Performance indexes of pigment color paste and its influence on coatings

Performance indexes of pigment color paste and its influence on coatings
1、Color of pigment
The color of pigment is the result of selective absorption of different wavelengths of visible light by pigment, and it is affected by the physical properties such as crystalline shape, particle size and dispersing performance, etc. For example, the color of iron oxide red changes from orange-red to purplish-red with the increase of the particle size of the particles; the color of pigment is also affected by the light irradiated on it, for example, in darkness, the pigment doesn’t show any color, and the color under strong light is brighter than that under dark light, and the color under different light sources (such as sunlight, incandescent light, fluorescent light, etc.) appears brighter than that under dark light. For example, in the darkness, the pigment does not show any color, in the strong light, the color is brighter than that in the dark light, and the same pigment under different light sources (such as sunlight, incandescent light, fluorescent light, etc.) can also show different colors.

2、Coloring power
The coloring power of pigment refers to the ability of a pigment and another pigment to show the depth of color after mixing. 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 water resistance of the color paste paint and the smaller the influence of the coating film performance are. 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 degree of dispersion, the stronger the coloring power.
3、Light resistance and weather resistance
Under the action of light, the color of pigment will produce certain changes in different degrees. The color of inorganic pigment will gradually darken under the sunlight for a long time, and some pigments will also produce chalking phenomenon under the action of ultraviolet rays in the sunlight. The exterior paint should choose the pigment with good light resistance and weather resistance, generally the light resistance is more than 7~8 grade, 8 grade is the best, the weather resistance is more than 4~5 grade, 5 grade is the best. Inorganic pigment such as iron oxide system of light resistance 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 the organic color paint is a price of one penny.

4、Covering power
The pigment in the coating film can cover the surface of the object to be coated, so that the substrate is covered and no longer visible through the coating film. The strength of pigment’s covering power mainly depends on the refractive index, ability to absorb light, crystal structure, and the degree of dispersion and other factors. The covering power of pigment not only depends on the ability of the coating to reflect light, but also depends on its ability to absorb the light irradiated on the surface of the coating. For example, carbon black can completely absorb the light irradiated on it, and thus its covering power is extremely strong. 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 common pigments
Pigment Covering power
Titanium white 50g/m2
Lide powder 120g/m2
Iron oxide yellow 60g/m2
Iron oxide red 60g/m2

5、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.
6, 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 will also lead to floating colors and flowers.
7、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 react when it meets acid, so it should be chosen carefully when it is used. If you choose a very low price, non-professional production of latex paint manufacturers produce yellow, blue, etc., because the price is very low or do not know its pigment properties, latex paint will soon have faded chalky alkali and other phenomena, so the customer selection of paints and latex paint color must pay attention to the choice.
Color oil is a kind of liquid pigment concentrate without resin carrier. At present, color oil is mainly used in bottle embryo in China.
01
Advantages
1、 Low additive ratio, usually 0.1-0.5% for transparent series, 0.3-3.0% for pearlescent/solid color series;
2, excellent dispersion, the color is more uniform and consistent, the color is more brilliant, the product has a higher luster; color stability, reduce coloring defects;
3、 The material only passes through the high temperature process once, keeping the physical properties of the raw material resin unaffected;
4、 Optimal inventory management, only need a small space to complete the storage of color oil. Relative color masterbatch saves three-quarters of the storage space. Reduce the overall inventory and working capital pressure;
5、 Color oil adding equipment is simple, low cost, simple and fast color change process, improve the freedom of production scheduling, saving staff time, machinery and energy loss;
6, applicable to all polyolefins (such as PP / PE), polystyrene resin (PS), PET resin and other engineering resins.
02
Disadvantages
1. Cannot add antistatic agent in color oil, resulting in the product can not be dustproof in the shelf or storage;
2. The shelf life of color oil products is shorter than that of masterbatch products;
3. Color oil needs special color oil adding equipment, i.e. color oil metering pump to supply color oil to the injection molding machine to produce the desired color products.