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
1998-05-01
2001-07-17
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S094000, C525S095000, C525S097000, C525S098000, C525S099000, C525S185000, C525S190000, C525S228000, C525S229000, C525S237000, C525S240000, C525S241000
Reexamination Certificate
active
06262175
ABSTRACT:
The present invention relates to a thermoplastic elastomer composition containing substantial quantities of vulcanized rubber crumb and polyolefin. The vulcanized crumb may be, but is not necessarily, derived from scrap tires, and in such case may typically consist primarily of styrene-butadiene rubber, but in such admixtures with natural rubber, and other types of synthetic rubbers as may from time to time be used by the tire producers in their compound recipes.
Applicant is aware of various prior proposals for such compositions, for example in U.S. Pat. No. 5,514,721 (Hart). However, compositions disclosed in Hart have a high content of relatively expensive styrene block copolymer, greater than about 25%, for example.
Other prior-proposed compositions of which the applicant is aware have had relatively poor physical properties. For example, U.S. Pat. No. 5,157,082 (Johnson) discloses compositions comprising ground vulcanized rubber, polyolefin and a functionalized olefin polymer. Compositions of this type, however, tend to have relatively low ultimate elongation and tear strength.
Applicant has found that thermoplastic elastomer compositions having excellent physical properties, including excellent ultimate elongation and tear strength can be obtained by blending vulcanized rubber crumb and polyolefin together with uncured rubber or styrene-based thermoplastic rubber and vinyl based polymer. The uncured rubber or curable thermoplastic rubber and vinyl based polymer together constitute a two stage compatibilizing system which provides superior physical properties over known compositions.
In accordance with the present invention there is provided a thermoplastic elastomer composition comprising a blend of the following components:
(a) about 5% to about 90% vulcanized rubber crumb;
(b) about 5% to about 60% polyolefin;
(c) about 2% to about 30% uncured rubber or styrene-based thermoplastic elastomer; and
(d) about 2% to about 30% vinyl polymer selected from the group consisting of vinyl homopolymers, copolymers and mixtures thereof;
and with the proviso that when said component (c) or (d) comprises styrene block copolymer said composition contains in total less than 15% styrene block copolymer.
Unless otherwise indicated, all percentages herein are by weight based on the total weight of the composition.
Without wishing to be bound by any theory, it is believed that the uncured rubber or styrene-based thermoplastic rubber component (c) of the composition imparts excellent strength properties to the composition as a result of the entanglement of the molecular chains constituting the rubber polymer molecule. These molecular chains are believed to form interpenetrating random coils, and it is believed that this molecular structure is capable of imparting excellent strength properties.
Further, it is believed the vinyl polymer portion (d) serves to provide adhesion to the tire crumb at the molecular level, and that the excellent physical properties result from improved adhesion or bonding between the tire crumb and the remaining components of the composition.
In one especially preferred form of the present invention, the vinyl polymer comprises polymer chains having pendant oxygen-containing groups. These compositions provide exceptionally good ultimately elongation values and tear strengths. The rubber molecules in the tire crumb tend to have polar sites as a result of the chemical composition of the rubber and minor oxidation occurring during mechanical comminution. Without wishing to be bound by any theory, it is believed that the polymers having pendant oxygen-containing groups provide improved adhesion to the rubber crumb as a result of the affinity with these polar sites on the rubber crumb.
The vulcanized rubber crumb used in the present composition may be obtained by grinding or otherwise comminuting any source of vulcanized rubber compound, such as road vehicle tires, roofing membrane, hoses, gaskets and the like, and is preferably obtained from recycled passenger car tires using any conventional procedure. Any steel or other metallic inclusions should be removed from the ground tires before use in the compositions of the invention. Since the compositions of the invention are preferably fiber-free, all fibrous material such as tire cord fibers is preferably likewise removed from the ground rubber using conventional separation procedures before use in the compositions of the invention. Desirably, the vulcanized rubber crumb is of a particle size in the range about 20 to about 100 mesh (Tyler standard sieve). The use of rubber crumb of a particle size substantially coarser than about 20 mesh tends to result in molded products which are insufficiently homogeneous and tend to have relatively poor strength properties. The use of crumb which is substantially finer than about 100 mesh tends to significantly increase the energy costs of the comminution operation, without significant improvement of the properties of the compositions. As noted above, desirably the compositions of the invention comprise about 5 to about 90 weight percent of the vulcanized rubber crumb. Compositions comprising greater than about 90% by weight of the cured rubber crumb can exhibit processing problems and tend to have poor strength properties, while compositions containing less than about 5% of the rubber crumb tend to be excessively costly, as a result of their low content of the relatively low cost cured rubber crumb material. Preferably, the composition comprises about 25 to about 75% by weight of the rubber crumb, more preferably about 40 to about 60%.
The polyolefin component (b) may comprise any solid high molecular weight polyolefin homopolymer or copolymer, or mixtures thereof. Examples of olefin polymers suitable for use in the present compositions include homopolymers or copolymers of ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 5-methyl-1-hexane and mixtures thereof. Preferably, the polyolefin comprises polyethylene, polypropylene or a copolymer of ethylene and propylene.
Preferably, as noted above, the compositions of the invention comprise about 5% to about 60% by weight of the polyolefin homopolymer, copolymer or mixtures thereof. Compositions having a polyolefin content of greater than about 60% may tend to be excessively stiff and to exhibit poor elongation values, while polyolefin contents of less than about 5% by weight tend to result in the composition may exhibit processing problems and tend to have relatively poor strength properties. More preferably, the composition comprises about 10 to about 40% by weight of polyolefin, still more preferably about 20 to about 30% by weight of the total composition. Preferably, the composition comprises polyethylene and polypropylene in a weight ratio of about 1.5 to 3 parts by weight polyethylene per part by weight of polypropylene, more preferably about 1.8 to about 2.8 parts by weight polyethylene per part polypropylene.
The uncured rubber or styrene-based or styrenic thermoplastic rubber component of the present composition is considered to provide adhesion or bonding between the remaining components of the composition and the vulcanized rubber crumb component and to provide elasticity for the composition.
Compositions that contain less than about 2% by weight uncured rubber or styrene-based thermoplastic elastomer tend to be excessively stiff, while compositions containing greater than about 30% by weight of uncured rubber or styrene-based thermoplastic elastomer may tend to be excessively soft and have insufficient strength properties. Preferably, the composition comprises about 4 to about 20 weight percent of uncured rubber or styrene-based elastomer, more preferably about 5 to about 15% uncured rubber or styrene-based thermoplastic elastomer, based on the total weight of the composition.
The term “rubber” as used herein is to be interpreted as it would be understood by those skilled in the art, to mean natural rubber and all natural or synthetic polymers having mechanical propertie
Chien Alfred Wing Yan
Jury James R.
Mullis Jeffrey
NRI Technology Inc.
Ridout & Maybee
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