LESSON 3 INTRODUCTION TO DYEING STRUCTURE 1.0 OBJECTIVES 3.1 INTRODUCTION 3.2 HISTORICAL BACKGROUND 3.3 METHODS OF DYEING 3.4 THE DYEING PROCESS

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1 LESSON 3 INTRODUCTION TO DYEING STRUCTURE 1.0 OBJECTIVES 3.1 INTRODUCTION 3.2 HISTORICAL BACKGROUND 3.3 METHODS OF DYEING STOCK DYEING TOP DYEING YARN DYEING PIECE DYEING DOPE DYEING GARMENT DYEING 3.4 THE DYEING PROCESS DIRECT DYES VAT DYES REACTIVE DYES 3.5 VALUE ADDITION 3.6 ASSIGNMENTS CLASS ASSIGNMENTS HOME ASSIGNMENTS 3.7 SUMMING UP 3.8 POSSIBLE ANSWERS TO SELF-CHECK QUESTIONS 3.9 TERMINAL QUESTIONS 3.10 REFERENCES AND SUGGESTED FURTHER READING 3.11 GLOSSARY 27

2 3. INTRODUCTION TO DYEING In Lessons 1 and 2 preparatory processes like fabric bleaching and various classes of dyes that are used to give colour to the fabric were described. In this lesson, we will describe the various methods of dyeing that are used to give colour to the fabric. 3.0 Objectives After going through this lesson, you will be able to learn about:- The historical background of dyeing. Methods of dyeing. The processes used for dyeing. How further value is added to dyed fabrics. 3.1 Introduction Fig. 3.1 Dyed fabrics Colour plays an important role in our choice of a fabric. In the market fabrics with a variety of colours and shades are available (Fig 3.1). Dyeing is usually carried out by immersing textile materials in an aqueous solution of the dye called dye liquor (Fig 3.2). Normally the dye liquor consists of the dye, water and some auxiliaries like levelling agents, swelling agents, anti-foaming agents, wetting agents, dispersing agents, etc. The addition of electrolytes increases the rate of dye pick up by the fibre. Heat may sometimes be applied to improve the effectiveness of dyeing. Fig. 3.2 Dye liquor and dyed textile material 27

3 3.2 Historical Background The primitive way of ornamentation of textiles was to use natural products like; leaves, flowers, or sticks etc (Fig. 3.3). These were stuck into the fabric with Albumin or Clotted blood. The second method was to rub crushed pigments into cloth. These proved to be fast to light but not fast to water or wear. The demand for permanently fixed colours stimulated experiments. Fig. 3.3 Natural dyed fabric Crushed fruit berries (Fig. 3.4) were boiled to impart colour to the fabric but this did not result in a fast colour. Sun rays were used to bleach. Fire and smoke gave scorching effects. Finally the natural dyes were discovered which actually coloured the fibres by diffusing into them rather than not just providing a surface coating over them. Fig. 3.4 Fabric dyed with crushed fruit berries Dyeing has been a very ancient art, the first recorded account being during the Bronze Age in Europe ( BC). This first use of the blue dye, indigo obtained from the leaves of a plant called woad (Fig. 3.5), beloved by the ancient Britons, may have originated in Palestine where it was found growing wild. The most famous and highly prized colour down the ages was Tyrian purple, a dye obtained from certain Shellfish. Its use persisted through the middle ages and because of the high cost of collection, it was a mark of nobility. Fig.3.5 Woad plant and dye extracted from this plant By the eleventh century, Florence became a centre of the dyeing industry. The dye most commonly used at this time was indigo and later on Saffron. The history of dyeing took a new turn in 1856, the year in which Perkin discovered Mauveine. During the period before this, lasting many thousands of years, all the dyes used, came from natural sources (Fig. 3.6). The new era that started in the dye manufacturing industry after 1856 has resulted in several thousand synthetic dyes (Fig. 3.7). But only those dyes which are 28

4 easy to apply and which give shades of satisfactory fastness are converted into commercial products. Fig. 3.6 Natural dye Fig. 3.7 Synthetic dye Self Check Questions 1. What was the primitive way of applying colour to the textiles? 3.3 Methods of Dyeing There are six main methods of dyeing and are briefly described below: Stock dyeing Stock dyeing (Fig. 3.8) refers to dyeing staple fibres before they are spun. The old method consists of transferring the stock of packed fibres from the bale into large Vats and circulating dye liquor through the mass of fibre at elevated temperatures. The newer method, bale dyeing, which is applicable to wool and all types of manmade fibres, is that of splitting the bale covering on all six sides, placing the entire bale in a specially designed machine (the straps need not be removed), and then forcing the dye liquor through the bale of fibre. This latter method obviously saves time and cost. Cotton fibres are not dyed by this method. Fig. 3.8 Stock dyeing Top dyeing One-step nearer to the finished yarn than stock dyeing is what is called top dyeing (Fig. 3.9) in the worsted industry. Top refers to wool that has been combed to take out the short fibres, and then delivered from the combs in a rope like form about 3cm thick. The top is wound on perforated spools and the dye liquor is circulated through the perforations of the spool. Very even dyeing is possible with this method. Fig. 3.9 Top dyeing 29

