Dyeing - Various Methods of Dyeing & types.ppt
- 1. VARIOUS METHODS OF DYEING INTRODUCTION TO SPECTROSCOPY Prof. C. Nandhakumar Assistant Professor Department of Chemistry Sri Ramakrishna College of Arts & Science Coimbatore - 641 006 Tamil Nadu, India 1
- 4. Direct Dyes can be simply defined as a dye that is soluble in water and is primarily utilized within the textiles industry. Direct dyes are effectively utilized to colour materials that are made from wool, cotton, and silk. Depends on – nature of dye and conditions of dyeing Direct Dyes through hydrogen bonding and electrostatic forces are attracted to the fabric material that is being utilized.
- 5. Direct dyes are generally utilized by the incorporation of spraying, immersion, and padding processes. Direct dye is also used to dye leather, paper, and other materials. The primary limitation of direct dye is that it is prone to fade and might even start to bleed colour when exposed to sunlight or due to frequent washing. However, it is essential to note that direct dyes are easy to use and do not require harmful chemicals to complete the dyeing procedure.
- 6. Properties of Direct Dye: Solubility: Direct dyes are soluble in water and can be easily applied to the fiber. Brightness: Direct dyes offer good brightness and intense colour. Affinity: Direct dyes have a high affinity for cellulosic fibers and can be easily absorbed by them. Easy to apply: Direct dyes are easy to apply and require simple processing. Cost-effective: Direct dyes are relatively cheap compared to other types of dyes. Usage: Direct dyes are commonly used to dye cellulosic fibers such as cotton, rayon, and paper.
- 7. DYE BATH - PREPARATION Dye in cold water Sodium sulphate and sulphuric acid or Acetic acid Material is introduced in dye bath T-60˚C Common salt or Glauber’s salt Material is rinsed and dried
- 8. Washing fastness is improved by following treatments 1. Development with diazonium salts 2. Diazotisation and development 3. Treatment with chromium fluoride or sulphate 4. Treatment with formaldehyde 5. Treatment with copper salts Useful in modifying the shade of the dyed fibre
- 9. Cotton, Linen and Rayon- do not show affinity for many dyes that are used for wool and silk. So, they can be dyed with direct dyeing method. Steps : Dye is dissolved in hot water. 5-20% of sodium sulphate & 0.5- 2% Sodium carborane are added. Now fibres are introduced in dyeing bath at 50-60˚C and then raised to 85-95 ˚C. Dyeing is completed in 1 hour.
- 11. The word vat means, ‘Vessel’. The dyes take their name from vatting. The vat dyes are naturally coloring matter and kept in wooden vat and make solubilise vat dyes by the process of fermentation – so it is called vat dye. Properties Vat dyes are natural colouring dyes. Vat dye is water insoluble and can’t be applied directly on textile material. Vatting process is needed for making the insoluble vat dyes into soluble form.
- 12. Vat dyes retain C=O chromophore in structure, which renders water insolubility. These are water-insoluble dyes and cannot be used on fabrics directly. vat dyes require a vatting process which involves the conversion of water-insoluble dyes into water- soluble leuco form. During the vatting process, reducing agents such as sodium hydrosulfite and sodium hydroxide are added.
- 13. DYE BATH PREPARATION – VAT DYE DYE (Form of paste with water) Water containing caustic soda and Hydrosulphite Water Cotton cloth is impregnated in the above vat liquor Steaming process (proper fixation of leuco compound to the fabric) Bath containing oxidising agents (Chromate, acetic acid or perchlorate) Generation of Colour Soaped, rinsed and dried 1 2 3 4 5 6 7
- 14. EXAMPLE
- 15. The vat dyes have excellent light fastness due to stable electron arrangement in the chromophore (colour-bearing group) of the dye molecule and presence of numerous benzene rings. Vat dyes have excellent wash fastness owing to the aqueous insolubility of the oxidized dye absorbed in the fiber and due to large vat dye molecules trapped within the polymer system. However, vat dyes are usually very expensive and need more expertise for their application because of greater number of steps involved in dyeing. USES
- 17. A mordant or dye fixative is a substance used to set (i.e., bind) dyes on fabrics. It does this by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in cell or tissue preparations. Although mordants are still used, especially by small batch dyers, it has been largely displaced in industry by directs.
