4-Hydroxy -4'-isopropoxydiphenyl sulfone developer dispersion, method of wet grinding, and thermal recording media

A method for wet grinding a 4-hydroxy-4′-isopropoxydiphenylsulfone developer, comprising the step of wet grinding a 4-hydroxy-4′-isopropoxydiphenylsulfone developer in the presence of a hydration inhibitor,

• the hydration inhibitor being:
• (i-1) 1, 1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane,
• (i-2) 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane and 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, or
• (ii) 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid,
• the proportion of the hydration inhibitor being 0.02 to 25 parts by mass per 100 parts by mass of the developer.

A heat-sensitive recording material comprising a sheet-form support and a heat-sensitive recording layer formed on at least one surface of the sheet-form support,

• the heat-sensitive recording layer being formed by coating the sheet-form support with a heat-sensitive recording layer coating composition comprising a substantially colorless dye precursor and a developer, and then drying the coating,
• the heat-sensitive recording layer coating composition containing a 4-hydroxy-4′-isopropoxydiphenylsulfone developer dispersion obtainable by wet grinding a 4-hydroxy-4′-isopropoxydiphenylsulfone developer in the presence of a hydration inhibitor,
• the hydration inhibitor being:
• (i-1) 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane,
• (i-2) 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane and 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, or
• (ii) 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid,
• the proportion of the hydration inhibitor being 0.02 to 25 parts by mass per 100 parts by mass of the developer.

A heat-sensitive recording material comprising a sheet-form support and a heat-sensitive recording layer formed on at least one surface of the sheet-form support,

• the heat-sensitive recording layer being formed by coating the sheet-form support with a heat-sensitive recording layer coating composition comprising a substantially colorless dye precursor and a developer, and then drying the coating,
• the heat-sensitive recording layer coating composition comprising a 4-hydroxy-4′-isopropoxydiphenylsulfone developer dispersion obtainable by wet grinding a 4-hydroxy-4′-isopropoxydiphenylsulfone developer in the presence of a hydration inhibitor,
• the hydration inhibitor being:
• 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,
• the proportion of the hydration inhibitor being 0.05 to 10 parts by mass per 100 arts by mass of the developer.