Practical Application of Vat Dyes

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. The eration of these variables can be used to dium hydroxide (caustic soda) concentra- better the preparation, the more uniform effect process optimization in any particu- tion, all of which tend to promote higher the dyeing. Careful preparation may not lar case. substantivity and exhaustion at equilib- put money in the bank, but it could stop Temperature: The temperature at rium. second quality goods from eating away the start of the dyeing is determined by the W stands for the German/English assets. The use of sequestering (chelating) classification of the dye used (see Table I). word, warm. Dyes in this group are more agents or protective colloids which com- Vatting is normally carried out prior to substantive, and can be dyed at 40-50C plex with calcium and magnesium ions is dyeing for about 10 minutes in a long (100-120F) with less salt and slightly recommended. Oxidative bleaching pre- liquor. During the dyeing the temperature more alkali. treatments along with the use of strong can be gradually raised to about 80C N stands for the German/English word, alkalis, dispersing agents and sequestering (170-180F), or even higher if the dyes are normal. Such dyes are even more substan- agents often precede dyeing; but it is not sensitive to over-reduction and a more tive, require more alkali but no salt, and possible with vat dyes to take advantage of stable alternative to hydro is used as the can be dyed at 60C (140F). The IN the highly alkaline dyebaths and both reducing agent. Temperatures of 100C Special dyes require even more alkali. prepare and dye greige goods at the same (212F) and a little higher may also be Table I shows the conditions under time. used, where leveling in lighter shades or which 2% owg shades can be dyed at 1O:l poor penetration in tighter constructions liquor-to-goods ratio for IK, IN and IW Dye Anion Solubility may be a problem. Towards the end of the dyes. The concentrations of chemicals The solubility of the sodium leuco-deriva- dyeing cycle, the temperature might be increase with increasing dye concentra- tives of vat dyes varies considerably with lowered to 40-50C (100-120F) to increase tions and liquor-to-goods ratios. For more structure, with some higher than 80 grams the percentage exhaustion. details a reputable dye supplier should be per liter and some lower than 15 grams per 0 Tinre. The time at the maximum consulted, since different dye organiza- liter. The C.I. Vat Blues 4,6 and 14, based dyeing temperature can vary from about tions use different methods of categoriza- on indanthrone, have a tendency both to 45 minutes at 60C (140F) to about 20 tion (5). Also, read carefully the units in lose solubility on standing and, along with minutes at 1OOC (2 12F), but will depend which concentrations are expressed. Con- several others, to form insoluble salts of on the amount of circulation in the equip- veniently, few of the vat dyes in use today calcium, magnesium or iron in hard water. ment. fall outside the IW and IN categories. Asmentioned earlier, a sequestering agent 0 Salts: Additional sodium chloride or When it is necessary to dye mixtures of IW can alleviate this latter problem. At higher sodium sulfate may be added to dyebaths and IN dyes, the IN conditions are to be temperatures, these same indanthrones towards the end of the dyeing in order to selected because the higher temperature are also subject to over-reduction, and C.I. improve exhaustion. and lower salt are least likely to cause Vat Blue 6 can lose its chloro groups. 0 Reducing System: The amounts of unlevelness due to too rapid dyeing. Additions of glucose or sodium nitrite may caustic soda and hydrosulfite used will 'pelp eliminate over reduction. depend not only on the concentration of Batch Dyeing Processes dye present but on the temperature, There are at least two distinct types of vat Leuco-Vat Dyeing whether the vessel is open to the air or dyeing processes which will be discussed The earliest and the most fundamental vat enclosed, and on the area of exposed here. They may be characterized as leuco dyeing process is the leuco-process in surface. The amounts should be sufficient

