PURPOSE: To obtain the subject fiber improved in adhesion without requiring an increase in pickup of an adhesive or rise in heat-treating temperature by treating polyester fiber with a specific bonding solution and then heat-treating the resultant fiber.

CONSTITUTION: (A) A precondensate of resorcin with formaldehyde is mixed with a rubber latex and aged. (B) A solution (with 20wt.% solid concentration and ≥70cP viscosity at 20°C) containing a condensate of 2,6-bis(2',4'- dihydoxyphenylmethyl)-4-chlorophenol with 2,6-dihydroxymethyl-4-chlorophenol and resorcin in aqueous ammonia and (C) a carboxylated vinylpyridine latex are added and mixed with the resultant aged solution to provide a bonding solution, which is used to treat polyester fiber and then carry out heat-treatment at 210-250°C.