Rumman Rizvi TCP

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TEXTILEPRINTING

November 28

2011National Institute of Fashion Technology Rumman Rizvi


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CONTENTS

SR.NO TOPIC PAGE NO

1 INTRODUCTION 3

2 HISTORY 5

3 THE THREE STYLES OF PRINTING 12

4 METHODS OF PRINTING 17

5 STEPS IN PRINTING PROCESS 37

6 PIGMENT PRINTING 40

7 PRINTING MACHINES 42

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INTRODUCTION

Textile printing is the process of applying colorto fabric in definite patterns or designs.In properly printed fabrics the color is bonded with the fiber, so as to resist washing and

friction. Textile printing is related to dyeing but, whereas in dyeing proper the wholefabric is uniformly covered with one color, in printing one or more colors are applied to itin certain parts only, and in sharply defined patterns.

In printing, wooden blocks, stencils,engraved plates, rollers, or silk screens are used toplace colors on the fabric. Colorants used in printing contain dyes thickened to preventthe color from spreading by capillary attraction beyond the limits of the pattern ordesign.

Traditional textile printing techniques may be broadly categorized into three styles:

Direct printing, in which colorants containing dyes, thickeners, andthe mordant or substances necessary forfixing the color on the cloth are printed

in the desired pattern.

Resist dyeing, in which a wax or other substance is printed onto fabric which issubsequently dyed. The waxed areas do not accept the dye, leaving uncoloredpatterns against a colored ground.

Discharge printing, in which a bleaching agent is printed onto previously dyedfabrics to remove some or all of the color.

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http://en.wikipedia.org/wiki/Colourhttp://en.wikipedia.org/wiki/Textilehttp://en.wikipedia.org/wiki/Patternhttp://en.wikipedia.org/wiki/Printinghttp://en.wikipedia.org/wiki/Fiberhttp://en.wikipedia.org/wiki/Dyeinghttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Stencilhttp://en.wikipedia.org/wiki/Engravinghttp://en.wikipedia.org/wiki/Dyeshttp://en.wikipedia.org/wiki/Capillary_attractionhttp://en.wikipedia.org/wiki/Mordanthttp://en.wikipedia.org/wiki/Fixativehttp://en.wikipedia.org/wiki/Resist_dyeinghttp://en.wikipedia.org/wiki/Waxhttp://en.wikipedia.org/wiki/Bleachhttp://en.wikipedia.org/wiki/Colourhttp://en.wikipedia.org/wiki/Textilehttp://en.wikipedia.org/wiki/Patternhttp://en.wikipedia.org/wiki/Printinghttp://en.wikipedia.org/wiki/Fiberhttp://en.wikipedia.org/wiki/Dyeinghttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Stencilhttp://en.wikipedia.org/wiki/Engravinghttp://en.wikipedia.org/wiki/Dyeshttp://en.wikipedia.org/wiki/Capillary_attractionhttp://en.wikipedia.org/wiki/Mordanthttp://en.wikipedia.org/wiki/Fixativehttp://en.wikipedia.org/wiki/Resist_dyeinghttp://en.wikipedia.org/wiki/Waxhttp://en.wikipedia.org/wiki/Bleach


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COMPARISON BETWEEN DYEING AND PRINTING

Though the dyeing and printing are the coloration processes using the same classes of

dyes and other chemicals, they differ in the following aspects.

Dyeing Printing

1. Uniform application on both sides of

the fabric surface with single color only.

1. Single or multicolor application on

one side of the fabric at selected

portions only.

2. Dyes are applied in dilute form. 2. Dyes are applied in paste form.

3. In fabric preparation, Half bleaching

is enough.

3. full-bleaching with optical whitener is

necessary.

4. Color penetrates through the fabric. 4. Color is applied only on the surface.

5. More time is required in batch

application.

5. Not applied in batch process.

Applied only by continuous process

alone. Therefore requires less time.

6. Fabric need not be in dry condition. 6. Fabric should be in dry state.

7. Requires single machine and the

process is simple.

7. Requires complex machinery and

the process is also complex.

8. Dyeing consumes more water. 8. Printing consumes less water.

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HISTORY OF PRINTING

Textile printing is the process of applying colour to fabric in definite patterns ordesigns. In properly printed fabrics the colour is bonded with the fiber, so as to resistwashing and friction. Textile printing is related to dyeing but, whereas in dyeing proper

the whole fabric is uniformly covered with one colour, in printing one or more colours areapplied to it in certain parts only, and in sharply defined patterns.

In printing, wooden blocks, stencils, engraved plates, rollers, orsilkscreens are used toplace colours on the fabric. Colourants used in printing contain dyes thickened toprevent the colour from spreading by capillary attraction beyond the limits of the patternor design.

Traditional textile printing techniques may be broadly categorised into four styles:

Direct printing, in which colourants containing dyes, thickeners, and the mordants

or substances necessary for fixing the colour on the cloth are printed in thedesired pattern.

The printing of a mordant in the desired pattern prior to dyeing cloth; the coloradheres only where the mordant was printed.

Resist dyeing, in which a wax or other substance is printed onto fabric which issubsequently dyed. The waxed areas do not accept the dye, leaving uncolouredpatterns against a coloured ground.

Discharge printing, in which a bleaching agent is printed onto previously dyedfabrics to remove some or all of the colour.

Resist and discharge techniques were particularly fashionable in the 19th century, as

were combination techniques in which indigo resist was used to create bluebackgrounds prior to block-printing of other colours.[1] Most modern industrialisedprinting uses direct printing techniques.

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http://en.wikipedia.org/wiki/Colourhttp://en.wikipedia.org/wiki/Textilehttp://en.wikipedia.org/wiki/Patternhttp://en.wikipedia.org/wiki/Printinghttp://en.wikipedia.org/wiki/Fiberhttp://en.wikipedia.org/wiki/Washinghttp://en.wikipedia.org/wiki/Frictionhttp://en.wikipedia.org/wiki/Dyeinghttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Stencilhttp://en.wikipedia.org/wiki/Engravinghttp://en.wikipedia.org/wiki/Silkscreenhttp://en.wikipedia.org/wiki/Dyeshttp://en.wikipedia.org/wiki/Capillary_attractionhttp://en.wikipedia.org/wiki/Mordanthttp://en.wikipedia.org/wiki/Fixativehttp://en.wikipedia.org/wiki/Resist_dyeinghttp://en.wikipedia.org/wiki/Waxhttp://en.wikipedia.org/wiki/Bleachhttp://en.wikipedia.org/wiki/Indigo_dyehttp://en.wikipedia.org/wiki/Textile_printing#cite_note-0http://en.wikipedia.org/wiki/Colourhttp://en.wikipedia.org/wiki/Textilehttp://en.wikipedia.org/wiki/Patternhttp://en.wikipedia.org/wiki/Printinghttp://en.wikipedia.org/wiki/Fiberhttp://en.wikipedia.org/wiki/Washinghttp://en.wikipedia.org/wiki/Frictionhttp://en.wikipedia.org/wiki/Dyeinghttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Stencilhttp://en.wikipedia.org/wiki/Engravinghttp://en.wikipedia.org/wiki/Silkscreenhttp://en.wikipedia.org/wiki/Dyeshttp://en.wikipedia.org/wiki/Capillary_attractionhttp://en.wikipedia.org/wiki/Mordanthttp://en.wikipedia.org/wiki/Fixativehttp://en.wikipedia.org/wiki/Resist_dyeinghttp://en.wikipedia.org/wiki/Waxhttp://en.wikipedia.org/wiki/Bleachhttp://en.wikipedia.org/wiki/Indigo_dyehttp://en.wikipedia.org/wiki/Textile_printing#cite_note-0


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Origins

Woodblock printing is a technique for printing text, images or patterns used widelythroughout East Asia and probably originating in China in antiquity as a method ofprinting on textiles and later paper. As a method of printing on cloth, the earliestsurviving examples from China date to before 220, and from Egypt to the 4th century.[2]

Textile printing was known in Europe, via the Islamic world, from about the 12th century,and widely used. However the European dyes tended to run, which restricted the use ofprinted patterns. Fairly large and ambitious designs were printed for decorativepurposes such as wall-hangings and lectern-cloths, where this was less of a problem asthey did not need washing. When paper became common, the technology was rapidlyused on that for woodcut prints. [3] Superior cloth was also imported from Islamiccountries, but this was much more expensive.

