Textile printing can often be consideredpart of the finishing industry. Fabricprinting is an art form and can be done inmany different ways.It is essentially a decorative pattern ordesign that is applied to constructed fabric.
Textile printing is an ancient art form found on cloth inEgyptian tombs dating to about 5000B.C. Greek fabricsdating from the 4th century B.C. have also been found.Block prints were first seen imported from India to theMediterranean in 5th C B.C.During the renaissance, Indian chintz was imported toEurope, where it became popular and was imitated. Francebecame a leading centre of this type of cloth productionduring that time. Stencil work, a highly developed form ofprinting from Japan was another early discovery of applyingpattern to fabric.
This process involves a print paste (like a thick paint) thatis applied to an engraved roller, and the fabric is guidedbetween it and a central cylinder. The pressure of theroller and central cylinder forces the print paste into thefabric. Because of the high quality it can achieve, rollerprinting is the most appealing method of printing designerand fashion apparel fabrics.
Long runs of the same The design is cut into thefabric design are produced surface of copper rollers;on a roller print cylinder by varying the depth of themachine operating at engraving on the roller thespeeds between 50 and shade depth can be altered.100 yards a minute. As Sharpness of line and finemany as 10 different detail can be achieved thiscolors can be printed in way. A typical printingone continuous operation, machine has a large paddedbut each colour must have drum or cylinder, which isa separate roller. surrounded by a series of copper rollers, each with its own dye trough and doctor blade that scrapes away excess dye.
The tubular screens rotate at the same velocity as thefabric, the print paste is distributed inside a tubularscreen, which is forced into the fabric as it is pressedbetween the screen and a printing blanket (a continuousrubber belt). It picks up colour from the engraved area ofeach roller in sequence. The printed cloth is driedimmediately and conveyed to an oven that sets the dye.Knitted fabric is mostly printed in this method as it doesnot pull or stretch the fabric.
In flat screen printing, a screen on whichprint paste has been applied is loweredonto a section of fabric. A squeegeethen moves across the screen, forcingthe print paste through the screen andinto the fabric. The screen is the imagecarrier made from a porous meshstretched tightly over a metal frame. A positive stencil using negative art work is produced on the mesh either manually or photo chemically. Ink is then forced through the fine mesh openings using a squeegee that is drawn across the screen allowing print paste to pass through only the areas where no stencil is applied.
Block printing is a traditional process dating back to Indiain the 12th century. Wooden blocks made of seasoned teakin different shapes and sizes are cut by trained craftsmen.Each block has a wooden handle and two or three holesdrilled into the block to the passage of air and release ofexcess print paste.Fabric is stretched over a printing table and fastenedwith small pins. Printing starts from left to right, firstthe colour is evened out in the tray and then the block isdipped in. Then the block is applied to the fabric withcareful registration and pressure is applied.
Multiple colour designs are labourintensive and require a lot of skill toregister the prints exactly.Colour variation is hard to avoid withthis method as print ink can vary inquality of depth or colour. The Japanese took wood block printing to new levels and developed unparalleled skill in the construction of fine delicate prints.
This is essentially transferring an image to fabric from apaper carrier. When heat and pressure are applied tothis paper the inks are transferred. Some transfers aretopical, and the image sits on the surface of the fabric.Other transfers are absorbed into the fibres of thefabric. Heat transfer printing is clean and environmentally safe. The only by-product is the paper carrier. It is the perfect print method for short run and sample production, but can also be used for batch production as well.
Dye sublimation allows photo lab quality picture printing.During the dye sublimation printing process, an image isdigitally printed in reverse with dye sublimation toners orinks onto media. That image is then placed on top of afabric and subjected to high heat and pressure to form aheat press. The dye sublimation toners or inks sublimate– the inks go from a solid state to a gaseous state withoutbecoming liquid in between and flow into the fabric,dyeing the threads.This creates a gentle gradation of colour and doesnot distort or fade over time.
Discharge printing is one method of resist printing andinvolves using a chemical paste called a disperse dye. Itmust be used with a ‘reactive dye’ as a ground colourfor the process to work. It also has to be ‘cured’ orfixed with steam so the dye reacts with the fabric andcauses a colour reaction. Discharge printing producesthe brightest, lightest prints on dark-colouredgarments and can be very striking. This method canonly be used on natural fibres and fabrics that willdischarge colour. Another method of resist printing is Batik. Natural materials such as cotton or silk are used as they absorb the wax that is applied in the dye resisting process. The fabrics must be of a high thread count (densely woven) for best results.
Although experts disagree on the origins of Batik, itis very popular in Indonesia and Africa.The cloth that is used for batik is washed and boiledin water many times before the wax can be applied sothat all traces of starches, lime, chalk and othersizing materials are removed. Before modern-daytechniques, the cloth would have been pounded with awooden mallet or ironed to make it smooth and suppleso it could receive the wax design. The designer usesa ‘tjanting’ (wax pen) to draw the design on the cloth.The wax is kept fluid in a melting pot.
After the wax has been applied, the fabric isready for the dye bath. Today most batikfactories use large concrete vats, above the vatsare ropes with pulleys that the fabric is drapedover after it has been dipped into the dye bath.The amount of time it is left in the bathdetermines the hue of the colour (longer fordeeper colours)
Printing techniques are renowned for their damage to theenvironment and the health of the workforce producing them.There is a lot of washing preparation done to the fabricbefore it can be printed on and this sends chemicals into theair and water and pollutes the outside environment. A typicalprocess will often include sequestrates, alkalis, bleachingagents, stabilisers, catalysts, crease-resisting agents, aciddyes, exhausting agents, soaping agents and softeners.Probably 20–30 chemicals per process. Harsh and hazardouschemicals are used in the dyeing and printing methods offabrics and toxins like carbon monoxide, carbon dioxide,sulphur dioxide and zinc oxides carcinogenic are commonlyfound in these processes. Transfer printing is the mostenvironmentally friendly form of printing onto fabric and alsothe most cost effective. As a result it is fast becoming thetextile manufacturer’s choice for the future.
The most commonly used processes for imparting colour to cotton are piece dyeing and yarn dyeing.In piece dyeing, which is used primarily for fabrics that are tobe a solid colour, a continuous length of dry cloth is passedfull-width through a trough of hot dye solution. The cloth thengoes between padded rollers that squeeze in the colour evenlyand remove the excess liquid. In one variation of this basicmethod, the fabric, in a rope-like coil, is processed on a reelthat passes in and out of a dye beck or vat. Yarn dyeing, which occurs before the cloth is woven or knitted, is used to produce gingham checks, plaids, woven stripes and other special effects. Blue dyed warp yarns, for example, are combined with white filling yarns in denim construction.
One of the most commonly used yarn-dyeing methods ispackage dyeing. In this system, yarn is wound on perforatedcylinders or packages and placed on vertical spindles in a rounddyeing machine.Dye solution is forced alternately from the outside of thepackages inward and from the inside out under pressure. Computers are used increasingly in dyeing processes to formulate and match colours with greater speed and accuracy.
Finishing, as the term implies, is the final step in fabricproduction. Hundreds of finishes can be applied to textiles,and the methods of application are as varied as the finishes.Cotton fabrics are probably finished in moredifferent ways than any other type of fabrics. Somefinishes change the look and feel of the fabric, whileothers add special characteristics such as durablepress, water repellency, flame resistance, shrinkagecontrol and others. Several different finishes may beapplied to a single fabric.