SELECTION OF DYEING PROCESS FOR DYEING OF TEXTILE MATERIAL

SELECTION OF DYEING PROCESS:

Even dyes that belong to the same class can have differing degrees of colorfastness to the same condition, so that the consumer has no real guarantee of color permanence unless a label specifies that a particular fabric is colorfast. Dye performance labeling is not required by any form of legislation or regulation. Some manufacturers do, however, include colorfastness information on labels. Such labels will generally describe the conditions under which the fabric is colorfast, such as “colorfast to laundering, but not to chlorine bleaching” or “colorfast to sunlight.” A few terms may be found on labels that carry an assurance of colorfastness, such as trademarks that have been applied to solution-dyed synthetic fibers. The colorfastness of one class of dyes, the vat dyes, is so consistently good for laundering that the term “vat dyed” on labels has come to be accepted as an assurance of good colorfastness.

Textile may be dyed at any stage of their development from fiber into fabric or certain garments by the following methods:

• Stock dyeing, in the fiber stage

• Top dyeing, in the combed wool sliver stage

• Yarn dyeing, after the fiber has been spun into yarn

• Fabric/ Piece dyeing, after the yarn has been constructed into fabric

• Solution pigmenting or dope dyeing before a manmade fiber is extruded through the spinneret

• Garment dyeing after certain kinds of apparel are knitted /Woven

Stock Dyeing:

Mass Coloration

Mass coloration is the addition of color to manufactured fibers before they are extruded. These fibers have been variously known as spun-dyed, solution-dyed or doped.:; ed. iib.,is extruded, it carries the coloring material as an integral part of the

fiber.This “locked-in” color is extremely fast to laundering (that is, it will not diminish); however, such colors can be sensitive to light and bleaching or may fade. The range of colors in which solution dyeing is done is rather limited for economic reasons.

The fiber manufacturer must produce substantial quantities of fiber to justify the expense of adding an extra step during the manufacturing process. Furthermore, fiber production takes place well in advance of the time when fabrics reach the market.

Fashion color trends may change fairly rapidly, so that, by the time a mass colored fabric reaches the market, the color may be out of fashion and not salable. For this reason, spun-dyed fabrics are generally produced in basic colors. Mass coloration is used on acetate to prevent gas fading. Gas fumes in the air may turn some blue or green dyes used for acetate to pink or brown.

Dyeing Fibers

When color is added at the fiber stage, this process is known as fiber dyeing or stock dyeing. It is a batch process in which loose (usually staple) fibers are immersed in a dyebath. dyeing takes place, and the fibers are dried. Exhaustion is quicker in fiber dyeing because the dye liquor has better access to fiber surfaces.

Levelness may be a problem but its effect can be minimized by blending fibers later during yarn processing. Stock-dyed fibers are most often used in tweed or heather effect materials in which delicate shadings of color are produced by combining fibers of varying colors. The yarns in Harris Tweed fabrics are a distinctive example of fiber dyeing. Fiber-dyed fabrics can be identified by untwisting the yarns to see whether the yarn is made up of a variety of different colored fibers. In solid-colored yarns untwisted stock-dyed fibers will be uniform in color, with no darker or lighter areas. Stock dyeing refers to dyeing a staple fiber before it is spun.

There are two methods.

The first method, bale dyeing, applied mostly on wool and all types of manmade fibers, is that of splitting the bale covering on all six sides, placing the entire bale in a specially designed machine (the covering and straps need not be removed), and then forcing the dye liquor through the bale of fiber. In stock dyeing, which is the most effective and expensive method of dyeing, the color is well penetrated into the fibers and does not crock readily.

**yarn & fabric dyeing **

Yarn Dyeing

When dyeing is done after the fiber has been spun into yarn, it is described as yarn dyeing. Cloth made of dyed yarns is called yarn-dyed. Yarn-dyed fabrics are usually deeper and richer in color. Yarn-dyed fabrics intended for laundering must be quite colorfast, or bleeding could occur. The primary reason for dyeing in the yarn form is to create interesting checks, stripes, and plaids with different-colored yarns in the weaving process.

If color has not been added either to the polymer or the fiber, it can be applied to the yarns before they are made into fabrics. Yarns may be dyed in skeins, in packages, or on beams. Special dyeing equipment is required for each of these batch processes. In skein dyeing, large skeins of yarn are loosely wound on sticks and placed in a vat for dyeing. In package dyeing, the yarn is wound onto a number of perforated tubes or springs. The dye is circulated through the tubes to ensure that the yarns have maximum contact with the dye. Beam dyeing is a variation of package dyeing, which uses a larger cylinder onto which a set of warp yarns is wound.

Many types of fabrics utilize yarn of differing colors to achieve a particular design. Stripes in which contrasting sections of color alternate in the length or crosswise direction, chambrays in which one color is used in one direction and another color is used in the other direction, complex dobby or jacquard weaves, and plaids may all require yarns to which color has already been added.

Yarn-dyed fabrics may be identified by unraveling several warp and several filling yarns from the pattern area to see whether they differ in color. Not only will each yarn be a different color, but the yarns will have no darker or lighter areas where they have crossed other yarns.

Usually yarns are dyed to one solid color, but in a variant of the technique called space dyeing, yarns may be dyed in such a way that color-and-white or multicolored effects are formed along the length of the yarn.

Skein (Hank) Dyeing:

Yarn may be prepared in skein, or hank, form and then dyed. The loose arrangement of the yarn allows for excellent dye penetration. The skeins are hung over a rung and immersed in a dye bath in a large container.

Piece Dyeing

Fabrics that are to be a solid color are usually piece dyed. In piece’ dyeing, the finished fabric is passed through a dye bath where the fibers in the fabric absorb the dye. A number of different methods are used for piece dyeing, each of which differs slightly in the way in which the fabric is handled. Fabrics may be dyed in either continuous or batch processes. In continuous dyeing, the cloth continually passes through the dyebath. This is the cheaper process and, where possible, is used for dyeing large yardages. Batch dyeing is used for shorter fabric lengths.

Some fabrics are dyed in open, Rat widths. Knitted fabrics and those woven materials that are not subject to creasing are handled in “rope” form, that is, bunched together and handled as a narrower strand. They are usually attached at the ends to form a continuous loop. Some dyeing methods are especially suitable for certain types of fabrics and unsuitable for others. Many different kinds of machines can be used for piece dyeing. The great bulk of dyed fabric on the market is dyed in the piece.

