Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Patent
1997-05-08
2000-05-16
Foelak, Morton
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
521 51, 521 79, 521 81, 521139, C08J 934, B32B 900
Patent
active
060634855
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to foamed articles formed from a blend of a styrenic polymer and at least one acrylic polymer.
It is well known that polystyrene may be readily foamed by a variety of processes, including extrusion. The density of such industrially produced polystyrene foam, absent any particular treatment is usually of the order of 32 kg.m.sup.-3.
GB 2146941 discloses the preparation of a polystyrene foam by an extrusion process.
EP 0411923 is directed towards the preparation of polystyrene foam having a density from 32 to 160 kg.m.sup.-3 using an extrusion process in which liquid carbon dioxide is employed as a blowing agent.
Low density polystyrene foam, i.e. foam having a density less than 32 kg.m.sup.-3 is difficult to manufacture and typically requires that the original foam is either foamed directly into a sub atmospheric pressure environment or else is subjected to some form of controlled re-expansion, for example U.S. Pat. No. 4,552,904 discloses the preparation of a polystyrene foam having a density of less than 32 kg.m.sup.-3 by the re-expansion of an extruded foam. Such requirements add to the complexity of the foam making process and the expense of the low density foam with a consequence that such low density polystyrene foam is not widely available even though the benefits of using such foam in the building and other industries is well recognised.
It is an object of the present invention to provide a relatively low density polystyrene foam using a conventional foaming method such as extrusion, without the need to use re-expansion or an other such technique.
Accordingly, in a first aspect the present invention provides a foamed article having a closed cell structure formed from a polymer blend comprising at least 50% by weight of a styrenic polymer and up to 50% by weight of an acrylic polymer which has an average molecular weight which is less than 90% of that of the styrenic polymer.
The styrenic polymer may be a homopolymer or a copolymer of at least one of styrene, methyl styrene and acrylonitrile. Preferably at least 50% of the monomer units of the styrenic polymer are derived from styrene and in particular the styrenic polymer is a homopolymer of styrene.
Suitably, the styrenic polymer has an average molecular weight from 180000 to 250000, and preferably from 180000 to 230000, for example about 200000.
The acrylic polymer may be a homopolymer or a copolymer of at least one C.sub.1-5 alkyl (C.sub.1-4 alkyl)acrylate, for example methyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate. Preferably the acrylic polymer is a copolymer, particularly a copolymer containing a methacrylate, e.g. methyl methacrylate, and an acrylate, such as methyl acrylate or ethyl acrylate. The acrylic polymer preferably contains from 50 to 100%, particularly from 80 to 95, and especially 90 to 95 by weight of monomer units which are derived from a methacrylate, e.g. methyl methacrylate, with the balance of the monomer units being derived from at least one acrylate. The acrylic polymer has an average molecular weight which is less than 90%, preferably less than 80%, particularly less than 75% and especially from 50 to 60%, that of the styrenic polymer. Suitably, the acrylic polymer has an average molecular weight from 50000 to 180000, preferably from 50000 to 150000 and particularly from 80000 to 140000.
The foamed article has a closed cell structure. Typically, the closed cells have sides from 100 to 1000 .mu., particularly from 100 to 900 .mu.and especially from 100 to 600 .mu..
The average density of the foamed article is typically from 5 to 40%, preferably from 10 to 40 and particularly from 20 to 35% less than that of a similarly foamed article formed from the styrenic polymer alone.
The properties of the foamed article, such as thermal conductivity, remain comparable, although consistently lower, to those of a similarly foamed article formed from the styrenic polymer alone. Typical thermal conductivities of foamed articles immediately after manufacture thus range
REFERENCES:
patent: 3903023 (1975-09-01), Boutillier
patent: 4196267 (1980-04-01), Watanabee et al.
patent: 4925606 (1990-05-01), Francis
patent: 4983639 (1991-01-01), Hahn et al.
patent: 4990540 (1991-02-01), Hahn et al.
Database WPI, Week 9208, Derwent Publications Ltd., London, GB; AN 92:061823 `Foamed polystyrene with uniform, fine cell structure.` & JP,a,4 008 738 (CHISSO CORP.) Jan. 13, 1992, see abstract.
Cross Bernard John
Smith Peter John
Foelak Morton
Imperial Chemical Industies PLC
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