Method of producing acrylic fiber bundle and method of producing carbon fiber bundle

A method of producing an acrylic fiber bundle in which an acrylic polymer solution is spun to make a coagulated thread bundle, and

• the coagulated thread bundle is then subjected to at least an in-bath treatment step and an oil agent application step,
• wherein:
• the in-bath treatment step includes an in-bath cleaning step;
• the in-bath cleaning step is a step in which the plurality of coagulated thread bundles travel in parallel and are cleaned in one or more washing baths including an inflow portion and an outflow portion for a cleaning solution;
• at least one of the washing baths is a counterflow washing bath in which the cleaning solution flows into from the inflow portion located at a lower stream side position of a traveling direction of the coagulated thread bundles, and flows out from the outflow portion located at an upper stream side position of the traveling direction of the coagulated thread bundles;
• and
• an average of coefficients of variation CV of linear speeds of the cleaning solution in the inflow portion of the counterflow washing bath is 0.30 or less, and
• an average of coefficients of variation CV of linear speeds of the cleaning solution in the outflow portion of the counterflow washing bath is 0.30 or less,
• wherein the inflow of the cleaning solution is performed by at least one of a) to c):
• a) inflow due to overflow using an overflow weir in which a difference in height between both end portions with respect to a central portion of the weir is 0.0 to ±7.0 mm;
• b) inflow from a nozzle having 0.5 N or more holes (N is an integer of 3 or more, which is the number of coagulated thread bundles caused to be travelled in parallel);
• and
• c) inflow from a plate having a plurality of holes, wherein, a ratio of the sum of areas of the plurality of holes to an area of the plate (opening ratio) is 10 to 60%.