Compositions of expandable vinyl aromatic polymers with an improved thermal insulation capacity, process for their production and expanded articles obtained therefrom

Abstract

Expandable vinyl aromatic polymers comprising: —a matrix obtained by polymerizing 50-100% by weight of one or more vinyl aromatic monomers and 0-50% by weight of at least one co-polymerizable monomer; —1-10% by weight, calculated with respect to polymer (a), of an expanding agent embedded in the polymeric matrix; 0-25% by weight, calculated with respect to polymer (a), of a filler comprising carbon coke having an average diameter of between 0.5 and 100 μm, with a surface area, measured according to ASTM D-3037/89, ranging from 5 to 200 m 2 /g; 0.05-10% by weight, calculated with respect to polymer (a), of expanded graphite in particle form, with a particle average diameter (size) ranging from 1 to 30 μm, a surface area, measured according to ASTM D-3037/89, ranging from 5 to 500 m 2 /g and a density ranging from 1.5 to 5 g/cm 3 .

1 . Expandable vinyl aromatic polymer compositions comprising:
 a) a polymeric matrix prepared by polymerizing a base comprising 50-100% by weight of one or more vinyl aromatic monomers and 0-50% by weight of at least one copolymerisable monomer;   b) 1-10% by weight, calculated on polymer (a), of an expanding agent embedded in the polymeric matrix; and an athermanous filler comprising:   c) 0-25% by weight, calculated on polymer (a), of particulate carbon coke with mean particle diameter (d 50 ) (size) in the range of from 0.5 to 100 μm, and surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 200 m 2 /g; and   d) 0.05-10% by weight, calculated on polymer (a), of particulate expanded graphite with mean particle diameter (d 50 ) (size) in the range of from 1 to 30 μm and surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 500 m 2 /g,   
       provided that when carbon coke is 0%, the mean particle diameter of expanded graphite is in the range of from 1 to 10 μm. 
     
     
         2 . Compositions according to  claim 1 , wherein the athermanous filler comprises up to 5% by weight, calculated on polymer (a), of carbon black. 
     
     
         3 . Compositions according to  claim 2 , wherein the carbon black has a mean particle size (d 50 ) in the range of from 10 to 500 nm and a surface area in the range of from 5 to 40 m 2 /g. 
     
     
         4 . Compositions according to anyone of the preceding claims comprising from 0.1 to 8% by weight, with respect to polymer (a), of a brominated self-extinguishing additive and from 0.05 to 2% by weight, still based on polymer (a), of a synergist containing at least one labile C—C or O—O bond. 
     
     
         5 . Compositions according to anyone of the preceding claims, wherein the expanded graphite has a density in the range of from 1.5 to 5 g/cm 3 . 
     
     
         6 . Expanded articles obtainable with the expandable vinyl aromatic polymer compositions according to anyone of the preceding claims having a density in the range of from 5 to 50 g/l and a thermal conductivity in the range of from 25 to 50 mW/mK. 
     
     
         7 . Extruded expanded sheets of vinyl aromatic polymers comprising a cellular matrix of a vinyl aromatic polymer having a density in the range of from 10 to 200 g/l, a mean cell size in the range of from 0.01 to 1.00 mm and containing from 0.1 to 35% by weight of said athermanous filler comprising said particulate coke with mean particle diameter (d 50 ) in the range of from 0.5 to 100 μm and surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 200 m 2 /g and said expanded particulate-form graphite with mean particle diameter (d 50 ) (size) in the range of from 1 to 30 μm, surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 500 m 2 /g. 
     
     
         8 . Extruded sheets according to  claim 7 , wherein said athermanous filler comprises up to 5% by weight, calculated on the polymer, of said carbon black. 
     
     
         9 . Extruded sheets according to  claim 7  or  8 , wherein the expanded graphite has a density in the range of from 1.5 to 5 g/cm 2 . 
     
     
         10 . Process for preparing the expandable vinyl aromatic polymer compositions, in the form of beads or granules, according to  claims 1  to  5 , which comprises polymerizing in an aqueous suspension one or more vinyl aromatic monomers, possibly together with at least one polymerisable comonomer in an amount up to 50% by weight, in the presence of said athermanous filler comprising said particulate coke with mean particle diameter (size) in the range of from 0.5 to 100 μm and a surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 200 m 2 /g and said expanded particulate-form graphite with mean particle diameter (d 50 ) (size) in the range of from 1 to 30 μm, surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 500 m 2 /g and at least in the presence of a peroxide radical initiator and an expanding agent added before, during or at the end of the polymerization. 
     
     
         11 . Process according to  claim 10 , wherein said athermanous filler also comprises up to 5% by weight, calculated on the polymer, of said carbon black. 
     
     
         12 . Process according to  claim 10  or  11 , wherein the viscosity of the reacting solution of vinyl aromatic monomers, to be suspended in water, is increased by dissolving some vinyl aromatic polymer in said solution, up to a concentration in the range of from 1 to 30% by weight with respect to the weight of the vinyl aromatic monomers. 
     
     
         13 . Process according to  claim 10  or  11 , wherein the viscosity of the reacting solution of vinyl aromatic monomers, to be suspended in water, is increased by prepolymerizing the monomer, or monomer mixture in bulk, until a polymer concentration in the range of from 1 to 30% by weight is obtained. 
     
