| abstract |
High-strength synthetic fibers obtained by stretching filaments which are being heat-softened up to at least a glass transition point by irradiating with infrared fluxes fibers consisting of either one of polyester fibers, nylon fibers and polyether-keton fibers. A fiber processing device provided with an infrared irradiating means (13) which includes a laser for applying infrared fluxes to filaments (1), running by being supplied and taken up, so as to soften them, and which is located between a means (10) for continuously supplying filaments (1) at a constant speed v and a take-up means (11) for taking them up at a speed V higher than the speed v. |