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

Technologica l revolutions In textile printing

R B Chavan

Department o f" Texlilc T.:ch no logy. Ind ian Inslitute of" Tel:hnol ogy. ew Delhi 11 001 6. India

, Widespread acceptance of demand-ac ti vated manufac turing architectu re (DAMA) and j ust-in -time (J IT) sa les and market i ng co nccpts have placed tremend ous pressure on tcx ti le printers. Prescn tl y avai lable continuo us ro tary scrcen printing equipment are often inflexible in tcrm ~ of quick customer responsc and shoJ'l runs. I n the prescnt article. an attempt has been made to review critically two tcchnological innova tIons in tc xtile pri nt ing, vii. xerography and in.k jCt pri nt ing. 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<.; tth l: tec!lnol ogy fo r production print ing. It is envisaged that by the turn o f thi s cent ury, a customer instead of purchasing th c printed fabric ava ilabl e in thc stores may be able to scan the designs on computer, se lec t the des ign and colour combination, or cl-c~! t e the new design a nd load the informat ion to the computer of the printcr <lnli ge t the pr inted kngt h of the fabri c wi th a dcsign o f hi s/her choice.

Keywords: In k je t printing, Textile printing, Xerography

J Introduction ~otary sc reen printing machine was introduced in

196.1 and since then there is continued ri se in its popu­la rit y. Worldwide, 60 % of fabric print ing is done by iota ry screen printing a nd 18(% by flat screen print­ing. Although rotary screen printing machines a re most suited for production runs, they are not idea l to meet the requirements of dema nd-activa ted ma nufa­cturing architecture (DAMA) a ndjust in time (lIT) concepts. According to these concepts the tex til e pri­nters must respond to the delivery of hi gh quality fas­hion designs with wide range of colour combinations in extremely short time . In addition, there is also eq­ual pressure on textile printers to produce bulk prints in an environment-friendly ma nner.

Prior to 1980, the majo rity of printers followed essentially a totally manual approach to the produc­tion of textile prints , from the initial design stage to first bulk production. fig. I shows the a pproach foil · owed in textile printing a t that time 1.2.

After ITM"x 83 show in Milan the situa tion chan­ged with the availability of rela ti vely low-cost a nd increasing powerful PC-based sys tems. Since ITMA' 91 in Hanover, there has been dramatic increase in the associated technology of visual di splay unit s, graphic controllers, scanners and high volume data storage sys tems . With the right investment the printers now scan designs into a CAD system where a number o f colour combinations can be changed , designs mani­pulated, put into repeat, colourways c rea ted and col-

o ur separations prod uced . The digital in fo rmatio n genera ted can subsequently be used tQ produce scre­ens direc tl y by the lates t laser engraving technol ogy o r by the conventional means using computer prod u­ced tran sparencies. Fig. 2 shows integra tion of CAD sys tem' into print production.

In spit e of these developments, the currentl y domi­nent rotary screen printing method has seve rallimita­tions, such as colour and pattern changes require long process set-up time, sc reen productio n is slow a nd ex pensive, and screens have relati ve ly short lives a nd req uire considerable storage space even when no t be­ing used. Thus, a new technology for fabric printing is needed tha t will pe rmit frequent style a nd colour cha­nges with minimum downtime for ch a ngeover and will a ll ow comp ute r sto rage o r design info rma ti o n. Two revo lu tio na ry printing techniques, viz. xerogr~l­

phic printing a nd ink je t printing, ha ve the potentia l o f meeting these requirement

2 Xerographic Printing The commonly known xerograp hy o r photocopy­

ing technique is esse ntiall y ba sed 0 11 e lect ros tatic powder print ing techno logy. The basic steps involved ill xerographic printing4 - 7 a re: • Formation of a nega tive image o n a light sensitive photoconductive (PC) surface (o ften a se lenium or polymer coated drum) via light reflectio n from a prin­led master sheet. More recently, the process is accom­plished by impingement with a lase r bea m controlled

CHAVAN: TECHNOLOGICAL REVOLUTIONS IN TEXTILE PRINTING 51

Original Manuallracing

Sample

~ design ......... and separalion r-- Engraving r-- prinling produclion

C I u s I Colour Fabric

0 mixing preparation

m

• • e r

Bulk production prinVsleamlwashing finishinglinspeclion

II Sample production: time scale 2-8 weeks

III Bulk production: time scale 3- I 2 weeks

(including u~ production)

