US 5,443,769 AGranted

Polystyrene foam sheet manufacture

AssigneeOwens-Illinois Plastic Products Inc.

InventorsJames A. Karabedian, Maurice W. Blackwelder

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Abstract

The method of making polystyrene foam for foam products which includes utilizing atmospheric gases as the blowing agents or preferably mixing one or more of these gases and a blending agent which is non-volatile at the extrusion temperatures, introducing the mixture to a molten thermoplastic polystyrene resin containing nucleating agents such as sodium bicarbonate and citric acid and extruding the thermoplastic in the form of a foam. The resultant foam has substantially no residual blowing agent, is dimensionally stable at ambient temperatures and when used with a non-volatile blending agent can be made with small amounts of blowing agent permitting cooling of the melt without high loading on the extruder. The foam may be coextruded with one or more layers of thermoplastic film so that the resultant product is adapted for use for plates, cups, food containers or packaging and for labels for containers such as glass and plastic containers and for labels that are shrunk in place on a container.

Claims15

Dependent claims

The method of making heat shrinkable foam sheet material adapted to be used to form shrinkable labels on containers or cups which comprises

introducing atmospheric gas as the blowing agent into a molten thermoplastic resin in an amount of less than 2% by weight,
coextruding a plastic film layer and a foam layer such that the foam layer and plastic film layer form a frustoconical tubular web comprising a foam layer and a plastic film at an angle to the axis of the extruder,
passing said frustoconical web over an internal cooling mandrel to cool the interior of the web,
simultaneously applying cooling air to the outside of the frustoconical web,
said step of applying cooling air to the outside of the frustoconical web comprising applying cooling air axially to the outside of said frustoconical web at an acute angle tangentially to the web whereby the cooling air moves in a direction parallel to the frustoconical web from adjacent the extruder to adjacent the internal cooling mandrel such that the external surface of the frustoconical web is cooled by cooling air and by the ambient air drawn by the cooling air against the external surface of the frustoconical web,
such that the resultant coextruded sheet material comprises a foam layer and a plastic film has substantially no residual blowing agent, and is substantially dimensionally stable at ambient temperatures and has greater shrinkage in a machine direction than in a cross direction at elevated temperatures, and shrinkage properties which do not change substantially when the foam material is stored.

3 more elements

An apparatus for forming an extruded thermoplastic foam product comprising

means for heating and extruding a resin in the form of a tubular web,
means for introducing said resin to said means for heating and extruding,
means for introducing an atmospheric gas as a blowing agent to said means for heating and extruding,
means for coextruding a plastic film layer with said foam layer to form a frustoconical web at an acute angle to the axis of the extruder,
means for passing said frustoconical web over an internal cooling mandrel to cool the interior of the web, and
said means for applying cooling air to the outside of the frustoconical web comprising means for applying cooling air axially to the outside of said frustoconical web at an acute angle tangentially to the web whereby the cooling air moves in a direction parallel to the frustoconical web from adjacent the extruder to adjacent the internal cooling mandrel such that the external surface of the frustoconical web is cooled by cooling air and by the ambient air drawn by the cooling air against the external surface of the frustoconical web,
means for simultaneously applying cooling air axially to the outside of said web whereby the cooling air moves in a direction along the frustoconical web from adjacent the extruder to adjacent the internal cooling mandrel such that the external surface of the frustoconical web is cooled by the cooling air against the external surface of the frustoconical web and such that the resultant foam has substantially no residual blowing agent and is substantially dimensionally stable at ambient temperatures and has substantially no corrugations.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/118,081Filed 24 Nov 1993 · division
Priority: 14 Jun 1990
Granted: 22 Aug 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification15 codes

B29C 44/3419
Heating or cooling: quick cooling
B29C 44/3402
Auxiliary operations: details of processes or apparatus for reducing environmental damage or for working-up compositions comprising inert blowing…
B29C 44/3442
Auxiliary operations: mixing, kneading or conveying the foamable material
B29C 44/507
Using pressure difference, e.g. by extrusion or by spraying: extruding the compound through an annular die