To enable realization of a bag which is excellent in freestanding stability, which can be subjected to heat cooking by a microwave oven with a bag body kept as it is and which is free from escape of a content liquid or the like, by a method wherein a plastic material of which the surface has a non-thermal-adhesion property and the inner surface a thermal adhesion property is folded, the opposed parts having the thermal adhesion property are heat-bonded and the bottom part is shaped like the bottom of a ship.
Front and rear walls 1 and 2 each of which has a surface (p) having a non- thermal-adhesion property and an inner surface (q) having a thermal-adhesion property are put on each other with the inner surfaces (q) opposed. A bottom wall 4 folded in the shape of an inverted V with the inner surface (q) outside and having notch parts 3 in both side edges is inserted into a lower end part between the front and rear walls, and the walls 1, 2 and 4 are laminated. A plastic bag A is manufactured in such a manner that side seal parts 5 are formed by heating the laminated parts of the walls 1 and 2, 1 and 4 and 2 and 4 in both side edge parts of these walls, seal parts 6 are formed by heating the laminated parts of the walls 1 and 2 through the intermediary of the notch parts 3, a bottom seal part 7 is formed by heating the laminated parts of the walls 1 and 4, and 2 and 4, in the bottom edge part and oblique seal parts 8 are formed in the laminated parts of the walls 1 and 4, and 2 and 4, from parts of the side top parts (r) of the wall 4 toward the seal part 7.
NAKAGOME TAKASHI
HONDA MASAHIKO
HAYAKAWA MASANAKA
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