Granted Patent B2

US 12,441,860 · App. 18/569,292 · Granted Oct 14, 2025

Inventors: Takumi Sakamura (Tochigi, JP); Hajime Ohta (Tochigi, JP)

Assignee: JSP CORPORATION

C08J9/228B29B9/12C08J9/18B29K2023/12B29K2105/046B29K2105/048B29K2995/0082C08J2205/052C08J2323/14

Abstract

Claims (25)

1. A polypropylene-based resin expanded bead having a tubular shape with a through-hole, comprising:

a foamed core layer constituted by a polypropylene-based resin; and

a fusion-bondable layer covering the foamed core layer,

wherein

an average hole diameter d of the through-hole in the expanded bead is less than 1 mm, and a ratio d/D of the average hole diameter d to an average outer diameter D of the expanded bead is 0.4 or less,

a mass ratio of the foamed core layer and the fusion-bondable layer is foamed core layer:fusion-bondable layer=99.5:0.5 to 85:15, and

the polypropylene-based resin constituting the foamed core layer has a flexural modulus of 800 MPa or more and less than 1200 MPa and a melting point Tmc of 150° C. or lower.

2. The polypropylene-based resin expanded bead according to claim 1 , wherein a circularity of the through-hole is 0.90 or more in a cross-section of the expanded bead in a direction perpendicular to a penetration direction of the through-hole.

3. The polypropylene-based resin expanded bead according to claim 1 , wherein a ratio of an apparent density to a bulk density of the expanded bead is 1.7 or more and 1.9 or less.

4. The polypropylene-based resin expanded bead according to claim 1 , wherein an average outer diameter D of the expanded bead is 2 mm or more and 5 mm or less.

5. The polypropylene-based resin expanded bead according to claim 1 , wherein an average wall thickness t of the expanded bead, which is represented by the following formula (I), is 1.2 mm or more and 2 mm or less:

average wall thickness t =(the average outer diameter D −the average hole diameter d )/2  (I).

6. The polypropylene-based resin expanded bead according to claim 1 , wherein a closed cell content of the expanded bead is 90% or more.

7. The polypropylene-based resin expanded bead according to claim 1 , wherein the fusion-bondable layer is constituted by a polyolefin-based resin, and a melting point of the polyolefin-based resin constituting the fusion-bonding layer is lower than a melting point of the polypropylene-based resin constituting the foamed core layer.

8. The polypropylene-based resin expanded bead according to claim 1 , wherein an apparent density of the expanded bead is 10 kg/m 3 or more and 100 kg/m 3 or less.

9. A molded article of polypropylene-based resin expanded beads formed by in-mold molding the polypropylene-based resin expanded beads according to claim 1 ,

wherein an open cell content of the molded article of expanded beads is 2.5% or more and 12% or less.

10. A method for producing a polypropylene-based resin expanded beads, comprising:

dispersing multilayer resin particles each having a tubular shape with a through-hole in a dispersion medium in a sealed container;

impregnating the multilayer resin particles dispersed in the dispersion medium with a blowing agent; and

producing expanded beads by expanding the multilayer resin particles containing the blowing agent, wherein

the multilayer resin particles each have a core layer constituted by a polypropylene-based resin and a fusion-bondable layer covering the core layer,

an average hole diameter dr of the through-holes in the multilayer resin particles is less than 0.25 mm, and a ratio dr/Dr of the average hole diameter dr to an average outer diameter Dr of the multilayer resin particles is 0.4 or less,

a mass ratio of the core layer and the fusion-bondable layer in the multilayer resin particles is core layer:fusion-bondable layer=99.5:0.5 to 85:15, and

the polypropylene-based resin constituting the core layer has a flexural modulus of 800 MPa or more and less than 1200 MPa, and a melting point Tmrc of 150° C. or lower.

Assignments (1)

Priority Claims (1)

Continuity (1)

References Cited (51)