fabric dyeing

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GARMENTS DYEING TOPIC-8 Fabric Dyeing History: Fabric dyeing dates back to several thousand years BC according to ancient Chinese manuscripts. The process of using natural dyes to color textiles has been used by people from every continent on the planet; it has been celebrated as an art and exploited as a dominating global industry. The most famous and highly prized color in ancient history was purple, found on textiles worn by Alexander the Great and Tai Kang of the Xia Dynasty dating back to 1070 BC. This color was considered luxurious because it comes from the tropical Murex Snail. There were so many snails needed to produce an ounce of dye that only royalty could afford it.

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Fabric Dyeing of Garments in Bangladesh.

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Page 1: Fabric Dyeing

GARMENTS DYEING

TOPIC-8

Fabric Dyeing History:

Fabric dyeing dates back to several thousand years BC according to ancient Chinese manuscripts. The process of using natural dyes to color textiles has been used by people from every continent on the planet; it has been celebrated as an art and exploited as a dominating global industry. The most famous and highly prized color in ancient history was purple, found on textiles worn by Alexander the Great and Tai Kang of the Xia Dynasty dating back to 1070 BC. This color was considered luxurious because it comes from the tropical Murex Snail. There were so many snails needed to produce an ounce of dye that only royalty could afford it.

Fabric dyeing became popular in London, England around 1100 AD; many guilds were formed attracting aspiring fabric dyers from neighboring countries like

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France and Italy. By late 1100, fabric dyeing became a substantial trade in London gaining the attention of foreign countries. Prior to the 19th century, people boiled crushed fruit, vegetables, berries and minerals to extract dye that could then be rubbed onto the fabric. This was not very effective since the colors were not fast to water and often bled in the rain and with perspiration.

There are three basic ways to color a fabric; the first is by staining the cloth, which is a method by rubbing or soaking the dye into the cloth. The second is pigmentation, where the color is fixed to the surface by an adhesive. The third is by dyeing, where the color is deposited to the fabric with an insoluble formula containing the dye.

An innovation in coloring occurred in 1856, when English chemist William Henry Perkin discovered the process of manufacturing dyes in a textile laboratory. The dye was made from material found in coal tar known as the indanthrenes, and led to the production of synthetic dyes that are now mass produced and used for fabric dyeing in textile dye houses around the world. This discovery proved that dyes could be produced synthetically and it was no longer necessary to gather natural products for use as colorants. In addition, the color is more consistent from dye lot to dye lot.

In 1716 seaweed was discovered as an effective means of bleaching cloth in Scotland. Near the end of the century, chlorine was used in place of seaweed, which is still used today.

There are many different methods of dyeing fabrics used by modern factories; typically a factory will specialize in fabric dyeing processes similar to the way a doctor specializes in their area of expertise

What is "Garment \Dyeing" - Definition &Explanation

The garment is first produced, then the complete garment is dyed.The process where garments or part garments are dyed after manufacture (garments are made up). This enables

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the client to make late decisions about the colours that can be used, which means it can be more tailored to the changes in the market place.

Introduction

In the recent years, the garment dyeing has been slowly emerging as a process to meet the ephemeral fashion trends adopted by the consumers and new machines and methods have made this process to wear a brighter future for it. However, the garment dyeing is not coming without any strings attached to its, the cautions are often pronounced in terms of fabrics and their preparation, accessories used in the garments for safe operation. Along with raw stock dyeing, yarn dyeing and piece dyeing, garment dyeing has also taken its place as another form of dyeing textiles. In the case of garment dyeing, the volume of popular and unpopular colours can be increased or decreased as envisaged from the market requirements.

GarmentDyeing

Garment dyeing may be defined [1] as the “application of colour to fully fashioned apparel articles, may be in the form of garments cut and sewn either prepared or unprepared knitted fabrics and then dyed, garments and / or components knitted from either prepared or unprepared yarn and then dyed, garments manufactured from either prepared or unprepared woven fabric and then dyed and mixed fabric garments i.e. woven and knitted fabrics manufactured from prepared fabrics and then dyed”. The benefits of processing good through garment dyeing procedure revolve around quick response and improved inventory control. Differentiation is made between garment dyeing and hosiery dyeing where socks and ladies stockings have been dyed in the prepared form [2]. Garment dyeing is the obvious way to meet the needs i.e. quick response to fashion change, lead times have been reduced to 4 to 5 days from 2 to 3 weeks as minimum with other processing routes (Fig. 1) [3].

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Greige / PFD Garments

Garmentsare made from either “greige” or “prepared” fabrics. The technique involved in garments is the same as the standard exhaust procedures of the dyes, except for pigments. Garment dyeing articles include hosiery, socks, sportwear, shirts, T-shirts, trousers, bath robes, bath mats, throw rugs. Dyeing of garments made from polyamide and their blends [4 - 8], acrylics, polyesters and mixtures of these fibres have discussed in the past.

Dyeing of cotton is more suitable for relaxed look associated with casual wear and leisurewear garments. In greige fabric garments, a full scour / bleach procedure is recommended [9] with the following recipe shown in the Table 1.

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In the case of PFD (prepared for dyeing) garments, a small amount of chemicals is used to enhance the processing such as softeners, anti-curls; lubricants must be removed to ensure proper dyeing. After 10 minutes run at 80 – 90o F, 5.0 – 8.0% of 50% NaOH is added and treated for 30 – 45 minute at 205o F.

