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Abstract

A sizing agent for fibers is provided, which contains a polyester resin, and is capable of improving the emulsification stability and the sizing property while maintaining adhesive property with a matrix resin. The sizing agent for fibers is an aqueous solution or an aqueous emulsion, which contains a polyester resin (A) that satisfies all the following conditions (i)-(iv) and an aqueous medium: (i) that the polyester resin (A) is made from a dicarboxylic acid or its anhydride (a) and diols (b); (ii) that at least one of the diols (b) is diol (b1) that has an average 4.5-60 contiguous oxyethylene groups; (iii) that the weight percentage of the average 4.5-60 contiguous oxyethylene groups in the polyester resin (A) is 25-50 wt %; and (iv) that a mixture of 10 parts by weight of the polyester resin (A) and 90 parts by weight of water forms an uniform transparent solution or an uniform emulsion at 25.degree. C.

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First Claim