4’ Chapter 3/Part 2: Practical Application of Vat Dyes By J. R. ASPLAND, School of Textiles, Clemson University, Clemson, S. C. N the 1980s vat dyes, bearing about 60 Vat Dye Classification and is, unfortunately, not very predict- 1 C.I. Names (I), were available in the The products in all dye application classes able(4). U.S. under about 260 different trade may be differentiated in several ways: e.g., Another occasional problem is photo- names. This collection of dyes has not by their chemical nature, by the fastness tendering, in which some vat dyes, such as changed much in recent years. About 60% properties of the dyeings (and conse- C.I. Vat Orange 2, are partly reduced of them have C.I. Numbers-i.e., ihe quently, their end-uses), by their dyeing under the influence of light. In the dark, in chemical structure of the principle color characteristics, or even by their color. the presence of atmospheric oxygen and component is known; 85% are derivatives Because vat dyes are sold as pigments, it is the cellulose, they are regenerated; but of anthraquinone, and of these almost 50% important to be aware that dissolution and with oxidative tendering of the fiber by fall into only five chemical structure sub- other dyeing related properties can be peroxides formed as by-products. The groups; indigo derivatives and the related affected by the particle size distribution of author’s wife has a pocket handkerchief thioindigo derivatives account for about the products (2). which once sported a vat-printed pattern 10% of the list. As a class, vat dyes are of small dogs. The dogs are nearly all gone expensive, although they share this char- Vat Dye Synthesis now, leaving small dog-shaped holes. acteristic with some fiber reactive dyes. Vat dyes are difficult chemicals to make Despite some drawbacks, which can be One shouid not overlook the 10% of and their structures are complex. Some of circumvented by proper dye selection, vat so-called sulfurized vat dyes, which are these will be shown in the subheading Vat dyeings have several good properties more economical hybrids of sulfur and vat Dyes. The different chemical structures which make themvery difficult to overlook dyes. affect the solubility of the sodium leuco- for dyeing some industrial yarns, terry vat, its stability towards over-reduction cloth, industrial work clothing and shirt- and over-oxidation, its substantivity, its ing fabrics. They also are the only class of rate of diffusion into and out of the fiber dyes which does not suffer severe shade and the ultimate properties of the dyeing. changes during the application of topical, But since these application properties can- cellulose reactive, flame retardant fin- ABSTRACT not be readily deduced from the dye ishes. The practical details of using vat dyes in structures alone, classification by struc- both batch and continuous processes ture will not generally be much help in the Color Characteristics are covered in this second and final part dyehouse, although all indanthrones (C.I. All surface colors can be characterized in of Chapter 3. Vat dyes generally offer Vat Blues 4, 6 and 14) are susceptible to terms of three independent parameters- superior fastness properties. Potential over-reduction and over-oxidation. lightness (or darkness), chroma and hue. drawbacks to selecting vat dyes include Chroma is also called colorfulness, satura- a tendency for phototendering and a Fastness Properties tion or brightness (or dullness). We will limited color gamut. Based on the substantivities of leuco-vat anions, the In exchange for their cost, vat dyes can use the word brightness here, even though traditional classification system for vat deliver dyeings with the highest levels of it is not the ideal synonym for chroma and dyes offers batch dyers a better means washing and wetfastness properties. In- is not to be confused with lightness. Hue is for selecting vat dyes to be used digo, as mentioned earlier, is atypical in the property of appearing red, yellow, successfully in combination. Leuco-vat this regard. For staining of adjacent cotton green or blue or something in between. dyeing, prepigmentation, semi- goods and shade changes on washing, vat The color distribution of vat dyes avail- pigmentation and batch aftertreatments dyeings are rarely rated less than 4-5 on a able in the U.S. is as follows: 25% blue, are covered. While continuous dyeing scale of 5. 