Fiber spots caused by uneven formaldehyde vapor during PVA acetalization

The formaldehyde rate and temperature distributed in the impregnation tank cause the rigid functional groups to lock quickly while main chain movement is restricted, resulting in ring-shaped spots.Countermeasure: multiple liquid circulation metering supplementation..When this defect appears in melt-spun products, it is usually closely related to spinning temperature, metering pump accuracy, spinneret condition or cooling air field uniformity.Spinning defects are characterized by distribution along the length of the filament, and filament-level defects can affect the quality of the entire tow.Continuous occurrence will lead to increased filament breakage frequency, degraded package quality and difficulties in downstream processing; systematic troubleshooting from both spinning components and process parameters is required.

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

1. Process parameter optimization and adjustment: multiple liquid circulation metering supplementation. 2. Systematic troubleshooting method: spinning problem troubleshooting follows the sequence of "chip → temperature → metering → spinneret → cooling air".First check the chip dryness and IV value, then verify the temperatures of each section of the spinning manifold and pipelines, then calibrate 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 air speed and temperature uniformly distributed. 3. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product set, and regularly conduct process capability index (CPK) evaluations.For recurring problems, use fishbone diagrams or 5Why analysis to trace root causes, 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 Fiber spots caused by uneven formaldehyde vapor during PVA acetalization in melt spinning, and 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 troubleshoot down to the equipment and component level.