Dyes on Acrylic Fibers

Acrylic fibers (PAC) are, together with PES and PA, the most important synthetic fibers [154], For methods of production and properties of PAC fibers see [96, pp. 629-642], To obtain fibers with satisfactory dyeing properties, anionic comonomers are used. In this way, the glass transition temperature Tg is lowered and anionic groups are available that can act as dye sites for cationic dyes. Thus, acrylic fibers are reliably and economically dyeable wth cationic dyes. 

The main advantages of acrylic fibers are their similarity to wool in feel, heat retention, and processing, as well as good dyeability. In Western Europe and the United States, ca. 60% are used for clothes and 30% for household textiles. 

Dyeing is performed mainly by exhaustion processes (batchwise). Another dyeing method with increased importance is the gel dyeing process. Dyeing in the gel state takes place during production of the fiber, i.e., after the fiber has been extruded and the solvent has been washed out, but before the fiber is stretched and dried (see Section 4.14.6). Continuous dyeing of stock, cable, and tops is also possible according to the pad steam process. 

Acrylic fibers can be dyed wih cationic dyes only above the glass transition temperature Tg, which has a characteristic value for each type of fiber and for most fibers lies between 70 and 80°C [96, p. 469], Cationic dyes form a heteropo-lar bond with anionic groups of the fiber. The number of anionic sites in the fiber determine the saturation value SV, i.e. the maximum amount of dye wich can be taken up by the fiber. Tg and SV are indicated by the fiber producer. 

The dyeing process is governed by the affinity of the dyes to the fiber and their diffusion in the fiber. Since cationic dyes have a very high affinity to acrylic 

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A "Permanent" Cationic Retarder for Cationic Dyes on Acrylic Fibers... 

True leveling agent for cationic dyes on acrylic fibers. Promotes dye migration. 

Uses Retarder, leveling agent for basic dyes on acrylic fibers Properties Liq. 50% cone. 

Uses Retarding agent for ensuring level dyeing of modified basic dyes on acrylic fibers... 

Orange dye that gives on qiiaternizalion a new fast-ted dye oti acrylic fibers... 

Transfer of Basic Dyes on Acrylics. This test is identical in concept to the transfer of disperse dye on polyester except that basic dyes, acryhc fiber, and a standard dyebath for dyeing acryflc is used. 

BURCO PAW is a retarding agent for the dyeing of acrylic fibers with cationic, e.g., BURCOCRYL dyes. As a cationic substance, it competes with the dyestuff for available dye sites on the fiber, and facilitates uniform dye uptake by the acrylic fiber. 

Aminopyridine is prepared conventionally by the substitution of the pyridine ring via the so-called Chichibabin reaction using sodium amide in dimethylaniline [36]. 2-Aminopyridine is used in the manufacture of several chemotherapeutics and of dyes for acrylic fibers, and as an additive for lubricants [37]. Alkyl thiocyanates react [38] to give 2-alkylthiopyridines (eq. (12)) which are otherwise accessible only by multistep synthetic pathways [39]. The catalytic reaction (eq. (12)) seems to offer on easy entry into the pyrithione systems. 

Maretard. [Lenmar] Cationic retarders for basic dyes on acrylic, nylon, or polyester fibers. 

The material discussed up to this point has been intended to give the reader an understanding of how the majority of acrylic fibers are manufactured. In this section, we discuss some of the less conventional spinning processes that could be used to produce fibers for special applications. We also include a section on optimization of spinnability in which some of the more fundamental aspects of the rheological behavior of the fiber in the spin bath are discussed. Completing this section is a discussion of the dyeing of acrylic fibers. 

Dyes, basic n. A class of positive-ion-carrying dyes known for their brilliant hues. Basic dyes are composed of large-molecule, water-soluble salts that have a direct affinity for wool and silk and can be applied to cotton with a mordant. The fastness of basic dyes on these fibers is very poor. Basic dyes are also used on basic-dyeable acrylics, modacrylics, nylons, and polyesters, on which they exhibit reasonably good fastness. 

