| 摘要 |
The method of the invention includes a step of jointing, in a sheet (1) formed in a rectangular shape, end portions (4,5) of a pair of mutually opposed two sides in such a manner as to form a jointed portion of a predetermined width along a planar direction of the sheet (1). In the rectangular sheet (1), a pair of mutually opposed two end portions (4,5) are jointed by a joint portion formed along the planar direction of the sheet. |
