| 摘要 |
PURPOSE:To permit efficient forming of filters in production processing without becoming a sector-shaped during the forming by making every side of the base length of a triangular part formed at both ends of a filter paper to be folded, substantially identical. CONSTITUTION:A filter 10 has folds provided on a rectangular filter paper 11. The folds are composed of triangular folds 12a, 12b spreading to one end and triangular folds 13a, 13b likewise spreading to the other end provided alternately at a predetermined interval. Then the lengths l1, l2 of the base of a triangular part surrounded by the triangular folds on the respective ends are allowed to become substantially the same. Subsequently, if the filter paper 10 is folded along the folds, it does not become sector-shaped, but becomes rectangular with both ends in parallel. Therefore, these filters can easily be carried by a conveyor in production. Further, they may be slightly deformed, but are not damaged, even if they are formed in annular shapes.
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