Small lots of fabrics of all fibers are dyed in batches. Piece dyeing is thoroughly satisfactory as regards levelness, penetration, and overall fastness, assuming that the proper dyes have been used. Fabric may be piece-dyed whether it is composed of only one kind of fiber or yarn or of blends of different fibers or combinations of different yarns. When the fabric is made of one kind of fiber or yarn, then dyeing is relatively uncomplicated because the one appropriate dye is used. However, when the fabric contains a blend of fibers or combination of different yarns, then special procedures are required which employ different dyes that are each specific for the particular fibers used. These procedures are called union dyeing and cross dyeing.

Union Dyeing:

This process of dyeing piece goods made of different fibers or yarns in one color may be readily accomplished. Although different fibers may require different dyes to obtain the same color, this may be done by putting the appropriate color dye that is specific to each type of fiber into one dye bath.

Cross Dyeing:

One method is a combination of stock dyeing or of yarn dyeing with subsequent piece dyeing. Cross dyeing produces varied effects. For instance, either the warp or the filling yarns may be stock-dyed or yarn-dyed, one set of yarns being left undyed. The fabric is piece-dyed after weaving; thus, color is given to the undyed yarn in a second dyebath, and the yarns that were originally stock-dyed or yarn-dyed acquire some additional coloring, which blends with the piece-dyed portion of the fabric. If yarns of vegetable fibers have been combined with yarns of animal fibers in a fabric that is to be piece-dyed, two separate dye baths must be used. The fabric is dipped into both solutions, each of which affects the fiber for which it has an affinity. This provides colorful effects. Still another method of cross-dyeing is to immerse a fabric composed of two different types of fibers into one dye bath containing two different dyes, one specific for each of the fibers. One of methods of piece dyeing is described below.

Beck Dyeing(Beam dyeing)

Long lengths of cloth that are to be dyed on a continuous process are very often beck-dyed, or box-dyed, by passing the fabric in tension-free rope form through the dyebath. The rope of cloth moves over a rail onto a reel, which immerses it into the dye and then draws the fabric up and forward to the front of the machine. The process is repeated as long as necessary to dye the material uniformly to the desired intensity of color.

Beam dyeing, which is used for lightweight, fairly open-weave fabrics, utilizes the same principle as beam dyeing of yarns. The fabric is wrapped around a perforated beam and immersed in the dyebath. Tightly woven fabrics would not allow sufficient dye penetration; hence, this method must be applied to loosely woven cloth. It has the added advantage of not putting tension or pressure on the goods as they are processed.

Jig Dyeing:

This method utilizes the basic procedure of beck dyeing. However, in jig dyeing, the fabric is held on rollers at full width rather than in rope form as it is passed through the dye bath. The rope of cloth moves over a rail onto a reel, which immerses it into the dye and then draws the fabric up and forward to the front of the machine. The process is repeated as long as necessary to dye the material uniformly to the desired intensity of color. Batch processes that dye fabric in flat widths are jig and beam dyeing. Jig dyeing is a process that places greater tension on the fabric than the beck and jet machines. Fabrics are stretched across two rollers that are placed above a stationary dyebath. The fabric is passed through the dyebath and wound on one roller. The motion is then reversed until the desired exhaustion or depth of shade is achieved. The tension created by placing the fabric on the rollers means that this process must be reserved for fabrics with a fairly close weave that will not lose their shape under tension.

Jig dyeing

Jet dyeing: - Jet dyeing is a newer method that uses propulsion of the dye liquor through the fabric to improve dye penetration. Dyeing takes place in a closed system that carries a fast-moving stream of pressurized dye liquor. A fluid jet of dye penetrates and dyes the fabric. After it passes through this jet, the fabric is floated through an enclosed tube in which the fluid moves faster than the fabric. This prevents the fabric from touching the walls, keeping it constantly immersed in the dyebath. Turbulence is created by locating elbows in the tube. The turbulence aids in diffusing dyes and dyebath auxiliaries. Since no pressure is put on the fabric, even delicate fabrics can be dyed by this process. Jet dyeing has the advantage of being economical in operation and at the same time allowing a high degree of quality control

1. Fabric guide roll

2. Loading & unloading port

3. Header tank

4. U tube

5. Suction control

6. Suction control

7. Suction control

8. Delivery control

9. Main control

10. Filter

11. Heat exchanger

12. Service tank

Solution Pigmenting, or Dope Dyeing

During the production of manmade fibers, a great deal of time and money can be saved if the dye is added to the solution before it is extruded through the spinnerets into filaments. This method also gives a greater degree of colorfastness. A process called solution pigmenting, or dope dyeing, has been used for manmade fibers ranging from rayon through saran and glass fiber.

Garment Dyeing

Certain kinds of non-tailored apparel, such as hosiery, pantyhose, and sweaters can be dyed as completed garments because they are each made of a single component and will not be readily distorted. However, allowance must be made for anticipated shrinkage. 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. Except for dyeing socks and narrow fabrics, garment dyeing, is the process of dyeing completed garments, remained a rather unimportant novelty until the second half of the 1980s; Industry sources credit two factors with a sharp increase in the amount of garment-dyed apparel. First, fashion demanded small lots of garments from fabrics with stonewashed, ice-washed, tie-dyed, overdyed, and distressed effects. These effects were more readily achieved through garment dyeing than traditional dyeing methods. The second factor was the ability of manufacturers to achieve Quick Response or Just-In-Time production through garment dyeing.

The lead time required for delivery of orders in the traditional dyeing system is about eight weeks. For garment-dyed products lead time is about two weeks. Although the process of garment dyeing is more costly than traditional piece dyeing (estimated at $1 to $3 per item), savings are achieved in the long run because manufacturers and retailers need not maintain large inventories. If undyed merchandise is left from one season, it can be dyed for sale the following season. However, if it has already been dyed and a different color is wanted, it must be overdyed, given a second dyeing to a different color. Manufacturers can be more responsive to fashion trends by producing small dye lots.

Garment dyeing is primarily applied to cotton fabrics; however, high-pressure equipment can be used to process polyester and cotton blends. To achieve consistently good results with garment dyeing, manufacturers must exercise care in a number of areas.

1. Fabric. All fabric used in one garment must come from the same bolt of fabric. If, for example, one trouser leg of a pair of jeans is cut from one bolt of fabric, and the other from another bolt, each leg may dye to a different shade. The result would be jeans in which the legs do not match.

2. Shrinkage. Fabric must also be tested for shrinkage before cutting of garments, and garments must be cut large enough to allow for shrinkage so that sizes will be accurate.

3. Thread. Thread must be chosen carefully and tested to be sure it will accept the dye in the same way as the fabric. One hundred percent cotton thread is preferred, but even with allcotton thread there may be problems. For example, mercerized thread will dye to a darker shade than unmercerized garment fabric. This will make the stitching stand out from the background fabric.

