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
1998-05-26
2001-02-20
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, C524S494000
Reexamination Certificate
active
06191205
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to new rubber compositions having a base of precipitated silica intended for the manufacture of road tires of improved resistance to rolling.
Since savings of fuel and the need for protecting the environment have become a priority, it is desirable to produce polymers having good mechanical properties and as low a hysteresis as possible in order to be able to use them in the form of rubber compositions which can be employed for the manufacture of various semi-finished products entering into the creation of tire bodies such as, for instance, underlayers, calendering layers, or sidewalls or treads, and to obtain road tires (cycles, motorcycles, passenger-car tires, heavy-vehicle tires) having improved properties which in particular are of reduced resistance to rolling.
In order to achieve this object, numerous solutions have been proposed consisting, in particular, of modifying, inter alia, the nature of the diene polymers and copolymers towards the end of polymerization by means of coupling or starring or functionalizing agents. All of these solutions have been concentrated essentially on the use of modified polymers with carbon black as reinforcing filler in order to obtain a good interaction between the modified polymer and the carbon black. It is known, in general, that in order to obtain the optimal reinforcement properties conferred by a filler, the latter should be present in the elastomeric matrix in a final form which is both as finely divided as possible and distributed as uniformly as possible. Now, such conditions can be realized only to the extent that, on the one hand, the filler is of very good ability of being incorporated in the matrix upon the mixing with the elastomer and of disintegrating or deagglomerating itself, and of being dispersed uniformly in the elastomer. The use of reinforcing white fillers and particularly of silica has proven inappropriate by reason of the low level of certain properties of such compositions and therefore of certain properties of the tires using these compositions.
Furthermore, for reasons of reciprocal affinity, the silica properties have a harmful tendency, in the elastomeric matrix, of agglomerating with each other. These silica/silica interactions have the harmful result of limiting the reinforcement properties to a level which is substantially below that which would be theoretically possible to obtain if all the silica/elastomer interactions capable of being created during the mixing operation were actually obtained.
Furthermore, the use of silica raises difficulties of processing due to the silica/silica interactions which tend in raw state (before curing) to increase the consistency of the rubber compositions, and in any event to make the processing more difficult than the processing of the carbon black.
The interest in silica reinforced compositions has been recently brought up again with the publication of European Patent Application EP-A-0 501 227 which discloses a sulfur-vulcanizable rubber composition obtained by thermo-mechanical working of a conjugated diene copolymer and an aromatic vinyl compound prepared by solution polymerization with 30 parts to 150 parts by weight for 100 parts by weight of elastomer, of a special precipitated silica. The use of such a silica has, to be sure, reduced the difficulties in processing mixtures containing it, by way of majority or not, as reinforcing filler, but the processing of such rubber compositions nevertheless remains more difficult than the processing of carbon black.
SUMMARY OF THE INVENTION
The object of the present invention is still further to reduce the resistance to rolling of road tires without substantially impairing the other properties.
It has been discovered, surprisingly, that the above problem can be solved by the use as reinforcing filler in diene rubber compositions of a precipitated silica having a relatively high specific surface and special properties of porosity.
The present invention has as its object a sulfur-vulcanizable rubber composition intended for the manufacture of road tires having a base of at least one diene polymer, characterized by the fact that it contains as reinforcing filler a precipitated silica having:
a BET specific surface of between 185 and 250 m
2
/g,
a CTAB specific surface of between 180 and 240 m
2
/g,
a pore distribution such that the pore volume V2 formed by pores, the diameters of which are between 175 and 275 Å, represent less than 50% of the pore volume V1 formed by the pores of diameters less than or equal to 400 Å,
a pore volume (V
d1
) formed by pores of a diameter less than 1 &mgr;m, more than 1.65 cm
3
/g;
a fineness index (F.I.) of between 70 and 100 Å;
a ratio of fines (&tgr;
f
), after ultrasonic deagglomeration, of at least 50%.
The silica has a relatively high specific surface. Its BET specific surface is between 185 and 250 m
2
/g and preferably between 195 and 225 m
2
/g, in particular between 200 and 220 m
2
/g; its CTAB specific surface is between 180 and 240 m
2
/g, and preferably between 185 and 220 m
2
/g, in particular between 190 and 205 m
2
/g.
In general, it has a BET specific surface ratio to CTAB specific surface varying between 1.0 and 1.2, that is to say, a low microporosity.
One of the characteristics of the precipitated silica resides in the distribution of the pore volume and, in particular, in the distribution of the pore volume which is generated by the pores of diameters of less than or equal to 400 Å. The silica has a pore distribution such that the pore volume constituted by pores whose diameter is between 175 and 275 Å represents less than 50%, and in particular at most 48%, and in particular between 25 and 45%, of the pore volume formed by pores of diameters less than or equal to 400 Å. In accordance with a preferred variant, the pore distribution is such that the V
2
/V
1
ratio is between 0.25 and 0.45.
The silica has a pore volume (V
d1
) formed by pores of a diameter less than 1 &mgr;m, more than 1.65 cm
3
/g; this pore volume is preferably at least 1.70 cm
3
/g, and in particular between 1.70 and 1.80 cm
3
/g.
The silica, preferably, has a pore volume (V3) formed by pores the diameter of which is between 100 and 300 Å, which is at least 0.82 cm
3
/g, in particular at least 0.85 cm
3
/g; it is customarily at least 0.86 cm
3
/g.
The silica has in general a total pore volume (TPV) of more than 3.0 cm
3
/g, for instance between 3.1 and 3.4 cm
3
/g and its fineness index (F.I.) is between 70 and 100 Å, and preferably between 80 and 100 Å, for instance between 82 and 98 Å.
The silica used in the composition of the invention thus has special characteristics of porosity which confer upon it an ability to dispersion (dispersibility) which is very satisfactory, that is to say it is a highly dispersible silica. Thus, it has a ratio of fines (&tgr;
f
) or rate of particles of a size of less than 0.3 &mgr;m, after deagglomeration by ultrasonics, of at least 50%, and preferably at least 55%, which rate can, for instance be at least 60%.
In general, its ultrasonic deagglomeration factor (F
D
) is more than 5.5 ml, in particular greater than 9 ml or even 13 ml, and it may have a median diameter (ø
50
) after ultrasonic deagglomeration of less than 8.5 &mgr;m, and in particular between 5 and 7 &mgr;m.
The silica used in the composition of the invention customarily has a pH of between 6.0 and 7.5 and in particular of between 6.3 and 6.9.
Its tapped filling density (DRT) is in general more than 0.26, and particularly 0.28; it is, for instance at least equal to 0.30.
The silica has an oil absorption (DOP) varying generally between 230 and 330 ml/100 g, and preferably between 240 and 300 ml/100 g.
It may be present in the form of powder, granules or, advantageously, in the form of substantially spherical balls.
The silica powders preferably have an average size of at least 15 &mgr;m; it is, for instance, between 15 and 60 &mgr;m (in particular, between 20 and 45 &mgr;m) or between 30 and 1
Chevallier Yvonick
Micouin Jean-Marie
BakerBotts L.L.P.
Cain Edward J.
Compagnie Generale des Establissements Michelin--Michelin & Cie
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