Textile Dyeing - Theory of Dyeing & Classification of Dyes

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Dyeing & PrintingClassification of Dyes, Application of Dyes on Textile Materials, Introduction to Different types of Dyeing Machineries

Dyeing & Printing Title of Contents1.0. 2.0. 3.0. Introduction to Textile Dyeing Classification of Dyes Dyeing Process 3.1. 3.2. 3.3. 3.4. 3.5. 3.6. 3.7. 3.8. 3.9. 3.10. 3.11. 3.12. 4.0. Dyeing Methods Comparison of Dyeing in Various Stages Special Dyeing Effects Application of Dyes on Textile Materials Direct Dyes Azoic Colors Reactive Dyes Vat Dyes Acid Dyes Basic Dyes Sulphur Dyes Disperse Dyes 03 05 07 07 09 10 11 11 12 15 20 25 28 29 30 31

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Introduction to Different Dyeing Machineries

Dyes, Theory of Dyeing, Classification of Dyes and its application

Dyeing & Printing1.0. Introduction to Textile Dyeing

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Dyeing is the process of imparting colours to a textile material in loose fibre, yarn, cloth or garment form by treatment with a dye. Dyeing is also the process of coloring textile materials by immersing them in an aqueous solution of dye, called dye liquor. Normally the dye liquor consists of dye, water and an auxiliary. To improve the effectiveness of dyeing, heat is usually applied to the dye liquor. 1.1. Color Definition Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates. Because perception of color stems from the varying sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully explain the psychophysical perception of color appearance. The science of color is sometimes called chromatics. It includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light). 1.2. Definition Dye By definition Dyes can be said to be coloured, ionizing and aromatic organic compounds which shows an affinity towards the substrate to which it is being applied. It is generally applied in a solution that is aqueous. Dyes may also require a mordant to better the fastness of the dye on the material on which it is applied. The dyes were obtained from animal, vegetable or mineral origin with no or very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale. 1.3. Definition Pigment Pigment is the substance or powder that makes up the color of paint. Pigments are either organic (derived from plant or animal sources, e.g. ivory black, indigo) or inorganic (derived from salts or metallic oxides e.g. ocher, cobalt blue).Dyes, Theory of Dyeing, Classification of Dyes and its application

Dyeing & Printing

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Pigment is a substance that can absorb light and reflect some lights to show color but it is water insoluble substances. Normally it is used for printing (with the presence of binder) or mass-coloration of the synthetic fibers. 1.4. Theory of Dyeing The general theory of dyeing explains the interaction between dye, fiber, water and dye auxiliary. More specifically, it explains: i. Force of repulsion which are developed between the dye molecules and water and ii. Force of attraction which are developed between the dye molecules and fibres. These forces are responsible for the dye molecules leaving the aqueous dye liquor entering and attaching themselves to the polymers of the fibres 1.4.1. Dye Molecule Dye molecules are organic molecules, which can be classified as: 1. Anionic in which the color is caused by the anionic part of the dye molecule; 2. Cationic in which the color is caused by the cationic part of the dye molecule; 3. Disperse in which the color is caused by the whole molecule. The first two dye molecule types are applied from an aqueous solution. The third is applied from an aqueous dispersion. A dye stuff is a substance which is capable of coloring a textile material in such a manner that it associate closely with the fiber, that it is not removable by simple physical means (e.g.: rubbing or mild deterging). It must be soluble in water, are capable of going into solution by chemical means, whereby a highly dispersed condition may be regarded as a form of solution An essential feature of the dyeing process is that the dye molecule must be capable of entering the fiber structure, the path for the dye molecules is provided by the intermolecular spaces in the fiber and once the dye has entered the fiber structure it becomes firmly attached to the surface of the molecules either by purely physical forces (Secondary Valences) or by chemical combination. The former mode of attachment is believed to be prevalent in the dyeing of cellulosic fibres, the latter mode in the dyeing of protein fibres. Acetate rayon and synthetic fibres resist penetration by the dye molecules, but certain dyes are capable of forming a solid solution with the fibrous molecule; for dyeing with other dyes, the synthetic fibres may be swollen with suitable agents. Swelling of the fibers appears to play a large part in dyeing of all fibres, and is principally affected by water (or solvents in the case of synthetics) and by raising the temperature of the dye bath.Dyes, Theory of Dyeing, Classification of Dyes and its application

Dyeing & Printing1.4.2. The Dyeing Process

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The dyeing process can thus be considered as taking place in three phases (i) Attachment of the dye molecule to the surface of the fiber (ii) Penetration into the intermolecular spaces as well as diffusion through the fiber & (iii) Orientation (and fixation) along the long chain molecules. Dyeing is governed by three factors, the dye, the fiber and the dye liquor. All the three lead an independent assistance which influences the technique of dyeing. A dye must be water soluble in order to dye textile materials. It may be soluble by nature of its chemical interference. The solution of the dye from which it is applied is called the dye bath. A dye may have direct affinity for a fiber (or vice versa) i.e., it is held by the fibre either physically (absorption) or chemically (combination) as soon as the fiber is immersed in the dye bath. Accumulation of the dye in the fiber is a gradual process, the rate of such building up being referred to as the rate of dyeing. 1. This rate of dyeing is governed by the condition of the dye bath, namely concentration of dye, temperature, and presence of electrolytes; it is proportional to all three factors. 2. The rate of dyeing is also influenced by the Material to liquor which is expressed by a fraction, e.g. 1:20, which means one part (by weight) of the textile material dyed in twenty times its weight of dye bath. 3. The rate of dyeing decreases with increasing ratio of goods to liquor. Dyeing is carried out to produce a certain Shade by which is meant a certain color, difference in shade being due to different Hue. A blue shade may, for instance, have a greenish or a reddish hue. The amount of dye needed for the production of a certain depth of shade is expressed as a percentage of the weight of the material. A 1% dyeing represents a shade produced by the coloring of 100 lbs. of material with one lb. of (commercial) dye under well defined dyeing conditions. It is necessary to define these conditions because of their influence on the exhaustion of the dye bath. Exhaustion determines that amount of dye which is taken up the fiber or in directly, that amount which remains in the dye bath after equilibrium between dye and fiber is reached, i.e., at that point where no further dyeing takes place. 2.0. Classification of Dyes Dyestuffs can be classified by many methods as follows: y their ionic e.g. Cationic, anionic and non-ionic) y their fiber dye abilities e.g. On cellulosic, protein, polyester, polyamide etc.) y their names e.g. Acid, direct, disperse, reactive, basic etc.)Dyes, Theory of Dyeing, Classification of Dyes and its application

Dyeing & Printingy their chemical structures e.g. azo, anthraquinone, stilbene etc.) y their origins e.g. Natural, synthetic) y their colors e.g. Red, green, black etc.) 2.1. Classification of Dyes by their Names

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Though several classifications were available classification of dyes by their names is the widely used one. COLOURING MATTER

DYES

PIGMENTS

Ready made dyes

Ingrain dyes

Azoic

Oxidation

Mineral

Water-soluble

Water insoluble

Vat

Sulphur

Disperse

Direct

Acid

Basic

Reactive

So the Colouring matters can be classified as pigments and dyes. Dyes may be of readymade dyes and ingrain dyes. Ready made dyes are dyes which are readily available in powder form, liquid form. These ready made are available in both water soluble and water in soluble form. Ingrain dyes are those which will not be available in ready made form, two or more compounds are combined together in the dyeing process to obtain the color in the final finished product.

Dyes, Theory of Dyeing, Classification of Dyes and its application

Dyeing & Printing3.0. Dyeing Process