Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-01-24
2002-10-15
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332600, C525S188000, C525S219000, C525S225000, C525S226000, C524S094000, C524S261000, C524S263000, C524S265000, C524S267000, C152S209100
Reexamination Certificate
active
06465581
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to use of stabilized unsymmetrical coupling agents for use in conjugated diene-based rubber compositions reinforced with silica-based reinforcement, namely use of stabilized 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide and 3-(triethoxysilyl)propyl-N-maleamic acid. Said stabilized unsymmetrical coupling agent materials may be provided for mixing with said diene-based rubber(s), for example, as individual materials, as at least one of said materials being pre-reacted with aggregates of precipitated silica, said precipitated silica having hydroxyl groups (e.g. silanol groups) on its surface. The invention includes an article of manufacture, including a tire, having at least one component comprised of such rubber composition.
BACKGROUND OF THE INVENTION
For various applications utilizing rubber compositions, carbon black and/or synthetic amorphous silica-based materials are conventionally used as particulate reinforcing fillers for the elastomer(s) of the rubber composition(s).
Often a coupling agent is used together with the silica in order to couple, or otherwise enhance, its elastomer reinforcement effect for the elastomer(s) and such use of a coupling agent is well known to those having skill in such art.
Historically, such coupling agents are composed, for example, of one moiety (e.g. a silane-based moiety such as, for example, an alkoxysilane moiety) which is reactive with hydroxyl groups (e.g. silanol groups) on the surface of a synthetic amorphous silica and another moiety (e.g. a polysulfide bridge) which becomes interactive with a conjugated diene-based elastomer. Typically, such coupling agents are symmetrical compounds.
For example, bis-(3-trialkoxysilylpropyl) polysulfides having an average of from 2 to 4 connecting sulfur atoms in their polysulfidic bridge are often used as coupling agents to enhance coupling of synthetic amorphous silicas, such as for example, aggregates of precipitated silica, to various conjugated diene-based elastomers. Use of such symmetrical coupling agents is well known to those having skill in such art.
However, use of unsymmetrical coupling agents can represent problems not normally encountered by use of the aforesaid symmetrical coupling agents.
For example, various unsymmetrical coupling agents may tend to pre-react with themselves before mixing with a blend of an elastomer and precipitated silica, with their intended use of a coupling agent being seriously impaired if not altogether nullified by the relative short shelf life of the unsymmetrical coupling agents.
Exemplary of unsymmetrical coupling agents contemplated herein are 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide and 3-(triethoxysilyl)propyl-N-maleamic acid. Such unsymmetrical coupling agents have a relatively short shelf life since they inherently tend to react with themselves or with each other if used in combination and therefore have a limited use, in practice, as coupling agents for manufacturing products on an industrial scale.
For example, 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide can proceed to react with itself and form 2-mercaptobenzothiozole and symmetrical disulfides, thereby severely limiting its use as a silica coupling agent.
For example, 3-(triethoxysilyl)propyl-N-maleamic acid can proceed to react with itself to liberate ethanol and form an insoluble polymeric siloxane network, thereby severely limiting its use as a silica coupling agent.
In the description of this invention, the term “phr” is used to designate parts by weight of a material per 100 parts by weight of elastomer. In the further description, the terms “rubber” and “elastomer” may be used interchangeably unless otherwise mentioned. The terms “vulcanized” and “cured” may be used interchangeably, as well as “unvulcanized” or “uncured”, unless otherwise indicated.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with one aspect of this invention, a rubber composition is provided which comprises
(A) 100 parts by weight of at least one diene hydrocarbon based elastomer,
(B) about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of about 25 to about 100, alternately about 35 to about 90, phr of synthetic amorphous silica aggregates and, correspondingly, from zero to about 75, alternately about 10 to about 65, phr of at least one of carbon black and silica treated carbon black having domains of silica on its surface, wherein said silica aggregates and said silica domains on the surface of said treated carbon black contain hydroxyl groups (e.g. silanol groups) on their surface; and
(C) about 1 to about 100, alternately about 8 to about 15, phr of a pre-treated silica as aggregates of precipitated silica which contain hydroxyl groups (e.g. silanol groups) on their surface which have been reacted with:
(1) 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide, or
(2) 3-(triethoxysilyl)propyl-N-maleamic acid.
A significant aspect of this invention is the use of a composite of a pre-treated silica by reaction with the 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide or 3-(triethoxysilyl)propyl-N-maleamic acid.
For example, by reaction of the triethoxysilylpropyl moiety of the 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide with the hydroxyl groups of the precipitated silica, its degradation and associated formation of 2-mercaptobenzothiazole and symmetrical disulfides is substantially retarded and the resulting composite of pre-treated silica is readily available for use as a coupling agent for coupling precipitated silica to a diene-based elastomer.
For example, by reaction of the triethoxysilyl moiety of the 3-(triethoxysilyl)propyl-N-maleamic acid with the hydroxyl groups of the precipitated silica, its degradation and associated formation of insoluble polymeric siloxane network is substantially retarded and the resulting composite of pre-treated silica is readily available for use as a coupling agent for coupling precipitated silica to a diene-based elastomer.
In practice, the said composite of pre-treated silica is preferably comprised of about 1 to about 20 percent by weight by weight of the precipitated silica and, correspondingly, about 5 to about 15 weight percent derived from reaction of said 2-benzothiazyl-3-(triethoxysilylpropyl) disulfide or 3-(triethoxysilyl)propyl-N-maleamic acid.
In further accordance with this invention, an article of manufacture is provided which contains at least one component comprised of the rubber composition of this invention.
In additional accordance with this invention, a tire is provided which contains at least one component comprised of the rubber composition of this invention.
In further accordance with this invention, a tire is provided having a tread comprised of the rubber composition of this invention.
It is to be appreciated that additional coupling agents may be used in the practice of this invention to aid in coupling the silica to elastomer(s). Such coupling agents would conventionally have a moiety reactive with hydroxyl groups on the silica (e.g. silanol groups) and another moiety interactive with one or more elastomers. Use of such coupling agents for such purpose is well known to those having skill in such art.
For example, a coupling agent as a bis-(3-trialkoxysilylalkyl) polysulfide having from 2 to 8, with an average of from 2 to 2.6 or from 3.5 to 4, connecting sulfur atoms in its polysulfidic bridge might be used.
Representative of such coupling agent is bis-(3-triethoxysilylpropyl) polysulfide having from 2 to 8, with an average of from 2 to 2.6 or from 3.5 to 4, connecting sulfur atoms in its polysulfidic bridge.
The aggregates of precipitated silica is intended to include precipitated aluminosilicates as a co-precipitated silica with a minor amount of aluminum.
Such precipitated silica is, in general, well known to those having skill in such art. For example, such precipitated silica may be precipitated by controlled addition of an acid such as, for example, hydrochloric acid or sulfuric acid, to a basic solution (e.g. sodium hydroxid
Folk Theodore Lamson
Sandstrom Paul Harry
Wideman Lawson Gibson
Lee Rip A
The Goodyear Tire & Rubber Company
Wu David W.
Young, Jr. Henry C.
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