Fig. I- Textile printing by conventional methods

I !":o H ~OM H ... _a_: .. _re_!n._M

_' _~_'..JH Eng .. ~ I SeaMing • Cleaning-up (flat becUdrum) • Rf'duce colours

• Put Into repeal • CoIou ring • Separations

Post printing ...-slages

• Steaming • Washing-oH • Finishing

, Hardcopy printer

~ Textile • Paper

Protjuction printing

• Flat screen • Rotary • Roller

• Laser (led Of'Stork)

• Conventional

r- Sample printing

• Sample printer • Coupon prinler • Bulk machine

Fig. 2- lntegration or CAD systems into print production

by a computer into whose software the desired image has been digitally scanned from a CAD station . • Developing a negative image into a positive with a powder developer system, transferring toner to the still charged design a reas of the drum. • Transferring the positive toner image from drum to copy paper via electrostatics'. • Melting the toner by heated roll, and air coo ling to fix the print. • Cleaning the PC drum and recycling any untrans­ferred toner to begin a repeat of the print cycle.

The coloured xerox prints a re obtained using ma­uve (red), cyan (blue), yellow and black toners. The manufacturers claim that by using these four toners as many as 30,000 shades can be produced via overlap­ping and subsequent melt blending of the primary toners . Xerographic colour print production on pa-

per has reached a sophisticated level of technology and is widely used for printing office, industrial and computer stationery.

2. 1 Xerographic Printing of Textiles

Considerable research work 4 . 5 has been carried out at Georgia Institute of Technology in the past live years for adapting xerographic printing to the patter­ning of textile fabrics . The research in this area is dire­cted in two directions, viz. system development and toner development.

2.1 .1 System Development

Current systems of xerography are developed for paper printing which operate primarily batch-wise and for fairly narrow width (8 .5 in). A single sheet of 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 faced by the xerography technology for fabric print­ing are handling larger widths and continuous print­ing at a speed required in modern printing. Therefore, a copier for printing textiles would be different since it must operate continuously at a speed of up to 50 m/min. Information storage and input for image for­mation should be accomplished using a computeri­zed system which would facilitate fast style and col­our changeovers as well as aid in production of new designs. Considerable research is in progress at Geor­gia Institute of Technology for developing a suitable xerography system for continuous printing oftexti­les .

2.1.2 Toner Development

The second area of research for success in adaption of xerography for textile printing is the development of . tonerS . Xerography toner consists of a polymeric bindermixed with a suitable pigment colour, both hpving very low particle size. Binders in typical paper toners generally consist of styrene/acrylate copoly­mers or polyesters. Although excellent prints are obt­ainable on textile fabrics, such as polyester/cotton blends, by using pa per toners, the fastness properties, especially wet and dry crock fastne?s, are poor.

Typical screen printing binders, composed of com­plex acry lic terpolymers, are amorphous film-form­ing materials of high clarity. However, they cannot be converted to fine powder by spray drying or grinding. Therefore, \they are not suitable binders for xerogra­phy toners. The research work at Georgia Institute of Technology has indicated the suitability of modified epoxies, polyes ters and ethylene vinyl acetate (EVA) copolymers as toner binders for textile xerography. The epoxies under investigation are low molecular weight polymers that flow well under melt conditions and crosslink with fibre via reactive end groups dur­ing the flow period. As a result , their fastness propert­ies are comparable to those of conventional binders used in screen printing of pigment colours. However, the fabric ha ndle is stiff and unacceptable. Epoxies with fewer active end groups (thus producing fewer crosslinks per anit film area on cure) are being investi­gated to reduce the rigidity of the prints while mainta­ining fastness properties.

Polyester toner binders suitable for parer xerogra­phy exhibit poor binding capabilities to polyester/ cotton blends. EVA copolymers, depending on the relative percentage contribution of the two constitu­ent comonomers (ethylene and vinyl acetate) to the polymer backbone and their sequencing, do not grind or spray dry well to produce fine powders suitable for xerography. The search for suitable toner binder is in

progress through the route of new polymer systems or modification of existing polymers.

2.2 Advantages of Xerography in Textile Printing

Xerography has the following advantages in print­ing fabrics: • Information storage can be computerized, elimina­ting the need for large storage space for screens. • Since the system can be computerized, fast style and colour changeover are possible. • Potential for producing all shades using three prim­aries and the black . • Pigments which are generally less expensive than dyes and offer better light fastness and Jther propert­ies can be used for coloration . . • Washing and drying after printing are e liminated .

