Matters needing attention in paint toning

In addition to the protective function, another important function of the coating is the decorative function, and the coatings of different colors add great commercial value to the industrial products. The color of paint is increasingly valued by manufacturers and users. Excellent colorists can quickly and accurately allocate the target color, thereby improving production efficiency, reducing color difference between batches, stabilizing product quality, and improving product competitiveness. How to quickly and accurately adjust the color of paint depends on the understanding of color and the accumulation of experience.

1 Color properties and color matching methods

The properties of color are hue, lightness, and purity. Hue is the appearance characteristic of color, also called hue; lightness refers to the degree of lightness and darkness of color; purity is also called saturation or chroma, that is, the degree of vividness of color. The purity of the primary color is the highest, the secondary color is the second, and the secondary color is the lowest. Whether the lightness increases or decreases, the hue and purity will change. The essence of color matching is to make the three parameters of the color consistent with the sample color. The color of paint is based on the principle of subtraction. The color matching method is simply: add what is missing, and add the complementary color of this color if there is more color.

2 Influencing factors of visual colorimetry

2.1 Size

The same sample painted on the test panels of different sizes showed the difference in color. As can be seen from Figure 1, the same color, the color with a small area is not as bright and bright as the large area. The reason for the analysis may be that the large area reflects more light into the human eye, so it looks more vivid and brighter, which is the area effect. Therefore, the size of the test plate should be the same as that of the standard plate in the visual colorimetry. The correct plate making method is to dilute the sample to an appropriate viscosity and then paint it quickly and evenly along the vertical and horizontal directions. When spraying, the spray gun is about 20cm away from the surface to be coated, moving at a constant speed, and the air pressure is 0.2~0.4MPa. The viscosity of the sample has a great influence on the thickness of the coating film. If the viscosity is too large, the leveling of the test plate is not good, which affects the reflection of the color.

2.2 direction

Colors are directional and look very different from different angles. Especially with metallic paint, different angles are more different. This may be because different objects have different ability to reflect light, metal has high reflectivity to light, and the angle of light is different, and the light entering the human eye is more different. The national standard GB/T9761-1988 stipulates that the method of visual colorimetry is vertical observation, the incident angle is 0°, and the distance from the sample is 50cm.

2.3 environment
The color of the surrounding environment has a great influence on the visual colorimetry. Because the light reflected by the surrounding objects will be irradiated on the measured object as a part of the light source, which means that the color of the light source has changed, resulting in an error in color judgment. Therefore, the environment for visual color comparison should not have other bright colors except the experimental board, and the color matching personnel should not wear brightly colored clothes.

3 Problems that should be paid attention to in color matching

3.1  Resin Compatibility

When toning, it is necessary to choose coatings or colorants with the same resin system. If the compatibility is not good, precipitation, delamination and even gelation will occur. For example, if the blending paint is toned with epoxy color paste, it will cause the epoxy resin to precipitate and affect the product fineness. The tinting of water-based alkyd paint must not use alkyd to reconcile the paint colorant. Experience has shown that adding 1% of the blending paint color paste to the water-based alkyd paint will cause whitening, and the more the color paste is mixed, the lighter the color. The reason for the analysis may be that the alkyd blend paint has a long oil degree, weak polarity, and poor compatibility with water-based alkyd resin. After the blend paint color paste enters the system, the pigment separates from the blend paint resin and coagulates and sinks into the lower layer, causing floating. White.

The color paste solvent system has a great influence on the finished product. If the solubility of the solvent is too poor, the color paste cannot be stably dispersed in the resin. In severe cases, it may cause delamination, precipitation, flocculation and even scrapping. The solvency is too strong, and it may bite or bleed to the matching primer. The choice of solvent depends on the type of resin and the polarity of the system.

3.2 Influence of Auxiliary Raw Materials

When toning, the influence of raw materials such as dry material and curing agent on the color should be considered. The darker color of the dry material has a greater impact on the color of light-colored paints such as white. Epoxy amine curing agents are darker in color and should be used in larger amounts. There are also industrial paints that use polyamide wax to prevent sinking and sagging, but the addition of polyamide wax will affect the normal floating color of the pigment, which is slightly lighter than when it is not added; if it is used in silver powder paint, it will affect the floating type. The floating of silver powder may cause the silver powder paint to not be white enough. The fineness of the color paste is too high, which affects the utilization rate of the pigment, and also affects the appearance of the coating film. During the storage process, it will cause discoloration or even affect the use due to the flocculation of the pigment. In actual production, the fineness of the color paste is generally controlled below 20μm . If the viscosity of the color paste is too high, it is not easy to disperse, and the color development of the pigment is not sufficient, which will cause waste of the pigment; but if the color paste is too thin, and the pigment content is low, more color paste may be required, and components other than the pigment will be brought in, such as Resin or solvent will have a certain influence on the gloss of the coating film.

