Expandable polystyrenic resin particles and production process thereof, pre-expanded particles and molded foam product

• US 20100022674A1
• Filed: 10/25/2007
• Published: 01/28/2010
• Est. Priority Date: 10/26/2006
• Status: Active Grant

• Current Assignee: Sekisui Plastics Company Limited
• Original Assignee: Sekisui Plastics Company Limited
• Inventors: Morioka, Ikuo, Matsumura, Hideyasu, Tsutsui, Yasutaka
• Granted Patent: US 8,084,510 B2
• Time in Patent Office: Days
• US Class Current: 521/59
• CPC Class Codes: C08F 12/08 Styrene
• CPC Class Codes: C08F 2/44 Polymerisation in the presence of compounding ingredients, e.g. plasticisers, dyestuffs, fillers
• CPC Class Codes: C08J 2203/14 Saturated hydrocarbons, e.g. butane; Unspecified hydrocarbons
• CPC Class Codes: C08J 2325/06 Polystyrene
• CPC Class Codes: C08J 2351/06 grafted on to homopolymers or copolymers of aliphatic hydrocarbons containing only one carbon-to-carbon double bond
• CPC Class Codes: C08J 2423/00 Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
• CPC Class Codes: C08J 9/0061 characterized by the use of several polymeric components
• CPC Class Codes: C08J 9/18 by impregnating polymer particles with the blowing agent
• CPC Class Codes: C08J 9/20 by suspension polymerisation in the presence of the blowing agent
• CPC Class Codes: C08K 5/01 Hydrocarbons C08K5/0091 takes precedence
• CPC Class Codes: C08L 23/04 Homopolymers or copolymers of ethene
• CPC Class Codes: C08L 25/04 Homopolymers or copolymers of styrene
• CPC Class Codes: C08L 2666/06 Homopolymers or copolymers of unsaturated hydrocarbons; Derivatives thereof

Abstract

Expandable polystyrenic resin particles having superior resistance to cracking of a molded foam product, having superior retention of blowing agent and maintaining expandability over a long period of time, a production process thereof, and a molded foam product are provided. These expandable polystyrenic resin particles contain a volatile blowing agent in polystyrenic resin particles obtained by impregnating and polymerizing a styrenic monomer in polyolefin resin particles to form a polystyrenic resin, wherein together with the styrenic monomer being used at 140 to 600 parts by weight to 100 parts by weight of the polyolefin resin particles, the average thickness of the surface layer observed in scanning electron micrographs obtained by immersing sections cut into halves through the center from the surface of the resin particles in tetrahydrofuran followed by extracting the polystyrenic resin component and capturing cross-sections of said sections is 15 to 150 μm, and the volatile blowing agent is contained at 5.5 to 13.0% by weight.

Claims

1. A expandable polystyrenic resin particles comprising a volatile blowing agent in polystyrenic resin particles obtained by forming a polystyrenic resin in polyolefin resin particles by impregnating and polymerizing a styrenic monomer;

wherein,

140 to 600 parts by weight of the styrenic monomer are impregnated and polymerized to 100 parts by weight of the polyolefin resin particles,

the average thickness of the surface layer observed in scanning electron micrographs obtained by immersing sections cut into halves through the center from the surface of the resin particles in tetrahydrofuran followed by extracting the polystyrenic resin component and capturing cross-sections of said sections is 15 to 150 μ

m, and

the volatile blowing agent is contained at 5.5 to 13.0% by weight.

2. The expandable polystyrenic resin particles according to claim 1, wherein the average thickness of the surface layer is 20 to 100 μ

m.

3. The expandable polystyrenic resin particles according to claim 1 or 2, wherein the polyolefin resin contained in the polystyrenic resin particles is branched low-density polyethylene, linear low-density polyethylene or ethylene-vinyl acetate copolymer, and the polystyrenic resin is a polystyrene, a styrene-alkyl acrylate copolymer or styrene-alkyl methacrylate copolymer.

4. The expandable polystyrenic resin particles according to claim 1 or 2, wherein the volatile blowing agent is pentane.

5. The expandable polystyrenic resin particles according to claim 1 or 2, wherein the mean particle diameter is 800 to 2400 μ

m.