2.3 LiJllitations of Xerography in Textile Printing

While xerography has much promise for fabric pri­nting, current technology has been deve loped for pa­per printing. Fabric printing has requirements bey­onu those for paper printing. Xerographic paper pri­nting systems have been designed primarily for oper­ating in"bak:h mode for fairl y narrow widths. Fabric printing systems wi ll need to print much wider widths in a continuous mode. The toner binder requirements for fabric printing are quite different fro m those for paper printing. The paper toner binders consist of styrene/acry late copo lymers with poo r adhesion to textile fibres and low dryclea ning so lve nt fastness.

3 Ink. Jet Printing Ink jet prin~ing is a non-impact printing method ,

projecting drops of ink onto surfaces to be printed. The commercial developments in the area of ink jet printing are still limited to computer-aided office pri­ntouts, hare! copy output of textile design onto paper and in the printing ofcarpets and pile fabrics 8 . Att­empts are being made in developed countries with Ane resolution to print unt o textile subs tra te using the principle of ink jet printing.

3.1 Ink Jet Printing Technology for Textile

There are two types of ink jet printers. The coarse resolution type has a maximum resolution of 40 dpi and is based on va lve control technology. Printers offering the fine resolution (up to 300 dpi) can be sub­divided into two basic technologies-continuous stream (CS) and drop-on-demand (DOD). Within these two types, there are further subgroups. It is in this area offine resolution that there has been most recent research activities 1.3.

3.1.1 Continuous Stream

In thi s system, ink is forced at a high pressure thro­ugh a small je t (nozzle). The emerging stream of ink is

CHAVAN: TECHNOWGICAL REVOLUTIONS IN TEXTILE PRINTING 53

broken into small droplets. These droplets can be sel­ectively charged and' deflected while passing through high voltage plates. There are two possible methods of obtaining a design by this process. In the first meth­od, the charged droplets are deflected onto the substr­ate in a predetermined manner and the uncharged droplets collected in a feed tank and recycled. This is referred to as Raster-Scan Method .

In the second method, both uncharged droplets form the image and the charged droplets are deflected to feed tank. This is known as the Binary Jet System9 . IO .

3.1.2 Drop-on-Demand This technology as its name suggests produces an

ink droplet when required and fires this onto the subs­trate. The DOD printers fall into two broad classes: (i) systems that produce a drop using a Piezo-electric transducer, and (ii) systems that use thermal excita­tion such as the bubble jet type to produce a drop.

The important difference between DOD and conti­nuous stream systems is that with the continuous stream systems, more than one drop can be directed at any specific pixel location (0.1 mm x 0.1 mm ·area). In some continuous stream systems~ up to 15 drops of each of the four inks (Black, Cyan, Magenta and Yel­low) can be directed onto any pixel. Half tones are produced by using a matrix of drops to form a super­pixel, sometimes referred to as a dither pattern II.

3.2 Coarse Ink Jet Printers

These are normally based on valve technology and have essentially found use in the carpet industry . There are two main commercially available systems. The Millitron system uses an array of jets with contin­uous stream of dye liquids which can be deflected by a controlled air jetl 2. The Chromojet from the Austr­ian Company Zimmer uses computer activated on/ offvalve systems to control the flow ofliquids8 . Daw­son Ellis Ltd has also patented an approach that uses electromechanical valves which are computer contr­olled to open and close rapidly so that the liquid is fired in a succession short pulses 13 - 15 . The resolution ' of all these carpet jet printers is relatively coarse, reac­hing a maximum of 40 dpi which is unacceptable in the textile printing field .

The majority of recent developing work on ink jet technology for textiles has looked essentially at adap­ting computer ink jet printing technology rather than valve technology developed for carpets.

3.3 Ink Jet Textile Printing Projects

Over the last 20 years there have been a number of major projects in the field of ink jet printing of textiles. One of the first was by ICI (now called Zeneca Colo­urs) using continuous stream ink jet technology with

a purpose of achieving continuous multicoloured printing with a resolution of 100 dpi.

CSIRO in ,Australia was separately developing a variable continuous stream ink jet printing. Comme­rcialization of the work-was given to Wilcom Ltd of Sydney which produced a small-scale version. Other major projects included the one by the Burlington Corporation in USA which produced a full scale 2 m wide machine 16• A recently a~nounced project by Seiren 'of Japan aimed at full width printing is also based on continuous stream technology. A machine is believed to be running at Seiren factory in Fukai, Japan.

