Composition for forming a thin layer with low refractive index, manufacturing method thereof, and manufacturing method of a thin layer with low refractive index

A method for producing a low refractive index film-forming composition, comprising:

• generating a hydrolysate of (A) a silicon alkoxide by mixing the (A) silicon alkoxide represented by the following Chemical Formula (1) with (B) water in a proportion of 0.5 parts by mass to 2.0 parts by mass, (C) an inorganic acid or an organic acid in a proportion of 0.005 parts by mass to 0.5 parts by mass, and (D) an organic solvent such as an alcohol, a glycol ether, or a glycol ether acetate in a proportion of 1.0 part by mass to 5.0 parts by mass based on 1 part by mass of the (A) silicon alkoxide;
• and
• mixing the hydrolysate with (E) a silica sol, which is obtained by dispersing fumed silica particles having an average particle size within a range of 5 nm to 50 nm and a specific surface area (BET value) within a range of 50 m2/g to 400 m2/g in a liquid medium, such that a proportion of SiO2 in the (E) silica sol becomes 1 part by mass to 99 parts by mass when a proportion of SiO2 in the hydrolysate is regarded as being 1 part by mass,
• Si(OR)4 (1)
• here, R represents an alkyl group having 1 to 5 carbon atoms.