Different Types ok;f Dyeing

8/10/2019 Different Types ok;f Dyeing

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DIFFERENT TYPES OF DYEING:

Colour is applied to fabric by different methods of dyeing for different types of fiber andat different stages of the textile production process. Dyeing can be done during anystage in the textile manufacturing process. Textiles may be dyed as fibre, as yarn, asfabric, as garments, depending upon the type of the fabric or garment being produced.

These methods include direct dyeing; Stock dyeing; top dyeing; Yarn dyeing; Piecedyeing; Solution pigmenting or dope dyeing; Garment dyeing etc. Of these Direct dyeingand Yarn Dyeing methods are the most popular ones.

Direct DyeingWhen a dye is applied directly to the fabric without the aid of an affixing agent, it iscalled direct dyeing. In this method the dyestuff is either fermented (for natural dye) orchemically reduced (for synthetic vat and sulfur dyes) before being applied. The directdyes, which are largely used for dyeing cotton, are water soluble and can be applieddirectly to the fiber from an aqueous solution. Most other classes of synthetic dye, otherthan vat and sulfur dyes, are also applied in this way.

Stock DyeingStock dyeing refers to the dyeing of the fibers, or stock, before it is spun in to yarn. It isdone by putting loose, unspun fibres in to large vats containing the dye bath, which isthen heated to the appropriate temperature required for the dye application and dyeingprocess.

Stock dyeing is usually suitable for woolen materials when heather like color effects aredesired. Wool fibre dyed black, for example, might be blended and spun with un-dyed(white) wool fibre to produce soft heather like shade of grey yarn.

Tweed fabrics with heather like color effects such as Harris Tweed are examples ofstock dyed material. Other examples include heather like colours in covert and woolencheviot.

Top DyeingTop dyeing is also the dyeing of the fibre before it is spun in to yarn and serves thesame purpose as stock dyeing that is, to produce soft, heather like color effects. Theterm top refers to the fibres of wool from which the short fibres have been removed. Topis thus selecting long fibres that are used to spin worsted yarn. The top in the form ofsliver is dyed and then blended with other colors of dyed top to produce desired heathershades.


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Yarn DyeingYarn dyeing is the dyeing of the yarns before they have been woven or knitted intofabrics. Yarn dyeing is used to create interesting checks, stripes and plaids withdifferent-colored yarns in the weaving process. In yarn dyeing, dyestuff penetrates thefibers in the core of the yarn. There are many forms of yarn dyeing- Skein (Hank)

Dyeing, Package Dyeing, Warp-beam Dyeing, and Space Dyeing.

A. Skein (Hank) DyeingSkein dyeing consists of immersing large, loosely wound hanks (skeins) of yarn into dyevats that are especially designed for this purpose. Soft, lofty yarns, such as hand knittedyarns are usually skein dyed. Skein dyeing is the most costly yarn-dye method.

B.Package DyeingIn package dyeing the yarn is wound on a small perforated spool or tube called apackage. Many spools fit into the dyeing machine in which the flow of the dye bathalternates from the center to the outside, and then from the outside to the center of the

package. Package dyed yarns do not retain the softness and loftiness that skein-dyedyarns do. They are however satisfactory and very widely used for most types of yarnsthat are found in knitted and woven fabrics.

C. Warp Beam DyeingBeam dyeing is the much larger version of package dyeing. An entire warp beam iswound on to a perforated cylinder, which is then placed in the beam dyeing machine,where the flow of the dye bath alternate as in the package dyeing. Beam dyeing is moreeconomical than skein or package dyeing, but it is only used in the manufacture ofwoven fabrics where an entire warp beam is dyed. Knitted fabrics, which are mostlyproduced from the cones of the yarn, are not adaptable to beam dyeing.

Piece DyeingThe dyeing of cloth after it is being woven or knitted is known as piece dyeing. It is themost common method of dyeing used. The various methods used for this type of dyeinginclude jet dyeing. Jig dyeing, pad dyeing and beam dyeing.

Garment DyeingGarment dyeing is the dyeing of the completed garments. The types of apparel that canbe dyed are mostly non-tailored and simpler forms, such as sweaters, sweatshirts, T-shirts, hosiery, and pantyhose. The effect on sizing, thread, zippers, trims and snaps

must be considered. Tailored items, such as suits or dresses, cannot be dyed asgarments because the difference in shrinkage of the various components and liningsdisort and misshape the article.

Garment dyeing is done by placing a suitable number of garments (usually about 24sweaters or the equivalent, depending on the weight) into large nylon net bag. Thegarments are loosely packed. From 10 to 50 of the bags are placed in large tubs


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containing the dye bath and kept agitated by a motor driven paddle in the dye tub. Themachine is appropriately called a paddle dryer.

DYES:

A process of coloring fibers, yarns, or fabrics with either natural or synthetic dyes.Dyeing is an ancient art which predates written records. It was practised during theBronze age in Europe. Primitive dyeing techniques included sticking plants to fabric orrubbing crushed pigments into cloth. The methods became more sophisticated with time and techniques using natural dyesfrom crushed fruits, berries and other plants, which were boiled into the fabric and gavelight and water fastness (resistance), were developed. Dyeing can be done at any stageof the manufacturing of textile- fiber, yarn, fabric or a finished textile product includinggarments 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 themethod for dyeing the fiber, yarn or fabric

Dyes

Substances that add color to textiles. They are incorporated into the fiber bychemical reaction, absorption, or dispersion. Dyes differ in their resistance to sunlight,perspiration, washing, gas, alkalies, and other agents; their affinity for different fibers;their reaction to cleaning agents and methods; and their solubility and method ofapplication.

