DYEING

Dyeing is the process of imparting colours to a textile material in loose fibre, yarn, cloth or garment form by treatment with a dye.

HISTORY

Early evidence of dyeing comes from India where a piece of cotton dyed with a vegetable dye has been recovered from the archaeological site at Mohenjo-daro (3rd millennium BCE). The dye used in this case was madder, which, along with other dyes—such as Indigo—was introduced to other regions through trade.

Contact with Alexander the Great, who had successfully used dyeing for military camouflage, may have further helped aid the spread of dyeing from India.

DYE TYPES

For most of the thousands of years in which dyeing has been used by humans to decorate clothing, or fabrics for other uses, the primary source of dye has been nature, with the dyes being extracted from animals or plants. In the last 150 years, man has produced artificial dyes to achieve a broader range of colors, and to render the dyes more stable to resist washing and general use. Different classes of dye are used for different types of fiber and at different stages of the

textile production process from loose fibers through yarn and cloth to completed garments.

Acrylic fibers are dyed with basic dyes, nylon and protein fibers such as wool and silk are dyed with acid dyes, polyester yarn is dyed with disperse dyes. Cotton is dyed with a range of dye types including vat dyes which are similar to the ancient natural dyes and modern synthetic reactive and direct dyes.

PURPOSE OF DYEING

Dyeing can be done during any stage in the manufacture of textile product. Textiles may be dyed as fiber, as yarn, as fabric, or as garments, depending on the type of fabric or garment produced. Description of various stages and the reasons for their uses are given in the following sections. Dyeing will occur in the most efficient stage which will meet the requirements of the intended end uses.

VARIOUS STAGES OF DYEING

The various stages of dyeing are as under:

i) STOCK AND TOP DYEINGii) YARN DYEINGiii) PIECE DYEINGiv) GARMENT DYEING

STOCK AND TOP DYEING

Stock dyeing refers to the dyeing of fibers, or stock, before it is spun into yarn. It is done by putting loose, un-spun fibers into large vats containing the dye bath, which is less then heated to proper temperature. From 500 to 3000 pounds (227 to 1364 kilograms) of fiber are dyed at one time, and the average is about 1000 pounds (454 kilograms).

Top dyeing is also the dyeing of fiber before it is spun into yarn and serves the same purpose as stock dyeing-that is, to produce soft, heather=like colour effects. The term top refers to fibers of wool from which shorter fibers have been removed. Top is thus the select long fibers that are used to spin worsted yarn.The top in the form of silver is dyed and then blended with other colours of dyed top to produce desired blended heather shades.

FEATURES AND ADVANTAGES

Fabrics have soft, heather –like colouration. Easiest dye penetration.

LIMITATIONS AND DISADVANTAGES

Most costly dyeing method. Dyeing long before season begins carries risk of fashion changing. High percentage of fiber loss from dyeing and later yarn spinning.

TYPICAL DYED FABRICS

Cheviot Covert Melton Tweed

YARN DYEING

Yarn dyeing, as its name implies, is the dyeing of yarns before they have woven or the knitted into fabrics. The main reason for the dyeing of yarn is for the ultimate production of multi coloured designs such as plaids, stripes, and checks. Some typical yarn-dyed fabrics are multi coloured gingham, madras, brocade, and multi coloured weft knits. Yarn dyeing ia also used in special cases for solid-colour fabrics. Yarns may be dyed in different forms:

Skeins

Packages Beams

FEATURES AND ADVANTAGES

Used for fabrics with stripes, checks, plaids, and other multi-coloured patterns.

LIMITATIONS AND DISADVANTAGES

Second most costly dyeing method Dyeing before season begins carries risk of fashion changing, but less than

or stock dye.

TYPICAL DYED FABRICS

Chambray Gingham Brocade Jacquard knits

SKEIN DYEING

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

PACKAGE DYEING

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

BEAM DYEING

Beam dyeing is a much larger version of package dyeing. An entire warp beam is wound onto a perforated cylinder, which is then placed in the beam dyeing machine, where the flow of the dye bath alternates as in package dyeing.

