Synthetic fiber processing agents and synthetic fibers

Abstract

The invention solves the problem of improving, for synthetic fibers, the permeability of the interfacial binder and the effectiveness of fiber inhibition at high temperatures. The synthetic fiber treatment agent consists of: a smoothing agent (A) containing a total ester compound (Al) as defined below; and a dicarboxylic acid compound (B) as defined below. Total ester compounds (Al) are total ester compounds between a monovalent carboxylic acid and a trivalent or tetravalent alcohol. Dicarboxylic acid compounds (B) are at least one choice from C3-10 dicarboxylic acids with 0 or 1 hydroxyl group in the molecule and salts of the aforementioned dicarboxylic acids.