Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1999-11-18
2000-08-29
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
522 60, 522162, 522169, 521 50, 521 505, 521 82, C08J 900
Patent
active
061109835
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to formed and expanded beads of a crosslinked aliphatic polyester resin, a method for the production thereof and a foamed molding obtained therefrom.
BACKGROUND ART
Foamed plastic moldings, which are featured in their lightness in weight, elasticity, cushioning property, heat insulating property and moldability, are recently used in large amounts mainly as packing receptacles and cushioning materials. These foamed plastic moldings, however, pose a problem of pollution of natural environment by disposal thereof. To cope with this problem, biodegradable foamed moldings are proposed. EP-A-569143 discloses a method for obtaining a molded article in which biodegradable aliphatic polyester beads are impregnated with a blowing agent, followed by heat molding in a mold cavity. The foamed molding obtained with this method, however, undergoes considerable shrinkage during the molding step and has poor dimensional stability.
The present invention has been made in view of the problem of the above conventional technique and has as its prime object the provision of expanded beads of an aliphatic polyester which can afford foamed articles of the aliphatic polyester having excellent dimensional stability, heat resistance, cushioning property and mechanical property as well as biodegradability.
DISCLOSURE OF THE INVENTION
In accordance with one aspect of the present invention, there is provided foamed and expanded beads of a crosslinked aliphatic polyester resin having a gel fraction of at least 5% by weight.
In another aspect, the present invention provides a method for the production of foamed and expanded beads of a crosslinked aliphatic polyester resin, comprising the steps of crosslinking beads of a non-crosslinked aliphatic polyester resin with a crosslinking agent comprising an organic peroxide to obtain crosslinked resin beads having a gel fraction of at least 5% by weight; and expanding said crosslinked resin beads.
In a further aspect, the present invention provides a molded article of foamed and expanded beads of a crosslinked aliphatic polyester resin, having a gel fraction of at least 5% by weight.
A non-crosslinked aliphatic polyester resin of which non-crosslinked resin beads are formed is a resin having an aliphatic ester in the main chain thereof in an amount of at least 60 mole %, preferably 80-100 mole %, more preferably 90-100 mole %. Examples of the aliphatic polyester resins include polycondensation products of hydroxyacids such as hydroxybutyric acid, ring open polymerization products of lactones such as polycaprolactone, and polycondensation products between a glycol and a dicarboxylic acid such as polybutylene succinate. Additionally, the aliphatic polyester resin may be a product obtained by treating the above polymer with a coupling agent for increasing the molecular weight thereof, a blend of a plurality of the above polymers or a copolymer of the above polymer with a carbonic diester.
Examples of the coupling agents include diisocyanates such as 2,4-tolylenediisocyanate, diphenylmethanediisocyanate, 1,5-naphthylenediisocyanate, xylylenediisocyanate, hydrogenated xylylenediisocyanate, hexamethylenediisocyanate and isophoronediisocyanate; and aryl carbonates such as diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate and m-cresyl carbonate.
Particularly preferred aliphatic polyester resins are products obtained by polycondensing one or more glycols having not more than 4 carbon atoms with one or more aliphatic dicarboxylic acids having not more than 4 carbon atoms. The aliphatic polyester resin may contain other resins or rubbers, if desired. The aliphatic polyesters disclosed in the above-mentioned EP-A-569143 may be suitably used for the purpose of the present invention.
The melt viscosity of the aliphatic polyester resin is preferably 1.times.10.sup.2 -1.times.10.sup.5 Pa.multidot.s, more preferably 5.times.10.sup.2 -5.times.10.sup.3 Pa.multidot.s, at 190.degree. C. and at a rate of shear of 100 sec.sup.- 1. When the melt viscosity i
REFERENCES:
patent: 4769393 (1988-09-01), Kuwabara et al.
patent: 5218018 (1993-06-01), Tominaga et al.
patent: 5543438 (1996-08-01), Shibayama et al.
patent: 5939180 (1999-08-01), Kobayashi et al.
Shinohara Mitsuru
Shioya Satoru
Tokoro Hisao
Acquah Samuel A.
JSP Corporation
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