5 3.3.3 Yarn dyeing Fig Dyed yarn When dyeing is done after the fibre has been spun into yarn, it is referred to yarn dyeing. there are several methods of yarn dyeing. The purpose is to have the dyestuff penetrate to the fibres in the core of the yarn; this being similar to the penetration of the fibres in stock dyeing. Cloth made of dyed yarn (Fig. 3.10) is called yarndyed. Yarn-dyed fabrics are usually deeper and richer in colours. The primary reason for dyeing in the yarn form is to create interesting checks, stripes, etc with different coloured yarns in the weaving process Piece dyeing The great bulk of dyed fabric is dyed by this method. Piece dyeing (Fig. 3.11) is thoroughly satisfactory as regards levelness, penetration, and overall fastness, assuming that proper dyes have been used. Fig Piece dyeing Fabric may be piece dyed whether it is composed of one kind of fibre or yarn or of blends of different fibres or combinations of different yarns. When the fabric is made of one kind of fibre or yarn, then dyeing is relatively uncomplicated because only one appropriate dye is used. However, when the fabric contains a blend of fibres or combinations of different yarns, then special procedures are required which employ different dyes that are specific for the particular fibres used. These procedures are called union dyeing and cross dyeing Dope dyeing Fig Dyed filament During the production of manmade fibres, a great deal of time and money can be saved if the dye is added to the solution before it is shaped by passing through the spinnerets into filaments. This method also gives a greater degree of colour fastness. A process called solution pigmenting, or dope dyeing (Fig. 3.12), has been used for manmade fibres ranging from rayon to glass fibre. Effective results have been obtained. The pigment colours are the fastest known. They are to be preferred when fastness to almost any known factor is important. It may be noted that the term Dyeing used here is a misnomer as the dye is not actually entering the fibre. 30

6 3.3.6 Garment dyeing Certain kinds of non-tailored apparel (Fig. 3.13), such as hosiery and sweaters can be dyed as completed garments because they are each made of a single component and will not be readily distorted. A number of garments are loosely packed into a large nylon net bag. The bags are then put into a paddle dyer, which is a tub with a motor driven paddle that agitates the dye bath. Garment dyeing is an economical method. It also reduces the risk of building an inventory that could be affected by changes in colour fashion. Fig Garment dyeing Self Check Questions 2. Define the following: Stock dyeing Yarn dyeing 3.4 The Dyeing Process The dyeing process (Fig. 3.14) involves a dye formulation and selecting the appropriate dyeing conditions. These will be described for direct, vat and reactive dyes for dyeing cotton. As a general guide, the amount of dye on the amount of material to be dyed should be: 1. for light shade 0.5 to 1% dye 2. for medium shade 1% to 3% 3. for dark shade greater than 3% Direct dyes Fig Dyeing process Direct dyes (Fig. 3.15) are soluble in cold or warm water and cotton can be easily dyed in them. Very bright and brilliant coloured fabrics can be obtained but their wash fastness is not good. Hence only those products which do not need repeated washing should be made from fabrics dyed with direct dyes. 31

7 Fig Direct dyes The dye is dissolved in hot water (70º 90º) and after filtering, it is placed in a vessel which contains a small quantity of water. The dye dissolves on stirring and more water is added to ensure that the fabric is completely immersed in it. The fabric to be dyed is then introduced into the dye bath. After 15 minutes, 20 to 30 grams per litre of sodium chloride (common salt) is added and stirred with a wooden stick for about 30 minutes. After this the fabric is removed and washed with cold water before drying Vat dyes Vat dyes (Fig. 3.16) are very fast and clothes that require frequent washing should therefore be dyed with vat dyes. Vat dyes are insoluble in water. To make it soluble, 25 grams of the dye is taken in a vessel and water at a temperature of 50 to 60 degree Celsius is added to it. To this is added 50 grams of liquid caustic soda. Finally 50 grams of sodium hydrosulphite is very slowly added to the mixture, taking care to stir it with a wooden stick. The dye dissolves in the solution with a change in colour. After Fig Vat dyes 10 to 15 minutes the filtered solution is poured into the dyeing vessel in which water at degree celcius and 75 to 100 grams of caustic soda had already been placed earlier. Another 30 to 50 grams of hydro-sulphite is added to this dye bath. The goods to be dyed (yarn or fabric) are then immersed in this dye bath and moved around with the help of a wooden stick in the bath. After every 15 to 20 minutes, 15 to 25 grams of hydro-sulphite should be added to the bath and this may be repeated 2 to 3 times. The goods may be removed after one hour of dyeing and then washed a few times in cold water. They then may be kept for drying in the open where oxidation takes place over a period of time. To accelerate oxidation, they may be treated with hydrogen peroxide or sodium perborate and acetic acid. Finally, the dyed goods may be given a Treatment and then washed in hot and cold water followed by drying Reactive dyes Reactive dyes (Fig. 3.17) are fast and fabrics dyed in them (particularly mercerized cotton fabrics) can have bright and brilliant colours. They are available both for cold dyeing and hot dyeing. Fig Reactive dyes For dyeing cottons, linens, and viscose rayon, the following dyeing process is recommended: 32

