| 摘要 |
PROBLEM TO BE SOLVED: To maintain a high function, high quality characteristics and productivity in an optically functional film and to put it into a practical use by forming a low refractive index layer directly or via other layer on a surface of a base material film, and forming the index layer as an SiO2 gel layer obtained by gelling an SiO2 sol having a molecular weight of a specific range. SOLUTION: A low refractive index layer 2 is formed on a surface of a base material film 1. An SiO2 gel layer is made of an SiO2 gel obtained by gelling an SiO2 sol having a molecular weight of 10,000 to 100,000 or preferably 20,000 to 50,000. When the molecular weight of the sol is smaller than this range, adhesive properties to the film is low and cannot be put into a practical use. When the molecular weight is larger than this range, an insoluble gel of a large quantity is generated, hence its solubility in a solvent is remarkably lowered and not preferable. Thus, the sol having the high molecular weight for improving the adhesive properties to the film while holding optical characteristics as they are can be sufficiently gelled at a temperature of the degree for not damaging the film. |
