A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The sheet separation device includes a winding roller, a conveyance roller pair, and a separation claw. The winding roller rotates and winds the two-ply sheet. The conveyance roller pair conveys the two-ply sheet toward the winding roller. The separation claw is inserted into a gap between the two sheets at a position between the winding roller and the conveyance roller pair. The separation claw is disposed in a space that is bounded by an imaginary plane and includes the winding roller. The imaginary plane passes through a nip of the conveyance roller pair and a winding start position at which the two-ply sheet starts to be wound around the winding roller.

In a method for producing a collection (20) of pre-products by inserting a first pre-product (1) into a second pre-product (3), it is provided according to the invention that a first pre-product (1) and a second pre-product (3) are provided, wherein the second pre-product (3) has a wrapping fold (4) with a fold inner side (5). The second pre-product (3) is conveyed into an insertion position, in which the second pre-product (3) is opened and faces with the fold inner side (5) toward the first pre-product (1). The first pre-product (1) is conveyed into the opened second pre-product (3) and against the fold inner side (5) so as to form the collection (20), the second pre-product (3) assumes the conveying direction of the first pre-product (1), and the collection (20) is provided for further processing.

A sheet separation device includes a sheet separator and a conveyor. The sheet separator separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The conveyor conveys the two-ply sheet toward the sheet separator while bending the two-ply sheet in a direction that intersects a conveyance direction of the two-ply sheet.