Hard coat film for foldable display and use thereof

A hard coating film for a foldable display, the hard coating film comprising

• a polyester film being a polyethylene terephthalate film and having a thickness of 10 to 80 μm and a draw ratio of 1.2-fold to 2.0-fold in the longitudinal direction,
• an easy-to-adhere resin layer, and
• a hard coating layer, the easy-to-adhere resin layer and the hard coating layer being stacked in this order on at least one surface of the polyester film,
• wherein
• the easy-to-adhere resin layer is a cured product of a composition containing
• at least one compound selected from the group consisting of titanium compounds and zirconium compounds, and
• a polyester resin, which is formed from a dicarboxylic acid component and a diol component, containing a naphthalene dicarboxylic acid component as at least part of the dicarboxylic acid component, and
• the polyester film having the easy-to-adhere resin layer stacked thereon but not yet having the hard coating layer stacked thereon satisfies the following conditions (1) to (4):
• (1) the polyester film has a refractive index in the bending direction of 1.590 to 1.620,
• (2) the polyester film has a refractive index in the direction of a folding portion of 1.670 to 1.700,
• (3) the polyester film has a refractive index in the thickness direction of 1.520 or less, and
• (4) the polyester film has a density of 1.380 g/cm3 or more,
• wherein the bending direction refers to a direction orthogonal to the folding portion of the polyester film to be folded.