A method for producing a curable composition which includes a polymerizable monomer, inorganic particles that satisfy conditions (i) to (iv) below, and a polymerization initiator and which provides a cured product that produces a structural color of a predetermined color tone, the method comprising:
- a mixing step of mixing the polymerizable monomer, the inorganic particles and the polymerization initiator,
- wherein in the mixing step, mixing conditions are adopted in which it is confirmed, for a mixture obtained in the step, that a dispersed state of the inorganic particles in the cured product obtained by curing the mixture satisfies conditions (I) and (II) below, and the mixing is performed:
- [Conditions which need to be satisfied by inorganic particles]
- (i) the inorganic particles include an identical particle diameter spherical particle group (G-PID) which is formed with an aggregate of inorganic spherical particles having a predetermined average primary particle diameter within a range of 100 to 1000 nm and in which in a number-based particle size distribution of the aggregate, 90% or more of all the particles are present within a range of plus or minus 5% of the predetermined average primary particle diameter, and a number of the identical particle diameter spherical particle groups is one or more;
- (ii) when the number of the identical particle diameter spherical particle groups included in the inorganic particles is assumed to be a, and each of the identical particle diameter spherical particle groups are represented as G-PIDm (where when a is 1, m is 1 whereas when a is equal to or greater than 2, m is a natural number from 1 to a) respectively in ascending order of the average primary particle diameters thereof, the average primary particle diameters of each G-PIDm, differ from each other by 25 nm or more;
- (iii) when a refractive index of a cured product of the polymerizable monomer at 25° C. is assumed to be n(MX), and a refractive index of the inorganic spherical particles of each G-PIDm, at 25° C. is assumed to be n(G-PIDm), for any n(G-PIDm), a relationship of n(MX)<n(G-PIDm) holds true;
- (iv) the inorganic particles include a superfine particle group (G-SFP) that is formed with inorganic particles whose average primary particle diameter is less than 100 nm and is smaller than the average primary particle diameter of G-PID1 by 25 nm or more;
- [Conditions which need to be satisfied by dispersed state]
- (I) when a dimensionless number (r/r0) which is standardized by dividing a distance r from a center of an arbitrary one of the inorganic spherical particles dispersed in the cured product of the mixture by an average particle diameter r0 of all the inorganic spherical particles dispersed in the cured product of the mixture is assumed to be an x-axis, and a radial distribution function g(r) indicating a probability that another inorganic spherical particle is present at a point the distance r away from the center of the arbitrary inorganic spherical particle is assumed to be a y-axis, in a radial distribution function graph indicating a relationship of r/r0 and g(r) which corresponds to r at that time, a closest particle-to-particle distance r1 which is defined as r corresponding to a peak top of a peak closest to an origin among peaks appearing in the radial distribution function graph is a value that is 1 to 2 times the average particle diameter r0 of all the inorganic spherical particles dispersed in the cured product of the mixture;
- (II) when r corresponding to a peak top of a peak second closest to the origin among the peaks appearing in the radial distribution function graph is assumed to be a second closest particle-to-particle distance r2, a local minimum value of the radial distribution function g(r) between the closest particle-to-particle distance r1 and the second closest particle-to-particle distance r2 is a value of 0.56 to 1.10.