intended for high speed passenger vehicles the crown reinforcement can have, in addition to the working plies, one or more cord fabric plies, strips of cord fabric or of helically wound thread, the component cords or threads of which are substantially not inclined with respect to the circumferential direction, that is to say, they form an angle of zero degrees or close to zero degrees and are known as “zero-degree plies”. The cord is generally a cord of synthetic textile, in particular a polyamide.
The calendering rubber used for the working plies is generally formed exclusively of natural rubber or by a blend of natural rubber and a diene synthetic rubber or a mixture of diene synthetic rubbers, natural rubber being present, however, in a preponderant amount by weight. This calendering rubber is ordinarily reinforced by carbon black as a major filler. However, it is known to the person skilled in the art, for instance from French patent application FR 80 22131 and U.S. Pat. No. 4,229,640, to use silica in a small amount, on the order of 10 to 15 parts by weight, in order to increase the adherence of the rubber to the metal cable and in particular to a brass-plated metal cable. However, the silica is used in combination with a reinforcing resin, generally one having a base of resorcinol, in order to increase the modulus of the calendering rubber, it being well-known to the person skilled in the art that the use of silica in tires as reinforcing filler has been retarded for a long time due, inter alia, to the lower modulus of elasticity of silica-filled rubber mixes.
The use of silica in tires also been extensively retarded due to difficulties in working resulting from silica-silica interactions which tend, in raw state, to cause an agglomerating of the silica particles before and even after mixing, making the working more difficult than with carbon black and leading to hard raw rubbers as soon as the percentage of silica used in the composition is relatively high. Due to their hardness, such rubbers are unsuitable as calendering rubbers for cord fabric and furthermore give rise to major problems of coherence in cured state. The use of such rubbers leads to a premature separation of the cords from the rubber, in particular at the ends of the working plies.
U.S. Pat. No. 5,066,721 describes a rubber composition having a base of a diene polymer functionalized by means of a special silane compound having a non-hydrolyzable aryloxy group capable of being used as calendering rubber for the cord fabric, in particular of crown reinforcement working plies and capable of containing up to 20 parts by weight of a conventional silica, that is to say a silica which has a high CTAB specific surface area of more than 100 m
2
/g and is only slightly dispersible. The improvement in the rolling resistance of the tire is essentially due to the nature of the functionalized diene polymer, which makes it possible to increase in a very small proportion the silica content of the calendering rubber, but also, at the same time, to increase the problem of internal coherence of the rubber and the risk of premature separation of the cord fabric from the rubber.
SUMMARY OF THE INVENTION
The object of the present invention is essentially to decrease the rolling resistance of a radial carcass tire without significantly impairing the other properties of the tire, such as adherence, resistance to wear, and resistance to fatigue, particularly of the crown reinforcement, and without resulting in a significant impairment with respect to the manufacture of the tire, particularly in the field of the raw working and cohesion in cured state of the rubber composition used for the production of the crown reinforcement of said tire.
The applicant has discovered that the purpose in view is achieved in accordance with the invention by the use of a silica having a low CTAB and BET specific surface area as reinforcing filler for diene elastomer compositions which can be used as crown reinforcement rubber of a radial carcass tire.
The object of the invention is a radial carcass tire having a tread, two non-stretchable beads, two sidewalls connecting the beads to the tread, and a crown reinforcement located between the carcass and the tread having at least two cord fabric plies, said crown reinforcement comprising a diene elastomeric rubber containing, as reinforcing filler, a silica mentioned above which has a CTAB specific surface area less than or equal to 125 m
2
/g and a BET specific surface area less than or equal to 125 m
2
/g.
Another object of the invention is a diene elastomeric composition which can be used in the forming of a crown reinforcement of a radial carcass tire containing as reinforcing filler a silica having a CTAB specific surface area less than or equal to 125 m
2
/g and a BET specific surface area less than or equal to 125 m
2
/g.
The silica which can be used as reinforcing agent of the diene elastomeric rubber used in the overhead reinforcement is preferably a highly dispersible silica having a CTAB specific surface area of between 50 and 120 m
2
/g. When the specific surface area is less than 50 m
2
/g, the reinforcement is less and the cohesion reduced. When the CTAB specific surface area is more than 125 m
2
/g, rubber mixes of increased hardness are obtained which is detrimental for forming crown reinforcement calendering rubbers.
By highly dispersible silica there is understood any silica having the capability of disagglomeration and dispersion in a very large polymeric matrix, as can be observed by electronic or optical microscopy on fine sections. The dipersibility of the silica is also evaluated by means of an ultrasonic disagglomeration aptitude test (Fd) followed by a measurement, by diffraction on a granulometer, of the size of the silica particles in order to determine the median diameter (D50) of the particles after disagglomeration as described in European Patent Application EP 0 520 862, the content of which is inco
BakerBotts L.L.P.
Compagnie Generale des Etablissements Michelin & Cie
Hoke Veronica P.
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