Disperse Dyes on Cellulose Acetate

With simple partition the situation is comparable to the partition of a solute between two solvents. The bonding forces involved between uncharged dye and uncharged fiber, and uncharged dye and uncharged solvent are considered to be the same. The dye is sometimes referred to as in soHd solution in the fiber. This type of isotherm is found in practice with disperse dyes on cellulose acetate and polyester. It represents the dyeing situation with the minimum restrictions for the dye to enter the fiber the only restriction is when the fiber solution becomes saturated. 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

Table 3.18 Times of half-dyeing of disperse dyes on cellulose acetate at 85 °C [115]...

For printing disperse dyes on cellulose acetate, dyes are selected according to their colorfastness on 2.5-acetate and triacetate. Fixation is carried out for 2.5-acetate in saturated steam at 102°C for 20-40 min for triacetate 20-30 min at 0.25 MPa (127°C) or in superheated steam 8-6 min at 165-185 °C. 

Table 3.11 Partition coefficient and saturation value of disperse dyes on secondary cellulose acetate [85]...

Measurements of aqueous solubility and partition coefficient between cellulose acetate and water were compared for thirty disperse dyes and an approximate inverse relationship was postulated [60]. This can only be valid to a limited extent, however, because the partition ratio also depends on the saturation solubility of the dye in cellulose acetate. This property varies from dye to dye and is not directly related to aqueous solubility. The solubilities of four dyes in a range of solvents were compared with their saturation values on cellulose acetate. Solubilities in benzene showed no significant correlation. With the other solvents the degree of correlation increased in the order ethanol < ethyl acetate < 20% aqueous diethylene glycol diacetate (CH3COOCH2CH2OCH2CH2OCOCH3). The last-named compound was suggested as a model with polar groups similar to those in cellulose acetate [86]. 

The yield of disperse dyes on polyester is limited by their slow rate of diffusion into the fibre rather than by inherently low substantivity. If dyeing times are sufficiently long, saturation values on polyester approach those on cellulose acetate and often exceed those on nylon (Table 3.29 for structures of these dyes see Tables 3.14 and 3.18). 

Dyes for cellulose acetate are relatively simple molecules, typified by Cl Disperse Red 15 (6.39 X = OH), Cl Disperse Violet 4 (6.39 X = NHCH3) and Cl Disperse Blue 3 (6.40), the last-named being manufactured from leucoquinizarin and the appropriate amines. The unsymmetrically substituted product inevitably contains significant amounts of the related symmetrical compounds. The widely used Cl Disperse Blue 3 is known to cause skin sensitisation when on nylon [17] and can also provoke an allergic reaction [18]. Bright red 2-alkoxy-l-amino-4-hydroxyanthraquinones, such as Cl Disperse Red 4 (6.41), can be obtained from l-amino-2,4-dibromoanthraquinone by hydrolysis to give l-amino-2-bromo-4-hydroxyanthraquinone (Cl Disperse Violet 17), which is then condensed with the appropriate alcohol. 

Uncharged styryl (methine) disperse dyes were originally introduced to provide greenish yellow colours on cellulose acetate fibres. One such dye still in use is Cl Disperse Yellow 31 (6.226), which is made by condensing 4-(N-butyl-N-chloroethylamino)benzaldehyde with ethyl cyanoacetate. Suitable compounds for polyester usually contain the electron-accepting dicyanovinyl group, introduced with the aid of malononitrile. An increased molecular size leads to improved fastness to sublimation, as in the case of Cl Disperse Yellow 99 (6.227). A novel polymethine-type structure of great interest is present in Cl Disperse Blue 354 (6.228), which is claimed to be the most brilliant blue disperse dye currently available [85]. 

On cellulose acetate, developing dyes are still used, but for black only. Although dyeings are produced that are especially fast to wet treatments, the process is more tedious than dyeing with direct disperse dyes. 

For cellulose acetate-viscose or cotton fabric blends, cross-dyeing can be done, because cellulose acetate is unstained by many direct dyestuffs and because disperse dyes used for acetate do not dye viscose or cotton. Two-color and resist effects can be obtained on such blends from one dye-bath [37,77]. 

Phloroglucinol is Hsted in the Colourindex as Cl Developer 19. It is particularly valuable in the dyeing of acetate fiber but also has been used as a coupler for azoic colors in viscose, Odon, cotton (qv), rayon, or nylon fibers, or in union fabrics containing these fibers (157). For example, cellulose acetate fabric is treated with an aromatic amine such as (9-dianisidine or a disperse dye such as A-hydroxyphenylazo-2-naphthylamine and the amine diazotizes on the fiber the fabric is then rinsed, freed of excess nitrite, and the azo color is developed in a phloroglucinol bath at pH 5—7. Depending on the diazo precursor used, intense blue to jet-black shades can be obtained with excellent light-, bleach-, and mbfastness. 

The early yellow disperse dyes were based on phenolic coupling components, eg, Cl Disperse Yellow 3 (92) (diazotized 4-arninoacetanihde coupled to -cresol) which is still used today for the coloration of cellulose acetate and nylon fibers. 

The three most important types of synthetic fibres used commonly as textiles are polyester, polyamides (nylon) and acrylic fibres. Polyester and the semi-synthetic fibre cellulose acetate are dyed almost exclusively with the use of disperse dyes. Polyamide fibres may be coloured using either acid dyes, the principles of which have been discussed in the section on protein fibres, or with disperse dyes. Acrylic fibres are dyed mainly using basic (cationic) dyes. 

Much of the available published data on the aqueous solubility of disperse dyes was accumulated during the 1960s in the course of studies of the mechanism of dyeing cellulose acetate with disperse dyes. Most of the dyes examined were low-energy types for dyeing acetate (Table 3.5). Particular attention was given to monoazo dyes derived from aniline or... 

Disperse Dyes. These are substantially water-insoluble nonionic dyes for application to hydrophobic fibers from aqueous dispersion. They are used predominantly on polyester and to a lesser extent on nylon, cellulose, cellulose acetate, and acrylic fibers. Thermal transfer printing and dye diffusion thermal transfer (D2T2) processes for electronic photography represent niche markets for selected members of this class (see Chapter 6). 

Dyes for Cellulose Ester and Synthetic Polyamide Fibers. The first disperse dyes were developed for dyeing cellulose fibers, but the importance of these diminished considerably when other synthetic fibers appeared on the market. Synthetic polyamide fibers could be dyed with dyes used for acetate fibers very few new dyes had to be developed specifically for polyamide fibers. 

Cellulose acetate yarn, when it appeared on the market in 1921, presented a new problem because it had no adequate affinity for any of the existing dyestuffs. The first satisfactory method of coloration was due to Holland Ellis who observed that many simple insoluble azo dyes would be absorbed by cellulose acetate from an aqueous dispersion, stabilized with sulphated fatty alcohols or similar surface active compounds. A large number of dyes whose application depends on this principle have now made their appearance and are known as the disperse dyes. The demand for this group has increased very significantly with the advent of the truly synthetic man-made fibres. 

When the disperse dyes were in their early state of development it was observed that compounds containing an external sulphate group, having the general formula R NH.C2H4.0.S03Na, would dye cellulose acetate from an aqueous solution (B.D.C., Perkin and Bate, Brit. Pat. 237739). Little attention was paid to this at the time because it appeared that the disperse dyes would fulfil all requirements. In 1936 interest was revived and these dyes were placed on the market as the Solacet range by I.C.I. An example is Solacet Fast Scarlet B, formula (9), C.I. acid red 53. 

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