Processing Machinery
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Poor plasticization caused by lubrication imbalance of calcium-zinc stabilizers
Problem Phenomenon
When extruding PVC rigid pipes with a calcium-zinc stabilizer system, the main machine current is low, 20% below the normal value, the melt pressure fluctuates greatly, the product surface is rough and lusterless, mechanical properties decline with tensile strength reduced by more than 10%.
Cause Analysis
The calcium-zinc stabilizer contains excessive built-in internal lubricating components (calcium stearate, etc. have significant internal lubricating effects), which reduces the intermolecular friction of PVC and delays the plasticization process; excessive addition of external lubricant PE wax further blocks the screw shearing action; low processing temperature aggravates insufficient plasticization.
Solution
Test the lubrication value of the calcium-zinc stabilizer (evaluate plasticization torque and time via a torque rheometer); reduce or replace the external lubricant variety (replace PE wax with oxidized PE wax, reducing 0.1-0.2 phr); increase the barrel second zone temperature by 5-10°C to enhance plasticization; add 0.3-0.5 phr processing aid ACR to promote plasticization; adjust the internal lubrication/external lubrication ratio to 1:1.2~1:1.5.
Key Takeaway
The lubrication characteristics of calcium-zinc stabilizers need to be evaluated holistically at the formulation level; lubrication balance is achieved through plasticization torque measurement and coordinated adjustment of process parameters.
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