WO1996030180B1

WO1996030180B1 - Foamed rotationally molded articles

Info

Publication number: WO1996030180B1
Application number: PCT/US1996/003478
Authority: WO
Filing date: 1996-03-15
Publication date: 1996-10-31
Anticipated expiration: 1997-09-30

Abstract

Foamed rotationally molded articles and methods of manufacture are disclosed. The articles are prepared based upon inclusion of blowing agents in micro-pellets. The articles and the method for making them, display improved cell structure and uniformity leading to improved and generally uniform properties of the article, including for instance, insulation values and impact resistance.

Claims

23AMENDED CLAIMS[received by the International Bureau on 23 September 1996 (23.09.96); original claims 1-9 replaced by amended claims 1-8 (3 pages)]

1. A molded article comprising at least one foamed layer, said foamed layer having a density in the range of from 1 to 55 lb/ft³ (16 to 880 kg/m³); wherein said foamed layer includes a thermoplastic selected from the group consisting of polyethylene, polypropylene, polyamide, polyethylene terephthalate, polybutylene terephthalate, and combinations thereof, preferably from the group consisting of low density polyethyelene, linear low density polyethylenes, medium density polyethylene, high density polyethylene and combinations thereof, wherein said foamed layer has a cell structure wherein at least 70% of said cells have a diameter in the range of from 400 to 800 μm, and wherein said foamed layer includes cells wherein a majority of said cells are closed cells.

2. The molded article of claim 1 including at least a second layer, said second layer having a density in the range of from 850 to 1400 kg/m³; wherein said second layer includes a thermoplastic selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyvinyl chloride and combinations thereof, wherein said thermoplastic in said foamed layer may be the same or different than said thermoplastic in said second layer.

3. A molded article comprising : a) at least a first layer, said first layer including a foamed thermoplastic, said foamed thermoplastic having a density in the range of from 16 to 880 kg/m³ where said foamed thermoplastic includes cells wherein a majority of said cells are closed cells; and b) at least a second layer, said second layer including a thermoplastic, said thermoplastic having a density in the range of from 850 to 970 kg m³.

4. In a process for producing a molded part comprising: a) charging a plurality of micro-pellets into a mold; b) rotating said mold on at least one axis; c) heating said micro-pellets to a temperature effective to produce a molded object characterized in that said molded object includes at least one layer of a thermoplastic foam having a majority of closed cells, said thermoplastic foam having a density in the range of from 16 to 640 kg/m³; wherein said micro-pellets have a volume equal to the volume of a sphere having a diameter in the range of from 250μm to 750μm; wherein said thermoplastic foam have cells wherein at least 70% of cells have an average size in the range of from 400 to 800 μm; and wherein said micro-pellets include at least one thermoplastic resin and a chemical blowing agent, preferably wherein: a) said thermoplastic is selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyvinyl chloride, polyamide and combinations thereof; and b) wherein said molded part includes a second layer, wherein said second layer has a density in the range of from 850 to 1400 kg/m³, said second layer including a thermoplastic selected from the group consisting of polyethyene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyvinyl chloride, polyamide, and combinations thereof, preferably wherein said process is a roto-molding process.

5. The process of claim 4 further comprising: charging a thermoplastic powder to said mold, wherein said powder has an average particle size in the range of from 200 μm to 300 μm.

6. The process of claim 4 wherein the thermoplastic of said thermoplastic powder and the thermoplastic of said thermoplastic foam may be the same or different, and thermoplastic of said thermoplastic powder or the thermoplastic of said thermoplastic foam is selected from the group consisting of polyethyene, 25

polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyamide, and combinations thereof.

7. A thermoplastic pellet comprising: a) a thermoplastic, preferably wherein said thermoplastic is selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthlate, polyamide, and combinations thereof; and b) a blowing agent; characterized in that said pellets have a particle size equivalent to the volume of a sphere having a diameter in the range of from 25 μm to 1500 μm, preferably wherein said particle size is in the range of from 300 μm to 1200 μm; and wherein said blowing agent is a chemical blowing agent said blowing agent being present in said pellet in the range of from 0.1 to 3 parts per hundred parts of said thermoplastic, preferably wherein said blowing agent is selected from the group consisting of: azodicarbonamide, modified azodicarbonamides, p-toluene sulfonyl semi carbazide, p,p'-oxybis(benzene)-sulfonyl hydrazide, p-toluene sulfonyl hydrazide.

8. Use of a plurality of thermoplastic pellets according to claim 7 to form a molded article.preferably a rotationally molded article, wherein said molded article contains at least one foamed layer having a density in the range of from 16 to 855 kg/m³, wherein said foamed layer has at least 70% of cells of said foam have an average size described by a diameter in the range of from 50 to 1300 μm, and wherein a majority of said cells are closed cells.