CLASSIFICATION AND CHARACTERISTICS OF DYES:-
Classification and Characteristics of Dyes | Commercial Name of Dyes:-
Dyes in Textiles:-
Dyes are either soluble in the dyeing medium (e. g. water) or can dissolve into the textile substrate. They are designed to bond strongly to the polymer molecules that make up the textile fiber. They should have some substantivity or affinity for one or more textile materials and be absorbed from the aqueous solution. Dyes are synthesized in a reactor, filtered, dried, and blended with other additives to produce the final product. There are various way for classification of dyes. From the application point of view, dyes have been classified into different groups, each group being suitable for certain types of textile substrates. Some commonly used dyes and their suitability for different fibers. For example, the most commonly used type of dye for cotton, polyester and acrylic are reactive dyes, disperse dyes and basic dyes, respectively.
Characteristics of Dyes:-
The four major characteristics of dyes are as follows:
1)The colors should be intense, so that very little quantity is required for dyeing.
2)It should be permanently or temporarily soluble in water. Different dye classes require different extent of solubility and, hence, different solubilizing groups.
3)The dye should have affinity or substantivity toward one or more type of textile fibers. The substantivity may be imparted to a dye by introducing various chemical groups into it, such as anionic, cationic, polar groups, a large number of benzene group, and phenolic groups. The dyestuff may have reactive groups (e.g., chlorotriazine), which can form covalent bond with the fiber.
4) The dyed materials have diversified use. They are, consequently, subjected to treatment with several external agents under diversified conditions. The resistance to such external agents is known as fastness properties.
The most important fastness properties are:
1)Washing fastness.
2) Light fastness.
3) Rubbing fastness—wet and dry.
4) Fastness to perspiration.
5) Fastness to bleaching.
6)Fastness to dry heat.
The degrees of fastness are expressed numerically—“1” being the lowest and “5” the highest (8 for light fastness using blue wool method). The fastness grading may be intermediate between two full numbers and may be expressed as 2–3, 4–5 or 2.5, 4.5, and so on. In most of the tests, the grading is decided by the difference in color of the material before and after the test. The contrast is compared visually with the contrast represented by Grey Scale (ISO 105 A02 or BS1006 A02, 1978).
Classification of Dyes:-
The dyes are classified with regard to different aspects:
a) The chemical constitution permits a classification of dyes based on a major structural element in the chromophore, for example, an azo group, a carbonyl or quinoid group, disulphide sulphur bond, a phthalocyanine group and metal complexes.
b) Another principle of classification uses the field of application, for example, for cellulose fibers, wool, synthetic material and for screen printing or ink-jet printing. Other classes of dyes could cover food application, coloration of plastics, paints, cosmetics, printing of paper and so on.
c) For practical applications, different dyes have been grouped into a color gamut that exhibits comparable applicatory properties and thus can be used in mixtures to dye a material to a certain shade. In such color gamuts, we often find many different classes of dyes, for example, in reactive dyes the chromophore can be a mono-azo type, a diazo compound, an anthraquinone and a phthalocyanine.
d) In addition, the origin of a dye can be used to form a group: synthetic dyes versus natural colorants. Here even the same molecule, for example, indigo can be a representative of both classes, dependent on the route that had been used to isolate the product.
Generally dyes are classified in two ways based on :-
1) Chemical constitution
2) Dyeing properties
There is little correlation between the two methods. The members constitutionally classified as azo dyes are found among several of the classes based on application. The practical dyer will be concerned only with the classification of dyes according to methods of application. The chemical classification of dyes are more important for dye makers and researchers.
Classification of dyes according to the method of application:-
Classification by the method of application is important to the textile dyer applying dyes to produce the color required. To obtain the required shade, the dyer usually has to make mixtures of dyes and must ensure that these are compatible.
The basic features that control dye transfer from solution to fiber are:-
The pH of the solution in the dyebath (for acid and basic dyes)
An electrolyte (a solution of sodium sulfate or chloride)
The temperature (within the range of ambient to 400 K)
Chemicals, known as dispersing agents, that produce a stable aqueous dispersion of dyes of very low solubility
The dyes may be classified according to the methods of application as follows:
1) Direct dyes.
2) Acid dyes (including metal–complex acid dyes).