4. Labels, button, zippers. All of these supplies must be compatible with the garment fabric in terms of reaction to the dye and shrinkage. The machines used for garment dyeing are called paddle machines. To avoid entanglement during dyeing, garments are generally placed inside bags. Paddles in the machine rotate, changing directions periodically, to make sure that all pieces being dyed are equally exposed to the dye liquor. Garments are generally washed before dyeing, to remove any finishing materials that would interfere with dyeing, and after dyeing to remove excess dye.

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AUTOMATED PROCESS CONTROL IN TEXTILE AND APPAREL INDUSTRY

Textile and garments process control technology is not as specific as vision technology; process control encompasses all textile manufacturing sectors. The process controllers relevant to textile manufacturing are basic information-electronic systems that, installed on the textile and garments machine, control certain fundamental parameters relating to the production process carried out on the machine itself. Essentially, they can be broken down into 4 categories according to the technology of the controller involved, which is itself dependent upon the type of process being controlled.

AUTOMATION IN PROCESS CONTROL SYSTEM
1.Cycle programmers: These process control system are present on many dyeing machines and they are based on the general principle of activating outputs according to inputs of the process. But their actual functioning is more specific. Those control system are pre-programmed to manage a sequential cycle of operations automatically. This facilitates programming, because the only thing that has to be done is determine the sequence of the steps in the cycle and the conditions required for the passage from one step to the next (the reaching of a certain temperature, the expiry of a set time, the arrival of a go-ahead signal, etc.). There exist two types of cycle programmer: one based on a microprocessor whose hardware and software remains the property of the supplier, and one based on a PC- or PLC-formatted architecture, which offers all the advantages of standard hardware and flexible software of automated process control.

2. PC-driven Programmable Logical Controllers (PLCs): these systems of process control are equipped to receive logical information (from switch or pushbutton contacts, limit switches, photocells, any kind of ON/OFF sensor) and to activate logical outputs (electric drives, relay contacts, etc). A controller checks continuously the status of inputs (openings/closures, presence/absence of electrical current), and according to the configuration of the inputs, activates its own outputs (activated/deactivated, ON/OFF, command presence/absence). The logical correlation between input status and the output status consequently imposed is determined when programming the system. Thus, the PLC can be regarded as a completely general purpose tool, capable of carrying out, when duly programmed by the user for proper process control, the most diverse functions. In practice, PLCs are used to resolve all those problems relating to automation and sequence management that used to be resolved using electrical systems and relay logics for process control. They feature on practically all the systems used for automated process control, in textile finishing, for operations such as washing, mercerization, dyeing, drying, calendaring, raising, pad-batching and steaming.

3. Numerical Controls of process control: these control system are electronic systems, specifically designed to control the positioning of a number of moving organs (e.g., robot axes). Using special languages, they programmed the sequences of the positions of the various axes, each of which is controlled through measurement of the position of the organ. This measurement is carried out by high precision transducers (encoders, resolvers, optical rulers), which transmit to the numerical control a number (hence the name of the system) which represents that position.

4. Special programmers: This automated process control system is developed specifically to carry out dedicated functions of textile process. These programmers are designed with and for the machine, in such a way that input and output signals and processing capacity are kept to the absolute minimum. In order to reduce costs, size and maintenance of production, they are often engineered in the form of single electronic cards. The four systems of process control described above are can be integrated with one another, and are often used together.

Benefit of automated process control
 -Better process quality
 -Reduction of errors
 -Greater production flexibility
 -Rationalization of the cycle according to scientific criteria
 -Rapid personnel training
 -Greater familiarity with production characteristics
 -Scope for integration with other company information systems
 -Repeatability of procedures
 -End quality no longer dependent upon the skill and experience of staff

Limitation of automated process control
 -Need for organizational changes
 -Difficulty personalizing the system to specific requirements
 -Difficulty interfacing with different IT products
 -Need for assistance and maintenance

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AUTOMATED COLOR ANALYSIS AND COLOR CONTROL OF DYEING INDUSTRY

AUTOMATED COLOR ANALYSIS AND CONTROL OF DYE HOUSE

It is worth remembering that in the past the assessment of color reproduction was exclusively entrusted to the ability and to the experience of the eye of highly skilled operators working on the color kitchen, whose judgment, however, could be influenced by a number of physical, physiological and psychological restrictions. The success and the development of electronics have deeply transformed the color control task thanks to the introduction of new measuring instruments, which have allowed definitely scientific and objective assessment.

All the systems currently available on the market have basically the same fundamental structure and differ only in their performance and in the algorithms adopted for color analysis. These systems generally feature:

1. A spectrophotometer, which measures the different spectral components of the sample analyzed. Today the measurement is carried out by means of a xenon flash, a prism separating the chromatic components and a CCD sensor (of the type used for modern solid state television cameras that have only a single row of light-sensitive elements or pixels), which reads the intensity of all the components simultaneously;

NEW INVENTION IN TEXTILE DYEING AND FINISHING

Ultra and new modern technologies are always regarded as likely for dyeing and finishing of textile. Usually the process of textile dyeing and finishing are very slower and the process takes almost 8 to 12 hours for dyeing cotton knitted fabric with winch or jet  dyeing machine and almost 5 to 8 hours for finishing that fabric in finishing machine. It takes too much time, costly, labor depended. If we use new technology in textile dyeing and finishing, we will get a very good result.

 

On 16 January, the Hong Kong Productivity Council (HKPC) organized a seminar on dyeing/finishing and functional treatments of textiles. The seminar decision provides new perspectives on industrial upgrade by promoting new technologies in textile dyeing and finishing which both is energy saving and waste reducing. As part of the Cleaner Production Partnership Programme, the seminar aims at helping enterprises achieve green production and cost reduction at the same time.

Electrochemical Process Technology in textile dyeing and finishing:

A modern invention in textile dyeing and finishing is the development of Electrochemical process technology. Electrochemistry means the use of electrical energy in initiating chemical reactions, replacing traditional aid agents in direct chemical reactions. Taking sulphur dyes as example, in traditional technology, sulphides (such as sodium sulphide, Na2S) are used as reducing agents.

What ever the reduction process of dyeing is fast and direct, but it is wasted large amount of chemical energy and Green production has become necessary for enterprises under the update and conversion policy. The Hong Kong Productivity Council (HKPC) promotes new technologies in textile dyeing and finishing, injecting new thoughts to the industry.