Various classes and types are listed below:

Acid Dyes Natural Dyes Basic (Cationic) Dyes Synthetic Dyes Direct (substantive) Dyes Disperse Dyes Sulfur Dyes Pigment Dyes Mordant Dyes Vat Dyes Reactive Dyes Macromolecular Dyes Metallized Dyes Naphthol Dyes Premetallized Dyes Gel Dyeing Developed Dyes


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Azo Dyes Aniline Dyes Anthraquinone Dyes

Acid Dyes

A class of dyes used on wool, other animal fibers, and some manufactured fibers. Aciddyes are seldom used on cotton or linen since this process requires a mordant. Aciddyes are widely used on nylon when high washfastness is required. In some cases,even higher washfastness can be obtained by aftertreatment with fixatives.

Natural Dyes

Direct Printing, it is the most common approach to apply a color pattern onto a fabric. Ifdone on colored fabric, it is known as overprinting. The desired pattern is produced bypressing 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 waspreferred as a thickening agent for printing. Nowadays gums or alginates derived fromseaweed are preferred as they allow better penetration of color and are easier to washout. Most pigment printing is done without thickeners because the mixing up of resins,solvents and water produces thickening anyway.

Basic (Cationic) Dyes

Basic dyes are water-soluble and are mainly used to dye acrylic fibers. They are mostlyused with a mordant. A mordant is a chemical agent which is used to set dyes onfabrics by forming an insoluble compound with the dye. With mordant, basic dyes areused for cotton, linen, acetate, nylon, polyesters, acrylics and modacrylics. Other thanacrylic, 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 tothe fabrics that have already been dyed with acid dyes.

Synthetic Dyes

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

Direct (substantive) DyesDyes Direct dyes color cellulose fibers directly without the use of mordants. They areused for dyeing wool, silk, nylon, cotton, rayon etc. These dyes are not very bright andhave poor fastness to washing although they are fairly fast to light.

Disperse Dyes

Disperse Dyes Disperse dyes are water insoluble. These dyes are finely ground and areavailable as a paste or a powder that gets dispersed in water. These particles dissolve


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in the fibers and impart color to them. These dyes were originally developed for thedyeing of cellulose acetate but now they are used to dye nylon, cellulose triacetate, andacrylic fibers too.

Sulfur Dyes

Sulfur Dyes Sulfur Dyes are insoluble and made soluble by the help of caustic soda andsodium sulfide. Dyeing is done at high temperature with large quantities of salt so thatthe color penetrates into the fiber. After dyeing the fabric is oxidized for getting desiredshades by exposure to air or by using chemicals. Excess dyes and chemicals areremoved by thorough washing. These dyes are fast to light, washing and perspirationand 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 theirexcellent light fastness. They do not have any affinity to the fibers and are affixed to thefabric with the help of resins. After dyeing, the fabrics are subjected to hightemperatures.

Mordant Dyes

Mordant Dyes The mordant or chrome dyes are acidic in character. Sodium orpotassium bichromate is used with them in the dyebath or after the process of dyeing iscompleted. This is done for getting the binding action of the chrome. They are mostlyused for wool which gets a good color fastness after treatment with mordant dyes. Theyare 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, Theycan be made soluble by reduction in alkaline solution which allows them to affix to thetextile fibers. Subsequent oxidation or exposure to air restore the dye to its insolubleform. Indigo is the original vat dye. These dyes are the fastest dyes for cotton, linen andrayon. 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 solutionswhich are then alkalized in a separate process. Sometimes heat treatment is also usedfor developing different shades. After dyeing, the fabric is washed well with soap so asto remove any unfixed dye. Reactive dyes were originally used for cellulose fibers only


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but now their various types are used for wool, silk, nylon, acrylics and their blends aswell.

Macromolecular Dyes

A group of inherently colored polymers. They are useful both as polymers and as dyeswith high color yield. The chromophores fit the recognized CI classes, i.e., azo,anthraquinone, etc., although not all CI classes are represented. Used for mass dyeing,hair dyes, writing inks, etc.

Metallized Dyes

A class of dyes that have metals in their molecular structure. They are applied from anacid bath.

Naphthol Dyes

A type of azo compound formed on the fiber by first treating the fiber with a phenoliccompound. The fiber is then immersed in a second solution containing a diazonuimsalt that reacts with the phenilic compound to produce a colored azo compound. Sincethe phenolic compound is dissolved in caustic solution, these dyes are mainly used forcellulose fiber, although other fibers can be dyed by modifying the process. (Also seeDYES, Developed Dyes.)

Premetallized Dyes

Acid dyes that are treated with coordinating metals such as chromium. This type of dyehas much better wetfastness than regular acid dye. Premetallized dyes are usedon nylon, silk, and wool.

Gel Dyeing

Passing a wet-spun fiber that is in the gel state (not yet at full crystallinity or orientation)through a dyebath containing dye with affinity for the fiber. This process provides goodaccessibility of the dye sites.

Developed Dyes

Dyes that are formed by the use of a developer. The substrate is first dyed in a neutralsolution with a dye base, usually colorless. The dye is then diazotized with sodiumnitrate and an acid and afterwards treated with a solution of B-naphthol, or a similarsubstance, which is the developer. Direct dyes are developed to produce a differentshade or to improve washfastness or lightfastness.

Azo Dyes


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Dyes characterized by the presence of an azo group (-N=N-) as the chromophore. Azodyes are found in many of the synthetic dye classes.

Aniline Dyes

Dyes derived chemically from aniline or other coal tar derivatives.

Anthraquinone Dyes

Dyes that have anthraquinone as their base and the carbonyl group (>C=O) as thechromophore. Anthraquinone-based dyes are found in most of the syntheticdye classes.

Different Types ok;f Dyeing

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