In February 1993, Kanebo of Japan, a large textile firm, and Cannon, the Japanese paper copier giant, formed a consortiup1 to develop and market the first commercial jet printing machine for continuous pat­terning of textiles. Based on Cannon's bubble jet tech­nology which, in turn, revolves around molten drop­lets of pigment-binder that are selectively placed on the substrate to generate the pattern, the first generat­ion machine is targeted to be 66 in wide with a resolu­tion of 400 dpi and capability of processing 3,00,000 m of fabric annually. It is believed that the prototype was exhibited at a recent exhibition in Tok­yo. In the original announcement, plans were to restr­ict .the technology to Japanese use for five years followed by worldwide marketing and expansion.

3.4 Stork Trucolor Jet Printer

The first commercial system for ink jet printing of textiles was launched by Stork Brabant Bv at 1991 ITMA Exhibition in Hanover under the name Truco­lour Jet Printer. The system is designed for sample printing on 100% cotton fabric.

The Trucolour Jet Printer is based on the Hertz continuous stream technology 17 - 19. Fig. 3 shows principle of continuous stream ink jet printer (binary method). Essentially, a dye formulation is pumped at a constant pressure through a nozzle of 14.4 11m diam­eter. The continuous stream is broken up into dropl­ets by modulation at 625 kHz, i.e. 625000 droplets of colorant are formed per second. The printer uses digi­tal information from a CAD station to either negati­vely charge a droplet in a continuous stream emanat­ing from a colour nozzle or allows it to pass the gate uncharged. As the droplet train then enters an electri­cal field between two 1500 V plates, charged droplets are deflected, picked up and fed back into the colour container for recycle. Uncharged droplets pass thro­ugh the deflection plates in a group of up to 15 and reach the substrate in the desired pattern in an area covering only 0.1 mm x 0.1 mm or one pixel and thus producing smooth continuous tones.

54 INDIAN J. FIBRE TEXT. RES., MARCH 1996

Fig. 3- Principle of continuous stream ink jet printer (Binary method)

The three subtractive primaries plus black are used to produce needed shades via overlap printing. The most important feature ofTrucolour Jet Printer is the incorporation of high purity reactive dyes based on Procion P dyes into the ink formulations. This allows the subsequent print to be processed as in conven­tional printing, i.e. steam-wash-soap-wash-dryse­quence.

3.4.1 Ink Formulation for Ink Jet Printing For a jet print to be comparable to textile print

produced by conventional screen or roller printing, the ink formulation must make use of the same dye chemistry. Stork and Zeneca Colours have worked closely to develop extremely high purity versions of certain Procion P dyes and to incorporate these into formulations that satisfy and are compatible with the stringent requirements of the Stork Trucolour Jet Pri­nter l ? The reactive group used in the Procion P dye range is the monochloro-s-triazinyl group, which re­acts under hot alkaline conditions with cellulose. to produce a covalent dye-fibre bond producing prints of excellent fastness.

In conventional printing the dye is applied with alkali and other necessary chemicals in the form of print paste. The print is then normally steamed to fix the dye to cellulose and is washed to remove any unre­acted dye chemicals and thickener. Because of the stringent purity requirements and the conductivity specification required by continuous stream ink jet printers the conventional printing chemicals such as alkali, urea, sodium alginate thickener, etc. cannot be incorporated into the ink formulation .

3.4.2 Substrate Pretreatments The chemicals necessary for fixing reactive dyes on

cellulose can be padded onto fabric before the jet prin­ting stage. However, the resulting colour yield is still not comparable to that achieveable by conventional printing processes due to the small amount of reactive dye applied. After extensive research, Zeneca Colo­urs developed an auxiliary zeteK enhancer SJP which can increase the colour d ,~ velopment of the dye appl-

Pad

! Dry

~ Inkjet

T T

Steam

~ Wash-off

~ Dry

Matexll Enhanoer SJP Sodium bicarbonate Sodium alginate solution (migration inhi~tor)

Controlled conditions

200 partSll 000 25 partSllooo

150 parts/I 000

Using Procion dye formulation and Stof1( Trucolor jel printer

On completion of printing

Atmospheric: Iteam conditions (10~ )( 8 min)

Fig. 4--Process route for jet printing of mercerized cotton

ied by jet printing to a level similar to that achieveable by conventional printing. When this pretreatment agent is padded alongwith conventional print paste chemicals pJior to application of the dye, good colour yield can be obtained by wide range of cellulosic and protein fibres. Fig. 4 shows the typical route fo r jet printing of mercerized cotton.

