| 摘要 |
PROBLEM TO BE SOLVED: To obtain a curing agent for epoxy resins that can impart excellent curing properties, storage stability at room temperature and reliable humid resistance to epoxy resin compositions by mixing a specific latent catalyst with a specific phenolic resin under heating at a specific temperature. SOLUTION: A latent catalyst that comprises phosphonium borate represented by formula I (R1-R4 are each a monovalent organic group bearing an aromatic ring that forms a P-C bond with P; at least one of X1-X4 is a group that is formed by releasing one electron from a proton donor and the others are each a monovalent organic group bearing an aromatic ring; the proton donor gives an extracted water with a specific conductance of <=1,000μS/cm, when 1 g of the proton donor is mixed with 50 g of pure water, pressure-cooked in a pressure cooker at 125 deg.C for 20 hours and its specific conductance is measured) (for example, a compound of formula II) is mixed with a phenolic resin bearing 2 or more phenolic hydroxyl groups at a temperature higher than the softening point of the phenolic resin.
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