Packing bag for light sensitive materials and manufacturing method

Abstract

A bag for packing a light-sensitive material is disclosed. The bag has an outermost surface and an innermost surface and is essentially consisting of a material for making the bag which comprises not less than 70% by weight of polyethylene and 1 to 10% by weight of a light shielding material based on the weight of the material, in which a Vicat softening point of the outermost surface is higher by not less than 20.degree. C. than a Vicat softening point of the inner most surface. Further a method for producing a bag is disclosed. The method comprises the steps of, running a sheet for producing a bag; facing edges of the sheet which are parallel to a running direction of sheet to make an outer surface and an inner surface of the bag; heating a portion of the outer surface which is to be sealed in a heating means having a pair of heater bars with keeping a first distance between faced inner surfaces uniform and a second distance between the outer surface and one of the heater bars faced the outer surface wider than the first distance in the heating means, in which the heater bars are parallel to the running direction, the sheet is running between the heater bars continuously; and compressing the portion to be sealed.