Extrusion & Post
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Insufficient long-term weather resistance of outdoor products
Problem Phenomenon
PVC door and window profiles using calcium-zinc stabilizers show significant discoloration after 3-5 years of use, with the yellowness index increasing more than 10 times, and surface chalking; the decline range of mechanical properties exceeds that of organotin system products.
Cause Analysis
Calcium-zinc stabilizers themselves do not have light stabilization function; under ultraviolet irradiation, the PVC de-HCl reaction is photocatalytically accelerated; calcium-zinc metal soaps undergo photo-oxidative decomposition under ultraviolet light; the formulation lacks sufficient TiO₂ (rutile type) and UV stabilizer protection; the product surface lacks a protective coating.
Solution
In the calcium-zinc base formulation, increase the rutile-type TiO₂ dosage to 8-12 phr for coverage + ultraviolet shielding; add 0.3-0.5 phr benzotriazole-type ultraviolet absorbers (such as UV-326 or UV-329); add 0.2-0.3 phr hindered amine light stabilizer HALS such as 770/944 for synergistic protection; use acrylate-type impact modifier ACR to replace CPE to improve its own weather resistance; co-extrude a PMMA or ASA weather-resistant layer on the surface.
Key Takeaway
The shortcoming of calcium-zinc stabilizers in outdoor weather resistance needs to be compensated by strengthening with TiO₂ and light stabilizer systems; a co-extruded weather-resistant layer is the longest-lasting solution.
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