Injection-moldable transparent thermoplastic elastomer

• US 6,984,688 B2
• Filed: 05/02/2003
• Issued: 01/10/2006
• Est. Priority Date: 05/02/2003
• Status: Active Grant

• Current Assignee: Avient Corp.
• Original Assignee: GLS Corp. (Avient Corp.)
• Inventors: Gu, Jiren
• Primary Examiner(s): MULCAHY, PETER D
• Application Number:
  US10/428,685
• Publication Number:
  US 20040220323A1
• Time in Patent Office: 984 Days
• Field of Search: 524/476, 524/481, 524/505, 215/11.1
• US Class Current: 524/476
• CPC Class Codes: C08L 23/12 Polypropene
• CPC Class Codes: C08L 2666/06 Homopolymers or copolymers of unsaturated hydrocarbons; Derivatives thereof
• CPC Class Codes: C08L 53/02 of vinyl-aromatic monomers and conjugated dienes

Abstract

A plasticized HSBC blended with polypropylene and free of a filler material which adversely affects clarity, provides an injection-moldable composition for an article required to have specific properties, namely, tensile strength in the range from about 4.13 to 8.96 MPa (600 to 1300 psi); tear strength in the range from about 21 to 52.6 N/mm (120 to 300 lbs/in); softness in the range from about 45 but less than 65 Shore A; and haze less than 20%, measured by ASTM D1003 using a BYK Gardner Micro Tri-gloss 4525 meter; and it is essential that all of these properties, along with the physical dimensions of the molded article, remain substantially unchanged after immersion of the article in boiling water for 1 hour. Such a composition is may be injection molded to form a nipple for feeding an infant, or a teething ring, or goggles for a diver, and the articles are sterilizable and recyclable.

Claims

1. A thermoplastic, injection-moldable and recyclable composition consisting essentially of at least one triblock copolymer selected from the group consisting of

(a) a substantially colorless hydrogenated first styrene-conjugated diene-styrene block copolymer (HSBC) derived by hydrogenation of a triblock copolymer selected from the group consisting of high vinyl (styrene-butadiene-styrene) (SBS), high vinyl (styrene-isoprene-styrene) (SIS) and high vinyl (styrene-isoprene/butadiene-styrene) (SI/BS) to yield polystyrene-b-poly(ethylene/butylene)-b-polystyrene (high vinyl SEBS), polystyrene-b-poly(ethylene/propylene-3-methylbutene)-b-polystyrene (SEPS), and “

polystyrene-b-poly(ethylene-ethylene/propylene)-b-polystyrene (SEEPS), respectively, each triblock having at least 51 mole percent of the butadiene midblock polymerized at the 1,2-position, and/or at least 51 mole percent of the isoprene polymerized at the 3,4-position, wherein (a) has a resultant effective number average molecular weight (Mn) measured by gas permeation chromatography (GPC), lower than 130,000; and

(b) a blend of (a) with a second substantially colorless SEEPS present in a minor proportion relative to the first HSBC (a), wherein the second SEEPS is optionally high vinyl and (b) has a resultant effective number average molecular weight (Mn) measured by gas permeation chromatography (GPC), lower than 130,000;

a minor proportion by weight, relative to the amount of (a) or the combined amount of (a) and (b), of a polyolefinic modifier providing a continuous phase in the TPE, the polyolefinic modifier being selected from the group consisting of polypropylene homopolymer, and a copolymer of propylene with another lower olefin having from 2 to 6 carbon atoms, the modifier having a melt viscosity in the range from 1 to 150 gm/10 min as measured at 230°

C. under a load of 2.16 kg in accordance with ASTM D1238;

a minor proportion by weight, relative to the amount of (a) or the combined amount of (a) and (b), of a substantially colorless plasticizer or softening agent compatible with rubbery phases of the foregoing;

a minor proportion by weight relative to either (a), or (a) and (b), of an end block modifier which associates with the polystyrene, the end block modifier having a glass transition temperature Tg higher than 60°

C., a MMAP cloud point<

30°

C. and a weight average molecular weight Mw in the range from 2,000 to 50,000; and

,

at least one additive to enhance useful life of the composition.

