Ammonia → Melamine formaldehyde

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Previously, 50 parts of 20% liquor A (dispersion of aromatic isocyanate compound) and 100 parts of 30% 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 100 parts of a 40% aqueous solution of a polyacrylate ester copolymer as a water-soluble polymer and the mixture was homogenized to obtain a core material. To the core material was added 14 Parts of a 28% aqueous ammonia solution (corresponding to 5 parts by weight based on 100 parts by weight of the components contained in the microcapsules) to obtain a homogeneous mixture. Then, 424 parts of the mixture of the liquor A-liquor B-water-soluble polymer modulated with ammonia was gradually added to 160 parts of a 5% aqueous solution of sodium salt of styrene-maleic 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 21.3 parts of melamine, 53.3 parts of a 37% aqueous formaldehyde solution and 138.4 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 213 parts of a transparent melamine-formaldehyde precondensate. Then, 213 parts of this melamine-formaldehyde precondensate was gently added to 424 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%.

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