The color of PU pigments is due to the selective absorption of light of different wavelengths in visible light by PU pigments, and is affected by physical properties such as crystal shape, particle size and dispersion performance. The increase in particle size changes from orange-red to purple-red; the color of the pigment is also affected by the light shining on it, for example, in the dark, the pigment does not show any color, and the color in strong light is stronger than that in dim light Under different light sources (such as sunlight, incandescent light, fluorescent light, etc.) the same pigment can also show different colors.
2, tinting strength
The tinting strength of PU pigments refers to the ability of a pigment to show shades of color when mixed with another pigment. When the same color is adjusted, the stronger the tinting strength, the less the amount of color paste, the less the water resistance of the color paste coating and the less influence on the performance of the coating film. Therefore, the same color, the quality of the products of different manufacturers will be very different. The tinting strength of PU pigments depends not only on its properties, but also on its degree of dispersion. The greater the dispersion, the stronger the tinting strength.
3. Light resistance and weather resistance
The color of the pigment will change to some extent under the action of light. Inorganic pigments will gradually darken in color when exposed to sunlight for a long time, and some pigments will also chalk under the action of ultraviolet rays in sunlight. Exterior wall coatings should use pigments with good light resistance and weather resistance. Generally, the light resistance is greater than grade 7~8, and grade 8 is better, and the weather resistance is greater than grade 4~5, and grade 5 is better. Inorganic pigments such as iron oxide series generally have good light resistance, and the color retention of the corresponding color coatings is very good; organic pigments are relatively poorer than inorganic pigments, and the price is much higher. The higher the light resistance of organic pigments, the higher the price. For each level of light resistance, the price and weather resistance and color retention will be very different. When the light resistance is less than or equal to 6, and the weather resistance is less than or equal to 3, the price will differ by more than 4 times. Therefore, exterior wall coatings, especially organic color coatings, are worth every penny.
4. Covering power
The ability of the pigment in the coating film to cover the surface of the object to be painted, so that the substrate can no longer be exposed through the coating film. The hiding power of pigments mainly depends on factors such as refractive index, ability to absorb light, crystal structure, and degree of dispersion. The hiding power of a pigment depends not only on the ability of the coating to reflect light, but also its ability to absorb light impinging on the surface of the coating. For example, carbon black completely absorbs the light that falls on it, making it more opaque. The hiding power of opaque color pigments also depends on their selective absorption of light. The pigment is evenly dispersed in the base material, the particle size is small, the specific surface area is increased, and the covering ability is also increased. However, if the size of the pigment particle size is equal to half of the wavelength of light, the light will Proceed through the particle without refraction, leaving the particle transparent. The higher the crystallinity of the pigment, the stronger the hiding power. The hiding power of mixed pigments cannot be calculated according to the addition law of the hiding power of each component of the mixture. In fact, the hiding power of most mixed pigments is larger than the calculated value. Therefore, mixing the pigment and the filler in an appropriate ratio will not affect its covering power, and is conducive to reducing costs. The covering power of the coating is high, the brushing area is high, and the project cost is low.
5. Dispersion and adaptability
The so-called dispersibility of pigments refers to the ease with which the aggregated pigment particles are dispersed in the coating base material and the dispersion state after dispersion. It is affected by factors such as pigment properties, preparation methods, particle size and particle size distribution. . The dispersibility of the pigment has a significant impact on the hiding power and tinting strength of the pigment, and also has an impact on the physical and chemical properties of the coating film. Pigment compatibility issues, which are particularly important for emulsion-based architectural coatings. Due to different types of pigments, the effect of pigments will also show a certain degree of difference, and the tendency of organic pigments is more obvious. The pigments are poorly dispersed in the paint and have poor matching with the paint, and the paint will have potential flocculation or even fading.
6. Fineness
The fineness of the color paste is not as fine as possible, because pigments such as phthalocyanine blue and phthalocyanine green are themselves small molecular pigments. The fineness is too small, the particle size difference is large, the dispersibility is poor, and the compatibility with coatings is not Well, the cost of color correction will increase, and it will also lead to floating colors.
7. Acid and alkali resistance
The acid and alkali resistance of the pigment is also an important performance index for its use in architectural coatings. For example, iron blue or chrome yellow will decompose when exposed to alkali, and gray calcium powder and calcium carbonate will react with acid, so pay attention to the selection when using. If the price is very low, the yellow, blue, etc. produced by non-professional latex paint manufacturers, because the price is very low or the performance of the pigment is unknown, the latex paint will soon fade, chalk, pan-alkali, etc., so the customer chooses the paint And latex paint toning must pay attention to the choice.
