Indian Journal of Fibre & Research Vol. 2 1, March 1996, pp. 50-56

Technological revolutions In textile

R B Chavan Department o f" Texlilc T.:chno logy. Indian Inslitute of" Tel: hnology. ew Delhi 11 001 6. India

, Widespread acceptance of demand-acti vated manufacturing architecture (DAMA) and j ust-in-tim e (J IT) sa les and marketi ng co ncc pts have placed tremend ous pressure on tcx ti le printers. Prescn tl y avai lable continuous ro tary scrcen printing equipment are often inflexible in tcr m ~ of quick customer responsc and shoJ'l run s. I n th e presc nt article. an attempt has been made to review critically two tcchnological innova tIons in tc xtile pri nt in g, vii. and in.k jCt pri nt in g. QUi or these tWO , ink jet printing has achieved considerahle success till the pIc-prod ucti on stage. i.c. sample printing, a nd R&D work is continuing in deve lopcd countries to pcrfe<.; tthl: tec!lnol ogy for production printing. It is envisaged that by the turn of thi s cent ury, a customer in stead of purchasin g th c printed fabric ava ilabl e in thc stores may be able to scan th e designs on computer, se lec t the des ign and colour combination, or cl-c~! t e the new design a nd load th e information to the computer of the printcr

Keywords: In k jet printing, , Xerography

J Introduction o ur separations produced . The digital info rmatio n ~ o tary screen printing machine was introduced in genera ted can subsequently be used tQ produce scre­ 196.1 and since then there is continued ri se in its popu­ ens directl y by the latest laser engraving technology la rity. Worldwide, 60% of fabric printing is done by o r by the conventional means using computer produ­ iotary screen printing a nd 18(% by flat screen print­ ced transparencies. Fig. 2 shows integra tion of CAD ing. Although rotary screen printing machines a re system' into print production. most suited for production runs, they are not ideal to In spite of these developments, the currentl y domi­ meet the requirements of dema nd-activated ma nufa­ nent rotary screen printing method has seve rallimita­ cturing architecture (DAMA) a ndjust in time (lIT) tions, such as colour and pattern changes require long concepts. According to these concepts the tex til e pri­ process set-up time, screen productio n is slow a nd nters must respond to the delivery of hi gh quality fas­ ex pensive, and screens have relati ve ly short lives a nd hion designs with wide range of colour combinations req uire considerable storage space even when no t be­ in extremely short time. In addition, there is also eq­ ing used. Thus, a new technology for fabric printing is ual pressure on textile printers to produce bulk prints needed tha t will permit frequent style a nd colour cha­ in an environment-friendly ma nner. nges with minimum downtime for cha ngeover and Prior to 1980, the majo rity of printers followed will a ll ow computer sto rage o r design info rma ti o n. essentially a totally manual approach to the produc­ Two revolu tio nary printing techniques, viz. xerogr ~l­ tion of textile prints, from the initial design stage to phic printing a nd ink jet printing, have the potentia l first bulk production. fig. I shows the a pproach foil · o f meeting these requirement owed in textile printing a t that time 1.2. After ITM"x 83 show in Milan the situa tion chan­ 2 Xerographic Printing ged with the availability of relati vely low-cost a nd The commonly known xerography o r photocopy­ increasing powerful PC-based systems. Since ITMA' ing technique is essentiall y based 0 11 elect rostatic 91 in Hanover, there has been dramatic increase in the powder printing technology. The basic steps involved associated technology of visual di splay units, graphi c ill xerographic printing4 - 7 a re: controllers, scanners and high volume data storage • Formation of a nega tive image o n a light sensitive systems. With the right investment the printers now photoconductive (PC) surface (often a selenium or scan designs into a CAD system where a number o f polymer coated drum) via light reflectio n from a prin­ colour combinations can be changed, designs mani­ led master sheet. More recently, the process is accom­ pulated, put into repeat, colourways created and col- plished by impingement with a laser beam controlled CHAVAN: TECHNOLOGICAL REVOLUTIONS IN TEXTILE PRINTING 51

Manuallracing Original Sample and separalion Engraving design ...... r-- r-- prinling ~ produclion C I u s I Colour Fabric 0 mixing preparation m e r Bulk• production• prinVsleamlwashing finishinglinspeclion

Sample production: time scale 2-8 weeks II

Bulk production: time scale 3-I 2 weeks III (including u~ production)

Fig. I- Textile printing by conventional methods

M I!":o H ~OM H... _a_: .._re_!n._ _'_~_'..JH Eng ..~ I SeaMing • Cleaning-up , Hardcopy • Laser (led (flat becUdrum) • Rf'duce colours printer Of'Stork) • Put Into repeal ~ Textile • Conventional • CoIou ring • Paper • Separations

