Composite foamed polypropylene resin molding and method of producing same

Abstract

A composite foamed polypropylene resin molding including a plurality of sections which are fuse-bonded to each other, at least two of which differ from each other in color, apparent density, composition and/or mechanical strengths, each of which is formed from expanded polypropylene resin beads, and each of which shows a high temperature endothermic peak in a DSC curve thereof. At least one of the sections satisfies conditions (d) to (f) at the same time: (d) to be formed from specific expanded polypropylene resin beads of a base resin having a tensile modulus of at least 1,200 MPa, (e) to have an apparent density D2 of 10-500 g/L, and (f) to have such a high temperature endothermic peak with a calorific of E2 J/g, wherein D2 and E2 have the relationship 20−0.020×D2≦E2≦65−0.100×D2. The composite molding may be prepared by filling expanded polypropylene resin beads in each of a plurality of contiguous spaces defined in a mold cavity and heating the expanded beads to fuse-bond respective expanded beads together into a unitary body. At least one of the spaces is filled with the specific expanded polypropylene resin beads.

1 . A composite foamed polypropylene resin molding comprising a plurality of sections which are fuse-bonded to each other and at least two of which differ from each other in apparent density, 
 wherein each of said sections is formed from expanded beads of a base resin including a polypropylene resin,    wherein each of said sections shows a high temperature endothermic peak, in a DSC curve thereof, in addition to an intrinsic endothermic peak located at a lower temperature side of said high temperature peak,    wherein at least one of said sections satisfies the following conditions (a) to (c) at the same time:    (a) that section is formed from specific expanded polypropylene resin beads of a base resin having a tensile modulus of at least 1,200 Mpa,    (b) that section has an apparent density D2 g/L which is not smaller than 10 g/L but not greater than 500 g/L, and    (c) the high temperature endothermic peak of that section has a calorific value of E2 J/g, wherein D2 and E2 have the following relationship      20−0.020 ×D 2≦ E 2≦65−0.100× D 2.    
   
   
       2 . A composite foamed molding as claimed in  claim 1 , wherein each of said specific expanded beads has a surface region and an inside region, wherein each of said surface and inside regions shows a high temperature endothermic peak, in a DSC curve thereof, in addition to an intrinsic endothermic peak located at a lower temperature side of said high temperature peak, wherein said high temperature endothermic peaks of said surface region and said inside region have calorific values of Hs and Hi, respectively, and wherein Hs and Hi have the following relationship:  
         HS< 0.86 ×Hi.    
   
   
       3 . A composite foamed molding as claimed in  claim 1 , wherein one of two adjacent sections has a relatively high apparent density which is higher than that of the other one of said adjacent two sections and which is in the range of 30-450 g/L, with the other section having a relatively low apparent density in the range of 15-90 g/L.  
   
   
       4 . A composite foamed molding as claimed in  claim 3 , wherein the relatively high apparent density is 1.2-25 times as high as that of the relatively low apparent density.  
   
   
       5 . A composite foamed molding as claimed in  claim 1 , in the form of a shock absorber.  
   
   
       6 . A composite foamed molding as claimed in  claim 5 , wherein said shock absorber is a core of an automobile bumper.