Reinforcing film

A reinforcing film comprising:

• a film substrate;
• and
• a pressure sensitive adhesive layer,
• wherein
• the film substrate is a flexible film,
• the pressure sensitive adhesive layer is photocurable and before photocuring is laminated and fixed on one principal surface of the film substrate,
• the pressure sensitive adhesive layer is formed of a photocurable composition comprising an acrylic base polymer and a photocurable agent,
• a shear storage elastic modulus at 25° C. of the pressure sensitive adhesive layer before photocuring is 1×104 to 1.2×105 Pa,
• the acrylic base polymer includes, as a monomer unit, at least one selected from the group consisting of hydroxy group-containing monomer and carboxy group-containing monomer,
• the acrylic base polymer has a crosslinked structure,
• a gel fraction of the photocurable composition in the pressure sensitive adhesive layer before photocuring is 60% or more,
• after photocuring of the pressure sensitive adhesive layer, a shear storage elastic modulus at 25° C. of a photocured pressure sensitive adhesive layer is 1.5×105 to 2×106 Pa, and
• an adhesive force between the photocured pressure sensitive adhesive layer and a polyimide film is not less than 4 times an adhesive force between the pressure sensitive adhesive layer before photocuring and the polyimide film,
• the photocurable agent is polyfunctional (meth)acrylate, and
• the polyfunctional (meth)acrylate includes at least one selected from the group consisting of polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate and polytetramethylene glycol di(meth)acrylate.