[Na].C(C1=C[C:12](OC1=O)=[O:13])=CC1C=CC=CC=1.[N:17]1[C:24]([NH2:25])=[N:23][C:21]([NH2:22])=[N:20][C:18]=1[NH2:19].C=O.[OH-].[Na+]>O>[CH2:12]=[O:13].[N:17]1[C:24]([NH2:25])=[N:23][C:21]([NH2:22])=[N:20][C:18]=1[NH2:19]Previously, 50 parts of 20% liquor A (dispersion of aromatic isocyanate compound) and 50 parts of 40% liquor B (co-dispersion of imino compound-sensitizer) obtained by grinding and dispersing in the above (1) were mixed with each other until a homogeneous mixture was obtained. The resulting homogeneous mixture of liquor A and liquor B was mixed with 37.5 parts of a 40% solubilized emulsion (average particle diameter 0.05 μm) comprising microcrystalline wax having a melting point of 75° C. as a microemulsion and the mixture was homogenized to obtain a core material. Then, 137.5 parts of the liquor A-liquor B-microemulsion mixture was gradually added to 90 parts of a 5% aqueous solution of sodium salt of styrenemaleic anhydride copolymer adjusted to pH 4.0 with stirring. Stirring was continued for about 30 minutes to obtain roundish agglomerates having an average particle diameter of 10 μm and it was also found that the agglomerates were emulsified and dispersed. Separately, a mixture of 12 parts of melamine, 30 parts of a 37% aqueous formaldehyde solution and 78 parts of water was adjusted to pH 9.0 with sodium hydroxide and was heated at 60° C. with stirring to perform dissolution to obtain 120 parts of a transparent melamine-formaldehyde precondensate. Then, 120 parts of this melamine-formaldehyde precondensate was added gently to 227.5 parts of the above emulsified and dispersed liquid and reaction was allowed to proceed for 4 hours with stirring in a thermostat set at 60° C. Then, the product was cooled to room temperature to prepare microcapsules. It was confirmed that the resulting microcapsules had an average particle diameter of 10 μm which was almost the same as that of the agglomerates and had a roundish fusiform shape. Solid concentration of the aqueous dispersion of the microcapsules was 21%. Amount of the solubilized emulsion used here corresponds to 50 parts by weight based on 100 parts by weight of the three components (aromatic isocyanate compound, imino compound and sensitizer) in total.
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