Patent ID: 7291372

Claim:
A release process film consisting of a base material film and an adhesive layer disposed on one face of the base material film, and is used by attaching the release process film to a flexible printed circuit board comprising a plastic sheet, the release process film being operable to adhere to the plastic sheet, wherein said base material film is a film selected from the group consisting of polyethylene terephthalate film, polycarbonate film, amorphous polyolefin film, aramide film, polyethylene naphthalate film, polyphenylene sulfide film, aromatic polysulfone film, polyether imide film, polyarylate film, polyether ether ketone film; the base material film having a thickness of 16 to 200 μm and said adhesive layer has the following features: (a) the adhesive layer comprises an adhesive which comprises at least one acrylate-based copolymer comprising 40 to 99% by mass of a butyl acrylate unit and 1 to 20% by mass of at least one monomer unit having a crosslinking functional group and at least one crosslinking agent; (b) the adhesive layer having a gel fraction of 90% or greater; (c)) a holding power to the plastic sheet as an adherend is 70,000 seconds or greater as measured in accordance with a method of Japanese Industrial Standard Z0237; (d) an adhesive strength to the plastic sheet as an adherend is 0.05 to 2.0 N/25 mm as measured in accordance with a method of Japanese Industrial Standard Z0237 before being heat pressed; (e) an adhesive strength to the plastic sheet as an adherend is 0.1 to 4.0 N/25 mm as measured in accordance with a method of Japanese Industrial Standard Z0237 after being attached to the plastic sheet and heat pressed for 30 minutes under conditions of a temperature of 180° C. and a pressure of 4.3 N/mm 2 ; and (f) a shear value after heat pressing the release process film and the plastic sheet is 50 μm or smaller, said shear value being determined by attaching a face of the adhesive layer of the release process film to the plastic sheet, wherein the release process film has four corners and a size of 20 cm×20 cm and the plastic sheet has a size of 22 cm×22 cm, as an adherend, forming through holes having a diameter of 6 mm in the plastic sheet at the four corners of the release process film, heat pressing the release process film and plastic sheet for 30 minutes under the conditions of a temperature of 180° C. and a pressure of 4.3 N/mm 2 , measuring shears between the release process film and the adherend at the four corners and obtaining an average of measured shears at the four corners as a measurement of the shear value.