28 033 Vol. 24, No. 2 to maintain the dye in alkaline reduction chemicals into the dyebath, to have total piece may be bypassed. The pieces, in condition throughout the dyeing. Any control of the rate of formation of the order, are: padder, predryer, dryer, ther- additions require care. leuco-vat anion and, consequently, of lev- mosol oven, padder, steamer, washer units Auxiliary Chemicals: Two kinds of eling. (must be divisible into four separate sec- agents which may be used in leuco-vat tions) and dryer. dyeing are leveling and stripping agents. Batch Aftertreatments Only polyester/cellulosic blends re- They are essentially similar in their action, Regardless of the vat dyeing process used, quire the thermosol oven treatment in for both interact with the leuco-vat anions once the dyebath has been dropped, the which disperse dyes are fixed onto polyes- in solution to form complexes. These aftertreatments include the following ter fibers at 200-215C (390-420F). The complexes lower the effective concentra- steps: rinsing, oxidation, soaping and neu- thermosol process will be discussed in a tion of dye anions in the bath and hence tralization. Softening may be included but later chapter entitled Dyeing of Blended can lower the rate of dyeing and increase is not fundamental. Fibers and Fabrics. the rate of stripping. The difference be- 0 Rinsing: This process can be elimi- The author regrets that this is not the tween leveling and stripping agents is one nated if the exhaustion is very good, as it place to discuss the engineering aspects of of degree. The stability of the leuco-dye might be for pale shades; but with medium so many types of equipment, particularly anion/agent complex is greater for strip- shades it is important to rinse out most of since such knowledge would be valuable to ping than for leveling. the alkali, reducing agents and loose dye; plant engineers and dyers alike. It is an Protective colloids, sequestrants or che- with heavy shades it might be necessary to ongoing concern of AATCC that its con- lating agents may help facilitate dyeing of include one to two grams per liter of both stituency has been poorly served by publi- greigegoods (see the previous subheadings caustic soda and hydrosulfite and a little cations in this area, and the association on preparation and water quality). dispersing agent, in a reductive rinse, for would like to remedy this situation. For an about five minutes at ambient (plant) exception, see (6). Prepigmentation temperature. The principle dye range configurations Because the chemicals necessary for vat- Oxidation: Usually this is carried out used for cellulosic fiber dyeing are called ting make the leuco-vat dye anions in at approximately 60C ( 170- 180F) for the pad-steam (or pad-dry-steam) and solution highlysubstantive, there is always about 15 minutes with hydrogen peroxide wet-on-wet (or pad-pad-steam) processes. the possibility of unlevelness if circulation and acetic acid, or sodium metanitroben- of the dye liquor is inadequate. But what if zene sulfonate, or sometimes, perborates. Pad-Steam Process dispersions of vat pigments, with no sub- Soaping: This is usually carried out at The pad-steam process for continuously stantivity, were to be circulated and uni- 95C (200F) for about 10 minutes, fol- dyeing vat dyes is suitable for most flat formly distributed at the fiber surfaces lowed by rinsing. It may be necessary with cellulosic fabrics. Here a vat pigment before alkali and reducing agent were packages to split soaping into two steps, dispersion is padded onto the goods and added? Once the pigments were deposited, the first being really a dispersing process dried. A wet pickup of 60-70% might be vatting would result in anion formation conducted at about 60C (170- 180F) to suitable for many cotton and polyester/ just where it is needed, at the fiber sur- ensure that no loose color is available to cotton flat goods. This process would be faces. It