Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-02-07
2003-06-03
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S059000, C521S079000, C521S084100
Reexamination Certificate
active
06573308
ABSTRACT:
The invention relates to expandable polymer beads based on biodegradable polymers.
It is known that certain naturally occurring materials, e.g. cellulose and starch, are biodegradable, i.e. are decomposed by microorganisms, in particular during composting, to give low-molecular-weight substances. Some synthetic polymers, too, such as polyesters, are biodegradable. Although purely aliphatic polyesters have good biodegradablility, their low level of mechanical and thermal properties gives them poor suitability for practical applications. In contrast, aromatic polyesters have good mechanical properties but are not biodegradable.
WO 96/07687 discloses that copolyesters which comprise firstly aliphatic diols and secondly both aliphatic and aromatic dicarboxylic acids as monomer units have good mechanical and thermal properties and are at the same time biodegradable. This publication also mentions foamed moldings but nothing is said concerning their production.
WO 96/15173 likewise describes biodegradable copolyesters made from aliphatic diols and from a mixture of adipic acid and terephthalic acid, and modified by incorporating other esterification components. These polyesters can be used to make foams, by mixing a polymer melt with blowing agents and foam-extruding the mixture.
A disadvantage of the foam-extrusion process is that it can produce only foam moldings of simple shape, e.g. sheets or profiles. It is known that foam moldings of any desired shape can be produced by foaming and sintering expandable or, respectively, expanded polymer particles, for example those based on polystyrene or, respectively, on polyolefins.
Aliphatic/aromatic copolyesters degrade relatively slowly during composting. The degradation process can be adjusted as desired by admixing naturally occurring polymers which degrade rapidly.
EP-A 667 369 describes moldable foams made from biodegradable mixtures of thermoplastic starch and a synthetic thermoplastic polymer, e.g. an aliphatic polyester. The polymer mixtures here are extruded together with from 2 to 20% of water as blowing agent and pelletized to give expandable beads, which are then foamed in an extruder. The water content has to be set very precisely for each particular case. If the content is too high there is a risk that the polyester will hydrolyze and that the starch will begin to dissolve. Complicated drying of the foam beads is then required.
Finally, WO 97/44388 again describes foams made from moisture-resistant biodegradable mixtures of naturally occurring polymers, e.g. starch, with hydroxy-functional polyesters. These biodegradable materials, too, were foamed by the foam-extrusion process, using water as blowing agent.
REFERENCES:
patent: 6018004 (2000-01-01), Warzelhan et al.
patent: 198 02 718 (1999-07-01), None
patent: 667 369 (1995-01-01), None
patent: 94 06866 (1994-03-01), None
patent: 96/07687 (1996-03-01), None
patent: 96/15173 (1996-05-01), None
patent: 97/44388 (1997-11-01), None
Braun Frank
Glück Guiscard
LandOfFree
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