| 摘要 |
A product such as meat or a ready meal 12 is packaged in a tray 14 of a polymeric material, covered with a cover sheet 34. The cover sheet 34 is less than a third the thickness of the tray 14, which has a rim 16, and the cover sheet is welded to the rim of the tray by dielectric welding so as to form a seal along a welding line around the rim 16. Along that welding line the rim has a thinner portion 28 of thickness no more than twice the thickness of the cover sheet 34. The similarity in thickness between the two layers of polymeric material that are welded together makes dielectric welding easier to perform, and this provides the advantage that a good seal can be formed despite the presence of contamination on the surfaces, as is likely to occur when packaging foodstuffs. There is also no need for any surface bonding layer on either the tray or the cover film, or any adhesive. |
