Properties of color pastes and their influence on coatings
I. Coloring power
The coloring power of pigment refers to the ability to show the color shade after mixing one kind of pigment with another kind of pigment. When mixing the same color, the stronger the coloring power is, the less the dosage of color paste is, and the lower the degree of reduction of water resistance of color paste paint and the smaller the influence of coating film performance. So for the same color, the quality of products from different manufacturers will be very different. The strength of coloring power of pigment not only depends on its nature, but also has a certain relationship with its degree of dispersion. The larger the dispersion, the stronger the coloring power.
Light resistance and weather resistance
Under the action of light, the color will be changed in different degrees. The color of inorganic pigment will be gradually darkened under the sunlight for a long time, and some pigments will be chalked under the action of ultraviolet rays in the sunlight. The color paste with good light resistance and weather resistance should be used for the exterior paint, generally the light resistance is more than 7~8 grade, 8 grade is the best, and the weather resistance is more than 4~5 grade, 5 grade is the best. Inorganic pigment such as iron oxide is generally very good, corresponding to the color of the paint color retention is very good; organic pigment is relatively worse than inorganic pigment, and the price is much higher. The higher the light resistance of organic pigments, the higher the price, the worse each level of light resistance, price and weathering color retention will be a big difference, light resistance ≤ 6, weathering ≤ 3, the price will be more than 4 times the difference. So the exterior paint, especially organic color paint is a penny a penny.
Third, covering power
Covering power refers to the ability of the pigment in the coating film to cover the surface of the object to be coated, so that the substrate is no longer able to be exposed through the coating film. The covering power of pigment does not only depend on the ability of coating to reflect light, but also depends on its ability to absorb the light irradiated on the surface of coating. Carbon black, for example, completely absorbs the light that strikes it and therefore has an extremely high hiding power. The hiding power of opaque color pigments also depends on their ability to selectively absorb light. When the pigment is dispersed uniformly in the base material, the particle size is small, the specific surface area increases, and thus the covering power increases. However, if the size of the pigment particle size is equal to half of the wavelength of the light, the light will pass through the particles without refraction, and the particles will be transparent. The higher the crystallinity of the pigment, the stronger its covering power. The covering power of mixed pigment can not be calculated according to the covering power of each component of the mixture by the law of addition, in fact, the covering power of most of the mixed pigments is larger than the calculated value. Therefore, mixing pigment and filler in a suitable proportion will not affect the covering power and is favorable to reduce the cost. If the covering power of the paint is high, the painting area will be high and the project cost will be low. Covering power of commonly used pigments: titanium white 50g/m2, Lide powder 120g/m2, iron oxide yellow 60g/m2, iron oxide red 60g/m2.
Fourth, dispersibility and adaptability
The so-called dispersibility of pigment refers to the difficulty of pigment particles in aggregated state to be dispersed in coating base material and its dispersed state after dispersing, which is affected by pigment performance, preparation method, particle size and particle size distribution and other factors. The dispersibility of pigment has obvious influence on the strength of pigment’s covering power and coloring power, and also has influence on the physical and chemical properties of coating film. The problem of pigment adaptability, which is especially important for emulsion type architectural coatings. Due to the different kinds of pigments, the role of pigments will show a certain degree of difference, and this tendency of organic pigments is more obvious. If the pigment is poorly dispersed in the coating and poorly matched with the coating, the coating will have potential flocculation or even discoloration.
Fifth, fineness
The fineness of the color paste is not the finer the better, because like phthalocyanine blue, phthalocyanine green pigment itself is a small molecule pigment, the fineness is too small, the difference in particle size is large, the dispersion is poor, the compatibility with the coating is bad, the cost of mixing is increased, and it is also very easy to cause the floating color bloom.
Acid and alkali resistance
The acid and alkali resistance of pigment is an important performance index for its use in architectural coatings. For example, iron blue or chrome yellow will be decomposed when it meets alkali, and gray calcium powder and calcium carbonate will be reacted when it meets acid, so it should be chosen with care when it is used. If you choose a very low price, non-professional production of color paste manufacturers produce yellow, blue, etc., because the price is very low or do not know the performance of its pigments, latex paint will soon have fading chalky alkali phenomenon, so when choosing paint color paste must not be able to focus on the price of the low, the quality of their own brand is to improve the most advantageous weapon.