The dyeing of the garments requires more care than the dyeing of the fabric, though there is very little difference in the dyeing procedures. This is due to the fact that processing of garments involves value added goods. The entire garment dyeing activities may be broken down in to four categories namely fully fashioned garment dyeing carried out by major dyers and finishers, cut and sewn garment covering woven and knitted fabrics, dyeing of 100% cotton goods for boutique trade suitable for hand washing and washing, desizing, bleaching denim goods, leading to stone wash, snow wash, over dyeing and highlighting effects.

Review on denim garment processing has been carried out many authors in the past [10]. A multi-colour splatter effect called “splatter dyeing” has been made possible on denim garments without necessity of tieing or knotting, using wash-fast reactive dyes combining, exhaust dyeing, pad-batch and printing technologies [10]. A technique for estimating the fraction of the total perceived colour depth in the denim fabrics has been developed where more than one colour is used in the same fabric [3]. Since the majority of garments, currently, being dyed are constructed from cotton fabrics, reactive and direct dyes are the most popular classes though other classes are also used to some extent e.g. sulphur and vat dyes [9, 11, 12, 13].

Reactive dyes appear to be very much attractive in the dyeing of cotton garments similar to fabric dyeing [14, 15]. Dyeing of cotton fabrics with sulphur dyes require more precautions to avoid damage to the garments; presence of impurities like iron up to 20 ppm may alter the yield [16] and also adversely affects copper containing buttons.

Exhaust dyeing with pigments is possible only with materials pretreated with a cationic agent which imparts substantivity to overcome the non-substantitive in nature of the pigments. Exhaust dyeing of garments with pigment involves prewash-pretreatment-exhaust dyeing-stone wash (optional)-fixation-thermo treatment [17]. Once the goods are prepared it is necessary to apply a chemical auxiliary that will impart substantivity to the pigment e.g. cationic agent and once the cationic charge is applied to the cotton piece or garments, the pigments can be applied together with an antifoaming agent and anionic dispersing agent. The exhaust method is followed by curing operation at 120 – 130o C for 20 min in presence of the catalyst [18]. Colour differences observed in the selvedges in the case of fabric dyeing can be sorted out using clustering techniques and shade sorting (555) methods [19].

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Why Garments Dyeing?

Traditionally, garments are constructed from fabricks that are pre-dyed (piece dyed) before the actual cutting and sewing. The advantage of this process is the cost effectiveness of mass producing identieal garments of particular colors. A major drawback with this approach is the risk associated with carrying a large inventory of a particular style or color in today’s dynamic market.

Dyeing

Dyeing is a method which imparts beauty to the textile by applying various colors and their shades on to a fabric. Dyeing can be done at any stage of the manufacturing of textile- fiber, yarn, fabric or a finished textile product including garments and apparels. The property of color fastness depends upon two factors- selection of proper dye according to the textile material to be dyed and selection of the method for dyeing the fiber, yarn or fabric.

Dyes Dyes are used for coloring the fabrics. Dyes are molecules which absorb and reflect light at specific wavelengths to give human eyes the sense of color. There are two major types of dyes - natural and synthetic dyes. The natural dyes are extracted from natural substances such as plants, animals, or minerals. Synthetic dyes are made in a laboratory. Chemicals are synthesized for making synthetic dyes. Some of the synthetic dyes contain metals too.

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Natural Dyes

Direct Printing It is the most common approach to apply a color pattern onto a fabric. If done on colored fabric, it is known as overprinting. The desired pattern is produced by pressing dye on the fabric in a paste form. To prepare the print paste, a thickening agent is added to a limited amount of water and dye is dissolved in it. Earlier starch was preferred as a thickening agent for printing. Nowadays gums or alginates derived from seaweed are preferred as they allow better penetration of color and are easier to wash out. Most pigment printing is done without thickeners because the mixing up of resins, solvents and water produces thickening anyway.

Synthetic Dyes

Synthetic dyes are classified based upon their chemical composition and the method of their application in the dyeing process.

Basic (Cationic) Dyes

Basic (Cationic) Dyes Basic dyes are water-soluble and are mainly used to dye acrylic fibers. They are mostly used with a mordant. A mordant is a chemical agent which is used to set dyes on fabrics by forming an insoluble compound with the dye. With mordant, basic dyes are used for cotton, linen, acetate, nylon, polyesters, acrylics and modacrylics. Other than acrylic, basic dyes are not very suitable for any other fiber as they are not fast to light, washing or perspiration. Thus, they are generally used for giving an after treatment to the fabrics that have already been dyed with acid dyes

Direct (substantive) Dyes

Direct (substantive) Dyes Direct dyes color cellulose fibers directly without the use

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of mordants. They are used for dyeing wool, silk, nylon, cotton, rayon etc. These dyes are not very bright and have poor fastness to washing although they are fairly fast to light.

Mordant Dyes

Mordant Dyes The mordant or chrome dyes are acidic in character. Sodium or potassium bichromate is used with them in the dyebath or after the process of dyeing is completed. This is done for getting the binding action of the chrome. They are mostly used for wool which gets a good color fastness after treatment with mordant dyes. They are also used for cotton, linen, silk, rayon and nylon but are less effective for them.