The Incas of Peru, Chile and Mexico also practiced textile printing previous to theSpanish Invasion in 1519; but, owing to the imperfect character of their records beforethat date, it is impossible to say whether they discovered the art for themselves, or, insome way, learned its principles from the Asiatics.

During the latter half of the 17th century the French brought directly by sea, from theircolonies on the east coast of India, samples of Indian blue and white resist prints, andalong with them, particulars of the processes by which they had been produced, whichproduced washable fabrics.

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http://en.wikipedia.org/wiki/Woodblock_printinghttp://en.wikipedia.org/wiki/Printinghttp://en.wikipedia.org/wiki/East_Asiahttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Textilehttp://en.wikipedia.org/wiki/Paperhttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Egypthttp://en.wikipedia.org/wiki/Textile_printing#cite_note-1http://en.wikipedia.org/wiki/Lecternhttp://en.wikipedia.org/wiki/Woodcuthttp://en.wikipedia.org/wiki/Old_master_printhttp://en.wikipedia.org/wiki/Textile_printing#cite_note-Hind-2http://en.wikipedia.org/wiki/Woodblock_printinghttp://en.wikipedia.org/wiki/Printinghttp://en.wikipedia.org/wiki/East_Asiahttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Textilehttp://en.wikipedia.org/wiki/Paperhttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Egypthttp://en.wikipedia.org/wiki/Textile_printing#cite_note-1http://en.wikipedia.org/wiki/Lecternhttp://en.wikipedia.org/wiki/Woodcuthttp://en.wikipedia.org/wiki/Old_master_printhttp://en.wikipedia.org/wiki/Textile_printing#cite_note-Hind-2


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Technology

Textile printing was introduced into England in 1676 by a French refugee who openedworks, in that year, on the banks of the Thames near Richmond. Curiously enough thisis the first print-works on record; but the nationality and political status of its founder aresufficient to prove that printing was previously carried on in France. In Germany, too,textile printing was in all probability well established before it spread to England, for,towards the end of the 17th century, the district of Augsburg was celebrated for itsprinted linens, a reputation not likely to have been built up had the industry beenintroduced later than 1676.

On the continent of Europe the commercial importance of calico printing seems to havebeen almost immediately recognized, and in consequence it spread and developedthere much more rapidly than in England, where it was neglected and practically at astandstill for nearly ninety years after its introduction. During the last two decades of the17th century and the earlier ones of the 18th new works were started in France,Germany, Switzerland and Austria; but it was only in 1738 that calico printing was first,practiced in Scotland, and not until twenty-six years later that Messrs Clayton of BamberBridge, near Preston, established in 1764 the first print-works in Lancashire, and thuslaid the foundation of what has since become one of the most important industries of thecounty and indeed of the country. At the present time calico printing is carried onextensively in every quarter of the globe, and it is pretty safe to say that there is

scarcely a civilized country in either hemisphere where a print-works does not exist.

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From an artistic point of view most of the pioneer work in calico printing was done by the

French; and so rapid was their advance in this branch of the business that they sooncame to be acknowledged as its leading exponents. Their styles of design and schemesof colour were closely followed-even deliberately copied by all other European printers;arid, from the early days of the industry down to the latter half of the 10th century, theproductions of the French printers in Jouy, Beauvais, Rouen, Alsace-Lorraine, &c., werelooked upon as representing all that was best in artistic calico printing. This reputationwas established by the superiority of their earlier work, which, whatever else it mayhave lacked, possessed in a high degree the two main qualities essential to all gooddecorative work, viz., appropriateness of pattern and excellency of workmanship. If,occasionally, the earlier designers permitted themselves to indulge in somewhat bizarrefancies, they at least carefully refrained from any attempt to produce those pseudo-

realistic effects the undue straining after which in later times ultimately led to thedegradation of not only French calico printing design, but of that of all other Europeannations who followed their lead. The practice of the older craftsmen, at their best, was totreat their ornament in a way at once broad, simple and direct, thoroughly artistic andperfectly adapted to the means by which it had to be reproduced. The result was thattheir designs were characterized, on the one hand, by those qualities of breadth,flatness of field, simplicity of treatment arid pureness of tint so rightly prized by the artist;and, on the other, by their entire freedom from those meretricious effects of naturalisticprojection and recession so dear to the modern mind and so utterly opposed to theprinciples of applied art.

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Early Methods

The other forms of textile printing are stencil work, highly developed by Japaneseartists, and block printing. In the latter method a block of wood, copper, or other materialbearing a design in intaglio with the dye paste applied to the surface is pressed on thefabric and struck with a mallet. A separate block is used for each color, and pitch pins atthe corners guide the placing of the blocks to assure accurate repeating of the pattern.

In cylinder or roller printing, developed in 1785, the fabric is carried on a rotatingcentral cylinder and pressed by a series of rollers each bearing one color. Thedesign is engraved on the copper rollers by hand or machine pressure or etchedby pantograph or photoengraving methods; the color paste is applied to therollers through feed rollers rotating in a color box, the color being scraped off thesmooth portion of the rollers with knives.

More recent printing processes include screen-printing. This is a hand methodespecially suitable for large patterns with soft outlines, in which screens, one foreach color, are placed on the fabric. Then, the color paste is pressed through awooden squeegee.

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Spray printing, in which a spray gun forces the color through a screen; and

electro coating, used to apply a patterned pile are the other latest printingprocesses.

In certain cases, the cloth is painted by using a pen with dyes and mordants. Thismethod is known as kalamkari, a pen work. Printing the outline of the design andfilling in the details with a kalam, a pen, combines the techniques of printing andkalamkari.

Direct printing is practised all over India where a bleached cotton or silk fabric isprinted with the help of carved wooden blocks.

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Another technique employed was printing with the use of mordants. Mordants arechemicals that absorb the dye. The cloth is first printed with mordants and thenimmersed in a dye bath. Only the sections that have absorbed the mordantabsorb the dye. The cloth is then washed in flowing water and spread out to dryon the riverbank allowing the sun to develop the color. Then the untreated

sections were bleached with local ingredients like goat droppings, etc. Recently,discharge printing with the use of chemicals has been developed. Here dyeswhen printed react on one another, either bleaching the background material orproducing a different shade.

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DISCHARGE PRINTING

Discharge Printing is also called Extract Printing. This is a method of applying a designto dyed fabric by printing a color-destroying agent, such as chlorine or hydrosulfite, tobleach out a white or light pattern on the darker colored ground. In color-dischargeprinting, a dye impervious to the bleaching agent is combined with it, producing acolored design instead of white on the dyed ground.

Discharge printing has been around for decades. But only in the past 7-8 years screenprinters in the industry have recognized it seriously. In the early years of dischargeprinting, the finished discharge print needed to be steamed during the drying process.This discouraged the use of discharge systems in the finished garment arena. The

newly developed discharge ink systems are chemically reactive and dont need to besteam-neutralized. This advancement opened the door to discharge printing for theaverage screen printer.

Discharge printing has the ability to make bright, opaque colors on dark fabrics with asoft hand. Years ago the idea of opaque colors on dark fabrics and soft hand couldntco-exist.

