Mgf2 optical thin film including amorphous silicon oxide binder, optical element provided with the same, and method for producing mgf2 optical thin film

Abstract

An MgF 2 optical thin film is formed on an optical surface of a base material. The MgF 2 optical thin film includes MgF 2 particles and an amorphous silicon oxide-based binder which exists on the surfaces of the MgF 2 particles and between the MgF 2 particles. Owing to this amorphous silicon oxide-based binder, the optical thin film can have high mechanical strength and high adhesion to the base material, while having excellent environment resistance and a lower refractive index.

1 . A method for producing an MgF 2  optical thin film, comprising:
 preparing a sol solution, in which MgF 2  minute particles are dispersed, by mixing a magnesium compound and a fluorine compound in a solvent;   placing the sol solution in a vessel which is tightly closable and performing a pressurizing treatment and a heat treatment at the same time;   preparing a binder solution which contains a component capable of forming an amorphous silicon oxide-based binder by a reaction, the amorphous silicon oxide-based binder being composed of amorphous silica;   preparing a coating liquid by mixing the sol solution for which the pressurizing treatment and the heat treatment have been performed and the binder solution;   forming a film by coating the coating liquid on a base material and by performing drying; and   performing a heat treatment after forming the film, wherein the MgF 2  minute particles are connected to one another by the amorphous silicon oxide-based binder.   
     
     
         2 . A method for producing an MgF 2  optical thin film, the method comprising:
 preparing a sol solution, in which MgF 2  minute particles are dispersed, by mixing a magnesium compound and a fluorine compound in a solvent;   placing the sol solution in a vessel which is tightly closable and performing a pressurizing treatment and a heat treatment at the same time;   preparing a binder solution which contains a component capable of forming an amorphous silicon oxide-based binder by a reaction, the amorphous silicon oxide-based binder being composed of amorphous silica;   forming a porous film by coating the sol solution, for which the pressurizing treatment and the heat treatment have been performed, on a base material and by performing drying;   coating the binder solution on the porous film and impregnating the binder solution into the porous film; and   performing a heat treatment after the impregnation,   wherein the MgF 2  minute particles are connected to one another by the amorphous silicon oxide-based binder.   
     
     
         3 . The method for producing the MgF 2  optical thin film according to  claim 1  if wherein the magnesium compound is magnesium acetate, the fluorine compound is hydrofluoric acid, and the solvent is methanol. 
     
     
         4 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein a molar ratio of fluorine contained in the fluorine compound existing in the solvent to magnesium contained in the magnesium compound existing in the solvent is 1.9 to 2.0. 
     
     
         5 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein the component, which is capable of forming the amorphous silicon oxide-based binder, is an organic silicon compound. 
     
     
         6 . The method for producing the MgF 2  optical thin film according to  claim 5 , wherein the organic silicon compound is silicon alkoxide, a polymer thereof, or polysilazane. 
     
     
         7 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein an SiO 2 -converted concentration of silicon in the coating liquid is not more than 5% by weight. 
     
     
         8 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein the coating liquid is coated on the base material by a spin coat method or a dip coat method. 
     
     
         9 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein the coating liquid is coated on the base material in an atmosphere of relative humidity of 5% to 40% by a spin coat method. 
     
     
         10 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein the coating liquid is coated on the base material by a spin coat method by rotating the base material at a maximum number of revolutions of 500 rpm to 9,000 rpm within 3 seconds after supplying the coating liquid to the base material. 
     
     
         11 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein the MgF 2  optical thin film having a desired refractive index is produced by adjusting an SiO 2 -converted concentration of silicon in the coating liquid. 
     
     
         12 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein a plurality of pieces of the MgF 2  optical thin film having desired refractive index is produced by adjusting a molar ratio of fluorine contained in the fluorine compound to magnesium contained in the magnesium compound of the sol solution. 
     
     
         13 . The method for producing the MgF 2  optical thin film according to  claim 1 , wherein the MgF 2  minute particles have an average particle diameter of 1 nm to 100 nm. 
     
     
         14 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the magnesium compound is magnesium acetate, the fluorine compound is hydrofluoric acid, and the solvent is methanol. 
     
     
         15 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein a molar ratio of fluorine contained in the fluorine compound existing in the solvent to magnesium contained in the magnesium compound existing in the solvent is 1.9 to 2.0. 
     
     
         16 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the component, which is capable of forming the amorphous silicon oxide-based binder, is an organic silicon compound. 
     
     
         17 . The method for producing the MgF 2  optical thin film according to  claim 6 , wherein the organic silicon compound is silicon alkoxide, a polymer thereof, or polysilazane. 
     
     
         18 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein an SiO 2 -converted concentration of silicon in the binder solution is not more than 5% by weight. 
     
     
         19 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the sol solution is coated on the base material by a spin coat method or a dip coat method. 
     
     
         20 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the sol solution is coated on the base material in an atmosphere of relative humidity of 5% to 40% by a spin coat method. 
     
     
         21 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the sol solution is coated on the base material by a spin coat method by rotating the base material at a maximum number of revolutions of 500 rpm to 9,000 rpm within 3 seconds after supplying the sol solution to the base material. 
     
     
         22 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the MgF 2  optical thin film having a desired refractive index is produced by adjusting an SiO 2 -converted concentration of silicon in the binder solution. 
     
     
         23 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein a plurality of pieces of the MgF 2  optical thin film having desired refractive index is produced by adjusting a molar ratio of fluorine contained in the fluorine compound to magnesium contained in the magnesium compound of the sol solution. 
     
     
         24 . The method for producing the MgF 2  optical thin film according to  claim 2 , wherein the MgF 2  minute particles have an average particle diameter of 1 nm to 100 nm.