Vat Dyes

Vat Dyes Vat dyes are insoluble in water and cannot dye fibers directly. However, They can be made soluble by reduction in alkaline solution which allows them to affix to the textile fibers. Subsequent oxidation or exposure to air restore the dye to its insoluble form. Indigo is the original vat dye. These dyes are the fastest dyes for cotton, linen and rayon. They are used with mordants to dye other fabrics such as wool, nylon, polyesters, acrylics and modacrylics.

Reactive Dyes

Reactive Dyes Reactive dyes react with fiber molecules to form a chemical compound. These dyes, they are either applied from alkaline solution or from neutral solutions which are then alkalized in a separate process. Sometimes heat treatment is also used for developing different shades. After dyeing, the fabric is washed well with soap so as to remove any unfixed dye. Reactive dyes were originally used for cellulose fibers only but now their various types are used for wool, silk, nylon, acrylics and their blends as well.

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Disperse Dyes

Disperse Dyes Disperse dyes are water insoluble. These dyes are finely ground and are available as a paste or a powder that gets dispersed in water. These particles dissolve in the fibers and impart color to them. These dyes were originally developed for the dyeing of cellulose acetate but now they are used todye nylon, cellulose triacetate, anacrylic fibers too.

Sulfur Dyes

Sulfur Dyes Sulfur Dyes are insoluble and made soluble by the help of caustic soda and sodium sulfide. Dyeing is done at high temperature with large quantities of salt so that the color penetrates into the fiber. After dyeing the fabric is oxidized for getting desired shades by exposure to air or by using chemicals. Excess dyes and chemicals are removed by thorough washing. These dyes are fast to light, washing and perspiration and are mostly used for cotton and linen.

Pigment Dyes

Pigment Dyes Although pigments are not dyes in a true sense, they are extensively used for coloring fabrics like cotton,wool and other manmade fibers due to their excellent light fastness. They do not have any affinity to the fibers and are affixed to the fabric with the help of resins. After dyeing, the fabrics are subjected to high temperatures.

Dyeing Methods

Color is applied to fabric by different methods and at different stages of the textile manufacturing process.

Stock dyeing

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Stock dyeing The fiber is dyed even before it is spun.

Top dyeing

Top is the combed wool. In this method, the fiber is dyed in the stage just before the appearance of finished yarn.

Piece dyeing

Piece dyeing In this method, small batches of constructed natural colored fabric ardyed according to the demands for a given color.

Solution pigmenting or dope dyeing:

Dye is added to the solution before it is extruded through the spinnerets for making synthetic filaments.

Garment dyeing

Garment dyeing Dye is applied to finished products such as apparels and garments.

Stock dyeing

Stock dyeing is used to dye fibers. In this process, the staple fibers are packed into a vessel and then dye liquid is forced through them. Although the dye solution is pumped in large quantities, the dye may not penetrate completely into the fibers and some areas may be left without dyeing. However, the following

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blending and spinning processes mix up the fibers in such a thorough way that itresults in an overall even color. Woolens are usually stock dyed.

Top dyeing

Top is the combed wool sliver. It is wound on perforated spools and the dye solution is circulated through it. This method results in very even dyeing.

Yarn dyeing

Stock dyeing is used to dye fibers. In this process, the staple fibersare packed into a vessel and then dye liquid is forced through them. Although the dye solution is pumped in large quantities, the dye may not penetrate completely into the fibers and some areas may be left without dyeing. However, the following blending and spinning processes mix up the fibers in such a thorough way that it results in an

overall even color. Woolens are usually stock dyed.

When dyeing is done after the fiber has been spun into yarn, it is called yarn dyeing. In this method, the dyestuff penetrates the fibers to the core of the yarn.There are many forms of yarn dyeing- Skein (Hank) Dyeing, Package Dyeing,Warp-beam Dyeing,and Space Dyeing.

Skein (Hank) Dyeing

The yarns are loosely arranged in skeins or coils. These are then hung over a rungand immersed in a dyebath in a large container. In this method, the colour penetration is the best and the yarns retain a softer, loftier feel. It is mostly usedfor bulky acrylic anwool yarns.

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Package Dyeing

The yarns are wound on spools, cones or similar units and these packages of yarn are stacked on perforated rods in a rack and then immersed in a tank. In the tank, the dye is forced outward from the rods under pressure through the spools and then back to the packages towards the center to penetrate the entire yarn as thoroughly as possible. Mostly, the carded and combed cotton which are used for knitted outerwear is dyed through this method.

Warp-beam Dyeing It is similar to package dyeing but more economical. Here, the yarn is wound on toaperforated warp beam and then immersed in a tank for dyeing it applying pressure.

Space Dyeing

In this method, the yarn is dyed at intervals along its length. For these two procedures- knit- deknit method and OPI Space-Dye Applicator- are adopted. In the first method, the yarn is knitted on either a circular orflat-bed knitting machine and the knitted cloth is then dyed and subsequently it is deknitted. Since the dye does not readily penetrate the areas of the yarn where it crosses itself, alternated dyed and undyed

spaces appear. The OPI Space-Dye Applicator technique produces multi coloured space- dyed yarns. The yarns are dyed intermittently as they run at very high speeds through spaced dyebaths. They are continuously subjected to shock waves produced by compressed air having supersonic velocities.

