Vat dye pigments

Vat Dye Pigments. Vat clyes have been used for a long time for coloring textile fibers. As pigment technology evolved, new methods of particle size reduction have been successfully applied to largely insoluble dyes. Only... 

Indanthrone blue n. A member of a group of vat dye pigments. Relative to phthalocya-nine blue, it is considerably redder in hue and superior in bronze resistance lightfastness is excellent. It shows no tendency toward crystal growth in conventional paint thinners or solvents. 

The dianhydride of 1,4,5,8-naphthalene tetracarboxyhc acid [81-30-1] has been of research interest for the preparation of high temperature polymers, ie, polyimides. The condensation of the dianhydride with o-phenylenediamines gives vat dyes and pigments of the benzimidazole type. 

Approximately 90% of the phthalocyanines (predominantly copper phthalocyanine) are used as pigments (qv). In addition, they have found acceptance in many types of dyestuffs, eg, direct and reactive dyes, water-soluble and solvent-soluble dyes with physical and chemical binding, a2o-reactive dyes, a2o nonreactive dyes, sulfur dyes, and vat dyes (1) (see Dyes Dyes, reactive). 

Anthrapyrimidines. Anthrapyrimidines are yellow vat dyes and exhibit good fastness. Cl Vat Yellow 20 [4216-01 -7] (5) (Cl 68420) is the only example that is currendy produced. The production method is shown in the following scheme. This compound is also used as a high performance organic pigment (Cl Pigment Yellow 108). 

Flavanthrone. Flavanthrone [475-71-8] (177) (Cl 70600) has exceUent dyeiag properties, which ate due to the stabUity of the leuco form, but its fastness is not satisfactory. Only the unsubstituted flavanthrone is used as a vat dye, ie. Cl Vat YeUow 1 (177). It is mainly used as a pigment, ie. Cl Pigment YeUow 24. Synthetic routes ate iUustrated ia Figure 10. 

Among these dye classes, anthraquiaone dyes are ia an important position ia reactive dyes and vat dyes for cellulose fibers, disperse dyes for polyester, and acid dyes for polyamide. Application for high performance organic pigments for plastics and paints are also important areas. 

Most vat dyes are based on the quinone stmcture and are solubilized by reduction with alkaline reducing agents such as sodium dithionite. Conversion back to the insoluble pigment is achieved by oxidation. The dyes are appHed by either exhaust or continuous dyeing techniques. In both cases the process is comprised of five stages preparation of the dispersion, reduction, dye exhaustion, oxidation, and soaping. 

The chemistry of quinone dyes has been discussed in a series of books entitled The Chemistry of Synthetic Dyes, edited by Venkataraman.1 The general chemistry of quinoid compounds has been discussed by Patai.2 There have been many books that cover quinoid compounds as dyes and pigments but very few discuss the chemistry of the corresponding leuco dyes. Traditional vat dyes are applied to cellulosic fiber in the leuco form. The chemistry of the leuco form of vat dyes is rather simple. Some leuco quinones are quite stable in the solid state and can be stored for a year. Other leuco dyes are unstable in solution and gradually undergo aerial oxidation. 

Figure 4.2 Some polycyclic anthraquinone vat dyes and pigments...

A number of vat dyes developed originally for textile applications are suitable, after conversion into an appropriate pigmentary physical form, for use in many paint and plastics applications. Examples of these so-called vat pigments include the anthraquinones, Indanthrone Blue (215, C. I. Pigment Blue 60) and Flavanthrone Yellow (216, C. I. Pigment... 

This chromogen (1.13) is somewhat reminiscent of the indigoid and anthraquinone types but it has not yielded useful vat dyes. Bluish red pigments of the quinacridone class are especially important in violet and magenta colours or for deep reds in admixture with inorganic cadmium scarlets. 

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