The present invention relates to instant-processing film units suitable for daylight handling both before and after exposure. More specifically, the invention relates to such film units having an internal dark slide which is removeable from one end of the unit, and means for establishing a light seal between the dark slide and the film unit at such end, which light seal does not interfere significantly with the removal of the dark slide.
In cross-referenced U.S. patent application Ser. No. 834,589, entitled INSTANT-PROCESSING FILM UNIT HAVING INTERNAL DARK SLIDE, a film unit is disclosed which is suitable for daylight handling on a one-shot or single film unit basis both before and after exposure in commercially available apparatus. The film unit includes a photosensitive element for recording a latent image, a cover sheet preregistered with the element for facilitating the distribution of a processing composition over the element, and an internal dark slide removeably positioned between the element and sheet for shielding the photosensitive element from premature exposure or fogging. In operation, the film unit is daylight loaded into the exposure apparatus and then the dark slide is removed so the film unit can be exposed in the usual manner.
Film units of the abovementioned type offer significant advantages over previously available approaches. They are suitable for pre-exposure as well as post-exposure daylight handling on an individual or one-shot basis, yet they are relatively simple in physical construction and are easy to use with commerically available exposing apparatus. It has been found, however, that under certain handling conditions, the photosensitive element may be fogged by light entering between that element and the cover sheet at an end section of the unit. When the film unit is handled by its leading end, or even by the dark slide itself, for example, the leverage of the respective film-unit elements may lift the slide from its protective position relative to the photosensitive element.
The light sealing problem is exacerbated by the fact that the seal should remain secure under possible adverse handling conditions until after the film unit is positioned in the exposure apparatus. It should be remembered that in such position the seal is inaccessible. Moreover, while the interface between the seal and the dark slide must be sufficiently intimate to block light, it should not significantly interfere with the intended removal of the dark slide.