Post printing ...- Protjuction Sample slages printing r- printing

• Steaming • Flat screen • Sample printer • Washing-oH • Rotary • Coupon prinler • • Roller • Bulk machine Fig. 2- lntegration or CAD systems into print production by a computer into whose software the desired image per has reached a sophisticated level of technology has been digitally scanned from a CAD station. and is widely used for printing office, industrial and • Developing a negative image into a positive with a computer stationery. powder developer system, transferring toner to the still charged design areas of the drum. 2.1 Xerographic Printing of 4 5 • Transferring the positive toner image from drum to Considerable research work . has been carried copy paper via electrostatics'. out at Georgia Institute of Technology in the past live • Melting the toner by heated roll, and air cooling to years for adapting xerographic printing to the patter­ fix the print. ning of textile fabrics. The research in this area is dire­ • Cleaning the PC drum and recycling any untrans­ cted in two directions, viz. system development and ferred toner to begin a repeat of the print cycle. toner development. The coloured xerox prints a re obtained using ma­ uve (red), cyan (blue), yellow and black toners. The 2.1 .1 System Development manufacturers claim that by usi ng these four toners as Current systems of xerography are developed for many as 30,000 shades can be produced via overlap­ paper printing which operate primarily batch-wise ping and subsequent melt blending of the primary and for fairly narrow width (8 .5 in). A single sheet of toners. Xerographic colour print production on pa- paper is printed at a time. Thirty-six inch wide copiers 52 INDIAN J. FIBRE TEXT. RES., MARCH 1996

have been developed recently. Two major challenges progress through the route of new polymer systems or faced by the xerography technology for fabric print­ modification of existing polymers. ing are handling larger widths and continuous print­ ing at a speed required in modern printing. Therefore, 2.2 Advantages of Xerography in Textile Printing a copier for printing textiles would be different since it Xerography has the following advantages in print­ must operate continuously at a speed of up to 50 ing fabrics: m/min. Information storage and input for image for­ • Information storage can be computerized, elimina­ mation should be accomplished using a computeri­ ting the need for large storage space for screens. zed system which would facilitate fast style and col­ • Since the system can be computerized, fast style and our changeovers as well as aid in production of new colour changeover are possible. designs. Considerable research is in progress at Geor­ • Potential for producing all shades using three prim­ gia Institute of Technology for developing a suitable aries and the black. xerography system for continuous printing oftexti­ • Pigments which are generally less expensive than les. dyes and offer better li ght fastness and Jther propert­ ies can be used for coloration . . 2.1.2 Toner Development • Washing and drying after printing are eliminated. The second area of research for success in adaption of xerography for textile printing is the development 2.3 LiJllitations of Xerography in Textile Printing of. tonerS . Xerography toner consists of a polymeric While xerography has much promise for fabric pri­ bindermixed with a suitable pigment colour, both nting, current technology has been deve loped for pa­ hpving very low particle size. Binders in typical paper per printing. Fabric printing has requirements bey­ toners generally consist of styrene/acrylate copoly­ onu those for paper printing. Xerographic paper pri­ mers or polyesters. Although excellent prints are obt­ nting systems have been designed primarily for oper­ ainable on textile fabrics, such as polyester/cotton ating in"bak:h mode for fairl y narrow widths. Fabric blends, by using pa per toners, the fastness properties, printing systems wi ll need to print much wider widths in a continuous mode. The toner binder requirements especially wet and dry crock fastne?s, are poor. for fabric printing are quite different from those for Typical screen printing binders, composed of com­ paper printing. The paper toner binders consist of plex acrylic terpolymers, are amorphous film-form­ styrene/acrylate copolymers with poo r adhesion to ing materials of high clarity. However, they cannot be textile fibres and low dryclea ning solve nt fastness. converted to fine powder by spray drying or grinding. Therefore, \they are not suitable binders for xerogra­ 3 Ink. Jet Printing phy toners. The research work at Georgia Institute of Ink jet prin~ing is a non-impact printing method, Technology has indicated the suitability of modified projecting drops of ink onto surfaces to be printed. epoxies, polyesters and ethylene vinyl acetate (EVA) The commercial developments in the area of ink jet copolymers as toner binders for textile xerography. printing are still limited to computer-aided office pri­ The epoxies under investigation are low molecular ntouts, hare! copy output of onto paper 8 weight polymers that flow well under melt conditions and in the printing ofcarpets and pile fabrics . Att­ and crosslink with fibre via reactive end groups dur­ empts are being made in developed countries with Ane ing the flow period. As a result, their fastness propert­ resolution to print unto textile substra te using the ies are comparable to those of conventional binders principle of ink jet printing. used in screen printing of pigment colours. However, the fabric ha ndle is stiff and unacceptable. Epoxies 3.1 Ink Jet Printing Technology for Textile with fewer active end groups (thus producing fewer There are two types of ink jet printers. The coarse crosslinks per anit film area on cure) are being investi­ resolution type has a maximum resolution of 40 dpi gated to reduce the rigidity of the prints while mainta­ and is based on valve control technology. Printers ining fastness properties. offering the fine resolution (up to 300 dpi) can be sub­ divided into two basic technologies-continuous Polyester toner binders suitable for parer xerogra­ stream (CS) and drop-on-demand (DOD). Within phy exhibit poor binding capabilities to polyester/ these two types, there are further subgroups. It is in cotton blends. EVA copolymers, depending on the this area offine resolution that there has been most relative percentage contribution of the two constitu­ recent research activities 1.3. ent comonomers (ethylene and vinyl acetate) to the polymer backbone and their sequencing, do not grind 3.1.1 Continuous Stream or spray dry well to produce fine powders suitable for In this system, ink is forced at a high pressure thro­ xerography. The search for suitable toner binder is in ugh a small jet (nozzle). The emerging stream of ink is CHAVAN: TECHNOWGICAL REVOLUTIONS IN TEXTILE PRINTING 53

