Chapter 4/Part 2: Practical Application of Sulfur Dyes

Transcription

1 ADril 1992 Crfl Chapter 4/Part 2: Practical Application of Sulfur Dyes By J. R. ASPLAND, School of Textiles, Clemson University, Clemson. S. C..A search for sulfur dyes in the AATCC Buyer s Guide (I) (Part A, Section 1, Table 4, Dyes and Pigments Arranged by Colour Index Generic Names) will prove unrewarding for curious but uninitiated readers. They will find only about 15 products listed, under seven C.I. Names, from five manufacturers. Seven of the products are C.I. Sulfur Black 1. Two are solubilized sulfur dyes, which are the sulfur dye equivalent of solubilized vat dyes and which have no substantivity for cellulose unless reduced. Only if the product tradenames are known can the person searching find some 40 products from one major manufacturer (Table 3, Alphabetical List of Dyes and Pigments). ABSTRACT The variables involved with batch and continuous dyeing with sulfur dyes on cellulose are covered in this the second part of Chapter 4. Sulfur dyes bridge the gap between directs and vats with respect to fastness properties, and these vary widely within the dye class. End-uses for sulfur dyes include: continuous and batch dyeing of corduroy, bottoming and topping indigo on the slasher or on indigo warp dyeing ranges, and nontraditional shades on denim including black, gray, olive and tan. For deep shades of black, brown, blue and green, the fastness properties of sulfur dyes are good and their use quite economical. Processing of sulfur dyes and vat dyes are compared. Synthesis and Chemical characteristics are discussed as are physical form, classification and standardization methods. KEY TERMS Antioxidant Batch Dyeing Continuous Dyeing Dye Chemistry Dyeing Fastness Properties Leuco-Sulfur Dyeing Padding Polysu If ide Sulfur Dyeing Sulfur Dye Classification As with any class of dyes, there are differences between sulfur dye products which make some more suitable than others for a particular application. But in the case of sulfur dyes, the whole business of classification raises interesting and difficult commercial and technical questions. Colour Index The Colour Index (2,3), despite its size, is scarcely more helpful than the AATCC Buyer s Guide, listing current and obsolete sulfur dyes alike, under four main categories relating to their physical and chemical form-sulfur, leuco sulfur, solubilized sulfur and condensed sulfur. Of these, only the first two categories are of general interest to dyers, the third has utility mainly in blacks for paper, and the fourth, which included synthesized products similar to solubilized sulfur dyes, is effectively obsolete. Sulfurized vat dyes have no separate category. The major dye manufacturers have even begun to shy away from the use of Colour Index names for some of their products. Why? The reason is not hard to explain in the case of sulfur dyes. In simplistic terms, sulfur dyes were developed largely by the use of the socalled Edisonian method. Organic chemical intermediates or any economical available organic materials were taken and heated up with sulfur and sulfides by baking, or under reflux, in conditions which were varied, this way and that, in the hope of producing compositions which had desirable combinations of color yield, cost, color, application properties and fastness of the dyeings. Perhaps the addition of small amounts of other intermediates helped one or more of the properties. Perhaps varying the temperature or time, or the addition of solvents, or varying the intermediate to sulfur/sulfide/alkali ratios gave better or different properties. But the chemistry of the final products is still essentially unknown. Even if two manufacturers started with identical ingredients, it is highly unlikely that the precise chemical nature of the final products would be identical. On the other hand, it is not too difficult to find two sulfur colors from the same manufacturer which have the same Colour Index name but which are sold as two products of distinctly different colors. Since nobody knows the precise chemi- cal identity of most sulfur dye products, a Colour Index name merely identifies some of the principle organic ingredients. But it is not always the principle ingredients which are of major environmental importance, for very small amounts of materials may prove hazardous to the environment even if they are only by-products or processing adjuvants. It is understandable that the world s major dye companies, coming from a relatively densely populated Europe, have been making substantial investments to reduce the environmental impact of their products below any accepted