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
2002-09-06
2004-05-18
Harlan, Robert Deshon (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...
C524S571000, C524S572000, C524S575000, C524S856000
Reexamination Certificate
active
06737466
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to silica reinforced rubber compositions of matter having improved processability, storage stability and or cure for use in tires and mechanical goods.
BACKGROUND OF THE INVENTION
Particulate fillers such as silica, carbon black, clays, talc, calcium carbonate, silicates (Science and Technology of Rubber, edited by J. E. Mark et al., Academic Press Inc., San Diego, Calif., 1994 p 387-469) and starch (F. G. Corvasce et al., U.S. Pat. No. 5,672,639) have been generally used as reinforcing materials for rubbers to improve their physical properties such as modulus, tensile strength, abrasion, tear properties, and dynamic properties.
The reinforcement of elastomers with particulate fillers such as silica and carbon black has been extensively studied. Four major characteristics of the fillers, namely particle size, morphology, aggregate structure and surface activity, influence the physical and mechanical properties of the reinforced rubber compositions. These characteristics contribute to the reinforcement of the elastomers through interactions between elastomers and fillers, occlusion of the elastomer in the internal voids of the aggregate and agglomeration of the filler aggregates in the elastomer matrix (S. Wolff & M. J. Wang in “Carbon Black, Science & Technology,” editors: J. B. Donnet, R. C. Bansal & M. J. Wang, Marcel Dekker, Inc., New York 1993). It is known that several types of interactions exist between molecules which are close to one another, e.g., dispersive, dipole-dipole, induced dipole-dipole, hydrogen bonding and the like. Such interactions can result in different types of cohesive forces. The surface energy of a solid, &ggr;
s
, can be expressed as the sum of several components, each corresponding to a specific type of interaction. For most substances: &ggr;
s
=&ggr;
s
d
+&ggr;
s
sp
where &ggr;
s
d
is the dispersive component of the surface free energy and &ggr;
s
sp
(or specific component) is the sum of the other components of the surface free energy. It should be noted that &ggr;
s
sp
comprises polar components, e.g., dipole-dipole, hydrogen bonding, and the like.
The difference in the surface free energy of carbon black and silica results in significant differences in the filler-filler and filler-rubber interaction. Compared to carbon black, surface energies of silica with equivalent surface area and structure, have a low dispersive component and a high specific component (M. J. Wang & S. Wolff, Rubber Chemistry and Technology, 65, 329, 1992). The low dispersive component (related to weaker polymer-filler interaction) has been shown to produce low modulus at high strains (S. Wolff, M. J. Wang & E. H. Tan, American Chemical Society, Rubber Division Meeting, Denver, Colo., May 1993). The higher specific component of the surface free energy of silica results in strong filler-filler interaction, resulting in increased viscosity of the rubber composition, especially at low strain rates.
The surface characteristics and hence the surface energy of silica can be changed by surface modification, for example, when the silica surface is chemically modified with so-called coupling systems such as a polyfunctional organosilane, e.g., bis(3-triethoxysilyl propyl)tetrasulfide (TESPT). The specific component of the surface free energy (&ggr;
s
sp
) is significantly reduced, leading to improved interaction between silica and rubber for improved compatibility (M. J. Wang, S. Wolff, Rubber Chemistry and Technology, 65, 715, 1992). A reduction of filler-filler interaction results in better dispersion and reduced viscosity. Compared to reinforcing carbon black, silica retards the cure rate of the filled composition. This retardation in cure rate has been attributed to the adsorption of curatives on the silica surface (M. Fetterman, Rubber Chemistry and Technology, 58, 179, 1985).
