Instant film unit

Claim 1

In a film unit including first and second superposed sheets, said first sheet carrying photosensitive material for recording a processable latent image and said second sheet serving to aid in the distribution of a processing fluid over the photosensitive material, said film unit further including a mask between said sheets having an aperture defining an imaging area, side rails between said sheets spaced laterally on opposite sides of the aperture, and a pouch at one end of the imaging area for supplying the processing fluid; such film unit being adapted for use with processing apparatus which includes a pressure nip of predetermined length sufficient to span the aperture for rupturing the pouch and distributing the fluid between the sheets across the imaging area; the film unit improvement comprising: said mask having a predetermined thickness for controlling the nominal depth of the distributed processing fluid; said side rails having a predetermined thickness spacing the lateral edges of the sheets apart by an amount significantly greater than the nominal depth of the distributed fluid; and said lateral spacing between said side rails being slightly greater than the length of the pressure nip, whereby said rails are disposed outside of the nip during the distribution of the processing fluid where they accommodate fluid of greater depth than said nominal depth ahead of the nip and enhance the uniformity of the distribution controlled by the mask.