Theory and practice of pigment toning in powder coatings


Toning has always occupied a particularly important pos […]

Toning has always occupied a particularly important position in the production of powder coatings. Accurate and fast toning methods directly affect the sales of powder coatings. Compared with liquid coatings, powder coatings are quite different in terms of composition, physical state, construction medium and film forming process. Therefore, understanding and mastering the color matching theory and production of powder coatings, especially the relationship between the many changes in powder coating toning theory and practice, is very useful for a powder coating technician who is engaged in powder coating research or production. necessary.
The color is a reflection in our minds of the changes that occur after a part of the light is absorbed by the object. This reflection (i.e. color perception) is not only related to the inherent color characteristics of the object, but also affected by time, space, the appearance of the coated object, and the surrounding environment where the object is located. Factors such as sensitivity are related. All the methods for measuring and evaluating color prescribed by the International Commission on Illumination (CIE) are based on these variables. The light returning from the color plate to the observer's eye is usually equal to the sum of the reflected and scattered parts of the incident light, plus the balance of transmitted light and absorbed light. For each color plate, the above-mentioned parts of light usually change due to different wavelengths. Therefore, the light received by the observer is generally completely different from the light emitted by the light source. The difference between the colors of two objects that we can see can be characterized by the three quantities of hue (main color), color value (lightness) and chroma (color saturation).
2. Color allocation and control of powder coatings. Color allocation means that color A is equal to color B. How to adjust the various variables of the colorant (such as pigment, dispersion, dosage and ratio, etc.) to reproduce this visual characteristic? First of all, a good colorist must have good vision, long-term practice and good training, and secondly, the colorist should select the colorant suitable for color B and the appropriate amount of colorant according to color A. In this regard, powder coatings are more difficult to color, because powder coatings must be powdered (due to the different properties of resins, additives, and pigments, they need to be mixed, melted, extruded, and crushed. The random state is transformed into another uniform distribution state), the color effect of the color palette can be seen only after spraying, baking and curing, and there are many variable factors in the preparation process.
When two objects are viewed under the same light source, their colors may be the same, while when viewed under different light sources (such as incandescent or fluorescent lamps), their colors may be different. These two objects are usually called conditions, etc. Color body, also called conditional color matching or variable color matching body. Two objects are required to look the same under any light source, which means that the spectroscopic reflection curves of the two objects must be the same. This kind of color matching is called unconditional color matching or immutable color matching. Immutable color matching requires the use of the same colorant as the sample when matching powder coating colors. Therefore, it is almost impossible to make the prepared color and the color of the sample equal.