limits. It should also be obvious that they do not wish their dyes to be too closely associated-e.g., by C.I. name-with colors being produced in countries where environmental restraints have not yet been seriously considered, let alone enforced. Fastness Properties and End-Use Sulfur dyes may be thought of as bridging thegap between direct dyes and vat dyes as far as fastness properties are concerned, but they vary widely among themselves. Lightfastness is the most variable property, and, as might be expected, this falls with decreasing depth of shade. However, because of their economy and their relatively dull shades, sulfur dyes are rarely used in light depths except to shade other sulfur colors. Traditionally, the main use of sulfur dyes was for continuous dyeing of piece goods, such as corduroy, but as continuous dyeing has declined, piece goods dyeing, particularly in jets, is on the rise. Sulfur dyes are widely used in bottoming and topping indigo by dyeing on the slasher or on indigo warp dyeing ranges, and with the growth of indigo, sulfur dyes have seen growth in the denim area for such nontraditional denim shades as black, gray, olive and tan. Where heavy depth, good fastness properties and economy are all needed, especially in black, blue, brown and heavy green shades, sulfur colors are essentially irreplaceable. Sulfur colors do have generally poor fastness to hypochlorite and peroxide bleaching. In fact, a quick preliminary test to determine whether goods are dyed with sulfur or vat dyes is to spot a little domestic bleach on them and leave the spot to dry. Most sulfur colors will be seriously changed or destroyed by this simple expe-

2 Sulfur Dyes dient, whereas most vat dyes will show little change. Obviously sulfurized vat dyes will give ambiguous results as do some vat blues. Other fastness characteristics include: Lightfastness (xenon arc): At heavy depths the lightfastness of sulfur dyeings ranges from about 3-4 for yellows increasing through to 7 for blacks, with selected blues, greens, navies and browns generally between 5-6 and A Washfastness: The methods of washfastness testing vary from country to country and the AATCC Technical Manual should always be referred to for current US. practice (4). Sulfur dyes generally rate well on the 2A wash test, giving average ratings of 4-5 for both the shade alteration of the original and the staining of adjacent cotton. These values can be affected adversely by oxidation with hydrogen peroxide, and advantageously by post treatment with durable press or crease resist resins. Incidentally, these finishes also offer some degree of protection against mild bleaching. In extreme cases, the wetfastness properties of sulfur dyeings, along with the crock and rubbing fastness, can be made as horrible as the denim market seems to require, by allowing inadequate time for diffusion, plenty of premature oxidation, little rinsing, no soaping-off, and so on. Color Characteristics There is no doubt that sulfur dyes as a group have the least brightness of any dye application category. But if they are augmented by a synthesized copper phthalocyanine green, and a bright pinkish red, C.I. Sulfur Green 36 and Red 14, the range of heavy shades for which they are most suitable lacks principally in the heavy red areas-areas which are filled by azoic combinations.. Dyeing Characteristics Most dye application categories have hundreds of dyes and C.I. named products. The scarcity of sulfur dye manufacturers and the absence of truly equivalent products have left one dominant supplier in the U.S. as the only one with a knowledge of the comparative dyeing properties of a full range of sulfur colors. There is no good reason why this information should be divulged to any but customers. As a result there is no generally available classification of sulfur dyes by their dyeing characteristics. However, the strides taken internally by one company to increase the knowledge base, particularly with regard to continuous dyeing, will be discussed later in general terms. 