Mastering the Drying Process: A Deep Dive into PC/ABS Baking Temperatures and Techniques

In the field of engineering plastics processing, PC/ABS (Polycarbonate/Acrylonitrile-Butadiene-Styrene alloy) is widely used in automotive interiors, electronic housings, and office equipment because it combines the high heat resistance and strength of PC with the processing fluidity of ABS. However, one of the most frustrating problems for injection molding technicians is: "Why do silver streaks (splay marks) still appear on the molded product even after the material has been dried for a long time?"

The key to solving this problem lies in accurately mastering the drying temperature of PC/ABS. This article will analyze the PC/ABS drying process from three dimensions: technical parameters, drying mechanisms, and practical operational tips.

I. The Core Answer: What is the optimal drying temperature for PC/ABS?

Under normal circumstances, the recommended drying temperature for standard PC/ABS alloys is 90°C to 110°C for 3 to 4 hours.

However, in actual production, this value is not static. Specific temperature selection needs to be fine-tuned based on the material grade and ambient humidity:

• General Purpose PC/ABS: Recommended at 90°C - 100°C.

• High Heat Resistant PC/ABS: Due to higher PC content or heat-resistant modifiers, the temperature can be increased to 105°C - 110°C.

• Flame Retardant (FR) PC/ABS: Recommended to be controlled at 85°C - 95°C. Note that flame retardants are prone to degradation during long-term baking at high temperatures, which can cause the material to yellow.

II. Why Must the Drying Process Be Strictly Enforced?

PC/ABS is a hygroscopic material. Even when exposed to air for a very short time, the ester groups in its molecular chains will absorb moisture.

1. Impact on Mechanical Properties

If drying is incomplete, residual moisture will cause a hydrolysis reaction during the high-temperature melting process in the injection molding machine. Hydrolysis leads to the breaking of PC molecular chains and a reduction in molecular weight. The direct result is a sharp drop in the product's impact strength; a housing that was originally unbreakable may become as brittle as glass.

2. Impact on Aesthetic Quality

Moisture turns into gas at high temperatures and enters the mold cavity with the melt, forming radial white marks on the product surface—commonly known as silver streaks, splay marks, or gas clouds. For products requiring high-gloss surfaces or painting, such defects are fatal.

III. Deep Dive: Three Key Variables Affecting Drying Results

Simply setting the reading on the temperature controller is not enough. Drying is a systematic process involving temperature, time, dehumidified air, and dew point.

1. The Importance of Dew Point

Traditional hopper dryers rely on heated ambient air to carry away moisture. However, during rainy seasons or in high-humidity environments, the air itself contains moisture, making this heating method highly inefficient. Dehumidifying dryers are recommended. A dehumidifying dryer can reduce the air's dew point to below -40°C. This means the air is extremely dry and can act like a sponge to quickly absorb moisture from the core of the pellets.

2. The Balance of Drying Time

Insufficient drying time (<2 hours) prevents moisture in the core from escaping. Conversely, excessive drying time (>8–10 hours) can lead to thermal degradation or oxidative discoloration of the material.

Pro-tip: If the production line stops unexpectedly for more than 4 hours, it is recommended to lower the dryer temperature to around 50°C to prevent performance fluctuations caused by over-baking.

3. Layer Thickness and Airflow

Material accumulation in the hopper must not be too thick; otherwise, the air from the bottom cannot penetrate evenly to the top. Ensuring the fan is running normally and the air outlet is not blocked by dust is a prerequisite for accurate temperature control.

IV. Field Operations: How to judge if the material is "thoroughly dried"?

In the absence of precision moisture analyzers, experienced technicians usually use the following methods for a preliminary assessment:

• Air Shot Method (Purging Test): Perform an air shot of the dried material from the nozzle. If the extruded melt strand is smooth, transparent, and free of any bubbles or crackling sounds, the drying effect is good. If there is white smoke or tiny bubbles, the drying time must be extended.

• Breakage Method: Observe the dried pellets after cooling. Randomly pick a few; well-dried PC/ABS pellets are hard in texture. If they feel soft or sticky, it indicates the temperature was too high or drying was insufficient.

V. Solving the "False Temperature" Problem in PC/ABS Processing

Sometimes, the temperature controller shows 100°C, but the material inside the hopper has not actually reached that temperature. This is the "False Temperature" issue.

• Sensor Position: Check if the thermocouple is located at the air inlet. If the sensor is damaged or displaced, the displayed value loses its reference significance.

• Filter Cleaning: If the filter is clogged with dust, the airflow will decrease. Even if the hot air temperature is sufficient, the heat exchange efficiency will be greatly reduced.

• Material Color Differences: Black materials absorb heat faster than light-colored ones. When drying large batches of black PC/ABS, it is recommended to lower the temperature by about 5°C compared to light-colored materials to prevent local overheating.

VI. Summary and SOP Reference Table

To facilitate production management, the following data can be used as a Standard Operating Procedure (SOP) reference:

It is important to emphasize that for Electroplating Grade PC/ABS, moisture requirements are even stricter (must be below 0.01%). Excess moisture leads to poor adhesion of the plating layer, resulting in blistering or peeling. Therefore, the use of a high-performance honeycomb dehumidifier is strongly recommended.