New invention in Textile Dyeing and Finishing wastewater with high chemical oxygen demand (COD) value is produced, operation inefficiency become long-term. When electrochemical reduction is adopted, no reducing agents are needed and the

COD value of wastewater can be largely reduced, hence cost of wastewater treatment will be lowering. So using of direct electrochemical reduction is undoubtedly more efficient than the traditional technology, and the underlying chemical principle is also simple. However, as the stability and oxidizing/reducing power of different chemical substances are not the same, dyes can not be directly and effectively reduced by electrodes. Hence the scope of utilizing direct electrochemical reduction is quite narrow.

The system of indirect electrochemical reduction is the same, but in operation another strong oxidizing/reducing agent acts as medium, which makes the technology more applicable to different kinds of dyes. Taking indigo as example, traditional technology takes sodium dithionite (Na2S2O4) as a reducing agent, and the product should be re-oxidized in the air afterwards to fix the colour. Just like traditional reduction of

sulphides, large amount of chemical energy is wasted and wastewater with high COD value is produced.

Enterprises attempt to reduce the amount of sodium dithionite used in order to lower production cost, but such attempt produces other difficulties as well. For example, the oxidation of sodium dithionite can reduce by injecting nitrogen but is very costly. Addition of aldehydes or directly powering with electricity may devloped the reducing power of sodium dithionite, but the wastewater problem remains.

If electrochemical reduction is involved indirectly, sodium dithionite can replace as the reducing agent by the medium. The medium may supply both oxidizing and reducing substances and can regenerate so that both waste and pollution can be removed. Past experiments show that reduction by electrolysis can save about 90 percent of production cost when compared with reduction by sodium dithionite.

For reducing dyes, electrochemical process technology can be utilized in other aspects. Taking bleaching as example, the core principle of electrochemical mercerizing and bleaching is that bleaching chemicals can be produced by electrical energy and can be regenerated; hence the process is easily controlled, waste-reducing and energy-saving.

The process can be monitored so that bleaching occurs evenly. Also, the cost and danger of transportation is greatly reduced, particularly regarding hydrogen peroxide which is explosive.

Another emerging project is the technology of ozone electrolysis. Ozone is strongly oxidizing and can be used in decolorizing and other waterless dye treatments (e.g. ozone jets to prevent wearing out of jeans). As ozone can self decompose, it will not cause pollution problems once carefully treated. New perspectives on industrial upgrade by promoting new technologies which are both energy saving and waste reducing.

In conventional technology of dyeing with water, textiles should involved multiple processes with the help of aid agents, chemical salts, surfactants and reduction clearing agents. In contrast, for the supercritical waterless dyeing technology, only supercritical liquid is needed for dyeing and migration, after which the pressure and temperature can be lowered and the whole process is finished, without producing any wastewater. Also, as carbon dioxide automatically detaches from textiles and remaining dyes, the latter can be reused. More importantly, as operation procedures are reduced, the dyeing cycle is also shortened from several hours to 15 to 60 minutes; energy is also saved due to the lower operational temperature.

Regarding the cost, although the equipment required for the process is quite expensive, the supercritical substance (carbon dioxide) is cheap and the technology enjoys an overall advantage in cost. On the other hand, although the technology is not mature enough regarding application in natural fibres, the quality of the end-product made of synthetic fibres is high. Overall, the effects of interactions between different textiles with supercritical substances are yet to be fully discovered.

Plasma Treatment Technology in textle dyeing and finishing:

When a substance in its gaseous phase absorbs enough energy, the outermost electrons in the atoms will escape the nucleus’ control and become free electrons, while the atoms become positively charged. This chemical status of a substance is called plasma. As it is volatile, it can discharge electricity under certain physical conditions and react with other substances (including textiles), leading to various chemical fusions and fissions. These effects can alter the surface structure of textiles; hence plasma is suitable for surface treatment.

Since only the surface structure of materials is altered by plasma, the substrate characteristics of textiles will not be affected. Also, as small amount of plasma is enough to produce profound effect and one set of equipment can accommodate to different kinds of gaseous chemicals, the equipment is relatively cost effective and user friendly. The kinds of plasma undergoing testing are varied, including silanes (SinH2n+2) (waterproof), freons (increasing surface tension and oil- and dirt-proof effects) and phosphoruscontaining organic monomers (fireproof), etc.

Plasma treatment technology can also improve existing dyeing technology, including the newly developed technology of metallised fabrics. On the other hand, HKPC attempts to integrate plasma treatment technology and supercritical fluid dyeing technology, and replace supercritical fluid with plasma in the dyeing process. The lowpressure plasma dyeing technology is still being developed.

The textile dyeing and finishing industry is considered energy-wasting and highly-polluting, which will be forced to withdraw under the upgrade and transformation policy. However, with technological development on a full swing, traditional industries are able to overcome technical difficulties and revive after the financial crisis.

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DYEING WITH DYES

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DYEING

The color of a textile product may be its most important marketing attribute. It is the color of the dyed (or printed) fabric that first attracts and then draws consumers to particular items for sale. It is often the color of a product that sells the product. Dyeing is impregnating fiber, yarn, fabric or garment with a dyestuff. Dyes are colorants that are applied to, or formed in, a textile substrate in a molecularly dispersed form. they derive their color from the conjugated double bonds in their molecular structure.

The definition stresses that for use in textiles, dyes must be soluble or capable of being made soluble in the medium in which they are applied, or they must themselves be molecularly dispersible into the fibers. It is this property that distinguishes them from pigments. When a dye colors a fabric directly, without the aid of a fixing agent its called Direct Dye. In some other dyeing processes, a fixing agent is required to fix dye to fiber; the fixer is called mordent

Fastness of color is its ability to remain unchanged. Color fastness may be affected by such factors such as perspiration, dry cleaning, sunlight, salt water etc. Adding color to textiles, thus making fabrics marketable as fashion component, is a sophisticated and complex area where art and creativity meet with science and technology. Although the chemistry of dyes and dyeing are extremely complex, the development of electronic and computer science applied to the dyeing process has opened the world to rapid global trading and quick response systems. Matching shades of dyeing and the approval of colors may now be executed by phone and fax (without the necessity of seeing visual samples that must be sent by mail or courier) thus saving many weeks in international and domestic trade cycling. Details covering electronic and computer usage are included in this chapter as are explanations of the traditional processes of textile dyeing.

Although color is recognized as the most important element in textile sales and merchandising, it is also the source of most problems that consumers and the textile industry encounter in the production and use of fabrics. Fading, bleeding, color staining and color streaking are typical examples. Understanding the dyes and dyeing processes discussed in this chapter can aid in reducing or eliminating many of these problems.

