Thermoforming plastic articles

Claim 2

A PROCES FOR THE PRODUCTION OF A THERMOFORMED THERMOPLASTIC ARTICLE WHICH COMPRISES PROVIDING A RELATIVELY FLAT ORIENTED SHEET OF POLYSTYRENE FOAM, PREHEATING SAID SHEET TO AT LEAST ITS FORMING TEMPERATURE, THEREMOFORMING SAID PHREHEATED SHEET BY IMPRESSING IT AGAINST THE SURFACE OF A FIRST MOLD ELEMENT REMOVING SAID THERMOFORMED ARTICLE FROM SAID FIRST MOLD ELEMENT WHILE SAID THERMOFORMED ARTICLE IS STILL AT AN ELEVATED AND DEFORMABLE TEMPERATURE, DIRECTLY IMPRESSING POST MOLD COOLING MOLD ELEMENT AGAINST AT LEAST PORTIONS OF BOTH SIDES OF SAID THERMOFORMED ARTICLE THEREBY RESTRAINING AT LEAST SAID PORTIONS OF SAID ARTICLE AGAINST DEFORMATION AND SIMULTANEOUSLY COOLING SAID PORTIONS BELOW DEFORMATION TEMPERATURE TO AVOID SUBSTANTIAL DISTORTION OF SAID ARTICLE UPON REMOVAL FROM SAID POST MOLD COOLING MOLD ELEMENTS.

Claim 3

A process in accordance with claim 1 wherein the surface temperature of said second mold element is at least 5*F. below the surface temperature of said first mold element.

Claim 4

A process for the production of a thermoformed thermoplastic egg carton, said egg carton comprising a bottom cellular section, an inverted dish-like cover section integrally hinged along one longitudinal edge of said cover, and a latching flap hinged to the opposite longitudinal edge of the bottom cellular section, which process comprises providing a relatively flat sheet of oriented polystyrene foam material, preheating said sheet to at least its forming temperature, thermoforming said preheated sheet to form an egg carton of said structure by impressing said preheated sheet against the surface of a first mold element, removing the formed egg carton from said first mold element, and while said egg carton is still at an elevated and deformable temperature, directly impressing the interior and exterior surfaces of said egg carton cover and said egg carton latching flap against the surface of post mold cooling mold elements thereby restraining at least said cover and flap of said egg carton against deformation and simultaneously cooling below deformation temperature to avoid subsequent deformation and warpage of said carton upon removal from said post mold cooling mold elements.

Claim 5

A process for the production of a thermoformed thermoplastic egg carton, said egg carton comprising a bottom cellular section, an inverted dish-like cover section integrally hinged along one longitudinal edge of said cover, and a latching flap hinged to the opposite longitudinal edge of the bottom cellular section, which process comprises providing a relatively flat sheet of oriented polystyrene foam material, preheating said sheet to at least its forming temperature, thermoforming said preheated sheet to form an egg carton of said structure by impressing said preheated sheet against the surface of a first mold element, removing the formed egg carton from said first mold element, and while said egg carton is still at an elevated and deformable temperature, directly impressing the interior and exterior surfaces of said egg carton cover and said egg carton latching flap against the surface of post mold cooling mold elements thereby restraining at least said cover and flap of said egg carton against deformation and simultaneously cooling below deformation temperature to avoid subsequent deformation and warpage of said carton upon removal from said post mold cooling mold elements.

Claim 6

A process for the production of a thermoformed thermoplastic egg carton from oriented polystyrene foam sheet, said egg carton comprising a bottom cellular section, an iverted dish-like cover section integrally hinged along one longitudinal edge of said cover, said cover section having at least two inwardly projecting locking detents adapted to lockingly engage at least two inwardly projecting recesses located on a latching flap hinged to a longitudinal edge of said bottom cellular section, said recesses lockingly engaging said detents when said cover is in a closed position, said process comprising providing a relatively flat sheet of polystyrene foam, preheating said sheet to at least its forming temperature, thermoforming said egg carton in said preheated sheet by impressing said preheated sheet against the surface of a first mold element, removing the sheet containing said egg carton from said first mold element and, while the egg carton in said sheet is in an unsupported condition but still at an elevated temperature and deformable condition, immediately contacting the interior and exterior surfaces of only the cover and latching flap of the carton against the surface of post mold cooling mold elements simultaneously cooling said cover and said latching flap below their heat deformation temperature to avoid substantial distortion of said egg carton upon removal from said post mold cooling mold elements thereby maintAining said projecting locking detents and said projecting recesses in alignment for locking engagement when said carton is closed, and trimming said egg carton from said sheet.

Claim 7

A process for the production of a thermoformed thermoplastic egg carton from oriented polystyrene foam sheet, said egg carton comprising a bottom cellular section, an iverted dish-like cover section integrally hinged along one longitudinal edge of said cover, said cover section having at least two inwardly projecting locking detents adapted to lockingly engage at least two inwardly projecting recesses located on a latching flap hinged to a longitudinal edge of said bottom cellular section, said recesses lockingly engaging said detents when said cover is in a closed position, said process comprising providing a relatively flat sheet of polystyrene foam, preheating said sheet to at least its forming temperature, thermoforming said egg carton in said preheated sheet by impressing said preheated sheet against the surface of a first mold element, removing the sheet containing said egg carton from said first mold element and, while the egg carton in said sheet is in an unsupported condition but still at an elevated temperature and deformable condition, immediately contacting the interior and exterior surfaces of only the cover and latching flap of the carton against the surface of post mold cooling mold elements simultaneously cooling said cover and said latching flap below their heat deformation temperature to avoid substantial distortion of said egg carton upon removal from said post mold cooling mold elements thereby maintAining said projecting locking detents and said projecting recesses in alignment for locking engagement when said carton is closed, and trimming said egg carton from said sheet.