초록 ▼

The method of making polystyrene foam for foam products which comprises 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 polyst

The method of making polystyrene foam for foam products which comprises 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.

대표청구항 ▼

[ We claim:] [1.] An extruded thermoplastic heat shrinkable foam product comprisinga foam thermoplastic material which has been formed by introducing an atmospheric gas into a molten thermoplastic resin, continuously extruding said thermoplastic resin through an extruder in the form of a frustoconic

[ We claim:] [1.] An extruded thermoplastic heat shrinkable foam product comprisinga foam thermoplastic material which has been formed by introducing an atmospheric gas into a molten thermoplastic resin, continuously extruding said thermoplastic resin through an extruder in the form of a frustoconical tubular web at an angle to the axis of the extruder, continuously pulling and 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, characterized by(a) said product having substantially no residual blowing agent,(b) said product being dimensionally stable at ambient temperature and having substantially no corrugations,(c) said product being sufficiently resilient that it can be compressed to remove gauge bands,(d) said product having shrinkage properties which do not change substantially when the foam material is stored over extended periods of time,(e) said product having cell size, opacity, stiffness, smoothness, caliper, density that do not change over extended time of storage as contrasted to foam thermoplastic material formed using fluorocarbons or hydrocarbon blowing agents. [4.] A foam sheet material made in accordance with the method which comprisesintroducing atmospheric gas as the blowing agent into a molten thermoplastic resin in an amount of less than 2% by weight,coextrudng 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 non-foam 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 sheet material which(a) has substantially no residual blowing agent,(b) is dimensionally stable at ambient temperature and having substantially no corrugations,(c) is sufficiently resilient that it can be compressed to remove gauge bands if they had occurred,(d) has shrinkage properties at elevated temperatures which do not change substantially when the foam material is stored over extended periods of time,(e) has cell size, opacity, stiffness, smoothness, caliper, density that do not change over extended time of storage as contrasted to foam thermoplastic material formed using fluorocarbons or hydrocarbon blowing agents.