THERMOFORMING COEXTRUDED PLASTIC SHEETS

Abstract: A process of making thermoformed plastic objects (12, 14) comprising coextruding a multilayered sheet (36) having adjacent layers of plastics that do not bond together during coextrusion, thermoforming the multilayered sheet (36), and separating individual thermoformed objects (12, 14) of different layers.

Description: THERMOFORMING COEXTRUDED PLASTIC SHEETS Field of the Invention The invention relates to preparing objects thermoformed from p astic sheets. Background of the Invention Plastic sheets are often produced by appara¬ tus in which plastic material is heated and sup¬ plied under pressure to an extrusion die. The sheets can then be thermoformed to a desired shape, and individual objects can be trimmed from the thermoformed sheet. Summary of the Invention In general the invention features coextruding a multilayered sheet having adjacent layers of plastics that do not bond to each other during co¬ extrusion, thermoforming the multilayered sheet, and separating individual thermoformed objects of different layers. With such a method,' the produc¬ tivity of the extrusion, thermoforming, and trim¬ ming apparatus is multiplied by the number of layers in the sheet. In preferred embodiments one of the plastics in the multilayered sheet is polystyrene and another plastic is polypropylene; in some preferred embodiments one plastic is for a separator layer between plastic layers for the thermoformed objects, and in other preferred embodiments the thermoformed objects are made from more than one of the plastics of the layers of the multilayered sheet. The thermoforming of the multilayered sheet with poly¬ propylene and polystyrene layers is faster. than the slow, and therefore expensive, thermoforming of polypropylene alone- Description of the Preferred Embodiment The preferred embodiment of the invention will now be described after first describing the draw¬ ing, which is a diagrammatic view of a process of manufacturing plastic objects according to the in¬ vention. Referring to the drawing, there is shown ap¬ paratus 10 for manufacturing polypropylene bowls 12 and polystyrene bowls 14. Two heated containers 16, 18 serve as sources of the polystyrene (70% crystal styrene and ' 30% rub¬ ber modifying plastomer sold by Phillips Chemical Company under the trade designation Solprene 416P, a block polymer having a butadiene/styrene ratio of 70/30, a molecular weight of 140 M, a density of 0.94, and a melt flow index of 2 decigrams/ in) , and polypropylene- (available from Rexene Company, Paramus, New Jersey, and having a meltr flow index of 4 decigrams/ in) , respectively. Conduits 20, 22, 24, 26, 28 supply the heated materials to coextrusion block ' 30. There the ma¬ terials merge together to form under pressure a unitary, five-layer thick stream ' 32 of generally circular cross section. Stream ' 32 passes into extrusion die ' 34 "(e.g. , Welex standard 54" flex- lip die) for extrusion into continuous sheet ' 36. Sheet ' 36 then passes through a series of chill rolls 38. The sheet, after coextrusion, may then be thermoformed into bowls or wound into spools (not shown) for storage and later themoforming. To process sheet ' 36 into bowls, the sheet is passed through conventional thermoforming apparatus 40 (the vacuum forming type well known in the art) , * which impresses the bowl shape. After thermoforming, the shaped sheet 42 passes through trim press 44, in which the indivi¬ dual bowls 12 and 14 are trimmed. Because the polypropylene and polystyrene of bowls 12, 14, respectively, do not bond to each other during coextrusion or thermoforming, bowls 12, 14 can be easily separated from each other. The simultaneous coextruding of five sheets and thermoforming and trimming of five bowls act to increase the produc¬ tivity of the coextrusion, thermoforming, and trimming apparatus. by a factor of five. Also, the thermoforming of the five-layer sheet is faster than the slow, and therefore expensive, thermoform¬ ing of polypropylene alone. Other Embodiments Other embodiments of the invention are within the scope of the appended claims. For example, other plastics that do not bond to each other can be used in place of the polystyrene and polypropy¬ lene. Also, one of the plastic layers could be a thin separator layer which would be used for scrap after separating the thermoformed objects from each other. ^ . , .. :

Claims: Claims 1. A process of making thermoformed plastic objects comprising coextruding a multilayered sheet having adjacent layers of plastics that do not bond to¬ gether during coextrusion, thermoforming said multilayered sheet, and separating individual thermoformed objects of different layers. 2.. The process of claim 1 wherein said multilayered sheet is made of layers of polystyrene and poly¬ propylene. 3. The process of claim 1 wherein one said plastic is for a separator layer between layers for said objects. The process of claim 1 wherein said thermoformed objects are made of more than one of the plastics of the layers of said multilayered sheet.

Inventors: BONIS LASZLO J, BONIS, LASZLO, J.
Applicants: COMPOSITE CONTAINER CORP, COMPOSITE CONTAINER CORPORATION
Application year: 1983
Main classification: B29C17
IPC codes: B29C47, B29C51