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Piece Dyeing

The constructed fabrics are piece dyed for the flexibility they provide. The textile manufacturer can dye the whole fabric in batches according to the fashion demands of the time thus avoiding wastage and resultantly loss. There are several methods prevalent or piece dyeing.

Beck dyeing It is used for dyeing long yards of fabric. The fabric is passed in rope form through the dyebath. This rope of the fabric moves over a rail onto a reel which immerses it into the dye and then draws the fabric up and forward and brings it to the front of the machine. This process is repeated many times until the desired color intensity is obtained.

Jig dyeing

It is similar to the process of beck dyeing with a slight variation. The fabric in jig dyeing is held on rollers at full width rather than in rope form as it is passed through the dyebath.

Pad dyeing

Padding is also done while holding the fabric at full width. The fabric is passed through a trough having dye in it. Then it is passed between two heavy rollers which force the dye into the cloth and squeeze out the excess dye. Then it is passed through a heat chamber for letting the dye to set. After that it is passed through washer, rinser and dryer for completing the process.

Jet dyeing

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Fabric is placed in a heated tube where jets of dye solution are forced through it at high pressures. The fabric too moves along the tube. The solution moves faster than the cloth while coloring it thoroughly.

Solution pigmenting or dope dyeing This is a method applied for dyeing the synthetic fibers. Dye is added to the solution before it is extruded through the spinnerets for making synthetic filaments. This gives a colorfast fiber as the pigments are used which are the fastest known colors.

Garmendyeing

When the finished textile product such as hosiery or sweaters are dyed, it is called garment dyeing. A number of garments are packed loosely in a nylon net and put into a dyestuff filled tub with a motor driven paddle. The dye is thrown upon the garments by the moving paddles' effect.

Special chemicals for garments dyeing:

•Use of special chemicals and dyes become essential for garments dyeing. Because the use of special chemicals and dyes facilities additional advantages as well as saves accessories from risk of damage present in the garments. For example, zipper used in the garment may be protected from corrosion during garments dyeing by the use of special chemicals.

•Pretreatments of garments made from cotton grey fabrics prior to dyeing are very important because good pretreatment means half dyeing is completed. Normally pretreatment means Desizing; bacterial alpha amylase base Desizing agent provides better performance as because stability of enzyme activity is not

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affected by the variation of temperature and ph. normally at 70°c, ph 6-7.5, 60 mins processing is enough for satisfactory Desizing. Use of high temperature reduces processing time. Use of nonionic wetting agent in the bath improves Desizing effect. Water hardness helps in stability of Desizing agents. Biolase, Bactosol, etc are the example of some of such Desizing agents. •After Desizing of garments made from cotton grey fabric needs scouring and bleaching treatments to remove natural impurities present in the cotton fibers such as fats, waxes, pectins, pectose, ash, mineral organic compounds and coloring substances. During scouring and bleaching those impurities are removed from the cotton fibre. If those removed impurities forms insoluble compounds and suspended in the liquor, may redeposit on the garments fabric surface resulting color spot in the garment fabric after dyeing. To avoid such problem special chemicals like Sandopan LFW or sirrix A.K. liquid may be used.

•Metal compound containing copper, iron, etc can destroy the bleaching performance. Presence of aluminum may be damaged by the action of the alkali. To avoid the problems of metals, during chemical treatment, Sandoclear 8160 or Sandopan SF liquid may be used. During bleaching of cotton/nylon blended fabric, nylon fibre may be damaged by the action of peroxide bleaching agent. If Lanalbin PA powder is used during peroxide bleaching then the nylon fibers will be unaffected by the bleaching agent. During hydrogen peroxide bleaching, stabilizer AWN of sandoze can be used which is better as stabilizer for hydrogen peroxide; moreover it has some detergency power and softness handle property.

•To avoid the problem of crease marks formation during wet treatment, imacol brand as lubricant may be used in the chemical bath. Cotton fibres in garments form may be cataionised by sanden 8425 liquid @ 3% before garments dyeing to develop new color effect in the garments. During garments dyeing, some areas of the garments like collar, cuff, pocket and seam areas may be irregularly dyed due to interruption of dye penetration in those areas. To avoid the risk of irregular dyeing, leveling agent may be used in the bath. Drimagen E2R of clariant company if used in the dye bath, such types of problem can be avoided.

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Basic theory of garment dyeing :

•Depending on the wet fastness requirement of the fabrics, garments made from the cotton grey fabric are mainly dyed with direct dyes and reactive dyes. For low color fastness direct dyes are used and for high color fastness reactive dyes are used for cotton garments dyeing. If the cotton garments are dyed with reactive dyes then two types of reactive dyes are available in the market, namely:

•Hot brand reactive dyes.

•Cold brand reactive dyes.

•Among those two brands of reactive dyes, hot brand reactive dyes are commonly used for cotton garments dyeing. Because cotton garments dyeing with hot brand dyes facilitates easier and quicker dyeing process with reasonably good dyeing quality.Basic principle of garments dyeing with hot brand reactive dyes:

•Cotton garments may be dyed with hot brand reactive dyes as per following line diagram of basic dyeing principle:

•At first load hot water in the dye bath and add salt, lubricant, sequestering agent and maintain liquor ph at 7. Then load garments in the dye bath and start machine running. Raise the temperature of the dye bath to 80°c with in 30mins. After 5 mins at 80°c, add dye solution in the dye bath with in 15 mins time. Continue dyeing for 30 mins after dye addition in the liquor. Then add alkali to the dye liquor slowly with in 15 mins. After alkali addition, continue dyeing process for 30-60 mins. At the end reduce liquor temperature to 70°c and then drop the liquor. •After completion of dyeing, the garments are to be washed thoroughly at 40°c to 45°c for 5 mins to remove the unfixed dyes from the garments fabric surface. Then drop the liquor, again wash the garments only with the normal water for 5 mins to clean the garments again. At the end of the dyeing cycle, softener may be applied on the garments to improve the softness properties of the garments.