would certainly require very fine aggregate and filter out at the second step, unsatisfactory for corduroy and terry dispersions, with low particle size distribu- which is conducted at normal soaping cloth because the pigment will migrate to tions, but this problem has already been temperature. the fabric surfaces during drying. In addi- overcome, and vat pigments are indeed Neutralization/Rinsing: Depending tion to the issue of migration is the adverse available in such finely subdivided forms. on whether the oxidation was acidic or surface effect (flattening, distortion) if (See the upcoming section in this chapter neutral, the soaped goods could be neutral goods are not run wet-on-wet, avoiding on commercial forms of vat dyes.) or acetic acid rinsed, to ensure that tightly predrying and drying cans. Prepigmentation (before reduction) is a held alkali (particularly in the case of The goods are then padded with alkali particularly useful alternative for light viscose) is not left in thefibers. and reducing agent, enter the steamer, and medium shades where levelness might where vatting and leuco-vat anion diffu- be a problem. Circulation of the pigment Continuous Dyeing Processes sion take place, and are then successively can begin at any time and at any tempera- The main economic advantages of contin- rinsed, oxidized, soaped and rinsed ture between ambient plant temperature uous dyeing are to be derived from the through the four sections of washing units, and approximately 80C (170-1 80F); after rapid production of goods with veryconsis- followed by drying. about 20 minutes the chemicals are added tent shade. Speeds of 160 meters (175 to reduce the dye. Dyeing can then be yards) per minute are possible. But, the Wet-on-Wet Process completed with whatever temperature, potential benefits have been increasingly The wet-on-wet process is only suitable for time and salt conditions achieve the best curtailed by the shrinking size of individ- those fabrics which have the ability to results. uai dye lots, despite successful efforts by retain large amounts of water. These machinery manufacturers to make chang- include terry cloth and some styles of Semi-pigmen tation ingcolors as painless as possible. When the corduroy, The adverse surface effects of This is the name given to a process which is threaded up length of a nominal continu- flattening and distortion are avoided by a hybrid of the leuco-vat and prepigmenta- ous dye range may be 400 meters (440 not passing these goods through the pre- tion processes. All the chemicals and dyes yards), or even more, and the length of a dryer and over dry cans. So is the cost of required for the leuco-vat process are particular dye lot may be only 1800meters driving off very large amounts of water. added and circulated through the goods at (2000 yards), this spells potential shade The process parallels the pad-steam pro- plant temperature for 20 minutes before consistency problems for the continuous cess, but without the drying between raising the temperature to 60-80C (140- dyer. padders. It relies on the goods, which enter 180F) for 30 to 40 minutes. The pigmen- A conventional, fully continuous dye the second pad with a wet pickup of 60 to tary dispersion is slow to reduce at plant range suitable for dyeing polyestet/cellu- 70% of the vat pigment dispersion, leaving temperatures and is simultaneously but losic, cellulosic and other blended cellulo- the second pad with a higher total wet gradually deposited while it is reduced as sic fabrics in open width consists of at least pickup of 100 to 200%. The increase in wet the temperature is raised. 11 separate pieces of dyeing equipment pickup, the differential wet pickup, en- Variations on this theme include the strung together in line. Ideally, goods can sures that some alkali and hydro are added programmed metering of the vatting be taken up between these pieces, and any to the pigment to facilitate subsequent