The nature and distribution of acrylonitrile and comonomer or comonomers in the acrylic fibers affect the overall dyeability and the classes of dyes that may be used in dyeing these fibers. Both acrylic and modacrylic fibers can be dyed using disperse dyes, with the more hydrophobic and less crystalline modacrylic being more dyeable with this dye class. The polar cyanide groups in the acrylonitrile unit of these fibers have some affinity for acid dyes and particularly mordanted systems containing copper or chromium ions. Addition of an acid or basic comonomer such as acrylic acid or vinyl pyridine as comonomer imparts improved dyeability with basic and acid dyes, respectively, for these fibers. Vat dyes can be used on acrylic fibers to a limited extent. 

Uses Leveling agent for cationic dyes on syn. fibers antistat for acrylics, polyamides, and acetate fibers Properties Liq. water-sol. 

Highly colored, they have been used to dye cellulose acetate (552) and acrylic fibers (553). Cationic dyes prepared from 2-azothiazoles by simple alkylation on the ring nitrogen (552) have been used increasingly with the introduction of polyacrylonitrile fibers with basic sites that can be colored with such dyes (554). 

Recently, nitrilases have been applied to polymer modification, specifically to the modification of polyacrylonitrile (PAN). Nearly 3 x 106 tons of PAN are produced per annum and used in the textile industry. However, there is a great need to improve moisture uptake, dyeability with ionic dyes, and feel of this acrylic fiber. The cyano moieties of PAN have been successfully modified to carboxylates with the commercial Cyanovacta nitrilase, thus enhancing the aforementioned properties of PAN [98]. Nitrilase action on the acrylic fabric was improved... 

Sulfur dyes are used mainly for dyeing textile cellulosic materials or blends of cellulosic fibers (qv) with synthetic fibers such as acrylic fibers, polyamides (nylons), and polyesters. They are also used for silk (qv) and paper (qv) in limited quantities for specific applications. Solubilized sulfur dyes are used on certain types of leathers (qv). 

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). 

Practically all synthetic fibers can be printed with disperse dyes. Cationic dyes are used preferentially for acrylic fibers, and acid dyes and metal-complex dyes can be used for prints on polyamide fibers. The importance of printing with disperse dyes and the relative amount of different man-made fibers used for prints varies according to fashion and local requirements. Polyester fabrics alone or in combination with cotton are the most important. After precleaning, fabrics made from synthetic fibers must be heat-set to achieve dimensional stability and crease resistance. The usual setting conditions are 20-30 s at 190-210°C, and for texturized articles about 30°C lower. 

Disperse dyes can be used to produce light to medium deep shades on acrylic and modacrylic fibers [96, p. 639], The dyeing mechanism and process correspond to those used on PES and CA fibers (see Section 4.12). However, dyeing can be performed below 100°C. Addition of carriers is not required. The good migration properties of disperse dyes result in problem-free level dyeing. 

The acrylic fibers studied are based on an acrylonitrile (94%), methacrylate (6%) copolymer with a diameter of 12-20 microns. The cell used for the measurement is illustrated in Fig. 7-7. Resolution was 3 cm-1, and 50-150 scans were taken. Figure 7-8 shows the Raman spectra of a blue dye fiber, red dye fiber and an undyed methacrylic fiber. The dye vibrations can be readily observed. Figure 7-9 shows the subtraction spectrum (blue dyed fiber minus the undyed fiber). The subtracted spectrum (a) is compared to a blue cobalt dye (b), and the agreement is excellent. 

Pure acrylonitrile may polymerize at room temperature to polyacrylonitrile (PAN), a compound that, unlike polyamides and polyesters, does not melt at elevated temperatures but only softens and finally discolors and decomposes. Nor is it soluble in inexpensive low-boiling organic solvents. Because fibers made from it resist the dyeing operations commonly used in the textile industry, the usual practice is to modify it by copolymerization with other monomers, for example, vinyl acetate, styrene, acrylic esters, acrylamide, or vinyl pyridine in amounts up to 15 percent of the total weight (beyond which the final product may not be termed an acrylic fiber). The choice of modifier depends on the characteristics that a given manufacturer considers important in a fiber, the availability and cost of the raw materials in the manufacturer s particular area of production, and the patent situation. 

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