Precursor sol of aluminum oxide and method for producing optical member

1. A precursor sol of aluminum oxide, comprising:

a solvent; and

particles containing a hydrolysate of an aluminum compound and/or a condensate of the hydrolysate,

wherein the particles have an average particle size of 2.5 nm to 7 nm, and

wherein the solvent contains 50% by weight to 90% by weight of a monohydric alcohol having 5 to 8 carbon atoms and 10% by weight to 50% by weight of a water-miscible solvent having a boiling point of 110° C. to 170° C.

2. The precursor sol of aluminum oxide according to claim 1 ,

wherein a particle size distribution curve of the particles includes at least one peak having a single peak top, and

wherein the at least one peak has an average particle size of 2.5 nm to 7 nm, and

the area of the peak having an average particle size of 2.5 nm to 7 nm is 90% or more of the total peak area of the particle size distribution curve.

3. The precursor sol of aluminum oxide according to claim 1 , wherein the water-miscible solvent is glycol ether.

4. The precursor sol of aluminum oxide according to claim 1 , wherein the particles are amorphous.

5. A method for producing an optical member, comprising the steps of:

(1) feeding the precursor sol of aluminum oxide according to claim 1 onto at least one surface of a base;

(2) spreading the precursor sol of aluminum oxide on the base;

(3) drying and/or firing the base to form an aluminum oxide film; and

(4) immersing the aluminum oxide film in hot water with a temperature of 60° C. to 100° C. to form a textured structure comprising aluminum oxide boehmite.