3)Basic or cationic dyes.
4) Mordant dyes.
5) Azoic dyes.
6)Vat dyes.
7)Solubilized vat dyes.
8) Sulphur dyes.
9)Reactive dyes.
10) Disperse dyes.
11) Pigment colors.
12) Mineral colors.
13) Oxidation color.
14) Ingrain dyes.
Classification of dyes by their chemical structure:-
The Color Index assigns dyes of known structure to one of 25 structural classes according to chemical type. Amongst the most important are mentioned below:
1) Azo dyes.
2) Anthraquinone dyes.
3) Phthalocyanines.
Dye Classes and Textile Fibers:-
Suitability of various dye classes for textile fibers are summarized in Table.
Table:
Different Textile Fibers and Applicable Dye Classes
Fiber to Be Dyed ——————————-> Suitable Dye Class
Cellulosic (cotton, viscose, lyocell, etc.) –> Direct, azoic, sulphur, vat, solubilized vat, reactive, ingrain, mineral, pigment, oxidation colors (limited use).
Cellulosic (jute, flux) ———————-> Most of the aforementioned classes, except those require caustic alkali, in addition, acid and basic dyes.
Protein (wool, silk, nylon) —————–> Acid and selected direct dyes, basic dyes (limited use).
Polyester, cellulose acetate, and nylon —>Disperse dyes.
Acrylic and modacrylic ——————–> Conventional and modified basic dyes.
Indexing of Dyes:-
Thousands of dyes are being produced by various dyestuff manufacturers around the world. The industry is never static; new products are continually being introduced and established ones are sometimes withdrawn. The situation becomes complicated with frequent changes in the names of the products.
These difficulties were felt long back, and the need for a systematic classification and recording resulting in a system called color index was developed by the Society of Dyers and Colorists, UK, in 1924 and supplement in 1928. In 1945, American Association of Textile Chemists and Colorists (AATCC) collaborated and the publication is now being jointly published in eight volumes. The first four are original volumes, whereas the others are revisions and supplements.
Color Index International is a reference database, which was first printed in 1925 but is now published exclusively on the web (http://color-index.com).
Two numbers, such as C.I. generic number and C.I. constitution number, are allotted for each dye. The C.I. designations of two dyes, for example, may be C.I. Basic Violet 7 (48020) and C.I. Disperse Blue 3 (61505). Whereas the first portion is a generic number, the bracketed portion is a constitution number. The generic name consists of dye class according to usage (e.g., Direct, Acid, Basic), hue name (whether yellow, orange, red, violet, blue, green, brown, or black shade imparted by the dye on the substrate), and a unique number for each dye of a particular chemical structure.
Commercial Names of Dyes:-
The commercial name of a dye usually consists of the following:
A brand name, which denotes the specific dye class of a particular manufacturer, such as Sandolan, Cibacron, Dispersol, and so on.
Hue or color obtainable on the material after dyeing.
One or more suffix letters and figures indicating secondary hue or tone such as R, G, and B for red, yellow, and blue, respectively. The suffix G is for yellowness or greenness. These suffixes may be numbered to compare the tone among various similar dyes. One blue with suffix 2R will be redder than the blue dye with suffix R. The blue dye with suffix RR will be redder than R and less red than 2R.
Some special qualities such as F for fine, FF for superfine, L or LL for lightfast, N, W, or K for IN, IW, or IK class of vat dyes, respectively.
Strength, for example, 250%, 200%, or 150% for a brand of increased dye strength having less diluent as compared to normal brand of 100% strength. Nearly all dyes are standardized by mixing with colorless diluents, mostly common salt. The actual dye contained (purity) in a commercial dye is most often less than 40%.
As mentioned earlier, the dyes for yarn dyeing should have high fastness and stability to various chemical and physical treatments done during textile manufacturing processes. The most suitable dye classes for yarns of different fibers are listed in the following:
Cotton and other cellulosics: Vat, reactive dyes, and to a small extent azoic dyes in the decentralized (cottage) sector.
Wool, silk, and nylon: Acid dyes and metal–complex (1:1 and 1:2) dyes.
Acrylic:
Conventional and modified basic dyes.
Polyester:
Disperse dyes.
Ref:-https://textilelearner,
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