28 Batch Dyeing Processes Sulfur dyes are widely used in batch (and continuous) dyeing applications since they can be applied on all types of dyeing equipment. General processes for batch dyeing on various pieces of equipment are described in the literature (5.6) but more particularly in manufacturers shade cards. Preparation and Water Quality The best fastness and brightness results are always obtained on well prepared fabric, and EDTA or other sequestrants are always desirable to take care of the problems which result from too high concentrations of calcium and magnesium ions in the process water, or even from cotton when processed at very short liquor: goods ratios; e.g., in jets, jigs or package dyeing machines. Nonetheless, many sulfur dyes are applied in heavy shades directly to greige goods, provided the size used is not polyvinyl alcohol (PVA). Immature cotton is not generally a particular problem when dyeing sulfur dyes, and their coverage is frequently but not invariably superior to that of reactive dyes. Blended Cellulosic Goods If cotton is mercerized prior to dyeing, an apparent color yield increase of about 30% to 40% may be anticipated. But there is not such certainty of increased yield if regenerated cellulosic fibers (e.g., viscose) are used because they have such varied morphology. Some dyes, such as C.I. Sulfur Black 1, seem to cover all cellulosics fairly evenly at all depths, while others may show strong and increasing contrast between different cellulosic fibers in blended fabrics as the concentration is increased. In these cases the cotton usually dyes lightest. Selected sulfur dyes dye nylon and others dye acrylic fibers. Such apparent aberrations are very important in dyeing blends. Leuco-Sulfur Dyeing Leuco-sulfur dyes are commonly referred to as sulfur liquids. Regardless of the equipment to be used, the standard method of dyeing these products requires the following dyebath additives: a penetrant (not a nonionicone), a polysulfide (as an antioxidant), common salt or sodium sulfate (calcium free) and a chelating agent (usually EDTA). The procedure normally consists of the following elements: wet-out the goods with the penetrant and rinse off; set a fresh bath, at about 40C (IOOF), with more penetrant, antioxidant and chelating agent; add the reduced dyeslowly; add salt slowly; run for about 30 minutes; overflow wash at about 32C (90F); oxidize; rinse; soap at 9OC (195F) and rinse. There is a missing element: when and how high to raise the temperature to effect dyeing. As is normal for anionic dyes on cellulose, the rate of dyeing increases with temperature. But the temperature of maximum exhaustion varies among most reduced sulfur dyes. The optimum temperature isabout 65C (150F), but blacksdye better at 90C (195F). This is not an upper limit, for temperatures as high as 120C (250F) can be used, but the temperature of the bath must be lowered to around 70C (160F) for maximum exhaustion before rinsing. Whether it is better to add salt before or after the dyeing temperature has been reacheddepends tosome extent on the ease of making the addition. But to delay until some of the dye is already on the fiber is probably best, since it minimizes the possibility of unlevelness. The amount of salt used varies from 5 to 10 grams per liter for pale shades up to 10 to 20 grams per liter for heavy shades. The absolute amount of salt used per unit weight of fiber varies with the liquor-togoods ratio of the dyeing. For example, a heavy shade dyed at a liquor-to-goods ratio of 5:l will require 5 to 10% salt owg, whereas the same shade dyed at a 20:l liquor-to-goods ratio will require 20 to 40% salt owg. Either way, exhaustion of greater than 95% is normal. Compared with many reactive dyes, which have little intrinsic substantivity, these amounts of salt zre low and the exhaustion is very high-both of which are desirable from the environmental (effluent) standpoint. Low Sulfide Reduced Dyes Low sulfide reduced dyes can be characterized as requiring no polysulfide, but because of their lowered salt content, require somewhat more salt to exhaust properly. In a published jet dyeing procedure which calls for a 1O:l liquor ratio (7), the dyes are fully reduced using 12% (50%) caustic soda owg and 12% proprietary reducing agent owg, which is activated by raising the temperature to 75C (170F) for 5 minutes; the salt, 35% owg, or about 30 co3 Vol. 24, No. 4

3 Anril 1993 fm grams per liter, is added, following the same procedure recommended for direct dyeing, in three successive portions, each double the one before (5%, 10% and 20% owg); the temperature is then raised to 9OC (195F) followed by dyeing, cooling and the normal succession of rinsing, oxidation, soaping, rinsing, etc. Continuous Dyeing Processes Since their introduction in the late 193Os, pre-reduced leuco-sulfur dyes (sulfur liquids) have enjoyed a real processing advantage over vat dyes, which was held in check by the ingenuity of the vat dye manufacturers in devising competitive procedures. The advantages were that the dyes did not need to be dissolved in the dyehouse and that in continuous processing a drying step could often be saved. However, in the last two decades, as the yardages of individual color orders got shorter and shorter, sulfur