Februarv 1992 cQ3 29 Vat Dyes Steaming Continuous Warp Dyeing of Indigo A normal steaming time would be between The principles of dyeing ball warps, warp 30 and 60 seconds. The steamer should beams or piece goods with the leuco-indigo contain air-free, saturated steam very anion are easy to understand, and the slightly superheated; e.g., with a wet bulb present processes result from the low temperature that of the boiling point of substantivity of the anion for cellulose. For water, and a dry bulb temperature no more examples, see Kramrisch (8)and also (4). than about 5C (9F) higher. The dyeing equipment consists essen- reduction in the steamer. Problems can The steamer should be equipped with a tially of a series of open wash boxes arise from interchange of the two pad water seal at the exit end through which equipped with multiple upper and lower liquors in the second pad trough. This there should be a constant flow of water rolls, around which the goods are led in a differential pickup criterion cannot be met sufficient to maintain the temperature at serpentine path, with squeeze rolls be- by much flat goods, which have low water not more than 40C (105F). tween the boxes. Above the middle set of inhibition, but is fine for terry cloth and Increasing the time of steaming may four to six boxes (vats) skying rolls are corduroy. decrease the appearance of depth of shade provided. The process is carried out at without lowering the percentage of dye ambient temperature. Padding fixed. This may relate to dye diffusing After wetting out the goods in a first The function of padding is to mechanically deeper within the fiber bundles, and losing boxes, they pass at about 25 meters per place the aqueous compositions of dyes its effect on the surface color with in- minute to the middle set of boxes and are and/or chemicals where they are required, creased steaming. immersed in leuco-indigo dye liquors for uniformly across the goods from side to 10 to 30 seconds, squeezed to about 100% side, by saturating the fabric in the pad Aftertreatment wet pickup, and skyed for about two bath and then squeezing off the excess pad Washer units come in a variety of configu- minutes. These three steps are repeated in liquor. This process should leave a known rations, but whatever type they are they successive boxes, as many times as desired, amount of material held uniformly by the must be separable into four distinct groups up to about six. In each box some more wet fabric along its length and width pro- in which the functions of rinsing, oxidiz- leuco-indigo is imbibed, followed by air- vided that: ing, soaping and rinsing/neutralizing may oxidation, and the indigo pigment is grad- 0 The wet pickup is constant from be performed separately before the final ually built up, primarily on the fiber side-center-side of the fabric, which is drying. surfaces. dependent on the adjustment of the The indigo is usually dissolved in a stock squeeze rolls of the padder. Semi-continuous Dyeing Processes vat which contains indigo (loo%), caustic The immersion time remains con- If any one step in a batch dyeing process is soda and hydrosulfite at concentrations of stant and the goods are uniformly wetta- carried out continuously, then the term about 80, 70 and 60 grams per liter. The ble. For this, good preparation is required. semi-continuous can be applied to the stockvat is used to supply the boxes (vats), 0 The liquor temperature and composi- overall dyeing process. For example, cot- which are preset with caustic and hydro- tion remains constant. The latter depends ton fabrics to which vat pigments have sulfite, to maintain a level of indigo on whether the dyes or chemicals are been applied by padding followed by (loo%), caustic soda and hydrosulfite, at attracted preferentially out of the pad drying may have the shade developed by concentrations of about 5,2 and 1.5 grams liquor, by the fibers. Pigments have no transferring the goods to a jig where per liter. The heart of the process is in the fiber substantivity, so there should be no vatting, leuco-vat diffusion into the fiber, circulating of the liquor in the vats and problem with vat dispersions. rinsing, oxidation, soaping and rinsing can metering-in stock dye and chemicals to be effected. maintain constant, uniform dyeing condi- Predrying and Drying Dyeing polyester/cotton and other tions. The dyeing is concluded by carrying In order to control migration of vat pig- blended fabrics has other examples of the goods through several boxes of coun- ment particles to the fabric drying sur- selectively using sections of the continuous terflowing water. faces, a number of precautions are neces- dye range, all of which can contribute to sary. the efficient use of both continuous and Vat Dyes The heat in the dryers should be as other batch dyeing equipment, as well as to Earlier, the redox properties of vat pig- uniform as possible from side-center-side processing versatility. ments were discussed at some length. Vat and from back-face, for the water carrying pigment molecules generally have from the dispersion will preferentially travel one to three pairs of groups, suitable for towards the area of highest water evapora- reducing to soluble leuco-vat anions (see tion rate, and Table I and Fig. 2 from Part 1 of Chapter 3 The pad liquor should contain an and Fig. 1 in Part 2 of the Chapter 3) but antimigrant. An antimigrant causes floc- the chemical entities carrying these reduc- culation and aggregation of the pigment ible groups are pretty complex. particles as the pad liquor becomes con- centrated by drying. The flocculated pig- Chemical Structures ments are not sufficiently mobile to move The structures of all anthraquinonoid vat rapidly towards the drying surfaces along dyes are characterized by having at least the fiber and fabric capillaries. The pro- five and sometimes more than ten aro- pensity for a particular pad liquor to matic rings, many of them condensed encourage or discourage migration can be together. Most vat dyes have seven to nine checked using AATCC Test Method 140- rings. The structures of the anthraqui- 1990(7). nonoid vat dyes in the U.S. market today Among other things, particulate migra- fall into four principal chemical sub- tion is very dependent on fabric structure, groups: moisture content, air and moisture move- 0 Violanthrones: The structure of vio- ment in the dryer and the particle size lanthrone, C.I. Vat Blue 20, is shown in distribution of the vat pigment. Fig. la. Dyes based on this structure

