Removable seal of essentially gas-impermeable thermoplastic elastomer

• US 20020160137A1
• Filed: 02/12/2002
• Published: 10/31/2002
• Est. Priority Date: 02/13/2001
• Status: Active Grant

• Current Assignee: Avient Corp.
• Original Assignee: Great Lakes Synergy Corporation
• Inventors: Varma, Rajesh Kumar
• Granted Patent: US 7,056,971 B2
• Time in Patent Office: Days
• US Class Current: 428/35.7
• CPC Class Codes: B65D 39/0017 Injection-molded plastic closures for "Champagne"- or "Sekt"-type bottles
• CPC Class Codes: B65D 41/0442 Collars or rings B65D41/0457 takes precedence
• CPC Class Codes: B65D 53/02 Collars or rings
• CPC Class Codes: C08L 2205/02 containing two or more polymers of the same C08L -group
• CPC Class Codes: C08L 23/04 Homopolymers or copolymers of ethene
• CPC Class Codes: C08L 23/20 having four to nine carbon atoms
• CPC Class Codes: C08L 23/22 Copolymers of isobutene; Butyl rubber ; Homo- or copolymers of other iso-olefins
• CPC Class Codes: C08L 2666/04 Macromolecular compounds according to groups C08L7/00 - C08L49/00, or C08L55/00 - C08L57/00; Derivatives thereof
• CPC Class Codes: C08L 2666/24 Graft or block copolymers according to groups C08L51/00, C08L53/00 or C08L55/02; Derivatives thereof
• CPC Class Codes: C08L 53/00 Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 53/02 of vinyl-aromatic monomers and conjugated dienes
• CPC Class Codes: C08L 53/025 modified
• CPC Class Codes: C09J 123/04 Homopolymers or copolymers of ethene
• CPC Class Codes: C09J 153/02 Vinyl aromatic monomers and conjugated dienes
• CPC Class Codes: C09J 153/025 modified
• CPC Class Codes: Y10T 428/1352 Polymer or resin containing [i.e., natural or synthetic]

Abstract

A thermoplastic elastomer (“TPE”) which is oxygen-permeable is provided with excellent barrier properties against oxygen by melt-blending with a liquid polybutene oil plasticizer in an amount insufficient to render the plasticized elastomer tacky. If made tacky, enough detackifier is used to allow the product to be formed into a removable seal. The TPE may be a conventional thermoplastic vulcanizate or a block copolymer of a vinylaromatic compound, typically styrene, and a conjugated diene, typically butadiene or isoprene, or mixtures thereof; the block may be a diblock, triblock or higher block, but the preferred polyblock copolymer is a triblock with styrene end-blocks and a butadiene/isoprene mid-block. Preferably the diene mid-block is hydrogenated to provide a poly(lower)monoolefin mid-block. When the TPE is a TPV, some or all of the mineral oil used to make the TPV processable may also be substituted with the polybutene plasticizer. The elastomeric product is particularly useful for sealing elements for containers in which foods, beverages and medical products must be preserved for a long period.

Claims

1. In a plasticized thermoplastic elastomeric product selected from the group consisting of (a) a vinylaromatic-polyolefin polyblock copolymer, optionally hydrogenated to include a block of a mono(lower)olefin, and, (b) a thermoplastic vulcanizate,

the improvement wherein (a) and (b) each have uniformly distributed therewithin, polybutene fluidizable under melt-blending conditions of (a) and (b), the polybutene 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 polybutene being sufficient to provide the elastomeric product with a hardness in the range from Shore A 30 to 90 and an oxygen-permeability less than 40,000 cc.(2.54 μ

m)/m².day.atm at 23°

C.;

(a) having a number average molecular weight (“

Mn”

) in the range from about 40,000 to 1,100,000 and (b) having a 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.

2. The product of claim 1 having a hardness in the range from Shore A 40 to 80 and a thickness in the range from 0.1 mm to 10 mm, and (a) is at least partially hydrogenated.

3. The product of claim 1 wherein the elastomer is (a) and has homogeneously distributed therewithin, from 5 to 150 phr, based on 100 parts by weight of (a), of a poly(lower)monoolefin, the olefin having from 2 to 4 carbon atoms.

4. The product of claim 3 wherein the elastomer is (a) and the product has distinct Tgs for each of three phases, attributable to (a) vinylaromatic hydrocarbon, (b) conjugated diene, optionally hydrogenated, phase, and (c) a polyolefin phase.

5. The product of claim 1 wherein the poly(lower)monoolefin has a melt index in the range from 0.2 to 200 gm/10 min at 230°

C. and 2.16 Kg load, and is combined with from zero to an equivalent amount by weight of a mono(lower)olefinic rubber having Mn greater than 200,000.

6. The product of claim 1 wherein the elastomers (a) and (b) have homogeneously distributed therewithin, from 20 to 180 phr of polybutene, based on 100 parts by weight of (a) or (b), including in addition from 1 to 5 phr, based on 100 parts by weight of (a) or (b), of an additive selected from the group consisting of a non-reinforcing non-reactive filler, stabilizer, processing aid, antiblocking aid, antistatic agent, wax, foaming agent, pigment, and flame retardant.

