Thermoplastic resin foam and production process thereof

Abstract

Disclosed is a die plate for a die block having a coat-hanger-shaped flow path for extruding a molten foamable thermoplastic resin in a form of a sheet. The die plate is for arrangement on a downstream side of the coat-hanger-shaped flow path to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction. The die plate is provided with a multiplicity of delivery apertures. In the delivery apertures, the delivery apertures in opposite side regions have a diameter greater than a diameter which the delivery apertures in a center region have. A die unit composed of a die block, which has a multiple bifurcated manifold terminating in plural coat-hanger-shaped flow paths at downward ends thereof, and a like plural number of similar die plates as described above; a process for producing a wide thermoplastic resin foam by using the die unit; and the wide thermoplastic resin foam are also disclosed.

1 . A die plate for a die block having a coat-hanger-shaped flow path for extruding a molten foamable thermoplastic resin in a form of a sheet, said die plate being to be arranged on a downstream side of said coat-hanger-shaped flow path to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction, wherein:
 said die plate is provided with a multiplicity of delivery apertures, and   in said delivery apertures, the delivery apertures in opposite side regions have a diameter greater than a diameter which the delivery apertures in a center region have.   
   
   
       2 . A die plate according to  claim 1 , wherein the ratio (α/β) of the diameter (α) of said delivery apertures in said opposite side regions to the diameter (β) of said delivery apertures in said center region is 1.05 to 1.40. 
   
   
       3 . A die plate according to  claim 1 , wherein said delivery apertures in said opposite side regions are located within ranges of 30%, based on a width of said die plate, from opposite side edges of said die plate. 
   
   
       4 . A die plate according to  claim 1 , wherein the percentage of a minimum resin delivery rate per delivery aperture based on a maximum resin delivery rate per delivery aperture is 80% to 100%. 
   
   
       5 . A die plate according to  claim 1 , wherein said delivery apertures are arranged in horizontal arrays. 
   
   
       6 . A die plate according to  claim 1 , wherein boundary regions are arranged between said opposite side regions and said center region, respectively, and the delivery apertures in said opposite side regions, the delivery apertures in said boundary regions and the delivery apertures in said center region satisfy the following equation:
   α>γ>β   
     wherein
 α: Diameter of said delivery apertures in said opposite side regions, 
 β: Diameter of said delivery apertures in said center region, and 
 γ: Diameter of said delivery apertures in said boundary regions. 
 
   
   
       7 . An elongated die plate for a die block having plural coat-hanger-shaped flow paths for extruding a molten foamable thermoplastic resin in a form of a wide sheet, said elongated die plate being to be arranged on downstream sides of said coat-hanger-shaped flow paths to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction on downstream sides of said coat-hanger-shaped flow paths, comprising a like plural number of die plates as defined in  claim 1  integrated in said width direction such that said plural number of die plates correspond to said coat-hanger-shaped flow paths, respectively. 
   
   
       8 . A die unit composed of a die block and plural die plates, said die block having a multiple bifurcated manifold terminating in a like plural number of coat-hanger-shaped flow paths at downward ends thereof to permit extrusion of a molten foamable thermoplastic resin in a form of a wide sheet, and said die plates being to be arranged corresponding to said respective coat-hanger-shaped flow paths on downstream sides of said coat-hanger-shaped flow paths to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction on said downstream sides of said coat-hanger-shaped flow paths, wherein:
 said die plates are each provided with a multiplicity of delivery apertures, and   in said delivery apertures, the delivery apertures in opposite side regions have a diameter greater than a diameter which the delivery apertures in a center region have.   
   
   
       9 . A die unit according to  claim 8 , wherein in each of said die plates, the ratio (α/β) of the diameter (α) of said delivery apertures in said opposite side regions to the diameter (β) of said delivery apertures in said center region is 1.05 to 1.40. 
   
   
       10 . A die unit according to  claim 8 , wherein in each of said die plates, said delivery apertures in said opposite side regions are located within ranges of 30%, based on a width of said die plate, from opposite side edges of said die plate. 
   
   
       11 . A die unit according to  claim 8 , wherein in each of said die plates, the percentage of a minimum resin delivery rate per delivery aperture based on a maximum resin delivery rate per delivery aperture is 80% to 100%. 
   
   
       12 . A die unit according to  claim 8 , wherein in each of said die plates, said delivery apertures are arranged in horizontal arrays. 
   
   
       13 . A die unit according to  claim 8 , wherein said coat-hanger-shaped flow paths and said die plates are arranged as many as 2 to 16, respectively. 
   
   
       14 . A die unit according to  claim 8 , wherein said coat-hanger-shaped flow paths each have a width of 130 to 450 mm at downstream ends thereof. 
   