Vol. 24. Nn. 2 *.

I‘- ‘

0

a) Yellow 1 b) Yellow3

a) Violanthrone b) Anthraquinone Carbozole Fig. 2.TwoC.I.vatdyestructures.

\ H * ‘// H” H” 3 ‘

c) Indanthrone d) BenzanthroneAcridone

Fig. I. The parent structuresof the four principle chemical sub-groups of anthraquinonoid vat dyes. vat-acid forms of some vat dyes to make the corresponding water soluble sodium include C.I. Vat Blues 16, 18, 19 and 20; the form of either readily dispersible salts of the sulfate esters. The functional C.I. Vat Greens 1 and 9; and (2.1. Vat powders or as ready to use aqueous pastes group can be drawn as: \ Blacks 9 and 16. or liquids (not solutions). To achieve the = CC-O-S03-Na+. Anthraquinone Carbazoles: A simple desired particle size distribution requires From these water soluble anionic com- carbazole, C.I. Vat Yellow 28, is shown in extended milling in the presence of a pounds, the original pigment can be re- Fig. lb. Dyes based on this structure dispersing agent, which frequently is so- stored by oxidation with acidified sodium include C.I. Vat Oranges 1 1 and 15; C.I. dium lignin sulfonate, with or without nitrite (2).Economic considerations have other anionic surfactants. About 50% of Vat Green 8; (2.1. Vat Browns 1 and 3; and almost completely eliminated these inter- ’ the particles in a good vat dye dispersion C.I. Vat Black 27. esting vat dye derivatives from the U.S. Indanthrones: The parent member of have diameters of one micron or less; Le., market (1). this family, C.I. Vat Blue 4, jb.1901), 1 x 10-6meters(4). shown in Fig. IC, has been mentioned Review Powders earlier, and is joined by the offspring, C.I. The diversity of the dyeing methods now VatBlues6,12and 14. Vat dye powders fall into two principle possible, starting with the chemically 0 groups: those which can be used for either Benzanthrone Acridones: The basic complex but exceedingly stable vat pig- structure is shown in Fig. Id). Dyes based batch or continuous processes in which the ments, is a tribute to the ingenuity of dye fibers are pigmented prior to color devel- on this structure include C.I. Vat Green 3 application chemists. However, vat dyes opment, and those with a high color and 13; and C.I. Vat Black 25. are expensive. Their color gamut is re- content, relatively low dispersing agent Substituent Groups stricted and the strongly alkaline reducing and low fine particle content. Such pow- environment is not compatible with most Nitrogen often participates in the aro- ders are unsuitable for processes which other dyes and some fibers. So, despite matic ring structures of vat pigments involve fabric pigmentation. excellent fastness characteristics, their (compare Fig. lb, c and d, and in Fig. la Pastes or Liquids utility is self limiting, like that of all other and b from Part 1 of Chapter 3). Oxygen dye application classes for cellulose. and sulfur do so less often. Apart from the Vat dyes in the form of pastes and liquids pairs of reducing groups (called quino- are most frequently used in continuous nes), vat pigments are singularly free from dyeing in the U.S. Powders are preferred References substituent groups. Some chloro (-Cl) and in Europe. Vat dyes can be purchased in (1) AATCC Buyer’s Guide, AATCC, published bromo (-Br) substituents, some hydroxy, combination with disperse dyes for dyeing annually as the July issue of Textile Chemist and methyl and methoxy groups, (-OH, polyester/cotton blends continuously with Colorist. (2) Johnson, A., The Theory of Coloration of -CH3, -OCH3), and a few amido groups, vat disperse dye combinations, standard- Textiles, Second Edition, Society of Dyers and Co- -NH.CO-, take care of most contingen- ized by the manufacturer to give good lourists, 1989. cies. The absence of ionic solubilizing union shades. (3) AATCCTechnicalManual,Vo1.66,1991,p39. groups goes (almost) without saying. This (4) The Dyeing of Cellulosic Fibres, edited by should make drawings of vat pigment Solubilized Vat Dye Powders Clifford Preston, Society of Dyers and Colourists, 1986,Chapter 6. structures easy to recognize. For example, Vat dye makers have always been aware of (5) Colour Index, Society of Dyers and Colourists could either of the structures represented how desirable it could be to have readily andAATCC,Vol. 3,ThirdEdition. 1971. in Fig. 2 be a vat dye? water soluble products, and for many (6) Engineeringin Textile Coloration, edited by C. years water soluble derivatives of vat dyes Duckworth, Society of Dyers and Colourists, 1986. Commercial Forms of Vat Dyes (7) AATCC Technical Manual, Vol. 66, 1991, have formed a complete class of dyes unto p240. Vat dyes as sold are usually water insolu- themselves, They are called solubilized vat (8) Kramrisch, B., American Dyesfuf Reporter, ble pigments. These pigments are made in dyes. Such dyes are made by reacting Vol. 69,No. 1 1, November 1980,p34.

February 1992 co3 31