Colorfastness of dyeing:

A fabric that retains its color during care and use is said to be dyeing colorfast. Fastness that is affected by the factors discussed above is an important concern of consumers. Small aggregates of dye molecules distributed evenly throughout the fiber make for a more satisfactory result than do surface applications of dyes. Fabrics may be more or less colorfast to a variety of different substances or conditions.

The importance of colorfastness of dyeing depends on the use of the fabric. Colorfastness to laundering is, of course, important in those garments and household textiles that must undergo frequent laundering. Some dyes are not fast to laundering but are fast to dry cleaning, or vice versa. Perspiration may cause some color change and/or color transfer, and some colors are may be lost or diminished by hear. Dyeinf colorfastness to sunlight may be important in evaluating the - usefulness of fabrics for curtains, draperies, carpets, and outdoor clothing in case of dyeing.

Light fastness of dyeing is usually a function of the dye structure rather than its retention within the fibers. The molecular structure that provides the color can be interrupted by light, particularly ultraviolet light. Additives or finishes are available to stabilize dyes from this type of action in case of dyeing.

Some dyes tend to crock, or rub off on fabrics or other materials with which they come in contact. Others will bleed into water during laundering and may be picked up by lighter-colored fabrics. Chlorine bleaches will remove color from most dyed fabrics, but some dyes are more sensitive than others to the action of chlorine bleaches of dyeing.

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MORDANTS; DYE FIXATION OF NATURAL DYES

BATCH DYEING OF WOOL WITH REACTIVE DYES

WOOL DYEING PROCESS WITH REACTIVE DYES
Batch dyeing of wool with reactive dyes is a very popular process. In batch dyeing process reactive dyes are usually applied to wool at pH 5–6 using ammonium salts, and acetic acid as required. At higher pH values, exhaustion is too low, and at lower values rapid dyes uptake gives unlevel dyeings in batch dyeing process. Slightly higher pH values are used for dyeing paler shades (pH 5.5–6.0) and lower values (pH 5.0–5.5) for deep shades in batch dyeing of wool. Fibre Reactive dyes often give quite good exhaustion at temperatures below the boil but the dyeing temperature will eventually be raised to 100 °C to ensure that reaction with the wool is as complete as possible. Some procedures recommend a holding stage at an intermediate temperature of 65–70 °C for 15–20 min to allow the dye to migrate before it reacts with the wool.

Batch dyeing machine for with reactive dyes.

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REACTIVE DYES FOR WOOL FIBRES - Details about wool dyeing,

Because of their tendency to give unlevel, skittery dyeings, reactive dyes are usually applied to wool in the presence of proprietary levelling agents in case of batch dyeing process of wool. These are often amphoteric, having both cationic and anionic groups in the molecule. In contrast to most levelling agents, which decrease the dyeing rate, the auxiliary products for dyeing wool with reactive dyes accelerate dyeing. The anionic dye complexes with the cationic site in the auxiliary product but the remaining anionic site provide substantivity for the wool surface. The bulky dye–auxiliary complex exhausts well onto the fibre surface at relatively low temperature, better than the dye alone, but cannot penetrate into the fibres. The complex breaks down as the dyeing temperature increases so that the smaller liberated dye molecules can then absorb into the wool. The use of such products avoids unlevel, skittery dyeings and provides better compatibility of dye mixtures during the batch dyeing.

Deeply dyed wool fibre or fabric with reactive dyes in batch dyeing process must be aftertreated to remove unfixed dye so as to give the best wet fastness. This is particularly important to ensure that there is no staining of adjacent undyed material during washing. After dyeing of wool with reactive dye, the material can be washed at 80 °C for about 15 min using a dilute ammonia solution at pH 8.0–8.5, and then rinsed in water with a little acetic acid. To avoid any alkali damage to the wool after batch dyeing, washing can be done with hexamine (hexamethylenetetramine from formaldehyde and ammonia) at pH 6.5, or with sodium bicarbonate. Certain proprietary chemicals can be added to the dyebath on completion of dyeing and their hydrolysis increases the bath pH to around 7. For example, hydrolysis of sodium trichloroacetate gives chloroform, carbon dioxide, both of which are volatile, and sodium hydroxide (Scheme 16.6). The actual colour removed may consist of unreacted dye, hydrolysed dye and products of the reaction of the dye with soluble wool hydrolysis products such as ammonia and hydrogen sulphide or amino acids.

Reaction related to dyeing wool with reactive dyes:

CCl3 CO2Na + H2O = HCCl3 + CO2 +NaOH

Shrink-proof wool, which has been treated with resins in the Hercosett process, remains cationic on the surface and gives rapid uptake of reactive dyes. The usual auxiliary levelling agents may be less effective in this case. The deposited resin protects the wool from damage and the best fastness results for deep shades are obtained by dyeing at 110 °C for 30 min.

Wool dyed in deep shades with reactive dyes is better protected from damage during dyeing. A number of explanations for this have been proposed. These involve protein chain crosslinking, reaction with thiol groups that interferes with 357 the reformation of disulphide links, and reaction with non-keratinous proteins in the cell membrane complex and endocuticle. So reactive dye is best for dyeing wool fibre in batch dyeing process but proper care should be taken other wise shade will be uneven.

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Vinyl sulphone dyes or Remazol dyes are good quality Reactive dyes 

After Treatment And Stripping of Reactive Dye

Structural discussion of reactive dyes those suitable for cotton fibre

Informative articles on Dye reactivity, Application and Storage of Reactive dyes

 

REACTIVE DYES FOR WOOL FIBRES

Fig: Types of reactive dyes for wool

 

Fig: Reactions of bromoacrylamido reactive dyes with wool

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BATCH DYEING OF WOOL WITH REACTIVE DYES

Wool fibre is a animal protein fibre. The chemical construction of the wool fibre is very much complex but contains a reactive functional group that used to react with the reactive group of reactive dyes. The somewhat late development of fibre-reactive dyes was partly caused by a lack of appreciation of the considerable reactivity of made of cellulose fibres (specially cotton fibre) or proteins fibres (specially wool fibre).

A number of dyes developed for wool with 2-sulphatoethylsulphone or chloroacetylamino groups were not immediately recognised as reactive dyes. In fact, the development of reactive dyes really started with the introduction of the Procion reactive dyes for cotton by ICI in 1955. Despite the many possible reactive groups in reactive dyes capable of covalent bond formation with nucleophilic groups in wool, only a limited number of types of reactive dye have been commercially successful. Figure-1 shows the major types of reactive groups. The dye chromophores are essentially those used for cotton fibre reactive dyeing. The most important reactive groups in wool fibre are all nucleophilic and are found mainly in the side-chains of amino acid residues.






