Successful light-on-dark printing with plastisol relies on increased pigment loads, fillersand other additives to block out the color of the garment. Discharge inks modify thegarment color by removing the garment color and replacing it with the new ink color. In

simple terms, the discharge ink "bleaches" out the dye in the garment, thus allowing thepigment in the ink to absorb into the shirt fibers.

The real magic of discharge printing can be witnessed when printing four-color processon black 100% cotton shirts. The print before curing appears very transparent. One canbarely see the print until the garment exits the oven chamber, where the results can bequite remarkable: bright, vivid colors with a soft hand.

The graphics on the casino gaming tables are printed with discharge inks to avoid theinterference of the printed line with the roll of the dice. If the ink on these tables wereprinted with plastisol, the ink film (because it is a surface print) would change the speed

and direction of the dice, thus changing the way the dice land. Discharge ink, on theother hand, provides a dyed-in-the-fabric result, keeping the playing surface smooth.The decrease in the production time is the biggest bonus of all. The fact that you canskip flash curing completely saves hours of production time and eliminates registrationproblems between the designs colors and the white printer under base used in normalprinting on blacks.

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However, flash curing can be used in conjunction with discharge printing when printingdischarge as an under base.

Cleaner and more transparent inks can also be printed onto dark garments with the helpof discharge additives. Early discharge additives were designed only for water baseinks, but plastisol additives are available.

Characteristics that indicate a garment will work with discharge ink

The garment has to be made of natural fibers (100% cotton)

The dye used in the garment must be dischargeable. The best results areachieved with garments that are 100% cotton and dyed with a reactive dye.

The garment should not have been over dyed (when fabric is re-dyed to anothercolor). This often happens because of a shortage of a certain fabric color or, inmany cases, because quality control rejected the fabric color. These rejectedcolors are then over dyed with a black dye, which will bring nightmares to lifewhen trying to use discharge inks. The discharge ink might discharge the blackdye - only to reveal a phantom color underneath.

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Always test your garment to see if it is suitable for discharge printing. If you are a majorprinter doing large-volume printing, be aware that the shirts you order from the mill aretracked by lot numbers and it is possible that a completely different dye may be usedfrom one lot to the next. Let your sales representative know that you are doingdischarge printing and mention in writing that you need a dischargeable garment.

Discharge printing is frequently used for all-over prints because of its soft hand

DIRECT PRINTING

A direct print is one in which the design is printed on a white cloth or a previously dyedfabric. The later is called overprint and here the printed design must be of darker colorthan the background design. This style is also called application printing because thedesign is directly printed over the fabric.

It is the most common approach to apply a color pattern on fabric. It can be done onwhite or a colored fabric. If done on colored fabric, it is known as overprinting. Thedesired pattern is produced by imprinting dye on the fabric in a paste form. To preparethe print paste, a thickening agent is added to a limited amount of water and dye isdissolved in it. Earlier corn starch was preferred as a thickening agent for cotton

printing. Nowadays gums or alginates derived from seaweed are preferred becausethey are easier to wash out, do not themselves absorb any color and allow betterpenetration of color. Most pigment printing is done without thickeners as the mixing upof resins, solvents and water itself produces thickening.

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RESIST PRINTING

Resist printing involves two step procedure:

Printing a pattern design on fabric with chemical or wax like resinous substancethat will prevent or resist the penetration of dyes.

Piece dyeing the fabric

Resist or reserve printing is related to discharge printing in that the end-results are oftenindistinguishable. The resist style, however, offers the advantage that dyes of great

chemical stability, which could not be discharged, can be resisted to give prints of highfastness standards.The justification for both styles lies in the aesthetic appeal of a white or colored patternon colored grounds, an effect that very often could not be reproduced by any othertechnique. The difference, therefore, between discharge and resist printing is not one ofappearance, but of process. In discharge printing, the discharging agent is applied tothe fabric after it has been dyed and the dye in the printed areas is destroyed duringsubsequent processing. In resist printing, the resisting agent is printed on to the undyedfabric and effectively prevents the fixation or development of the ground color, which issubsequently applied by an appropriate dyeing technique, such as dyeing, padding oroverprinting. The result can be either a white resist or a colored resist, where a selected

dye or pigment is added to the resist paste and becomes fixed to the fiber duringsubsequent processing. Virtually every class of colorant is capable of being resisted, asis borne out by reference to older publications on textile printing. Many of the techniquesthey describe are too complex and time-consuming to be of commercial interest today,but they do illustrate the wide scope of the style, with the proviso that it has littleapplication to synthetic-fiber fabrics. The resisting agents employed, then as now,function either mechanically or chemically or, sometimes, in both ways. It is used wherebackground colors in a fabric cannot be discharged. It is usually not possible to visuallydifferentiate between the discharge and resist printed fabrics since both of themproduce the same results.

The mechanical resisting agents include waxes, fats, resins, thickeners and pigments,

such as china clay, the oxides of zinc and titanium, and sulphates of lead and barium.Such mechanical resisting agents simply form a physical barrier between the fabric andthe colorant. They are mainly used for the older, coarser and, perhaps, more decorativestyles in which breadth of effect and variety of tone in the resisted areas are of moreimportance than sharp definition of the pattern. A classical, and nowadays almostunique, example of a purely mechanical resist is to be found in the batik style, usingwax applied in the molten state. In a true batik the wax is applied by hand, but theprocess has been developed and mechanized for the production of those styles which

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now come under the general heading of Africa prints. It is not possible to apply anilluminating color with a wax resist but, after removal of the wax, another color can beprinted within the resisted area. A mechanical resist is usually used in conjunction with achemical resist, so improving the overall effect.

Chemical-resisting agents include a wide variety of chemical compounds, such as

acids, alkalis, various salts, and oxidizing and reducing agents. They prevent fixation ordevelopment of the ground color by chemically reacting with the dye or with thereagents necessary for its fixation or formation. The actual choice of chemical-resistingagent depends, therefore, on the chemistry of the dye being used and its fixationmechanism. Consequently, as in discharge printing, a working knowledge of therelevant chemistry is necessary when choosing effective resisting agents.

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METHODS OF PRINTING

There are several methods of printing namely:

Block printing Roller printing

Screen printing

Heat transfer printing

BLOCK PRINTING

Block printing is a special form of printing first developed in China. The earliest knownexample with an actual date is a copy of the Diamond Sutra from 868 A.D (currently in

the British Museum), though the practice of block printing is probably about twothousand years old.

The first step in block printing is the production of the original document. This is laid ona large, smooth wooden block and fixed into place, reversed. Next, craftsmen of variousskill levels, ranging from master carvers for the fine work to less talented artisans forcheaper blocks or less important sections, carve the original painted, drawn or writtenimage into the block of wood. The block can now be covered with ink and used in apress to create duplicates of the original.

Color paste must be applied to the block surface in a controlled manner, and this was

achieved by using a sieve. A small tub was nearly filled with a starch paste and awaterproof fabric, stretched on a frame, rested on the paste. A piece of woolen fabricwas stretched on a slightly smaller frame and fastened to make the sieve. The sieve assaturated with color paste and placed on the waterproof fabric. For each impression, thetiered (a boy) spread the color paste on the top surface of the woolen sieve with alarge brush and the printer charged the block by pressing it on the wool. The block wasthen carefully positioned on the fabric, using the pitch pins as guides, and struck with amallet. After printing a table length with the first block, the second was printed and thenany others required to complete the design. The fabric was then transferred to a fewelevated rollers or rods and allowed to dry, while the next table length was printed.

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ROLLER PRINTING

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It is a high speed process capable of producing 6000 yards of printed fabric per hour. Itis also called machine printing. Printing, originally a hand craft, developed into anindustrial art requiring the contributions of a range of specialists, coordinated bysomeone with a clear vision of the desired end-product. The first of the specialists is thecreator of the original design, which may already be suitable for reproduction but usually

is not, and is sometimes little more than an idea. Another specialist is the engraverwhose task is to convert the original design into a set of engraved rollers that will enablea printer to achieve an effective reproduction of the design on fabric. Sensitivity to theoriginal design objectives and awareness of the printers requirements are important aswell as skill and accuracy.

