Gel Particles/Fish Eyes

Transparent or translucent hard granular protrusions appear on the product surface, with a rough hand feel, especially obvious in films and pipes. The essence of fish eyes is incompletely melted ultra-high molecular weight components or crosslinked gel particles in the resin, which fail to fully fuse with the surrounding melt at the extrusion temperature and retain their original particle form. Fish eyes not only affect surface finish, but also become stress concentration points and fatigue crack initiation points.

1. Material/formulation factor: micro-crosslinking or ultra-high molecular weight portions exist in the resin. 2. Comprehensive factor: the spinning temperature is too low, so the gel particles cannot be completely melted and eliminated. 3. Comprehensive factor: insufficient filtration precision. 4. Cooling air field factor: the temperature, wind speed and uniformity of the side-blowing air or ring-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 thickness of individual filaments in the same bundle, and low wind speed leads to filament sticking and filament breakage; the air field parameters need to be precisely controlled.

1. Process parameter optimization and adjustment: increase the mesh count and filtration area of the spinning filter. 2. Mold/tooling improvement and maintenance: slightly increase the spinning temperature. 3. Equipment inspection and system maintenance: use more homogeneous chips to control at the source. 4. Troubleshooting of spinning problems follows the sequence of "chips → temperature → metering → spinneret → cooling air". First check the chip dryness and IV value, then verify the temperatures of each section of the spinning box and pipeline, next 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. 5. 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 the 5Why analysis method to trace the root cause, and solidify the 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.

The essence of fish eyes is incompletely melted ultra-high molecular weight components or crosslinked gel in the resin. The solution approach is "raising temperature + filtration + changing material": increase the plasticization temperature to ensure full melting, use filter screens to filter out gel particles, and select calendering/extrusion-specific resins with a narrower molecular weight distribution.