Abstract: A blank for a sleeve type casing with a cover for receiving a recording medium which is formed by punching out a plastic sheet and folding a punched sheet along ruled lines formed in it, and which has a U-shaped notched portion for finger touch at an edge for forming a part of an opening of the casing, wherein the blank has a cover flap with an insertion flap so that the cover flap covers the opening when the blank is formed into a box-like body and a seam-like cut line having a central portion of a U-shape and side portions extending linearly from both ends of the U-shape central portion so as to extend along the root portion of the cover flap.

Abstract: The abrasion resistance of a nonmagnetic substrate of a polyester film of a magnetic recording tape can be improved without the use of a backcoating layers by adding a pH basic filler to the polyester film. The pH basic filler should exhibit a blue color when Bromothymol Blue, a basicity indicator, is adsorbed thereon.