dyeing and printing new

8/13/2019 Dyeing and Printing NEW

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Dyeing and printing

SANALRAJ.M.K

JWM/OFIL


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Dyeing

DYEING: A process of coloringfibers, yarns, or fabrics with eithernatural or synthetic dyes.

Some of the major dyeing processesare described below


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Preparatory process to Dyeing

Scouring- to remove natural impuritieslike fats, oils, waxes by treating in 2%NAOH at high temperature. For kier

boiling, amixture of 5-10 g/l caustic soda solution,1% sodium silicate, 1% soap along withwetting agent. Boiling takes place at

101oC temperature for 6-8hrs underpressure


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Grey souring- the alkali present inthe yarn is removed by treating withmineral acid like Hcl or H2SO4.

Desizing here the starch appliedbefore weaving ,to impart strengthto the warp yarn is removed by

treating with enzyme like Amylase.


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Singeing

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Bleaching

Natural colouring matters areconverted to colourless leucocompounds by nascent hydrogen or

oxidised in to soluble colourlesscompound.

Bleaching agents :

Cotton- H2O2, Sodium hypochlorite

Wool,Silk- H2O2

Synthetics- Sodium Chloride


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Mercerisation

The treatment is usually carried outunder tension, with caustic soda 15-20% (approx.

270- 330 g/l).

The liquor temperature usuallyranges between 15-20C


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Mass colored or dope dyeing

Mass-Colored: A term to describe amanufactured fiber (yarn, staple, ortow) that has been colored by the

introduction of pigments or insolubledyes into the polymer melt orspinning solution prior to extrusion.

Usually, the colors are fast to mostdestructive agents. This is also calleddope dyeing


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Yarn dyeing

Yarn Dyeing: The dyeing of yarnbefore the fabric is woven or knit.Yarn can be dyed in the form of

skeins, muff, packages, cheeses,cakes, chain-wraps, and beams.


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Dyes

DYES: Substances that add color totextiles. They are incorporated into thefiber by chemical reaction, absorption, or

dispersion. Dyes differ in their resistanceto sunlight, perspiration, washing, gas,alkalies , and other agents; their affinityfor different fibers; their reaction to

cleaning agents and methods; and theirsolubility and method of application


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Acid dyes

Acid Dyes: A class of dyes used on wool,other animal fibers, and somemanufactured fibers.Acid dyes are seldom used on cotton or

linen since this process requires amordant. Acid dyesare widely used on nylon when high washfastness is required. In some cases, even

higherWash fastness can be obtained by aftertreatment with fixatives


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Basic dyes

Basic Dyes: A class of positive-ion-carrying dyes known for their brillianthues. Basic dyes are composed of large-molecule, water-soluble salts that have a

direct affinity for silk and can be applied tocotton with a mordant. The fastness ofbasic dyes on these fibers is very poor.Basic dyes are also used on basic-dyeableacrylics, modacrylics, nylons, andpolyesters, on which they exhibitreasonably good fastness


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Direct dyes

Direct Dyes: A class of dyestuffs that areapplied directly in a neutral or alkalinebath.

They produce full shades on cotton andlinen . Direct dyes give bright shades butexhibit poor wash fastness. Various aftertreatments are used to improve the wash

fastness of direct dyes, and such dyes arereferred to as after treated direct colors.


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Disperse dyes

Disperse Dyes: A class of slightlywater-soluble dyes originallyintroduced for dyeing acetate and

usually applied from fine aqueoussuspensions. Disperse dyes arewidely used for dyeing most of the

manufactured /synthetic fibers.


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Metal & Sulfur dyesMetallized Dyes: A class of dyes that havemetals in their molecular structure. They areapplied from an acid bath. Earlier this is used fordyeing drill fabrics.Sulfur Dyes: A class of water-insoluble dyes

that are applied in a soluble, reduced form from asodium sulfide solution and are then reoxidized tothe insoluble form on the fiber. Sulfur dyes aremainly used on cotton for economical darkshades of moderate to good fastness to washing

andlight.They generally give very poor fastness tochlorine.Umbrella cotton cloth is dyed by this.


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Vat dyes

Vat Dyes: A class of water-insoluble dyeswhich are applied to the fiber in areduced, soluble form (leuco compound)and then re-oxidized to the originalinsoluble form.

Vat dyes are among the most resistant

dyes to both washing and sunlight. Theyare widely used on cotton, linen ,rayon,and other cellulosic fibers.


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Reactive dyes

Fiber-Reactive Dyes: A type of water-soluble anionic dye having affinity forcellulose fibers. In the presence of alkali,they react with hydroxyl groups in thecellulose and thus are liked with the fiber.

Fiber-reactive dyes are relatively new

dyes and are used extensively oncellulosics when bright shades are desired.

These are used for dyeing curtain cloth.


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Methods of dyeing

PADDING: The application of aliquor or paste to textiles either bypassing the material through a bath

and subsequently through squeezerollers, or by passing it betweensqueeze rollers, the bottom one of

which carries the liquor or pasteThis is used for fabrics wherecreasing to be avoided.


