Extrusion & Post
10 조회수
PPA eliminates sharkskin defects in LLDPE blown film
문제 현상
In LLDPE blown film production, a sharkskin-like rough texture appears on the film surface (the surface shows bamboo-node-like ripples), film transparency decreases and haze increases by more than 5%, and customers complain that the appearance quality does not meet the standard.
원인 분석
LLDPE has a narrow molecular weight distribution and the melt undergoes stick-slip oscillation at the die exit under high shear rate (Shark-skin melt fracture), with the flow velocity difference between the melt surface layer and the inner layer exceeding the critical value; PPA is not added or the PPA dosage is insufficient (below 0.02%); a low extrusion temperature (<190°C) aggravates melt fracture.
해결 방법
Add 0.03-0.05% of PPA processing aid to the LLDPE formulation; PPA forms a fluoropolymer coating on the screw and die surfaces to reduce melt/metal interfacial friction; appropriately raise the die temperature by 5-10°C to reduce the melt surface layer viscosity; reduce the extrusion line speed by 10-15% as a short-term mitigation measure.
핵심 요약
PPA is the most effective means to solve the LLDPE sharkskin problem, and an addition of 0.03-0.05% can completely eliminate surface defects.
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