Analysis of organic pigments: How is the development mainstream? What about the development of new varieties and new technologies?
1. The mainstream of organic pigment development
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According to Ludwig, vice president of Sun Chemical Company of the United States, the total production of organic pigments in the world in 2000 was 21,000 tons, of which high performance pigments (HPP) produced 17,000 tons. At the same time, he believes that although the total output of organic pigments will increase at zero between 2000 and 2001, the total production of organic pigments will increase at a rate of 3% to 5% per year for the next five years. Thus, according to his point of view, the total output of organic pigments in 2002 should be between 21.6 and 220,000 tons, and in 2003 it will reach 22.3 to 230,000 tons. It should be pointed out that although the total output of organic pigments will increase by such a high degree, the increase of each organic pigment is uneven, and those which grow faster are those called HPP. Because even during the period from 2000 to 2001, when the total output of organic pigments was at zero growth, the production and demand of HPP increased by 3%, among which DPP-like CI pigment red 254, 264, 270, 272 and benzo Imidazoxanoids CI Pigment Yellow 151 and 154. It is no wonder that there are reports that the production of HPP in the world in 2002 was 35,000 tons. However, the author of this article believes that this number is too large. Nevertheless, from the above introduction, one can conclude that the development of HPP represents the mainstream of organic pigment development. In addition to the two classes of DPP and benzimidazolone mentioned above, the pigment classes belonging to HPP are quinacridones, dioxins, isoindolinones and isoporphyrins. Heterocyclic, rudder, condensed azo, yellow phthalocyanine green, etc., a total of 9 categories. Please note that blue phthalocyanine pigments are not in the category of high performance organic pigments.
2, new varieties
2.1 benzimidazolone-dioxazine pigment
As the cost of developing new chemical structures is getting higher and higher, and the profit margin for producing pigments is getting smaller and smaller, the number of new structural pigments newly launched in the past decade has been numerous. Among these new structural pigment varieties, one belongs to the benzimidazolone-dioxazine structure type, namely CI Pigment Blue 80.
The dioxazine precursor is a planar fused aromatic hydrocarbon. The compounds of this structure have good thermal, optical and chemical stability. By making them into pigments, they give them good heat resistance and resistance. Application fastness such as sun exposure. In addition, among the existing organic pigment varieties, the coloring power of the dioxazine pigment is the highest. On the other hand, the introduction of benzimidazolone in the molecule greatly reduces the solubility of the molecule in an organic solvent and improves product quality. For example, ordinary azo pigments can only be used in low-grade applications, but after the introduction of benzimidazolone in their molecules, the fastness is good, and the light fastness is 8 and the weather resistance is good. The fastness reaches 5, which is the highest level of pigment. Thus, azo pigments containing benzimidazolone units have become members of the high performance pigment family. The combination of a dioxazine precursor and a benzimidazolone unit is similar to what is often referred to as a "strong-strong combination." To this end, Clariant has introduced CI Pigment Blue 80, which has a reddish blue color between Pigment Violet 23 and Pigment Blue 60, but its tinting strength is higher than that of Violet 23, and it is resistant to gas. The degree is comparable to that of Pigment Blue 60. The main application areas are: automotive original paint and refinish paint, coil steel coating, architectural paint, etc.
The two intermediates for the synthesis of the pigment are 5-amino-6-alkoxybenzimidazolone and tetrachlorophenylhydrazine.
Whether it is CI Pigment Violet 23 (an old variety in dioxazine pigments) or CI Pigment Blue 80 (a new variety in dioxazine pigments), an intermediate is used in the production process, namely: tetrachlorobenzene. Oh, and in the process of producing tetrachlorophenyl hydrazine, a small amount of dioxins is inevitably formed, which is a known substance that is very toxic to humans. In order to comply with the high demands of society for environmental protection, a new class of dioxazine pigments containing no chlorine atoms has appeared in foreign patents.
In this synthesis, the tetrachlorophenyl hydrazine intermediate was completely rejected in the synthesis method, and 2,5-hydroxy-1,4-benzoquinone was used: in order to improve the performance of the new pigment, another intermediate 5-aminobenzene Various substituents have been introduced to the heterocyclic nitrogen atom of the imidazolidone. 2.2 benzothiazine-indigo trans-2-2'-bis-(4H-1,4-benzothiazide)
The color of this kind of pigment is yellow light red. The typical variety is CI Pigment Red 279 (unstructured). It is suitable for coloring of plastics, especially cable insulation materials. It has high light fastness and heat resistance and is suitable for use. Outdoor occasions.
2.3 Quinoxaline dione pigments Quinoline dione (quinoxalindione) pigments, although this type of compound has appeared in patents as early as 1977, but it has become a commercial yellow organic pigment or in recent years The typical variety is CI Pigment Yellow 213, which is strong green and yellow. The main application areas are: automotive original paint and refinish, coil steel coating, industrial paint, powder coating and so on. Its structure has not yet been disclosed, which is the penultimate variety of the yellow pigment serial number. The two intermediates for the synthesis of quinoxalinediones are 1-formyl-2-hydroxy-naphthalene-3-formylarylamine and barbituric acid:
2.4 Dibenzimidazolone azo pigment
The yellow benzimidazolone azo pigment itself has a relatively high light fastness and weather fastness, and is suitable for coloring of exterior wall paints, automobile original paints and refinish paints, and is made into a double azo structure, and then increased. The molecular weight also increases the average particle size, thus having a higher hiding power, and the coloring of the coating is more economical. There used to be a bisbenzimidazolone azo pigment, CI Pigment Yellow 180. Recently, Clariant has introduced a bisbenzimidazolone azo pigment, CI Pigment Yellow 214 (unstructured), which is the largest serial number of yellow pigments, that is, the latest listed variety of all yellow pigments. . Its green light is the strongest of all current yellow pigments and is mainly suitable for the coloration of plastic products.