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Advantages of the garment dyeing :

–Comparatively lower cost of production for any item of any color and shade.–Comparatively less time is required to produce and supply the garments.–No possibility of shade variation with in the garments.–Small lots of different item could be produced at lower cost with in the less time.–Old garments could be redyed, hence becomes look new garment.–Desizing, scouring, bleaching, dyeing, and finishing could be done in the same machine.–Comparatively lower capital investment cost to set up a garment dyeing project.–In some cases, lower liquor ratio in garment dyeing requires lower water, steam, and chemical consumption, hence lower garment dyeing cost.–During fabric cutting approximately 15 % fabric is cut out as wastage, if this 15 % fabric is cut out as grey fabric rather than colored fabric, then the wastage cost will be saved.

Disadvantages of Garment Dyeing :

1. High cost of processing.2. A little complicated dyeing

Garment accessories like zips, buttons, etc impose restrictions. The garment produced from woven fabrics create many problems and it has been found that the existing textile treatment styles as developed for piece dyed fabric cannot be just assembled for garment wet processing operation such as garment dyeing, unless, they have been engineered from the original design stage for garment dyeing.

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Precautions to be taken before garments dyeing:

–Garments design should be made from engineering point of view.

–If garment is made after Desizing, scouring and bleaching of grey fabrics and then dyed in garments form, then the possibility of problems will be reduced.

–If possible, garments should be made from the grey fabrics of the same lot and same source.

–The seams should not be too tight or too loose especially in the areas containing elastic like waistband, cuff etc which may create irregular dye penetration resulting irregular dyeing.

–The garments which are produced from woven and knitted fabrics combindly, the knit fabric should be preshrunk; otherwise seam pucker may develop after garments dyeing.

–If the garment fabric is of mixed fibers, during garments dyeing, dye selection should be done carefully, having equal dye pick up to avoid irregular dyeing.

–Poor quality metals should not be used as accessories in the garments, which may be damaged during dyeing by the action of salt and alkali. If any metal component is used in the garment should be made from nickel and its alloy.

–Sewing thread used for making the garments should be of same fiber like the garment fabric, otherwise color difference may occur between the garment fabric and sewing thread.

–Button used in the garment should be selected carefully. Button made from casin, cellulose, nylon etc. may be damaged during garments dyeing but PET button is saved in this respect.

–If elastic is used in the garments and the elastic is made from the natural rubber or polyurethane fiber like Lycra may create problem during garments dyeing. To avoid such problem dye should be selected tobe copper free. During bleaching, polyurethane fibers may be damaged by the chlorine. PET type electrometric fiber is Safe in per oxide bleaching.

-Interlining is used in the most garments. Only those interlinings should be used in the garments to be dyed only recommended for the

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garment dyeing. Otherwise the performance of interlining may be destroyed.

–The garments made from compactly woven cotton fabric should be dyed with hot brand reactive dyes; otherwise problem of irregular dye penetration may occur.

–For some specific color, if specific dyes are used then the dyeing cost will be lower. For example, navy blue and black color could be produced in the garments by using sulpher dyes at lower cost.

–Presence of mineral impurities in the cotton fibers may vary which may impede the stability of the peroxide liquor during bleaching with hydrogen peroxide; even insoluble compounds may form during hydrogen peroxide bleaching. Those insoluble compounds may redeposit on the garments fabric, special chemicals are available to avoid such problem.

–Crease marks may develop in the cotton garments during dyeing. To avoid such problem, special chemicals like “Imacol brand” may be used.

Problems in garments dyeing:

With today’s exploding clothing markets of leisure, casual wear and sports wear garments wet processing has emerged as one of the best production rotues towards meeting the quick changing fashion markets.Unlike fabric or yarn as a substrate, a garment is not a uniform in texture, it is full of thick place lick seams, multilayered sits licks pockets, cuffs and shoulders. At times certain unevenness lick puckered seamslend a distinct style often highly valued but it could result into rejection of goods at other times.Here we will try to figure out certain key problems associated with garment dyeing and their possible causes, so that a garment can analyze and overcome these problems.

