1. Azo pigments
Water-insoluble organic compounds containing azo groups (-N=N-) in the molecular structure are the most diverse and most productive category of organic pigments. Azo pigments are diazo components prepared by diazotization of aromatic amines or heteroaryl amines and then combined with acetyl arylamine, 2-naphthol, pyrazolone, 2-hydroxy-3-naphthoic acid or 2-hydroxy - 3-naphthoyl aromatic amine and other coupling components are coupled to form water-insoluble precipitates, which are general azo pigments. Its synthesis method is basically the same as that of azo dyes, but the latter is water-soluble. Commonly used general azo pigments are orange, yellow and red pigments such as: Permanent Orange RN (C.I. Pigment Orange 5), Golden Red (C.I. Pigment Red 21), Benzidine Yellow G (C.I. Pigment Yellow 12). In order to improve the performance of pigments such as light fastness, heat resistance, and organic solvent resistance, two molecules can be condensed into macromolecules through aromatic diamines. The pigments made in this way are called macromolecular pigments or condensed azo pigments, such as: macromolecular orange 4R (C.I. pigment orange 31), macromolecular red R (C.I. pigment red 166).
2. Lake
Water-soluble dyes (such as acid dyes, direct dyes, basic dyes, etc.) are water-insoluble pigments produced by the action of precipitating agents. It has brighter shade, more complete chromatogram, lower production cost, and higher light fastness than the original water-soluble dyes. Precipitating agents are mainly inorganic salts, acids, carriers, etc. Inorganic salt precipitation is to use barium chloride, calcium chloride, manganese sulfate, etc. as a precipitant to react with water-soluble dyes to generate water-insoluble salts of barium, calcium, manganese, etc. such as: permanent red F5R (C.I. Pigment Red 48: 2), Golden Red C (C.I. Pigment Red 53:1). Acid precipitation is to use phosphoric acid-molybdic acid, phosphoric acid-tungstic acid, tannic acid, etc. (C.I. Pigment Violet 3). Carrier precipitation is to deposit water-soluble dyes on the surface of aluminum hydroxide, barium sulfate and other carriers to form water-insoluble lakes such as: acid golden yellow lake (C.I. Pigment Orange 17), light-fast lake blue lake (C.I. Pigment Blue 17) .
3. Phthalocyanine pigment
The main body in the molecule is phthalocyanine, the structural formula is:
They are water-insoluble organic matter, mainly blue and green pigments. In 1934, the British Bunemen Chemical Industry Company and the German Farben Company respectively produced the first variety—phthalocyanine blue. Most products contain divalent metals, such as copper, nickel, iron, manganese, etc., and the benzene ring in the molecule is replaced with a pyrrole ring or other rings, and other groups are introduced into the molecule. Different structures have different performance and use. The main species of phthalocyanine pigments is copper-containing phthalocyanine blue (C.I. Pigment Blue 15). The main industrial production method is to react phthalic anhydride and urea (or phthalonitrile directly) with cuprous chloride in the presence of ammonium molybdate catalyst, and the crude product obtained is commonly known as "copper phthalocyanine". The methods of post-treatment of pigments are different, and different commodities can be obtained. If the crude product is dissolved in concentrated sulfuric acid, and then slowly precipitated in water, the α crystal form can be obtained, which is a reddish blue organic pigment; if the crude product is dissolved in concentrated sulfuric acid, then a small amount of Chlorine gas, with 1 to 2 chlorine atoms on the molecule, the color of the obtained product is greener than that without chlorine; if the crude product is ground with dry sodium chloride in a ball mill, a stable green β-crystal product can be obtained . The crude product is heated to about 220°C in the melt of aluminum trichloride and sodium chloride, and chlorine gas is introduced to introduce 14 to 16 chlorine atoms into the molecule, and the obtained product is a bright green pigment; if a small amount of bromine is introduced , the color of the resulting product is more yellow and brighter.
4. Quinacridone pigments
The basic structure of the molecule is a quinacridone pigment:
In 1958, it was produced by DuPont Company of the United States. The production method is to obtain the quinacridone pigment of gamma crystal form through self-condensation of diethyl succinate, condensation with aniline, ring closure, refining and oxidation. Because its heat resistance, light fastness, and vividness are comparable to those of phthalocyanine pigments, the product is called phthalocyanine red (C.I. Pigment Violet 19), but the molecular structure of the two is completely different. If different conditions are used during oxidation, the β-crystal quinacridone pigment with a bluer shade can be obtained, and the commercial product is called phthalocyanine violet.
In addition to the above-mentioned varieties, there are also some varieties with excellent performance, such as dioxazine pigments, the representative variety is Permanent Violet RL (C.I. Pigment Violet 23); isoindolinone pigments, the representative variety is Pigment Yellow 2GLT (C.I. Pigment Yellow 109); benzimidazolone pigment, the representative variety is Permanent Orange HSL (C.I. Pigment Orange 36).
The research focus of organic pigment workers is on the improvement of pigment post-treatment, such as selecting a better crystal form, producing finer particles with a small particle size distribution, improving the wettability of pigments, etc., so that organic pigments can play a greater role. utility.
Organic pigment English name: organic pigment
