ABSORBING FINE PARTICLE DISPERSION LIQUID AND ABSORBING FINE PARTICLES DISPERSION BODY HAVING EXCELLENt LONG-TERM STABILITY, AND METHOD FOR PRODUCING THEM

An absorbing fine particle dispersion body containing absorbing fine particles dispersed in a medium and a phosphite ester compound,

• the absorbing fine particles being one or more kinds of oxide fine particles selected from tungsten oxide fine particles represented by a general formula WyOz (where W is tungsten, O is oxygen, 2.2≤z/y≤2.999), and composite tungsten oxide fine particles represented by a general formula MxWyOz (where, M is one or more elements selected from H, He, alkali metal, alkaline earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, T, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, I, and Yb, W is tungsten, O is oxygen, 0.001≤x/y≤1, 2.0≤z/y≤3),
• the phosphite ester compound being a phosphite ester compound represented by the following structural formula (1), and an addition amount of the phosphite ester compound being more than 500 parts by mass and 50000 parts by mass or less with respect to 100 parts by mass of the absorbing fine particles,
• where in the structural formula (1), R1, R2, R4 and R5 are each independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an alicyclic group having 5 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms or an aromatic group,
• R3 is either a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and
• X is any one of a single bond or a sulfur atom or a divalent residue represented by structural formula (1-1),
• A is either an alkylene group having 2 to 8 carbon atoms or a divalent residue represented by structural formula (1-2),
• one of Y and Z is a hydroxyl group, an alkyl group having 1 to 8 carbon atoms, an alkoxyl group having 1 to 8 carbon atoms, or an aralkyloxy group having 7 to 12 carbon atoms, and the other one is either a hydrogen atom or an alkyl group having 1 to 8 carbon atoms,
• in the structural formula (1-1), R6 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and
• in the structural formula (1-2), R7 is either a single bond or an alkylene group having 1 to 8 carbon atoms, and * indicates that the residue is bonded to an oxygen atom side of the phosphite ester compound represented by the structural formula (1).

A method for producing an absorbing fine particle dispersion liquid, comprising:

• mixing absorbing fine particles which are one or more kinds of oxide fine particles selected from tungsten oxide fine particles represented by a general formula WyOz (where W is tungsten, O is oxygen, and 2.25≤z/y≤2.999), and composite tungsten oxide fine particles represented by a general formula MxWyOz (where M is one or more elements selected from H, He, alkali metal, alkaline earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, I, Yb, and W is tungsten, O is oxygen, 0.001≤x/y≤1, 2.0≤z/y≤3), and water, an organic solvent, a liquid resin, an oil and fat, a liquid plasticizer for the resin, a high molecular monomer, or a mixture of two or more selected from these groups, then, performing dispersion treatment, to obtain a dispersion liquid of absorbing fine particles;
• adding more than 500 parts by mass and 50.000 parts by mass or less of phosphite ester with respect to 100 parts by mass of the absorbing fine particles while stirring the dispersion liquid;
• and
• continuing the stirring after the addition, to obtain a dispersion liquid of the absorbing fine particles whose surfaces are coated with the phosphite ester compound.