2. The compositon of claim 1 wherein the propylene has a melt flow rate of from 5 to 100 gm/10 min as measured at 230°

C. under a load of 2.16 kg in accordance with ASTM D1238; and

the end block modifier has a Mw in the range from about 10,000 to 20,000.

3. The composition of claim 2 wherein only the first HSBC is present and it has a number average molecular weight in the range from about 60,000 to 125,000.

4. The composition of claim 2 wherein both, first and second HSBCs are present, the first HSBC is present in a major amount relative to the second, and the second HSBC is hydrogenated poly(styrene-b-isoprene/butadiene-b-styrene) (SEEPS) having a number average molecular weight in the range from about 60,000 to 100,000.

5. The composition of claim 4 wherein at least a portion of the hydrogenated poly(styrene-b-isoprene/butadiene-b-styrene) (SEEPS) present is high vinyl.

6. The composition of claim 2, when injection molded, has tensile strength in the range from about 4.13 to 8.96 MPa (600 to 1300 psi);

tear strength in the range from about 21 to 52.6 N/mm (120 to 300 lbs/in);

softness in the range from about 45 Shore A but less than 65 Shore A; and

haze lower than 20%, measured by ASTM D1003 using a BYK Gardner Micro Tri-gloss 4525 meter; and

the aforesaid properties, along with the physical dimensions of a molded article, remain substantially unchanged after immersion of the article in boiling water for 1 hour.

7. The composition of claim 6 wherein

blend (b) has a major amount by weight of SEBS and a minor amount of SEEPS with a resultant effective Mn in the range from about 60,000 to lower than 130,000;

25 to 50 parts by weight of polypropylene having a melt flow rate of from 10 to 50 gm/10 min as measured at 230°

C. under a load of 2.16 kg in accordance with ASTM D1238; and

remaining ingredients of the composition include

45 to 90 parts by weight of a substantially colorless hydrocarbon oil having a kinematic viscosity at 40°

C. in the range from 10 to 1000 mm²/sec.;

5 to 20 parts by weight of the end block modifier; and

,

one or more additives including a nucleating agent to control the size of domains, and a stabilizer to enhance the useful life of the molded product.

8. The composition of claim 2 wherein polystyrene domains are enriched with a vinylaromatic end block modifier having a Tg in the range from 80°

C. to 120°

C.

9. A recyclable, thermoformed, substantially clear and soft, shaped article comprising,

a thermoformed blend consisting essentially of at least one triblock copolymer selected from the group consisting of (a) a substantially colorless hydrogenated first styrene-conjugated diene-styrene block copolymer (HSBC) derived by hydrogenation of a triblock copolymer selected from the group consisting of high vinyl (styrene-butadiene-styrene) (SBS), high vinyl (styrene-isoprene-styrene) (SIS) and high vinyl (styrene-isoprene/butadiene-styrene) (SI/BS) to yield polystyrene-b-poly(ethylene/butylene)-b-polystyrene (high vinyl SEBS), polystyrene-b-poly(ethylene/propylene-3-methylbutene)-b-polystyrene (SEPS), and “

polystyrene-b-poly(ethylene-ethylene/propylene)-b-polystyrene (SEEPS), respectively, each triblock having at least 51 mole percent of the butadiene midblock polymerized at the 1,2-position, and/or at least 51 mole percent of the isoprene polymerized at the 3,4-position, wherein (a) has a resultant effective number average molecular weight (Mn) measured by gas permeation chromatography (GPC), lower than 130,000; and

(b) a blend of (a) with a second substantially colorless SEEPS present in a minor proportion relative to the first HSBC (a), wherein the second SEEPS is optionally high vinyl and (b) has a resultant effective number average molecular weight (Mn) measured by gas permeation chromatography (GPC), lower than 130,000;

a minor proportion by weight, relative to the amount of (a) or the combined amount of (a) and (b), of a polyolefinic modifier providing a continuous phase in the TPE, the polyolefinic modifier being selected from the group consisting of polypropylene homopolymer, and a copolymer of propylene with another lower olefin having from 2 to 6 carbon atoms, the modifier having a melt viscosity in the range from 1 to 150 gm/10 min as measured at 230°