An original design must be put into repeat and the dimensions adjusted so that one ormore repeats will fit accurately around the roller circumference. If the repeat is small itmay be that the mill-engraving method should be used. This starts with the handengraving of a few repeats on a small soft-steel cylinder, which is then hardened. Thedesign is then obtained in relief by running the first cylinder (the die) under pressure in

contact with a second soft-steel roller. This relief roller (the mill) is hardened and run incontact with the copper cylinder to obtain the desired depth of impression, and this isrepeated across the cylinder until the full width is engraved. The raised copper aroundeach groove must then be polished off.

In the roller printing process the print paste is applied over an engravedA roller and thefabric is guided between this roller and a central cylinder. The pressure of the roller andthe central cylinder forces the paste into the fabric. Approximately 26% of printed goodsare printed using engraved roller printing.

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Advantages

High design capability

Fine detail

Multiple tones

Disadvantages

copper cylinders very expensive

not economical for short runs

requires highly skilled workers

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SCREEN PRINTING

Screen-printing is the most flexible printing process. It can be used to print on a widevariety of substrates, including paper, paperboard, plastics, glass, metals, fabrics, andmany other materials including paper, plastics, glass, metals, nylon and cotton. Some

common products from the screen-printing industry include posters, labels, decals,signage, and all types of textiles and electronic circuit boards. The advantage of screen-printing over other print processes is that the press can print on substrates of anyshape, thickness and size.

An important characteristic of screen-printing is that a greater thickness of ink can beapplied to the substrate as compared to the other printing techniques. This allows forvarious interesting effects that cannot be achieved through the other printing methods.Because of the simplicity of the application process, a wider range of inks and dyes areavailable for use in screen-printing than for use in any other printing process.

Utilization of screen printing presses has begun to increase because production rateshave improved. This has been a result of the development of the automated and rotaryscreen printing press, improved dryers, and U.V. curable ink. The major chemicals usedin screen-printing include screen emulsions, inks, and solvents, surfactants, causticsand oxidizers used in screen reclamation.

Overview of the Screen Printing Process

Screen-printing consists of three elements

The screen which is the image carrier The squeegee

Ink

The screen printing process uses a porous mesh stretched tightly over a frame made ofwood or metal. Proper tension is essential for accurate color registration. The mesh ismade of a porous fabric or stainless steel. A stencil is produced on the screen eithermanually or photo chemically. The stencil defines the image to be printed. In otherprinting technologies this is referred to as the image plate.

Screen printing ink is applied to the substrate by placing the screen over the material.Ink with a paint-like consistency is placed onto the top of the screen. Ink is then forcedthrough the fine mesh openings using a squeegee that is drawn across the screen,applying pressure thereby forcing the ink through the open areas of the screen. Ink willpass through only in areas where no stencil is applied, thus forming an image on theprinting substrate. The diameter of the threads and the thread count of the mesh willdetermine how much ink is deposited onto the substrates.

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Many factors such as composition, size and form, angle, pressure, and speed of theblade (squeegee) determine the quality of the impression made by the squeegee. Atone time most blades were made from rubber, which, however, had a tendency to warpand distort. While blades continue to be made from rubber such as neoprene, most ofthem are now made from polyurethane, which can produce as many as 25,000

impressions without significant degradation of the image.

If the item is to be printed on a manual or automatic screen press the printed productwill be placed on a conveyor belt, which carries the item into the drying oven or throughthe UV curing system. Rotary screen presses feed the material through the drying orcuring system automatically. Air-drying of certain inks, though rare in the industry, is stillsometimes utilized.

The rate of screen-printing production was once dictated by the drying rate of thescreen print inks. As a result of improvements and innovations in the printingtechnology, the production rate has greatly increased. Some specific innovations, which

affected the production rate and have also increased screen press popularity include:

Development of automatic presses versus hand operated presses, which havecomparatively slow production time.

Improved drying systems, which significantly improve production rate.

Development and improvement of U.V. curable ink technologies

Development of the rotary screen press, which allows continuous operation ofthe press. This is one of the recent technology developments.

Screen Preparation

Screen (or image transfer) preparation includes a number of steps. First the customerprovides the screen printer with objects, photographs, text, ideas, or concepts of whatthey wish to have printed. The printer must then transfer a "picture" of the artwork to beprinted into an image which can then be processed and eventually used to prepare thescreen stencil.

Once the artwork is transferred to a positive image that will be chemically processedonto the screen fabric (applying the emulsion or stencil) and eventually mounted onto ascreen frame that is then attached to the printing press and production begins.

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HAND SCREEN PRINTING

The silk screen is a wooden or aluminum frame with a fine nylon or silk mesh stretchedover it. The mesh is coated with a light sensitive emulsion or film, which - when dry - willblock the holes in the mesh. The image that needs to be printed is output to film eitherby camera or image-setter. This film positive and the mesh on the screen aresandwiched together and exposed to ultraviolet light in a device called a print-downframe. The screen is then washed with a jet of water which washes away all the lightsensitive emulsion that has not been hardened by the ultraviolet light. This leaves youwith an open stencil which corresponds exactly to the image that was supplied on thefilm. Next the fabric to be printed is pinned on a wooden table so that it is evenlystretched and there are no ripples.

Alternatively a wax table is used. The surface of the table is covered with wax. Belowthere are a network of pipes through which steam is passed. This causes the wax tosoften and the fabric is just firmly pressed on to the table.The wooden frame of thescreen is fitted with metal handles which will fit onto to corresponding woodenprotrusions on the table. This is to aid placement, when two or more colors are beingused. The dye is poured on the screen A rubber blade with a wooden handle is firmlypulled across the top of the screen; it pushes the ink through the mesh onto the surface

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of the fabric which is being printed. Another person stands at the other side of the table.He takes hold of the rubber blade and repeats the process.

Since the nonprinting areas on the silk screen are blocked out, the ink is pushedthrough only the porous areas corresponding to the design and is thus transferred to the

fabric. If more colors are used, the process is repeated with another screen and color.The screen is always washed with a lot of water immediately after use. If this is notdone, the dye dries on the screen and clogs up the design.

FLAT BED SCREEN PRINTING

A screen printing press comprising a main frame, a printing bed supported on the mainframe, a rectangular printing frame having a rear end pivoted to said main frame formovement between a first printing position generally parallel to said printing table and asecond flood position angled with respect to said printing table, said printing frameincluding elongated side members, a front member and a rear member, each of saidside members defining an elongated track, a squeegee and flood bar carriage engagingsaid elongated tracks and movable along said side members, said carriage including a

pair of spaced side plates, a pair of slides, each slide extending from one of said sideplates and into a respective one of said tracks, a pair of pivot plates, each pivot platepivoted to one of said side plates, a squeegee support member extending between saidpivot plates and a flood bar support member extending between said pivot plates inspaced, parallel relationship, said squeegee and flood bar support members beingengaged by said pivot plates so that pivoting of said pivot plates alternately raises andlowers said squeegee and flood bar support members.

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pivot plate actuating means operatively connected to said main frame and engaging atleast one of said pivot plates for automatically lowering said flood bar support memberwhen said printing frame is raised to its flood position and for automatically loweringsaid squeegee support member when said printing frame is in its printing position, saidpivot plate actuating means including an elongated, rigid actuating member pivoted to

said printing frame and operatively connected to said main frame, said elongatedactuating member extending along and parallel to one of said side members of saidprinting frame a pivot bracket supporting said actuating member, said pivot bracketbeing pivoted to said printing frame;

shifting means fixed to said pivot bracket and operatively engaging said main frame forpivoting said pivot bracket as said printing frame moves between said first and saidsecond positions; and means operatively connecting said actuating member to one ofsaid pivot plates.