- 18. Mordant red 19 is a typical mordant dye. Like many mordant dyes, it features the azo group (RN=NR) and various sites for chelating to metal cations. Example:
- 19. Common dye mordants Tannic acid oxalic acid Alum chrome alum sodium chloride and certain salts of aluminium, chromium, copper, iron, iodine, potassium, sodium, tungsten and tin.
- 20. PROPERTIES OF MORDANT DYES Mordant dyes - Economical dyes and are used to produce dark green, blue and blacks. Good levelling and colour fastness properties. The interaction between fibre and dye is established through strong ionic bonds which are formed between the anionic group of colourant and ammonium cations on the fibres. Chromium or metal ion acts as bridge between dye and the fibre which gives strong linkage and excellent fastness properties.
- 21. Whenever mordant dyes are applied– Pretreatment of the fibre is most important. The mordant becomes attached to the fibre and then combines with the dye to form an insoluble complex called a LAKE. Eg. Mordant- Aluminium hydroxide Aluminium hydroxide gets precipitated in the cotton fibre. When Alizarin (dye) is added, this mordant binds to it and forms Aluminium lake.
- 22. DYE BATH PREPARATION- MORDANT DYE Dye+2-5% acetic acid and 10% of sodium sulphate Temperature is maintained at 50-60˚C Fibre is introduced in to dye bath Temperature is raised to boil till uniformity is attained Temperature is dropped and sodium dichromate (1/2 the weight of dye) is added Rinsed and dried Step: 1 Step: 2 Step: 3 Step: 4 Step: 5 Step: 6
- 24. The term ‘Disperse dye’ is an organic colouring substance which is free from ionizing group are of low water solubility and are suitable for dyeing hydrophobic textile materials. It has low molecular weight and derivatives of Azo, Anthra – quinine, Di phenyline amine and other components. It is used for dyeing polyester fibres. Developed from cellulose acetate and polyamide fibres.
- 25. PROPERTIES OF DISPERSE DYES Disperse dyes are non-ionic dyes. So they are free from ionizing group. They are ready made dyes and are insoluble in water or have very low water solubility. They are organic colouring substances which are suitable for dyeing hydrophobic fibres.
- 26. Disperse dyes are used for dyeing man made cellulose ester and synthetic fibres specially acetate and polyester fibres and sometimes nylon and acrylic fibres. Carrier or dispersing agents are required for dyeing with disperse dyes. Disperse dyes have fair to good light fastness with rating about 4-5. The wash fastness of these dyes is moderate to good with rating about 3-4. Of all dyestuffs disperse dyes are of smallest molecular size.
- 27. METHOD OF APPLICATION Dye is pasted on the fibre at 40˚C Dispersing agent and carrier are added to the dye bath Carrier- Trichlorobenzene, biphenyl or o-phenyl phenol Temperature- 80 ˚C Alternate process- Thermosol process Sublimation (Vaporisation) Finishing Finishing 1 2 3 4
- 29. Azo dyes are organic compounds bearing the functional group R−N=N−R , in which R and R ′ ′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N=N- C linkage. Azo dyes are synthetic dyes and do not occur naturally. Most azo dyes contain only one azo group but there are some that contain two or three azo groups, called "diazo dyes" and "triazo dyes" respectively.
- 30. Azo dyes comprise 60-70% of all dyes used in food and textile industries. Azo dyes are widely used to treat textiles, leather articles, and some foods. There are about 2000 kinds of azoic dyes on the market. The dyes containing azo groups – N = N – are called Azoic Dye. These are not ready made dyes but are produced by reaction of two components – Diazocomponent or Base/Salt and coupling component (Napthol). Dye formation in fiber occurs on the basis of coupling reaction.
- 31. Chemical structure of Solvent Yellow 7 an orange coloured azo dye.
- 32. PROPERTIES Light fastness property is admirable. Brightness of shade is also admirable. It is insoluble in water. These dye stuffs are always used in dyeing cellulosic material. Here dyeing operation is completed by two bath arrangement. One is called impregnation bath and another is called developing bath. Suitable for lighter shade dyeing.