dye makers and their customers had to face a problem caused by the high level and range of substantivities of leuco-sulfur dyes in the padding operation. This was the difficulty of rapidly establishing a consistent shade. After a brief review of the continuous dyeing of sulfur dyes, the padding operation will be considered in more detail. Conventional Processing (Pad-Steam) Besides. leuco-dye, there is no need for additives other than polysulfide and penetrant.in the normal continuous dyeing of sulfur liquid dyes on cellulosic fibers. The procedure is a foreshortened version of the application method for vat dyes, requiring only the following pieces of functional equipment: pad; roller-steamer; washboxes, divided into at least three groups for rinsing, oxidizing and washing, respectively; and drying cans. The goods are padded through the liquid sulfur dyebath at anywhere from 38 to82c (100 to 180F), squeezed and passed into the steamer for 30 to 60 seconds in saturated steam at 102 to 104C (215 to 218F); Le., a little over atmospheric boil. The goods are then rinsed, preferably at temperatures which rise from about 40C (104F) in the first washbox to 60C (140F) just prior to oxidation. The goods are then oxidized in 5 to 10 grams per liter of a commercial mixture of sodium bromate catalyzed by sodium vanadate with 1 to 2 grams per liter acetic acid, controlled to give ph of about 4. Oxidation is followed by asvigorous washing as can be squeezed out of the remaining washboxes. With blacks it may include a soaping and a final rinse through dilute soda ash solution. There is a distinct strategy associated with the optimal use of the available washboxes. Some place the emphasis on removal of loose color prior to oxidation, some on the removal of such color after oxidation. The former would seem preferable. Alternative Processing (Pad-Dry-Steam) The overall appearance of dyed cellulosic goods can sometimes be improved (at the cost of the intermediate drying) if the goods are first padded, then dried, then repadded through a reducing bath prior to steaming. Otherwise, the same considerations apply as in conventional processing. Padding When cellulosic fabrics first are padded through solutions containing substantive anions, such as leuco-sulfur dye anions (as in sulfur liquids), there are several consequences. The goods are wet-out by the solution, known as the pad bath or pad liquor; someof the substantiveanion (dye) is preferentially sorped by the fiber surfaces, lowering the concentration of this anion in the liquor wetting the goods; some of the diluted liquor is returned to the pad trough when the excess liquor is squeezed from the fabric, at the nip; the pad trough becomes progressively more dilute; subsequent goods passing through the diluted pad liquor pick up less dye, and for some period of time the goods become progressivelylighter in shade. Meanwhile, suppose that further pad liquor is being added to the pad trough from a feed tank at the original concentration, to replace the liquid being carried off by the fabric. Eventually the rate at which dye is being introduced into the pad from the feed tank (to maintain a constant volume) will becomeequal to therateat whichdyeis being removed by the fabric, and a steady-state, or dynamic equilibrium, will be achieved. But the amount of dye on the goods leaving the pad will be less than that on the goods which went through the pad initially, Le., the concentration of the liquor in the pad trough will settle down to a value less than that in the feed tank. In the meantime several hundred yards of goods may have been run with gradually decreasing depth of shade and perhaps even changing hue. Dyers have known about these considerations for a long time. They have known that they are only important when applying dye anions of high substantivity, such as those of leuco-vat dyes and sulfur liquid dyes, and they have developed the art, or skill, of partially overcoming the problems. For example, if the steady-state condition has the liquor in the pad trough at a lower concentration than that in the feed tank, it would be reasonable to start the process with this condition already satisfied, hoping that, as a result, the concentration in the pad will stay more or less constant. It has also been well known that decreasing the size of the pad trough diminishes the length of time needed to reach a steady state during running goods continuously. Even the language of a continuous dyehouse reflects these phenomena with inter-related phrases such as: Strike Rate: The speed at which dyes transfer preferentially to the goods, due to their high substantivity. 