Fiber sizing agent

Abstract

Provided is a technique for achieving sizing properties and also achieving a storage stability of an aqueous dispersion of a polyurethane resin that is used in a fiber sizing agent. A fiber sizing agent includes an aqueous dispersion of a polyurethane resin, and the polyurethane resin includes, as constituent components, a polyol (a) component containing no sulfonic acid group or sulfonate group; a polyisocyanate (b) component; and a compound (c) component containing at least one of a sulfonic acid group or a sulfonate group and containing an active hydrogen group. The polyol (a) component includes a polyester polyol (a1) and a polyether polyol (a2), and the component of the polyether polyol (a2) is present in an amount of 10 parts by mass or greater and 30 parts by mass or less per 100 parts by mass of the total amount of the polyol (a) component, the polyisocyanate (b) component, and the compound (c) component.

Dependencies are inferred from the claim text.