13. Pre-expanded particles having a bulk density of 0.015 to 0.25 g/cm³ obtained by forming the expandable polystyrenic resin particles according to claim 1 or 2.

14. A molded foam product obtained by molding the pre-expanded particles according to claim 13 in a mold.

6. A process for producing expandable polystyrenic resin particles comprising the steps of:

1) melt-extruding a polyolefin resin followed by granulating to obtain polyolefin resin particles, and

     2) dispersing the polyolefin resin particles in an aqueous medium, impregnating the polyolefin resin particles with a styrenic monomer while polymerizing in the presence of an oil-soluble radical polymerization initiator, and impregnating with a volatile blowing agent either during or following completion of polymerization;

wherein,

the melt-extrusion of the polyolefin resin of step

     1) is carried out in the presence of 0.005 to 0.5 parts by weight of a radical scavenger to 100 parts by weight of polyolefin resin, and the polymerization of step

     2) uses 140 to 600 parts by weight of styrenic monomer, in which the content of phenylacetylene is 150 ppm or less, to 100 parts by weight of polyolefin resin particles.

7. The process for producing expandable polystyrenic resin particles according to claim 6, wherein the polyolefin resin is branched low-density polyethylene, linear low-density polyethylene or ethylene-vinyl acetate copolymer, and the styrenic monomer is a styrene, a comonomer of styrene and an alkyl acrylate having styrene has a main component thereof, or a comonomer of styrene and an alkyl methacrylate having styrene has a main component thereof.

8. The process for producing expandable polystyrenic resin particles according to claim 7, wherein the styrene is obtained by dehydrating α

-phenylethyl alcohol.

9. The process for producing expandable polystyrenic resin particles according to any of claims 6 to 8, wherein the radical scavenger is a phenol-based antioxidant.

10. The process for producing expandable polystyrenic resin particles according to any of claims 6 to 8, wherein a water-soluble radical polymerization inhibitor is used at 0.001 to 0.04 parts by weight to 100 parts by weight of water of the aqueous medium.

11. The process for producing expandable polystyrenic resin particles according to claim 10, wherein the water-soluble radical polymerization inhibitor is a nitrite.

12. The process for producing expandable polystyrenic resin particles according to any of claims 6 to 8, wherein impregnation and polymerization of styrenic monomer are carried out under conditions such that the content of styrenic monomer in the polyolefin resin particles is 35% by weight or less.

15. A process for producing pre-expanded particles comprising the steps of:

1) melt-extruding a polyolefin resin followed by granulation to obtain polyolefin resin particles, wherein melt-extrusion of the polyolefin resin is carried out in the presence of 0.005 to 0.5 parts by weight of a radical scavenger to 100 parts by weight of polyolefin resin;

     2) dispersing the polyolefin resin particles in an aqueous medium, impregnating the polyolefin resin particles with styrenic monomer while polymerizing in the presence of an oil-soluble radical polymerization initiator, and impregnating a volatile blowing agent either during or following completion of polymerization to obtain expandable polystyrenic resin particles, wherein the polymerization uses 140 to 600 parts by weight of styrenic monomer having a phenylacetylene content of 150 ppm or less to 100 parts by weight of polyolefin resin particles; and

     3) pre-expanding the resulting expandable polystyrenic resin particles.

16. A process for producing a molded foam product comprising the steps of:

1) melt-extruding a polyolefin resin followed by granulation to obtain polyolefin resin particles, wherein melt-extrusion of the polyolefin resin is carried out in the presence of 0.005 to 0.5 parts by weight of a radical scavenger to 100 parts by weight of polyolefin resin;

     2) dispersing the polyolefin resin particles in an aqueous medium, impregnating the polyolefin resin particles with styrenic monomer while polymerizing in the presence of an oil-soluble radical polymerization initiator, and impregnating a volatile blowing agent either during or following completion of polymerization to obtain expandable polystyrenic resin particles, wherein the polymerization uses 140 to 600 parts by weight of styrenic monomer having a phenylacetylene content of 150 ppm or less to 100 parts by weight of polyolefin resin particles;

     3) pre-expanding the resulting expandable polystyrenic resin particles to obtain pre-expanded particles; and

     4) molding the resulting pre-expanded particles in a mold.