Agent for imparting durable liquid permeability and fiber applied therewith

The present invention provides fiber and fiber products for topsheet of diapers and sanitary napkins having superior surface properties attained by a fiber-treating agent. The surface properties attained by the fiber-treating agent include decreased wet-back of excreted liquid through topsheet, which has been attained by modifying the structure of disposable diapers or sanitary napkins, improved durable hydrophilicity of topsheet and minimized time-dependent reduction of the durable hydrophilicity of topsheet. The present invention also provides a fiber treating agent for imparting liquid permeability to fiber, consisting of (a) 20 to 60 weight percent of alkyl phosphate salts, (b) 10 to 30 weight percent of a trialkylglycine derivative, (c) 5 to 20 weight percent of polyoxyalkylene-modified silicone and (d) 10 to 35 weight percent of an ester of dicarboxylic acid and alkoxylated ricinolein and/or hydrogenated product thereof, wherein at least one of hydroxyl groups is esterified with saturated and/or unsaturated monocarboxylic acid.