0 Affinity Factor: The extent to which some dyes prefer the fiber to the pad liquor (another reference to substantivity). 0 Feeding-Up: Increasing the concentration of dyes in the feed tank to maintain a constant (lower) concentration ofdyes in the pad trough during dyeing. 0 Tailing Effect: A gradual changing of the shade or depth of the continuously dyed goods, with time. Some basic research in this area was conducted in the early 1950s by Marshall (8) quoted in (9). Practical implementation of the work required first, the wide use of continuous dye ranges and then the trend towards shorter yardages of single color orders for continuous dyeing. This latter point makes it imperative that as little goods as possible are run (with tailing) before the pad liquor reaches the steady state. It helps to think of the goods leaving the padder as having undergone a batch dyeing process of short duration in a dyebath where the dye has very high substantivity. The following factors influence the achievement of the steady state: 0 Pad Volume: Theory and practice agree that the pad liquor must be turned over 1.5 to 2.0 times to achieve equilibrium; but although this implies that the trough must be small, it must be big enough to allow for adequate wetting of the goods and little or no cross-shading (see later). There is a lower limit to how small the pad trough can be. e Wet Pickup/Cloth Weight: Both directly influence the rate at which the pad liquor is turned over. Range Speed: This influences both therate of pad liquor turnover and the time of exposure of dye to the goods; ie., the immersion time. With a travel from dip to nip of one meter, on a range running at 60 meters per minute, goods will only be exposed to the pad liquor for one second before the nip. Goods passed through typical sulfur liquid pad liquor will pick up a certain amount of dye in this time, but can pickup about 80% more in two seconds and 120% more in three seconds. This means that the level of the pad liquor and the speed of the range must both be carefully controlled, or the depth of shade will vary. Such variation will destabilize any pad liquorlfeed tank concentration equilibrium which may have been achieved. 0 Affinity Factor: If a nonsubstantive material (NS) in aqueous solution of known concentration (Cgrams per liter) is padded onto fabric, its concentration on the goods leaving the pad (% owg) can be calculated from the relationship:

4 an fyy Vnl 34 Nn A Sulfur Dyes a) benzothiazole b) thianthrene a) quinoneimine b) indophenol Fig. 1. Groups formed in sulfur dye making. Fig. 2. Groups introduced by intermediates. (%owg) = (%wpu) x (c) i 1,000 where % wpu is the percentage increase in the weight of the goods due to the solution picked up during padding. Suppose the concentration of (NS) on the fabric is 0.8% owg. If a substantive dye (S) at the same pad liquor concentration were to be padded onto the same goods under the same conditions, the concentration of (S) on the fabric would be greater than 0.8% owg; e.g., it might be 1.2% owg. The affinity factor is the ratio of the actual dye concentration (present on a fabric after padding) to the concentration which would have been there if the dye had not been substantive. The affinity factor for the dye in the above example would be 1.5, (Conc.(S) i Conc. (NS) or ). Dye Concentration/Temperature: Both these variables affect the rate of dyeing. With increasing dye concentration, the dye anions tend to be less and less efficient at competing for the fiber; they compete and interfere with one another as well, and gradually cease to behave as efficiently as single anions. As a result, the affinity factor, like the percentage exhaustion at any given time, falls with increasing concentration. Raising the temperature should increase the rate of exhaustion, the activity of the dye anions and the affinity factor, although the size of increase will vary from dye to dye. When it is possible to run dark shades on very absorbent, heavyweight goods, with high wet pickup, at great speed, through low volume pad troughs with good liquor level control-luck is on your side-the problems of tailing, affinity factor, strike rate and feed-up will be minimized. But such situations are rare. Even more important is that individual dyes have their own unique behavior and affinity factors. Dyers have traditionally had three options: 0 To run the feed and the pad liquor at the same concentration until equilibrium is established. This approach accepts tailing (and second quality) and still requires great experience in guessing what the shade will be when the tailing ends. 0 To run the feed at a higher concentration