Vacuum skin package, and process and apparatus for making same

Abstract

In the prior art, vacuum skin packaging processes are performed by placing the product to be packaged on an impervious backing board; placing the product and board in a vacuum chamber; positioning a sheet of thermoplastic film above the product and backing board in the chamber; evacuating the chamber; then, either pulling the film down over the product or pushing the product up into the film; and, thereafter sealing the film to the board. In the present invention, a portion of the film is drawn by differential air pressure against the concave interior surface of the upper portion of a vacuum chamber; the film is then heated by surface contact; and then, after evacuation of the chamber, air pressure is used to blow the film down over the product and against the backing board. Thus, in the present invention, the film is shaped in a concave fashion surrounding the upper portion of the product and it is not necessary for the product to move. The height of the chamber may be adjusted for different products so that excess film is not used and wrinkling is prevented.

Having thus described our invention, we claim: 
     
       1. A vacuum skin packaging process comprising: a. placing the product to be packaged on a gas impervious supporting member;   b. shaping a .Iadd.heat softenable, .Iaddend.flexible sheet member into a concavity .Iadd.by differential air pressure; .Iaddend.   c. maintaining the concave shape of said sheet .Iadd.by said differential air pressure while heating said sheet to its softening and forming temperature; .Iaddend.   d. positioning said sheet over said product and supporting member so that said sheet partially covers but does not contact either said product or supporting member;   e. evacuating gases from the space between said sheet and said supporting member, which contains said product .Iadd.while maintaining said sheet in its concave shape at its softening and forming temperature until it is released to move against the product; .Iaddend.   f. moving said sheet from its concave shape and position so that it closely contacts said product and supporting member; and,   g. sealing said sheet against said supporting member.   
     
     
       2. A process for vacuum skin packaging a product on an impervious supporting member .Iadd.by forming a heat formable thermoplastic member around said product .Iaddend.comprising the steps of: a. drawing by differential air pressure .[.a.]. .Iadd.said .Iaddend.formable plastic sheet member against a concave surface;   b. heating said concave surface to at least the softening temperature of said thermoplastic member;   c. maintaining said differential air pressure; while   d. positioning said sheet member over said product on said supporting member;   e. evacuating the space between said supporting member and said sheet member .Iadd.while retaining said sheet member against said heated concave surface to maintain said sheet member at its softening temperature until it is released to move against the product; .Iaddend.   f. releasing the differential air pressure which maintained the concave shape of said sheet member, thereby causing said sheet member to collapse over and around said product and against said supporting member; and,   g. sealing said thermoplastic sheet member to said supporting member as it collapses thereagainst.   
     
     
       3. A vacuum skin packaging process comprising: a. providing a supporting platform within the lower portion of a vacuum chamber;   placing a product on an impervious backing member on said supporting platform;   c. shaping a heat softenable thermoplastic film in the cavity of the upper portion of said vacuum chamber;   d. retaining said thermoplastic film in said shape while   e. heating said film to its softening and forming temperature;   f. positioning said upper portion of said chamber over said product and closing said chamber, said thermoplastic film being clamped between the upper and lower portions of said chamber;   g. evacuating said chamber .Iadd.while maintaining said film at its softening and forming temperature until it is released to move against the product; .Iaddend.and,   h. releasing said thermoplastic film from its retained position whereby it collapses around said product and is driven against said supporting member.   
     
     
       4. The process of claim 3 including the step of adjusting the height of the upper portion of said chamber in accordance with the height of the product to be packaged by adding a shim member to the lower periphery of said chamber. 
     
     
       5. The process of claim 3 wherein the thermoplastic material is polyethylene. 
     
     
       6. The process of claim 3 wherein the polyethylene is coated with a polymer of ethylene vinyl acetate. 
     
     
       7. The process of claim 3 wherein the impervious supporting member is made from thermoplastic foam. 
     
     
       8. The process of claim 7 wherein the thermoplastic foam is polystyrene foam and the heat softenable material is polyethylene coated with a polymer of ethylene vinyl acetate. .Iadd. 9. A process for vacuum skin packaging a product positioned between two impervious sheet members one of which supports the product comprising the steps of: a. drawing by differential air pressure one of said impervious sheet members which is a heat-softenable, formable plastic material against a concave surface which is shaped to partially enclose the product to be packaged;   b. maintaining said differential air pressure while;   c. heating said concave surface to at least the forming and softening temperature of said heat softenable and formable plastic sheet member;   d. positioning one sheet member over said product on said supporting member with the product therebetween and said formable sheet member on said concave surface partially enclosing said product; and   e. evacuating the space between said supporting member and said sheet member while retaining by said differential air pressure the formable sheet member in contact with said heated concave surface to maintain said formable sheet member at its forming and softening temperature;   f. then increasing the air pressure on the exterior of the formable sheet member to cause it to be released from contact with the concave surface thereby causing the formable sheet member to collapse around and into conforming contact with the product and against said other sheet member; and   g. sealing the heat formable and softenable sheet member to the other sheet member as the heat formable and softenable sheet member collapses thereagainst..Iaddend.