PIECE DYEING

The dyeing of cloth after it has been woven or knitted is known as piece dyeing. It is the most common method of dyeing used. The various methods used for this type of dyeing include :

Jet dyeing Jig dyeing Pad dyeing Beam dyeing

When heavy or densely woven fabrics, or tightly twisted yarn fabrics, are pieced dyed, sometimes the dye does not penetrate into the centre of the yarn material.

The condition, known simply as poor penetration, leaves the fibers in the center of the yarn, or at fabric interlacing, lightly coloured or un-dyed. It can be recognized by taking some yarns out of the fabric, untwisting them, and observing the non uniform colour of fibers in the twisted yarn. There is no problem with inghowever, fabrics such as uniform clothing, children’s wear, upholstery fabrics, and other fabrics subjected to hard use take on a faded appearance at points of wear, and white, un-dyed fibers shift towards the fabric surface. For this reason, many high-quality, heavy-weight, and densely woven fabrics, especially furniture though more costly, eliminates the problem of poor dye penetration.

FEATURES AND ADVANTAGES

Least costly stage for dyeing of fabrics. Adaptable to all fabrics – woven and knitted. Dyeing is close to fashion season; minimal colour risk.

LIMITATIONS AND DISADVANTAGES

Limited to solid colours(except for cross-dye).

TYPICAL DYED FABRICS

Batiste Broadcloth Challis Corduroy Satin

JET DYEING

In the jet dying process, the fabric being dyed is circulated in a rope form through a closed-system dyeing machine on a jet flow of the dye bath. The fabric is moved by the fast moving dye bath. Since no pressure and little tension occurs with the material, even delicate fabrics can be dyed using this process. Most jet dyeing machines can be pressurized and are capable of achieving dyeing temperatures exceeding the boiling point of water.

JIG DYEING

The jig dyeing process involves treating fabric in an open width. Fabric is not immersed in a dye bath, but rather is passed through a stationery dye bath. Upon completion of the first pass, the fabric reverses and is passed again through the dye bath. To produce darker colours the fabric must pass through the dye bath more times than when a lighter shade is desired.

PAD DYEING

Pad dyeing is accomplished with a machine called a dye pad. Its appearance somewhat resembles a giant clothes wringer. Fabric in open width first passes through the dye bath, and then through the rollers where the dye solution is squeezed into the fabric.

BEAM DYEING

Beam dyeing for piece dyeing is practically identical to beam dyeing used for yarns. Fabric is wound on to a perforated cylinder where the dye bath is forced through the fabric layers. The fabric remains stationery.

GARMENT DYEING

Garment dyeing is the dyeing of completed garments. The types of apparel that can be dyed are mostly non tailored and simpler forms, such as sweaters, sweat-shirts, T-shirts, hosiery, and pantyhose. The effect on sizing , threads, zippers and snaps must be considered. Tailored items, such as suits or dresses, cannot be dyed as garments because the difference in shrinkage of the various components and linings distort and misshape the article.

Garment dyeing is done by placing a suitable number of garments (usually about 24 sweaters or the equivalent, depending on weight) into a large nylon net bag. The garments are loosely packed. From 10 to 50 of the bags are placed in large tubs containing the dye bath and are kept agitated by a motor-driven paddle in the dye tub. The machine is appropriately called a paddle dyer.

FEATURES AND ADVANTAGES

Choice of colours closet to fashion season. Elimination of material (yarn and fabric) waste from prior processing.

LIMITATIONS AND DISADVANTAGES

Limited to garments of simple construction.

TYPICAL DYED FABRICS

Hoisery Pantyhose Sweaters T-shirts etc.

Printing

Printing is a process for reproducing text and image, typically with ink on paper using a printing press. It is often carried out as a large-scale industrial process, and is an essential part of publishing and transaction printing.

History

The development of printing was preceded by the use of cylinder seals in Mesopotamia developed in 3500 BC, and other related stamp seals. The earliest form of printing waswoodblock printing, with existing examples from China dating to before 220 AD[1] and Egypt to the 4th century. Later developments in printing include the movable type, first developed by Bi Sheng in China[2], and the printing press, a more efficient printing proccess developed by Johannes Gutenberg in the 15th century

DIFFERENT STYLES OF PRINTING

1. DIRECT PRINTING

2. DISCHARGE PRINTING

3. RESIST PRINTING

Direct Printing

In this type of printing dye is applied onto the fabric by carved block, stencil, screen, engraved roller etc.The dye is imprinted on the fabric in paste form and any desired pattern may be produced.

