| 摘要 |
PROBLEM TO BE SOLVED: To provide a design of an overlap width and its forming method for realizing the unsealing of a sealed letter, which involves an unreversible and controlled breaking without using an edged tool or the like and irregularly breaking a sheet in the case where a sealed letter made of paper for information is unsealed on the receiver's side. SOLUTION: A rectangular envelope for a sealed letter is formed by using a wood-free sheet, which is within the range of 81 to 162 g per m2, or a coated sheet, and by applying a pressure-sensitive adhesive to a portion where one side or a plurality of sides are overlapped. In this case, a space having a distance of 0.5 to 10 mm from a portion to which the pressure-sensitive adhesive is applied is provided by a straight line or by a curved line at the whole edge or at part of an edge along an edge at an adhered portion of a joint by the pressure-sensitive adhesive. A cut having a depth of at most 1/2 of the thickness of the sheet is provided in both of or in one of the joint surfaces of the overlapping sheets, and the sheets are then joined to each other, thus forming the envelope.
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