broken into small droplets. These droplets can be sel­ a purpose of achieving continuous multicoloured ectively charged and' deflected while passing through printing with a resolution of 100 dpi. high voltage plates. There are two possible methods CSIRO in ,Australia was separately developing a of obtaining a design by this process. In the first meth­ variable continuous stream ink jet printing. Comme­ od, the charged droplets are deflected onto the substr­ rcialization of the work-was given to Wilcom Ltd of ate in a predetermined manner and the uncharged Sydney which produced a small-scale version. Other droplets collected in a feed tank and recycled. This is major projects included the one by the Burlington referred to as Raster-Scan Method. Corporation in USA which produced a full scale 2 m 16 In the second method, both uncharged droplets wide machine • A recently a~nounced project by form the image and the charged droplets are deflected Seiren 'of Japan aimed at full width printing is also to feed tank. This is known as the Binary Jet based on continuous stream technology. A machine 9 IO System . . is believed to be running at Seiren factory in Fukai, Japan. 3.1.2 Drop-on-Demand This technology as its name suggests produces an In February 1993, Kanebo of Japan, a large textile ink droplet when required and fires this onto the subs­ firm, and Cannon, the Japanese paper copier giant, trate. The DOD printers fall into two broad classes: (i) formed a consortiup1 to develop and market the first systems that produce a drop using a Piezo-electric commercial jet printing machine for continuous pat­ transducer, and (ii) systems that use thermal excita­ terning of textiles. Based on Cannon's bubble jet tech­ tion such as the bubble jet type to produce a drop. nology which, in turn, revolves around molten drop­ The important difference between DOD and conti­ lets of pigment-binder that are selectively placed on nuous stream systems is that with the continuous the substrate to generate the pattern, the first generat­ stream systems, more than one drop can be directed at ion machine is targeted to be 66 in wide with a resolu­ any specific pixel location (0.1 mm x 0.1 mm ·area). In tion of 400 dpi and capability of processing some continuous stream systems~ up to 15 drops of 3,00,000 m of fabric annually. It is believed that the each of the four inks (Black, Cyan, Magenta and Yel­ prototype was exhibited at a recent exhibition in Tok­ low) can be directed onto any pixel. Half tones are yo. In the original announcement, plans were to restr­ produced by using a matrix of drops to form a super­ ict .the technology to Japanese use for five years pixel, sometimes referred to as a dither pattern II. followed by worldwide marketing and expansion.

