Shrink-wrap packaging system

Abstract

A shrink-wrap packaging system comprising a supply of shrink-wrap film, a sealer system and an oven. The sealer system includes a hot-knife assembly, which encapsulates items being packaged by cutting, joining and sealing layers of shrink-wrap film that an operator fits around the items. The hot knife includes a double-edged blade having an electrical surface heater element fixed thereto. The heater element comprises a first layer of electrical insulation fixed directly to the blade, a serpentine resistive film deposited on the first layer and a second layer of insulation covering the resistive film. The oven includes a tunnel in which the encapsulated items are heated to form a shrink-wrap package. The oven includes heat exchangers that mount adjacent the tunnel. The heat exchangers generate heat via an array of electrical surface heater elements similar to those mounted on the hot knife.

What is claimed is:  
     
         1 . A hot knife comprising: 
 a blade having an extended surface and an operative edge;    an electrical heater element fixed to said extended surface adjacent said edge; and    an outer layer of electrical insulation covering said heater element.    
     
     
         2 . The hot knife of  claim 1 , wherein said heater element includes an inner layer of electrical insulation fixed directly to said extended surface and an electrical resistive film fixed to said inner layer and extending adjacent said edge.  
     
     
         3 . The hot knife of  claim 2 , wherein said electrical resistive film has a pair of electrical contacts with a serpentine strip of resistive material stretching between said contacts.  
     
     
         4 . The hot knife of  claim 3 , wherein said blade is ceramic, said inner and outer layers of insulation are glass, and said serpentine strip of resistive material is deposited as a thick-film resistor on said inner layer.  
     
     
         5 . The hot knife of  claim 3 , wherein said blade is metal and said inner and outer layers of insulation are rubber.  
     
     
         6 . The hot knife of  claim 3 , wherein said edge tapers to a sharp edge coated with a non-stick material.  
     
     
         7 . The hot knife of  claim 3 , wherein said edge tapers to a blunt surface coated with a non-stick material.  
     
     
         8 . The hot knife of  claim 3 , wherein said hot knife further includes a second operative edge spaced from said first-mentioned operative edge, and with said electrical heater element located between said first-mentioned edge and said second edge to form a double-edged hot knife.  
     
     
         9 . An electrical oven for heating items comprising: 
 a tunnel having an exit port, an entrance port and opposed side walls;    conveyor means mounted in said tunnel between said side walls for transporting items from said entrance port to said exit port;    a heat exchanger mounted adjacent said side walls and extending between said entrance and exit ports on either side of said conveyor means, said heat exchanger including an extended permeable surface with a plurality of electrical surface heater elements fixed thereto; and    an air circulating system mounted adjacent said tunnel, said air circulating system including a blower having a blower input and a blower output, an intake ductwork communicating with said blower input and said tunnel adjacent said exit port, and an output ductwork communicating with said blower output and said tunnel via said heat exchanger.    
     
     
         10 . The electrical oven of  claim 9 , wherein said heater elements each include an inner layer of electrical insulation fixed directly to said extended permeable surface and an electrical resistive film fixed to said inner layer.  
     
     
         11 . The electrical oven of  claim 10 , wherein said electrical resistive film has a pair of electrical contacts with a serpentine strip of resistive material stretching between said contacts.  
     
     
         12 . The electrical oven of  claim 11 , wherein said permeable surface is metal, each of said heater elements is covered with an outer layer of electrical insulation, and said inner and outer layers of insulation are rubber.  
     
     
         13 . The electrical oven of  claim 11 , wherein said heat exchanger includes a plurality of parallel flanges projecting into said output ductwork and said electrical surface heater elements mount on said flanges.  
     
     
         14 . The electrical oven of  claim 13 , wherein said heat exchanger includes a plurality of radial flanges projecting into said output ductwork and said electrical surface heater elements mount on said flanges.  
     
     
         15 . A shrink-wrap system for packaging items comprising: 
 a supply of shrink-wrap film;    a sealer system having a hot-knife means for encapsulating items in said film, said hot-knife means includes at least one elongated blade with an operative edge, a first electrical heater element fixed to said blade and an outer layer of insulation covering said heater element; and    an electrical oven system having a tunnel, and a heat exchanger having at least one extended permeable surface mounted adjacent said tunnel and a plurality of electrical surface heater elements mounted on said extended permeable surface.    
     
     
         16 . The shrink-wrap system of  claim 15 , wherein said first electrical heater element includes a first layer of electrical insulation fixed directly to said blade and a first electrical resistive film fixed to said first layer and extending adjacent said edge.  
     
     
         17 . The shrink-wrap system of  claim 16 , wherein said plurality of electrical surface heater elements each include a second layer of electrical insulation fixed directly to said extended permeable surface and a second electrical resistive film fixed to said second layer.  
     
     
         18 . The shrink-wrap system of  claim 16 , wherein said first electrical resistive film and said second electrical resistive films each has a pair of electrical contacts with a serpentine strip of resistive material stretching between said contacts.  
     
     
         19 . The electrical oven of  claim 18 , wherein said heat exchanger includes a plurality of parallel flanges with a plurality of said second electrical surface heater elements mounted thereon.  
     
     
         20 . The electrical oven of  claim 18 , wherein said heat exchanger includes a plurality of radial flanges with a plurality of said electrical surface heater elements mounted thereon.