Color measurement and color difference control of powder coatings

This paper introduces the color measurement and color difference control methods of powder coatings, not only covering the basic principles of color measurement, including human visual inspection, color difference meter measurement, color scheme and control in the production process. The whole process of using the instrument color scheme is introduced in detail, and it is pointed out that satisfactory color control must combine human visual judgment, practical experience and instrument measurement reasonably.

The development of powder coatings mainly uses metal corrosion protection in the early days. With the continuous progress of powder coating production and application technology, the strengthening of environmental protection awareness and regulations in various countries around the world, the application scope of powder coatings continues to expand, and the decorative and beautifying effect of powder coatings is also increasing. It has attracted people's attention, and the assembly line processing and assembly of modern enterprises (such as instrumentation, metal doors and windows, aluminum profiles, refrigerators, air conditioners, mechanical and electrical equipment and other manufacturers) requires a high degree of stability in the internal and external quality of the coated products, and the color of the coating between batches is consistent. It has become an important requirement for customers.

How Color is Measured   

Method 1: Visual inspection 

GB/T9761-98 "Visual Colorimetric Comparison of Paints and Varnish Paints" and other effects all adopt the ISO3668-1976 standard, which regulates the visual colorimetric method of coating colors, which can be detected under the artificial standard light source of natural light and colorimetric box. The commonly used light sources are D65 and A. Visual colorimetry requires higher requirements for observers. Observers responsible for colorimetric inspection should pass the inspection of colorblind inspection glasses. Lenses wearing glasses need to have uniform spectral transmittance in the entire visible spectrum; because color vision varies with age, observers over 40 years old should also be examined by colorblind inspection glasses. Continuous work of observers will reduce the quality of colorimetry. Visual inspection is the most direct and highly perceptual detection method, and instrument measurement in color schemes can only be an important auxiliary means of quality control.   

Method 2: Instrument measurement   

What is the principle of instrument measurement?

The interaction between light and materials produces specular reflection, diffuse reflection, directional transmission, scattering transmission and light absorption, and the color of an object is mainly determined by its diffuse reflection. Use a Spectrophotometer to measure the spectral reflection factor of the powder coating (such as K/S ratio), the three-stimulus value can be calculated, and then the difference between different colors can be calculated and compared. The measuring device is shown in Figure 1. Connect it to a computer and special software to display, store and output color data, color effects, K/S curves, and color differences.