A PVC window or door profile is made on a twin-screw extrusion line where resin and additives are mixed, melted, shaped in a die, cooled in a calibrator, and pulled to length. Each additive has one job in that chain: the calcium zinc stabilizer stops heat damage, the ACR processing aid fuses the melt, the acrylate impact modifier absorbs shocks, and the internal lubricant keeps flow smooth. This article explains the line step by step and shows where Shitong's additives earn their place.
PVC profile extrusion is a continuous, tightly timed process. Resin and a dry-blend of additives first tumble in a high-speed cooler mixer, then feed a parallel twin-screw. Inside the barrel the compound is heated, sheared, and plasticized into a uniform melt. That melt is forced through a profile die, where the hollow chamber shape is set. The hot profile enters a vacuum calibrator sprayed with water, locks to dimension, passes past haul-off rollers, and is cut to length.
The whole window of thermal exposure lasts only two to four minutes, but PVC begins to release hydrochloric acid above roughly 110°C. That is why the additive package is loaded before the screw, not added later.
The calcium zinc stabilizer is the backbone. Composed of calcium zinc metal soap with high-quality hydrotalcite and functional additives, it captures the HCl that forms during processing and slows the chain reactions that turn PVC brittle and yellow. Without it the melt degrades before it ever reaches the calibrator.
The ACR processing aid promotes fusion and builds melt strength so the profile holds its shape at the die exit. A general processing aid with moderate viscosity and a wide processing window keeps the line forgiving when screw speed or temperature drifts.
The acrylate series impact modifier is a core-shell polymer. Its soft crosslinked acrylate core absorbs impact energy, while the methacrylate shell bonds to PVC. This is what stops a window frame from cracking in a cold snap. For thin-wall or complex chambers, dosage rises.
The internal lubricant balances the system. Lubricant G60, a polyol fatty acid ester, gives clean internal lubrication with good transparency and dispersion, while PE wax and oxidized PE wax manage external release and surface gloss. Get the ratio wrong and you see die buildup, plate-out, or a dull surface.
Treat the package as one system, not a shopping list. Push impact modifier up and you may need more processing aid to keep fusion on time. Switch to a more external lubricant and the stabilizer may not distribute evenly. The profile you see on the line is the sum of these trade-offs, which is why Shitong supplies both the additives and a starting recipe.
Scenario | Additive emphasis | Why | Shitong product |
Standard white indoor profile | Baseline CaZn + processing aid + 5 phr impact | Cost-balanced, adequate toughness | |
White outdoor / high-UV climate | Higher impact + TiO2 + weather-grade CaZn | Resist hail, thermal cycling, chalking | |
Colored or foil-coextruded profile | Tighter lubricant balance, no plate-out | Color streaks come from poor dispersion | |
Thin-wall / multi-chamber profile | More impact modifier + more processing aid | Walls crack at corners without melt strength |
Shitong's application cases show the same additive logic applied across rigid PVC product families, and the calcium zinc stabilizer page documents lead-free stabilization for profiles and pipes alike. Formulators who started from a Shitong recipe reported steadier haul-off and fewer rejects on thin-wall lines.
Across profile compounders who switched to Shitong's calcium zinc system, the recurring feedback is "no more yellowing at the die" and "the line runs longer between cleans." Several noted that G60 gave clearer surfaces on transparent and co-extruded lines without the waxy haze they saw from commodity PE wax. These are aggregate field impressions, not individual endorsements.
Add stabilizer and filler first in the mixer, then processing aid and impact modifier, lubricant last, so each coats the resin in the right order. Keep mixer batch temperature near 115–125°C and discharge below 45°C to avoid pre-gelling. Re-check the internal-to-external lubricant ratio whenever you change impact modifier grade or pigment load.
Environmental Protection Calcium Zinc Stabilizer — calcium zinc metal soap + hydrotalcite, lead-free, typical reference 4–6 phr in rigid profile (confirm with Shitong).
Acrylate Series Impact Modifier — core-shell, typical 5–8 phr, more for thin/complex chambers.
General Processing Aid — typical 1–2 phr.
Lubricant G60 — polyol fatty acid ester, typical 0.5–1.5 phr, transparent and foamed grades.
Certifications: ISO 9001 / ISO 14001 / ISO 45001 reported; REACH/RoHS alignment for export. Shitong is a national high-tech enterprise with a joint R&D center with Qingdao University of Science and Technology. Contact cindy@stgaocai.com for recipe support and MOQ.
Do I need both processing aid and impact modifier in profiles? Yes. Processing aid fuses the melt; impact modifier adds toughness. They solve different failures.
Why does my profile turn yellow at the die? Usually under-stabilized or overheated melt — raise CaZn stabilizer or lower barrel temperature.
Can I use the same lubricant for white and colored profiles? Often not. Colored and co-extruded lines need a tighter G60/PE-wax balance to avoid streaks.
What dosage of impact modifier for thin-wall chambers? Typically higher than standard; confirm exact phr with Shitong for your chamber design.
Is calcium zinc stabilizer enough for outdoor frames? Yes with TiO2 and a weather-grade package; impact modifier dosage also rises for cold climates.
How should I order additives in the mixer? Stabilizer and filler first, then processing aid and impact modifier, lubricant last.
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