TextileChemist and Colorist December1977/ Vol.9, No. 12 O)J

OlneyMedalAddress

A Review of Disperse Dyes

By J. M. STRALEY,Tennessee Eastman Co., Kingsport, Tenn.

HE textile industry, particularly its plored and used briefly. Water solubi- T dye segment, should take great lizing groups which would be removed pride in the fact that organic chemis- in the dyebath were attached to the try, with all its later benefits to man- dye molecules. However, release of kind, was its child. Without the incen- these groups from different molecules tive to color our garments and furnish- varied greatly, and the pH changes nec- ings, the advances. in chemistry of essary affected the tenacity of the fiber, aromatics would have been delayed which could not afford to lose any of considerably. For centuries man had this property. Saponification of the been dyeing fabrics with vegetable, fiber in order to utilize cellulosic dyes shellfish and insect derivatives, but was tried, but, here again, control ABSTRACT their constitutions had not been even proved to be impossible. Hydrophilic guessed at. groups, such as sulfato, were attached Disperse dyes have been the chief Suddenly, in the middle 1800's, to the dye molecule, but the products coloring matter for hydrophobic fibers, chemists began the synthesis and iden- were useful in only weak to medium beginning with cellulose acetate in tification of the structures of natural shades. The use of solvents such as the 1920's. The dyes were relatively and man-made colors. The skill of methanol to swell the fiber survived simple and were required to display only a few fastness properties. Since those ancient scientists, von Hofmann, much longer than any of the other then, requirements of the trade have Perkin, von Bayer, Griess, Caro, Fried- methods just discussed. demanded higher dye performance. At ander, Scholl, and all the rest, never Chemists from several British com- the same time, the more drastic dyeing ceases to amaze me. They had no thin panies found that grinding the dye with conditions and improved methods layer chromatography, microanalysis, surface active agents (one of the first which developed along with the newer fibers have allowed the use of more no nuclear magnetic resonance, infra- was sulforicinoleic acid) and the pres- red or mass spectroscopy, yet they ence of a slightly hydrophilic group complex molecular structures, although many acetate dyes are still used on came up with accurate structures and such as hydroxyl on the dye molecule polyesters and nylon. reasonable syntheses for some of the was the answer. This system is still in most intractable compounds then use today. Although not then apparent, Azo, anthraquinone, o-nitrodiphenyl- known. Nor, as far as I have been able it turns out that this combination pro- amine, methine and quinophthalone to determine, did they have the bene- vided the transitory water solubility chemical classes provide the major commercial disperse dyes. None of fits of job description, skill analysis, necessary to invade the fiber. Many these is a new chromophoric system, five-year plans, or governmentally im- colored substances can be prepared in but intensive investigation and novel posed environmental and safety stan- extremely fine aqueous dispersion but elegant synthetic methods have re- dards. without some water solubility no dye- sulted in dyes exhibiting superior prop- The first hydrophobic fiber, cellulose ing occurs. Some may say that to call erties, especially on the newer fibers. acetate, appeared in the 1920's and was this process solvent extraction is an Disperse dyes are also used in the prized for its luster and the drapability oversimplification, but in any case, the newly popular transfer print process, and hand of fabrics constructed from product is a solid solution. which requires coloring matters of poor sublimation fastness, a source of it. But the dyes in use for the natural In general, commercially successful trouble in conventional printing. hydrophilic fibers, cotton, wool and dyes must possess properties other silk, had no affinity for the newcomer. than color; lightfastness, washfastness, KEY TERMS These dyes were almost all ionic sub- resistance to atmospheric contami- stances, at least at one stage in their nants, changes in dyebath pH, etc. Cellulose Acetate application water soluble, and the new The dyes for man-made fibers also Disperse Dyes fiber was only slightly stained by any require resistance to sublimation. They Dyeing of them. It was not a question of find- have measurable vapor pressures and Hydrophobic Fibers ing new chromophoric systems-these tend to leave the fiber under conditions Olney Medal Address were almost all known. of pleating, ironing, heatsetting, etc. Several methods of dyeing were ex- A requirement for dyed fibers in gen-