3.2 Coarse Ink Jet Printers 3.4 Stork Trucolor Jet Printer These are normally based on valve technology and The first commercial system for ink jet printing of have essentially found use in the carpet industry. textiles was launched by Stork Brabant Bv at 1991 There are two main commercially available systems. ITMA Exhibition in Hanover under the name Truco­ The Millitron system uses an array of jets with contin­ lour Jet Printer. The system is designed for sample uous stream of dye liquids which can be deflected by a printing on 100% cotton fabric. controlled air jetl 2. The Chromojet from the Austr­ The Trucolour Jet Printer is based on the Hertz ian Company Zimmer uses computer activated on/ continuous stream technology 17 - 19. Fig. 3 shows 8 offvalve systems to control the flow ofliquids . Daw­ principle of continuous stream ink jet printer (binary son Ellis Ltd has also patented an approach that uses method). Essentially, a dye formulation is pumped at electromechanical valves which are computer contr­ a constant pressure through a nozzle of 14.4 11m diam­ olled to open and close rapidly so that the liquid is eter. The continuous stream is broken up into dropl­ fired in a succession short pulses 13 - 15. The resolution ' ets by modulation at 625 kHz, i.e. 625000 droplets of of all these carpet jet printers is relatively coarse, reac­ colorant are formed per second. The printer uses digi­ hing a maximum of 40 dpi which is unacceptable in the tal information from a CAD station to either negati­ textile printing field . vely charge a droplet in a continuous stream emanat­ The majority of recent developing work on ink jet ing from a colour nozzle or allows it to pass the gate technology for textiles has looked essentially at adap­ uncharged. As the droplet train then enters an electri­ ting computer ink jet printing technology rather than cal field between two 1500 V plates, charged droplets valve technology developed for carpets. are deflected, picked up and fed back into the colour 3.3 Ink Jet Textile Printing Projects container for recycle. Uncharged droplets pass thro­ Over the last 20 years there have been a number of ugh the deflection plates in a group of up to 15 and major projects in the field of ink jet printing of textiles. reach the substrate in the desired pattern in an area One of the first was by ICI (now called Zeneca Colo­ covering only 0.1 mm x 0.1 mm or one pixel and thus urs) using continuous stream ink jet technology with producing smooth continuous tones. 54 INDIAN J. FIBRE TEXT. RES., MARCH 1996

Pad Matexll Enhanoer SJP 200 partSll 000 Sodium bicarbonate 25 partSllooo Sodium alginate solution 150 parts/I 000 ! (migration inhi~tor) Dry Controlled conditions ~ Inkjet Using Procion dye formulation and Stof1( Trucolor jel printer Fig. 3- Principle of continuous stream ink jet printer (Binary method)

The three subtractive primaries plus black are used T On completion of printing to produce needed shades via overlap printing. The most important feature ofTrucolour Jet Printer is the incorporation of high purity reactive dyes based on T Procion P dyes into the ink formulations. This allows Steam Atmospheric: Iteam conditions (10~ )( 8 min) the subsequent print to be processed as in conven­ tional printing, i.e. steam-wash-soap-wash-dryse­ ~ quence. Wash-off

3.4.1 Ink Formulation for Ink Jet Printing For a jet print to be comparable to textile print Dry~ produced by conventional screen or roller printing, the ink formulation must make use of the same dye Fig. 4--Process route for jet printing of mercerized cotton chemistry. Stork and Zeneca Colours have worked closely to develop extremely high purity versions of ied by jet printing to a level similar to that achieveable certain Procion P dyes and to incorporate these into by conventional printing. When this pretreatment formulations that satisfy and are compatible with the agent is padded alongwith conventional print paste stringent requirements of the Stork Trucolour Jet Pri­ chemicals pJior to application of the dye, good colour nter l ? The reactive group used in the Procion P dye yield can be obtained by wide range of cellulosic and range is the monochloro-s-triazinyl group, which re­ protein fibres. Fig. 4 shows the typical route for jet acts under hot alkaline conditions with cellulose. to printing of mercerized cotton. produce a covalent dye-fibre bond producing prints of excellent fastness. 3.5 Toxot .Jet Printer In conventional printing the dye is applied with Toxot Science and Applications Corporation of alkali and other necessary chemicals in the form of France (US represe ntative Irnaje Corporation) has print paste. The print is then normally steamed to fix been developing over the past five years an ink jet the dye to cellulose and is washed to remove any unre­ printer specifically for patterning textiles and allied acted dye chemicals and thickener. Because of the substrates, e.g. wall paper4. The proprietory techno­ stringent purity requirements and the conductivity logy is based on electrostatic deflection of colour dro­ specification required by continuous stream ink jet plets from a continuous stream. The interesting feat­ printers the conventional printing chemicals such as ure is that uv-curable binders have been developed alkali, urea, sodium alginate thickener, etc. cannot be for ToxotjImaje inks that allow complete fixation of incorporated into the ink formulation. the colours on textile s ubstra~es without a thermal postcure or an after scour-wash-dry seq uence. A ra­ 3.4.2 Substrate Pretreatments nge of ink colollrs is now available for ei ther the"quad­ The chemicals necessary for fixing reactive dyes on richromic approach to textile printing or for use of six cellulose can be padded onto fabric before the jet prin­ or seven colours to obtain more accurately the full ting stage. However, the resulting colour yield is still colour spectrum. However, the information on the not comparable to that achieveable by conventional fastness and other textile performance propcrties of printing processes due to the small amount of reactive these uv-curable inks is not available. dye applied. After extensive research, Zeneca Colo­ The ToxotjImaje is currently claiming print reso­ urs developed an auxiliary zeteK enhancer SJP which lutions of 120 dpi. The system allows rapid changeo­ can increase the colour d ,~ velopment of the dye appl- ver from one ink colour to another. Both scan and CHAVAN: TECHNOWGICAL REVOLUTIONS IN TEXTILE PRINTING 55