3.5 Toxot .Jet Printer

Toxot Science and Applications Corporation of France (US representative Irnaje Corporation) has been developing over the past five years an ink jet printer specifically for patterning textiles and allied substrates, e.g. wall paper4. The proprietory techno­logy is based on electrostatic deflection of colour dro­plets from a continuous stream. The interesting feat­ure is that uv-curable binders have been developed for ToxotjImaje inks that allow complete fixation of the colours on textile substra~es without a therma l postcure or an after scour-wash-dry seq uence . A ra­nge of ink colollrs is now available for ei ther the"quad­richromic approach to textile printing or for use of six or seven colours to obtain more accura tely the full colour spectrum. However, the informat ion on the fastness and other textile performance propcrties of these uv-curable inks is not available.

The ToxotjImaje is currently claiming print reso­lutions of 120 dpi. The system allows rapid changeo­ver from one ink colour to another. Both scan and

CHAVAN: TECHNOWGICAL REVOLUTIONS IN TEXTILE PRINTING 55

Customer

Design

Imploved design selec1ionl colourway choic:e

Ink jet print lextilelp8pef

Printing fac:tOty

Improved quahty and speed of response 101 samptes Imdtng to increased productivtty

Colour kitchen automatic sampl,"g

COlour k',tchen automahC

bulk

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

CAD data input capabilities to the printers operating computer are available. In a batch configuration desi­gned for semi-continuous T-shirt printing, a uv lamp has been incorporated on a moving print head system to provide curing after printing, thereby eliminating all postprint treatments and shortening the overall process.

4 Future Developments With the introduction of jet printer capable of pro­

ducing samples using reactive dyes, the possible desi­gn/sample selection procedure (Fig. 5) could become a reality in future. The customer could submit a new design or the digital information produced from his/ her own CAD system. The textile printer could then scan the design into a CAD system, subsequently working through the necessary cleaning up, repeat setting, separation and colouring stages that many of the new systems are capable of carrying out. The key element of the procedure is that the textile printer can use. the CAD generated digital information to drive the jetprinter- and produce a sample print on cellulosic fabrics using reactive dyes. This enables the production of realistic samples in a short time without the need to engrave screens as in case of conventional screen printing. The customer can make decisions on designs and colour combinations (including the des­igns that will not run in bulk) in a much more informed manner.

Only when firm decisions have been made, screens could be engraved and a conventional sample printed

for final approval prior to bulk production. This stage could, as the technology develops, be eliminated and the final approval could well come from the jet printed sample. Fig. 5 also shows that the computer system can equally drive the other production functions such as laser engraving, colour match prediction, and sam­ple and bulk print paste production.

With the current speed of technological advance­ment it seems unlikely that the advantages of jet print­ing will ever be limited to sample production. Furth­er, in the future lie the prospects of semi-bulk produc­tion and eventually full-scale production of textiles usingjet printing, thus removing (i) limitations on the number of colours in a design imposed by the need to use only a few screens to keep the cost down, (ii) const­raints in the use of intricate designs with sharp outlin­es, and (iii) the need to use discharge and resist tech­niques on many cellulosic fabric designs because of design fitting problems.

Jet printing may, therefore, open new windows of opportunity that will allow textile printing industry to grow and flourish into the next century.

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(1993) 147. 4 Cook F L, Text World. 145 (1995) 73. 5 Carr W W, Cook F L, Lanigan W R, Sikarski M E & Tincher W

C, Text Chern Color. 23(5) (1991) 33. 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. London). 1975.

8 Dawson T L & Roberts B. J Soc Dyers CO/aliI' . 93 (1977) 439. 9 Heinzl J & Hertz C H. Adl' Electron , Electron Phy.l', 65 (1985)

91. 10 Lyne M B. J Imagillg Tee//IIol, 12 (1986) 80. II Dawson T L. ReI' Prog Color. 22 (1992) 22. 12 Dunkerly K. ReI' ?rog Color , II (1981) 74.

13 Dawson Ellis Ltd. Br Pat, 2186419 ( 1987).

14 Kramrisch B, Dyer , 170(2) (1990) 8 ..

15 Ahmed A, J Soc Dyers Colollr, 108 (1992) 422.

16 Graham L. Text Chem Color. 21(6) ( 1989) 27.

17 Masselink H & Provost J R, Chemijasem , 42 (1992) 398.

18 New developments in jet printing (Boxmeer, Stork Xcel Bv.), 1990.