3.3 Dry time

The wet color of the paint is generally lighter, and becomes darker when it dries, but there are differences between different systems. There is a big difference between the wet and dry color of water-based paint.

Alkyd blends are next, nitro, acrylic, epoxy and polyurethane are less different. Because nitro, acrylic, epoxy and polyurethane have a short drying time, colors such as black and blue are already dry before they can float on the surface. However, water-based alkyd and alkyd blended surface drying is relatively slow, and the easy-to-float black, blue and other pigments float for a long time, so the color is darker after drying.

3.4 The effect of surfactants

When formulating multi-color paint, due to the variety of pigments, the difference in oil absorption, density and particle size may cause floating color, usually floating white, floating blue, floating yellow, etc. An appropriate amount of dispersant (Deqian 904S, Deqian 983, etc.) can be added to improve the anti-floating agent, and the dosage is 0.1%~0.5%. The variety and dosage of surfactants should be determined through experiments according to different resin systems and different pigment combinations.

3.5 Use of complementary colors

Complementary colors should pay attention to the use of very bright colors must not use complementary colors. The color is bright because the saturation of the color is relatively high. In layman’s terms, the color saturation is high. After the complementary color produces black, the color saturation decreases, the ash content increases, and the color looks darker.

3.6 Pigment selection and collocation

The selection of pigments is based on and applicable to the application of the coating. If you use it outdoors, you must choose a lightfast pigment. If you use it as a primer or indoors, you can ignore the lightfastness of the pigment.

To make a brighter purple, be sure to use permanent purple instead of red and blue. Although big red powder and phthalocyanine blue will produce a more purple color, the yellow phase in big red will complement the purple to produce black, which will make the purple darker; in addition, big red is easy to float, and the opening effect is poor. As for iron red, it cannot be used. First of all, iron red itself is dark, and it is impossible to make a brighter color; secondly, there is less red in iron red, and a small amount of purple will be produced with blue, but the purple produced will be destroyed by iron red itself. The yellow is consumed with little left. Therefore, if you want to make more purple colors, do not use iron red and phthalocyanine blue, because iron red contains less red, and it is impossible to produce too much purple with blue, which will only make the color darker. If the blue phase of gray is too heavy, you can use iron red and a suitable amount of yellow to offset the blue phase.

To make a brighter green, phthalocyanine green is the first choice, not yellow and blue. Because phthalocyanine blue generally has a blue-violet phase, although there is not much purple, it will complement yellow to make the color darker; in addition, light yellow and medium yellow both show a red phase, and the red in the green and yellow pigments produced by the combination of yellow and blue will complement each other. Darken the green. Available in blue with yellow head and yellow with green head (lime yellow).

Orange is usually paired with red and yellow, anti settling agent for water based paints, but to make a fresher orange, lemon yellow must not be used. Because lime yellow is greenish, green and red complement each other to darken the color. Don’t choose blue with red (such as purplish red), because the orange produced by red and yellow and the blue in purplish red complement each other, which will darken the color. Yellow with red head (such as medium yellow and light yellow) and red with yellow head (such as molybdenum chrome red, big red, etc.) should be used.

3.70 Aluminum powder paint
For paints with flash silver, aluminum powder, and pearlescent powder, be sure to choose a transparent color paste when toning to ensure the metallic effect. The color, shape and particle size of flash silver, aluminum powder and pearl powder should be carefully screened, and they should be wetted and dispersed in a solvent before adding to avoid affecting the fineness. The influence of the types and amounts of additives such as hammer pattern agent and embossing agent on the texture of the coating film should also be considered.

3.81 water-based paint

In the water-based system, the wetting ability of the resin to the pigment is worse than that of the solvent-based system, and it is prone to discoloration after the color is formulated and stored for a period of time. The analysis may be that different resins in the system have different wetting abilities to pigments. After the color paste enters the system, various resins in the system begin to compete for pigments. The pigment is detached from the resin in the color paste and combines with the resin with better wettability in the system to enhance the color development and the color becomes darker; on the contrary, if the pigment is detached, flocculation will cause the color to become lighter. The use of resin-free colorants can solve the problem of discoloration. If there is no resin in the color paste, there will be no separation of the pigment and the resin. After entering the system, the pigment and the resin in the system can freely choose the best combination, and the system is relatively stable and not easy to change color.

4 Conclusion

Although many paint manufacturers have computer color matching, because computer color matching is highly dependent on the stability of the masterbatch; the color measurement error of coatings with different gloss and textured surfaces is relatively large; for curved surfaces, special-shaped workpieces cannot be used. Color measurement; the color matching of matt and matt systems is not accurate enough, so the color matching work of the paint is ultimately done manually. Continue to accumulate, summarize and improve, in order to better complete the paint toning work.