Patent ID: 7537823

Claim:
A moisture absorbing fiber-having high color stability against washing, bleaching and being allowed to stand, wherein said moisture absorbing fiber has been obtained by (1) treating acrylic fiber comprising acrylonitrile copolymer in which a (meth)acrylate compound as a copolymer component is less than 5% by weight, with a hydrazine compound whereby introduction of crosslink and increase in nitrogen content to an extent of 1.0˜10.0% by weight is obtained, (2) treating the fiber of (1) with an aqueous solution of alkaline metal salt, whereby carboxyl group of a metal salt type by which CN group is hydrolyzed is produced in an amount of 4.0˜10.0meq/g and (3) treating the fiber of (2) with a reduction treatment agent selected from the group consisting of hydrosulfite, thiosulfate, sulfite, nitrite, thiourea dioxide and an ascorbate compound, and wherein said moisture absorbing fiber has the following properties (a)-(c): (a) discoloration of the fiber after washing according to a JIS-L0217-103 method, using “Attack” manufactured by Kao as detergent, for five times and evaluation by a grey scale for assessing staining according to JIS-L0805 being grade 4 or higher; (b) discoloration of the fiber after bleaching with hydrogen peroxide where a bleaching treatment is carried out under the conditions of 0.5% by weight of hydrogen peroxide, pH 10 by NaOH, and a bath ratio of 1/50 at 80° C. for 60 minutes, and evaluation by a grey scale for assessing staining according to JIS-L0805 being grade 4; and (c) discoloration of the fiber after being allowed to stand in the co-presence of water in an amount of water that is more than saturated water absorption at 80° C. for 16 hours, and evaluation by a grey scale for assessing staining according to JIS-L0805 being grade 4 or higher.