18% brown, 14% black (and olive), 11% with vats offers economic advantages, Fastness to industrial laundering with orange, 10% red, 10%green, 6% violet and several precautions are required to ensure a satisfactory result. The hypochlorite and towards peroxide and 6% yellow. There is a good palette for blue, chemical structure and commercial hypochlorite bleaching are generally oui- green and earth tones of very good fast- forms of vat dyes are also covered. standing, as are the fastness properties ness, with similar dye cost to normal fiber towards sunlight, weathering and perspi- reactive dyes. The range of colors which ration. Even the paler shades of vat dye- can be dyed with any one application class KEY TERMS ings generally have high lightfastness rat- of dyes is known as the color gamut, which ings, in the order of 5-6 on a scale of 8, and is a volume of colorspace within which Anthraquinonoid Vat Dyes 7-8 at heavy depths. For further informa- Batch Aftertreatments these dyes are useful. The color gamut of Color Gamut tion on lightfastness testing and rating, see vat dyes is restricted by the absence of very Commercial Form (3). It is the limited variability of these bright colors, particularly in the red and Continuous Dyeing ratings, as well as their high values, which turquoise hue areas, and only sulfur dyes Dye Classification distinguishes vat dyeings from direct and azoic combinations have smaller color Fastness Properties dyeings. However, some combinations gamuts. Indigo Dyeing of yellow and blue or green vat dyes do Pigmentation show anomalous behavior in which the Batch Dyeing Characteristics Vat Dyeing blue or green component is lost more No single classification of vat dyes by Wet-on-Wet Process readily on exposure to light than expected. dyeing characteristics has been as useful This is often referred to as catalytic fading, or as generally accepted as has the classifi- February 1992 co3 27 Vat Dyes I Table 1. Conditions for Dyeing Leuco-Vat Anions at 1O:l Liquor-to-Goods Ratio I cation of direct dyes into groups A, B and We Temperature Caustic Hydro Sodium C. Group C (F) Soda WL) (g/L) Sulfate (g/L) One method of classification divides vat IK 20-25 (70-80) 3.6 3:O 12.0 dyes into four principle sub-groups: IK, IW 40-50 (100-120) 4.8 4.0 12.0 IW, IN and IN Special, which still leaves a IN 60 (140) 8.8 5.0 - few dyes out, such as C.I. Vat Black 9. This classification is based on the different and prepigmentation methods, and there which the practical dyeing does not begin substantivities of the leuco-vat dye anions are also dyeing methods which are hy- until the vat-pigment is dissolved in caus- and the corresponding differences in dye- brids. But before we proceed to look at the tic soda and hydrosulfite solution. Here we ing temperatures and the salt, caustic soda different processes in turn, it would be have a classical case of anions in solution, and hydro concentrations necessary to desirable to reiterate a caution, given their sorption and diffusion into the give the best overall dyeing results. The earlier, regarding preparation and water nonionic cellulosic fiber. importance of these traditional groupings quality. This type of dyeing process is applicable is restricted to batch dyeing with the to cellulosic fibers from raw stock through leuco-va t anions. Preparation and Water Quality sliver, yarn packages and yarn skeins, to The I stands for Indanthren, and has When dyeing cotton with water soluble knit or woven fabrics where liquor-to- been a trademark for vat dyes since the anions under conditions of high substan- goods ratios of 10: 1 to 20: 1 would be in the synthesis of indanthrone. In the first three tivity, as is the case with leuco-vat anions, normal range. Its primary use is for heavy decades of the twentieth century, thanks to it is imperative to have the goods as free as shades, which exhaust less rapidly (see unusual Anglo-German co-operation be- possible from any impurities which might subheading in Chapter 1 titled Kinetics: tween Morton-Sundour Fabrics and be distributed nonuniformly and which Rate of Dyeing) and for which the possi- BASF, the name Indanthren rapidly be- are hydrophobic (e.g., oils, fats and wax- bility of unlevelness is not so critical. The came synonymous with outstanding light- es), or which can interact with the dye variety of machinery possible for dyeing and wetfastness on cellulosic fibers. anions to give hydrophobic (insoluble) fiber in all these forms makes any sugges- K stands for the German word, kalt, products; e.g., thecalcium and magnesium tion of a single optimal procedure absurd. meaning cold. Dyes (reduced leuco-vat cations present in process water and in the But thevariables which affect the levelness anions) in this group are dyed at room cotton itself, from the irrigation water. or uniformity on the one hand and the temperature with a relatively high salt Anything which might stand in the way of dyeing efficiency or exhaustion on the concentration (common salt or anhydrous uniformly wetting the goods with dye other are well understood. Careful consid- sodium sulfate) and a relatively low so- solution could cause unlevel dyeing.