Dyes in Fiber Blends

In the case of faulty dyeing, the dye can be largely stripped by treatment at 120°C with benzyl alcohol in an aqueous bath or with a carrier and a retarder which has a leveling effect in the presence of hydrosulfite in an alkaline liquor. 

Most textile dyes are anionic in nature or they are prepared with anionic finishing products. Therefore, whenever cationic dyes are used together with other dye classes, possible interactions between different dye classes should be considered. 

PAC-CEL Blends are used for household textiles and imitation fur. In these plush and fur materials, the pile consists of PAC fibers while the back is made of cellulose. Furthermore, they are used for leisure wear, sport stockings, drapery, and table linen. The percentage of PAC in the mixtures varies widely. Cationic dyes reserve CEL well, because of their high affinity for acrylics. For a survey of dyeing methods, see [50, pp. 474-476] and [6, pp. 608-610], 

Continuous dyeing of PAC-cotton plush with cationic and direct dyes by the pad steam process plays an important role. The choice of dyes must take into account liquor stability, reservation of PAC or CEL fiber, and solubility. Precipitation of cationic and anionic dyes present in the pad liquor at relatively high concentrations cannot be avoided solely by dye selection. Suitable auxiliary systems have been developed. Differently charged dyes are kept in solution separated from each other in two phases by the combination of anionic and nonionogenic surfactants. With the help of fixing accelerators, good penetration of PAC fibers can be achieved in 10-15 min with saturated steam at 98-100°C. 

PAC-CEL mixtures can also be dyed in a one-bath, two-step process with reactiveand cationic dyes. Here, too, the PAC component is predyed at pH 5 with cationic dyes, and after the pH is raised, the cellulose component is covered with reactive dyes. For the dyeing of yam, see [179], 

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The dyeing of fiber blends is difficult owing to the different affinities, the different dyeing material stabilities of individual dyes in the liquor, and so forth. In this case, both fibrous materials have to be dyed directly and evenly. 

Blends of polyester with cotton (qv) or viscose are first dyed with disperse dyes, then with sulfur dyes (see Fibers, polyester Fibers, regenerated CELLULOSics). Disperse and sulfur dyes can also be appHed simultaneously in a pad—dry—thermofix/chemical reduction pad—steam sequence. In this case, the sulfur dyes cannot be used in thein reduced form because of the effect of the sodium sulfide on the disperse dye. Therefore, this method is confined to the solubilized sulfur dyes or sulfur dyes in the dispersed form. 

When dyeing fiber blends it must be decided whether the fibers can be dyed simultaneously from the same dyebath, or separately and in what order from different dyebaths. The benefits of dyeing from separate dyebaths is that the conditions can be chosen to give the maximum dyeing efficiency for each dye—fiber combination. The disadvantage is that it is more time consuming. 

Dye Combinations. In certain cases it is desirable to print fiber blends with combiaations of the appropriate dye classes, rather than with pigments. Only polyester—ceUulose blends are of commercial importance and the foUowing dye systems have been developed for them. The dyes of the different classes are contained in the same print paste and, therefore, are appUed simultaneously in one print operation. 

Synthetic fiber blends, dyeing, 9 203-204 bleaching, 4 72 titanium dioxide in, 25 30 Synthetic fibers, 1 693... 

When dyeing fiber blends it must be decided whether the fibers can be dyed simultaneously from the same dyebath. or separately and in what order from different dyebaths. 

Wool-Cellulasic Fibers. One of (he oldest fiber blends in (he textile market is (he combination of wool and cotton or wool and viscose. In a one-bath process, selected direct and acid dyes are applied at pH 4.5-5.0 at 98 ItXfC. A phenolsulfonie acid condensation prodact is added as a reserving agent, to prevent the direct dyes from dyeing the wool under acid conditions, if optimum wetfastness properties are required, fiber-reactive dyes can be applied to both fibers by use of a two-bath process. 

Polyester Fiber Blends. Disperse dyeable and cationic dyeable polyester fibers are frequently combined in apparel fabrics for styling purposes. Whereas the disperse dyes dye both fibers, but in different depths, selected cationic dyes reserve the disperse dyeable fiber completely, resulting in color/while effects. 

Polyester Fiber-Nylon Blends. This fiber blend is used in apparel fabrics as well as in earpels. Disperse dyes dye both fibers, however they possess only marginal fastness properties on nylon. Therefore it is important to select those disperse dyes that dye nylon least under the given circumstances. The nylon is dyed with acid dyes, selected according to the fastness requirements. 

Polyester Fiber-Acrylic Fiber Blends. This liber blend is dyed in a similar fashion to that of the blends of the different polyester fibers. The selection of cationic dyes is substantially larger for the acrylic blend. 