Example:-Block Printing, Roller Printing, Screen Printing etc.

Fig: Direct Printing

DISCHARGE PRINTING

In this method the fabric is dyed and then printed with a chemical that will destroy the color in designed areas.

Sometimes the base color is removed and another color printed in its place.

Fig: Discharge Printing Diagram

RESIST PRINTING

In this method bleached fabric are printed with a resist paste ( a resinous substance that cannot be penetrated when the fabric is immersed in a dye ).

The dye will only affect only the parts that are not covered by the resist paste .

After the fabric has passed through a subsequent dyeing process the resist paste is removed, leaving a pattern on a dark background

Types of Printing

BLOCK PRINTING ROLLER PRINTING SCREEN PRINTING FLAT-SCREEN PRINTING ROTARY PRINTING TRANSFER PRINTING STENCIL PRINTING DIGITAL PRINTING BATIK PRINTING TIE & DYE etc.

Hand block printingIt is the oldest and simplest way of printing. In this method a wooden block with a raised pattern on the surface was dipped into the printing colorant and then pressed face down on to fabric. The desired pattern was obtained by repeating the process using different colors. Generally the wooden block is carved out of hand. Printing is done manually in this method.

Fig: Hand Block Printing

BLOCK PRINTING

ROLLER PRINTING

It is the machine method of printing designs on cloths by engraved rollers. The design is engraved on the surface of a metal roller, to which dye is applied, and the excess is scraped off the roller's surface, leaving dye in the engraved sections. When it rolls across the fabric, the dye on the roller transfers to the fabric.

Fig: Diagram of Roller Printing

ADVANTAGESSimple method of printingNo expensive equipment requiredNo limitation in repeat of size of style Prints produced have great decorative value and stamp of craftsmanship

DISADVANTAGES

Involves much manual workMethod is slow and therefore low outputGood skilled labors needed for multi color designFine and delicate designs hard to produce

Fig: Roller Printing Method

Advantage & Disadvantage of Roller Printing

ADVANTAGESLarge quantities of fabric at the rate of 914-3658m per hour can be printed.Faulty joints or joint marks are absent. Fine sharp outlines and good prints can be obtained which is difficult to get in block printing.

DISADVANTAGES

Not economical for short run of fabrics.Difficult to produce blotch designs.Repeat of design limited to the size of the rollers.Setup cost of roller printing m/c is high

STENCIL PRINTING

It is one of the oldest ways of printing. In it color is applied to the fabric by brushing or spraying the interstices of a pattern cut out from a flat sheet of metal or water proof paper or plastic sheet or laminated sheet. A stencil is prepared by cutting out a design from a flat sheet of paper, metal, or plastic.

Fig: Stencil Printing

Advantage & Disadvantage of STENCIL PRINTING

SCREEN PRINTING

It involves the application of the printing paste through a fine screen placed in contact with the fabric to be printed. A design is created in reverse on the screen by blocking areas of the screen with a material such as an opaque paint. The screen is then placed over the fabric and the printing paste is forced

ADVANTAGESSimple and cost effective.Stencils can be made rapidly and can be used for small orders.Color combination is good in it.

DISADVANTAGESGood design is difficult to obtain.Process is laborious. Not suitable for large scale production.

through the open areas of the screen using a flexible synthetic rubber or steel blade known as a squeegee.

Fig: Process of Screen Printing

Advantage & Disadvantage of Screen Printing

FLAT-SCREEN PRINTING

It is the advanced version of screen printing by using automatic m/c to do work. It consists of printing table, conveyor belt, number of screens, mechanism to print on the fabric, etc. First the fabric is brought on the printing

SCREEN PAPER SIDE SCREEN SQUEEZE SIDE

ORIGINAL PRINT PRINT ON FABRIC

ADVANTAGESSimple and cost effective.Quick pattern making16 colors can be used in a design.Sharp lines and features easily produced.

DISADVANTAGESFor high production large no. of tables required.Delicate shading difficult to obtain.Screen clogging may be there in fine areas.

table through a feeding arrangement and it is gummed to the conveyor belt on the table

Conveyor brings fabric periodically under screen and stops while the screen are lowered on the required parts of the fabric.