7. The product of claim 1 wherein (a) is a block copolymer having vinylaromatic end-blocks and a mid-block selected from the group consisting of polyisoprene, polybutadiene, and hydrogenated copolymers thereof, having blended therein from 30 to 100 phr of polybutene, based on 100 parts by weight of (a), and a compatible amount, from 1 to about 20 phr of a detackifier per 100 parts by weight of (a).

8. The detackified product of claim 7 wherein (a) is a triblock copolymer, the vinylaromatic end-blocks are polystyrene, and the mid-block is selected from the group consisting of poly(isoprene) and poly(butadiene), and hydrogenated forms thereof in heterogeneous relative order, including styrene-ethylene-butylene-styrene.

9. The detackified product of claim 8 wherein the vinylaromatic end-blocks are polystyrene and the mid-block is selected from the group consisting of polyisoprene and polybutadiene;

and the detackifier is selected from the group consisting of a silicone oil and an epoxidized vegetable oil.

10. The product of claim 6 wherein the polybutene is present in an amount from about 30 to 100 phr respectively, per 100 parts of (a) or (b).

11. The detackified product of claim 8 having a oxygen-permeability in the range from about 2,000 to 20,000 cc.(2.54 μ

m)/m².day.atm at 23°

C.

12. The detackified product of claim 8 wherein the polybutene has a number average molecular weight in the range from about 200 to 6000.

13. The detackified product of claim 8 wherein (a) has a number average molecular weight in the range from about 70,000 to about 500,000.

14. The detacldfied product of claim 8 wherein (b) has a number average molecular weight in the range from about 70,000 to about 500,000.

15. The product of claim 1 wherein (b) is a blend of polypropylene and ethylene-propylene diene monomer rubber having blended therein from 20 to 180 phr of polybutene, based on 100 parts by weight of (b), and a compatible amount, from 1 to about 20 phr of a detackifier per 100 parts by weight of (b).

17. The closure means of claim 16 wherein (a) is a triblock copolymer having vinylaromatic end-blocks and a mid-block selected from the group consisting of polyisoprene, polybutadiene, poly(lower)olefin, the olefin having from 2 to 4 carbon atoms, and a hydrogenated copolymers thereof, and the sealing element has a hardness in the range form about Shore A 40 to 80, and includes from about 1 to 20 phr of a detackifier.

18. The closure means of claim 16 wherein the sealing element is light-permeable.

19. The closure means of claim 16 wherein the sealing element is provided by (a) having homogeneously distributed therewithin, from 5 to 150 phr, based on 100 parts by weight of (a), of a poly(lower)monoolefin, the olefin having from 2 to 4 carbon atoms.

20. The closure means of claim 16 wherein the closure means is a bottle cap and the container is a bottle.

21. The closure means of claim 16 wherein the closure means is a stopper and the container is a bottle.

16. A closure means comprising an elastomeric sealing element having a thickness in the range from about 0.1 mm to about 10 mm, held in removably sealing relationship with the closure means, for sealing a container against permeation of an oxygen-containing gas, wherein the sealing element is an elastomer selected from the group consisting of (a) a vinylaromatic-polyolefin polyblock copolymer, optionally hydrogenated to provide a block of a mono(lower)olefin, and, (b) a thermoplastic vulcanizate, wherein (a) and (b) each have uniformly distributed therewithin, polybutene fluidizable under melt-blending conditions of (a) and (b), present in an amount in the range from about 30 to 150 phr, per 100 parts of (a) or (b), the polybutene 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 polybutene being sufficient to provide the elastomeric product with a hardness in the range from Shore A 30 to 90 and an oxygen-permeability less than 40,000 cc.(2.54 μ

m)/m².day.atm at 23°

C.;

(a) having a number average molecular weight (“

Mn”

) in the range from about 40,000 to 1,100,000; and

,

(b) having a 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.

22. A method for providing an essentially oxygen-impermeable elastomeric sealing element comprising blending an elastomer selected from the group consisting of (a) a vinylaromatic-polyolefin polyblock copolymer, optionally hydrogenated to provide a block of a mono(lower)olefin, and, (b) a thermoplastic vulcanizate, wherein (a) and (b) each have uniformly distributed therewithin,

polybutene 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) or (b), the polybutene 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,

thermoforming a seal having a hardness in the range from about Shore A 30 to 90 and an oxygen-permeability less than 40,000 cc.(2.54 μ

m)/m².day.atm at 23°

C.

24. The resin of claim 22 wherein (a) is a triblock copolymer having vinyl-aromatic end-blocks and a mid-block selected from the group consisting of polyisoprene, polybutadiene, and hydrogenated copolymers thereof, and has homogeneously distributed therewithin, from 5 to 150 phr, based on 100 parts by weight of (a), of a poly(lower)monoolefin, the olefin having from 2 to 4 carbon atoms.

23. A resin composition which comprises from 100 parts by weight of an elastomer selected from the group consisting of (a) a vinylaromatic-polyolefin polyblock copolymer, optionally hydrogenated to provide a block of a mono(lower)olefin, and, (b) a thermoplastic vulcanizate, wherein (a) and (b) each have uniformly distributed therewithin, polybutene 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) or (b), the polybutene 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;

(a) and (b) each having a number average molecular weight (“

Mn”

) in the range from about 40,000 to 1,100,000; and

,

the resin having a hardness in the range from about Shore A 30 to 90 and an oxygen-permeability less than 40,000 cc.(2.54 μ

m)/m².day.atm at 23°

C.