Propylene resin foamed particle and foamed particle molded body

1. Expanded propylene resin beads comprising a core layer being in a foamed state, having a tubular shape having a penetrating tubular hole, and being constituted of a propylene-based resin composition (a) and a cover layer covering the core layer and being constituted of an olefin-based resin (b),

the propylene-based resin composition (a) satisfying the following (i) and (ii), and the olefin-based resin (b) satisfying the following (iii) or (iv):

(i) the propylene-based resin composition (a) is a mixture of 75% by weight to 98% by weight of a propylene-based resin (a1) having a melting point of 100° C. to 140° C. and 2% by weight to 25% by weight of a propylene-based resin (a2) having a melting point of 140° C. to 165° C., provided that a sum total weight of the propylene-based resin (a1) and the propylene-based resin (a2) is 100% by weight;

(ii) a difference between the melting point of the propylene-based resin (a2) and the melting point of the propylene-based resin (a1) [(melting point of a2)−(melting point of a1)] is 15° C. or more;

(iii) the olefin-based resin (b) is a crystalline olefin-based resin having a melting point (TmB) that is lower than a melting point (TmA) of the propylene-based resin composition (a), with a difference between the melting point (TmA) and the melting point (TmB) [TmA−TmB] being more than 0° C. and 80° C. or less; and

(iv) the olefin-based resin (b) is a non-crystalline olefin-based resin having a softening point (TsB) that is lower than the melting point (TmA) of the propylene-based resin composition (a), with a difference between the melting point (TmA) and the softening point (TsB) [TmA−TsB] being more than 0° C. and 100° C. or less,

wherein a melt flow rate range for the propylene-based resin (a1) is from 1 to 100 g/10 min. and a melt flow rate range for the propylene-based resin (a2) is from 2 to 18 g/10 min.

2. The expanded propylene resin beads according to claim 1 , wherein in the foregoing (ii), the difference in melting point between the propylene-based resin (a2) and the propylene-based resin (a1) [(melting point of a2)−(melting point of a1)] is 15 to 25° C.

3. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin (a1) is a propylene-based resin obtained through polymerization in the presence of a metallocene-based polymerization catalyst.

4. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin (a1) and the propylene-based resin (a2) each is a propylene-based resin obtained through polymerization in the presence of a metallocene-based polymerization catalyst.

5. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin composition (a) has a flexural modulus of 900 MPa to 1,200 MPa.

6. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin composition (a) has a content of the propylene-based resin (a1) of more than 90% by weight and 98% by weight or less and a content of the propylene-based resin (a2) of 2% by weight or more and less than 10% by weight, provided that a sum total weight of the propylene-based resin (a1) and the propylene-based resin (a2) is 100% by weight.

7. The expanded propylene resin beads according to claim 1 , wherein the olefin-based resin (b) is an ethylene-based resin obtained through polymerization in the presence of a metallocene-based polymerization catalyst.

8. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin composition (a) is blended with at least one flame retardant selected from a brominated bisphenol A-based flame retardant, a brominated bisphenol S-based flame retardant, a brominated butadiene-styrene block copolymer flame retardant, and a brominated polyphenyl ether flame retardant.

9. An expanded propylene resin beads molded article having interconnected voids, which is obtained through in-mold molding of the expanded propylene resin beads according to claim 1 .

10. The expanded propylene resin beads according to claim 1 , wherein a maximum outer diameter D in the cross section of the core layer in the perpendicular direction to the axial direction through which the tubular hole of the core layer penetrates is 3 to 12 mm.

11. The expanded propylene resin beads according to claim 1 , wherein a minimum hole diameter d MIN in the cross section of the core layer in the perpendicular direction to the axial direction through which the tubular hole of the core layer penetrates is 1 to 6 mm.

12. The expanded propylene resin beads according to claim 1 , wherein the core layer is in a foamed state and has a tubular shape having a penetrating tubular hole which satisfies the following formulae (1) and (2):

d MIN ≥1.0 (mm)  (1)

d MIN /D MIN ≤0.80  (2)

wherein d MIN is a minimum hole diameter (mm) in the cross section of the core layer in the perpendicular direction to the axial direction through which the tube-shaped tubular hole penetrates, and D MIN is a minimum outer diameter (mm) of the core layer in a position of the cross-section of the core layer, at which the hole diameter is d MIN .

13. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin (a1) is a propylene-based random copolymer obtained through polymerization in the presence of a metallocene-based polymerization catalyst, and the propylene-based resin (a2) is a propylene-based copolymer.

14. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin (a1) has a melting point of 130° C. or more and less than 140° C.

15. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin (a2) has a melting point of 150° C. or more and less than 165° C.

16. The expanded propylene resin beads according to claim 1 , wherein the propylene-based resin (a2) has a melting point of 150° C. to 160° C.

17. The expanded propylene resin beads according to claim 1 , wherein a length of the core layer in the axial direction through which the tubular hole of the core layer penetrates is 2 to 20 mm.

18. The expanded propylene resin beads according to claim 11 , wherein a minimum hole diameter d MIN is 1.9 to 6 mm.

19. The expanded propylene resin beads according to claim 12 , wherein the core layer being in a foamed state and having a tubular shape having a penetrating tubular hole satisfies the following formula (2):

d MIN /D MIN =0.53 to 0.80  (2).

20. The expanded propylene resin beads molded article according to claim 9 , wherein the voidage of the expanded beads molded article of the present invention is 7 to 50%.