Extrusion & Post
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Relationship between zinc content and plate-out effect
Fenómeno del problema
When PVC calendered film is produced using calcium-zinc stabilizers, yellow adhesive deposits (zinc soap precipitation) appear on the calender roll surface, causing transverse streaks and color difference on the film surface; the calender rolls need to be shut down for cleaning every 4 hours of operation.
Análisis de la causa
Under the high calendering temperature of 180-200°C and shear force, part of the zinc stearate in calcium-zinc stabilizers with excessively high zinc content precipitates and migrates to the hot roll surface; the temperature difference of calender rolls causes aggravated local zinc soap deposition; ZnCl₂ forms zinc chloride volatiles at high temperatures that condense and deposit; improper calcium-zinc ratio (Zn proportion >40%) accelerates zinc precipitation.
Solución
Adjust the calcium-zinc metal ratio to reduce the zinc content to 25-30%; replace zinc stearate with high molecular weight zinc soaps (such as zinc laurate or zinc naphthenate); add 0.5-1 phr epoxidized soybean oil to the formulation to chelate free Zn²⁺; regularly clean the calender rolls and apply release agent; control the calender roll temperature difference to no more than ±1°C.
Conclusión clave
Zinc content and zinc soap variety are key control factors for the plate-out behavior of calcium-zinc stabilizers; the comprehensive performance is best when the calcium-zinc metal ratio is 2:1~3:1.
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