276/11 OlneyMedalAddress Obviously, we cannot run a wear less sensitive to hydrolysis. Because test on human beings for every experi- the fiber is often heated to tempera- mental dye-fiber combination. But how tures far above those used with the can we compensate for the lack of older fibers dyes of extreme resistance human flesh behind our dyed fabrics? to sublimation must be used. Because What was the effect of the temperature of the popularity of the durable press or chemical content of New York eral is brightness. Therefore, it be- process, the dyes must not be sensitive comes somewhat frustrating to the dis- Finger Lake water on the boss's wife's to the acidic metal salts used as cat- perse dye chemist to find that someone bathing suit? Usually, accelerated tests alysts. ("Catalyst" seems to be a strange has paid money to add delusterants to provide at least a comparative view of term for a substance which comprises the fibers with which he must deal. actual performance. Why the enor- 15-20% of the total solids in the resin Actually, we should not refer to the mous discrepancy in the case of the mix.) Because the substance is a poly- fastness of a dye but rather to that of C.!. Disperse Blue 27-experimental ester/cotton blend, the dyes should not the dye-fiber system. These vary con- polyester system? stain cotton since disperse dyes or- siderably. A dye that is fast to light on The first disperse dyes were of rather dinarily have no lightfastness on cel- polyester is often fugitive on nylon. low molecular weight, because temp- lulose. Barre is a substantial problem Dyes that fade rapidly on cellulose eratures higher than 80C affect the with polyesters, also. acetate when exposed to the oxides of textile properties of cellulose acetate, Polyesters are not very receptive to nitrogen show little deterioration on and of basic or phenolic character. dyes used in an aqueous bath at atmo- nylon or polyester. These differences They were chemically from the azo, spheric pressure. For efficient dyeing are found within even a chemical class. anthraquinone, and o-nitrodiphenyl- rates the glass transition temperature of the fiber must be exceeded. Several Quite often dyes fast to light on poly- amine classes. The last was chiefly re- methods are used to arrive at this con- (ethylene terephthalate) are unsatisfac- sponsible for yellow shades; reds and blues came from the other two classes. tory on poly( 1,4-cyclohexylenedime- dition. The temperature can be in- thylene terephthalate) and vice versa. The major problem was the blues. creased by dyeing under pressure or There was no lightfast, gasfast blue. the dye dispersion can be padded on The azo blues showed poor lightfast- and then subjected to dry heat-a very Accelerated Tests ness, while the lightfast anthraquinones popular method for blends with cotton. Much reliance as to actual perfor- quickly faded in the presence of the Both of these methods require special- mance has been placed on accelerated oxides of nitrogen. In the early 1950's, ized equipment. The other approach is fastness tests. In many cases these are two blues, one from the naphthazarin to use a carrier, usually a water-in- reliable but once in a while an excep- class (1), and an anthraquinone (2) soluble organic substance, which tion appears. About 25 years ago our overcame this difficulty. Actually, loosens the molecular structure of the first director of research made in in- these were not completely gasfast, but, fiber, allowing penetration by the teresting observation concerning his since they faded on tone, the change dye molecule. However, many of the wife's acetate bathing suit. The fabric was much less noticeable than that of most effective carriers are toxic and was a print, chiefly of C.I. Disperse the earlier compounds which reddened others affect the lightfastness of the Red 1 on a white ground. The apparent rapidly. dyeings. All of them are difficult to lightfastness was much better than our The second hydrophobic and first contain or destroy in the mill so that Fade-Ometer results indicated. The truly synthetic fiber on which disperse adherence to air or water pollution floral pattern was not a busy one so dyes were used was nylon-one of the codes may be difficult. optical illusion was ruled out. We had most versatile fibers yet invented. Ac- no Weather-Ometer then, so we de- tually, acid wool dyes adequately en- AzoDyes vised all sorts of intermittent wetting hance this fiber as far as fastness prop- schedules on our Fade-Ometer for 15 erties are concerned, but the problem The two major classes of disperse of our commercial dyes. The result of barre caused by nonuniform con- dyes are the azos and anthraquinones. was confusion. Each dye had its own ditions in preparation of melt-spun The azo dyes are prepared by a simple behavioral pattern-there was no ap- fibers is best covered by some disperse reaction of nitrous acid with an aro- parent correlation with color, struc- dyes. It may have been this fiber that matic amine followed by coupling to ture, water solubility, or any other prompted the saying that the dyehouse a receptive compound-at least it looks measurable property. Unfortunately, is expected to correct everyone else's simple on paper. This process is very the need for finding new saleable dyes mistakes. Because of nylon's extra- sensitive to temperature, solvent, ma- shelved this project permanently. ordinary acceptance of most classes of terials of construction of the reaction During the intense investigation of dyes and the fact that the dyebath can vessel, impurities in the starting ma- new polyesters during the 1950's, an be run at the boil, dyes of higher mo- terials and sometimes methinks the economically attractive prospect was lecular weight and increased negativ- phases of the moon. The overall re- discovered. However, lightfast dyes for ity can be used. Here again there is a action is a competition between the it were difficult to obtain-especially problem with disperse blues. The one decomposition of the intermediate the blues. C.!. Disperse Blue 27 was most widely used is the ancient and diazonium and its coupling to the the best available, and let me tell you expensive C.I. Disperse Blue 7. There designated substance. Quite often the it was terrible -on the Fade-Ometer. is no lightfast blue that completely coupler itself encourages decomposi- Not only did it fade badly, there was withstands "Gulf Coast Fade." This tion of the diazo. While on a 100% a horrible dark reaction. Exposed dye- fault varies with the method of tex- basis azo dyes appear to give a high ings after a few months storage dis- turizing the fiber and can be duplicated tinctorial yield, the commercial prod- integrated at the touch of a fingernail. by exposure to ozone at high humidity. uct is often contaminated with de- In the meantime, wear test garments composition and side reaction prod- dyed in dark brown and navy shades Polyesters ucts that cause off-colored goods and in which C.I. Disperse Blue 27 was the impaired fastness properties. major component had been prepared. The advent of polyesters, the most Many of the azo dyes are derived On these suits after 10 years of normal important hydrophobic fibers, at least from homocyclic diazos. This was true wearing not only was there no fabric as far as disperse dye use is concerned, in general of the early members of the disintegration but no apparent loss of both increased the number of and in- series. Lightfast blues were not then blue. How many desirable products tensified the conditions which the dyes to be found, but a recent elegant have we discarded because of mislead- must withstand. Because of the higher method of introducing cyano groups ing results of accelerated test methods? dyebath temperatures, dyes must be into the molecule by replacing halogen