Mechanization of hand screen process

Fabric glued to blanket

Screens rise and fall

Printing done while screen in down position

Rod or blade squeegee system

Up to four strokes possible

Slow process

.

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All the screens for the design, one screen for each color are positioned accurately alongthe top of a long endless belt, known as a blanket. A machine intended to printtraditional furnishing designs might have space for 15 or more screens. The width of the

gap between the areas printed by any two adjacent screens must be a whole number oflengthways design repeats. This need not necessarily be the same as the lengthwaysscreen repeat as there may be several design repeats per screen repeat; for example,where there are three design repeats per screen repeat, the gap between adjacentscreens need only be onethird of a screen repeat.

The fabric is gummed to the blanket at the entry end and moves along with the blanketin an intermittent fashion, one screen-repeat distance at a time. All the colors in thedesign are printed simultaneously while the fabric is stationary; then the screens arelifted and the fabric and blanket move on. When the fabric approaches the turning pointof the blanket, it is pulled off and passes into a dryer. The soiled blanket is washed and

dried during its return passage on the underside of the machine.

Advantages

large repeats

Multiple strokes for pile fabrics

Disadvantages

Slow

No continuous patterns

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ROTARY SCREEN PRINTING

In rotary-screen printing, continuous rotation of a cylindrical screen while in contact with

the fabric ensures genuinely continuous printing. Print paste is fed into the inside of thescreen, and during printing is forced out through the design areas with the aid of astationary squeegee.

The design of most machines follows the pattern established for fully automatic flat-screen machines: an endless driven blanket, screen positions along the top, andblanket washing and drying effected underneath during the return passage. Provisionfor the use of a thermoplastic adhesive is common on rotary machines, with a curved-surface heating plate to heat the fabric before it is pressed on to the blanket. Thecylindrical screens can be much closer together than is possible with flat screens and sothe blanket is shorter (for a given number of colours). The fabric dryer, however, mustbe longer to enable the printed fabric to be adequately dried at higher running speeds.Typically, speeds of 3070 m min1 are used depending on the design and the fabricquality. It is quite possible to run the machine faster than this, the limitations often beingthe length and efficiency of the cloth and blanket dryers and the difficulty of observingPrinting faults at high running speeds. Print paste is often poured into flat screens byhand, even in fully automatic machines, but the continuous movement of a cylindricalscreen and the restricted access necessitates automation of this operation. The printpaste is pumped into the screen through a flexible pipe from a container at the side ofthe machine; inside the screen, the paste pipe has a rigid structure as it also acts as asupport for the squeegee. Holes in the pipe allow the paste to run down into the bottomof the screen; since the paste is pumped in from one end, the holes need to be larger atthe end furthest from the pump to achieve an even spread across the full width of the

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screen. A sensor (level control) actuates the pump when the paste level falls below apreset height.

Continuous screen printing process

Fabric glued to blanket

Fabric moves under rotating screens

Rod or blade squeegee system

Fine adjustments easily made

Speeds up to 100 yds per min

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Advantages

Fast

Quick changeover of patterns

Continuous patterns

Disadvantages

Design limitations

Small repeats

HEAT TRANSFER PRINTING

Transfer printing is the term used to describe textile and related printing processes inwhich the design is first printed on to a flexible nontextile substrate and later transferredby a separate process to a textile. It may be asked why this devious route should bechosen instead of directly printing the fabric. The reasons are largely commercial but,on occasion, technical as well and are based on the following considerations:

1. Designs may be printed and stored on a relatively cheap and nonbulky substratesuch as paper, and printed on to the more expensive textile with rapid response to salesdemand.

2. The production of short-run repeat orders is much easier by transfer processes than itis by direct printing.

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3. The design may be applied to the textile with relatively low skill input and low rejectrates.

4. Stock volume and storage costs are lower when designs are held on paper ratherthan on printed textiles.

5. Certain designs and effects can be produced only by the use of transfers (particularlyon garments or garment panels).

6. Many complex designs can be produced more easily and accurately on paper thanon textiles.

7. Most transfer-printing processes enable textile printing to be carried out using simple,relatively inexpensive equipment with modest space requirements, without effluentproduction or any need for washing-off.

The design on a paper is transferred to a fabric by vaporization. There are two mainprocesses for this- Dry Heat Transfer Printing and Wet Heat Transfer Printing. InConventional Heat Transfer Printing, an electrically heated cylinder is used that pressesa fabric against a printed paper placed on a heat resistant blanket. In Infrared HeatVacuum Transfer Printing, the transfer paper and fabric are passed between infraredheaters and a perforated cylinder which are protected from excessive heat by a shield.The Wet Heat Transfer Printing uses heat in a wet atmosphere for vaporizing the dyepattern from paper to fabric.

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The process of transfer printing to a substrate comprising applying onto a temporarytransfer support in a desired pattern a heat transfer printing ink composition, bringingsaid transfer support containing said ink into close contact with said substrate, the inkbeing in direct contact with the substrate, thereby temporarily transferring a portion ofsaid ink to said substrate as a result of the direct contact, and permanently transferringsaid ink to said substrate by applying heat and, optionally, pressure, wherein said ink isapplied to said transfer support by the following computerized method inputting animage of a desired pattern into a computer central processing unit having a keyboard

and a peripheral video display terminal and printer by means of an optical characterreader, employing in said printer said heat transfer printing ink composition, and printingsaid desired pattern onto conventional computer paper, said computer paper being saidtemporary transfer support.

Advantages

Easier handling of units

Easier training of operators

Better registration and clarity

Fewer seconds

Inventory in paper

Pollution free

Disadvantages

Slow

Limited to synthetic fibers, mainly polyester

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OTHER METHODS OF PRINTING

Duplex Printing

Printing is done on both sides of the fabric either through roller printing machine in twooperations or a duplex printing machine in a single operation.

Stencil Printing

The design is first cut in cardboard, wood or metal. The stencils may have fine delicatedesigns or large spaces through which colour is applied on the fabric. Its use is limiteddue to high costs involved.

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Transfer Printing

The design on a paper is transferred to a fabric by vaporization. There are two main

processes for this- Dry Heat Transfer Printing and Wet Heat Transfer Printing. InConventional Heat Transfer Printing, an electrically heated cylinder is used that pressesa fabric against a printed paper placed on a heat resistant blanket. In Infrared HeatVacuum Transfer Printing, the transfer paper and fabric are passed between infraredheaters and a perforated cylinder which are protected from excessive heat by a shield.The Wet Heat Transfer Printing uses heat in a wet atmosphere for vaporizing the dyepattern from paper to fabric.

Blotch Printing

It is a direct printing technique where the background color and the design are bothprinted onto a white fabric usually in a one operation. Any of the methods like block,roller or screen may be used.

Airbrush (Spray) Painting

Designs may be hand painted on fabric or the dye may be applied with a mechanizedairbrush which blows or sprays color on the fabric.

Electrostatic Printing

A dye- resin mixture is spread on a screen bearing the design and the fabric is passedinto an electrostatic field under the screen. The dye- resin mixture is pulled by theelectrostatic field through the pattern area onto the fabric.Photo Printing

The fabric is coated with a chemical that is sensitive to light and then any photographmay be printed on it.

Differential Printing

It is a technique of printing tufted material made of yarns having different dyeingproperties such as carpets. Up to a ten color effect is possible by careful selection ofyarns, dyestuffs and pattern.

Warp Printing

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It is roller printing applied to warp yarns before they are woven into fabric.

Tie Dyeing

Firm knots are tied in the cloth before it is immersed in a dye. The outside of theimmersed portion is dyed but the inside is not penetrated. There are various forms ofTie dyeing like Ikat Dyeing where bundles of warp and/ or weft yarns are tie dyed priorto their weaving. In Plangi Dyeing the gathered, folded or rolled fabric is usually heldwith stitching to form specific patterns.

