Surface roughness is one of the most important characteristics in the production of fibers for artificial hair. It was recently found that the fibers with highly developed surface roughness can be formed in the melt spinning of polyamide 6 (PA6)/poly (ethylene terephthalate) (PET) blend fibers under certain spinning conditions. To elucidate the conditions necessary for the development of roughness on the fiber surface, melt spinning of various combinations of blend polymers was carried out under a wide range of spinning conditions. It was concluded that the surface roughness can be developed when (1) the minor component is a crystalline polymer, (2) the major component is either an amorphous or crystalline polymer, but is melt processable at a temperature lower than the melting temperature of the minor component, and (3) the extrusion temperature is lower than the melting temperature of the minor component. From the wide-angle X-ray diffraction measurement of amorphous co-PA/PET blend fibers, the crystallization of the PET component in the as-spun fibers was confirmed only for the fibers with surface roughness. Differential scanning calorimetry measurement of the as-spun fibers in the heating and cooling processes revealed that the PET component maintained its high crystallizability even after its melting, when the PET component was crystallized and surface roughness was developed in the spinning process.Keywords blend fiber, melt spinning, rough surface, artificial hair, crystallization Formation of surface roughness is one of the most important research subjects for the development of synthetic fibers for artificial hair. Several conventional technologies have been developed for the formation of surface roughness. Firstly, enhancement of the formation of spherulites in the melt spinning of polyamide fibers was utilized. 1 In this process, polyamide 6 (PA6) or polyamide 66 filament extruded from an extruder was passed through a water bath of elevated temperature to reduce cooling speed. The temperature of the bath was 30-80 C. It was concluded that there was an enhancement of roughness development with the increase of the bath length. It was also reported that fibers with surface roughness can be produced through the extraction of the soluble component after the formation of blend fibers. 2 In this process, fibers were prepared using PA6 blended with alkali-soluble co-polyester (co-PCT) containing 1-40 wt% of inorganic powder. The rough surface fibers were produced by treating the fibers with 5 wt% aqueous solution of sodium hydroxide at 95 C for 4 hours. The most recent technology in this field is the erosion of the fiber surface by sand-blasting. 3 It was reported that multiple polyamide filaments can be treated simultaneously at the moving speed of 200-300 m/min. This means that the melt-spinning process and the sand-blasting process

In the course of the development of fibers for artificial hair, we found that the polyamide ６ (PA ６)based blend fibers with granular rough surface can be prepared through the melt spinning of PA６／Poly (ethylene terephthalate) (PET) blend polymer under particular spinning conditions. The surface roughness was found to be enhanced with the decrease of extrusion temperature and the increase of PET composition. Observation of the surface and cross-section of fibers after the acidand alkali-treatment revealed that the rough-surface of the fiber was composed of the sea component of PA ６ whereas PET was dispersed evenly in the cross-section to form island component. Observation of the fibers captured from the spinning line revealed that the development of rough surface proceeded between the spinning nozzle and the water-quenching bath, in that the surface roughness was enhanced as distance from the spinning nozzle increased. It was difficult to clarify the fundamental mechanism for the development of rough surface even after analyzing the variations of the temperature of molten polymer and the size of the dispersed PET component in the extrusion system and the variation of the die-swell ratio depending on the extrusion conditions. It was speculated that further investigation is necessary from the view point of the crystallization behavior of PET in the process.

We have reported recently that fibers with surface roughness can be produced through the melt spinning of polyamide 6 (PA6) blended with 20 wt% of poly(ethylene terephthalate) (PET) if the extrusion temperature is lower than the melting temperature of PET. This technology is applicable for the production of fibers for artificial hair. Three kinds of optical equipment, including an optical microscope, were applied for the quantitative evaluation of the surface roughness of PA6/ PET blend fibers. There was a good correlation between the roughness values evaluated using the edge-detection type diameter monitor (EDDM) and the back-illumination type diameter monitor (BIDM), even though resolution of the BIDM is lower than that of the EDDM. Through the on-line measurement of spin-line diameter performed at various positions along the spin-line using the BIDM, it was revealed that roughness developed with the increase of distance from the spinneret.