Foamed resin article

Abstract

The present invention relates to a method for producing a foamed article by which a foamed article having a high expansion ratio, having uniform fine cells in a high closed cell ratio and capable of being recycled, which is utilizable as heat insulating materials for construction, cushioning materials for wrapping, cushioning floats for ships, floats for sports and leisure and the like, can be obtained readily and safely using a clean inorganic gas as a foaming agent, and to a foamed article obtained by the method. That is, the present invention provides a method for producing a foamed resin article comprising a melting step of feeding a thermoplastic resin into an extruder and heating it to melt, a kneading step of mixing an inorganic gas with the thermoplastic resin in the extruder to produce a kneaded material, and a foaming step of discharging the kneaded material from a mold having a tubular channel mounted to the end of the extruder to form the foamed article, wherein extrusion molding is carried out within the range where a numeric X, which is defined by the following expression: X= 100 P +3.5 H where a resin feeding pressure of the thermoplastic resin from the extruder to the mold is represented by H (kgf/cm 2 ) and an expansion ratio is represented by P, and the resin feeding pressure H satisfy the following expressions simultaneously: 780≦X≦4000, and 80≦H≦1000 and the like.

What is claimed is:  
     
         1 . A method for producing a foamed resin article comprising a melting step of feeding a thermoplastic resin into an extruder and heating it to melt, a kneading step of mixing an inorganic gas with the thermoplastic resin in the extruder to produce a kneaded material, and a foaming step of discharging the kneaded material from a mold having a tubular channel mounted to the end of the extruder to form the foamed article, wherein extrusion molding is carried out within the range where a numeric X, which is defined by the following expression:  
         X= 100 P+ 3.5 H    
       where a resin feeding pressure of the thermoplastic resin from the extruder to the mold is represented by H (kgf/cm 2 ) and an expansion ratio is represented by P, and the resin feeding pressure H satisfy the following expressions simultaneously:  
       780≦X≦4000, and 80≦H≦1000  
     
     
         2 . The method for producing a foamed resin article according to  claim 1 , wherein a numeric Y, which is defined by the following expression:  
         Y= 100 P+ 3.5( H− 10 G )  
       where the amount of the inorganic gas supplied to 100 g of the thermoplastic resin is represented by G g, satisfies the following expression:  
       760≦Y≦4000  
     
     
         3 . The method for producing a foamed resin article according to  claim 1  or 2, wherein the shape of the tip (lip) of the mold having a tubular channel satisfies the following expressions simultaneously:  
       0.1≦L≦1; 0.1≦tan θ≦6; and  
       5≦T≦500  
       where a lip gap, a taper angle, and a taper land are represented by L (mm), θ, and T (mm), respectively.  
     
     
         4 . The method of producing a foamed resin article according to any one of  claims 1  to  3 , wherein, as for the shape of the tip (lip) of the mold having a tubular channel, an angle α which is formed by the center axis of the core of the lip and the taper land satisfies the following expression:  
       0.1≦tan α≦6  
     
     
         5 . The method for producing a foamed resin article according to any one of  claims 1  to  4 , wherein the inorganic gas is carbon dioxide.  
     
     
         6 . The method for producing a foamed resin article according to any one of  claims 1  to  5 , wherein the thermoplastic resin is a propylene-based polymer.  
     
     
         7 . The method for producing a foamed resin article according to  claim 6 , wherein the propylene-based polymer is a polymer which is obtained by continuous production comprising polymerizing, in the first stage, monomers mainly composed of propylene to produce a crystalline propylene-based polymer (A) having a limiting viscosity of 5 dl/g or more and successively polymerizing, in the second stage, monomers mainly composed of propylene to produce a crystalline propylene-based polymer (B) having a limiting viscosity of less than 3 dl/g and which is composed of the crystalline propylene-based polymer (A) and the crystalline propylene-based polymer (B) wherein a content of the polymer (A) is in the range of 0.05% by weight or more and less than 35% by weight, a limiting viscosity of the whole polymer is less than 3 dl/g, and Mw/Mn is less than 10.  
     
     
         8 . The method for producing a foamed resin article according to  claim 7 , wherein the propylene-based polymer satisfies the following expression:  
         W   A ≧400 ×EXP (−0.6[η A ])  
       where [η A ] (dl/g) is the limiting viscosity of the crystalline propylene-based polymer (A) and W A  (% by weight) is the crystalline propylene-based polymer (A) content in the whole polymer.  
     
     
         9 . The method for producing a foamed resin article according to  claim 7  or  8 , wherein, the propylene-based polymer is composed of the crystalline propylene-based polymer (A) and the crystalline propylene-based polymer (B), each of them being a propylene homopolymer, a random copolymer of propylene and 10% by weight or less of ethylene, a random copolymer of propylene and 30% by weight or less of butene, or a random terpolymer of propylene, 10% by weight or less of ethylene and 30% by weight or less of butene.  
     
     
         10 . The method for producing a foamed resin article according to any one of  claims 7  to  9 , wherein, as for the propylene-based polymer, the crystalline propylene-based polymer (A) has a limiting viscosity [η A ] of 7 dl/g or more.  
     
     
         11 . The method for producing a foamed resin article according to any one of  claims 7  to  10 , wherein, as for the propylene-based polymer, the crystalline propylene-based polymer (A) contains ethylene, as a comonomer, in a proportion of 1% by weight or more and 10% by weight or less.  
     
     
         12 . The method for producing a foamed resin article according to any one of  claims 7  to  11 , wherein the propylene-based polymer is one produced continuously by a production method wherein a catalyst containing Ti, Mg and halogen as essential components is used, the polymerization rate of the crystalline propylene-based polymer (A) in the first step is 2000 g or more per gram of the catalyst per hour and the polymerization rate of the crystalline propylene-based polymer (B) in the second step is 4000 g or more per gram of the catalyst per hour.  
     
     
         13 . A foamed resin article which is obtained by the method of any one of  claims 1  to  12 .