Acrylic based composite fiber and method for production thereof, and fiber composite using the same

An object of this invention is to provide an acrylonitrile based composite fiber having a new feeling different from that of an ordinary cellulose acetate fiber, cellulose fiber and acrylic fiber, excellent spinability, fiber properties and process ability of yarn spinning, and excellent functions, in particular, a deodorizing function and a moisture absorbing and retaining property.The composite fiber is comprised of 10 to 40% by weight of cellulose acetate and/or cellulose and 60 to 90% by weight of an acrylonitrile based polymer, and has a structure with the cellulose acetate and/or cellulose forming an island component in a cross section perpendicular to a fiber axis and the acrylonitrile based polymer forming a sea component. Preferably, the cellulose acetate and/or cellulose as the island component communicate with another island component in the fiber axis direction, a vacant hole is provided inside the fiber, or a ratio of the longest diameter and the shortest diameter of the fiber cross section is 2 or less, and 5 or more recess parts of 0.3 mum or more and 3 mum or less width and 0.3 mum or more and 3 mum or less depth are provided in a fiber cross section outer circumferential part. Further preferably, by applying a heat treatment under alkali in a production stage, the moisture absorbing and retaining property can be improved.