Optical element, liquid crystal display device member with the optical element, liquid crystal display device with the liquid crystal display device member, method of producing the optical element and method of evaluating birefringence functional layer

A method of evaluating a birefringence functional layer, comprising:

• measuring an amount of residual double bonds of a birefringence functional layer in an optical element, comprising a light-transmitting substrate, a birefringence functional layer made of a polymerizable liquid crystal material provided above the light-transmitting substrate, a coloring layer provided between the light-transmitting substrate and the birefringence functional layer, directly or indirectly on a surface of the birefringence functional layer, and an alignment film for aligning a driving liquid crystal material provided directly or indirectly on a surface of the birefringence functional layer,
• whereby the birefringence functional layer is formed by aligning a polymerizable liquid crystal monomer having a polymerizable group at least at one terminal followed by fixation, and a degree of reduction of residual double bond in the birefringence functional layer before and after heat treatment at 250° C. for 1 hr is less than 0.25;
• applying heat treatment at 250° C. for 1 hr, followed by leaving until the optical element comes to room temperature;
• measuring an amount of residual double bonds of the heat-treated birefringence functional layer;
• and
• calculating a difference between the amounts of the residual double bonds before and after the heat treatment to obtain another degree of reduction of residual double bonds.