Blue Color Change of Fibers on Heat Setting Rolls (Optical Layer Thickness Interference)

If the fiber heat setting temperature is too low, it leads to large shrinkage and dimensional instability; if the temperature is too high, it causes the fiber to deform and harden, worsening the hand feel. Heat setting is a key process for orientation relaxation and crystallization perfection of fiber molecular chains—temperature and time determine the final shrinkage, crystallinity, and mechanical property balance of the fiber. Improperly heat-set fibers continue to shrink and deform during subsequent processing and use, and the fabric dimensional stability fails to qualify.

1. Spinning temperature factors: The spinning temperature determines melt viscosity and rheological behavior, directly affecting the spinnability, fineness uniformity, and surface quality of the fiber. Excessively high temperature leads to degradation yellowing and filament breakage; excessively low temperature leads to poor plasticization and increased extrusion pressure; it needs to be precisely set according to the chip IV value and stably controlled. 2. Cooling air field factors: The temperature, wind speed, and uniformity of side-blowing or circular-blowing air determine the solidification and forming quality of the fiber—too fast cooling leads to rough surface and increased internal stress, uneven cooling leads to inconsistent fineness among filaments in the same bundle, and low wind speed leads to filament sticking and filament breakage; air field parameters need to be precisely controlled.

1. Process parameter optimization and adjustment: The product is a physical optical phenomenon produced by the micro-thin-film effect, not chemical erosion, but if it needs to be eliminated, the surface roughness of the hot roll can be fine-tuned. 2. Systematic troubleshooting method: Troubleshooting of spinning problems follows the order of "chips → temperature → metering → spinneret → cooling air". First check the chip dryness and IV value, then verify the temperature of each section of the spinning manifold and piping, then verify the metering pump accuracy and pressure stability, further check the spinneret cleanliness and hole shape condition, and finally adjust the cooling air field parameters to make the wind speed and temperature evenly distributed. 3. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

This problem is a typical manifestation of blue color change of fibers on heat setting rolls (optical layer thickness interference) in melt spinning. The core of the solution lies in the precise stability of spinning temperature, high-precision control of metering supply, and optimized maintenance of the spinneret/cooling air field. It is recommended to start with chip quality and spinning parameters and gradually investigate to the equipment and component level.