Dyes, types

A defining characteristic of dyes is the abiUty to dissolve in a given medium. Dissolution leaves no particles to refract or scatter light and thus a dye solution is transparent. A distinct advantage of a soluble-type stain is this transparency and brightness afforded by use of various dye types. SolubiUty is increased by agitation or heat, or a combination of the two. 

Equalizers can be either pigmented or dye-type stains used to tone down or lighten dark areas of wood prior to finishing. Although it is not as effective, equalizing is sometimes done in place of bleaching. Because there are no white dyes, white pigment or pead essence is usually incorporated with the dyes to achieve the desired look. 

Stains. Nongrain-raising stains are usually sprayed overall and contribute the greatest to the overall undertone color of a finished piece. These stains are also sometimes referred to as body stains or overall stains. They are usually dye-type and can be formulated, depending on the type of dye powder and solvent system, to minimise the effect of the stain on the substrate. 

The color and effect produced by NGR stains and any stain mixture depend on several factors other than the colors or type of dyes used. Those factors include strength of the mixture, the amount appHed, the type of substrate, and the solvent system used for the stain. The role of the wood stain is not to provide protection rather, the primary function of the stain is to impart color effects by accentuating grain patterns. The transparency and brightness needed to enhance the natural beauty of the wood are optimized by using dye-type stains for wood. 

Classification by usage or appHcation is the principal system adopted by the Colour Index (5). Because the most important textile fibers are cotton (qv) and polyester, the most important dye types are those used for dyeing these two fibers, including polyester—cotton blends (see Fibers, polyester). 

Sulfur Dyes. These dyes are synthesized by heating aromatic amines, phenols, or nitro compounds with sulfur or, more usually, alkah polysulfides. Unlike most other dye types, it is not easy to define a chromogen for the sulfur dyes (qv). It is likely that they consist of macromolecular stmctures of the phenothiazone-thianthrone type (72), in which the sulfur is present as (sulfide) bridging links and thiazine groups (1). 

There is Httle correlation between classifications according to chemical type and appHcation properties. AppHcation classifications are of most practical usefulness to the dyer, and therefore the chemical constitutions of dyes are described here only briefly. Further detailed information on dye types (10) and their chemical manufacture (11) can be found elsewhere, and ia many other Eniyclopedia articles to which references are made. 

The FBAs used to brighten wool are mainly DAST types and pyrazolines of the acid dyeing type already discussed in section 11.8. Examples include the three most cotton-substantive DAST brighteners listed in Table 11.1, although on wool these give light... 

Temperature provides another means of control although this is rarely the only technique employed. The control of pH is of particular importance, as the optimal pH varies with different types of acid dyes. This can be seen in Table 12.1, which shows the pH values generally required to give 80-85% exhaustion [1]. However, in some cases, either by modification of the dye type or by addition of certain auxiliaries, different pH values from those listed may be used. 

Table 12.30 Suitability of various sulphur dye types for application with anthra-quinonoid or iron-complex redox systems [214]...

X. Zhang, R. Boytner, J.L. Cabrera and R. Laursen, Identification of yellow dye types in pre Columbian Andean textiles, Anal. Chem., 79, 1575 1582 (2007). 

As earlier noted, PET has no dye attachment sites for chemically active dyes. It is possible to add ionic dyeability by forming copolymers of PET with monomer species that possess active sites, for example, on a pendant side chain. The most common of these has been the incorporation of a sodium salt of a dicarboxylic acid, e.g. of 5-sulfoisophthalic acid (Figure 12.14). The acidic sulfo group allows the attachment of cationic dye molecules. If both the modified and the unmodified fibers are put into a dye bath containing a mixture of disperse and cat dyes, they will emerge with two different colors. This is useful in the creation of specialty fabrics, e.g. when two different dye types are woven into fabrics with a predetermined pattern. The multicolored pattern emerges upon dyeing. 

Methine Dyes. The condensation products of 4-dialkylaminobenzaldehydes with cyano acetic esters have long been used to dye acetate fibers. Brilliant greenish yellow dyes with excellent lightfastness are obtained on polyester fibers with the corresponding condensation products of malonodinitrile. The sublimation fastness of this dye type can be improved by introducing suitable substituents into the alkyl residue of the amino group or by doubling the molecular size, e.g., C.I. Disperse Yellow 99, [25857-05-0] (11) [12,30,31],... 

The three major dye types, i.e., neutral, anionic, and cationic, are subdivided by use the neutral dyes comprise disperse, vat, and solvent dyes the anionic dyes, acid, direct, and reactive dyes and the cationic dyes, dyes for polyacrylonitrile fibers and other fibers modified to contain acid groups. 

In describing the separate dye types it is useful to distinguish between the mono azo and the disazo dyes, and to further break down the disazo dyes into primary and secondary types on the basis of chemicostructural principles. 

Some of the key properties of a photosensitizer are high efficiency of singlet-oxygen generation, strong absorption in the red and particularly near-IR (660-800 nm), preferential affinity for tumor rather than healthy tissue, and rapid clearance from the body. Porphyrin and phthalocyanine dyes fit these criteria best, and much work has been done on these dye types [76], Photofrin, a hemato-porphyrin derivative, was the first photosensitizer to be approved for clinical use. It is a complex mixture of monomeric porphyrins (protoporphyrin, hematopor-phyrin (84), and hydroxyethylvinyldeuteroporphyrin) and oligomers of these porphyrins. 

Synthetic dyes are mainly aromatic organic compounds, and they can be classified as cationic (basic dyes), anionic (direct, acid, and reactive dyes), or nonionic (disperse dyes) type [134]. Synthetic dyes are mainly used in the textile industries, but they have many other applications such as in printing, leather, papermaking, drug, and food industries [85]. Total world colorant production is estimated to be... 

Structurally related dyes are synthesized by condensing phenols with phthalic anhydride to give a colorless intermediate lactone (32) that reacts with alkali to give the colored form. An example of this dye type is phenolphthalein, the synthesis of which is shown in Fig. 13.108. 

Rice has suggested that in order to conserve historic colorants, it is necessary to know what constitutes the color, what chemicals affect it and how, and what factors cause it to fade or change (16), The specific objectives of this investigation were two-fold to discover dye types and characteristics in the voile fabric to discover if and how the fabric color changes in response to selected conditions it could have encountered in its wear life. This information could indicate possible factors to explain the types of discolorations on the dress. Experimental procedures and results for both objectives followed separate courses and therefore will be discussed separately. Results from the investigation of the first objective in part determined testing procedures for the second. 

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