Customer Printing fac:tOty

Design

Ink jet print lextilelp8pef

Colour kitchen automatic sampl,"g

COlour k',tchen automahC bulk

Imploved design selec1ionl Improved quahty and speed of response 101 colourway choic:e samptes Imdtng to increased productivtty

Fig. 5-The possible design/sample selection procedure in future

CAD data input capabilities to the printers operating for final approval prior to bulk production. This stage computer are available. In a batch configuration desi­ could, as the technology develops, be eliminated and gned for semi-continuous T-shirt printing, a uv lamp the final approval could well come from the jet printed has been incorporated on a moving print head system sample. Fig. 5 also shows that the computer system to provide curing after printing, thereby eliminating can equally drive the other production functions such all postprint treatments and shortening the overall as laser engraving, colour match prediction, and sam­ process. ple and bulk print paste production. With the current speed of technological advance­ 4 Future Developments ment it seems unlikely that the advantages ofjet print­ With the introduction ofjet printer capable of pro­ ing will ever be limited to sample production. Furth­ ducing samples using reactive dyes, the possible desi­ er, in the future lie the prospects of semi-bulk produc­ gn/sample selection procedure (Fig. 5) could become tion and eventually full-scale production of textiles a reality in future. The customer could submit a new usingjet printing, thus removing (i) limitations on the design or the digital information produced from his/ number of colours in a design imposed by the need to her own CAD system. The textile printer could then use only a few screens to keep the cost down, (ii) const­ scan the design into a CAD system, subsequently raints in the use of intricate designs with sharp outlin­ working through the necessary cleaning up, repeat es, and (iii) the need to use discharge and resist tech­ setting, separation and colouring stages that many niques on many cellulosic fabric designs because of of the new systems are capable of carrying out. The design fitting problems. key element of the procedure is that the textile printer Jet printing may, therefore, open new windows of can use. the CAD generated digital information to opportunity that will allow textile printing industry drive the jetprinter- and produce a sample print on to grow and flourish into the next century. cellulosic fabrics using reactive dyes. This enables the production of realistic samples in a short time without References the need to engrave screens as in case of conventional 1 Provost J R, Text Chern Color. 27(6) (1995) 1 I. screen printing. The customer can make decisions on 2 Provost J R & Aston S 0, J Soc Dyers Colour. 111 (1995) 4. designs and colour combinations (including the des­ 3 Aston S 0 , Provost J R & Masselink H, J Soc Dyers Colollr. 109 igns that will not run in bulk) in a much more (1993) 147. informed manner. 4 Cook F L, Text World. 145 (1995) 73. 5 Carr W W, Cook F L, Lanigan W R, Sikarski M E & Tincher W Only when firm decisions have been made, screens C, Text Chern Color. 23(5) (1991) 33. could be engraved and a conventional sample printed 6 Tanaka T, J Imaging Technol. 15 (J 989) 198. 56 INDIAN 1. FIBRE TEXT. RES., MARCH 1996

7 Schaftent R M. E/('ctrop/wlOgraphy. 2nd edn (Focal Press. 13 Dawson Ellis Ltd. Br Pat, 2186419 ( 1987). London). 1975. 14 Kramrisch B, Dyer , 170(2) (1990) 8 .. 8 Dawson T L & Roberts B. J Soc Dyers CO/aliI'. 93 (1977) 439. 15 Ahmed A, J Soc Dyers Colollr, 108 (1992) 422. 9 Heinzl J & Hertz C H. Adl' Electron, Electron Phy.l', 65 (1985) 16 Graham L. Text Chem Color. 21(6) ( 1989) 27. 91. 10 Lyne M B. J Imagillg Tee//IIol, 12 (1986) 80. 17 Masselink H & Provost J R, Chemijasem, 42 (1992) 398. II Dawson T L. ReI' Prog Color. 22 (1992) 22. 18 New developments in jet printing (Boxmeer, Stork Xcel Bv.), 12 Dunkerly K. ReI' ?rog Color, II (1981) 74. 1990.