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ContdJET DYEING MACHINE: A high-temperature piece dyeing machinethat circulates the dye liquor througha Venturi jet, thus imparting a

driving force to move the fabric. Thefabric, in rope form, is sewn togetherto form a loop

high temperatures (maximumtemperature ranges between 135and 140C), with very limited liquor

ratio (1:5-1:15).


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When fibers in a blend are dyed thesame color, the dyeing is referred toas "union dyeing," whereas dyeing

fibers in a blend of different colors isreferred to as "cross dyeing."


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PRINTING

PRINTING: A process for producing apattern on yarns, warp, fabric, or carpetby any of a largenumber of printing

methods. The color or other treatingmaterial, usually in the form of a paste,isdeposited onto the fabric which is thenusually treated with steam, heat, or

chemicals for fixation.Printing is called localised dyeing


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Contd

Block Printing: The printing offabric by hand, using carved woodenor linoleum blocks, as distinguished

from printing by screens or roller

Blotch Printing: A process whereinthe background color of a design is

printed rather than dyed.


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Contd

Discharge Printing: In white dischargeprinting, the fabric is piece dyed, thenprinted with a paste containing a chemical

that reduces the dye and hence removesthe color where the white designs aredesired. In colored discharge printing, acolor is added to the discharge paste in

order to replace the discharged color withanother shade.

Eg: stencil printing


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Contd

Resist Printing: A printing method inwhich the design can be produced:1) by applying a resist agent in thedesired design, then dyeing the fabric, in

which case, the design remains whitealthough the rest of the fabric is dyed; or

(2) by including a resist agent and a dye inthe paste which is applied for the design,

in which case, the color of the design isnot affected by subsequent dyeing of thefabric background.

Eg; Batik, tie and dye


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Contd

Roller Printing: The application ofdesigns to fabric, using a machinecontaining a series of engraved metalrollers positioned around a large padded

cylinder. Print paste is fed to the rollersand a doctor blade scrapes the paste fromthe unengraved portion of the roller. Eachroller supplies one color to the finisheddesign, and as the fabric passes between

the roller and the padded cylinder, eachcolor in the design is applied. Mostmachines are equipped with eight rollers,although some have sixteen rollers.


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Contd

Screen Printing: A method of printingsimilar to using a stencil. The areas of thescreen through which the coloring matter

is not to pass are filled with a waterproofmaterial. The printing paste whichcontains the dye is then forced throughthe untreated portions of the screen onto

the fabric below.


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Mechanical Finishing

Raising (Napping)

This operation is particularly suitablefor wool and cotton fabrics; it gives a

fuzzy surface by abrading the clothand pulling the fibre end to thesurface. During those last

years this process has also beenapplied on polyester/viscose blendsand acrylic fabrics


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Stabilisation

This process produces greater density andstability (e.g. the Sanforset process) and givesthe

fabric a controlled compression shrinkage, which

eliminates distortions originated during

previous processes. The fabric finished with thistreatment keeps its shape also after repeated

washing thus providing an excellent dimensional

stability of the textile substrate


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Calendering gives smoothness to thefabric

Stentering is used for heat setting.

Embossing is used for impartingcertain designs.


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Chemical Finishing

Most of the chemical finishes are applied bypadding

Crease resistant finish

A certain crease resistance can be obtained byadding to fibres complex inorganic compounds ofboron, as well as zinc and barium silicate.However, today the only products applied aresynthetic thermosetting resins eg:N.N-

l.3dimethylol-4.5-dihydroxyethylenurea(DMDHEU)

ammonium salts or complex compounds ,areused as catalysts.


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Flame-retardant Treatments

One process that has a particularly importantapplication is the Proban process. This processexploits the copolymerisation of THPC andmethylolmelamine to form a highly flame-repellent resin that contains phosphorous andnitrogen

THPC-urea process (or process with melamine,dicyandiamide or guanidine). The fabric is

impregnated with THPC and one of the above-mentioned nitrogenous substances. A good andwash-resistant effect is obtained.THPC-tetrakishydroxymethylol phosphoriumChloride.


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Water repellent finish

Evoral G20

Water proof finish

Dipsanil-V

Waxol-PVelan PF


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SOIL RELEASE treatment

These products are emulsions, basedon polymers or copolymers of acrylicor metacrylic acids,or on the relative

salts, as well as on additionalethylene oxide compounds, andfluoride compounds.


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Anti-static Treatments

ECCOSTAT:A moderately durable anti-static agent, cationic in nature andcompletely soluble in water for application

purposes. With moderate to fairly highdrying temperatures, this leaves theresidue as a durable antistatic materialremaining. This material, of course, is

useful on synthetic fibers in general andwill not impair the tensile strength of the

fabric.


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Anti Bacterial Finish

Triclosan (2,4,4-hydrophenyltrichloro (II) ether)


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Extra points

Elastic is used in Lycra yarn

Increasing the bulkiness of synthetic yarnis called texturising

Father of Textile chemistry- John MercerSilk gum is called - sericin

No of strands in degummed silk-02

First synthetic fiber- nylonDelustering agent used in the spinningsolution of manmade fiber- titaniumdioxide.


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Kevlar comes under Aramid fibers

Standard atmospheric conditions-

RH-65+-2%Temp-27+-2oc


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THANK YOU

dyeing and printing new

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