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
2000-10-18
2004-03-23
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...
C524S519000, C524S567000, C524S578000, C152S525000
Reexamination Certificate
active
06710116
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to transparent and colorable elastomeric compositions and, more particularly, to transparent and colorable elastomeric compositions that can be used in reinforcing applications having a high abrasion resistance and traction.
BACKGROUND OF THE INVENTION
Rubber compositions are used in a variety of applications, including tire components such as treads and sidewalls, hoses, belts, footwear components, vibration isolation devices and bladders. While the particular rubber compositions used in each of these applications vary widely in their physical properties, one attribute remains the same—their color. Most rubber compositions are black. Furthermore, most rubber compositions eventually become discolored due to heat, light, ozone, etc. This is particularly true for rubbers used in stressful, demanding applications such as tire treads and sidewalls.
Practitioners in this field will point to the presence of the reinforcing filler “carbon black” as a prime reason that most rubbers are black. While this is true, carbon black is not the only factor. In fact, a wide variety of other fillers, curatives, antidegradants, oils and the rubbers themselves can all result in a dark color that is essentially impossible to pigment. This is evident in compositions where carbon black has been replaced with a silica filler and the rubber is still discolored. For example, European Patent 0 682 071 B1 discloses a silica reinforced tire tread which, due to the presence of the aromatic processing aid, coupling agent, antidegradants and a sulfur curative system, will still be dark in color. In fact, it is uncertain how many of the ingredients present in the rubber composition would have to be changed to produce a colorable composition.
There are some colorable and transparent elastomeric compositions that are currently used. For example, clear EPDM elastomers are available. However, these elastomers do not covulcanize with other rubbers. Since many rubber applications involve combining several types of rubber to form a single article (i.e. tires), these EPDM elastomers are limited in their usefulness. A related patent, serial number 09/592,757 (assigned to the assignee of the present invention), discloses improved blends of rubbers and other elastomers with silica to form transparent elastomeric materials. However, these materials may not be suitable for applications requiring high abrasion resistance while maintaining the colorability of the composition. Such is the case for, example, tire sidewalls and shoe soles.
White sidewalls on tires are a form of colorable rubber. The white color is achieved by using fillers such as silica, clay, talc and carbonates instead of carbon black and adding titanium dioxide as a whitening pigment. However, the white color comes with a price. The fillers are more fragile than carbon black and result in a weak rubber composition that does not reinforce the tire.
In applications such as shoe soles and tire treads where a large amount of a filler such as silica is used, it is desirable to maintain and adequately adjust certain physical properties such as the processability of the rubber, the cure rate, and final cure characteristics such as traction and abrasion resistance. In particular, abrasion resistance is important for colorable rubber compositions in, for example, tire sidewalls where there is a need for resistance to curb-scuffing. Also, in shoe soles and other shoe applications there is a need for an elastomeric composition that has long wear. An object of the present invention it to provide a colorable elastomeric composition that has improved abrasion resistance and other improved physical characteristics, while maintaining the colorability and transparency of the composition.
SUMMARY OF THE INVENTION
The present invention provides improved transparent and colorable elastomeric compositions. The transparent elastomeric compositions are halogenated isoolefin/para-alkylstyrene elastomers which can be alone in the composition or can be covulcanized with rubbers such as polybutadiene, polyisoprene, styrene-butadiene rubber, styrene-isoprene-butadiene rubber, isoprene-butadiene rubber, ethylene-propylene diene rubber, high cis-polybutadiene or natural rubber. The colorable rubber compositions have sufficient properties to function as a reinforcing member in an automobile tire or sufficient traction and abrasion resistance to function as a shoe sole. Preferably, both the transparent and colorable elastomeric compositions include at least one copolymer of a C
4
to C
7
isoolefin and a para-alkylstyrene, silica, a coupling agent, and a processing aid such as a low molecular weight saturated polymer.
The “elastomeric composition” of the present invention is a mixture of at least the halogenated isoolefin/para-alkylstyrene, a filler agent (described below), and the processing aid (described below). The elastomeric composition may also contain other rubbers as listed above, as well as a cure system when another rubber is present.
The elastomeric compositions of the present invention are useful in a variety of applications, particularly pneumatic tire components, hoses, belts, solid tires, footwear components, rollers for graphic arts applications, vibration isolation devices, pharmaceutical devices, adhesives, sealants, protective coatings and bladders for fluid retention and curing purposes.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an elastomeric composition comprising a copolymer of a C
4
to C
7
isoolefin and a para-alkylstyrene, a filler; and a low molecular weight, saturated processing aid. The composition may also comprise a rubber selected from the group consisting of polybutadiene, polyisoprene, styrene-butadiene rubber, styrene-isoprene-butadiene rubber, Isoprene-butadiene rubber, ethylene-propylene diene rubber, high cis-polybutadiene or blends thereof.
The colorable elastomeric compositions of the present invention have sufficient properties to function as shoe soles and other shoe components and as a reinforcing member in an automobile tire, as well as other applications where a colorable, transparent material is desired. The colorable elastomeric compositions of the present invention are useful in making colored elastomeric products capable of meeting current performance requirements. These colorable compounds were produced by replacing carbon black filler with a non-staining mineral filler such as, but not limited to, fumed or precipitated silicas, clays, talcs, calcium carbonates, aluminum oxides, titanium oxides, and zinc oxides. The mineral filler must reinforce the polymer system and not inhibit pigmentation to be effective. In addition, the remaining components of the colorable compound were selected on the basis that they will not interfere with the colorable nature of the elastomer. The cured, colorable compounds of the present invention still have the same dynamic and physical properties that meet the performance demands of current black-colored tire treads.
All components of the transparent and colorable elastomeric compositions must be carefully selected so that they will not interfere with the transparency and/or colorability of the composition. For example, the elastomers, fillers, processing aids, antidegradants and curatives should not discolor the composition during the formation of the elastomeric composition. Furthermore, the components should not discolor the elastomeric composition as a result of exposure to light (including UV), heat, oxygen, ozone and strain.
In one embodiment of the present invention, an elastomeric composition is produced which exhibits transparent properties. The term “transparent”, as used herein is defined as transmission of light without substantial scattering such that visual identification can be made of objects behind the elastomeric composition. Degrees of transparency can vary from contact transparency to complete transparency. However, other embodiments of the invention are not limited to transparent compositions, such as those blende
Poulter Robert Ryan
Waddell Walter Harvey
Arechederra Leandro
ExxonMobil Chemical Patents Inc.
Faulkner Kevin M.
Mulcahy Peter D.
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