   
       15 . A die unit according to  claim 8 , wherein said plural die plates each satisfy the following conditions:
   D1≧2 mm, and       W 1/ D 1≧10   
     wherein
 D 1 : Total height of said delivery apertures in each die plate, and 
 W 1 : Total width of said plural die plates. 
 
   
   
       16 . A die unit according to  claim 8 , wherein in each of said die plates, boundary regions are arranged between said opposite side regions and said center region, respectively, and the delivery apertures in said opposite side regions, the delivery apertures in said boundary regions and the delivery apertures in said center region satisfy the following equation:
   α>γ>β   
     wherein
 α: Diameter of said delivery apertures in said opposite side regions, 
 β: Diameter of said delivery apertures in said center region, and 
 γ: Diameter of said delivery apertures in said boundary regions. 
 
   
   
       17 . A die unit composed of a die block and plural die plates, said die block having a multiple bifurcated manifold terminating in a like plural number of coat-hanger-shaped flow paths at downward ends thereof to permit extrusion of a molten foamable thermoplastic resin in a form of a wide sheet, and said die plates being to be arranged corresponding to said respective coat-hanger-shaped flow paths on downstream sides of said coat-hanger-shaped flow paths to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction on said downstream sides of said coat-hanger-shaped flow paths, wherein:
 said die plates are each provided with a multiplicity of delivery apertures,   in said delivery apertures, the delivery apertures in opposite side regions have a diameter greater than a diameter which the delivery apertures in a center region have, and   said plural die plates comprise an elongated die plate according to  claim 7 .   
   
   
       18 . A process for producing a wide thermoplastic resin foam by feeding a molten foamable thermoplastic resin through a multiple bifurcated manifold terminating in plural coat-hanger-shaped flow paths at downward ends thereof, extruding the molten foamable thermoplastic resin as foamed strands through said coat-hanger-shaped flow paths, and then coalescing said foamed strands together, wherein:
 said foamed strands are extruded through delivery apertures formed in plural die plates arranged corresponding to said respective coat-hanger-shaped flow paths on downstream sides of said coat-hanger-shaped flow paths; and in each of said plural die plates, the delivery apertures in opposite side regions have a diameter (α) greater than a diameter (β), which the delivery apertures in a center region have, to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction on said downstream sides of said coat-hanger-shaped flow paths.   
   
   
       19 . A process according to  claim 18 , wherein in each of said die plates, the ratio (α/β) of the diameter (α) of said delivery apertures in said opposite side regions to the diameter (β) of said delivery apertures in said center region is 1.05 to 1.40. 
   
   
       20 . A process according to  claim 18 , wherein in each of said die plates, said delivery apertures in said opposite side regions are located within ranges of 30%, based on a width of said die plate, from opposite side edges of said die plate. 
   
   
       21 . A process according to  claim 18 , wherein in each of said die plates, the percentage of a minimum resin delivery rate per delivery aperture based on a maximum resin delivery rate per delivery aperture is 80% to 100%. 
   
   
       22 . A process according to  claim 18 , wherein in each of said die plates, said delivery apertures are arranged in horizontal arrays. 
   
   
       23 . A process according to  claim 18 , wherein in each of said die plates, boundary regions are arranged between said opposite side regions and said center region, respectively, and the delivery apertures in said opposite side regions, the delivery apertures in said boundary regions and the delivery apertures in said center region satisfy the following equation:
   α>γ>β   
     wherein
 α: Diameter of said delivery apertures in said opposite side regions, 
 β: Diameter of said delivery apertures in said center region, and 
 γ: Diameter of said delivery apertures in said boundary regions. 
 
   
   
       24 . A process for producing a wide thermoplastic resin foam by feeding a molten foamable thermoplastic resin through a multiple bifurcated manifold terminating in plural coat-hanger-shaped flow paths at downward ends thereof, extruding the molten foamable thermoplastic resin as foamed strands through said coat-hanger-shaped flow paths, and then coalescing said foamed strands together, wherein:
 said foamed strands are extruded through delivery apertures formed in plural die plates arranged corresponding to said respective coat-hanger-shaped flow paths on downstream sides of said coat-hanger-shaped flow paths; and in each of said plural die plates, the delivery apertures in opposite side regions have a diameter (α) greater than a diameter (β), which the delivery apertures in a center region have, to make a flow rate of the molten foamable thermoplastic resin uniform in a width direction on said downstream sides of said coat-hanger-shaped flow paths; and   said plural die plates comprise an elongated die plate according to  claim 7 .   
   
   
       25 . A wide thermoplastic resin foam having an expansion ratio of at least 10 times, a width of 500 mm to 2,500 mm, a thickness of at least 5 mm and a width/thickness ratio of at least 10, and the percentage of a minimum thickness of said foam being at least 90% based on a maximum thickness of said foam.