What is inorganic pigment
Pigments made of natural minerals or inorganic compound. Natural mineral pigments generally have lower purity and darker color, but their prices are low. And the synthetic inorganic pigments have a complete variety of chromatography, bright and pure colors, and strong covering power.
Inorganic pigments have been used by humans for a long time, and prehistoric black, chalk, clay, and natural iron oxide have been used as pigments. From 3000 to 2000 BC, the production method of lead white was already mastered. Around 200 BC, China used artificially refined silver (HgS) as a pigment. In 1704, German Disbach invented the color pigment Prussian blue, a deep blue pigment with the main component Fe4 [Fe (CN) 6] 3? The manufacturing method of xH2O. 1809 France L- N. Volkland was made into chrome yellow. In 1831, I.B. Gimme of France established a factory near Lyon to produce ultramarine, and in 1874, the Widennis factory under the British company Osborne Zinc White produced lithopone. In 1916, titanium composite pigments (containing 225% TiO2) and in 1923, pure titanium dioxide (titanium dioxide) were put into production, which greatly advanced the level of pigment production. At present, the chromatography of inorganic pigments is basically fully equipped.
Inorganic pigments are widely used in industrial production departments such as coatings, plastics, synthetic fibers, rubber, building materials, stationery, painting pigments, ink, paper, glass, enamel, ceramics, etc. Inorganic coloring pigments can be divided into two categories: colorless pigments and colored pigments. Achromatic pigments include a series of pigments ranging from white, gray to black, which only exhibit differences in the amount of reflected light, i.e. brightness. Colored pigments can selectively absorb light of a certain wavelength and reflect light of other wavelengths to present various colors.
In the early 1980s, the annual production capacity of inorganic pigments in the world was 3.6Mt, with titanium dioxide accounting for 74%, iron oxide pigments accounting for 14.6%, chrome yellow accounting for 5.0%, rust proof pigments accounting for 4.6%, chromium oxide green accounting for 1%, cadmium pigments accounting for 0.2%, and others accounting for 0.6%. The annual production capacity of novel composite pigments has also increased to 10 kt. There are over a hundred manufacturers of inorganic pigments in China, with a total output of over 200kt. (See color image)
White pigments mainly include titanium dioxide, lithopone, zinc oxide, and other varieties. Titanium dioxide is currently the most widely used white pigment. Its whiteness, covering power, coloring power, weather resistance, and chemical resistance are all superior to other white pigments. The world's annual production is approximately 2.7Mt. Lithopone has slightly poor performance and is prone to pulverization. The coloring power and covering power of zinc oxide are worse than those of the above two. Coatings with higher acidity are prone to the formation of zinc soap, and are currently less commonly used except as anti rust pigments.
The chemical composition of titanium dioxide is titanium dioxide, which has two main crystal forms with practical significance, namely anatase type and rutile type. After surface treatment of titanium dioxide particles with salts of aluminum, silicon, titanium and zirconium, various types of pigment titanium dioxide can be obtained. Titanium dioxide used as a pigment is mainly used in the production of coatings.
Lithopone is also known as Lithopone. Barium sulfide solution produced by chemical processing of barite reacts with zinc sulfate solution to obtain barium sulfate zinc sulfide coprecipitate, which is then calcined, water milled and dried to obtain lithopone. The surface treated lithopone has good grinding and wetting properties, making it suitable for industrial applications such as coatings, rubber, and ink.
There are two production methods for zinc oxide: direct method and indirect method. Direct zinc oxide contains a lot of impurities, with a dark and gray color, but has strong rust resistance. The indirect method of zinc oxide has a pure white color, but its price is relatively expensive. Zinc oxide is mainly used in the manufacturing of rubber products, coatings, metal soaps, catalysts, lubricating greases, feed, and soil additives. High purity zinc oxide is used in the manufacturing of medical adhesive tapes. (See Zinc Oxide)
Black pigments are important pigments second only to white pigments. The main variety is carbon black. The properties of carbon black used in pigments are different from those used in rubber processing. The main quality indicators of pigment carbon black are blackness and color phase.
The red pigment in inorganic pigments is mainly iron oxide red. Iron oxide has various colors, from yellow to red, brown to black. Iron oxide red is the most common iron oxide pigment. It has good covering and coloring power, chemical resistance, color retention, dispersibility, and is relatively inexpensive. Iron oxide red is used in the production of floor paint and ship paint. Due to its significant rust resistance, it is also the main raw material for making rust resistant paint and primer. Grind the particles of iron oxide red to ≤ 0.01 μ When m is used, the hiding power of pigments in organic media significantly decreases. This type of pigment, called transparent iron oxide, is used to make transparent paint or metal flash paint, and has better color retention than using organic dyes.
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 produces the largest amount. The world's annual production is about 180 kt, while China's annual production is about 10 kt. Lead chrome yellow has strong covering power, bright color, and is easy to disperse, but it tends to darken under sunlight. Zinc chrome yellow has poorer covering and coloring power compared to lead chrome yellow, but has a lighter color and good light resistance. Cadmium yellow has good heat resistance, light resistance, and bright color, but its coloring and covering power are not as good as lead chrome yellow, and its cost is also high, which is limited in its application. Lead chromium yellow and cadmium yellow both contain heavy metals and cannot be used for coloring children's toys, stationery, and food packaging. The iron yellow color is darker, but it has good durability, dispersibility, covering power, heat resistance, chemical resistance, alkali resistance, and low price, making it widely used for coloring building materials.
Lead chrome yellow can be produced by combining lead nitrate or lead acetate with various raw materials such as sodium dichromate (or potassium dichromate), sodium hydroxide, aluminum sulfate, etc. in different ratios and reaction conditions to produce various colored lead chrome yellow.