3. New technology
3.1 Technology for synthesizing composite pigments
DPP pigments are a new class of pigments that have already had large sales in the market. These pigments have both good application properties and low economic costs. However, the alkali fastness of DPP pigments is not ideal. In order to improve the alkali fastness of DPP pigments, CIBa often uses the method of preparing "mixed crystals" to make up for it. In the early days, the preparation of such "mixed crystals" was generally carried out by a physical method, that is, by dissolving two or more kinds of pigments by concentrated sulfuric acid to make the pigments in a molecular state, and then mixing the two or more pigment solutions and then pouring them together. Into the water, the pigment is re-precipitated, so that the crystal produced is a kind of "mixed crystal". In recent years, CIBa's patent discloses a method for preparing a chemical type "mixed crystal" type DPP pigment, which involves modifying a DPP pigment molecule with another pigment molecule in the preparation process. Pigments are also known as composite pigments.
Preparation of Chemical Type "Mixed Crystal" DPP Pigments In the process of synthesizing DPP pigments, in order to obtain higher yields, the reaction must be carried out in an alkaline medium, and the amount of the base must be greatly increased. The base used is generally an alkali metal element such as sodium metal, potassium or the like. In this way, an intermediate, a salt of DPP and an alkali metal, is formed during the reaction. This intermediate has considerable reactivity and can contain "active hydrogen" groups (such as -NH2, -OH, -CONH2). Other pigments, etc., act to form a "complex" compound containing bifunctional molecules. The latter has a low solubility in water or an alcohol solvent, so that such a "complex" compound can be precipitated from the medium at a desired particle size as long as it is properly controlled, thereby obtaining a substance having pigment properties. If in the reaction of the alkali metal salt of DPP with other pigment molecules, the molar ratio of the two is controlled, a mixture can be obtained in the final "precipitation" process, in which the mixture has both pure DPP molecules and There are simple other pigment molecules, and more "composite" molecules of DPP and other pigment molecules, so that "mixed crystals" are formed during the formation of crystals. Obviously, different "mixing crystals" can be obtained by changing different reaction conditions, that is to say, pigments having different application properties can be obtained.
Unsubstituted parent pigment molecules, their various derivatives (except for substitutions on the imine group), can chemically react with DPP pigment molecules to form hybrid pigments.
3.2 "Sustainable" pigment synthesis technology
Insoluble organic pigments are introduced into the molecule by reaction to some groups which contribute to dissolution, so that they have a better solubility in an organic solvent, for example, in an DMF or an N-alkylpyrrolidone, an imino group-containing The organic pigment is reacted with t-butyl dicarbonate, and as a result of the reaction, an acyl group having a t-butyl group is introduced into the molecule. The pigment of such a structure has a large solubility in an organic solvent, but is also unstable to heat. Heating the compound at a certain temperature causes the acyl group to fall off and re-establish the compound of the original structure. However, since such a dissolution-precipitation process occurs in an organic solvent, the obtained pigment particles may be different in crystal form from the original. Such a method of preparing a mixed crystal is identical in principle to acid dissolution with concentrated sulfuric acid, except that the acid dissolution method is a purely physical process, and the above method is a chemical method.
3.3 Application of “Dissolved†pigments in high-tech fields
Organic pigments are insoluble in organic solvents or have very low solubility, so it is not easy to use them in high-tech fields. In order to fabricate component electronic devices together with other materials (for example, polymer materials or metal materials), high vacuum evaporation methods have conventionally been used to cover them on the surface of other materials. This process is difficult to control and is not suitable for making large devices. The above method is now used to achieve a "temporary" solubility of the organic pigments used, so that their solutions are readily obtained and then uniformly coated onto the surface of other materials by "spin coating" techniques. After the solvent is volatilized, the acyl group originally introduced into the molecule is removed by heating to recover the insoluble organic crystal.
The application of "dissolvable" pigments in textile digital inkjet printing inks. The use of digital inkjet printing for textiles or other substrates can produce a variety of different styles of products. The nozzles used for inkjet have a pore size of about 50μm. In order to prevent clogging of the head, the particle diameter in the ink is required to be less than 0.5 μm. To do this, it is necessary to process the organic pigment particles to refine the particles using a series of techniques, which is very difficult in itself. Furthermore, it has been difficult to ensure that the particles that have been refined are no longer agglomerated during storage. It is conceivable to use a "dissolving" technique to dissolve it in the ink, thus ensuring that there are no large particles in the ink. After the pigment is sprayed on the substrate, it is decomposed by heat treatment (heating) to regain an insoluble organic pigment.
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