Garment size control and appearance Variations in yarn size/ twist Ends per inch Picks per inch Courses per inch in the knitted fabrics

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Spirality in knitted fabrics Twist of the yarn Fibre parameters Yarn formation system Yarn geometry Knit structure Fabric finishing

Poor tear strength of garment Degradation of cotton during Pretreatment Dyeing and Finishing such as stone/ enzyme washing

Pilling Low twisted yarns Use of low staple length cheaper fibre in manufacture of yarns Surface friction of fabrics/ garments during wet processing and handling Reworking of goods Cylinder rotation is too high Liquor ratio is too low Excessive cycle time

Puckering of seams during dyeing Improper selection of stitching thread Due to high twist in sewing thread High residual and wet shrinkage of sewing threads High stitching tention and improper stitch length

Poor rubbing fastness Improper washing and soaping treatment after dyeing Too much unexhausted dye in dyebath Loosely held surface indigo dyes Considerabe back staining in each step Exposure to atmospheric ozone

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Poor light fastness Use of reactive dyes which are not light fast Use of formaldehyde based dyefixing agents White , undyed or light seams Use of improper thread such as polyester thread on cotton garments Use of mercerized thread on unmercerized garments Mixing of different types of threads such as mercerized and unmercerized High tention stitching Unmatched shrinkage behavior of garment and thread

Dullness around metallic fittings Corrosion and chemical reaction between metallic parts in Pretreatment Bleaching Dyeing Finishing

Streakmarks/lines/creases Overloading of machine Friction between garments Entanglement of garments

Shade nonuniformity Differences in fabric preparation processes like1. Desizing2. Scouring3. Bleaching Inconsistency in the garment assembly

Poor dye yield Garments contain a finish,softener,or an optical brightener Garments were allowed to dry out after pretreatment stage Liquor ratio is too high Agitation is too slow Excessive washin between cycles

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Excessive time spent in any cycle Too much/ too little pretreatment Not pretreated for correct time and/ or temperature

Blotchy or non-uniformly dyed garments Garments contain a finish, softener,or an optical brightener Liquor ratio is too low(want 20:1) Excessive bath temperature at beginning of pretreat or dye cycie Dye bath temperature ramped too quickly Improper addition or dilution of dyes/chemicals Live steam injection into bath Hard water Garments not scoured Garments were allowed to dry out after pretreatment stage Garments not allowed to wet-out sufficiently before adding pretreatment

Patchy dyeing Starting temperature too high Heating rate too high Salt addition at high temperature Addition of dyes and chemical at once

Spotting Formation of foam Improper washing Machine not clean Excess pretreat not rinsed from garment before dyeing Dye not properly diluted or stirred before bath addition Incompatibility of auxiliaries

Harsness Insufficient size removal Use of high quantities of alkali Poor softner application

Smell

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Acetic acid Residual chlorine Cationic softners

Back staining Improper maintenance1. pH2. Temperature

Blotchy /unlevel dyeing in pigment dyeing Improper preparation Higher dosage of cationic reactant High rate of rise in temperature during cationization Direct contact of steam with garment Too low mlr hence uneven build-up of cationizer

Batch to batch shade reproducibility in pigment dyeing Change in pH during cationization

Dyeing of Cotton Fabric with Reactive Dyes

Introduction :

A dye, which is capable of reacting chemically with a substrate to form a covalent dye substrate linkage, is known as reactive dye.

Here the dye contains a reactive group and this reactive group makes covalent bond is formed between the dye molecules and the terminal –(OH) group of cellulosic fibres on between the dye molecules and the terminal –NH2 (amino) group of polyamide or wool fibres.

Three basic steps are as follows for reactive dyeing of cellulose fibres with reactive dyes:

1. Exhaustion of the reactive dye from an aqueous bath containing common salt or Glauber’s salt normally used in neutral condition.

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2. Addition of alkali to promote to further reactive dye uptake and chemical reaction of absorbed reactive dye with the fibres.

3. Dyed material with reactive dye is then rinsed and soaped to remove electrolyte, alkali and unfixed reactive dyes.

History :

Reactive dyes first appeared commercially in 1956, after their invention in 1954 by Rattee & Stepheness at the Imperial chemical Industry (ICI). Dyestuffs Divion site in Bleckley, Manchetor UK.

Usages :

By reactive dyes the following fibres can be dyed successfully :1) Cotton, rayon,flax and other cellulosic fibres.2) Polyamide and wool fibres.3) Silk and acetate fibres.

Trade names :

Trade name Manufacturer CountryProcion I.C.I U.K.Ciba cron Ciba SwitzerlandRemazol Hoechst GermanyLavafix Bayer Germany Reactone Geigy SwitzerlandPrimazin BASF GermanyDrimarine Sandoz Switzerland

Properties of reactive dye :

1) Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein and polyamide fibres.

2) Reactive dyes are found in power, liquid and print paste form.3) During dyeing the reactive group of this dye forms covalent bond with fibre

polymar and becomes an integral parts of the fibre.4) Reactive dyes are soluble in water.

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5) They have very good light fastness with rating about 6. The dyes have very stable electron arrangement and can protect the degrading effect of ultra-violet ray.

6) Textile materials dyed with reactive dyes have very good wash fastness with rating Reactive dye gives brighter shades and has moderate rubbing fastness.

7) Dyeing method of reactive dyes is easy. It requries less time and low temperature for dyeing.

8) Reactive dyes are comparatively cheap.9) Reactive dyes have good perspiration fastness with rating 4-5.10) Reactive dyes have good perspiration fastness.

Classification of reactive dyes :

Reactive dyes may be classified in various ways as below:

1) On the basis of reactive group :a) Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle,

like 3 types- Triazine group Pyridimine group Quinoxaline dyes

Example :Triazine derivatives: procion, cibacron.Pyridimine derivatives: reactoneQuinoxaline derivatives:levafix.

b) Activated vinyl compound : Vinyl sulphone Vinyl acrylamide Vinyl sulphonamide

Example :Vinyl sulphone: remazolVinyl acrylamide : primazineVinyl sulphonamide : levafix.

