Dyes, classification direct

Clarke-Othmer process Clark oxygen electrode Clary sage oil [8016-63-5] Class A direct dyes Classification of dyes Classified removal Classifiers Clathrate... 

In order that the liquor ratio may remain constant, the dyeings and the migration tests should be carried out in conical flasks with a reflux condenser, or a simple device such as is shown in I ig. 16.5 has proved very useful. The classification of many of the direct dyes is given in the Colour Index of the Society of Dyers and Colourists, and it is now usual to give this information in the dyestuff manufacturers catalogues. 

Classification of some direct dyes for high temperature dyeing... 

There are, of course, many varieties in each of these chemical classifications, so that the result is hundreds of individual dyes each with its own specific characteristics for hue and use on substrates. Dyers have arranged this very complex and large group of chemical products into ten categories arranged by the method of application to the fiber or substrate acid dyes, azoic dyes, basic dyes, direct dyes, disperse dyes, reactive dyes, solvent dyes, sulfur dyes, vat dyes, and mordant dyes. It is in these categories that dyestuffs are discussed in the trade. 

Direct dyes are anionic dyes that are substantive to cellulose when applied from an aqueous dye bath containing an electrolyte. Although anionic, they are not classificated as acid dyes because the acidic substituent is not the means of attachment to the fiber. 

Direct or substantive dyes are colored compounds that are mainly used to dye materials made from natural or regenerated cellulose (e.g., cotton, jute, viscose, or paper) without employing mordants as auxiliaries. The essential requirement for classification of a dye in this group is its substantivity, i.e., its absorption from an aqueous salt-containing solution onto cellulosic materials. Absorption onto cotton takes place in a neutral to soda alkaline medium, and onto paper in a weakly acid to neutral medium. 

Shortly after this classification was suggested, the report of the Committee appointed by the Society of Dyers and Colourists to discuss the properties of direct cotton dyes was published (J.S.D.C., 1946,62,281). They recommended the recognition of the three classes referred to by Lemin et al. (loc. cit.), and concluded that two tests would provide a satisfactory basis for assigning any dyestuff to its proper class. Those which passed the first test for migration W ould fall into Class A and those which failed w ould be classified B or C by the second salt controllability test. 

A close-packed monolayer of long, planar molecules must necessarily contain at least "islands" of local order in which molecules are packed plane-to-plane. One notices that crystals of these dyes tend to pack in sheets, within which the molecules have their long axes parallel to one another and parallel to the plane of the sheet. The molecular short axes are nearly perpendicular to the plane of the sheet, and the intermolecular contacts within the sheet tend to occur at the graphitic distance, except for molecules which are bent or twisted out of planarity. Twisted molecules ("overcrowded" in Brooker s classification) generally make poor sensitizers, probably because they have a fast route of deexcitation directly from the excited singlet state to the ground state opened by the existence of the twisted, stressed structure. 

There are three general classifications of acid dyes depending on their method of application acid dyes that dye directly from the dyebath, mordant dyes that are capable of forming metallic lakes on the fiber when aftertreated with metallic salts, and premetallized dyes. 

Absorption.—The studies reported here are conventional one-photon absorption studies on ground-state molecules and atoms. The use of a rapidly tuneable CW dye laser for direct absorption spectroscopy has been described.98 Transition probabilities in the spectra of Ne (I),97 and the classification of the 650.4 nm line of Xe97 have been discussed. Pressure-broadening coefficients for the atomic iodine 2P4-2Pj transition for C02, N2, He, Ne, Ar, Kr, and Xe have been measured as 7.4 0.7, 6.2 0.8, 3.6 0.3, 4.3 0.4, 5.1 0.5, 4.4 0.4, and 3.0 0.3, respectively.98 Measurements of the polarizabilities of alkali-metal atoms have been described,99 and hyperfine interactions in the excited states of sodium discussed.100 Excitation parameters in the vacuum-u.v. region... 

Dyes may be classified according to their constitution, such as azo dyes, phthaleins, alizarines, etc., but from the standpoint of the dyer the more important classification is that which is based on the behavior of the dyes with fibers. Dyes are grouped in this way as substantive or direct, and adjective or mordant. Dyes are also classed as acidic and basic. In addition to the dyes belonging to these classes, there are a few, such as indigo and other Vat dyes, aniline black, and the so-called ingrain colors, which are produced by chemical reactions within the fiber. 

Azo dyes are classified according to a color index system based on usage and chemical constituents. These are subdivided into monoazo, disazo, trisazo, and polyazo derivatives with a specific assigned range of color index number. Another classification system involves dividing dyes into dyeing classes such as acid, basic, disperse, direct, mordant, and reactive dyes. Azo compounds are used extensively as dyes to color varnishes, paper, fabrics, inks, paints, plastics, and cosmetics. They are used in color photography. 

Mishra and Tripathy (1993) proposed a simplified classification as follows anionic (direct, acid, and reactive dyes), cationic (basic) dyes, and nonionic (disperse) dyes. There are many structural... 

Further classification was obtained by direct analysis of pen strokes on paper (without elution) using laser desorption ionization (LDl) time-of-flight (TOF) mass spectrometry. However, only basic dyes and pigments could be identified by positive mode LDFMS. 

What is the difference between a pigment and a dye According to the principles of color technology, pigments are applied to a surface with the use of a vehicle that allows it to be spread dyes need no such binder and can inhere in the substrate directly. Thus, any substance may be classified as a pigment or a dye depending upon how it is applied to the substrate, and both should be discussed under the more general classification of colorants . 

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