Polypropylene resin foamed particles, in-mold foam molded body of polypropylene resin, and method for manufacturing same

Abstract

An expanded polypropylene resin particle is obtained from a base material resin having a melting point of 140° C. to 150° C., wherein the base material resin includes a polypropylene resin A including 3 weight % to 15 weight % of 1-butene and having a melting point of 130° C. to 140° C.; and a polypropylene resin B having a melting point of 145° C. to 165° C., and wherein the expanded polypropylene resin particle has an average cell diameter of 100 μm to 340 μm.

What is claimed is: 
     
         1 . An expanded polypropylene resin particle, obtained from a base material resin having a melting point of 140° C. to 150° C., wherein the base material resin comprises:
 a polypropylene resin A comprising 3 weight % to 15 weight % of 1-butene and having a melting point of 130° C. to 140° C.; and 
 a polypropylene resin B having a melting point of 145° C. to 165° C., and 
 wherein the expanded polypropylene resin particle has an average cell diameter of 100 μm to 340 μm. 
 
     
     
         2 . The expanded polypropylene resin particle according to  claim 1 , wherein the polypropylene resin A further comprises 2 weight % to 10 weight % of ethylene. 
     
     
         3 . The expanded polypropylene resin particle according to  claim 1 , wherein the base material resin comprises:
 50 weight % to 70 weight % of the polypropylene resin A; and   30 weight % to 50 weight % of the polypropylene resin B, wherein the polypropylene resin A and the polypropylene resin B together account for 100 weight %.   
     
     
         4 . The expanded polypropylene resin particle according to  claim 1 , wherein the average cell diameter is 120 μm to 250 μm. 
     
     
         5 . The expanded polypropylene resin particle according to  claim 1 , wherein the melting point of the base material resin is 145° C. to 150° C. 
     
     
         6 . The expanded polypropylene resin particle according to  claim 1 , wherein the melting point of the base material resin is 146° C. to 148° C. 
     
     
         7 . The expanded polypropylene resin particle according to  claim 1 , wherein the polypropylene resin B is a propylene-ethylene random copolymer or a propylene-ethylene-1-butene random copolymer. 
     
     
         8 . The expanded polypropylene resin particle according to  claim 1 , wherein the polypropylene resin A is obtained using a Ziegler catalyst. 
     
     
         9 . The expanded polypropylene resin particle according to  claim 1 , wherein
 the expanded polypropylene resin particle is an expanded composite particle comprising an expanded polypropylene resin core layer covered with a polypropylene resin covering layer,   the expanded polypropylene resin core layer is obtained from a base material resin comprising the polypropylene resin A and the polypropylene resin B; and   the polypropylene resin covering layer comprises the polypropylene resin A.   
     
     
         10 . A polypropylene resin in-mold expanded molded product formed by subjecting the expanded polypropylene resin particles according to  claim 1  to in-mold foaming molding. 
     
     
         11 . The polypropylene resin in-mold expanded molded product according to  claim 10 , wherein the polypropylene resin in-mold expanded molded product has a density and a 50%-strained compressive strength satisfying the following:
   [50%-strained compressive strength (MPa)]≧0.0069×[Molded product density (g/L)]+0.018.
   
     
     
         12 . The polypropylene resin in-mold expanded molded product according to  claim 10 , wherein the polypropylene resin in-mold expanded molded product has a density of 20 g/L to 40 g/L. 
     
     
         13 . A method of producing a polypropylene resin in-mold expanded molded product, comprising:
 placing polypropylene resin particles, water, and an inorganic gas foaming agent in a pressure-resistant container, forming a mixture, wherein the polypropylene resin particles is obtained from a base material resin having a melting point of 140° C. to 150° C., the base material resin comprising:   a polypropylene resin A comprising 3 weight % to 15 weight % of 1-butene and having a melting point of 130° C. to 140° C.; and   a polypropylene resin B having a melting point of 145° C. to 165° C.,   dispersing the polypropylene resin particles while stirring the mixture, obtaining a dispersion liquid,   increasing a temperature and a pressure in the pressure-resistant container,   releasing the dispersion liquid from the pressure-resistant container into a region having a pressure lower than the pressure in the pressure-resistant container, producing expanded polypropylene resin particles each having an average cell diameter of 100 μm to 340 μm; and   obtaining the polypropylene resin in-mold expanded molded product by filling a mold with the expanded polypropylene resin particles, and then heating the expanded polypropylene resin particles.   
     
     
         14 . The method according to  claim 13 , wherein the polypropylene resin A comprises 2 weight % to 10 weight % of ethylene. 
     
     
         15 . The method according to  claim 13 , further comprising:
 melting and kneading the polypropylene resin A and the polypropylene resin B in an extruder and obtaining the polypropylene resin particles.   
     
     
         16 . The method according to  claim 13 , further comprising:
 obtaining the polypropylene resin A by polymerization using a Ziegler catalyst.   
     
     
         17 . The method according to  claim 13 , wherein
 the expanded polypropylene resin particles are each an expanded composite particle comprising an expanded polypropylene resin core layer covered with a polypropylene resin covering layer,   the expanded polypropylene resin core layer is obtained from a base material resin comprising the polypropylene resin A and the polypropylene resin B; and   the polypropylene resin covering layer comprises the polypropylene resin A.   
     
     
         18 . The method according to  claim 13 , wherein
 the expanded polypropylene resin particles are heated with steam having a pressure of 0.22 MPa (gauge pressure) or less, and   the polypropylene resin in-mold expanded molded product has a density and a 50%-strained compressive strength satisfying the following:
   [50%-strained compressive strength (MPa)]≧0.0069×[Molded product density (g/L)]+0.018.