Infrared absorbing thin film containing rutile-type titanium oxide crystal and method for producing the same

A method for producing an infrared absorbing thin film containing a rutile-type titanium oxide crystal doped with a transition metal ion selected from the group consisting of iron, zinc, manganese, copper, cobalt, vanadium, tungsten, and nickel, the method comprising:

• a step (I) of dispersing or dissolving a complex (y) of an amino group-containing basic polymer (x) and a transition metal ion selected from the group consisting of iron, zinc, manganese, copper, cobalt, vanadium, tungsten, and nickel in an aqueous medium;
• a step (II) of obtaining a composite having a polymer/titania layered structure in which the complex (y) of the amino group-containing basic polymer (x) and the transition metal ion is sandwiched between layers of titania with a distance of 1 to 3 nm, by mixing the aqueous dispersion or aqueous solution prepared in the step (I) with a water-soluble titanium compound (z) in the aqueous medium at a temperature of 50° C. or lower to cause a hydrolysis reaction;
• a step (III) of calcining the composite having the layered structure in an air atmosphere at a temperature of 650° C. or higher to dope a surface of a titanium oxide crystal with the transition metal ion confined in the layered structure and simultaneously to cause growth into a rutile-type crystal phase;
• a step (IV) of pulverizing the obtained crystal into a powder;
• a step (V) of mixing the obtained powder with a sol of a metal alkoxide and/or a dispersion liquid of metal oxide nanoparticles to prepare a fluid liquid composition;
• a step (VI) of coating a surface of a substrate with the obtained fluid liquid composition;
• and
• a step (VII) of aging the coating film.