Gel particles / fish eyes

Transparent or translucent hard granular protrusions appear on the product surface, rough to the touch, especially obvious in films and pipes. The essence of gel particles (fish eyes) is ultra-high molecular weight components or cross-linked gel particles in the resin that are not completely melted; they fail to fully fuse with the surrounding melt at extrusion temperature and retain their original particle form. Gel particles not only affect surface finish but also become stress concentration points and fatigue crack initiation points.

1. Material/formulation factors: Ultra-high relative molecular mass components or cross-linked gels exist in the resin. 2. Material/formulation factors: Insufficient melt plastication temperature causes part of the resin to not fully melt. 3. Operational factors: Incomplete cleaning when changing material grades causes cross-contamination. 4. Equipment factors: Poor screw mixing effect. 5. Die design factors: The geometry of the die flow channel, the land length, and the outlet dimensions directly affect melt flow stability and product dimensional accuracy. Unreasonable flow channel design (presence of dead corners, excessively large convergence angle) is an important root cause of melt fracture, material buildup, and flow marks, and must be addressed starting from optimization of the die structure.

1. Process parameter optimization and adjustment: Increase barrel temperature to ensure full plastication. 2. Mold/tooling improvement and maintenance: Use a screen to filter out gels. 3. Equipment inspection and system maintenance: Use purging material to thoroughly clean when changing materials. 4. Material/formulation optimization: Select a screw with better mixing effect; add a static mixer if necessary. 6. 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.

The essence of gel particles (fish eyes) is ultra-high molecular weight components or cross-linked gels in the resin that are not completely melted. The solution approach is "heat up + filter + change material": increase plastication temperature to ensure full melting, use screens to filter gel particles, and select calendering/extrusion-specific resins with narrower molecular weight distribution.