8 Dissolve the dye (about 10 grams) in half a litre of warm water and stir. In a separate container dissolve the common salt (4 tablespoons) and Soda ash(15 to 20 grams per litre) in half a litre of water and stir. The sample to be dyed, which has undergone preparatory processes, is wetted and when it is ready for dyeing, mix the two solutions together in a dye bath and dip the material in the bath. Move the fabric constantly for the first 10 min. and then intermittently the rest of the dyeing time which may be 1 hour or more. The dyeing may be carried out at a higher temperature (upto 70 0 c) to get better colour yields with some of the dyes. Once the dyeing is over, the fabric is taken out and rinsed thoroughly. Then the fabric may be subjected to soaping, washing and drying. 3.5 Value Addition Dyeing fabrics results in significant value addition. We can create wonderful effects by dyeing the textile material in different colours. After dyeing, we can enhance the ornamentation of the dyed textile adding on to it some extra work like a little hand embroidery work, fabric painting with acrylic colours, bead work, or machine embroidery etc (Fig. 3.18). Fig Value addition Self Check Questions 3. Which dyeing method is used for dyeing fabrics in small batches? 4. How can we add value to a dyed fabric? Activity 1. Give tabular presentation of the dyeing process for two dyes of your choice. Name of the Dye Characteristics Solublizing medium of the dye Temp of Dyeing Auxiliaries to be added Time required for dyeing After treatments to be given 33

9 3.6 Assignments Class assignment i) Dye any pretreated cotton fabric in two colours i.e. golden yellow and red Home assignment ii) Embellish the dyed fabric by doing some embroidery or fabric painting work 3.7 Summing Up To sum up, in this lesson we first trace the historical background of dyeing. The different methods of dyeing were then considered. Finally the dyeing procedures for Direct, Vat and Reactive dyes were described. 3.8 Possible Answers to Self-check Questions 1. The primitive way of applying colour to textiles was to rub crushed pigments into cloth. 2. (a) Stock dyeing: Stock dyeing refers to dyeing staple fibres before they are spun. (b) Yarn dyeing: When dyeing is done after the fibre has been spun into yarn. 3. Piece dyeing 4. The dyed fabric can be decorated by doing some embroidery work or some extra hand painting work on it. 3.9 Terminal Questions 1. Describe the dyeing process of following dyes: Direct dyes Vat dyes Reactive dyes 2. Write an essay on dyeing 3. Write the historical background of dyeing in your words. 34

10 3.10 References 1. Browne, T. (Ed.) Dyeing & Printing. Excalibur Books. 2. Gurjar, S Vastra Rangai Taknik. Rajasthan Hindi Granth Academy, Jaipur. 3. Trotman, E. R Dyeing & Chemical Technology of Textile Fibres. 6 th Ed. B.I. Publications, New Delhi. 4. Vidyasagar, P.V Handbook of Textiles. Mittal Publications., New Delhi 3.11 Suggested Further Reading 1. Gulrajani, M. L. and Gupta, D. (Eds.) Natural Dyes and their Applications to Textiles. Indian Institute of Technology, Delhi. 2. Miles, L. W. C. (Ed.) Textile Printing, Dyers Co. Publication Trust, U.K. 3. Yates, M Textiles: A handbook for designers. W.W. Norton and Co., London Glossary 1. Albumin A simple water-soluble protein found in many animal tissues and liquids 2. Ancient Very old 3. Aqueous Dissolved in water 4. Auxiliary Relating to something that is added but is not essential 5. Bale A large bundle bound for storage or transport 6. Blend Mix together different elements 7. Bronze Tan 8. Bulk Large volume 9. Circulated Cause to be distributed 10. Commenced Started 11. Distorted Strained or wrenched out of normal shape 35

11 12. Dyestuff A usually soluble substance for coloring e.g. Fabrics or hair 13. Elevated Upgraded, increased 14. Hosiery Of hose, knitted fabric 15. Immersing Thrust or throw into 16. Impart Convey 17. Indigo A blue dye obtained from plants or made synthetically 18. Liquor A liquid solution used for dyeing 19. Penetrate Sink in 20. Persisted To be persistent 21. Resources A supply that may be drawn upon when needed 22. Rubbing Move over something with pressure 23. Saffron A shade of yellow tinged with orange 24. Shellfish Aquatic invertebrate with a shell 25. Shrinkage Contraction, Becoming less or smaller 26. Spun Work fibers into a thread 27. Stimulated Induced 28. Staple Short fibres 29. Stock A supply of something available for future use 30. Suspended Cause to be held in suspension in a fluid, of articles, in chemistry 31. Union To join 32. Vat A large open container for holding or storing liquids 33. Woad A plant from which a blue dyestuff is obtained 36