Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2003-04-10
2004-08-10
Roberston, Jeffrey B. (Department: 1712)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S466000, C528S030000
Reexamination Certificate
active
06774255
ABSTRACT:
FIELD OF INVENTION
The present invention relates to polyfunctional coupling agents usable in particular for coupling reinforcing inorganic fillers and diene elastomers in rubber compositions intended, for example, for the manufacture of tires.
BACKGROUND OF THE INVENTION
It is generally known that in order to obtain the optimum reinforcement properties imparted 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 homogeneously as possible. Now, such conditions may only be obtained insofar as the filler has a very good ability firstly to be incorporated into the matrix during mixing with the elastomer and to disagglomerate, and secondly to be dispersed homogeneously in this matrix.
It is fully known that carbon black has such abilities, which is generally not true of inorganic fillers. For reasons of mutual attraction, the inorganic filler particles have an irritating tendency to agglomerate together within the elastomeric matrix. These interactions have the harmful consequence of limiting the dispersion of the filler and hence the reinforcing properties to a substantially lower level than that which it would be theoretically possible to achieve if all the (inorganic filler/elastomer) bonds that could be created during the mixing operation were in fact obtained; these interactions furthermore tend to increase the consistency of the rubber compositions in the uncured state and therefore to make them more difficult to work (“processability”) than in the presence of carbon black.
Since fuel economies and the need to protect the environment have become priorities, it has however, proved necessary to produce tires having reduced rolling resistance, without adversely affecting their wear resistance. This has been made possible in particular due to the discovery of new rubber compositions reinforced with specific inorganic fillers referred to as “reinforcing” fillers, which are capable of rivalling conventional tire-grade carbon black from the reinforcing point of view, and furthermore offering these compositions lower hysteresis, which is synonymous with lower rolling resistance for the tires comprising them.
Such rubber compositions, comprising reinforcing inorganic fillers of the siliceous or aluminous type, have for example been described in patents or patent applications EP-A-0501227 (or U.S. Pat. No. 5,227,425), EP-A-0735088 (or U.S. Pat. No. 5,852,099), EP-A-0810258 (or U.S. Pat. No. 5,900,449), EP-A-0881252, WO99/02590, WO99/02601, WO99/02602, WO99/28376, WO00/05300 and WO00/05301.
Mention will be made in particular of documents EP-A-0501227, EP-A-0735088 or EP-A-0881252, which disclose diene rubber compositions reinforced with precipitated silicas of high dispersibility, such compositions making it possible to manufacture treads having a significantly improved rolling resistance, without adversely affecting the other properties, in particular those of grip, endurance and wear resistance. Such compositions having such a compromise of contradictory properties are also described in applications EP-A-0810258 and WO99/28376, with specific aluminous fillers (aluminas or aluminium (oxide-)hydroxides) of high dispersibility as reinforcing inorganic fillers, or alternatively in applications WO00/73372 and WO00/73373, which describe specific titanium oxides of thc reinforcing type.
Although the use of these specific, highly dispersible inorganic fillers as reinforcing fillers, whether or not as the majority component, has reduced the difficulties of processing the rubber compositions containing them, such compositions are still more difficult to process than are rubber compositions filled conventionally with carbon black.
In particular, it is necessary to use a coupling agent, also known as a bonding agent, the function of which is to provide the connection between the surface of the inorganic filler particles and the elastomer, while facilitating the dispersion of this inorganic filler within the elastomeric matrix.
It will be recalled that (inorganic filler/elastomer) “coupling agent” should, in known manner, be taken to mean an agent capable of establishing a sufficient chemical and/or physical connection between the inorganic filler and the diene elastomer; such a coupling agent, which is at least bifunctional, has, for example, the simplified general formula “Y—W—X”, in which:
Y represents a functional group (“Y” function) which is capable of bonding physically and/or chemically with the inorganic filler, it being possible to establish such a bond, for example, between a silicon atom of the coupling agent and the hydroxyl (OH) surface groups of the inorganic filler (for example, surface silanols in the case of silica);
X represents a functional group (“X” function) which is capable of bonding physically and/or chemically with the diene elastomer, for example by means of a sulfur atom;
W represents a divalent group making it possible to link Y and X.
The coupling agents must in particular not be confused with simple agents for covering the inorganic filler which, in known manner, may comprise the Y function which is active with respect to the inorganic filler but are devoid of the X function which is active with respect to the diene elastomer.
Coupling agents, in particular silica/diene elastomer coupling agents, have been described in numerous documents, the best known being bifunctional organosilanes bearing at least one alkoxyl function as the Y function, and, as the X function, at least one function capable of reacting with diene elastomer, such as for example a sulfur function (i.e. comprising sulfur).
Thus it was proposed in patent applications FR-A-2094859 or GB-A-1310379 to use a mercaptoalkoxysilane coupling agent for the manufacture of treads for tires. It was quickly shown, and is today well known, that mercaptoalkoxysilanes are capable of giving excellent silica/elastomer coupling properties, but that these coupling agents cannot be used industrially because of the high reactivity of the thiol-SH type sulfurised functions (X functions), which very rapidly results in premature vulcanization during the preparation of the rubber composition in an internal mixer, this also being known as “scorching”, in very high viscosities in the uncured state and, finally, in rubber compositions which are virtually impossible to work and process industrially. Mention may be made, for example, of documents FR-A-2206330, U.S. Pat. No. 3,873,489, U.S. Pat. No. 4,002,594 to illustrate this problem.
To overcome this drawback, it has been proposed to replace these mercaptoalkoxysilanes by alkoxysilane polysulfides, in particular bisalkoxysilylpropyl) polysulfides such as described in numerous documents (see for example FR-A-2149339, FR-A-2206330, U.S. Pat. No. 3,842,111, U.S. Pat. No. 3,873,489, U.S. Pat. No. 3,997,581, EP-A-680997 or U.S. Pat. No. 5,650,457, EP-A-791622 or U.S. Pat. No. 5733963, DE-A-19951281 or EP-A-1043357, WO00/53671). Among these polysulfides, bis-3-triethoxysilylpropyl tetrasulfide (abbreviated to TESPT) and bis-3-triethoxysilylpropyl disulfide (abbreviated to TESPD) must in particular be mentioned.
These alkoxysilane polysulfides, in particular TESPT, are generally considered to be the products which achieve, for vulcanized rubber compositions comprising a reinforcing inorganic filler, in particular silica, the best compromise in terms of resistance to scorching, ease of processing and reinforcing action. Today, they are in this respect the most widely used coupling agents in rubber compositions for tires, even if they are relatively costly and, furthermore, must most frequently be used in a relatively large quantity.
The alkoxysilane polysulfides do, however, have the disadvantage of substantially retarding the vulcanization kinetics of the rubber compositions containing them in comparison with the kinetics of conventional compositions reinforced with carbon black. The resultant longer duration of curing may impair industrial processing of these rubber compositions reinforced
Belin Laure
Blanchard Christiane
Tardivat Jean-Claude
Crecente Christopher P.
Csontos Alan A.
Farley Felipe J.
Michelin & Recherche et Technique S.A.
Roberston Jeffrey B.
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