than the pad bath. This is done by feeding the pad and then diluting the pad liquor with water before beginning the run. Only the experienced know how much dilution is necessary, and it varies from dye to dye. 0 To run the pad trough and feed tank with different formulations calculated to start and run without tailing. Dyers have reduced continuous sulfur dyeing to an art, but very few dyers have the experience for such an attempt. Given the appropriate dye range, shade and fabric parameters, it is now possible to take the guesswork from eliminating the tailing when dyeing sulfur dyes. Access is available to results from a computer program based on relationships established nearly40 years ago (8,9). While still on the complex subject of padding, it is worthwhile to point out padding variables which can be controlled to reduce the problem of cross shading or side-center-side shade variation. The first is the position of the manifold for the pad liquor feed from the mix-tanks. This could be placed between the fabric and the fabric entry side of the pad trough; in the middle of the trough with fabric on both sides; or between the fabric and the fabric exit side of the pad trough. The results indicate these positions give most, less and least cross shading, respectively. The second is the width of the pad trough relative to that of the fabric. Experience shows that when the edges of the fabric are far removed from the sides of the pad trough, cross shading is minimized. But when the fabric is nearly as wide as the pad trough, the cross shading is marked. This result appears to be caused by local concentration differences of dye anions due to fluid flow (circulation) patterns in the pad box. Of course, any attempt to reduce cross shading by increasing the pad width will automatically increase tailing by increasing the pad volume. Dyers, like politicians, must be skilled in the art of compromise. Special Problems One problem with sulfur dyed goods, but seldom experienced, is acid tendering. In severe conditions of heat and humidity, some few sulfur dyeings, notably black, can generate a small amount of sulfuric acid within the cellulosic fibers, leading to tendering. AATCC Test Method , Ageing of Sulfur Dyed Textiles: Accelerated, is used to determine whether sulfur dyed textile materials deteriorate under normal storage conditions (IO). A combination of thorough washing before oxidation, alkaline rinsing in the last washbox or even resin finishing appears to have eliminated complaints of tendering for all practical purposes. Chemistry The chemistry of the di- and polysulfide linkages and their reduction has been dealt with already, as has the fact that most sulfur dyes have an unknown constitution. It should suffice to touch on the two principle kinds of intermediates used in making sulfur dyes, and the two manufacturing process types, while indicating some of the structural features known to be present in sulfur dyes. Bake-Pot Colors A miscellaneous group of chemicals, some of which contain both methyl and nitro or methyl and amino groups substituted into aromatic rings, can be dry heated (baked) at 200 to 300C (390 to 660F), with sulfur, with or without sodium sulfide, to give sulfur dyes. The resulting dyes are mostly browns, oranges or yellows, all of which contain aromatic ring structures substituted by thiol and polysulfide groups, -SH,-S,-. Some have been shown to include the benzothiazole group Fig. la but therest of thestructuresareessentially unknown. Indophenolic Colors Indophenolic colors, known also as quinoneimines, are normally produced by refluxing aqueous or alcoholic solutions of selected organic compounds with alkaline polysulfides. These organic starting materials can generally be drawn as shown in Fig. 2. Here the bridging group (X) is optional. If it is present, it may be an imino group, -NH-, or a thioether group, -S-. (R), indicates a number and variety of possible substituents. The double arrows indicate that the reduction, which converts the quinoneimine (structure a) to the indophenol (structure b), is reversible by oxidation. The only new structure (beside those aromatic thiols and polysulfides) known to be formed by the refluxing process is the thianthrene ring shown in Fig. 1 b. However, the key to many of the properties of the red-brown, blue, green and black indophenolic sulfur colors is that the basic structure of some of the intermediates (Fig. 2) stays intact through the sulfurization step, to yield dyes which have not only functional groups (Fig. 1, Part 1) which can be reduced and re-oxidized (-S-S , but also the quinoneimine groups in the chromophore itself. Such sulfur dyes give very different colors in the leuco form from those in the

