Foamed polyolefin resin beads

Abstract

The present invention relates to foamed polyolefin resin beads. Further, the present invention provides foamed resin beads obtained by foaming and expanding composite resin beads which include a core layer constituted by a polyolefin resin and a covering layer which covers the core layer constituted by a polyolefin resin, wherein (a) the polyolefin resin constituting the core layer is a crystalline polyolefin resin, (b) the polyolefin resin constituting the covering layer is a crystalline polyolefin resin which has a lower melting point (B) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(B)] between the melting point (B) and the melting point (A) is more than 0° C. and 80° C. or less, or a noncrystalline polyolefin resin which has a softening point (C) lower than the melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(C)] between the softening point (C) and the melting point (A) is more than 0° C. and 100° C. or less, and 10% by weight or more and less than 50% by weight of polymer type antistatic agent is contained in the covering layer. The foamed polyolefin resin beads of the present invention provide foamed polyolefin resin beads are excellent in fusion properties between beads at the time of molding in a mold, capable of providing a molded foamed article which is excellent antistatic performance, has no deterioration of the antistatic performance with age, whose antistatic performance is not humidity dependent, does not contaminate packaging products, has a good molded foamed article surface, and has excellent mechanical properties.

1 . Foamed polyolefin resin beads obtained by foaming and expanding composite resin beads which include a core layer constituted by a polyolefin resin and a covering layer which covers the core layer constituted by a polyolefin resin, wherein
 (a) the polyolefin resin constituting the core layer is a crystalline polyolefin resin,   (b) the polyolefin resin constituting the covering layer is a crystalline polyolefin resin which has a lower melting point (B) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(B)] between the melting point (B) and the melting point (A) is more than 0° C. and 80° C. or less, or a noncrystalline polyolefin resin which has a softening point (C) lower than the melting point (A) of the polyolefin resin constituting the core layer wherein a temperature difference [(A)−(C)] between the softening point (C) and the melting point (A) is more than 0° C. and 100° C. or less, and 10% by weight or more and less than 50% by weight of polymer type antistatic agent is contained in the covering layer.   
     
     
         2 . The foamed polyolefin resin beads according to  claim 1 , wherein the polyolefin resin constituting the covering layer is a crystalline polyolefin resin which has a lower melting point (B) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(B)] between the melting point (A) and the melting point (B) is in the range of 1 to 80° C., or a noncrystalline polyolefin resin which has a lower softening point (C) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(C)] between the melting point (A) and the softening point (C) is in the range of 1 to 100° C. 
     
     
         3 . The foamed polyolefin resin beads according to  claim 1 , wherein the polyolefin resin constituting the covering layer is a crystalline polyolefin resin which has a lower melting point (B) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(B)] between the melting point (A) and the melting point (B) is in the range of 5 to 60° C., or a noncrystalline polyolefin resin which has a lower softening point (C) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(C)] between the melting point (A) and the softening point (C) is in the range of 5 to 60° C. 
     
     
         4 . The foamed polyolefin resin beads according to  claim 1 , wherein the core layer does not substantially contain the polymer type antistatic agent. 
     
     
         5 . The foamed polyolefin resin beads according to  claim 1 , wherein 5 to 15% by weight of polymer type antistatic agent is contained in the core layer. 
     
     
         6 . The foamed polyolefin resin beads according to  claim 1 , wherein the crystalline polyolefin resin constituting the core layer is a polypropylene resin. 
     
     
         7 . The foamed polyolefin resin beads according to  claim 6 , wherein the polyolefin resin constituting the covering layer is the polypropylene resin. 
     
     
         8 . The foamed polyolefin resin beads according to  claim 1 , wherein a weight ratio of the core layer and the covering layer is in the range of 99.5:0.5 to 80:20. 
     
     
         9 . The foamed polyolefin resin beads according to  claim 1 , wherein the weight ratio of the core layer and the covering layer is in the range of 98:2 to 80:20. 
     
     
         10 . The foamed polyolefin resin beads according to  claim 1 , wherein the weight ratio of the core layer and the covering layer is in the range of 96:4 to 90:10. 
     
     
         11 . The foamed polyolefin resin beads according to  claim 1 , wherein the polyolefin resin constituting the covering layer is a polyolefin resin polymerized with a metallocene polymerization catalyst. 
     
     
         12 . The foamed polyolefin resin beads according to  claim 1 , wherein a ratio (X/Y) of an apparent density (X) of foamed beads after pressurizing with a compressed air under conditions of 30° C. and 0.2 MPa (G) for 24 hours and leaving under an ordinary pressure at 23° C. for 24 hours to an apparent density (Y) of foamed beads before the pressurization is in the range of 0.8 to 1.0. 
     
     
         13 . The foamed polyolefin resin beads according to  claim 1 , wherein the covering layer of the foamed beads is substantially solid. 
     
     
         14 . A molded foamed article of polyolefin resin produced by molding the foamed polyolefin resin beads according to  claim 1  in a molding cavity, wherein the molded foamed article has the surface resistivity of less than 1′ 1014 W.