Reactive dyes are well suited to dye blends of cellulose and PA fibers. Clear shades with very good fastness are obtained. Like with vat dyes, the depth of shade of reactive dyes depends relatively strongly on the type of PA and structural differences. Dyeing is carried out in a three-step process with appropriately selected products. First, the reactive dyes in a weakly acidic liquor are allowed to absorb on the PA component. Salt is then added to improve the yield on the cellulose component. Finally, the liquor is made alkaline for reaction with the cellulose fiber. Dyes (e.g., with MTC anchor) that dye PA from a neutral liquor in the presence of salt are applied in a two-step process, as in the case of cellulose. In the reversal of this dyeing process, the cellulose component is dyed first at alkaline pH, followed by neutralization with acid, and the PA component is then covered at elevated temperature. 

Apart from cellulose, direct dyes have a strong affinity to wool and polyamide fibers. Blends of cellulose with wool ( half wool ) used to occupy a considerable segment of the market, but are today without any significance. However polyamide (PA) fibers are included in articles made of cellulose fibers to improve dimensional stability, ease of care, and durability, e.g., in sportswear and knitwear, corduroy fabrics, or plush articles, in which a PA pile is often anchored to a cellulose fabric base. Different dyeing methods are described in [50 pp. 433-4371, [6, p. 570],... 

Approximately 15% of cellulose libers and cellulose-containing fiber blends are dyed with vat dyes. The total consumption of vat dyes in 1993 was about 22 000 t/a of commercial products, excluding indigo. 

For stretch cord and similar articles made of PA-CEL blends, metal-complex dyes that are resistant to reducing agents are added to dye the PA fibers, because only a few sulfur dyes stain PA sufficiently. Water-soluble sulfur dyes can be combined with selected reactive dyes. In this manner, more brilliant shades are obtained. 

In the case of PES-CEL fiber blends, the larger part of the liquor is absorbed by the CEL fiber during drying, because of its higher absorption capacity. Nevertheless, in the subsequent thermofixing step, disperse dyes are almost completely fixed to the PES fiber. Transfer from the CEL to the PES fiber occurs both by migration via direct fiber contact and through the gas phase. The type of transfer depends on the sublimation behavior of the dyes [120],... 

Thermosol Process. The most important continuous dyeing process for PES fibers is the thermo sol process. It is applied primarily to PES-CEL blends (see Section 4.12.4). The thermosol process consists of four individual steps (1) Padding of the dye liquor on the fabric, (2) Drying, (3) Fixing of the dyes in the fiber, (4) Aftertreatment. The four individual steps usually follow one another in one pass. Systems also exist that include the subsequent overdyeing of the cellulose component in blended fabrics [e.g., by using the pad steam technique (see Section 4.1.1)]. 

After the dyes are fixed, dyes and auxiliaries that adhere superficially must be washed out, if necessary, by an alkaline reductive treatment. In the case of PES-CEL fiber blends, this washing can be combined conveniendy with afterdyeing of the cellulose component, e.g., simply by overdyeing with vat dyes (see Section 4.4.3). For details of the thermosol process, see [85, pp. 122-131],... 

Since disperse dyes diffuse very slowly into PES fibers, efforts have been made to increase the rate of dye strike by chemical or physical alteration of the fiber. The fiber is also modified to reduce the pilling tendency, to increase shrinkage and elasticity, and to reduce flammability. Such modified fibers exhibit improved dye receptivity. Fibers with improved dyeability can be dyed with disperse dyes at boiling temperature without a carrier or with basic dyes when they are modified with acidic components (5-sulfoisophthalic acid). Fibers of this type are used if dyeing cannot be carried out easily above 100°C (e.g., in the case of floor coverings, articles made of PES-wool blends, stretch materials, and cord). Strongly crimped PES bicomponent fibers are produced for special purposes. These fibers are normally also dyeable at the boil and without a carrier [136, 137, 138],... 

In a two-bath, two-step dyeing process, other dyes suited to dye CEL fibers may also be used for PES-CEL blends. For instance, in spite of its tediousness, Naphtol AS dyeing is still employed (see Section 4.8), especially for wetfast red shades, and the Phthalogen process is used for turquoise (see Section 4.9.5). Pigment dyeing is also applied to PES-CEL blends. 

Promotes reserving of component fibers in acrylic blends when dyeing with cationic dyes... 

Functions as a leveling agent for both fibers in a blend when dyeing with disperse and acid dyes on cellulosics. 

The methods of apphcation of dyes in textile dyeing and printing have undergone several modifications to meet the requirements of the new synthetic fibers and their blends with the natural fibers and new classes of dyes. However, the basic operations of dyeing remain the same and include the following ... 

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