Moisture is one of the most common — and overlooked — causes of processing instability and surface defects in PC/ABS injection molding. Understanding proper drying is the first step to consistent quality.
Why Moisture Affects PC/ABS Performance
PC/ABS is hygroscopic due to its polycarbonate (PC) component. During melt processing, absorbed moisture can trigger hydrolysis in the polycarbonate molecular chains, leading to a reduction in molecular weight and gradual deterioration of mechanical performance.
Although the ABS phase improves processability, it does not prevent hydrolysis of the PC matrix. As a result, parts may appear visually acceptable while internal strength has already been affected.
Moisture Content vs. Processing Impact
In humid environments, opened material may absorb sufficient moisture within several hours to become unsuitable for direct molding — even if it was perfectly dry before opening.
Typical symptoms of under-dried PC/ABS material include:
Silver Streaks / Surface Splay
Characteristic silver lines or splash marks on part surface from steam vaporization.
Surface Bubbling / Foaming
Trapped moisture vaporizes during molding, creating voids and foam-like defects.
Unstable Shot Weight
Inconsistent melt viscosity from hydrolysis leads to variable shot-to-shot filling.
Reduced Impact Performance
Hydrolysis of PC chains degrades mechanical properties even when surface looks acceptable.
Recommended Drying Conditions for PC/ABS
Proper drying conditions depend on material grade and ambient humidity. The following parameters are commonly used in industrial production:
| Parameter | Recommendation | Note |
|---|---|---|
| Drying Temperature | 80 – 100°C | Grade-dependent; avoid overheating |
| Drying Time (Standard) | 3 – 4 hours | Under normal humidity conditions |
| Drying Time (High Humidity) | 4 – 6 hours | Summer / rainy season adjustment |
| Target Moisture Level | <0.02% (200 ppm) | Critical threshold before molding |
| Tray Depth (Oven Drying) | ≤ 50 mm | Ensures uniform heat penetration |
Stable airflow and consistent temperature control are more important than simply increasing drying time. Excessive temperature or prolonged drying may increase the risk of oxidation or slight color shift.
Drying Equipment Selection
Equipment choice significantly impacts your ability to reach and maintain the required moisture level, particularly as ambient humidity fluctuates.
Dehumidifying Dryer
Hot-Air Oven Dryer
Need Help Optimizing Your PC/ABS Process?
Our material engineers can review your current drying setup, recommend equipment upgrades, and help establish verified pre-processing procedures tailored to your production environment.
Moisture Control During Production
Drying alone is not sufficient — moisture control must be maintained throughout the entire workflow. A well-dried material can re-absorb enough moisture during improper handling to reintroduce defects.
Storage
Keep sealed packaging in a dry environment below 30°C. Once opened, reseal promptly to minimize moisture uptake. Consider dedicated dry storage rooms for high-volume operations.
Material Transfer
Minimize exposure time between dryer and hopper. For continuous production, closed conveying systems help maintain consistent dryness and eliminate the transfer window entirely.
Downtime Management
During production stops, it is generally recommended to keep resin in the dryer when possible to avoid repeated moisture cycling, which stresses the material unnecessarily.
Seasonal Adjustment
Drying time may need to be extended during periods of high humidity — particularly in summer or rainy seasons. Monitor ambient dew point and adjust protocols accordingly.
Practical Moisture Checks on the Shop Floor
Without laboratory equipment, several simple methods can help evaluate resin condition before committing to a production run.
Melt Strand Test
A properly dried material forms a smooth, continuous strand. Bubbling, rough surface, or intermittent steam indicates residual moisture.
Air Shot Observation
Foaming or splay during air shots often suggests insufficient drying. Perform several shots before evaluating part quality.
First-Shot Inspection
Early molded parts should be checked for silver streaks or surface instability before approving full production.
These shop-floor checks are fast and require no instruments. Make them a standard part of your pre-production checklist, especially after material changeovers or extended shutdowns.
Conclusion
Effective moisture control is a fundamental processing requirement for PC/ABS injection molding. Proper drying not only reduces surface defects but also helps maintain mechanical integrity and process stability across production runs.
Proactive Approach
Establish consistent, verified drying procedures before every production run. This prevents defects rather than reacting to them — saving both time and material.
Reliable Practice
Adjusting processing parameters after defects appear is far less effective than maintaining proper pre-processing discipline. The dryer is your first line of defense.
