PURPOSE: To provide an acid anhydride mixture useful as a hardener of epoxy resin and capable of imparting sufficient hardness and flexibility to cured product, by mixing an alicyclic or aromatic polycarboxylic acid anhydride with 4- ketopimelic acid dilactone at a specific ratio.
CONSTITUTION: The objective acid anhydride mixture contains (A) 95W30(wt)% alicyclic or aromatic polycarboxylic acid anhydride (preferably methylhexahydrophthalic anhydride and/or methyltetrahydrophthalic anhydride which is liquid at normal temperature) and (B) 5W70% 4-ketopimelic acid dilactone of formula. The content of succinic anhydride in the acid anhydride mixture is preferably ≤1%. When the acid anhydride mixture is used as a hardener of an epoxy resin, the ratio of epoxy resin to the acid anhydride mixture is preferably 100/30W 100/150.
SAITOU TAKAYUKI
KOBAYASHI AKIHIRO
GOTOU HITOSHI
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