The Possible Injection Molding Problems of PC/ABS FR UL-94 V0 Material

PC/ABS FR UL-94 V0 is an engineering plastic alloy composed of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS), flame-retardantly modified to meet the UL94 V-0 standard. In the below article, we have collected some of the common issues while injecting PC/ABS FRV0 materials. 

I. Material Degradation & Surface Defects

• Silver Streaks, Yellowing, Color Variation

    Causes:  

    - Insufficient drying (moisture content must ≤0.04%, ideally ≤0.02%) causing PC hydrolysis;  

    - Excessive barrel temperature (>280°C) or prolonged residence time (>10 min) leading to thermal degradation.  

    Solutions:  

    - Use dehumidifying dryers (dew point ≤-30°C), dry at 80–95°C for 4–6 hours (avoid exceeding 48 hours);  

    - Set shot volume to 60–80% of machine capacity to reduce residence time.  

• Black Streaks/Burning Marks

    Causes: 

- Localized overheating or excessive shear (e.g., screw speed >70 RPM) decomposing flame retardants.

    Solutions:

    - Reduce screw speed (30–70 RPM) and back pressure (3–10 kg/cm²);  

    - Optimize mold venting to prevent trapped gas.  

II. Mechanical & Structural Defects

• Brittle Cracking/Paint Delamination

    Causes:  

    - Internal stress concentration (esp. at weld lines), exacerbated by paint solvents (ketones/esters);  

    - Excessive packing pressure (>80% injection pressure) or low mold temperature (<50°C) increasing residual stress.  

    Solutions:  

    - Raise mold temperature to 50–80°C to enhance molecular mobility;  

    - Lower packing pressure (60–80% of injection pressure);  

    - Avoid paints containing aromatic/ketone solvents.  

• Low Tensile Strength/Cavities on Fracture Surface
  

    Causes:  

    - Poor ABS phase dispersion (rapid cooling causing discrete particles instead of continuous phase);  

    - Suboptimal material ratio/compatibility (e.g., lacking compatibilizers).  

    Solutions:

    - Optimize cooling rate to ensure continuous ABS phase;  

    - Add compatibilizers (e.g., PE-g-MAH, SMA) to improve PC/ABS interfacial bonding.  

III. Flow-Related Issues

• Delamination/Peeling

    Causes:  

    - Melt fracture from high shear (e.g., small gates, high friction on textured surfaces);  

    - Poor PC/ABS compatibility causing phase separation.  

    Solutions:  

    - Enlarge gate size, adopt **ramped injection speed** to reduce shear;  

    - Add compatibilizers (e.g., acrylic copolymers).  

• Weak Weld Lines

    Causes: 

    - Weak bonding at melt fronts due to flame retardants affecting flow.  

    Solutions:  

    - Increase mold temp (>60°C) and melt temp (250–270°C) to promote molecular diffusion;  

    - Reposition gates to avoid weld lines in high-stress areas.  

IV. Mold & Machine Compatibility

• Unsuitable Screw Design:  

 High compression ratio screws (>2.5:1) cause shear-induced overheating. Use low-compression screws (2:1–2.5:1).  

- Insufficient Clamping Force: Match projected part area with clamping force (constant: 0.5–0.8 t/cm²) to prevent flash.  

Summary: Critical Control Points 

1. Thorough Drying: Dehumidifying dryer (dew point ≤-30°C) is essential;  

2. Precise Temp Control: Melt temp ≤280°C, residence time ≤5 min, mold temp ≥50°C;  

3. Low-Shear Process: Screw speed ≤70 RPM, back pressure ≤10 kg/cm², ramped injection speed;  

4. Mold Optimization: Gate sizing, adequate venting, weld lines away from high-stress zones.