     
         14 . Process according to anyone of  claims 10  to  13 , wherein the expanded graphite has a density in the range of from 1.5 to 5 g/cm 3 . 
     
     
         15 . Process according to anyone of  claims 10  to  14 , wherein at the end of the polymerization substantially spherical expandable polymer beads/granules having a mean diameter in the range of from 0.2 to 3 mm are obtained, said athermanous filler being homogenously dispersed therein. 
     
     
         16 . Process for preparing through continuous bulk polymerization the expandable vinyl aromatic polymer compositions, as beads or granules, according to  claims 1  to  5 , which comprises the following series of steps:
 i. mixing a vinyl aromatic polymer in granules or in powder form or already in the molten state, with mean molecular weight MW in the range of from 50.000 to 250.000, with said athermanous filler comprising said particulate coke, with mean particle diameter (d 50 ) in the range of from 0.5 to 100 μm and a surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 200 m 2 /g and said expanded particulate-form graphite with mean particle diameter (d 50 ) (size) in the range of from 1 to 30 μm, surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 500 m 2 /g and with possible further additives; 
 ii. possibly, if it is not already in the molten state, bringing the polymer mixture to a temperature higher than the melting point of the vinyl aromatic polymer; 
 iii. incorporating the expanding agent and possible other additives, such as said extinguishing system, in the molten polymer; 
 iv. mixing the polymer composition thus obtained by means of static or dynamic mixing elements; and 
 v. granulating the composition thus obtained in a device comprising a die, a cutting chamber and a cutting system. 
 
     
     
         17 . Process according to  claim 16 , wherein the athermanous filler also comprises up to 5% by weight, calculated on the final polymer, of said carbon black. 
     
     
         18 . Process according to  claim 16  or  17 , wherein the expanded graphite has a density in the range of from 1.5 to 5 g/cm 3 . 
     
     
         19 . Process according to  claim 16 ,  17  or  18 , wherein at the end of granulation substantially spherical expandable polymer beads/granules with mean diameter in the range of from 0.2 to 3 mm are obtained, said athermanous filler being homogenously dispersed therein. 
     
     
         20 . Process according to anyone of  claims 10  to  19 , wherein it is possible to incorporate at least said athermanous additives in a master-batch, based on a vinyl aromatic polymer of average molecular weight in the range of from 50.000 to 250.000. 
     
     
         21 . Process according to  claim 20 , wherein the content of athermanous filler, comprising said coke, said expanded graphite and possibly said carbon black, is in the range of from 15 to 60% by weight in the master-batch. 
     
     
         22 . Process according to anyone of claims from 10 to 15, wherein the pellet master-batch is dissolved into the vinyl aromatic monomer. 
     
     
         23 . Process according to anyone of claims from 16 to 19, wherein the pellet master-batch is mixed with the granulated material or with the molten state polymer from the solution polymerization. 
     
     
         24 . Process according to anyone of claims from 16 to 19, wherein the pellet master-batch is dissolved in the vinyl aromatic monomer/solvent mixture before this is fed to the solution polymerization reactor. 
     
     
         25 . Process for producing the extruded expanded vinyl aromatic polymer sheets according to  claim 7 ,  8  or  9 , which comprises:
 a1. mixing a vinyl aromatic polymer in pellet form and at least one athermanous filler comprising of from 0 to 25% by weight, calculated on the polymer, of said particulate coke with mean particle diameter (d 50 ) (size) in the range of from 0.5 to 100 μm and a surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 200 m 2 /g and of from 0.05 to 10% by weight, calculated on the polymer, of said expanded particulate-form graphite with mean particle diameter (d 50 ) (size) in the range of from 1 to 30 μm, surface area, measured according to ASTM D-3037-89 (BET), in the range of from 5 to 500 m 2 /g; 
 b1. heating mixture (a1) to a temperature in the range of from 180 to 250° C. so as to obtain a polymeric melt, which is subjected to homogenization; 
 c1. adding at least an expanding agent and possibly said additives, e.g. said extinguishing system, to the polymeric melt; 
 d1. homogenizing the polymeric melt incorporating the expanding agent; 
 e1. homogenously cooling down the polymeric melt (d1) to a temperature not exceeding 200° C. and not below Tg of the resulting polymer composition; 
 f1. extruding the polymeric melt through a die so as to obtain a polymer expanded sheet. 
 
     
     
         26 . Process according to  claim 25 , wherein said athermanous filler added to the vinyl aromatic polymer comprises up to 5% by weight, calculated on the polymer, of said carbon black. 
     
     
         27 . Process according to  claim 25  or  26 , wherein the expanded graphite has a density in the range of from 1.5 to 5 g/cm 3 . 
     
     
         28 . Process according to anyone of  claims 25  to  27 , wherein the pellet vinyl aromatic polymer is substituted, totally or partially, by the vinyl aromatic polymer compositions, in the form of beads/granules, described or prepared according to anyone of  claims 10  to  24 . 
     
     
         29 . Process according to anyone of  claims 25  to  27 , wherein the pellets of vinyl aromatic polymer are substituted, totally or partially, by vinyl aromatic polymers in which said athermanous filler has been dispersed as either master or as derivatives from post-consumption products.