Macrocellular polyolefin foam having a high service temperature for acoustical applications

Abstract

Macrocellular polyolefin foams that can withstand temperatures above 110° C. are described for use in sound absorption and insulation applications, especially in elevated temperature and/or moist environments. These foams have a large cell size (≧1.5 mm), are open or closed-cell foams, and preferably have at least one perforation per square centimeter and/or a density less than 25 kg/m 3 . They are obtainable by extruding a high melt strength (HMS) polypropylene resin (PP), or preferably a blend of a HMS PP resin and a free radical polymerized ethylene polymer present in the blend in a weight ratio of at least 35:65, optionally another polymer such as a substantially random interpolymer, a cell size enlarging agent such a glycerol monostearate, an antioxidant, carbon black and/or flame retardant additives, using a volatile organic compound, e.g. isobutane, as blowing agent.

What is claimed is:  
     
         1 . A cellular thermoplastic polymer foam having an average cell size of at least about 1.5 mm, a density not greater than about 300 kg/m 3 , an average sound absorption coefficient of at least about 0.2, and a heat distortion temperature of at least about 110 degrees Celsius, wherein the thermoplastic polymer comprises: 
 (A) at least one predominantly isotactic, propylene polymer having a tan δ value not greater than 1.5 and optionally    (B) at least one ethylene polymer produced via a free radical process blended with the propylene polymer,    wherein the thermoplastic polymer foam satisfies at least one of the following two conditions:    the thermoplastic polymer comprises ethylene polymer blended with the propylene polymer and the weight ratio of the propylene polymer (A) to the ethylene polymer (B) is at least about 35:65 and/or    the foam has at least one surface, the at least one surface having defined therein a multiplicity of perforation channels extending from the at least one surface into the foam such that there is an average of at least one perforation channel per 10 square centimeters of the at least one surface.    
     
     
         2 . The foam of  claim 1  having an open cell content of less than 50 percent measured according to ASTM D2856-A.  
     
     
         3 . The foam of  claim 2  having an open cell content not greater than 20 percent measured according to ASTM D2856-A.  
     
     
         4 . The foam of  claim 1  wherein the foam has the perforation channels and the perforation channels have an average diameter at the at least one surface of 0.1 mm.  
     
     
         5 . The foam of  claim 4  wherein the at least one surface has an average of at least 10 perforation channels per 10 square centimeters extending from the at least one surface into the foam.  
     
     
         6 . The foam of  claim 1  having an average cell size of at least about 5 mm and a density not greater than about 60 kg/m 3 .  
     
     
         7 . The foam of  claim 1  having an average sound absorption coefficient of at least about 0.3.  
     
     
         8 . The foam of  claim 1  having a heat distortion temperature of at least about 140 degrees Celsius.  
     
     
         9 . The foam of  claim 1  having a water absorption not more than 10 percent by volume measured according to European Norm 12088 at 50 degrees Celsius based on a test period of 14 days exposure.  
     
     
         10 . The foam of  claim 1 , wherein the thermoplastic polymer comprises ethylene polymer blended with the propylene polymer and the ethylene polymer is selected from the group consisting of low density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), and ethylene-acrylic acid copolymer (EAA).  
     
     
         11 . The foam of  claim 1 , wherein the propylene polymer has (1) a tan δ value not greater than 1.0, (2) a melt tension of at least 15 centiNewtons (cN), and/or (3) a melt strength of at least 25 centiNewtons (cN).  
     
     
         12 . The foam of  claim 1 , wherein the propylene polymer has a branching index less than 0.9.  
     
     
         13 . The foam of  claim 1 , wherein the propylene polymer comprises at least 90 weight-percent propylene monomer-derived units.  
     
     
         14 . The foam of  claim 10 , wherein the at least one ethylene polymer is low density polyethylene.  
     
     
         15 . The foam of  claim 14 , wherein the at least one surface has an average of at least 10 perforation channels per 10 square centimeters extending from the at least one surface into the foam.  
     
     
         16 . The foam of  claim 14 , wherein the weight ratio of the propylene polymer (A) to the ethylene polymer (B) is at least about 35:65.  
     
     
         17 . The foam of  claim 15 , wherein the polymer foam has an average cell size of at least about 5 mm and a density not greater than 60 kg/m 3 .  
     
     
         18 . The foam of  claim 16 , wherein the polymer foam has an average cell size of at least about 5 mm and a density not greater than 60 kg/m 3 .  
     
     
         19 . The foam of  claim 1 , wherein the polymer foam has a density less than 25 kg/m 3 .