Do You Know How Colour Masterbatch is Tested?

1. What is Colour Masterbatch?

Colour masterbatch is a concentrated mixture of pigments or dyes, and special additives encapsulated in a carrier resin. It's used to add colour to plastic during the molding or extrusion process, offering better dispersion, easier handling, and improved colour consistency compared to direct pigment dosing.

Colour masterbatch is widely used across various industries, including packaging, automotive, consumer goods, medical devices, and textiles.

2. Why Testing Colour Masterbatch Matters

Even slight inconsistencies in colour can lead to product rejection, increased waste, or damage to brand perception. Testing ensures:

• Consistency in colour shade across batches

• Accurate pigment concentration

• Good dispersion of colour in the base resin

• Compliance with industry standards (RoHS, FDA, REACH, etc.)

• Resistance to heat, light, and environmental conditions

3. Key Colour Masterbatch Testing Methods

3.1. Colour Matching & Spectrophotometry

Spectrophotometers measure the reflected light from a coloured sample and compare it to a target standard, typically in the CIELAB (Lab*) colour space.
Key parameters measured:

• Delta E (ΔE): Colour difference between the masterbatch sample and the standard

• L* (lightness), a* (red-green), b* (yellow-blue)

• Tight ΔE values (typically under 1.0 or 2.0, depending on the application) indicate good colour matching.

3.2. Dispersion Testing

Dispersion refers to how uniformly pigments are distributed in the polymer matrix. Poor dispersion leads to streaks, inconsistent colour, and weaker mechanical properties.

Common tests include:

• Microscopic analysis (optical or electron microscope)

• Melt flow dispersion on film or plaque samples

Masterbatch should display a uniform appearance with no visible specks or agglomerates.

3.3. Melt Flow Index (MFI) Testing

Melt Flow Index, commonly abbreviated as MI, is a measure of the melt flow of plastic, also known as Plastic Flow Index (Melt Flow Rate-MFR). This index is primarily used to evaluate the flow characteristics of plastic materials under specific temperature and pressure conditions.

Measured in: grams per 10 minutes (g/10 min) under specified load and temperature

Too high or too low MFI may indicate processing issues or incompatible carrier resin.

3.4. Heat Stability Testing

Pigments and dyes must resist degradation under heat during processing (usually between 180°C to 300°C).

Method:

• Expose the masterbatch to elevated temperatures

• Measure colour shift (ΔE) post-exposure
  
  

3.5. Light Fastness Testing

Exposure to UV or sunlight can cause pigments to fade. Light fastness testing ensures long-term performance in outdoor or exposed environments.
Standard methods:

• Xenon arc testing (ISO 4892-2)

• Blue Wool Scale (1 to 8, with 8 being best)

3.6. Weathering Tests

These simulate outdoor conditions—UV exposure, humidity, and temperature changes—to predict real-world durability.

Standards: ISO 4892-2, ASTM G155

3.7. Migration and Extraction Tests

For food contact or medical applications, pigments must not leach or migrate from the final product.

Tests performed under:

• EU Regulation 10/2011

• FDA 21 CFR compliance

3.8. Physical Property Testing

Sometimes, the masterbatch affects the mechanical properties of the final plastic. Thus, tensile strength, elongation, and impact resistance may be checked.
Testing ensures that the addition of colourant doesn’t compromise structural performance.

4. Typical Quality Control Workflow in Masterbatch Production

• Raw Material Testing: Pigments, additives, and carrier resins are tested before mixing.

• Lab-scale Sample Production: Pilot samples are produced for initial evaluation.

• Masterbatch Production: Full-scale production under controlled conditions.

• Batch Testing: Apply the above-mentioned tests for each production lot.

• Customer Simulation: In some cases, customer-specific tests are performed using their resin or processing method.

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