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- 1. Auxiliaries What are printing Auxiliaries? • The chemicals added to printing paste that facilitate production of effective and quality are called printing auxiliaries. • There are different printing auxiliaries. They are classified according to their function and various uses. • These auxiliaries selected based on the method of printing, dye class, fabric to be printed and compactivity with other ingredient in the paste. • 1. Thickeners 2. Wetting agent Thickener • A large number of thickeners are available for printing. • The choice of thickener will depend upon the class of dye to be printed and style of printing. • The compatibility of thickener with other ingredients in the printing paste should also be considered during its selection. • Carbohydrates form the most important and largely used varieties of thickening agents. • Wheat starch and maize starch have been used as thickeners in printing for a very long time. • Starch is not suitable as a thickener in the preparation of paste in which acids are to be added. (A) Natural Thickener: (I) Starch: • It is a vegetable substance manufactured from cereals and tubes such as rice, wheat, maize, potato etc. • It is insoluble in cold water. • Starch has the property of swelling when heated with water to give a viscous paste. (II) Plant exudates (Gum): (a)Gum Senegal or Gum Arabic: • It is obtained from the exudation of Acasia plant. • 30 – 50 % of gum paste is required for printing. • It is stable under both strongly alkaline and strongly acidic conditions. • Gum arabic and gum Senegal are both traditional thickenings, but expense prevents them from being used for any but pale, delicate tints. (b)Gum Tragacanth or Gum Dragon: • It is obtained from the ligneous plant. • The advantage of this gum is that it leaves the cloth quite soft. • Generally 4 – 5 % gum paste is used in printing. • It is stable under mildly alkaline conditions but not under strongly alkaline conditions. • When added to a starch paste it increases its penetrative power and adds to its softness without diminishing its thickness, making it easier to wash out of the fabric. • Used by itself it is suitable for printing all kinds of dark grounds on goods that are required to retain their soft "clothe" feel. (c) Gum Karaya: • This gum is obtained from the Karaya tree. • It is not much used at present. (III) Roots and seeds: (a) Guar Gum:- • Guar gum is obtained from the endosperm of the guar plant seed. It gives high viscosity pastes. • It forms viscous colloidal solution when hydrated in cold water. • Its derivatives are used in printing synthetic fabric. (b)Locust Bean Gum: • It is obtained from the hard seeds of the locust bean of carob tree. • Only 2 – 3 % of this gum gives print paste of required viscosity. It is neutral and soluble in water. (c)Tragasol Gum:- • It is a special product of locust bean. • It has better stability to mild alkalis and acids than locust bean gum. (IV)Sea weeds:- (a)Sodium Alginate: • It is sodium salt of alginic acid which is found in sea weeds. • Small amount of sodium alginate is required in printing paste. • It solubilise in cold as well as in hot water, so absorption of dye by fiber is excellent. (B)Modified natural thickeners:- (I)Starch derivatives: (a)Dextrin or British Gum:- • Dextrin or dark British gum is a degradation product of starch obtained by heating it with mineral acid or roasting at 160°C till it becomes completely soluble in water. • Generally 20 – 50 parts of dextrin per 100 parts of printing paste is used. (b)Cellulose Derivatives:- (b-I) Methyl Cellulose:- • Methyl ether of cellulose is prepared from wood pulp or cotton linters. • The ether is insoluble in boiling water and also in presence of alkali but soluble in cold water. • It retains its consistency satisfactorily during storage. (b-II)Sodium Carboxy Methyl Cellulose (CMC): • It is prepared by reacting alkali cellulose with monochloro acetic acid. • This thickener is stable to alkali and hence can be used for printing vat colours • The removal of CMC from the cloth after printing is very easy. (b-III)Gum derivatives:- • Indica meyprogam is a modified guar gum which is resistant to acids and alkalises. (C) Synthetic thickener:- • Synthetic thickening agents are molecular substances generally co-polymers of unsaturated organic acids such as acrylic and malefic anhydride. • They have the following properties:- • High degree of purity • Rapid preparation of stock thickening • Simple printing recipe • Good