They are, in order of decreasing reactivity, thiol (the –SH of cysteine), amino (–NH– and –NH2 of say histidine and lysine) and hydroxyl groups (–OH of serine or tyrosine). Difluorochloropyrimidines undergo aromatic nucleophilic substitution of one or both fluorine atoms, the fluorine between the two nitrogen atoms being the most reactive. Bromoacrylamido groups are stable in boiling water at pH 7 and react by both nucleophilic addition to the double bond and nucleophilic substitution of the bromine atom. They can form a three-membered aziridine ring that can react further with the protein fibre resulting in a new crosslink. The actual reactive dyes are probably dibromopropionamides, which eliminate HBr on dissolving in hot water. Methyltaurine-ethylsulphones and 2 sulphatoethylsulphones form the vinyl sulphone reactive group of reactive dyes relatively slowly at pH 5–6 (1 h at the boil). This allows some textile levelling during dyeing before the vinyl sulphone dyes reacts with the wool fibre and becomes immobilized. 

This is useful in hank and winch dyeing where the liquor/goods interchange is less favourable. In fact, all commercial reactive dyes for wool have absorption rates that are greater than the rate of reaction with the wool fibre to allow some migration. Chloroacetylamino groups (–NHCOCH2Cl) react by an SN2 mechanism (Scheme 16.5). Wool reactive dyes are applied like acid dyes in weakly acidic solution. The degree of exhaustion and fixation are usually very high and clearing of unfixed dye from the goods may only be needed for deep shades. Reactive dyes for wool tend to be unlevel dyeing and are prone to give skittery dyeings. They are used more on loose fibre and slubbing than on piece goods, where they accentuate fibre nonuniformity and poor, uneven fabric preparation. A number of amphoteric or weakly cationic auxiliary products are available to assist level dyeing. Despite their good light fastness and very good washing fastness, they are still not widely used, partly because of their high cost. Red to maroon shades are very popular but there are no black reactive dyes available that can match the chrome blacks on wool fibre.

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Informative articles on Dye reactivity, Application and Storage of Reactive dyes 

Structural discussion of reactive dyes those suitable for cotton fibre 

After Treatment And Stripping of Reactive Dye 

Vinyl sulphone dyes or Remazol dyes are good quality Reactive dyes

  

REFERENCES

1. J Shore, in Cellulosics Dyeing, J Shore, Ed (Bradford: SDC, 1995).

2. D M Lewis, in Wool Dyeing, D M Lewis, Ed (Bradford: SDC, 1992).

3. A H M Renfrew, Adv. Colour Sci. Technol., 1 (1998) 12.

4. A H M Renfrew and J A Taylor, Rev. Prog. Coloration, 20 (1990) 1.

5. D A S Phillips, Adv. Colour Sci. Technol., 1 (1998) 1.

6. J A Taylor, Rev. Prog. Coloration, 30 (2000) 93

Informative articles on Dye reactivity, Application and Storage of Reactive dyes

Dye reactivity is very important terms for dyeing cellulose fibre. Shed of dyed textile fabric directly depend on the reactivity of reactive group. Highly reactive group of reactive dyes makes strong covalent bond with cotton fibre structure. The reactive groups of different types of reactive dyes have different chemical structures and show a wide range of reactivities. They were originally divided into cold- and hot-dyeing types but many current ranges would be better called warm dyeing. The most reactive types, such as DCT reactive dyes, are applied at lower temperatures (20–40 °C) and for dyeing process only require a weak alkali such as NaHCO3 or Na2CO3 for fixation. The less reactive types, such as MCT dyes required higher temperatures (80–90 °C) and stronger alkalis such as Na2CO3 plus NaOH. Many reactive dyes manufacturers now market several ranges of reactive dyes for cotton fibre , each with its own particular recommended dyeing procedure.

Gives some typical examples of reactive dyes based on the type of reactive grouping.
 

Reactive group	Commercial name of reactive dyes	Reactivity	Exhaust dyeing temperature (°C)
DCT	Procion MX (BASF)	high	25–40
MCT	Procion H (BASF) Basilen (BASF) Cibacron (Ciba)	low	80–85
MFT	Cibacron F (Ciba)	moderate	40–60
DCQ	Levafix E (DyStar)	low	50–70
DFCP	Drimarene K (Clariant) Levafix E-A (DyStar)	moderate to high	30–50
VS	Remazol (DyStar)	moderate	40–60
TCP	Drimarene X (Clariant)	low	80–95
NT	Kayacelon React (Nippon Kayaku)	moderate to high	100–130   *

Because most reactive dyes are prone to hydrolysis, their handling and use requires care. Most of the reactive dyes are readily water-soluble dye and the dye solution in dye bath is prepared in the usual way by pasting with water and then adding more water. The temperature of the water used depends upon the ease of solution and the reactivity of the dye. Hot water is not recommended for dissolving dyes of high reactivity, because of the risk of hydrolysis of the reactive group, but is suitable for the less reactive types.
 Special care must be taken for storing reactive dyes. Highly reactive dyes could be react with air. Once the dye solution of reactive dye has been prepared, it cannot be stored for later use without some risk of hydrolysis of the reactive group of reactive dyes. This decreases its fixation ability after dyeing and is a particular problem with the most reactive types of dye. Dyes containing a 2 sulphatoethylsulphone group, however, can be dissolved in neutral water at the boil without risk of hydrolysis. Formation of the reactive vinyl sulphone group requires the addition of alkali. Reactive dyes for printing are usually dyes of low reactivity so that the print paste can be stored for some time at room temperature without deterioration from hydrolysis of the reactive group. Reactive dyes of low reactivity and relatively high substantivity are valuable for dyeing using long (high) liquor ratios, using a winch machine for knitted fabric and twill tape dyeing. Exhaust dyeing method with low reactivity of reactive dyes at the higher temperatures required for fixation allows better penetration of the dyes into the cotton fibres. For continuous dyeing with reactive dyes stabilised liquid forms are available. Although these contain special pH buffers and stabilisers to minimise the hydrolysis reaction, they only have a limited shelf life. Many commercial reactive dyes are dusty powders but all physical forms must be handled with care. These dyes react with the amino groups in proteins in the skin and on mucous surfaces. Inhalation of the dust is dangerous and a dust mask is obligatory during handling. Reactive dye powders and grains are sometimes hygroscopic and drums must be carefully re-sealed. Most reactive dyes have a limited storage period, after which some deterioration can be expected. Standardisation and comparison of reactive dye powders or liquids cannot be done by the usual spectrophotometric procedure involving absorbance measurements of standard solutions. Both the reactive dye and its hydrolysed form are evenly coloured, but only the former is capable of reaction with the cellulose fibre during dyeing. Therefore, dyeing must be prepared and their colors compared with standard dyeings. Chromatographic techniques usually allow separation and quantitative measurement of the relative amounts of a reactive dye and its hydrolysis product in a given dye.
 