Batik Dyeing

It is a resist dyeing process. Designs are made with wax on a fabric which is then

immersed in a dye. The unwaxed portion absorbs the color.

Jet Spray Printing

Designs are imparted to fabrics by spraying colors in a controlled manner throughnozzles.

Digital printing

In this form of printing micro-sized droplets of dye are placed onto the fabric through aninkjet print head. The print system software interprets the data supplied by academic_Textiledigital image file. The digital image file has the data to control thedroplet output so that the image quality and color control may be achieved. This is thelatest development in textile printing and is expanding very fast. Digital Textile Printing

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STEPS IN PRINTING PROCESS

1. Preparation of print paste

2. Printing of fabric

3. Drying

4. Fixation of dyestuff

5. Washing off

PREPARATION OF PRINTING PASTE

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Type of specific formulation used depends on the fiber, the colorant system used and tosome extent the type of printing machine.

Typical ingredients used include:

Dyes or pigments

Thickeners

Binders, cross linking agents

Sequestering agents

Dispersing agents

Water retaining agents

Adhesion promoters

Defoamers

Catalysts Hand modifiers

1. dyestuff or pigments

Depending on the nature of the fiber on which the printing is done, suitable dyes orpigments are selected. Pigment color can be used for printing on all types of fibers.Reactive, vat or azoic colors are used for cotton; disperse dyes for polyester andacid dyes and basic dyes for wool and silk.

2. Thickener

To make viscous paste of dyes in water, a thickener is used. For example: emulsionthickener, sodium alginate and starch etc. the thickener will be dependent on theclass of dyes to be printed and the style of printing.

3. wetting agent

It helps in obtaining a smooth paste of dyes without any lumps, for example: TROand ethylene oxide condensator.

4. defoaming agent

Formation of foam during print paste preparation and application is quite commonbut should be avoided. Foam may produce specky dyeing. The antifoaming agentshelp in foam generation.

5. acid or alkali

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Depending on the types of dyes used in printing, acid or alkali is used in the printpaste. An acid liberating salt is commonly used, for example ammonium chlorideand diammonium hydrogen phosphate. For reactive printing on cotton, sodiumcarbonate or sodium bicarbonate are used.

6. oxidizing or reducing agentThey are used in printing with solubilised vat colors and also in discharge and resistprinting. Discharging agents such as Sodium sulphoxylate formaldelyde (Rongalite)are used in the discharge printing.

7. Hygroscopic agentsThe function of hygroscopic agents is to take up sufficient amount of water(moisture) during steaming to give mobility to lthe dyes to move into the fibre. Eg.Urea and Glycerin.

8. Dispersing AgentDispersing agents are necessary in the print paste to prevent aggregation of thedyestuff in the highly concentrated pastes.E.g. Diethylene glycol

9. PreservativesPreservatives are used to prevent the action of bacteria and fungus to make it dilute.Eg. Salicylic acid.

10. BindersBinders are used in pigment printing as a thin film forming polymer.Eg. Melamine formaldehyde resin.

Fixation methods

1. Atmospheric steam

treatment at 212 degrees f with saturated steam

used with

o Direct dyes

o Vat dyes

o Napthol dyes

o Acid dyes

o Cationic dyes

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o Reactive dyes

festoon steamer most common equipment

Acid agar for acid dyes

2. Pressure steam

treatment at 230 degrees f under pressure

used with disperse dyes

Turbo-autoclave most common equipment.

3. High temperature steam

treatment with superheated steam at temperature up to 420 degrees f

used with disperse dyes and pigments

can also be used as an atmospheric steamer

4. Dry heat

treatment with dry heat at temperatures up to 420 degrees

used with disperse dyes and reactive dyes.

PIGMENT PRINTING

70% of all printed fabrics in U.S. are printed with pigments. Since the pigments usedcontain significant amounts of dispersing agent, and since the polymeric binder is also adispersion with its own dispersing agent, the printed deposit is readily redispersed inwater after a short drying process. Only when the printed fabric has been raised to an

adequate temperature is the binder given enough energy to form a continuous film thatincorporates the pigment particles and adheres satisfactorily to the fibre surfaces. At thesame time, crosslinking of the binder molecules is completed if appropriate monomersor agents have been incorporated, and the required pH and temperature achieved.

Composition of print paste

Pigment

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Thickener(emulsion or all aqueous )

Binder (acrylic polymer )

Low crock binder

Softener

PROCESS

1. Print2. Dry3. Care

Advantages

All fibers and fiber blends

No after wash

Disadvantages

Poor crock fastness

Harsh hard

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PRINTING MACHINES

Machines used for printing the fabrics are explained in the forth coming section Fabricare printed conventionally using the table screen printing machines manually. Moreperfection and production can be achieved using as modern automatic flat bed screenprinting machine.

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Todays most important development in printing machinery lies in rotary screen printingmachines. Before we go into the details of the printing machinery, let us discuss aboutthe preparation of the screens used for flat bed and rotary screen printing.

SCREEN PREPARATION

Flat Bed Screens

A piece of nylon bolting cloth or metal gauge (phosphobraze) is stretched and nailed toa strong wooden frame, strengthened by metal brackets at the corner. The frames areusually 26 x 55 (measured externally) and 23 x 52 (measured internally) for printing45 wide cloth. When metal frame is used for making the screen, the bolting cloth maybe fixed to the frame by using a solution of polyvinyl acetate in a suitable solvent.Photochemical method is the most widely used method for preparing screen. This isbased on the principle that when a coating of solution ammonium dichromate gelatine

or ammonium dichromate polyvinyl alcohol is dried and exposed to light,insolubilisation takes place. The photosensitive coating may be given to the boltingcloth, fixed to the screen frame, dried and exposed to light after keeping in contact witha positive film and after insolubilisation of exposed portion, the unexposedphotosensitive coating may be given to the bolting cloth, fixed to the screen frame, driedand exposed to light after keeping in contact with a positive film and after insolubilisationof exposed portion, the unexposed photosensitive coating is washed out leading theblocking of the interstices of the cloth at the exposed portions and keeping them open(for forcing of the print paste later while printing) at the unexposed portion. Thesensitizing solution may be prepared as follows:

Chrome Gelatine SolutionSolution A200 g pure gelatine500 g boiling water

700 g

Solution B70 g Ammonium dichromate150 g boiling water

80 g liquor ammonia

300 g

Solution A and Solution B are mixed in dark room.

Chrome-polyvinyl alcohol solution

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600 g polyvinyl alcohol (15% solution)120 ml ammonium dichromate (33% solution)240 ml cold water 1 litre with cold water

After applying the solution to the screen cloth, it is dried in the dark room at roomtemperature. The positive of the design is placed on a glass-topped table and the driedphotosensitive screen is placed over it. The exposure is started from under the glasstable using mercury vapor lamp or fluorescent tube lights with uniform intensity of lightall over the screen. The screens are then washed in the dark, first with hot and then withcold water. The hardening of the insolubilised chrome-gelatine complex is done byplacing the screen in a solution containing.

50 g chrome alum50 g formaledehyde25 g sodium dichromate

1 literFor 5 minutes at room temperature, washed with cold water and dried. In the case ofchrome-polyvinyl alcohol complex, the hardening is done in a solution containing,

50 ml acetaldehyde50 ml Isobutyraldehyde80 ml water 20 ml sulphuric acid (168 Tw)1 litre with cold water

It is boiled at 15 to 25 degree C for 1 to 2 hours. It is then washed with cold water anddried.

