Envelope intermediate with integral mail-back piece

Claim 1

A folded envelope including an integral two-ply mail-back piece which is detachable from said envelope without opening said envelope, said envelope comprising: a substrate sheet having first and second surfaces, first and second opposite parallel longitudinal edges, and first and second opposite end edges; first, second and third transverse fold lines formed in said substrate perpendicular to said parallel longitudinal edges, dividing said substrate into first, second, third and fourth panels, said first fold line separating said first and second panels, said second fold line separating said second and third panels, said third fold line separating said third and fourth panels; a first adhesive pattern provided on said second surface of at least one of said second and third panels, and lines of weakness disposed in said second and third panels; a second adhesive pattern provided on said second surface of at least one of said first and fourth panels adjacent said first and second longitudinal edges of said substrate sheet; and said substrate sheet being folded such that: (a) said second surfaces of said second and third panels lie in contact and are adhered together by said first adhesive pattern to form said integral two-ply mail-back piece, said lines of weakness permitting detachment of said mail-back piece without opening said envelope, and (b) said second surfaces of said first and fourth panels lie in contact and are adhered together by said second adhesive pattern to form said envelope; said envelope further including a third adhesive pattern provided on said first surface on at least one of said first and second or third and fourth panels so that when said substrate is folded about said first and third fold lines said first surfaces of either said first and second or said third and fourth panels lie in contact and are adhered together by said third adhesive pattern.