Achieving consistent color in plastic products requires understanding color measurement, masterbatch selection, and processing effects. This guide covers ΔE, carrier compatibility, and quality control.
1. Color Measurement and ΔE
CIELAB Color Space - L*: Lightness (0 = black, 100 = white) - a*: Red/green axis (+a = red, -a = green) - b*: Yellow/blue axis (+b = yellow, -b = blue)
ΔE Calculation ΔE = √(ΔL*² + Δa*² + Δb*²)
ΔE Interpretation: - ΔE < 1.0: Imperceptible difference - ΔE 1.0-2.0: Slight difference (acceptable match) - ΔE 2.0-3.0: Noticeable difference (marginal match) - ΔE 3.0-5.0: Clear difference (unacceptable) - ΔE > 5.0: Different colors
Industry Standards: - Automotive: ΔE < 1.0 (interior), ΔE < 2.0 (exterior) - Consumer products: ΔE < 2.0 - Packaging: ΔE < 3.0
Measurement Conditions: - Illuminant: D65 (daylight), A (incandescent), F2 (fluorescent) - Observer: 2° or 10° standard observer - Specular: SCI (include) or SCE (exclude)
2. Masterbatch Selection
Carrier Compatibility - PE masterbatch: For PE, PP (polyolefin) - PP masterbatch: For PP specifically - ABS masterbatch: For ABS, SAN - PA masterbatch: For PA6, PA66 - Universal carrier: Limited compatibility
Incompatibility Issues: - Delamination at interface - Poor dispersion - Reduced mechanical properties - Surface defects
Pigment Concentration - High concentration (40-60%): Lower addition rate, better economics - Medium concentration (20-40%): Standard grade - Low concentration (10-20%): Easy dispersion, higher addition
Addition Rate Calculation Addition % = (Target pigment %) / (Masterbatch pigment %) × 100
Example: 2% pigment target, 50% masterbatch Addition = 2 / 50 × 100 = 4%
Typical Addition Rates: - Injection molding: 1-4% - Extrusion: 2-6% - Film: 3-8%
3. Processing Effects on Color
Temperature Effects - High temperature: Pigment degradation, color shift - Residence time: Longer time = more shift - Thermally stable pigments: Inorganic > organic
Shear Effects - High shear: Better dispersion, potential pigment breakdown - Low shear: Poor dispersion, streaks
Color Shift by Process: - Injection molding: Minimal (if temperature controlled) - Extrusion: Slight (longer residence) - Blow molding: Moderate (stretch orientation) - Film: Moderate (thin section, high surface area)
Preventing Color Shift: - Use thermally stable pigments - Optimize processing temperature - Minimize residence time - Regular color QC checks