TABLE SCREEN PRINTING

In Table Screen Printing the fabric is stuck to the printing table, which is covered with aresilient felt, wax cloth or rubber material. Each screen is placed on the fabric in turn,the paste applied to one end of the screen and the squeegee drawn by hand throughthe paste and across the screen, forcing it through the open mesh areas on to the fabric

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beneath, Guide rails along the edges of the table ensure each screen is applied inregister. Although the highly skilled printer can produce good quality prints by a handscreen technique, the production rates are extremely slow.

FLAT BED SCREEN PRINTING MACHINE

The printing operation in a flat bed screen printing machine can be made fully automaticby standardizing the stages of preparation and producing the print including screenholding, addition of print paste, pressing the paste on to the cloth, lifting the screen andcarrying the cloth forward to the next screen printing screen position. The automation ofthese stages makes the reproduction of printing results quite easy. The fabric is suitablyfed to the machine in a crease free manner. The print pattern is registered on the fabricby pressing the printing paste through the specially engraved portions on the flatscreens. There are as many number of screens as the number of colors in the print

pattern. The fabric to be printed is conveyed, i.e. carried forward, with each color,register by register, while the flat engraved screens continuously rise and come down,at each repeat of the color pattern are printed at the same time, but on differed printingplaces of the cloth. The entire colored pattern will be printed only when the far endscreen completes its printing operation.

Good quality nylon gauzes with superfine construction fulfill all the demands made onthe screens by the automatic screen printing machines. These demands can besummarized as follows: Very thin application of the dyestuff paste on the screen;Optimum color permeability in relation to the fabric; Minimum number of squeegeestrokes; Maximum mechanical resistance on the part of the screen gauze to the highsqueegee strokes.

ROTARY SCREEN PRINTING MACHINE

This system with the matrix consists of the required number of protrusions per square-inch (or square cm) Metallic nickel is electro-deposited in the hexagonal gaps inbetween the protrusions. The most common mesh sizes used are 60, 80, 100 and 120.Needless to say, the finer the mesh number, the finger is the pattern printed through theparticular mesh. The cylindrical perforated rotary screens are formed in the forcingtrimmer. The copied designs are transferred to the rotary screen by using a photo-emulsion of suitable sensitivity. The exposed portions retain the emulsion. Theemulsion from the unexposed portion is washed away, thus forming the design as far asthe color which is to be passed on to the cloth from that particular screen. For eachcolor one separate cylindrical perforated screen is used. The entire pattern is formed onthe fabric when the rotary screens pertaining to all the colors in the pattern have beenprinted on the fabric through the respective color screens. The chosen design isengraved by one of the methods mentioned earlier. The rotary engraved screens

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belonging to the desired pattern are placed and fixed in their proper positions in apredetermined order. Although patterns with 12 to 14 colors are sometimes printed,only 5 or 6 colored designs are usually most commonly used. The printing paste isintroduced in the centre of the rotary screen by means of the colour pump and thecolour distribution system. The colour paste is well distributed all over the interior of the

rotary screen and is pressed onto the fabric by means of a well designed squeegeesystem.

The substrate, i.e., the cloth, travels over and along the endless printing conveyerblanket to the end of the printing table top. The printing process is completed at thisstage, and the printed cloth is then led to the continuous dryer. The dryer, having anadequate evaporation capacity is suitably designed. After drying the fabric is passed ont the plaiting down arrangement. The rotary screens run in continuous pressurizedcontact with the fabric which is to be printed and also the endless printing conveyor belt.

CURING PROCESS

Curing ChamberIn case of pigment printing the printed fabric has been raised to an adequatetemperature for giving the binder enough energy to form a continuous film. This bindsthe pigment particles and achieves satisfactory adhesion to the fibre surface. At thesame time, cross linking of binder molecules is achieved if suitable monomers or agentshave been used, and the required pH and the temperature achieved. The equipmentfor this purpose is the roller baker curing oven. It has an arrangement for carryingwoven fabrics through hot air, with as many fabric transport rollers as are required toprovide sufficient exposure time and fabric speed desired. Treatment time varies from 5to 8 minutes and the temperature of the treatment ranges from 140 to 160 C.

Loop AgerLoop ager is continuous process equipment in which the cloth is handled in loop formwith least contact and transported in tensionless manner. It is a versatile machine bywhich hot air curing, saturated steaming water injection along with steam is involved.Before starting, the inner parts are cleaned and made free of water. The air inside canbe expelled by slow injection and closing the manhole door. According to processtemperature, heating value lines are kept open and temperature is set. The speed ofmachine is set as per process time and loop length. Pieces of printed fabric (single ordouble web) are stitched to the leader fabric and fed into the chamber.After the process the cloth is drawn out form chamber and is carried to plaiter throughtop guide rolls.

Advantages

Continuous process leading to consistency in fixation.

Higher productivity and facility of process double webs.

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Better temperature control and less scope for variations.

Disadvantages

Not economical for short runs.

Consumes time and energy for heating and cooling.

Risk of loop rods struck up falling and damage to fabric.

MACHINERY

Flat-Screen Printing

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Flat-screen and rotary-screen printing are both characterized by the fact that the printingpaste is transferred to the fabric through openings in specially designed screens. Theopenings on each screen correspond to a pattern and when the printing paste is forcedthrough by means of a squeegee, the desired pattern is reproduced on the fabric. Aseparate screen is made for each colour in the pattern.

Screen printing with automatic squeegee system

Flat-screen printing machines can be

Manual Semi-automatic

Completely automatic.

One type of machine, which is still commonly found in printing houses, can be describedas follows.

The fabric is first glued to a moving endless belt.

A stationary screen at the front of the machine is lowered onto the areathat has to be printed and the printing paste is wiped with a squeegee.

Afterwards the belt, with the fabric glued on it, is advanced to the pattern-repeat point and the screen is lowered again.

The printed fabric moves forward step by step and passes through adryer. The machine prints only one colour at a time.

When the first colour is printed on the whole length of the fabric, the driedfabric is ready for the second cycle and so on until the pattern iscompleted.

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flat-screen printing machine

In other fully mechanized machines all the colours are printed at the same time. Anumber of stationary screens (from 8 to 12, but some machines are equipped with up to24 different screens) are placed along the printing machine. The screens aresimultaneously lifted, while the textile, which is glued to a moving endless rubber belt, isadvanced to the pattern-repeat point. Then the screens are lowered again and the pasteis squeezed through the screens onto the fabric. The printed material moves forwardone frame at each application and as it leaves the last frame it is finally dried and it isready for fixation.

Mechanized screen printing machine with stationary screens mounted in a frame

In both machines the continuous rubber belt, after pulling away the fabric, is moveddownward in continuous mode over a guide roller and washed with water and rotatingbrushes to remove the printing paste residues and the glue, if necessary. After this, thebelt is sent back to the gluing device.

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In some cases the glue is applied in liquid form by a squeegee, while in other machinesthe belts are pre-coated with thermoplastic glues. In this case the textile is heated andthen it is squeezed by a roller or simply pressed against the rubber-coated belt, causingthe glue to soften and instantly adhere.

After printing, the screens and the application system are washed out. It is commonpractice to squeeze the color from the screens back into the printing paste mixingcontainers before washing them. Specially developed Screen printing machine for Flatprinting application

Features

These flat screen printing machines are extensively used for printing on flat surfaceslike PVC, Metal, Glass, Paper, Board and PCB. These are highly cost effective as theserequire less power. The salient features are as below:

Pneumatically drive.

Low noise

Printing table with X, Y and Rotation for accurate registration.

Printing table with powerful Vacuum to hold the substrate on to its positionwhile printing.

Maximum Substrate height 40 mm.

Squeegee /coater pressure with fine adjustment.

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Angle can be set as per requirement.

