Poor interlayer adhesion in coextrusion

Interlayer separation and delamination occur in multilayer coextruded products, interlayer adhesion strength is insufficient, and peel force tests are below standard required values. Poor coextrusion interlayer adhesion can occur in multilayer pipes (such as PE-aluminum-PE composite pipes), multilayer films, and composite sheets. Interlayer separation causes the product to lose the design function of the composite structure — barrier layer failure, reinforcement layer detachment, adhesive layer cracking, and the overall performance of the product drops significantly.

1. Comprehensive factors: Interlayer interface temperature too low causes insufficient thermal fusion. 2. Material/formulation factors: Poor compatibility of the two materials or excessive viscosity difference. 3. Material/formulation factors: Adhesive layer (tie layer) thickness insufficient or formulation improper. 4. Process parameter factors: Die flow channel design causes insufficient pressure after the layers converge. 5. Cooling and sizing factors: The cooling rate and uniformity of extruded products determine crystallinity, internal stress level, and dimensional stability. Uneven cooling causes pipe ovality, profile deformation, and internal stress concentration; the cooling water circuit layout and water temperature control must be optimized.

1. Process parameter optimization and adjustment: Increase the temperature of the die section after convergence. 2. Mold/tooling improvement and maintenance: Select material combinations with better compatibility or compatibilizers. 3. Equipment inspection and system maintenance: Appropriately increase adhesive layer thickness and optimize formulation. 4. Material/formulation optimization: Optimize coextrusion die flow channel design to increase convergence pressure. 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.

This problem is a typical manifestation of poor interlayer adhesion in coextrusion in extrusion molding. The core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, speed, pressure) and precision correction of the die/sizing system. It is recommended to start with parameter adjustment and gradually go deeper into the equipment and tooling levels.