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
2000-01-10
2001-11-06
Lipman, Bernard (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...
C524S437000, C524S506000, C524S526000, C524S573000, C524S575000
Reexamination Certificate
active
06313205
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sulfur-vulcanizablerubber compositions intended for the manufacture of tires or semi-finished products for tires, in particular, treads of such tires.
It relates more particularly to novel diene rubber compositions reinforced with a white filler and comprising a coupling agent (white filler/elastomer)based on a multifunctionalized polyorganosiloxane(“POS”) bearing both alkoxy and mercapto-alkyl (or alkyl-thiol) functions.
(Multi)functionalizedPOS are widely known and have been described in references, in particular, patent application WO 96/16125, which describes the multifunctionalisation of POS. WO96/16125 discloses the preparation of POS comprising, in particular, ≡Si—(O-alkyl) and ≡Si— (chain with various sulfur-containing groups, in particular SH) functional units. The —(O-alkyl) function is introduced onto an appropriate polyhydrogeno-organosiloxane by a dehydrogeno-condensation reaction starting with the alcohol from which the —(O-alkyl) function is derived (in this stage a fraction of the original ≡SiH groups are substituted by alkoxy functions). Then the—(chain with various sulfurized groups) function is introduced by hydrosilylation of an olefin bearing the sulfur-containing group, by the remaining ≡SiH groups.
Since fuel economy and the need to protect the environment have become priorities, it is desirable to produce elastomers with good mechanical properties and as low a hysteresis as possible so that they can be used in the form of rubber compositions suitable for the manufacture of various semi-finished products involved in the constitution of tires, such as, for example, underlayers, calendering rubbers or sidewalls or treads, and to obtain tires with improved properties, in particular, reduced rolling resistance.
Numerous solutions have been proposed to achieve this objective, in particular, those concentrating on the use of elastomers modified by agents such as coupling, starring or functionalizing agents, with carbon black as the reinforcing filler, with the aim of obtaining a good interaction between the modified elastomer and the carbon black. It is, in fact, generally known that to obtain the optimum reinforcement properties imparted by a filler, the latter should be present in the elastomer matrix in a final form, which is both as finely divided as possible and distributed as homogeneously as possible. Now, such conditions can only be realized to the extent that on the one hand, the filler has very good ability to be incorporated into the matrix during mixing with the elastomer and to become disagglomerated and, on the other hand, to be dispersed homogeneously in the elastomer.
It is well known that carbon black has such abilities, which is generally not true of white fillers. For reasons of mutual attraction, white filler particles, especially silica particles, have an irritating tendency to agglomerate together within the elastomer matrix. These interactions have the harmful consequence of limiting the dispersion of the filler and decreasing its reinforcing properties to a far lower level than that which it would be theoretically possible to achieve if all the (white filler/elastomer) bonds that could be created during the mixing operation were in fact obtained. Furthermore, these interactions tend to increase the consistency of the rubber compositions and therefore to make them more difficult to work in the raw state than in the presence of carbon black.
However, interest in compositions reinforced with white filler(s) was greatly revived by the publication of European Patent Application EP-A-O 501 227, which discloses a sulfur-vulcanizable diene rubber composition, reinforced with a special precipitated silica of the highly dispersible type, which makes it possible to make a tire or tread with much better rolling resistance, without affecting the other properties, in particular those of adhesion, endurance and wear resistance.
The recently published European Patent Application EP-A-0 810 258 discloses a novel diene rubber composition reinforced by another special white filler, in this case a specific, highly dispersible alumina (Al
2
O
3
) with which tires or treads with a similar excellent balance of contradictory properties can also be produced.
The use of these specific and highly dispersible silicas or aluminas as reinforcing fillers, whether or not as the major component, has reduced the difficulty of working the compositions that contain them, but they are still more difficult to work than compositions filled conventionally with carbon black.
In particular, it is necessary to use a coupling agent, also known as a bonding agent, whose purpose is to ensure the connection between the surfaces of the white filler particles and the elastomer, while also facilitating the dispersion of the white filler within the elastomer matrix.
The term “coupling agent” (white filler/elastomer) is understood by the person skilled in the art to mean an agent capable of establishing a sufficient chemical and/or physical connection between the white filler and the elastomer. Such a coupling agent, which is at least bifunctional, may for example have the simplified general formula “Y—T—X”, in which:
Y represents a functional unit (“Y” function) capable of bonding physically and/or chemically to the white filler, such a bond being established for example between a silicon atom of the coupling agent and the hydroxyl (OH) groups on the surface of the white filler (for example the surface silanols in the case of silica);
X represents a functional unit (“X” function) capable of bonding physically and/or chemically to the elastomer, for example via a sulfur atom;
T represents a hydrocarbon group that connects Y and X.
Coupling agents are not to be confused with covering agents that simply cover the white filler, in particular silica, which in known manner comprise the Y function which is active towards the white filler, but do not have the X function which is active towards the elastomer.
Silica/elastomer coupling agents, in particular, have been described in numerous documents, the best known being bifunctional organosilanes.
Thus, in patent application FR-A-2 094 859 it was proposed to use a mercaptosilane for the manufacture of tire treads. It was soon discovered, and is today well known, that the mercaptosilanes, in particular &ggr;-mercaptopropyltrimethoxysilane and &ggr;-mercaptopropyltriethoxysilane, are capable of giving better silica/elastomer coupling properties. However, those coupling agents cannot be used industrially because the high reactivity of their —SH functions very rapidly leads to premature vulcanization during the preparation of the composition in an internal mixer, also known as “scorching”, which results in very high Mooney plasticity values and, at the end, compositions which are virtually impossible to work and utilize industrially. FR-A-2 2-6 330 and U.S. Pat. No. 4,002,594 illustrate this result from using such coupling agents bearing —SH functions and the compositions that contain them industrially.
The replacement of these mercaptosilanes by poly-sulfurized organosilanes has been proposed to overcome these drawbacks (see for example FR-A-2 206 330). Among these compounds, the tetrasulphide of bis-3-triethoxysilylpropyl (“TESPT”) is particularly regarded as the product which, for vulcanized rubber compositions filled with silica, provides the best balance in terms of resistance to scorching, ease of working and reinforcing power.
This coupling agent, however, is very costly and has to be used in large amounts, in the order of 2 to 3 times as much as the quantity of &ggr;-mercaptopropyltrimethoxysilane needed to obtain equivalent coupling results.
It was therefore desirable, particularly to reduce the overall cost of the formulations, to be able to industrially prepare rubber compositions reinforced with silica, or more generally with a reinforcing white filler, which contain coupling agents in smaller amounts than those used in the case of the polysulftirized organo
Chiron Frédéric
Laforet Claude
Mangeret Jean-Luc
BakerBotts L.L.P.
Compagnie Generale des Etablissements Michelin--Michelin & Cie
Lipman Bernard
LandOfFree
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