Essentially gas-impermeable thermoplastic elastomer

A closure means consisting essentially of an elastomeric sealing element free of tackiness having a thickness in the range from about 0.1 mm to about 10 mm, held in removably sealing relationship within the closure means, for sealing a container against permeation of an oxygen-containing gas, wherein the sealing element consists essentially of a thermoplastic elastomer free of tackiness selected from the group consisting of (a) an at least partially hydrogenated polyblock of a vinylaromatic compound and a conjugated diene so as to provide a block of a mono(lower)olefin, the olefin having from 2 to 4 carbon atoms, and, (b) a thermoplastic vulcanizate, wherein (a) is block copolymer having vinylaromatic end-blocks and a mid-block selected from the group consisting of polyisoprene, polybutadiene, and hydrogenated copolymers thereof,

• (a) having uniformly distributed therewithin,
• from 5 to 150 phr, based on 100 parts by weight of (a), of a polymer of an olefin having from 2 to 4 carbon atoms, the polymer having a melt index in the range from 0.2 to 200 gm/10 min at 230° C. and 2.16 Kg load, combined with from zero to an equivalent amount by weight of a mono(lower)olefinic rubber having Mn greater than 200,000, and
• (a) and (b) having blended therein from 20 to 180 phr of a liquid polyisobutene oil plasticizer, based on 100 parts by weight of (a) and (b), the plasticizer having a number average molecular weight (“Mn”) in the range from 200 to 6000, fluidizable under melt-blending conditions of (a) and (b), present in an amount in the range from about 20 to 180 phr, per 100 parts of (a) and (b), the polyisobutene selected from the group consisting of(i) a homopolymer of polyisobutylene and (ii) a copolymer of isobutene and butene, butene repeating units being present in a minor molar proportion;
• the amount of polyisobutene oil being sufficient to provide the elastomeric sealing element with a hardness in the range from Shore A 40 to 80 and an oxygen-permeability less than 20,000 cc. (2.54 μ/m2.day.atm at 23° C.;
• and
• a compatible amount, from 1 to about 20 phr of a detackifier per 100 parts by weight of (a),
• (a) having Mn in the range from about 40,000 to 1,100,000;
• and,
• (b) having a Shore A hardness in the range from 30 to 100, tensile strength at 100% elongation in the range from about 0.5 to 10 MPa and specific gravity in the range from 0.9 to 0.99.

A method for providing an essentially oxygen-impermeable elastomeric sealing element free of tackiness comprising blending an elastomer selected from the group consisting of (a) an at least partially hydrogenated polyblock of a vinylaromatic compound and a conjugated diene polyblock copolymer, so as to include a block of a mono(lower)olefin, the olefin having from 2 to 4 carbon atoms, and, (b) a thermoplastic vulcanizate, wherein (a) is block copolymer having vinylaromatic end-blocks and a mid-block selected from the group consisting of polyisoprene, polybutadiene, and hydrogenated copolymers thereof,

• wherein (a) has uniformly distributed therewithin,
• from 5 to 150 phr, based on 100 parts by weight of (a), of a polymer of an olefin having from 2 to 4 carbon atoms, the polymer having a melt index in the range from 0.2 to 200 gm/10 min at 230° C. and 2.16 Kg load, combined with from zero to an equivalent amount by weight of a mono(lower)olefinic rubber having Mn greater than 200,000, and
• (a) and (b) having blended therein a liquid polyisobutene oil plasticizer having a number average molecular weight (“Mn”) in the range from 200 to 6000, fluidizable under melt-blending conditions of (a) and (b), present in an amount in the range from about 20 to 180 phr, per 100 parts by weight of (a) and (b), the polyisobutene selected from the group consisting of (i) a homopolymer of polyisobutylene and (ii) a copolymer of isobutene and butene, butene repeating units being present in a minor molar proportion and,
• a compatible amount, from 1 to about 20 phr of a detackifier per 100 parts by weight of (a);
• (a) having Mn in the range from about 40,000 to 1,100,000;
• and,
• (b) having a Shore A hardness in the range from 30 to 100, tensile strength at 100% elongation in the range from about 0.5 to 10 MPa and specific gravity in the range from 0.9 to 0.99;
• and,
• thermoforming a seal having a hardness in the range from about Shore A 40 to 80 and an oxygen permeability less than 20,000 cc. (2.54 μm)/m2.day.atm at 23° C.