- 33. Two bath of individual recipe is used for dyeing with azo dyes. Impregnation Bath. Developing Bath. USES Firstly, the color fastness of the azoic color is good. Secondly, it has a wide color range. Thereafter, it has a versatile application area. Moreover, it is cost-effective than other dyes. It is compatible to use with different dyeing, and printing techniques. Also, it has the ability to absorb light. Lastly, the environmental impact is low.
- 35. The term “acid dye” derives from the dyeing process, which is carried out in an acidic aqueous solution (pH 2.6). Acid dyestuff is so called mainly due to two reasons. In the first place these classes of dyestuff were applied in a bath containing mineral or organic acids like sulphuric, acetic or formic acid and secondly most of them are sodium salts of organics acids. They are commonly used for dyeing protein fibers (e. g. wool and silk) and nylon fibers. Acid dyes are anionic in nature, and their negatively charged anions are attracted by positively charged amino groups in wool under acidic conditions.
- 36. A common property of these dyes is their mechanism of interaction with the fiber polymers, which leads to strong binding of the dye to the material. The binding of the dye at least partly can be understood to follow an ion exchange mechanism. Ionic bonds are formed between charged groups present in the fiber polymer and the charged dyestuff molecule. The dyes are important for coloration of protein fibers (wool, silk) and polyamides, which contain ammonium groups at low pH. These cationic groups serve as binding anchor to build an ionic bonding with negatively charged groups, for example, sulphonate groups in the acid dye and metal complex dye.
- 37. Chemical structure of acid dye
- 38. To achieve water solubility of the dye To build an ionic bond linkage to the fiber Besides the ionic bond, also secondary attractive forces (Van der Waals forces) contribute to strengthening of the dyestuff–fiber interaction.
- 39. Properties of acid dyes Acid dyestuff is soluble in water. These dyes are anionic in nature. They are usually combined with basic dyes. These dyes are suitable for wool, silk, polyamide and modified acrylics. These dyes are generally applied in the presence of acids like sulphuric, acetic or formic acid to neutral pH bath. These dyes have no affinity for cotton cellulose hence not suitable for cellulosics. They have substantivity towards protein and polyamide fibers. These dyes combine with the fiber by hydrogen bonds, vander waals forces or through ionic linkages. The dyed acid colors have good light fastness and moderate washing fastness.
- 40. DYE BATH PREPARATION- ACID DYES DYE in cold water Small qty of sodium sulphate and sulphuric or acetic acid Fibre is introduced in to the dye bath Temperature is gradually increased Dyeing is completed at boiling temperature (one and half hours) Rinsed and dried
- 42. A dye, which is capable of reacting chemically with a substrate to form a covalent dye substrate linkage, is known as reactive dyes. The reactive dyes constitute the most commonly used class of dyes for dyeing cellulosic textiles, because of their good all-round properties, such as water solubility, ease of application, variety of application methods, availability of different shades, brightness of color shades, good to excellent wash and light fastness and moderate price. Reactive dyes may have poor fastness to chlorine bleach.
- 43. Here the dye contains a reactive group and this reactive group makes covalent bond with the fibre polymer and act as an integral part of fibre. This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group of cellulosic fibres on between the dye molecules and the terminal –NH2 (amino) group of polyamide or wool fibres. Fibresdyed Cotton, rayon, flax and other cellulosic fibres. Polyamide and wool fibres. Silk and acetate fibres.
- 44. Dyeing methods employed Impregnation by padding Dyeing in the dye bath First method Dye is dissolved in one vessel Wetting agent- sod.sulphate and sod. bicarbonate----in another vessel Mixing these 2 solutions Cotton fabric is padded and dyed above 100˚C Function of bicarbonate- is to yield alkali which fixes the reactive dye on the fabric. Function of Sodium sulphate- is to prevent the movement of the dye during drying.
- 45. SECOND METHOD Dyeing with certain reactive dyes (2-3%) of the dye + High concentration of common salt USES Medical Industry Food Industry Leather Colouration Dyeing of Fur Skins Dyeing of Double Weave Cloths Wood Staining and Coating Ink Formulation Jute Dyeing