Phase difference film, circularly polarizing plate, and display device

A phase difference film comprising:

• a first optically anisotropic layer;
• a second optically anisotropic layer;
• a third optically anisotropic layer;
• and
• a fourth optically anisotropic layer in this order,
• wherein the first optically anisotropic layer and the second optically anisotropic layer are in direct contact with each other or are laminated through an adhesion layer,
• the second optically anisotropic layer and the third optically anisotropic layer are in direct contact with each other or are laminated through an adhesion layer,
• the third optically anisotropic layer and the fourth optically anisotropic layer are in direct contact with each other or are laminated through an adhesion layer, and
• the phase difference film satisfies at least one of the following Requirements 1 to 4,
• Requirement 1:
• a difference between an average refractive index of the first optically anisotropic layer and an average refractive index of a layer in contact with a surface of the first optically anisotropic layer on the second optically anisotropic layer side is 0.10 or less,
• Requirement 2:
• at least one of a difference between an average refractive index of the second optically anisotropic layer and an average refractive index of a layer in contact with a surface of the second optically anisotropic layer on the first optically anisotropic layer side, or a difference between an average refractive index of the second optically anisotropic layer and an average refractive index of a layer in contact with a surface of the second optically anisotropic layer on the third optically anisotropic layer side is 0.10 or less,
• Requirement 3:
• at least one of a difference between an average refractive index of the third optically anisotropic layer and an average refractive index of a layer in contact with a surface of the third optically anisotropic layer on the second optically anisotropic layer side, or a difference between an average refractive index of the third optically anisotropic layer and an average refractive index of a layer in contact with a surface of the third optically anisotropic layer on the fourth optically anisotropic layer side is 0.10 or less,
• Requirement 4:
• a difference between an average refractive index of the fourth optically anisotropic layer and an average refractive index of a layer in contact with a surface of the fourth optically anisotropic layer on the third optically anisotropic layer side is 0.10 or less.

A phase difference film comprising:

• a first optically anisotropic layer,
• a second optically anisotropic layer;
• a third optically anisotropic layer;
• and
• a fourth optically anisotropic layer in this order,
• wherein the first optically anisotropic layer is a C-plate,
• the second optically anisotropic layer is an A-plate,
• the third optically anisotropic layer is a layer formed by fixing a liquid crystal compound twist-aligned along a helical axis extending in a thickness direction,
• the fourth optically anisotropic layer is a C-plate,
• at least one pair of the first optically anisotropic layer and the second optically anisotropic layer, the second optically anisotropic layer and the third optically anisotropic layer, or the third optically anisotropic layer and the fourth optically anisotropic layer are laminated through an adhesion layer, and
• a difference between an average refractive index of the adhesion layer and an average refractive index of the optically anisotropic layer adjacent to the adhesion layer is 0.10 or less.