Plastic article or earthenware shaping or treating: apparatus – Preform reshaping or resizing means: or vulcanizing means... – Including shaping means comprising fluid pressure contacting...
Reexamination Certificate
1999-04-05
2001-07-10
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Preform reshaping or resizing means: or vulcanizing means...
Including shaping means comprising fluid pressure contacting...
C425S388000
Reexamination Certificate
active
06257866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus for forming plastic sheet and, more particularly, to accurately thermoforming plastic sheet in registration with a mold.
2. Description of Related Art
Cold forming of plastic sheet material in conformance with a mold has the benefit of not requiring delays for cooling purposes associated with thermoforming sheet material at a temperature in excess of the transition (T
g
) temperature. However, cold forming requires significant pressures in the range of 50-300 bars depending upon the characteristics of the sheet material and the nature of the mold. Moreover, the resulting stretching of material, particularly for deep drawn plastic pieces, usually results in distortion of any indicia disposed upon the sheet material. Accordingly, the indicia must be applied subsequent to the cold forming process or through use of an added sheet material containing the indicia.
Thermoforming sheet material by conventional heating of the sheet to at least the softening temperature produces sag of the material prior to contact with a mold. Such sag may distort any indicia disposed upon the sheet. Moreover, the heating is usually not uniform across the sheet and will produce cold spots and hot spots. The uneven heating will result in uneven stretching of the material over a mold.
SUMMARY OF THE INVENTION
Thermoforming plastic sheet material in conformance with a mold is initiated by locating the sheet material against a heated planar plate. Above ambient or below ambient air pressure or a combination thereof may be used to position the sheet material adjacent the surface. Heat from the plate is uniformly transferred by conduction to the sheet material. By a rapid reversal of the air pressure applied to opposed sides of the heated sheet material, it is placed adjacent and deep drawn about a mold. Usually, indicia on the sheet material corresponds with the high surfaces of the article to be molded and the initial contact of the sheet material with such elements of the mold brings about immediate and rapid cooling to prevent deformation of the indicia during the subsequent near instantaneous deep drawing of the sheet in response to the pressures imposed. Registration pins or the like fixedly position the sheet material with respect to the mold to ensure registration of the indicia with the corresponding surfaces of the mold. The use of temperature sensors sensing heat radiating from the sheet material during the heating step permits controlled heating without impinging upon or otherwise affecting the sheet material during either heating, forming, or cooling of the sheet material. If two or more sheets are adjacent one another, they can be fused or bonded to one another during the heating step.
It is therefore a primary object of the present invention to provide apparatus for accurately forming plastic sheet material in conformance with a mold.
Another object of the present invention is to provide apparatus for heating sheet material during a thermoforming process without permitting the sheet material to sag during the heating process.
Still another object of the present invention is to provide a pressure environment to maintain plastic sheet material adjacent a heating surface and to rapidly deep draw the sheet material about a mold after heating.
A further object of the present invention is to provide a sealed pressure environment using a combination of above and below ambient gas pressures to position sheet material during the heating step and the molding step of a thermoforming process.
A still further object of the present invention is to provide registration pins for positioning sheet material with respect to a mold during the heating and the deep drawing of the sheet material about the mold.
A yet further object of the present invention is to fuse a plurality of sheets and form the fused sheets about a mold.
A yet further object of the present invention is to provide a method for thermoforming plastic sheet material.
These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds.
REFERENCES:
patent: 3632252 (1972-01-01), Amberg
patent: 3661484 (1972-05-01), Psota et al.
patent: 3661486 (1972-05-01), MacDonald
patent: 4239727 (1980-12-01), Myers et al.
patent: 4836762 (1989-06-01), Davis, Jr.
patent: 5162124 (1992-11-01), Hausler et al.
patent: 5217563 (1993-06-01), Niebling et al.
patent: 5264172 (1993-11-01), Rosica et al.
patent: 5283029 (1994-02-01), Ellemor
patent: 5529479 (1996-06-01), Souders
patent: 5641524 (1997-06-01), Rush et al.
Article entitled “In Mold Decorating Technical Guide”, General Electric Company, 12/95, pp. 2-16 and title page.
Article entitled “Injection Moulded Parts with a Decorative Surface—A Comparison of the Different Processes”, based on the paper first publ. in Plastverarbeiter 44 (1993) submitted by Mr. D.L. Joachim Wank, (6 pages).
Case Wayne L.
Fritz Alton L.
Fritz Kenneth A.
Fritz Michael L.
Gasiorek Edward J.
Cahill Sutton & Thomas P.L.C.
Hy-Tech Forming Systems, Inc.
Mackey James P.
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