Apparatus for forming slits

A slit forming apparatus for forming slits in the lateral direction of a strip-shaped material, said strip-shaped material having a main central portion and side margin portions, which apparatus comprises a first rotating member having a rotation axis and a periphery and rotating in a first direction, a second rotating member having a rotation axis, said first rotating member having blades for forming lateral slits only in said main central portion, said blades having a longitudinal extension and being located on said periphery of said first rotating member such that said longitudinal extension is parallel to said rotation axis, said second rotating member having a peripheral surface and a backing portion for backing said main central portion and rotating in a second direction opposite to said first direction, said blades penetrating said strip-shaped material when said first rotating member rotates and said strip-shaped material passes between said first rotating member and said second rotating member, said second rotating member having recessed portions for receiving said blades when they penetrate said main portion;

• and conveying means for conveying said strip shaped material by pulling only said side margin portions in a third direction to separate said side margin portions from said first rotating member and to position said side margin portions at an angle with respect to said main central portion wherein said third direction is diagonal to said rotation axis of said second rotating member such that said main central portion passes between said first rotating member and said second rotating member and is pressed portions said backing portion, a tension along a part of said peripheral surface of said second rotating member is applied to said side margin portions, and the longitudinal movement of said strip-shaped material is controlled.