running properties • Optimum depth of shade • Brilliance of the prints, excellent stability • Synthetic thickeners have the ability to produce prints with better smoothness, levelness and sharpness as compared to natural and modified thickeners and are suitable for photographic and multicolour prints. (D) Emulsion Thickener:- • Emulsion thickening derives its viscosity from a dispersion of tiny droplets of one liquid in another with a dispersing agent. • The two liquids must not mix or be soluble. With development of pigments color emulsion came into existence. • Emulsions are available in disperse phase and dispersing medium. • For printing textile material, oil in water type of emulsion is populaly used. • Widely accepted is kerosene based emulsion. • Choice of a thickener will depend upon the class of dye to be printed and style of printing. • Ex: British gum and starch tragacanth thickener for direct dye. • British gum for vat, • Sodium alginate for disperse, • Synthetic for reactive. ______________________________________________________________________________________________ ______________________________________________________________________________________________ Wetting agent What is wetting? • Substances that make solid materials more susceptible to water immersion. • By reducing its surface tension or interfacial tension, so that the water can be expanded on the surface of solid materials, or penetrate the surface, and the solid material wetting • The use of wetting agent is generally beneficial in dissolving dyestuff eg. Turkey red oil (T.R.O.), caster oil, olive oil, animal oil, glycerine etc. • During the penetration of printing paste the dyestuff which is usually in the powder form is dissolve in a small amount of water. • In case of direct, acid, basic & reactive dyes, which are water soluble, lump formation can take place if water is poured over the dye powder or if the dye powder is added to water. • The correct procedure is to add a little amount of water to the dye powder & to make a paste by proper stirring. • When all the dye is pasted, further quantity of water is added & heated to the required temperature and stirred till complete solution is obtain. • If the pasting is not proper prior to addition of water, small lumps of the dye powder remain undissolved & during printing, these small lumps get deposited on the fabric & produce dark spots. • Therefore it is necessarily used a suitable wetting agent while dissolving the dye. • The wetting agent reduces the surface tension of water & facilitates the wetting of dye particles & ultimately results in solubilising of the dye by chemical reaction. • Wetting agent is used to obtain a smooth paste of the dyestuff without formation of any lumps. • It is used to dissolve the dye powder. It is not required in case of water soluble dyes. (I)Solvents/ dispersing agents: Function:- • To get bright designs • To assist dye penetration as well as dye fixation • To spread dye molecules evenly in the paste. • To prevent aggregation of dye molecules in the highly concentrated of the dye. • To prevent precipitation • To increase solubility of the dyes • To make proper printing shade • In printing paste only a limited amount of water has to be used, in which dyes reach saturation • Commonly used solvents include Acetone, alcohol, glycerine, urea etc.. • These are used as additives to printing paste to produce better prints & high colour value. • It is useful in printing vat & azoic for increasing solubility of dyes, so that deeper & better penetrated shade can be obtain. • Glycine – A (BASF), Glycine – B (ICI) (thiodiethylene glycol) are excellent solvents for basic, direct, acid & disperse dyes. Deforming agents (Anti- foaming agents) • To prevent the foam generation during printing • In roller printing; one colour may be blue & other may be red, the foam of one colour may fall on the other, sometimes mixing of colours may occur. • The foam formed in the colour box produce faulty prints & to avoid this fault defoamer should be incorporated in the printing paste. • example:- Silicone, Sulphated oil, Perminol KB, Emulsified pine oil, Turpentine, Emulsifiable hydrocarbons • Silicone defoamer readily emulsifiable hydrocarbon, sulphated oils, etc. may be used for this purpose. • Perminal KB (ICI) is neutral yellowish brown liquid containing an aqueous emulsion of sulphated sperm oil & pine oil. • Emulsified pine oil is readily miscible with water & can be used as defoamer. • Triactyl phosphate is also a very good defoaming agent.