Surface treatment agent comprising inorganic-organic hybrid material

A surface treatment agent comprising:

• (A) a hydrolyzable metal alkoxide or a hydrolyzate thereof,
• (B) a fluorocompound containing a perfluoroalkyl group and a functional group reactive with the hydrolyzable metal alkoxide (A),
• (C) an adhesion improvement agent, and
• (D) a fluoropolymer having a number-average molecular weight of at least 500,
• wherein a one-layer film formed from the surface treatment agent has a graded refractive index structure, and
• the fluoropolymer (D) is a polymer of the general formula (3):
• -(M)x-(N)y-
• wherein x and y are from 1 to 500,
• the structural unit M is derived from a fluorine-containing ethylenic monomer and is a structural unit derived from a fluorine-containing ethylenic monomer of the formula (M):
• (in which, X1 and X2 are, the same or different, H or F,
• X3 is H, F, CH3or CF3,
• X4 and X5 are, the same or different, H, F or CH3,
• Rf1 is an organic group wherein 1 to 3 Y3 groups (Y3 is a hydroxyl group, a glycidyl group, an amino group, an alkoxy group, a carboxyl group, an isocyanate group, or a C1–C10 monovalent organic group having at least one of these reactive groups) are bonded to a C1–C40 fluorine-containing alkyl group or a C2–C100 fluorine-containing alkyl group having an ether linkage,
• a is an integer of from 0 to 3, and
• b and c are, the same or different, 0 or 1), and
• the structural unit N is a structural unit obtained by reacting an unsaturated carboxylic acid of the formula (A):
• (in which R1 is a divalent organic group having 1 to 7 carbon atoms, which may be substituted with a fluorine atom,
• X6 is H, F, CH3 or CF3,
• X7 and X8 are, the same or different, H or F, and
• f is 0 or 1),
• or a derivative thereof, with the Y3 group in the Rf1 group of the ethylenic monomer giving the structural unit M.