| 摘要 |
PURPOSE:To visually identify a degree of thermal welding to ensure an airtightness and an easy to openability by a method wherein a color difference produced by softening and reducing in thickness a white layer film and a welding layer film at the time of thermal welding is made to correspond to a wall thickness reduction ratio of the resin layers depending on a heating value. CONSTITUTION:A resin film cover body is formed by successively laminating a substrate film 11, a printing layer 12, a white layer film 13, and a welding layer film 14. The laminated film cover body is put on an opening of a closure edge part 10 with the welding resin layer brought into contact with the closure edge part 10. The cover body is pressurized along the peripheral part of the closure opening by abutting a heating die on the substrate film 11, thereby being thermally welded to the closure edge part 10. At this time, the white layer film 13 and the welding layer film 14 are reduced in thickness to produce a color difference from an unsealed part having no change in thickness. In this case, since the wall thickness is reduced in accordance with a heating value of thermal welding, the color difference is proportional to the wall thickness reduction ratio of the white layer film 13. In this manner, a degree of thermal welding can be identified as a color difference visually or using an image sensor. |