2) On the basis of reactivity :

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a) Lower reactive dye : Medium reactive dye : here pH is maintained 11-12 by using Na2CO3 in dye bath.

b) Higher reactive dye : here pH is maintained 10-11 by using NaHCO3 in dye bath.

3) On the basis of dyeing temperature :

a) Cold brand : These types of dyes contain reactive group of high reactivity. So dyeing can be done in lower temperature i.e. 320-600C.For example : PROCION M, LIVAFIX E.

b)Medium brand : This type of dyes contains reactive groups of moderate reactivity. So dyeing is done in higher temperature than that of cold brand dyes i.e. in between 600-710C temperatures.For example,Remazol, Livafix are medium brand dyes.

c) Hot brand : This type of dye contains reactive groups of least reactivity. So highTemperature is required for dyeing i.e. 720-930 C temperature for dyeing.For exmple PROCION H, CIBACRON are hot brand dyes.

Dyeing mechanism of reactive dye:

The dyeing mechanism of material with reactive dye takes place in 3 stages:-1.Exhaustion of dye in presence of electrolyte or dye absorption.2. Fixation under the influence of alkali.3. Wash-off the unfixed dye from material surface.Now they are mentioned below:Dye absorption:When fibre is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fibre.Fixation:

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Fixation of dye means the reaction of reactive group of dye with terminal -OH or –NH2 group of fiber and thus forming strong covalent bond with the fiber. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below: 1.D-SO2 -CH2-CH2-OSO3Na +OH-Cell=D-SO2-CH2-CH2-O- Cell+NaHSO3

2.D-SO2-CH2-CH2-OSO3Na+OH-Wool=D-SO2-CH2-CH2-0-Wool + NaHSO3

3. Wash –off:As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.

Application method:

These are 3 application procedures available:1. Discontinuous method-

-Conventional method-Exhaust or constant temperature method-High temperature method-Hot critical method2.Continuous method--Pad-steam method-Pad dry method

-Pad thermofix method

3.Semi-continuous method--Pad roll method-Pad jig method-Pad batch method.

CONTINUOUS METHOD OF REACTIVE DYEING:

Reactive dyeing process of pad steam method:

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This method is suitable for all types of reactive dyes. Recipe is given below:Shade Dyestuff g/l Migration

inhibitorSoda ash g/l

Salt g/l Urea g/l

Light 0-10 Small quantity of Na-alginate

5 40-60 150

Medium 10-20 same 5-10 60-80 150Heavy >20 same 10-20 80 150

Reactive dyeing process of pad steam method:

In pad steam method of reactive dyeing in the 1st bowl padding is done with reactive dye solution and urea at a temp of 60-800c. here urea helps to dissolve the reactive dye completely in water and also to penetrate the reactive dye within the fiber . some industries Na-alginate is used which act as a migration inhibit inor may be add in the 1 st bowl and other industries used Na-alginate in a separate bath just after padding with reactive dye and urea. After padding with reactive dyes, urea and migration inhibitor, the fabric is then added with soda ash and salt at 600c which is known as chemical padding. Then the fabric is passed through the steam chamber at a temp of 100-1020c where it takes 30-60 sec for fixing the reactive dye with the fabric. Then the fabric is subsequently rinsed, soaped at boil and finally washed and dried to complete the dying operation.

Reactive dyeing process of pad thermo fixation method:

Recipe :

Dye-2% on the weight of materialSoda ash-1% on the weight of materialSalt-8%on the weight of materialUrea-15% on the weight of materialNa-alginate- little amountProcess of reactive dyeing:In this method reactive dyestuff, alkali (soda ash),salt, urea and Na-alginate are mixed in the dyebath. The fabric is padded in the padding bath at room temperature. Then the padded fabric is dried in the drying unit. After drying the fabric treated for 5 minutes at 1600c in a heating chamber for thermofixation.

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After thermofixation the fabric is rinsed, soaped and rinsed. This method is suitable for moderate reactivity dye.

Semi continuous method of reactive dyeing:

Pad batch reactive dyeing method:

Recipe:

Dye-3% on the weight of materialSoda ash-15 g/lSalt-60 g/lUrea-150 g/lNa-alginate-little amount

Process of reactive dyeing:

The fabric is padded with reactive dye, alkali, salt, urea and Na-alginate at a temp of 20-250c.The padded fabric in roll form is transferred to a chamber where the temp is 200c and relative humidity is 100%.Four such rolls are prepared at the same time and they are kept at revolving condition so that dyes can’t be settled due to centre of gravity at the lower part of the roll casuing unevenness. On the basis of reactivity batching is done for 2-4 hours. Then the fabric is rinsed, soaped and rinsed. This method is suitable for high reactivity dye.Pad-Jig method of reactive dyeing:Process of dyeing:In this method of reactive dyeing the fabric is padded with dye liquor in a padding mangle. No alkali and salt is added in this stage of padding. When the fabric is padded with reactive dye it is worked at room temperature. The padded fabric is then transferred to a jigger dyeing m/c. In this machine the dye is developed with the addition of salt and alkali. After the fixation of the dye in the jigger dyeing machine the fabric is rinsed, soaped and rinsed thoroughly. This method is suitable for closely woven fabric and also for fabrics made with hard twisted yarn.

