Tinctorial strength

Both molecules favor the o-quinone-hydrazone form over the o-hydroxyazo form. Corresponding studies on a selection of monoazo pigments and several (i-naphthol and Naphthol AS pigments are described in the respective chapters. 

The primary chemical aspect of a mesomeric pigment system concerns the correlation between tinctorial strength and extent of electron delocalization. A higher degree of conjugation in a molecule is associated with a bathochromic shift color strength improves with the intensity of absorption. A resonating system proliferates by  

Molecular dimerization, as in the transition from Hansa Yellow to disazo yellow pigments, increases the color strength considerably. A comparison of a Naph-thol AS/disazo condensation pigment pair gives similar results  

Eulitz [13] studied the correlation between chemical constitution and tinctorial strength directly on dissolved pigment samples. He was able to exclude physical crystal parameters, such as particle size distribution and degree of dispersion, by achieving molecular dispersion. His analysis demonstrated the following  

The transmission spectra of constitutionally similar pigment pairs, such as Pigment Yellow 1 / Pigment Yellow 3, or the pair Pigment Yellow 12 / Pigment Yellow 13, were evaluated according to Lambert-Beer. 

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The use of 2-aminothiazole derivatives as dyeing compounds is direct related to the development of synthetic fibers. Some typical examples are given in Table VI-14. The importance of these dyes lies in their performance on acetate fibers. They have excellent fastness to gas fumes, produce a bright blue shade, and have a high tinctorial strength. Their only disadvantage is their relatively low light fastness, which does limit their application. 

Water-based flexo inks can be formulated with either a soluble toner or with the Day-Glo EPX Series which is a tme pigment and can be formulated like a conventional pigment dispersion. The Radiant Aquabest or the Day-Glo WST can be formulated in an alkaline water-soluble system to yield strong inks. They have limited shelf life and inferior fade, but do not necessarily requite additional binder. Day-Glo EPX must be formulated with a binder such as a hard resin or can be used with one of the soluble toners such as WST. The EPX Series has several advantages over soluble toners such as much superior fade, exceUent ink stabiHty, and some hiding power over kraft-type papers. A disadvantage of the EPX is its lower tinctorial strength than other fluorescent toners. 

These pigments are sensitive to heat and bleed ia most paint solvents. They are, however, resistant to acids and bases. Their tinctorial strength is considerably greater than that of inorganic yellows but they are weaker than the diaryUde yellows. They are used extensively ia emulsion paints, paper coating compositions, inks (qv), and, depending on particle size, can ia some cases be used outdoors because of excellent lightfastness ia full shades. 

The pigments are manufactured either by reaction of the dianhydride with an amine or N,N -diaLkylation of the diimide. They are characterized by high tinctorial strength, excellent solvent stabiUty, very good weatherfastness, moderate brightness, and range in color from red to violet. An exception is the dianhydride which is not stable to alkah. 

Triphenylmethane dyes comprise one of the oldest classes of synthetic dyes. They are of bdUiant hue, exhibit high tinctorial strength, are relatively inexpensive, and may be appHed to a wide range of substrates. However, they are seriously deficient in fastness properties, especially fastness to light and... 

Paprika and its oleoresin are approved for use in foods in general where its appHcation as a color additive frequendy ovedaps its use as a spice. Both products have good tinctorial strength and are used at 0.2—100 ppm to produce orange to bright red shades. 

In addition to the color and the tinctorial strength, which ate very important factors for the molecular design of anthraquinone dyes, affinity for fibers, various kinds of fastness (light, wet, sublimation, nitrogen oxides (NO ) gas, washing, etc), and apphcation properties (sensitivity for dyeing temperature, pH, etc) must be considered thoroughly as well. 

Anthrimides. Despite the facts that anthrimides have excellent leveling properties and cover a wide range of colors from yellow to black, they have htde commercial importance because of their duller shades and lower tinctorial strength. However, the anthrimides are important intermediates for manufacturing anthrimidocarbazoles. Some examples of anthrimide dyes are Cl Vat Orange 20 [6370-69-0] (149), (Cl 6302S), Cl Vat Violet 16 [4003-36-5] (150) (Cl 65020] Cl Vat Black 28 [128-79-0] (151) (Cl 65010] and Cl Vat Red 48 [4478-06-2] (152) (Cl 65205) (Fig. 6). 

Anth nthrones. Halogenated derivatives have been developed to improve the dyeing properties of anthanthrones, which have low tinctorial strength and poor affinity to cellulose fibers. The only example of commercial significance is Cl Vat Orange 3 [4378-614] (4) Cl 59300). This compound is prepared from l,l -dinaphthyl-8,8 -dicarboxyhc acid (173) with oleum and bromine as follows ... 

In the manufacture of colored papers, it is best to add the dyestuffs before addition of rosin size and alum. This is not always possible in continuous dyeing procedures where dyestuffs must be added to stock containing size and/or alum, and this may cause premature laking of the dyestuffs and subsequent loss of tinctorial strength and/or dullness of shade. The proper selection of dyestuffs can help to reduce these disadvantages. 

Commercially produced metal-substituted chlorophylls such as copper chlorophylls and copper chlorophyllins that can be obtained by chemical modification of natural chlorophylls have better stability, solubility, and tinctorial strength, but they cannot be considered natural food colorants and will be discussed later. 

Although chlorophyll and chlorophyllin colorants seem to be easily obtained, in practice their production as natural food colorants is rather difficult. The sensitivity of chlorophylls to certain enzymes, heat, and low pH, and their low tinctorial strength greatly limit their manufacture and application as food additives, principally when the pigments are isolated from the protective environment of the chloroplasts. The well-known instability of chlorophylls prompted extensive research for developing... 

Sikora, M., Tomasik, R, and Palasilski, M., Enhancement of tinctorial strength of non-ammonia caramels, Starke, 41, 275, 1989. 

Triphenylmethane dyes show inferior lightfastness properties. They are, however, still one of the most important groups of synthetic dyes due to their brilliance, high tinctorial strength, and low cost. Several reviews have appeared on di- and triphenylmethane dyes.1-5 However, the color-forming precursors — leuco dyes — have received less attention in the literature. 

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