The silanol content, the adsorbed water content and the surface area of the silica, also affect the cure time (S. Wolff et al., American Chemical Society, Rubber Division Meeting, Denver, Colo., May 1993; M. P. Wagner, Rubber Chemistry & Technology, 49, 703, 1976). Silica, because of its high specific component of surface energy, has a strong tendency to agglomerate and is difficult to disperse in hydrocarbon rubbers. Polyfunctional organosilanes with sulfur linkages such as TESPT improve interactions of filler (e.g., silica) with a polymer, thereby improving the physical properties of vulcanizates such as abrasion resistance and reduced tan &dgr; at 60° C. The scorch and cure times are also affected (S. Wolff, M. J. Wang, Tyre Technology Conference, Basel 1993, and Wolff et al., U.S. Pat. No. 4,229,333; Thurn et al., U.S. Pat. No. 3,873,489; Wideman et al., European Patent Application No. EP 0780429A1; R. J. Pickwell, Rubber Chemistry and Technology, 56, 94, 1983; K. J. Sollmann et al., Rubber Division Meeting, American Chemical Society, Cincinnati, Ohio, Fall 1972).
Epoxidized natural rubber (ENR) with up to 50 mole percent epoxidation has been used alone and in combination with other diene rubbers such as natural rubber, styrene butadiene rubber, or butadiene rubber at levels higher than 30 phr (parts per one hundred parts of rubber, on a weight basis) with precipitated silica and mixture of silica with carbon black to improve wet skid resistance, but with poor tire tread abrasion and tear properties. The use of epoxidized natural rubber was accompanied by increased viscosity, retardation of cure rate and poor processability on storage (“Natural Rubber Science and Technology,” edited by A. D. Roberts, p.359-456, Oxford University Press, UK, 1988; S. Varughese et al., Kautschuk Gummi und Kunststoffe, 43, 871, 1990). ENR, because of the higher mole percent epoxide groups (10-50%), is reinforced by silica even in the absence of coupling systems such as TESPT or &ggr;-mercaptopropyltrimethoxysilane. The addition of a coupling system enhances the cure rate and strength properties of silica-filled ENR (10-50 mole % epoxidation). (M. Nasir et al., European Polymer Journal, 25, 267, 1989; S. Varughese and D. K. Tripathy, Journal of Applied Polymer Science, 44, 1847, 1992). Epoxidized natural rubbers with an epoxy content from 15 to 85 mole percent have been reportedly used in blends with other diene rubbers such as polyisoprene, butadiene, carboxylated nitrile at a 1-15 phr level in silica or silica/carbon black reinforced tread compositions. A synergistic effect of ENR with a carboxylated nitrile was reported to improve vulcanizate properties (Sandstrom, U.S. Pat. No. 5,489,628).
ENR at 5-30 phr was also reportedly used in blends with diene rubber and a coupling system (TESPT) to improve the abrasion and adhesion properties of the vulcanizate. (Segatta et al., U.S. Pat. No. 5,396,940). The addition of glycols, amines or guanidines to rubber compositions containing silica has been reported to counter the retarding effect of silica on the cure rate during vulcanization. Addition of diethylene glycol or triethanolamine in silica-filled rubber reduced the Mooney viscosity and scorch time. The reduction in Mooney viscosity was storage temperature dependant and was not apparently effective at higher storage temperature (M. P. Wagner, Rubber Chemistry and Technology, 49, 703, 1976). Diene rubber compositions with excellent processability and improved dispersibility of silica have been claimed when dicyclohexylamine and diene polymers modified with —COOH, epoxy, amino or hydroxyl group are used in the rubber composition (H. Takamata et al., Japanese Patent No. JP 07292159). Epoxidized soybean and linseed oils have been reported to enhance the adhesion properties of rubber compositions, containing carbon black as major filler and silica as minor filler, with steel cords. No significant effects on viscosity and processability of compositions containing epoxidized soybean and linseed oils were reported with the aforementioned filler blend (Stevens et al., DE 19700967A1, Jul. 16, 1998).
Accordingly, it would be an advantage to provide a process for reducing th
Coran Aubert Y.
Mowdood Syed K.
Schaal Stephane
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Harlan Robert Deshon
Pirelli Pneumatici S.p.A.
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