Zinc chrome yellow, also known as zinc yellow. Suspend zinc oxide in water, then add potassium dichromate and chromic acid to obtain basic zinc chromate potassium K2CrO4? 3ZnCrO4? Zn (OH) 2 is a zinc chrome yellow pigment. Sulfuric acid or hydrochloric acid can also be used to replace some chromic acid, but the generated potassium sulfate or chloride must be thoroughly washed away before filtration and drying. Basic zinc potassium chromate can be used as lemon yellow pigment or as a primer in combination with iron oxide red. Another type of zinc chrome yellow is produced by reacting zinc oxide with chromic acid, also known as tetrabasic zinc chromate ZnCrO4? 4Zn (OH) 2, commonly used in the manufacture of phosphating primers.
Cadmium yellow Cadmium yellow includes pure cadmium yellow and cadmium yellow coprecipitation with barium sulfate. Add sodium sulfide or a mixture of sodium sulfide and sodium selenide to the aqueous solution of cadmium salt, precipitate cadmium sulfide yellow or cadmium sulfide red, wash, filter, and calcine at 500-700 ° C in a rotary kiln (see kiln) to obtain cadmium yellow or cadmium red pigments of different colors from lemon yellow to orange red.
Iron Yellow Natural Iron Oxide Yellow is a hydrated iron oxide containing various impurities, mainly silicates. In the past, the preparation of iron oxide yellow was based on the waste iron mud from the reduction of nitrobenzene to produce aniline. Another production method is to hydrate ferrous sulfate by heating it in the presence of iron and oxygen, resulting in the formation of iron oxide yellow. The thermal stability of iron oxide yellow is poor, and when heated above 180 ° C, it dehydrates and turns into iron oxide red.
There are two main types of green pigments: chromium oxide green and lead chromium green. Chromium oxide green has excellent light resistance, heat resistance, and chemical resistance, but its color is darker and its coloring and covering power are poor. The durability and heat resistance of lead chromium green are not as good as that of chromium oxide green, but it has a bright color, good dispersibility, and is easy to process. Due to its toxic heavy metals, the amount of lead chromium green used has gradually decreased since the emergence of organic pigments such as phthalocyanine green.
Chromium oxide green, also known as chromium trioxide, is made from chromic anhydride, sodium dichromate (or potassium, ammonium salt) and carbon or sulfur by roasting at high temperature. Its color ranges from bright green to dark green. Mainly used for coloring metallurgical products and cement. It has a high particle hardness and can be used as a polishing agent for optical materials and metal grinding; Its spectral reflectance characteristics are very close to chlorophyll, so it can be used as military camouflage paint.
Lead chrome green is a mixture of chrome yellow and iron blue. Iron blue wet paste is added during the manufacturing process of chrome yellow. By adjusting the amount of iron blue added, various green pigments with different colors can be obtained, ranging from yellow light green (2% -3% iron blue) to deep green (60% -65% iron blue). Lead chrome green can be used for general coatings. Another mixture of chrome yellow and phthalocyanine blue (see organic pigments), also known as lead chrome green, has a bright color and good other properties.
Blue pigments mainly include iron blue, cobalt blue, ultramarine, and other varieties. Among them, the yield of ultramarine is relatively high, and ultramarine is alkali resistant but not acid resistant, with bright and bright colors and high temperature resistance. Iron blue is acid resistant but not alkali resistant, with higher covering and coloring power than ultramarine blue, and poorer durability than ultramarine blue. Since the introduction of phthalocyanine blue into the market, its coloring power has been twice that of iron blue, and its other properties are also good, resulting in a decrease in the amount of iron blue used year by year. Cobalt blue has high temperature resistance and excellent light resistance, but its coloring and covering power are slightly poor, and its price is high, which limits its use.
Iron blue is formed by the reaction of ferrous sulfate, yellow blood salt (potassium ferrocyanide), and ammonium sulfate to form white slurry, which is then oxidized with chlorate. Qingguang Iron Blue is called China blue, while Hongguang Iron Blue is called Milori blue. Iron blue is a hydrophilic pigment that has poor affinity with media such as oil and resin. Treatment with surfactants can improve its lipophilicity and easy grinding performance. Dark blue coatings made from iron blue are prone to copper luster on the surface after exposure to sunlight. Mainly used for manufacturing ink and stationery.
Qunqing is made by mixing clay, sulfur, soda ash, mirabilite, carbon black, and quartz powder according to different formulas, filling them in pottery jars, roasting them at high temperatures, and then undergoing refining processes such as water washing. The product can range from light blue to deep blue. After mixing with ammonium chloride and heat treatment, it can be made into pink and purple pigments. Used for painting pigments, rubber, plastics, coatings, etc. Ultramarine green turns white when exposed to calcium hydroxide, therefore it cannot be used for coloring cement.
The research and development direction of new inorganic pigments in recent years mainly includes: ① developing composite pigments, such as bright blue (CoO Cr2O3 Al2O3), titanium nickel yellow (TiO2 NiO Sb2O3), etc. Adding chromium, cobalt, iron, zinc and other oxides into the titanate of nickel and antimony can make yellow, green, blue, brown and other low toxic to non-toxic pigments with high temperature resistance, durability, and chemical resistance, bright color and excellent performance, which can be used for coloring building materials, coatings, engineering plastics with high durability requirements and preparing painting pigments. ② Develop the surface treatment technology of pigment particles to form a color film on the surface of pigment particles with inorganic compound or organic compound, which can change the surface performance of pigment particles, improve the light resistance, heat resistance, wetting and other characteristics, expand the application range and improve the use value. ③ Manufacturing and processing pigments, allowing users to apply them directly, saving a lot of grinding and processing costs.
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