Inorganic coloring pigments can be divided into two types: decolorizing pigments and color pigments. Achromatic pigments include a series of pigments ranging from white, gray to black, and they only show the difference in the amount of reflected light, that is, the difference in brightness. Color pigments can selectively absorb light of a certain wavelength, and reflect the light of other wavelengths to present various colors.
Black pigment It is an important pigment second only to white pigment. The main variety is carbon black. The performance of carbon black for pigments is different from that for rubber processing. The main quality indicators of pigmented carbon black are blackness and hue.
Red pigment The red pigment in inorganic pigments is mainly iron oxide red. Iron oxide comes in various colors, from yellow to red, brown to black. Iron oxide red is the most common iron oxide pigment. It has good hiding power and tinting power, chemical resistance, color retention, dispersion, and low price. Iron oxide red is used in the production of floor paint and marine paint. Because of its remarkable anti-rust performance, it is also the main raw material for making anti-rust paint and primer. When the particles of iron oxide red are ground to ≤0.01μm, the hiding power of the pigment in the organic medium is significantly reduced. This kind of pigment is called transparent iron oxide, which is used to make transparent colored paint or metallic flash paint, which is more effective than organic dyes. Better color retention.
Yellow pigments mainly include lead chrome yellow (lead chromate), zinc chrome yellow (zinc chromate), cadmium yellow (cadmium sulfide) and iron yellow (hydrated iron oxide). Among them, lead chrome yellow is the most widely used and has the largest output. The world's annual output is about 180kt, and China's annual output is about 10kt. Lead chrome yellow has strong hiding power, bright color and easy to disperse, but it is easy to darken under sunlight. The hiding power and tinting power of zinc chrome yellow are inferior to that of lead chrome yellow, but it is lighter in color and has good light resistance. Cadmium yellow has good heat resistance, light resistance and bright color, but its tinting power and hiding power are not as good as lead chrome yellow, and its cost is high, so its application is limited. Both lead chrome yellow and cadmium yellow contain heavy metals and cannot be used for coloring children's toys, cultural and educational supplies and food packaging. Iron yellow is darker, but it has good durability, dispersibility, hiding power, heat resistance, chemical resistance, and alkali resistance, and it is inexpensive, so it is widely used for coloring building materials.
Lead chromium yellow lead nitrate or lead acetate, sodium dichromate (or potassium dichromate), sodium hydroxide, aluminum sulfate and other raw materials, according to different proportions, different reaction conditions, can produce various colors of lead chromium yellow.
Zinc Chrome Yellow Also known as Zinc Yellow. Suspend zinc oxide in water, then add potassium dichromate and chromic acid to obtain basic potassium zinc chromate K2CrO4·3ZnCrO4·Zn(OH)2 which is zinc chrome yellow pigment. Sulfuric acid or hydrochloric acid can also be used to replace part of chromic acid, but the generated potassium sulfate or potassium chloride must be thoroughly washed off before filtering and drying. Basic zinc potassium chromate can be used as a lemon yellow pigment, and can also be combined with iron oxide red to make a primer. Another kind of zinc chrome yellow is made by reacting zinc oxide with chromic acid, also known as tetrabasic zinc chromate ZnCrO4·4Zn(OH)2, which is mostly used in the manufacture of phosphating primer.
Cadmium Yellow There are two types of cadmium yellow, pure cadmium yellow and cadmium yellow co-precipitated with barium sulfate. Add sodium sulfide or a mixed solution of sodium sulfide and sodium selenide to the aqueous solution of cadmium salt to precipitate cadmium sulfide yellow or cadmium sulfide red, which is washed, filtered, and roasted at 500-700°C in a rotary kiln (see kiln). The pigment cadmium yellow or cadmium red of different colors from lemon yellow to orange red is obtained.
Iron Yellow Natural iron oxide yellow is a kind of hydrated iron oxide containing various impurities. The impurities are mainly silicates. In the past, iron oxide yellow was prepared with iron sludge, which is a waste material from the reduction of nitrobenzene to produce aniline, as a raw material. Another production method is to heat ferrous sulfate for hydration in the presence of iron and oxygen to produce iron oxide yellow. Iron oxide yellow has poor thermal stability. When heated above 180°C, it will be dehydrated and become iron oxide red.
Green Pigment There are mainly two kinds of chrome oxide green and lead chrome green. Chrome oxide green has excellent light resistance, heat resistance, and chemical resistance, but its color is darker, and its tinting power and hiding power are poor. The durability and heat resistance of lead chromium green are not as good as chromium oxide green, but it has bright color, good dispersibility, and easy processing. Because it contains toxic heavy metals, the amount of organic pigments such as phthalocyanine green has been gradually reduced.
Chromium Oxide Green, also known as chromium trioxide, is made of chromic anhydride, sodium dichromate (or potassium, ammonium salt) and carbon or sulfur after being roasted at high temperature. The color ranges from bright green to dark green. It is mostly used for the coloring of metallurgical products and cement. It has high particle hardness and can be used as a polishing agent for optical materials and metal grinding; its spectral reflectance is very close to chlorophyll, so it can be used in military camouflage paint.
Lead chrome green is a mixture of chrome yellow and iron blue. It is made by adding iron blue wet paste during the manufacturing process of chrome yellow. Adjusting the amount of iron blue added can be obtained from yellow light green (2%～3% iron blue) to Dark green (60%～65% iron blue) green pigments of various colors. Lead chrome green can be used for general paint. There is also a mixture of chrome yellow and phthalocyanine blue (see organic pigments), which is also called lead chrome green. This pigment is bright in color and has good other properties.
Blue Pigment There are mainly iron blue, cobalt blue, ultramarine blue and other varieties. Among them, ultramarine blue has a large output, which is alkali-resistant and acid-resistant, bright and bright in color, and resistant to high temperatures. Iron blue is acid and alkali resistant, its hiding power and tinting power are higher than ultramarine blue, and its durability is worse than ultramarine blue. Since phthalocyanine blue was put on the market, its tinting strength is twice higher than iron blue and other properties are good, so the amount of iron blue has been decreasing year by year. Cobalt blue has high temperature resistance and excellent light resistance, but its tinting power and hiding power are slightly worse, the price is high, and its use is limited.
Iron Blue is formed by the reaction of ferrous sulfate, yellow blood salt (potassium ferrocyanide), and ammonium sulfate to produce white pulp, which is then oxidized with chlorate. Cyan light iron blue is called China blue, and red light iron blue is called milori blue. Iron blue is a hydrophilic pigment and has poor affinity with oils, resins and other media. Treated with surfactants can improve its lipophilic and easy grinding properties. The dark blue paint made of iron blue has a surface after exposure. Prone to copper light phenomenon. Mainly used in the manufacture of inks and cultural and educational supplies.
6. Other categories:
Ultramarine is made by mixing clay, sulfur, soda ash, glauber's salt, carbon black and quartz powder according to different formulas, putting them in a clay pot, roasting at high temperature, and then washing with water. The product can range from light blue to dark blue. After being mixed with ammonium chloride and heat-treated, it can be made into pink and purple pigments. Used in paint, rubber, plastic, paint, etc. Ultramarine turns white when exposed to calcium hydroxide, so it cannot be used for cement coloring.
The main purpose:
Inorganic pigments are widely used in coatings, plastics, synthetic fibers, rubber, building materials, cultural and educational supplies, painting pigments, inks, and paper.
Glass, enamel, ceramics and other industrial production sectors.
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