Material Analysis
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Optical limitations in transparent product applications
Problem Phenomenon
Even when the addition amount of calcium-zinc stabilizer in PVC transparent sheet is reduced to 1.5 phr, the product haze still exceeds 8%, and the transparency cannot reach the same level as the organotin system (haze <3%), failing to meet high-end transparent packaging requirements.
Cause Analysis
Calcium-zinc metal soaps are solid powders that form micron-scale light scattering centers after being dispersed in PVC; the refractive index of calcium soap and zinc soap is about 1.50-1.55, which does not completely match PVC's 1.54, producing interfacial light scattering; auxiliary stabilizers such as hydrotalcite and zeolite further increase the scattering particle concentration; the crystalline morphology of metal soaps affects light transmittance.
Solution
Select liquid calcium-zinc composite stabilizers to replace the solid powder type; the liquid type's refractive index is closer to PVC; use ultrafine grinding technology to reduce the metal soap particle size to sub-micron level <1 μm; control the inorganic content in the stabilizer to no more than 10%; add 0.5-1 phr MBS resin (refractive index 1.54) as a transparency modifier; adopt low-temperature processing at 155-170°C to reduce decomposition discoloration.
Key Takeaway
The transparency of calcium-zinc is an inherent limitation; liquid-type stabilizers and ultrafine powder technology are currently the main means of improving transparency, but it is difficult to fully match the organotin system.
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