Stripping of reactive dye :

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The reactive dye cannot be satisfactory stripped from fibre due to covalent bond between dye moleculen and fibre. Stripping becomes necessary when uneven dyeing occurs. Different methods of reactive dye application:

1) Pad-batch method Pad batch processes are of two types-

a) Pad (alkali)-batch (cold) process.b)Pad (alkali)-batch (warm or hot) process

2) Pad dry method3) Pad steam method

Conclusion:

By this experiment we came to know the reactive dyes are of the least reactively because they take more temperature and more time for dveing

Defects in Dyening with Reactive Dyes

Defect : Colors are not fast to washing, Abrasion; Staining in the fabric when transporting from place to other, water maks on the fabric.

Remedy : Wash the fabric with soap and soda ash at right temperature. Adding sequestering agent will yield good results. Treating with Ammonia will also give good results.

Defects in the fabric due to Printing- Need to take out full color

Remedy : Treat the dyed fabric with Sodium Hydrosuphite with 5-10 gm Sodium Hydrosulphite at 75 C for 30-40 minutes. Add 5-7 gms Caustic Soda for even removal of colors. The color becomes light yellow or brown after removal. Wash it thoroughly with soap.

Or,

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The color can also be removed by solution of Sodium Hypochlorite. Treat the fabric with a sodium hypochlorite solution (3-5 gm Chlorine) for 20-30 minutes. Keep the pH between 9-10. The fabric is treated with Acetic acid after removal of color to remove chlorine and to neutraliza the fabric.

Or,

The fabric can be redyed after removal of color.

Defect : Bleeding in colors during washing, abrasion.

Remedy : Boil the fabric with caustic, Treat the fabric with Hydrogen Peroxide (5-10 gpl, 60-700 C) to make the color fast.

Defect : The fabric has been dyed in darker shade, uneven dyeing.

Remedy : To take out color from the fabric treat it with caustic for 45-60 min at 80-850 C.

Defect : Uneven dyeing, marks of water, marks of colors.

Remedy : Wash the fabric in soap and redye in a darker shade.

Defect : The fabric has become stiff and rough after dyeing.

Remedy : Finish after adding right softner.

Defect : Color staining of fabric, uneven dyeing.

Remedy : Redye the fabric in darker shade.

Defect : Color staining in fabrics of darker shade uneven undyeing.

Remedy : Dye the fabric in Sculpture black.

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Omitting the use of detergents in after washing of cotton dyed with reactive dyes

Description :

Both international literature and practical experience in textile mills show that detergents do not improve removal of hydrolyzed reactive dyestuffs from the fabric.

On the contrary, high temperatures do have an effect on rinsing effectveness. Tests carried out with rinsing at 90-950 C have shown that rinsing is more effective and faster at high temperatures. About 30% more unfixed hydrolysed reactive dyestuff is rinsed out after 10 minutes of rinsing at 950 C than at 750 C.

Many day houses already carry out hot rinsing and omit the use of detergents in rinsing after reactive dyeing. The product quality is not negatively affected. On the contrary, most often the fastness of the goods are better after the hot rinsing than after the traditional rinsing with deterjents, complexion agents and neutralization in the first rinse.

Energy should be recovered when using large volumes of hot process water. Energy reclamation can be done either by heat exchange between the hot outgoing process water and the cold incoming clean water or by reclamation of the hot water and re-use of both energy and water.

Main achieved enviromental benefits :

The main benefit is the reduction in consumption of detergents and pollution load discharged to the waste water. Obviously, the potential for reduction will vary according to the existing dyeing procedure at the company.

The experience of two dye houses (one mainly dyeing knitted fabrics and the other dyeing garments) shows that the average potential load reduction can be in the order of 1 kg detergent, 1 kg complexing agent and 1 kg acetic acid per 100 kg of textile.

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Additional advantages are the savings achievable in the amount of chemicals consumed to destroy reactive dyes by free radical treatment processes. In the Fenton reduction for example since the OH* radicals react very fast not only with the dyestuffs but also with many dertagents, a large amount of expensive H2O2 can be saved by omitting the use of detergents.

Operational data :

The high degree of fixation and the excellent wash-off properties typical of some new low–salt, polyfunctional reactive dyes are important factors that help obtain sufficient wash fastness with hot rinsing without the need for detergents.

It has been reported that difficulties might arise with accidental stops of the machinery. In such conditions the high tempreature of the rinsing water could cause irreversible cleavage of the bond between the reactive groups of the dye and the hydroxyl groups of cotton or viscos.

Cross- media effets :

Substituting cold rinsing with hot rinsing leads to higher energy consumption, unless thermal energy from the rinising effluent is recovered.

Applicability :

A Danish textile mills has during the last 5 years totally omitted the use of detergenrts in the rinsing process after reactive dyeing. The companytreats knitted and woven goods made of cotton/PES and dyes them all colores and shades. The application of this techinque may involve a change in the type of dyes employed. The referenced company works with bifunctional reactive dyes as Cabochon C or Bezaktiv S. Soft water is used.

Another textile mil dyeing garments of knitted and woven fabric has not used detergents during the last 5-6 years, apart from a few exceptions (i.e. red dark red or Bordeaux colours).

Economics :

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The only change in operating procedures is not omit the addition of detergents. Savings will depend on the number of reactive dyeings carried out at the company.

Driving force for implementation.

High cost for chemicals and waste water treatment.