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
2000-11-28
2002-02-19
Mulcahy, Peter D. (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...
C524S318000, C152S548000, C152S564000
Reexamination Certificate
active
06348531
ABSTRACT:
TECHNICAL FIELD
The subject invention relates to the processing and vulcanization of diene polymer and copolymer elastomer containing rubber stocks. More specifically, the present invention relates to the processing and vulcanization of diene polymer and copolymer elastomer-containing, silica-filled rubber stocks using a mixture of silanes as processing aids.
BACKGROUND OF THE INVENTION
In the art it is desirable to produce elastomeric compounds exhibiting reduced hysteresis when properly compounded with other ingredients such as reinforcing agents, followed by vulcanization. Such elastomers, when compounded, fabricated and vulcanized into components for constructing articles such as tires, power belts, and the like, will manifest properties of increased rebound, decreased rolling resistance and less heat-build up when subjected to mechanical stress during normal use.
The hysteresis of an elastomer refers to the difference between the energy applied to deform an article made from the elastomer and the energy released as the elastomer returns to its initial, undeformed state. In pneumatic tires, lowered hysteresis properties are associated with reduced rolling resistance and heat build-up during operation of the tire. These properties, in turn, result in lowered fuel consumption of vehicles using such tires.
In such contexts, the property of lowered hysteresis of compounded, vulcanizable elastomer compositions is particularly significant. Examples of such compounded elastomer systems are known to the art and are comprised of at least one elastomer (that is, a natural or synthetic polymer exhibiting elastomeric properties, such as a rubber), a reinforcing filler agent (such as finely divided carbon black, thermal black, or mineral fillers such as clay and the like) and a vulcanizing system such as sulfur-containing vulcanizing (that is, curing) system.
Previous attempts at preparing readily processable, vulcanizable, silica-filled rubber stocks containing natural rubber or diene polymer and copolymer elastomers have focused upon the sequence of adding ingredients during mixing (Bomal, et al.,
Influence of Mixing procedures on the Properties of a Silica Reiniforced Agricultural Tire Tread
, May 1992), the addition of de-agglomeration agents such as zinc methacrylate and zinc octoate, or SBR-silica coupling agents such as mercapto propyl trimethoxy silane (Hewitt,
Processing Technology of Silica Reinforced SBR, Elastomerics
, pp 33-37, March 1981), and the use of bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69) processing aid (Degussa, PPG).
The use of Si69 processing aid in the formulation of silica-filled rubber stocks has been successful, but generally requires a large amount of the additive, such as 10% by weight based on the weight of silica, in order to be effective.
Precipitated silica has been increasingly used as a reinforcing particulate filler in carbon black-filled rubber components of tires and mechanical goods. Silica- loaded rubber stocks, however, exhibit relatively poor processability.
The present invention provides a mixture of silanes for use as processing aids for silica-filled rubber stocks, which greatly improve the processability and properties of the formulations and resulting vulcanized product.
SUMMARY OF INVENTION
It is therefore an object of the present invention to provide rubber stock processing aids which improve the processability of formulations of diene polymer elastomers with silica-filler.
It is another object of the present invention to provide a method for reducing the viscosity of silica-filled elastomeric vulcanizable compounds.
It is another object of the present invention to provide a method for enhancing the processability of silica-filled elastomeric vulcanizable compounds.
It is another object of the present invention to provide vulcanizable silica-filled elastomeric compounds having enhanced physical properties.
The foregoing objects, together with the advantages thereof over the existing art, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
The present invention provides a process for the preparation of a silica-filled, vulcanized elastomeric compound comprising: mixing an elastomer with an amorphous silica filler, from 0 to less than about 1% by weight based on said silica filler of bis[3- (triethoxysilyl)propyl]tetrasulfide, an alkylalkoxysilane and a cure agent; and, effecting vulcanization. Preferably, the elastomer is a diene monomer homopolymer or a copolymer of a diene monomer and a monovinyl aromatic monomer.
The present invention further provides a vulcanizable silica-filled compound comprising an elastomer, a silica filler, from 0 to less than about 1% by weight based on said silica filler of bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69), an alkylalkoxysilane and a cure agent. Preferably, the elastomer is styrene butadiene rubber, optionally containing a carbon black filler. The compound is more readily processable during mixing, due to the use of the mixture of silane processing aids.
The present invention further provides a pneumatic tire comprising tread stock vulcanized from the inventive vulcanizable silica-filled compound.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In general, the present invention provides a means to reduce the level of Si69 needed to obtain good physical properties in a cured rubber stock containing silica as a filler. In addition, the present invention further provides maintenance of the processability of the compounded stock, as measured by Mooney viscosity, at the same level as achieved with high levels of Si69.
The present invention utilizes the presence of an alkylalkoxysilane as a silica hydrophobating agent, such that minimal amounts of Si69 are needed to obtain good processability, and yet still give good physical properties. According to the invention, therefore, a less costly silane can be substituted for the majority or all of the Si69 that would be normally used without any loss of processability or properties. Additionally, remilling can be eliminated, and the cure of the rubber stock is not dependent on the high sulfur level present in the Si69.
The silica-hydrophobating agents useful according to the present invention include those alkylalkoxysilanes of the formula (R
1
)
2
Si(OR
2
)
2
or R
1
Si(OR
2
)
3
, wherein the alkoxy groups are the same or are different; each R
1
independently comprising C1 to about C18 aliphatic, about C6 to about C12 cyclo-aliphatic, or about C6 to about C18 aromatic, preferably C1 to about C10 aliphatic, about C6 to about C10 cyclo-aliphatic, or about C6 to about C12 aromatic; and each R
2
independently containing from one to about 6 carbon atoms. Representative examples include octyltriethoxy silane, octyltrimethyloxy silane, (3-glycidoxypropyl)trimethoxy silane, (3- octyltrimethoxy silane, hexyltrimethoxy silane, ethytrimethyoxy silane, propyltriethoxy silane, phenyltrimethoxy silane, cyclohexyltrimethoxy silane, cyclohexyltriethoxy silane, dimethyldimethoxy silane, i-butyltriethoxy silane, and the like. Of these, octyltriethoxysilane is preferred.
According to the present invention, polymerized elastomer is compounded in the rubber stock, e.g., polybutadiene, polyisoprene and the like, and copolymers thereof with monovinyl aromatics such as styrene, alpha methyl styrene and the like, or trienes such as myrcene. Thus, the elastomers include diene homopolymers, A, and copolymers thereof with monovinyl aromatic polymers, B. Exemplary diene homopolymers are those prepared from diolefin monomers having from 4 to about 12 carbon atoms. Exemplary vinyl aromatic polymers are those prepared from monomers having from 8 to about 20 carbon atoms. Examples of conjugated diene monomers and the like useful in the present invention include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and 1,3-hexadiene, and aromatic vinyl monomers include styrene, a-methylstyrene, p-methylstyrene, vinyltoluenes and vinylnaphthalenes.
Cole William M.
Hergenrother William L.
Hilton Ashley S.
Arndt Barbara
Bridgestone Corporation
Hornickel John H.
Mulcahy Peter D.
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