Plastics : Measurement equipment and processes for matching colors in plastics

Below is a detailed explanation of color measurement equipment and processes for matching colors in plastics.

Color Measurement Equipment:

Spectrophotometer:

• Primary color measurement tool
• Measures color wavelengths
• Provides numerical color values: L for (Lightness), a for (Red-Green), b for (Blue-Yellow) and Delta E for (Color difference)

Different types of measurement:

• Benchtop (most accurate)
• Portable (field use)
• Online (production monitoring)
• Checking using light Boxes
• Checking using the standard lighting conditions

A benchtop is a testing or evaluation process where a small sample or quantity of material is tested under controlled conditions to verify quality, properties, or performance before full-scale production.

Using multiple light sources:

• D65 (daylight)
• CWF (cool white fluorescent)
• TL84 (store lighting)
• A (incandescent)
• UV light

These help to detect metamerism which is a phenomenon where two colors appear identical under one light source but look different under another light source. This is particularly important in color matching for plastics, textiles, and other materials.

Gloss Meters:

• Measures surface shine
• Important for appearance
• Units in GU (gloss units)
• Uses different angles, -60° (standard), -20° (high gloss) and -85° (low gloss)

Color Values and Codes:

• Lab Color Space : L* = Lightness (0-100), a* = Red/Green axis, b* = Blue/Yellow axis
• Universal color language
• Industry standard
• Delta E : measures color difference, a  lower number means a better match

Industry standards:

• ΔE < 1      : Not visible
• ΔE 1-2      : Slight difference
• ΔE 2-3.5  : Notable difference
• ΔE > 3.5  : Obvious difference

Color Tolerances are  set in acceptable ranges, usually in Delta E

Application specific:

• Automotive  : tight (ΔE < 1)
• Consumer    : medium (ΔE < 2)
• Industrial     : wider (ΔE < 3)

Measurement Process:

• Proper sample Preparation
• Use a clean surface
• Use a consistent thickness
• Use a proper conditioning
• Use multiple samples
• Standard backing

Measurement Steps:

• Calibrate equipment
• Use multiple readings
• Measure in different locations
• Uses the average of the results
• Document conditions
• Record data 
• Record color values
• Record gloss readings
• Record light source data
• Take into account the temperature conditions
• Take into account the humidity levels

Quality Control:

• Perform regular Checks
• Perform equipment calibration
• Use standard verification
• Take into account the environmental conditions
• Perform in-line monitoring
• Check Batches

Common Issues:

• Metamerism
• Surface texture effects
• Temperature influence
• Thickness variation
• Instrument reading variation
• Dispersion quality
• Contamination
• Take into account additives effect
• Take into account the moisture effects

Dispersion quality refers to how well additives, pigments, or other materials are distributed throughout the plastic. Good dispersion means particles are evenly spread with no clumps or uneven areas, resulting in consistent properties and appearance.

Surface texture effects are the visual and tactile characteristics of a material's surface, such as smooth, rough, matte, glossy, or textured patterns.