Why Plastic Processing Demands Humidity Control
Plastic resins — particularly engineering resins like PET, Nylon (PA), PC, ABS, and PBT — are highly hygroscopic. They absorb atmospheric moisture, which during melt processing causes:
- Hydrolysis of polymer chains, leading to brittle parts
- Splay marks and cosmetic surface defects on molded components
- Bubbles, voids, and inclusions in transparent parts (PC/PET)
- Inconsistent dimensions in precision mechanical parts
- Mold condensation ("sweating") on chilled tooling faces
The flexible packaging industry also depends critically on humidity control for rotogravure printing, lamination of barrier films, and bag converting.
Recommended Humidity & Dew Point Levels
| Application | Required Condition |
|---|---|
| PET Resin Drying | Dew point: –40°C, RH: <10% (in dryer) |
| PA / Nylon Drying | Dew point: –40°C, 80°C drying temp |
| PC (Polycarbonate) Drying | Dew point: –40°C, 120°C drying temp |
| PET Preform Storage | <50% RH, 22°C |
| PET Bottle Filling Hall | 50–60% RH, 22–25°C |
| Blister Pack Production | 35–45% RH, 22–25°C |
| Flexible Packaging Lamination | 45–55% RH, 22–25°C |
SORPS Applications in Plastic & Packaging Industry
1. PET Bottling Plants
PET bottling halls require active humidity control to prevent condensation on cold-filled bottles (which causes label adhesion failures and box collapse) and to keep stored preforms dry. SORPS supplies DD5000–DD20000 series units integrated with filling hall HVAC.
2. Centralized Plastic Resin Drying
Achieving a consistent –40°C dew point is crucial for drying moisture-sensitive polymers. Centralized dry-air supply systems from SORPS feed multiple hoppers efficiently, lowering power consumption compared to multiple individual dryers.
3. Injection Moulding Halls
Large moulding facilities (automotive parts, medical devices, preforms) benefit from controlled production-hall relative humidity. This prevents mold sweating on chilled molds, ensuring high cosmetic quality, consistency, and reduced cycle times.
Why SORPS for PET & Plastics
Frequently Asked Questions
Why is a –40°C dew point required for PET resin drying?
PET is highly hygroscopic. If processed with moisture content above 0.02%, it undergoes hydrolytic degradation during melting, which reduces molecular weight and causes the final preforms/bottles to be brittle and fail stress-crack tests. A –40°C dew point air stream is required to extract this deep-seated moisture.
How does mold sweat or condensation affect injection moulding?
To optimize cycle times, injection molds are run with chilled cooling water (typically 5–12°C). In humid conditions, atmospheric moisture condenses on these cold mold faces ("mold sweat"), causing water marks, surface blemishes on molded parts, and rust damage to expensive mold cavities. Controlled RH eliminates this condensation.
Can SORPS systems be retrofitted into existing resin drying hoppers?
Yes, we supply standalone desiccant dry-air generators (DD series) that can be ducted directly to supplement or replace existing OEM drying hoppers, improving energy efficiency and achieving stable –40°C dew points.
What is the typical drying time for Nylon/PA resins?
Nylon resins typically require drying at 80°C with –40°C dew point air for 4 to 6 hours before processing, depending on the initial moisture level and the specific grade of polyamide.
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