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Structural discussion of reactive dyes those suitable for cotton fibre

There are different types of reactive dyes that are usually compatible with cotton fibre. But molecular structure of cellolusic cotton fibre is complex. So the dyes which have more reactivity is suitable for that complex structure of cotton fibre. The molecular structures of reactive dyes resemble those of acid and simple direct cotton fibre dyes, but with an added reactive group. Usually the structure of  reactive dye assemble with azo anthraquinone  triphenodioxazine or copper phthalocyanine chromophores. The key structural features of a reactive dye are the chromophoric system, the sulphonate groups for water solubility, the reactive group, and the bridging group that attaches the reactive group either directly to the chromophore or to some other part of the reactive dye molecule. Each of these structural features can influence the dyeing and fastness properties of dyed textile material. Most of the commercial reactive dyes have a complete gamut of colours, many of which are particularly bright in color. Reactive dyes often have quite simple structures that can be synthesised with a minimum of coloured isomers and biproducts that tend to dull the shade of the more complex polyazo direct dyes. Some colours are difficult to obtain with simple chromophores. Dark blue and navy reactive dyes are often rather dull copper complexes of azo dyes and the production of bright green reactive dyes usually make. A wide range of possible fibre-reactive groups has been examined and evaluated by the dyestuff manufacturers. The final choices for commercial reactive dyes are limited by a number of constraints. The reactive group must exhibit adequate reactivity towards cotton fibre, but be of lower reactivity towards water that can deactivate it by hydrolysis. The hydrolysis of the dye’s reactive group is similar to its reaction with cellulose fibre but involves a hydroxyl ion in water rather than a cellulosate ion in the fibre. In addition, the dye–fibre bond, once formed, should have adequate stability to withstand repeated washing. Other factors involved are the ease of manufacture, the dye stability during storage and the cost of the final reactive dye.

Reactive groups are of two main types:

(1) Reactive dyes which are reacting with cellulose by nucleophilic substitution of a labile chlorine, fluorine, methyl sulphone or nicotinyl leaving group activated by an adjacent nitrogen atom in a heterocyclic ring.

(2) Reactive dyes those reacting with cellulose by nucleophilic addition to a carbon–carbon double bond, usually activated by an adjacent electron-attracting sulphone group. This type of vinyl sulphone group is usually generated in the dyebath by elimination of sulphate ion from a 2-sulphatoethylsulphone precursor group with alkali.

Although many of the early reactive dyes had only one reactive group in the dyestuff molecule, many of the newer reactive dyes are bifunctional with two or more identical or different reactive groups shows some typical fibre-reactive groups and the commonly used abbreviations for these groups. Dyes with nicotinyltriazine reactive groups (NT) will react with cotton on heating under neutral conditions. 

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After Treatment And Stripping of Reactive Dye

Washing-off of unfixed reactive dyes after dyeing:
Removal of hydrolysed and un-reacted dye from the goods is a vital step after dyeing. The amount of unfixed dye remaining in a cotton fabric dyed with reactive dyes may have to be less than 0.002% owf.

Both batch and continuous washing process involves three stages.
- Initially, the goods are rinsed in cold and warm water. This is a dilution stage in that removing as much salt and alkali from the goods as possible.
- Secondly, soaping stage much more efficient since at lower electrolyte concentrations the substantivity of the dyes less, making its desorption easier.
- Finally, again a warm rinsing to dilute the final dye solution adhering to the fibres to the point that the amount of unfixed dye carried over to the final drying is minimal. This residual quantity of dye will be deposited on the fibre surface on evaporation of the water during drying and will be easily removed by later washing. Obviously, the amount must be as small as possible.

After-treatment of Remazol dyes:
There are two factors are important during the aftertreatment of Remazol dyeing. The dyeing should not be soaped at the boil under alkaline conditions. This is ensured by neutralizing with acetic acid before soaping. The unfixed (hydrolysed) dye is best removed by boiling with a detergent solution at the boil. It is important to note that the substantivity of the unfixed dye is reduced at higher temperatures and at the boil, the dye has practically no affinity for the fibre and the loosely held dye rapidly diffuse out. If this dye is removed completely, it is not necessary to treat the dyeing with a cationic dye fixing agent to achieve the optimum perspiration and water fastness.

If the boiling after-treatment is carried out under alkaline conditions, some amount of the dye already fixed (reacted with the fibre) is separated by the rupture of the dye - fibre bond, since this bond is not stable to alkali especially at the boil.

When sodium silicate is used as the alkali for fixing the dye, neutralization with acetic acid should not be done. If it is neutralized insoluble silicic acid may get deposited in the fibre producing a harsh feel. In this case, an overflow rinsing with warm water should be given before theboiling after-treatment. (Sodium silicate is more easily washed off than caustic acid). Sodium hexametaphosphate 2 g/l is to be added to the boiling after-treatment bath. 

Stripping of dyed materials:
Partial stripping:
The material is treated in a solution containing 5 to 10 ml glacial acetic acid per 1000 ml. water at 85-95°C until the shade is reduced to the desired extent. In the case of viscose rayon 2.5-10 ml of formic acid (85%) is used in place of acetic acid. The material is then rinsed and soaped at boil for 15 minutes.

Full stripping:
It is difficult to strip fully fixed dyeing completely to a white, but they can be reduced to a form suitable for re-dyeing to dark shades. The material is treated at boil in a solution containing 5 gms of sodium hydrosulphite and 2 gms of soda ash per litre of water for 20 minutes. It is then washed and treated at room temperature in l°Tw sodium hypochlorite, soured, rinsed and soaped at boil for 1 0 - 1 5 minutes.

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Vinyl sulphone dyes or Remazol dyes are good quality Reactive dyes

Vinyl sulphone dye:
The vinyl sulphone group has played an important part in the field of reactive dyes. In1944 Farbwerke Hoech AG prepared reactive dyes with the name of Remazol Which have the formulae

  D-SO₂ –CH₂  -CH₂ –OSO₃H    and    D- SO₂- CH₂ –CH₂Cl

These substance are precursor from which, in the presence of mild alkali, sulphone derivatives are formed in the dyebath.
Other precursor are:
Thio sulphato ethyl sulphone
Dialkayl aminoethyl sulphone
Phosphato ethyl sulphone

In case of both P^H  and temp promote the liberation of the vinyl sulphone group which confers reactivity with cellulosic and protein fibers.