5 pigmentary form (cf. vat dyes) whereas with bake-pot colors the color differences between reduced and oxidized forms are quite small. Solubilized Sulfur Dyes Unlike the leuco sulfur dyes, solubilized sulfur dyes are not the reduced form of the sulfur pigment but are a reaction product of pigmentary di-sulfides with sodium sulfite or bisulfite to give the water soluble sodium salts of aromatic thiosulfates: D ye-s-s-d ye+ 2.Dye-S-S03-.Na" Eq. 1. These water soluble derivatives (known as a Bunte Salts) have no substantivity for cellulose. But the black salts give a great deal of color per dollar and are clean and easy to use for paper dyeing, where they are precipitated as insoluble salts by the fillers used in the paper making. To obtain the substantive reduced form, it is only necessary to add a suitable reducing agent (Eq. 4, Chapter 4, Part 1) to give the normal thiolate leuco-dye anion: Dye-S-SO3- + NazS - Dye-S- + NazS203 Eq. 2. Like solubilized vat dyes, these products have almost disappeared from the textile marketplace in the U.S. Physical Form Since most conventional sulfur dyes in the U.S. are sold in pre-reduced liquid form and since sulfurized vat dyes are sold as readily dispersible powders or pastes (cf. vat dyes), there is little further to discuss. Standardization Sulfur dyes are almost invariably standardized by dyeing methods, where a standard and a sample are padded under the same conditions and the relative strength and shade are assessed visually and/or instrumentally. They cannot be usefully standardized by transmission measurements on their reduced solutions for two reasons: most reduced sulfur dyes are yellow in solution, and therefore color discrimination is difficult if not meaningless; and most commercial sulfide and polysulfide solutions are also yellow. Review Is it old fashioned to dye with sulfur dyes? This question was asked rhetorically (and in German) by one of the leading sulfur dye experts in He answered then, and others have since, with a resounding, "No!" There are still problems to be handled regarding effluent treatment. While some problems are unique to sulfur dyes, effluent problems of one sort or another besiege many dye application categories at this time. For example, fiber reactive dye manufacturers are wrestling with low fixation and high levels of color and salts in the effluent. In all cases, if the public requires a cleaner environment, who is going to pay the piper? Nevertheless, whenever economy in heavy shades, with moderate to good lightfastness and good to excellent washfastness are required on cellulosic fabrics, sulfur dyes will be there. co3 References (I) AATCC Buyer's Guide for the Textile Wet Processing Industry, published annually as the July issue of Textile Chemist and Colorist. (2) Colour Index, Society of Dyers and Colourists and AATCC, VoL4,ThirdEdition, (3) ColourIndex,Vol. 3, ThirdEdition, (4) AATCCTechnicalManual,Vol. 61,1992,~94. (5) The Dyeing of Cellulosic Fibres, edited by Clifford Preston, Society of Dyers and Colourists, 1986,Chapter 7. (6) Tigler, L., Textile Chemist and Colorist, Vol. 12,No.6.June 1980,p43. (7) Cook, F. L., Textile World, Vol. 141, No. 3, March 1991.~68. (8) Marshall, W. J., Journal of the Society of Dyersand Colourists, Vol. 71, January 1955.~13. (9) Sherrill, W. T., Book of Papers AATCC International Conference and Exhibition, Nashville, p239. (10) AATCC Technical Manual, Vol p80. Portable spectrophotometer The performance of a b6nchtop unit in the palm oflyour hand Finally, a spectrophotometer that moves out of the laboratory and onto the production floor for convenient on-site color measurement. The X-Rite 968 SpectroPhotometer is built to provide the performance expected from a color measurement instrument. Its rugged design ensures accurate measurements, even in a production environment. This remarkablv comoact instr 'U I ment power, too. It supports several spectrally-based color difference calculations, including automatic CMC delta E tolerancing. Because the 968 is battery-powered, it can remotely read and store up to 500 color measurements in memory. The stored data can be downloaded into a personal computer with our Spectro- Start'" software for complete data analysis of your spectral measurements. Learn how this hand-held spectrophotometer can work in many of your textile applications... at a very affordable price. Call today for more information th Street, S.W. Grandviiie. Michigan Phone: (616) Fax: (61 6) Telex: Circle 11 on Reader Service Card 1. X-Rite" and SpectroStart" are trademarks of X-Rite. Incorporated. --