After years of production practice, our company, Highsun Synthetic Fiber Technologies Co., Ltd., gradually found out the influence of hot box temperature on crimping, strength and dyeing of nylon 6.
Under the production conditions of stretching ratio of 1.239 times, D/Y of 2.10 and speed of 700m/min, the crimp shrinkage and crimp stability increase with the increase of temperature in a certain range. This is because the plasticity of the fiber is improved with the increase of temperature, which makes it easy to deform. So the nylon 6 is fluffy and fully deformed. However, when the temperature is too low (below 182℃), the crimp rate and crimp stability of nylon 6 material become low too. The filament is soft and inelastic, which is called cotton silk. When the temperature is too high (higher than 196℃), the processed filament becomes tight and stiff. This is because the fibers become brittle under high temperature, resulting in fibrils which are bonded together and become stiff filaments. So the crimp shrinkage is greatly reduced.
During the production process, it was found that the temperature of hot box also had great influence on the strength of nylon 6. Under the technological conditions of loading speed 630m/min, stretching ratio 1.24 times and D/Y 2.03, the twisting tension decreases and the untwisting tension also decreases with the increase of temperature, which is due to fiber softening at high temperature. At relatively low temperature, the strength increases with the increase of temperature, but decreases with the further increase of temperature (193℃). This is mainly because at relatively low temperature, the activity ability of fiber molecules increases with the increase of temperature, which reduces the internal stress in the process of thermal deformation, makes it easy to deform and increases the strength of filament. However, with the further increase of temperature, the amorphous orientation in the fiber is easy to be de-oriented. When the temperature reaches 196℃, the produced fibers become tight and stiff with extremely poor appearance. After many experiments, it was found that nylon 6 had the highest strength when the temperature of hot box was 187℃. Of course, this should be adjusted according to the maximum loading speed of nylon POY. According to experience, oil pollution and dust will stick to the hot box with the decrease of machine cleanliness, which will reduce the heating efficiency.
When the temperature in the hot box is low, nylon 6 has lower crystallinity, strong dyeing affinity, and higher dyeing depth. On the contrary, the high temperature of hot box causes light dyeing and low dye uptake of nylon 6. Because the displayed temperature of the machine sometimes deviates greatly from the measured temperature, when the temperature is adjusted to 210°C in actual production, the appearance and physical indexes of nylon 6 are good, but the coloring effect is poor.