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
2002-01-29
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
06342552
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the processing and vulcanization of diene polymer and copolymer elastomer-containing rubber stocks. More particularly, the present invention relates to the processing and vulcanization of diene polymer and copolymer elastomer-containing, silica-filled rubber stocks using processing aids selected from the group consisting of alkyl alkoxysilane, fatty acid esters of hydrogenated and non-hydrogenated sugars and the polyoxyethylene derivatives thereof, and combinations and mixtures of these processing aids, with or without other reinforcing fillers, e.g., carbon black, or non-reinforcing fillers, e.g., mineral fillers. The present invention further relates to the processing and vulcanization of diene polymer and copolymer elastomer-containing, silica-filled rubber stocks using the above processing aids supported on the silica filler or other reinforcing or non-reinforcing fillers prior to mixing with the elastomer.
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 lower fuel consumption for 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 typically include at least one elastomer (that is, a natural or synthetic polymer exhibiting elastomeric properties, such as a rubber), a reinforcing (or non-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 a sulfur-containing vulcanizing (i.e., curing) system.
Recently, precipitated silica has been increasingly used as a reinforcing particulate filler in carbon black-filled rubber components of tires and mechanical goods. While providing excellent properties, including reduced hysteresis, to the rubber stocks, these silica-loaded rubber stocks are unfortunately not easily produced, exhibiting relatively poor processability characteristics.
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 Reinforced 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 in providing more readily processable rubber stocks. Disadvantageously, however, is the fact that, in order to obtain the desired processing results, a relatively large amount of the processing additive, on the order of at least 10 percent by weight based on the weight of silica, is required in order to be effective.
Thus, it is believed highly desirable to provide formulations for the processing and vulcanization of diene polymer and copolymer elastomer-containing, silica-filled rubber stocks which include processing aids other than Si69 that are effective in improving the processability and properties of the resulting silica-filled products. To that end, the present invention provides alkyl alkoxysilanes, fatty acid esters of hydrogenated and non-hydrogenated sugars, and mixtures thereof, for use as processing aids for silica-filled rubber stocks, which greatly improves the processability and properties of the formulations and the resulting vulcanized product, particularly where these processing aids are supported on silica or another reinforcing or non-reinforcing filler prior to being mixed with the elastomer. In addition, it has been found that mineral fillers as used in silica-filled elastomeric rubber stocks further improving tear strength and lower hysteresis, and can also be supported on silica or another filler.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide processing aids which improve the processability of formulations of diene polymer elastomers reinforced with silica filler.
It is another object of the present invention to provide formulations of diene polymer elastomers reinforced with silica filler having improved processability with decreased levels of bis[34triethoxysilyl)propyl]tetrasulfide (Si69).
It is still another object of the present invention to provide mineral and non-mineral fillers which improve the processability of formulations of diene polymer elastomers reinforced with silica filler.
It is a further object of the present invention to provide silica-supported, carbon black-supported or mineral filler-supported processing aids which improve the processability of formulations of diene polymer elastomers reinforced with silica filler.
It is still a further object of the present invention to provide reinforcing filler-supported additives, such as a mineral fillers, capable of improving the processability of the formulations of diene polymer elastomers reinforced with silica filler.
It is yet a further object of the present invention to provide a process for improving the processability of formulations of diene polymer elastomers reinforced with silica filler.
It is still a further object of the present invention to provide a process for reducing the viscosity of silica-filled elastomeric vulcanizable compounds.
It is yet a further object of the present invention to provide a process for decreasing the level of bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69) in silica-filled elastomeric vulcanizable compounds.
It is still a further object of the present invention to provide vulcanizable silica-filled elastomeric compounds having enhanced physical properties, including decreased hysteresis and increased tear strength.
At least one or more of 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 the steps of mixing an elastomer with from about 1 to about 100 parts by weight of an amorphous silica filler, from 0 to about 20 percent by weight, based on said silica filler, of bis[3-(triethoxysilyl)propyl]tetrasulfide, from about 0.1 to about 150 percent by weight, based on said silica filler, of an alkyl alkoxysilane, 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 about 20 percent by weight, based on said silica filler, of bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69), from about 0.1 to about 15
Cole William M.
Hergenrother William L.
Hilton Ashley S.
Oziomek James
Arndt Barbara
Bridgestone Corporation
Mulcahy Peter D.
Nornickel John H.
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