Printing paste is distributed throughout the full length of the screen.

The squeeze is pressed to the screen .

One or more strokes of the squeeze ensure simultaneous printing of the pattern by the common action of all screens which applies printing paste as required by the color in the design.

Fig: Flat Screen Printing M/C

ROTARY SCREEN PRINTING

Rotary screen printing involves a series of revolving metal cylinder , each with revolving screens, each with a stationary squeegee inside which forces the print paste onto the fabric.

Twenty or more colours can be printed at the same time.

The process is much quicker and more efficient than flat screen printing .

Fig: Rotary Screen Printing Diagram

ADVANTAGESGreater production than manual screen printingPrinting with different repeat can be made easilyGood print is obtained

DISADVANTAGESA big setup required for more number of screensPrints with more colors may not be possiblePrinting paste not evenly controlled

Feeding of color to rollers

TRANSFER PRINTING

It is a indirect method of printing in which dyes are transferred from paper to a thermoplastic fabric under controlled conditions of temperature, time and pressure. The image is first engraved on a copper plate. Then pigment is applied on these plates. The image is then transferred to a piece of paper, with a layer of glue applied . This is then placed on the fabric and heat and pressure applied which fixes the print onto fabric.

Process of transfer printing

RESIST PRINTING

• There are two types of resist printing

• BATIK PRINTING

• TIE & DIE PRINTING

BATIK PRINTING

Originated on island of Java and is a cottage based industry. Batik is derived from word “AMBATIK”. The resist-dyeing process, whereby designs are made with wax on a fabric which is subsequently immersed in a dye to absorb the color on the unwaxed portions, is known as batik printing.

Special feature is the fine lines of color running irregularly across the fabric

ADVANTAGESOperation is simple and no expensive m/c is required.No after treatment of fabric requiredPrint on fabric is of excellent quality

DISADVANTAGESProcess applicable to synthetic fabric like polyester .Color range is limited.Cost of printed paper high.Not economical for small orders.

TIE & DYE

It is same as that of batik printing but here the dye is resisted by knots that are tied in the cloth before it is immersed in dye bath. The outside of the knotted portion is dyed, but inside is not penetrated if the knot is firmly tied.

This gives a characteristic blurred or mottled effect .

ADVANTAGESGives a good artistic effectCheap printingGreater artistic designFabric has a rich and graceful appearance

DISADVANTAGESLaboriousTime takingCracking effectDye should be applied at low temperature than wax.

ADVANTAGEInteresting design created on fabricNo m/c cost is there

DISADVANTAGECostlyLaboriousTime takingSkilled labour required

DIGITAL PRINTING

• It is the more advanced type of printing.

• This includes :-

Jet spray printing

Electrostatic printing

Photo printing

Differential printing

Fig: Digital Printing Technique

Conclusion:

Now days Dyeing & Printing are an essential part of modern Textile. The desire to use textile fabrics as a carrier of designs for decoration or identification has existed for many centuries. The development of modern equipment and colorant technology has enabled textile manufacturers to be able to reproduce highly colored textile designs with excellent colorfastness. This can be performed on a wide variety of fibers and fabric constructions, employing cost effective processes. However, as good as textile-printing technology is today, the processes are continuing to improve. New technologies and new developments in existing methods promise to continue the expansion of the capabilities of textile printing well into the future.

REFERENCES

Mock, Gary N., Fundamentals of Dyeing, published by North Carolina State University, Raleigh, North Carolina, 1997.

Wikipedia, http://www.wikipedia.com/

Miles, Leslie W.C., Textile Printing, 2nd edition, Society of Dyers Colorists, Bradford, England, 1994.

Tincher, Wayne, Hu, Oui-Ang and Li Xiofei, “Ink-Jet Systems for Printing Fabric,” GeorgiaInstitute of Technology, Atlanta, Georgia, 1996.

Kool, RJM, Rotary Screen Printing in the Nineties, Worldwide Competition and a CompetitionEdge, 1998.

Storey, Joyce, The Thames and Hudson Manual of Textile Printing, Thames and Hudson, LTD, London, England, 1974.

Miles, Leslie W.C., Textile Printing, Dyers Company Publications Trust, Bradford, England, 1981.