The present invention relates to a monosheet type self-processing photographic film unit and a method of making the same.
In recent years, monosheet-type self-processing photographic film units (which are referred hereinafter to simply as film units) have become increasingly popular. Such a film unit has an image-receiving sheet onto which a positive image is transferred from a photosensitive sheet and which is peeled apart from the film unit as a print. One such film unit is known from U.S. Pat. No. 4,490,456 issued on Dec. 25, 1984. In the film unit disclosed in the above-mentioned publication, it is difficult to peel apart the supporting sheet with an image-receiving layer from the film unit because of the photosensitive sheet having the same size as the film unit and the film unit is expensive because of the usage of a large size of photosensitive sheet relative to the effective image-forming area in which an image is formed.
To solve the above-mentioned problems of the conventional monosheet-type self-processing film units, there has been proposed a peelable monosheet type of self-processing photographic film unit (which is hereinafter referred to simply as a peelable film unit) which is disclosed in U.S. patent application Ser. No. 07/269,016 filed on Nov. 9, 1988. Such a peelable film unit basically comprises a photosensitive sheet, which is shorter in length than the film unit, consisting of a supporting sheet on which are formed an image-receiving layer, a peelable interlayer and a photosensitive layer one upon another in that order; a masking sheet having an opening for defining an image-forming area in the photosensitive layer; and a peelable sheet attached to the back surface of the photosensitive sheet by means of an adhesive layer as one integral unit. The peelable film unit is covered with a transparent cover sheet attached to the front surface of the photosensitive sheet. For forming a uniform layer of developing reagent over the image-forming area of the photosensitive layer, an elongated spacer member is interposed along each side of the image-forming area between the photosensitive sheet and the cover sheet.
A problem with peelable film units, is that they are apt to bend at the end of the photosensitive sheet upon being pushed out with a claw to be withdrawn from a film pack. If in fact the film unit bends, it is hard to be grasped by and between a pair of processing rollers.
When manufacturing the peelable monosheet film unit or conventional monosheet film unit, there is the problem of adhering the spacer member to the masking sheet and the cover sheet, because the spacer member is applied with an adhesive layer, such as a hot-melt adhesive layer, to the respective surface, and the simultaneous heating of the respective hot-melt adhesive layers should be avoided. For this reason, the spacer member with hot-melt adhesive layers applied to the respective surfaces is first adhered or welded to the cover sheet, and thereafter the cover sheet is adhered or welded to the masking sheet through the spacer member. In this adhering process, it is necessary to overlap the cover sheet on the masking sheet so as to position exactly the spacer members adhered to the cover sheet on both sides of the image-forming area defining opening. When automatically manufacturing the film units, it is difficult to avoid defective or faulty film units that have inadequately positioned spacer members. To avoid defective film units, positioning means should be provided in the manufacturing apparatus or manufacturing line for exactly overlapping the cover sheet on the masking sheet. This complicates the film unit manufacturing apparatus or manufacturing line.
To manufacture film units at an acceptably rapid rate, it was previously thought that the spacer member should first be attached to the masking sheet. In such a procedure, because of the spacer member applied with hot-melt adhesive layers on both surfaces and being no greater in length than the photosensitive sheet, it is impossible to heat directly the spacer member with a heating head. Accordingly, the photosensitive sheet has to be heated with a heating head to weld the spacer member to the masking sheet. But when heating the photosensitive sheet, the heat transmitted to the spacer member through the photosensitive sheet and the masking sheet is insufficient to weld firmly the spacer member to the masking sheet. This causes a weak adhesion between the spacer member and the masking sheet.
It was also previously proposed to heat the back surface of the masking sheet to weld the spacer member to the front surface of the masking sheet. The back surface of the masking sheet should, however, not be directly heated with the heating head because of the masking sheet having a hot-melt adhesive layer for welding itself to the photosensitive sheet.