12/277 OX) Vol. 9, No. 12 groups by means of copper cyanide- The first commercial gasfast anthra- is no universal dispersing agent. Fur- solvent complexes (3) has produced quinone blue of practical dyeability on ther, mixing some dyes prepared with some excellent dyes for polyesters. acetate was C.I. Disperse Blue 27 (2). different dispersants may cause trouble Some of these dyes were known but no It is a modification of c.!. Disperse in dyeing. Agents added to the bath inexpensive synthesis for them was Blue 62, an ancient compound (7), for wetting and other purposes may be available. which later came into use on poly- detrimental to the desired result. While About 1950 serious consideration of esters. Although these are also derived much has been done privately to solve the use of heterocyclic diazos began. from polyfunctional anthraquinones, these antagonisms, much 'also remains Dyes from aminothiazoles (4) gave the reaction is much more easily con- to be done. It is no longer reasonable beautiful blue dyes, and, although the trolled, but impurities are also possible to let price be the dominant factor in yields were low and the lightfastness here. selecting the substances necessary to poor, their high extinction coefficients The higher resistance of polyester to allow our expensive dyes to penetrate and ready dischargeability made them drastic dyebath conditions has allowed the fiber. commercially attractive. A few posi- the use of dyes of higher molecular Sometimes a major fault can be tively substituted benzothiazoles (5) weight, particularly with the newer converted to an advantage. This has had been in use for dischargeable red blues. The chemistry of the extremely happened in the case of the heat trans- to violet shades, but their lightfastness popular C.!. Disperse Blue 73 has been fer printing process. Disperse dyes of was only mediocre. The use of nega- known (9) for many years. While this inferior sublimation fastness are print- tively substituted benzothiazoles (5) dye does not have outstanding fastness ed in a suitable vehicle onto paper. considerably improved this property properties, its bright shade and good The textile printer then heats the paper and gave some beautiful reds still in build-up under a variety of conditions in contact with a fabric, usually poly- use today. Extension of this investiga- make it very attractive. The brightest ester, to obtain the saleable product. tion to the thiadiazole series has given turquoise shades for polyester are con- The advantages to the textile printer beautiful bright reds in use on poly- tributed by C.I. Disperse Blue 60 and are the simple machinery required, amides. related types (10). They are prepared elimination of expensive skilled labor, The coupler portion of the azo dye by several methods, all of which are excellent register of the finished goods, molecule has also received intensive outstanding synthetic developments. and reduced contamination of the en- study. In particular, modification of the Some of the workhorse reds, such as vironment. The more obvious dis- old 2-alkoxy-5 -acetamino-N,N -dialky- c.!. Disperse Red 60 (8), have long advantages are reduced sublimation lanilines used in the early days for been available. These are l-amino-2- fastness, the generation of waste paper, blues (of medium lightfastness) has re- alkoxy (or aryloxy)-4-hydroxyanthra- and the fact that the conventional sulted in very popular navy blues (6) qui nones and provide beautiful, bright, printer cannot use his equipment on all of adequate lightfastness for polyesters. red to pink shades. classes of fiber. Heterocyclic couplers, particularly in From the beginning, yellow dyes the pyrazolone series, have given good from o-nitrodiphenylamines have been commercial yellows. very useful because of their excellent EnormousProgress lightfastness. Examples are c.!. Dis- perse Yellows 33 and 42, which are The years between 1923 and 1977 Anthraquinones also old chemicals (11). In general, have seen enormous progress in the these dyes are prepared by condensa- textile use of hydrophobic fibers. The The anthraquinones are usually not robust polyamides and polyesters have as cheaply prepared as the azo dyes tion of an aromatic amine with an o-halonitrobenzene in an inert solvent. penetrated areas not even dreamed of and usually have lower tinctorial by the frail cellulose acetate. And the power. These initial disadvantages may Workhorse yellows such as C.!. Dis- perse Yellows 54 and 64 for polyesters simple dye chemistry born in 1923 be compensated for by much better has grown in stride with every end- fastness properties and often bright- come from the quinophthalone series use for these fibers. ness. In many cases this latter effect (12). These are derived from the an- The blemishes of inadequate resis- is due to fluorescence. Although a few cient Quinoline Yellow, without the sulfonic acid group. Furthermore, the tance to light, poor gasfastness, dull- disperse azo dyes are fluorescent, none ness and sublimation have almost dis- has achieved commercial status. Here presence of a hydroxy group in the 3' again, the written reactions are de- position (on the quinoline moiety) has appeared. Old chemicals, new dyes ceptively simple. Some of our most resulted in much better lightfastness and improved methods of synthesis properties. have conspired to this end and will popular blues are named as homo- continue to do so with each new re- geneous products, while actually they The methine class of dyes contains quirement. CO) are mixtures. One of the most popular some of the brightest and fastest dyes on cellulose acetate, C.!. Disperse Blue for acetate and polyesters. Their struc- 3, is usually prepared by condensation ture gives them a tendency to hydro- References between two aliphatic amines and 1,4- lyze in the dyebath at pH above about 5.5, but recent structural modifications (1) Sandoz, U.S. Patent 2,553,048 (May 15, dihydroxyanthraquinone. Instead of 1951). only the three logically expected prod- have increased their affinity for the (2) Eastman Kodak, U.S. Patent 2,641,602 fiber so they are out of the dyebath (June 9, 1953). ucts, thin layer chromatography (3) Bayer, U.S. Patent 3,962,209 (June. 8, showed the presence of 10 to 18 com- before serious hydrolysis can occur. 1976). ponents, depending on the reaction They are readily prepared by conden- (4) Eastman Kodak, U.S. Patent 2,659,719 (Nov. 17, 1953). conditions. Here also the purity (or sation of p-N,n-disubstituted amion (5) Eastman Kodak, U.S. Patent 2,785,157 lack thereof) of the starting materials aromatic aldehydes with active methy- (Mar. 12, 1957). (6) Sandoz, U.S. Patent 3,178,405 (Apr. 13, is extremely important. lene compounds such as malononitrile. 1965). On cellulose acetate, the mixture These are all greenish yellow, and most (7) Bayer, German Patent 89,090 (June 1895); Fried/ander, Vol. IV, p314. just described appears to have better of them are highly fluorescent. (8) C%ur Index, 3rd Ed., Society of Dyers affinity than any of the isolated pure and Colourists, London, and AATCC, Re- components. This effect holds for search Triangle Park, N. C. Vol. 6, 1975, p6402. Dispersing Agents (9) Grassel1i Dyestuff, U.S. Patent 1,652,584 many mixes of closely related struc- (Dec. 13, 1927). (10) Du Pont, U.S. Patent 2,628,963 (Feb. 17, tures but should not be considered as The role of dispersing agents is not 1953); BASF, U.S. Patent 3,137,699 (June 16, general for all mixtures. On the con- 1964). completely clear. Their primary pur- (11) Fischer, P., Berichte der Deutschen trary, some mixes of differing molec- pose is to force the dye into the dye- Chemischen Gesellshaft. Vol. 24, 1891, p3794. ular structure seem to impede dyeabil- bath in a condition favorable for (12) BASF, British Patent 865.308 (Apr. 12, 1961); BASF, German Patent 1,229,663 (Dec. I, ity. problem-free dyeing. However, there 1966).

December 1977 CO) 278/13