Instant film unit

An instant film unit comprising:

• a mask sheet, having an exposure opening of rectangle shape which is constituted by a first side and a second side extending in a conveying direction and a third side and a forth side extending in a widthwise direction perpendicular to said conveying direction, said mask sheet including a first folded end portion and a second folded end portion disposed on both ends of said exposure opening in said conveying direction;
• a first sheet overlaid on said mask sheet to close said exposure opening;
• a second sheet, being transparent, having a predetermined space to said first sheet, and attached to said first folded end portion and said second folded end portion of said mask sheet;
• a developing solution pod, enclosed in said first folded end portion and extending in said widthwise direction, said developing solution pod for being torn open while passing through a spreading roller so that developing solution is pushed out of said developing solution pod to spread between said first sheet and said second sheet;
• a trapping member, enclosed in said second folded end portion, said trapping member for catching a surplus of said developing solution passing through the area on which said exposure opening is disposed;
• and
• corner mask portions, disposed on four corners of said exposure opening, wherein:
• said corner mask portions are formed by curving each corner of said exposure opening;
• and
• the radius r(mm) of said curve satisfies the condition:
• r>0.4×(Q2−Q1), where:
• Q1(μl) is the quantity of developing solution, necessary to spread on the whole area of said exposure opening with four right angle corners when said developing solution being pushed out of said developing solution pod spreads toward said trapping member;
• and
• Q2(μl) is the quantity of developing solution, necessary to spread on the whole area of said exposure opening with four curved corners when said developing solution being pushed out of said developing solution pod spreads toward said trapping material.

An instant film unit comprising:

• a mask sheet, having an exposure opening of rectangle shape which is constituted by a first side and a second side extending in a conveying direction and a third side and a forth side extending in a widthwise direction perpendicular to said conveying direction, said mask sheet including a first folded end portion and a second folded end portion disposed on both ends of said exposure opening in said conveying direction;
• a first sheet overlaid on said mask sheet to close said exposure opening;
• a second sheet, being transparent, having a predetermined space to said first sheet, and attached to said first folded end portion and said second folded end portion of said mask sheet;
• a developing solution pod, enclosed in said first folded end portion and extending in said widthwise direction, said developing solution pod for being torn open while passing through a spreading roller so that developing solution is pushed out of said developing solution pod to spread between said first sheet and said second sheet;
• a trapping member, enclosed in said second folded end portion, said trapping member for catching a surplus of said developing solution passing through the area on which said exposure opening is disposed;
• and
• corner mask portions, disposed on four corners of said exposure opening, wherein:
• said corner mask portions are formed by curving each corner of said exposure opening;
• and
• the conditions Q2−Q1=(2L−a)bt and (−a/b)x1+a<r+(2rx1−x12)1/2 are satisfied, where:
• Q1(μl) is the quantity of developing solution, necessary to spread on the whole area of said exposure opening with four right angle corners when said developing solution being pushed out of said developing solution pod spreads toward said trapping member;
• Q2(μl) is the quantity of developing solution, necessary to spread on the whole area of said exposure opening with four curved corners when said developing solution being pushed out of said developing solution pod spreads toward said trapping material;
• r(mm) is a radius of said curve;
• a(mm) is a length in said conveying direction of a solution-deficient area where the developing solution is not spread, said solution-deficient area being formed on each corner of said exposure opening with four right angle corners;
• b(mm) is a length of said solution-deficient area in said widthwise direction;
• L(mm) is a width of said exposure opening;
• t(mm) is a thickness of said developing solution on said exposure opening area;
• and
• x1(mm) is an arbitrary length, satisfying 0<x1<b.