Process for producing alkenyl aromatic foams using a combination of atmospheric and organic gases and foams produced thereby

Abstract

There is disclosed a process for producing alkenyl aromatic foams utilizing a combination of atmospheric and organic gases as blowing agent, preferably using greater than 30% by weight of atmospheric gas, and preferably also using a predetermined about of a masterbatch mix comprising a styrenic polymer, a rubbery block copolymer, and a solid blowing agent. Also disclosed are alkenyl aromatic foams produced by the process which exhibit increased densities, increased thermoforming capabilities, increased post-expansion properties, and increased retainment of the atmospheric and organic gases.

1. A process for producing a closed-cell polymer foam, said process comprising subjecting a foamable polymer composition comprising: (a) a predominant proportion of an optionally rubber-reinforced alkenyl aromatic polymer; and an additive for (a) comprising  consisting essentially of: (b) alpha-methylstyrene; and (c) a rubbery block copolymer to a temperature sufficient to provide a molten polymer; mixing a non- solid  blowing agent comprised of a combination of atmospheric and organic gases with said molten polymer; heating the mixture to a temperature and applying pressure such that the mixture does not foam; thereafter reducing the temperature of the mixture; and extruding the mixture. 
     
     
       2. A process according to  claim 1 , wherein the optionally rubber reinforced alkenyl aromatic polymer (a) is comprised of styrene. 
     
     
       3. A process according to  claim 1 , wherein the optionally rubber-reinforced alkenyl aromatic polymer (a) is comprised of a copolymer of interpolymer of styrene containing greater than 75 weight pent styrene. 
     
     
       4. A process according to  claim 1 , wherein the optionally rubber-reinforced alkenyl aromatic polymer (a) is comprised of a blend of styrene and a rubbery polymer. 
     
     
       5. A process according to  claim 1 , wherein the alpha-methyl styrene (b) has a Vicat softening temperature of between 45 and 82 at 50° C./hr. rise. 
     
     
       6. A process according to  claim 5 , wherein the alpha-methylstyrene (b) is selected from the group consisting of: a linear homopolymer of alpha-methylstyrene having a molecular weight of about 685, a softening point of about 99° C., and a flash point of about 210° C., a linear homopolymer of alpha-methylstyrene having a molecular weight of about 790, a softening point of about 118° C., and a flash point of about 224° C., and a linear homopolymer of alpha-methylstyrene having a molecular weight of about 960, a softening point of about 141° C., and a flash point of about 246° C. 
     
     
       7. A process according to  claim 1 , wherein the rubbery block copolymer (c) is selected from the group consisting of A-B, A-B-A, A-B-A-B, graft and radial block copolymers. 
     
     
       8. A process according to  claim 7 , wherein the rubbery block copolymer (c) is selected from the group consisting of: a styrene-butadiene-styrene block copolymer having a styrene/rubber ratio of about 31/69 (Kraton D-1101); a styrene-butadiene-styrene block copolymer having a styrene/rubber ratio of about 28/72 (Kraton D-1102); a stryene-isoprene-styrene block copolymer having a styrene/rubber ratio of about 14/86 (Kraton D-1107); a styrene-ethylene/butylene-styrene block copolymer having a styrene/rubber ratio of about 29/71 (Kraton G-1650); a styrene-ethylene/butylene-styrene block copolymer having a styrene/rubber ratio of about 32/68 (Kraton G-1651); a styrene-ethylene/butylene styrene block copolymer having a styrene/rubber ratio of about 29/71 and a ring and ball softening point (ASTME 28-67, 10% by weight in Kaydol oil) of about 141° F. (Kraton G-1652); a styrene-ethylene/butylene-styrene block copolymer having a styrene/rubber ratio of about 13/87 (Kraton G-1657X); a styrene-ethylene/propylene block copolymer having a styrene/rubber ratio of about 37/63 (Kraton G-1701X); and a styrene-ethylene/butylene block copolymer having a styrene/rubber ratio of about 30/70 (Kraton G-1726X). 
     
     
       9. A process according to  claim 8 , wherein the rubbery block copolymer (c) is selected from the group consisting of: a styrene-ethylene/butylene-styrene block copolymer having a styrene/rubber ratio of about 29/71 (Kraton G-1650) and a styrene-ethylene/butylene styrene block copolymer having a styrene/rubber ratio of about 29/71 and a ring and ball softening point (ASTME 28-67, 10% by weight in Kaydol oil) of about 141° F. (Kraton G-1652). 
     
     
       10. A process according to  claim 1 , wherein the  further comprising a blowing agent comprises  comprised of a mixture of (1) one or more solid organic acids and (2) an alkaline metal carbonate or alkaline metal bicarbonate. 
     
     
       11. A process according to  claim 10 , wherein the one or more solid organic acids is selected from the group consisting of oxalic acid, succinic acid, adipic acid, phthalic acid and citric acid. 
     
     
       12. A process according to  claim 10 , wherein the alkaline metal carbonate or alkaline metal bicarbonate is selected from the group consisting of sodium carbonate, potassium carbonate and sodium bicarbonate. 
     
     
       13. A process according to  claim 10 , wherein the alkali:acid equivalent ratios are from about 1:3 to about 3:1. 
     
     
       14. A process according to  claim 13 , wherein the alkali:acid equivalent ratio is from about 0.7:1 to 1.3:1. 
     
     
       15. A process according to  claim 10 , wherein the blowing agent is comprised of a combination of monosodium citrate and sodium bicarbonate. 
     
     
       16. A process according to  claim 15 , wherein the combination of monosodium citrate and sodium bicarbonate are encapsulated in vegetable oil and the alkali:acid equivalent ratio is from about 0.9:1 to about 1.1:1. 
     
     
       17. A process for producing a closed-cell polymer foam, said process comprising subjecting a foamable polymer composition comprising: (a) an optionally rubber-reinforced alkenyl aromatic polymer comprised of a copolymer or interpolymer of styrene-containing greater than 50 weight percent styrene; and an additive for (a) comprising  consisting essentially of: (b) alpha-methylstyrene; and (c) a rubbery block copolymer to a temperature sufficient to provide a molten polymer; mixing a non- solid  blowing agent comprised of a combination of atmospheric and organic gases with said molten polymer; heating the mixture to a temperature and applying pressure such that the mixture does not foam; thereafter reducing the temperature of the mixture; and extruding the mixture. 
     
     
       18. A process for producing a closed-cell polymer foam, said process comprising subjecting a foamable polymer composition comprising: (a) an optionally rubber-reinforced alkenyl aromatic polymer; comprised of a blend of styrene and a rubbery polymer; and an additive for (a) comprising  consisting essentially of: (b) alpha-methylstyrene; and (c) a rubbery block copolymer to a temperature sufficient to provide a molten polymer; mixing a non- solid  blowing agent comprised of a combination of atmospheric and organic gases with said molten polymer; heating the mixture to a temperature and applying pressure such that the mixture does not foam; thereafter reducing the temperature of the mixture; and extruding the mixture.