C. under a load of 2.16 kg in accordance with ASTM D1238;

a minor proportion by weight, relative to the amount of (a) or the combined amount of (a) and (b), of a substantially colorless plasticizer or softening agent compatible with rubbery phases of the foregoing;

a minor proportion by weight relative to either (a), or (a) and (b), of an end block modifier which associates with the polystyrene, the end block modifier having a glass transition temperature Tg higher than 60°

C., a MMAP cloud point<

30°

C. and a weight average molecular weight Mw in the range from 2,000 to 50,000; and

,

at least one additive to enhance the useful life of the shaped article.

10. The article of claim 9 having a shape mouthable by an infant, tensile strength in the range from about 4.13 to 8.96 MPa (600 to 1300 psi);

tear strength in the range from about 21 to 52.6 N/mm (120 to 300 lbs/in);

softness in the range from about 45 Shore A but less than 65 Shore A; and

haze lower than 20%, measured by ASTM D1003 using a BYK Gardner Micro Tri-gloss 4525 meter; and

the aforesaid properties, along with the physical dimensions of a molded article, remain substantially unchanged after immersion of the article in boiling water for 1 hour.

11. The article of claim 10 including a nipple body having the general shape of an inverted cylindrical truncated cone and including an integrally formed teat with an upper wall and annular flange at the base of the teat, the inner periphery of the flange being integrally joined to the teat with a smooth gently flaring curved wall.

12. The article of claim 11 wherein the teat has a central through-aperture in the teat'"'"'s upper wall.

13. The article of claim 11 wherein the flange is integrally formed with an arcuate teething ring having a generally circular cross-section.

14. A method for preparing a thermoplastic article, comprising,

blending together at least one triblock copolymer selected from the group consisting of

(a) a substantially colorless hydrogenated first styrene-conjugated diene-styrene block copolymer (HSBC) derived by hydrogenation of a triblock copolymer selected from the group consisting of high vinyl (styrene-butadiene-styrene) (SBS), high vinyl (styrene-isoprene-styrene) (SIS) and high vinyl (styrene-isoprene/butadiene-styrene) (SI/BS) to yield polystyrene-b-poly(ethylene/butylene)-b-polystyrene (high vinyl SEBS), polystyrene-b-poly(ethylene/propylene-3-methylbutene)-b-polystyrene (SEPS), and “

polystyrene-b-poly(ethylene-ethylene/propylene)-b-polystyrene (SEEPS), respectively, each triblock having at least 51 mole percent of the butadiene midblock polymerized at the 1,2-position, and/or at least 51 mole percent of the isoprene polymerized at the 3,4-position, wherein (a) has a resultant effective number average molecular weight (Mn) measured by gas permeation chromatography (GPC), lower than 130,000; and

(b) a blend of (a) with a second substantially colorless SEEPS present in a minor proportion relative to the first HSBC (a), wherein the second SEEPS is optionally high vinyl and (b) has a resultant effective number average molecular weight (Mn) measured by gas permeation chromatography (GPC), lower than 130,000;

a minor proportion by weight, relative to the amount of (a) or the combined amount of (a) and (b), of a polyolefinic modifier providing a continuous phase in the TPE, the polyolefinic modifier being selected from the group consisting of polypropylene homopolymer, and a copolymer of propylene with another lower olefin having from 2 to 6 carbon atoms, the modifier having a melt viscosity in the range from 1 to 150 gm/10 min as measured at 230°

C. under a load of 2.16 kg in accordance with ASTM D1238;

a minor proportion by weight, relative to the amount of (a) or the combined amount of (a) and (b), of a substantially colorless plasticizer or softening agent compatible with rubbery phases of the foregoing;

a minor proportion by weight relative to either (a), or (a) and (b), of an end block modifier which associates with the polystyrene, the end block modifier having a glass transition temperature Tg higher than 60°

C., a MMAP cloud point<

30°

C. and a weight average molecular weight Mw in the range from 2,000 to 50,000; and

,

at least one additive to enhance useful life of the article; and

,

thermoforming the blend at a temperature above the melt flow temperature of the blend.