METHOD FOR FORMING MESOPOROUS SILICA LAYER, ITS POROUS COATING, ANTI-REFLECTION COATING, AND OPTICAL MEMBER

1 . A method for forming a mesoporous silica layer composed of nanometer-sized, mesoporous silica particles on an optical substrate or a dense layer formed thereon, comprising the steps of (1) aging a solution comprising alkoxysilane, a catalyst, a cationic surfactant, a nonionic surfactant and a solvent to cause the hydrolysis and polycondensation of said alkoxysilane, thereby preparing composites comprising nanometer-sized, mesoporous silica particles, said cationic surfactant and said nonionic surfactant, (2) applying a solution containing said composites to said substrate or said dense layer, (3) drying said solution to remove said solvent, and (4) baking the resultant coating at a temperature of 120-250° C. in an oxygen-containing gas atmosphere to remove said cationic surfactant and said nonionic surfactant.

2 . A method for forming a mesoporous silica layer composed of nanometer-sized, mesoporous silica particles on an optical substrate or a dense layer formed thereon, comprising the steps of (1) aging a solution comprising alkoxysilane, a catalyst, a cationic surfactant, a nonionic surfactant and a solvent to cause the hydrolysis and polycondensation of said alkoxysilane, thereby preparing composites comprising nanometer-sized, mesoporous silica particles, said cationic surfactant and said nonionic surfactant, (2) applying a solution containing said composites to said substrate or said dense layer, (3) drying said solution to remove said solvent, and (4) subjecting the resultant coating to a plasma treatment using an oxygen-containing gas to remove said cationic surfactant and said nonionic surfactant.

3 . The method for forming a mesoporous silica layer according to claim 2 , wherein said plasma treatment step (4) is caused by plasma discharge in an atmosphere of said oxygen-containing gas.

4 . The method for forming a mesoporous silica layer according to claim 3 , wherein the power density of said plasma discharge per a unit area is 0.1-3 W/cm 2 .

5 . The method for forming a mesoporous silica layer according to claim 1 , wherein said composites-preparing step (1) is carried out by the steps of (i) aging a solution comprising said alkoxysilane, an acid catalyst, said cationic surfactant, said nonionic surfactant and said solvent to cause the hydrolysis and polycondensation of said alkoxysilane, and (ii) adding a base catalyst to an acidic sol containing the resultant silicate to prepare composites of nanometer-sized, mesoporous silica particles coated with said nonionic surfactant and containing said cationic surfactant in pores.

6 . The method for forming a mesoporous silica layer according to claim 1 , wherein the coating formed by said drying step (3) has a thickness of 500 nm or less.

7 . The method for forming a mesoporous silica layer according to claim 1 , wherein said cationic surfactant is n-hexadecyl trimethyl ammonium chloride, and said nonionic surfactant is a block copolymer represented by the formula of RO(C 2 H 4 O) a —(C 3 H 6 O) b —(C 2 H 4 O) c R, wherein a and c are respectively 10-120, b is 30-80, and R is a hydrogen atom or an alkyl group having 1-12 carbon atoms.

8 . The method for forming a mesoporous silica layer according to claim 1 , wherein a molar ratio of said cationic surfactant to said nonionic surfactant is more than 8 and 60 or less.

9 . A mesoporous silica layer formed by the method recited in claim 1 , which is composed of nanometer-sized, mesoporous silica particles having an average diameter of 200 nm or less, a refractive index of 1.09-1.25 and porosity of 45-80%.

10 . A mesoporous silica layer formed by the method recited in claim 2 , which is composed of nanometer-sized, mesoporous silica particles having an average diameter of 200 nm or less, a refractive index of 1.09-1.25 and porosity of 45-80%.

11 . The mesoporous silica layer according to claim 9 , wherein said nanometer-sized, mesoporous silica particles have a hexagonal structure.

12 . The mesoporous silica layer according to claim 10 , wherein said nanometer-sized, mesoporous silica particles have a hexagonal structure.

13 . The mesoporous silica layer according to claim 9 , which has a peak corresponding to the diameters of pores in particles in a range of 2-10 nm, and a peak corresponding to the diameters of pores among particles in a range of 5-200 nm, in a pore diameter distribution curve obtained by a nitrogen adsorption method.

14 . The mesoporous silica layer according to claim 10 , which has a peak corresponding to the diameters of pores in particles in a range of 2-10 nm, and a peak corresponding to the diameters of pores among particles in a range of 5-200 nm, in a pore diameter distribution curve obtained by a nitrogen adsorption method.

15 . A anti-reflection coating comprising the mesoporous silica layer recited in claim 9 , which is formed on an optical substrate or a dense layer formed thereon.

16 . A anti-reflection coating comprising the mesoporous silica layer recited in claim 10 , which is formed on an optical substrate or a dense layer formed thereon.

17 . An optical member comprising an anti-reflection coating formed on an optical substrate or a dense layer formed thereon, said anti-reflection coating comprising the mesoporous silica layer recited in claim 9 .

18 . An optical member comprising an anti-reflection coating formed on an optical substrate or a dense layer formed thereon, said anti-reflection coating comprising the mesoporous silica layer recited in claim 10 .