Heat-shrinkable foam films

Abstract

To provide a foamed film or multilayer foamed film excellent in heat insulating properties, a heat shrinkable foamed film or heat shrinkable multilayer foamed film made thereof, a heat shrinkable label, and a container covered therewith. A styrene foamed film characterized by having at least one foamed layer which contains a resin composition comprising from 20 to 100 parts by mass of the following (a) and from 0 to 80 parts by mass of the following (b) and which has a thickness of from 30 to 200 μm and a specific gravity of from 0.3 to 0.9: (a) a block copolymer wherein the ratio of a vinyl aromatic hydrocarbon to a conjugated diene is from 50/50 to 90/10, (b) at least one vinyl aromatic hydrocarbon polymer selected from the following (i) to (v): (i) a block copolymer of a vinyl aromatic hydrocarbon with a conjugated diene, (ii) a vinyl aromatic hydrocarbon polymer, (iii) a copolymer of a vinyl aromatic hydrocarbon with (meth)acrylic acid, (iv) a copolymer of a vinyl aromatic hydrocarbon with a (meth)acrylate, and (v) a rubber-modified styrene polymer.

1 . A foamed film characterized by having at least one foamed layer which contains a resin composition comprising from 20 to 100 parts by mass of the following (a) and from 0 to 80 parts by mass of the following (b) and which has a thickness of from 30 to 200 μm and a specific gravity of from 0.3 to 0.9: 
 (a) a block copolymer wherein the ratio of a vinyl aromatic hydrocarbon to a conjugated diene is from 50/50 to 90/10,    (b) at least one vinyl aromatic hydrocarbon polymer selected from the following (i) to (v):    (i) a block copolymer of a vinyl aromatic hydrocarbon with a conjugated diene,    (ii) a vinyl aromatic hydrocarbon polymer,    (iii) a copolymer of a vinyl aromatic hydrocarbon with (meth)acrylic acid,    (iv) a copolymer of a vinyl aromatic hydrocarbon with a (meth)acrylate, and    (v) a rubber-modified styrene polymer.    
     
     
         2 . The foamed film according to  claim 1 , wherein the uniaxial elongation viscosity η at 120° C. of the resin composition satisfies the following condition:  
         2.5>η1.5/η1>1.1  η1: elongation viscosity at Hencky strain 1    η1.5: elongation viscosity at Hencky strain 1.5    
     
     
         3 . The foamed film according to  claim 1 , wherein the above (a) is a block copolymer of the following (1) and (2): 
 (1) the mass ratio of the vinyl aromatic hydrocarbon to the conjugated diene is from 60/40 to 90/10,    (2) the mass ratio of a group of vinyl aromatic hydrocarbon polymer blocks having a weight average molecular weight of less than 5,000 to a group of vinyl aromatic hydrocarbon polymer blocks having a weight average molecular weight of at least 5,000, is from 60/40 to 90/10.    
     
     
         4 . The foamed film according to any one of  claims 1  to  3 , wherein (a) the block copolymer is a styrene/butadiene block copolymer, and (b) the vinyl aromatic hydrocarbon polymer is at least one polymer selected from the group consisting of a polystyrene, a styrene/methacrylic acid copolymer, a styrene/methyl methacrylate copolymer, a styrene/n-butyl acrylate copolymer, a styrene/n-butyl acrylate/methyl methacrylate copolymer and an impact-resistant polystyrene.  
     
     
         5 . A foamed multilayer film having at least one foamed layer as defined in any one of  claims 1  to  4  and at least one non-foamed thermoplastic resin layer.  
     
     
         6 . The foamed multilayer film according to  claim 5 , wherein at least one outer layer in the case of three or more layers, or one layer in the case of two layers, is a layer formed from the following (b′) vinyl aromatic hydrocarbon polymer: 
 (b′) at least one vinyl aromatic hydrocarbon polymer selected from the following (i′) to (v′):    (i′) a block copolymer of a vinyl aromatic hydrocarbon with a conjugated diene,    (ii′) a vinyl aromatic hydrocarbon polymer,    (iii′) a copolymer of a vinyl aromatic hydrocarbon with (meth)acrylic acid,    (iv′) a copolymer of a vinyl aromatic hydrocarbon with a (meth)acrylate, and    (v′) a rubber-modified styrene polymer.    
     
     
         7 . A heat shrinkable foamed film obtained by stretching the foamed film or the foamed multilayer film as defined in any one of  claims 1  to  6 .  
     
     
         8 . A heat shrinkable foamed multilayer film having a heat shrinkable film laminated on the foamed film or the foamed multilayer film as defined in any one of  claims 1  to  7 .  
     
     
         9 . The heat shrinkable foamed multilayer film according to  claim 7  or  8 , wherein the heat shrinkage is at least 10% at 70° C. in 10 seconds.  
     
     
         10 . The heat shrinkable foamed multilayer film according to any one of  claims 7  to  9 , wherein the natural shrinkage is at most 2.5% at 40° C. for seven days.  
     
     
         11 . A heat shrinkable label made of the heat shrinkable foamed multilayer film as defined in any one of  claims 7  to  10 .  
     
     
         12 . A container covered with the heat shrinkable label as defined in  claim 11.