Powder coating

1. Measuring Powder Coating Color

1.1 Visual Inspection

Following standards like GB/T9761-98 and ISO 3668-1976, visual color comparison is performed under natural or artificial light sources (commonly D65 and A). Observers must pass vision tests and avoid long continuous inspection to prevent reduced accuracy.

1.2 Instrumental Measurement

Principle

The powder coating color is determined mainly by diffuse reflection. Spectrophotometers measure spectral reflectance (K/S ratio) to calculate tristimulus values and determine color differences.

Instruments

• Colorimeters – Quick and portable but less precise.

• Spectrophotometers – More accurate, can perform both measurement and computer-aided color matching (e.g., X-Rite, Minolta).

Operation

Power on → calibrate with black/white plates → measure sample → input data → compare results.

2. Computer Color Matching for Powder Coating

2.1 Principle

Color matching uses Kubelka–Munk theory with K/S spectral data to select pigment combinations for accurate powder coating color reproduction.

2.2 Process

1. Pigment Selection – Based on heat resistance, weatherability, and test performance.

2. Database Creation – Maintain 20–25 pigment types, updated regularly.

3. Standard Input – Use customer samples or reference plates for accurate target colors.

4. Formula Selection – Choose from computer-suggested formulas considering cost, performance, and match quality.

5. Color Adjustment – Lab test, fine-tune pigment dosage, and check coating performance.

6. Scale-Up – Adjust formula for mass production equipment differences.

7. Batch Production – Keep raw material quality stable to control powder coating color variation.

3. Controlling Powder Coating Color Differences

3.1 Consistent Standards

Use production-line coated samples as standards to ensure reproducibility.

3.2 Avoiding Metamerism

Build a diverse pigment database to ensure the same powder coating color appears consistent under different light sources.

3.3 Reference Control

Always compare against the original color standard to prevent gradual drift.

3.4 Hiding Power

Control pigment loading to achieve good coverage without excessive cost.

3.5 Combining Visual and Instrument Data

Visual inspection remains essential, with instruments as a supporting tool.

4. Solutions for Color Difference Issues

1. Stricter Quality Control – For premium products, maintain ΔE ≤ 0.5 under multiple light sources.

2. Bulk Pigment Purchases – Reduce raw material variability.

3. Maintain Stock – Produce and store popular colors for small-batch customers.

4. Proactive Technical Support – Regular visits and communication to detect issues early.

5. Expand Pigment Library – Improve powder coating color matching capabilities.

Conclusion

By integrating accurate measurement, advanced computer matching, and strict process control, manufacturers can ensure consistent powder coating color across batches. This improves customer satisfaction, reduces waste, and strengthens market competitiveness.