Applications

Letterhead, wedding cards printing

Stickers printing

PCB printing

Metal sheet printing

Glass printing

Scale printing

Printing on Plastic plates

T.V Cabinet

Washing machine panels

Industrial control Panels

Membrane switches

Battery containers

Umbrella panels

T-shirts

Coaster printing

Container lids

Tube light fittings

Speedometer dials

Car stickers

ROTARY-SCREEN PRINTING

Rotary-screen printing machines use the principle in which, the colour is transferred tothe fabric through lightweight metal foil screens, which are made in the form of cylinderrollers. The fabric moves along in continuous mode under a set of cylinder screens

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while at each position the print paste is automatically fed to the inside of the screen froma tank and is then pressed through onto the fabric. A separate cylinder roller is requiredfor each colour in the design.

A Rotary-Screen Printing Process

A Rotary-Screen Printing Machine

A conventional paste feeding system for rotary-screen printing machines is as follows.

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A suction pipe leads from the paste vat to a pump, from where a printing hoseleads to the squeegee (dye pipe with squeegee). From here the paste is directedinside the cylinder roller.

The fill volume of this so-called printing paste input system is quite high and as aconsequence the amount of paste residue that has to be removed at each colour

change is also fairly significant.

Various systems have been introduced in order to lower the volume configurationof this equipment, which also reduces the amount of such wastes.

Another possibility, which has also already been implemented in somecompanies, is to recover and re-use these residues for making up new recipes.

Printing-paste feeding system for a rotary-screen printing machine

Rotary-screen printing machines are equipped with both gluing and washing devicesanalogous to those described earlier for flat-screen printing. The belt is washed in orderto remove the residues of paste and adhesive. Not only the belt, but also the screensand the paste input systems (hoses, pipes, pumps, squeegees, etc.) have to be cleaned

up at each colour change.

Rotary Screen Printing Machine

Rotary Screen Printing Machines are widely used in a large number of industries forfaster and finer printing solutions. These printing machines are specially designed

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keeping printing precision and clarity in mind. These printing machines are apt formedium to high volume printing. These machines are used for both industrial andgraphical applications.

Salient Features

Variable screen angle adjustment.

High grade aluminum castings.

Robust and sturdy, one-piece tubular steel base.

High precision tapered roller bearings for rotary sections.

Applications of Rotary Screen Printing Machine

Rotary screen printing machines are used in almost every industry as they providequick, easy and high quality printing solutions.

Specialty Advertising Industry

Pharmaceutical Industry

Cosmetic Industry

Automobile Industry

Membrane Switches

Metal or plastic Sheets

Glass and Ceramics

Roller Printing Machines

Roller printing machines works as follows.

In roller printing, the print paste is supplied from reservoirs to rotating copperrollers, which are engraved with the desired design. These rollers contact a maincylinder roller that transports the fabric.

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By contacting the rollers and the fabric the design is transferred to the fabric. Asmany as 16 rollers can be available per print machine; each roller imprints onerepeat of the design.

As the roller spins, a doctor blade in continuous mode scrapes the excess ofpaste back to the colour trough.

At the end of each batch the paste reservoirs are manually emptied intoappropriate printing paste batch containers and squeezed out.

The belt and the printing gear (roller brushes or doctor blades, squeegees andladles) are cleaned up with water.

Roller Printing Machine Recent Roller Printing Machine

JET PRINTING

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Jet printing is a non-contact application system originally developed for printing carpets,but now increasingly used in the textile sector.

The first commercial jet printing machine for carpets was the Elektrocolor, followed bythe first Millitron machine. The Millitron printing system works, as follows.

The injection of the dye into the substrate is accomplished by switching on andoff a dye jet by means of a controlled air stream.

As the carpet moves along, no parts of the machine are in contact with the faceof the substrate.

Air streams are used to keep continuously flowing dye jets, deflected into acatcher or drain tray. This dye is drained back to the surge tank, filtered and re-circulated.

When a jet is requested to fire, the air jet is momentarily switched off, allowingthe correct amount of dye to be injected into the textile substrate.

The dye is supplied in continuous mode to the main storage tank to compensatefor the amount of dye consumed.

MILLITRON SYSTEM

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Spray printing systems and first generation jet printing methods cannot be controlled toproduce a pre-specified pattern. Thus the equipment must first be employed to producea wide range of effects and only then can selections be made from these by thedesigner or marketing staff.

Digital Carpet Printing Machines

An early improvement was made by the first digital carpet printers (Chromotronic andTitan by Zimmer and Tybar Engineering, respectively). These machines are based onthe so-called drop on demand principle, namely the use of switch able electromagneticvalves placed in the dye liquor feed tubes to allow the jetting of discrete drops of dyeliquor in a predetermined sequence according to the desired pattern. The features ofthis machine are as follows.

In these machines, although the amount of dye applied can be digitally controlledat each point of the substrate, further penetration of the dye into the substrate isstill dependent on capillary action of the fibre and fibre surface wetting forces.

This can lead to problems of reproducibility (e.g. when the substrate is too wet)and means that it is still necessary to use thickeners to control the rheology ofthe dye liquor.

Some latest jet printing machines are:

o The latest improvement in jet printing of carpet and bulky fabrics is the

development of machines in which the colour is injected with surgical

precision deep into the face of the fabric without any machine partstouching the substrate. Here, the control of the quantity of liquor applied tothe substrate (which may vary for example from lightweight articles toheavy quality fabrics) is achieved by varying the firing time and thepumping pressure.

o Another digital jet printing machine commercially available is Zimmer's

Chromo jet. In the Chromo jet system, the printing head is equipped with512 nozzles. These are magnetically controlled and can open and closeup to 400 times a second. The carpet is accumulated into a J-box, and is

then steamed and brushed. When it reaches the printing table it isstopped. The jets are mounted on a sliding frame that can itself be movedin the direction of the warp while the carpet remains stationary during theprinting process.

o Ink-jet printing is another digital printing technique with its origins in paper

printing technology that is now also increasingly used in the textileindustry. In ink-jet printing, colour is applied to the surface of the substrate

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without variation in firing time, pressure or velocity. For this reason it canonly be applied for flat light fabrics, especially silk.

o The TAK printing system can still be found in the carpet industry. With this

technique irregular patterns can be produced. The carpet, previously dyed

with a ground shade, is provided with coloured spots through dripping.The size and the frequency of the coloured spots can be varied byadjusting the overflow groove placed along the carpet width.

HOT STAMPING MACHINE FOR FLAT OBJECTS

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A wide range of hot stamping machines are used for flat objects. These machines arewidely acknowledged for their high Accuracy and smooth movement. These are ideally

used for hot stamping on Plastic Panel, Clock, Paper Box, Garments, Books, LeatherGoods, Wood and Paper Products.

Specifications:

PowerRequirement

AC 220V 50 Hz , 800 W

Temperature 0-400C

Time control 0-9 sec

Cylinder

Diameter

100mm

Stroke 100mm

Size of baseplate

340 x 370mm

MaximumPressure

1500kg

MaximumGap

220mm

Weight 300kgs.

Dimension L1140xW620xH1750mm

Features

Operator friendly Machine design.

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Strong Machine construction

X, Y table with Micro Adjustment

Easy Up and down movement of the stamping Head

Low pressure can be controlled easily.

3 timer controls for better performance

For pressure time.

For delay time,

For foil feed adjustment.

Special design for foil feeder.

High efficient heater device for quick and easy hot stamping,

Operating temperature can be adjusted from 0 ~ 400C easily and accurately.

Foil feed roll guide.

High efficiency structure of pneumatic system and an auto lubricator is employed witheasy adjustment and high stability and durability.

Inductive sensor is easy to adjust and accurate.

The level of heater can be easily adjusted.

Accurate depth adjustment can be achieved with micro-adjustment.

Foil feeder with special motor rotates very accurately.

Both hands push button prevent industrial accident.

The machine can be easily moved by the working table with wheels.

Single Cycle and Auto cycle operation

Applications

Video cassette panel

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Clock frame etc.

Documents

Rumman Rizvi TCP