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Twin-sheet-thermoforming-process-with-shell-reinforcement

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Twin-sheet thermoforming process with shell reinforcement

Details

Inventors: Breezer, Harlon W.; Price, William F.;
Assignee: TriEnda Corporation (Portage, WI)
Primary Examiner: Watkins; William
Assistant Examiner:
Attorney, Agent or Firm: Lathrop & Clark

A process is disclosed for producing reinforced twin-sheet thermoformed articles comprising the steps of heating first and second sheets of thermoplastic material; forming the sheets in molds; heating a reinforcing insert of thermoplastic material; placing the heated insert on the first sheet in its mold at the location to be reinforced; pressing the second sheet into contact with the heated first sheet and the heated insert to form the insert between the sheets so that a fusion of the thermoplastic sheets and the insert takes place to produce a reinforced section of the article having a desired shape and thickness. Alternative processes are disclosed wherein a heated quantity of thermoplastic liquid material is extruded or injected between the first and second sheets within the first and second molds either by inserting the liquid material before the molds are closed or by injecting it through one of the molds. Also disclosed are twin-sheet thermoformed articles with reinforced sections which are thicker than the combined thicknesses of the two thermoformed sheets at a particular location. The articles may advantageously be reinforced with plastic identical to the plastic of the two sheets. The articles are also easily recycled as they are entirely plastic with no non-plastic matter included.

DETAILED DESCRIPTION We claim: 1.
A process for producing a reinforced twin-sheet thermoformed thermoplastic article having a reinforced portion, the process comprising the steps of: (a) heating first and second sheets of thermoplastic material; (b) forming the first sheet in a first mold; (c) forming the second sheet in a second mold; (d) pressing the heated second sheet in the second mold into contact with the heated first sheet in the first mold such that the two sheets are fused together at selected areas of contact and mate to form a hollow cavity at a selected reinforced location; and (e) injecting under pressure a quantity of liquid thermoplastic material through at least one of the molds and one of the sheets into the cavity to substantially fill the cavity with thermoplastic material so that the quantity of liquid thermoplastic material fuses with the two sheets defining the cavity to form an article having a continuous integral reinforced portion of a desired shape and thickness at the selected reinforced location.
2.
The process of producing a reinforced thermoplastic article having a reinforced portion of claim 4, wherein the first sheet, the second sheet, and the quantity of liquid thermoplastic material are all formed of the same thermoplastic material.

Description:
FIELD OF THE INVENTION The present invention relates to twin-sheet thermoformed plastic articles and processes for making such articles in general, and to selectively reinforced articles and twin-sheet thermoforming processes for making such reinforced articles in particular.
BACKGROUND OF THE INVENTION The thermoforming process may be used to form plastic articles of all sizes, and is particularly effective when it is desired to form large plastic articles at low cost.
Articles thermoformed from a single sheet of thermoplastic material are generally limited in wall thickness to the thickness of the sheet or less, throughout.
By utilizing a twin-sheet thermoforming process articles of greater thickness and stiffness may be formed

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