Product packaging

Abstract

A product such as meat or a ready meal ( 12 ) is packaged in a tray ( 14 ) covered with a cover film ( 34 ), these being bonded together by dielectric heating between opposed electrodes ( 18, 24 ). The dielectric heating is carried out through at least one barrier layer ( 22, 28 ) comprising a foam material of a polymeric material that is not susceptible to RF. The film ( 34 ) may be of laminated form, for example comprising a polymer such as APET laminated to a bonding layer of polyethylene. This welding process avoids heat wastage, it can provide narrower seals, and enables a good seal to be obtained despite contamination of the surface of the tray.

1 . A method for packaging a product, using a tray and a cover sheet, the method comprising bonding the cover sheet to the tray by dielectric welding between opposed electrodes, wherein at least one of the electrodes is covered by a barrier layer comprising a foam material of a polymeric material.  
     
     
         2 . A method as claimed in  claim 1  wherein the foam layer is self-adhesive.  
     
     
         3 . A method as claimed in  claim 1  wherein the foam layer is of acrylic foam.  
     
     
         4 . A method as claimed in any  claim 1  wherein the foam layer is itself covered with a non-porous polymer layer.  
     
     
         5 . A method as claimed in  claim 1  wherein the tray comprises aluminium foil.  
     
     
         6 . An apparatus for packaging a product, using a tray with a rim, and a cover sheet, the apparatus comprising a die defining a recess to locate the tray, the die acting as an electrode, and an opposed electrode whereby the rim and the cover sheet can be located between the die and the opposed electrode to be subjected to dielectric welding, the apparatus also comprising means to supply RF signals between the die and the opposed electrode, wherein at least one of the electrodes is covered by a barrier layer comprising a foam material of a polymeric material.  
     
     
         7 . An apparatus as claimed in  claim 6  wherein the foam material is an acrylic foam.  
     
     
         8 . An apparatus as claimed in  claim 6  wherein the foam layer is itself covered with a non-porous polymer layer.  
     
     
         9 . A method of dielectric welding using opposed electrodes, wherein at least one of the electrodes is covered by a barrier layer comprising a polymeric foam material.  
     
     
         10 . A plant for packaging food products in trays, wherein each tray is supported in an aperture in a plate, wherein each plate is electrically insulated from the remainder of the plant, the plant also incorporating a radio-frequency signal generator, means to connect the plant to earth and means to connect the plate to the signal generator, so the trays are welded to a cover film by dielectric welding, wherein the dielectric welding is carried out through a barrier layer comprising a foam material of a polymeric material.