D-SO₂- CH=CH₂  + HO-Cell   =   D-SO₂-CH₂-CH₂-O-Cell

D-SO₂-CH=CH₂  + H₂HR       =     D-SO₂-CH₂-CH₂-HNR  

The dyes according to their type, can be applied at ambient temperature 40⁰C and 60⁰C, the total time required for absorption and fixation being 2 hours, 1.5 hours and 1 hours respectively. 

Application of Remazol dye:

    The application in winch dyeing with Remazol dyes is very easy process. The dyebath is raised between 20⁰ C and  30⁰C and polyphosphate(e.g Calgon), the dissolved dye, electrolyte and appropriate quantity alkali are added. The temperature and the corresponding times of dyeing are as following:

20-30⁰C         Dye for 2 hours

40⁰C               Raise to 40⁰C in 10 minutes and continue to run for 90 minutes in 1.5 hours

60⁰C               Raise to 60⁰C in 20-30 minutes and continue to run for 60 minutes

Dyeing instruction regarding quantities of phosphate, electrolyte and alkali are tabulated below:

Liquor ratio is 1:15 to 1: 30

Dyeing temp                              60⁰C                  40⁰C                  20-30⁰C

Phosphate (g/l)                            1                           1                        1

NaCl (g/l)                                   50                         50                       50

Tri sodium phosphate (g/l)          5-10                    10-15                      -

Or Na₂CO₃(g/l)                          20                          -                          -

NaOH 32.5% ml/l                       1                          1-2                      2-4  

The main feature of vinyl sulphone dyes are:

           • Possess excellent brightness and good wet fastness.

           • The dyes are dischargeable.

           • The dyes are suitable for exhaust and different paddyeing methods and discharge printing.

           • Ease of washing off unfixed dyestuffs i.e.minimum staining of the white ground in printing.

           • They are applicable at 40°C and 60°C.

  

Precaution for dyeing with vinyl sulphone dves:

 For dyeing with vinyl sulphone dyes, it is advisable to ensure that the residual alkali has been removed from the fibre surface or neutralized prior to soaping since hydroxide ion can catalyse hydrolysis of the ether type dye-fibre bond and result in additional colour bleeding from the dye-fibre bond stability at around PH 4-5, whereas the corresponding value for dyes based on halogenated nitrogen heterocles is 6-7. the later type have dye-fibre bonds that are more sensitive to acid-catalysed hydrolysis.

Dye – O – Cell + H2 0 = Dye – OH + Cell – OH

The dyeing temperature and the nature and concentration of the alkali required are determined by the reactivity of the dye. Its degree of sulphonation and its substantivity.

Bi-functional reactive dyes:

The most obvious deficiency of reactive dyes lies in the fact that their dyeing efficiency is significantly less than 100% and may be nearer 70%. More recently, improvements have been made by introducing more than one reactive group into the reactive dye molecule so that even though one group may hydrolyse, there is another left for reaction with cellulose. Dyes with suitable diffsubstantivity properties, but carrying two reactive groups, have been carefully selected.

Bi - functional reactive dyes with two reactive groups of different reactivity towards the cotton, which have different optimal fixation conditions, sjive a more uniform decree of fixation over a wide range of dyeing temperature and fixation PH than dyes containing two identical groups.

Therefore, process control does not need to be so stringent. These types of reactive dyes give quite high fixation yields and thus less colour in the dye house effluent. Other important types of bi-functional reactive dyes include the MFT-VS type (Cibacron C, Ciba) and the MCT-Vs type used in the Sumifix Supra dyes (Sumito). The Kayacelon react range of dyes (Nippon Kayaku) are also bi-functional reactive dyes, having two NT reactive groups in each dye molecule.

There are two types of bi-functional reactive dyes, where one type is homo-functional which have two reactive groups are similar type in nature and another is haterofunctional which have two reactive groups are dissimilar type in nature reactive dyes.      

A major advantage of MCT/VS, dyes over the dyes containing either MCT or VS reactive group is the higher degree of fixation of the former and is 1.3 to 2.3 times  more than the latter. It can easily be assessed that dyeswith two identical reactive groups and dyes with two different reactive group exhibit a higher fixation yield than dyes with one group.

Studies have demonstrated that their excellent solubility, higher degree of fixation, good leveling and good –to-excellent fastness properties etc.

Dyeing method of bi-functional reactive dyes

Exhaust dyeing method:

Bi-functional reactive dyes are applicable by exhaust dyeing method in following different ways.

              1.Increase temperature method

              2.Constant temperature method

              3.All-in method 

Increase temperature method of bi-functional Reactive dye:
Procedure:

 Set the dye bath at 25⁰ C with dye solution and carry out dyeing for 10 minutes. Then add half amount of salt and continue dyeing by raising temperature to 45°C in 10 minutes. Add remaining half the amount of salt at 45°C and. Raise the temperature to 60°C in 10 minutes with continued dyeing. Continue dyeing at 60°C for further 5 minutes and then add half amount of soda ash and continue dyeing for 10 minutes. Add the remaining half amount of soda ash and dyeing is continued for further 50minutes at 60°C. The goods are then washed off. 

Constant temperature method of bi-functional Reactive dye:
Procedure:

Set theusion anSet the dye bath at 60°C with dye solution and carry out dyeing at 60°C for 10 minutes. Then add salt at 60°C and continue dyeing 25 minutes. Add half amount of soda ash

and continue dyeing for 10 minutes. Then add the remaining half amount of soda ash and dye ing is continued for further 50 minutes at 60°C. The goods are

then washed off.

All-in method

This method is particularly suitable for unmercerised cotton to produce deep shades. Moreover this method is applicable to vinylsulphone dyes and hence combination of vinylsulphone dyes is possible.

Procedure

Set the dye bath at 20-30°C. Add salt and continue dyeing for 5-10 minutes. Then add dye solution and continue for 15-20 minutes. Now add half amount of alkali and dye for 5-10 minutes. Add remaining half the amount of alkali and dye for further 5-10 minutes. Then raise the temperature to 60 C in 20 minutes (1-5⁰ C rise/minutes) and continue dyeing at 60°C for 45-60 minutes.

Salt and alkali requirements:

% shade	Glaubers salt (g/l)	Soda ash (g/l)
1.0 to 2.0	35-50	15
2.0 to above	50	15-20

For light shades of less than 1%, quantity of Glauber’s salt and soda ash to be reduced appropriately.

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