Bleached fiber product production method, apparatus to be used therefor, and bleached fiber product produced thereby

A bleached fiber product production method for bleaching a fiber product mainly including at least one of a natural fiber and a regenerated fiber to produce a bleached fiber product, the method comprising the steps of:

• loading the fiber product into a lidded hermetic vessel serving as a treatment vessel;
• forcibly circulating a treatment liquid in contact with the fiber product loaded in the treatment vessel through a forcible circulation pipe attached to the treatment vessel to thereby wet the fiber product;
• supplying an ozone gas into the treatment liquid to provide an ozone-containing liquid, and forcibly circulating the ozone-containing liquid in contact with the wetted fiber product through the forcible circulation pipe to thereby bleach the fiber product;
• forcibly circulating hot water heated up to a temperature not lower than 50° C. in contact with the bleached fiber product through the forcible circulation pipe to thereby yellow the bleached fiber product;
• forcibly circulating an ozone decomposing chemical agent liquid in contact with the yellowed fiber product through the forcible circulation pipe to thereby simultaneously achieve removal of a yellowing substance from the yellowed fiber product and decomposition of ozone;
• and
• rinsing the fiber product after the removal of the yellowing substance and the decomposition of the ozone;
• wherein an ozone concentration in the treatment vessel is measured over time in the fiber product bleaching step, and maintained at a constant ozone concentration level by increasing an ozone gas supply amount if the measured concentration is lower than a predetermined range, and reducing the ozone gas supply amount if the measured concentration is higher than the predetermined range.