INK JET PRINTING ON TEXTILES

Transcription

1 INK JET PRINTING ON TEXTILES Dr John Provost Abstract With the increased pressure from developing textile markets in the Far East the textile printer in Europe, Japan and the USA must respond with both increased quality and shorter time of response. This means supplying new design concepts, sample and production printed fabrics in a wide range of colour ways in a time frame unheard of a few years ago. One area that has seen development is in the pre-printing area with increasing use of CAD/CAM systems and digital printing systems,with ink jet printing systems being targeted.since the 1991 ITMA digital textile printing systems have been available that can be used for proofing and small sample production. A considerable number of major research projects ( in Europe, Japan and the USA ) aimed at taking digital textile printing to the full production scale are underway. The present paper will review the latest development in the digital ink jet printing of textiles and highlight the future direction this technology will take in textile printing. Introduction The textile printing business is a large and complex business with production of prints required on all textile substrates from cotton to the wide range of synthetic fibres. Each of these fibres has to be printed with a dyestuff class to enable fixation (by various chemical or physical methods) to the textile to impart the 'wash and wear' characteristics demanded by the consumer. Total production of textile prints approaches 19 linear billion metres of fabric per year and shows an average growth rate of the order of ~2% per year.however, hidden behind these small growth figures are a relative decline in the developed Western textile printing markets and a much larger growth in the developing markets in the Far East. For the Developed print markets to survive into the 21st century a strategy has to be developed based on (i) speed of response, (ii) short lot production, (iii) short delivery times, (iv) increased innovation and new fashion ideas, and (v) the formation of 'partnerships' with the major retail groups (the printers' customer). 1 1

2 To achieve this strategy the printer must take an integrated approach to the whole textile printing process ( design /proofing and production ) (1). The printer has to examine: * the pre-printing stage (CAD/CAM) * the quicker production of sample prints (using digital printing technologies whether direct ( ink Jet ) or indirect ( transfer technologies ) * selection of a compatible dye range to ensure minimum transfer from sample to bulk production and consequent less down time when designs are proofed /sampled on digital systems before being printed on analogue systems. The first two steps, the use of CAD systems and the quick production of sample prints are the 'key' starting elements of this strategy. It is in this area that we have seen rapid developments in the use of ink jet printing techniques using the digital output from CAD systems. The major reason for the concentration of research programmes on ink jet printing is the realisation that dyes used in digital technologies could be modified and adapted from the same dyes used in current conventional screen textile printing. It should therefore be possible to develop new systems, initially for 'proofing /sample' printing,that would eliminate the need for preparing full separations and engraving. The technology is advancing at a rapid rate with machines available up to the 100 square metre /hour level with further advances expected at the 1999 ITMA in Paris and over the subsequent next 5 years. Full scale production machines which will replace conventional analogue systems are still many years away. The development of full size ink jet print systems is the target of a number of ambitious plans with projects both in Europe,USA and Japan. Pre Print Stage in Textile Printing If we examine the production time scale of a textile print from design conception to bulk print we can see the considerable advantages to be gained from design selection and sampling using ink jet print technology. To obtain a "feel" for the production time scale of a textile print let us examine the situation for a totally manual approach to the production of a textile print. Figure 1 gives an overview of the stages carried out in the production of a textile print. 2 2

3 CONVENTIONAL TEXTILE PRINTING PRODUCTION C U S T O M E R ORIGINAL DESIGN COLOUR MIXING SAMPLE PRINTING SAMPLE PRODUCTION: TIME SCALE 2-8 WEEKS BULK PRODUCTION: TIME SCALE 3-12 WEEKS (INCLUDING SAMPLE Figure 1 Textile Printing by Conventional Manual Methods In conventional textile printing,an original design was manually traced, films produced and individual screens or rollers engraved for each colour (i.e. if a textile design has 24 colours then 24 screens have to be produced unlike the CMYK process colour system used in the graphic arts industry). A 'proof' (or sample ) print was produced in a number of colour ways on the textile substrate supplied by the customer prior to submitting to the customer for approval.. The time scales indicated in Figure 1 are still typical of those currently achievable by the textile printer who has not adopted digital technologies. However over the last few years there has been considerable investment by the printer and the majority of textile printers now have CAD systems. With the right investment the printer can scan designs into a CAD system where he can reduce the number of colours, manipulate designs, put into repeat, colour and produce separations. The digital information produced can then subsequently be used to produce screens directly, via the latest laser engraving technology, or by conventional means using computer produced films. However, the 'rate determining step' and major bottleneck is the production of the many colour ways at the sample print stage. Digital printing technologies can reduce these bottlenecks considerably. These new technologies can reduce the time taken for colour way/sample selection and have greatly increased the efficiency of the printer in bringing design concepts to the market place. 3 3

4 This has consequently led to much more increased research activity in the field of textile ink jet printing. Integration of an ink jet printing system into the already available digital technologies( CAD, Laser Engraving etc ) would give the possibility of shortening the time to market dramatically. A future scenario is shown in Figure 2,where the acceptance of the sample by the customer is made on the basis of an ink jet print. This is not a full reality at present, however with possible developments it could well become a possibility. TEXTILE SAMPLE (PROOFING) BY INK JET SAMPLE ACCEPTANCE BULK PRODUCTION 1-3 DAYS 2 WEEKS Figure 2 Possible Future Scenario for Sample to Bulk Production The first systems were developed as long ago as the 1970 s ( the ICI /CCL continuous ink jet developments) (2). Although there were a number of ambitious programmes over the subsequent years, it was not until the early 1990 s that programmes in Europe and Japan produced commercially available systems. Although the current paper is concerned with ink jet printing for textiles with consequent requirement for fine jet technology there were major developments in the carpet industry during those early years of digital printing.two commercial systems were developed, the Millitron system (3) which uses an array of jets with continuous streams of dye liquor which can be deflected by a controlled air jet and the 'ChromoJet' system ( from the Zimmer Comapany of Austria (4). Both these systems offer only coarse resolution which has not proved acceptable to the textile printer. However, they did indicate the many benefits of adopting ink jet printing technologies. 4 4

5 For sample and proofing purposes Stork of Holland introduced the 'Trucolor' TCP system at the 1991 ITMA exhibition in Hanover (5). The Stork system is system is based on the Hertz binary continuous jet system (6). A full description of the principles can be found in the paper by Hertz and Samuelson (7). Over the last 25 years there have been many projects in the textile ink jet field. These projects have used in many cases differing print head technologies. It is significant in the textile printing field that no one single print head technology has become established. The complete range of print head technologies are currently being researched by the many published projects. An excellent review of textile ink printing has been published by Dawson (2). Textile projects in jet printing have been considerable over the last 25 years, some of the major projects are listed below. Continuous Multi-Level Deflected Technology C.S.I.R.O (Australia ) TOXOT (Image) Zimmer ( Jemtex Print heads ) Continuous Binary Systems Burlington Project (10) Amethyst (STORK) (5) 5 5

6 Thermal Ink Jet Technology ("Drop on Demand" System) Canon "Wonderprint" Systems (11) (12) (13) Encad (USA ) Shima Seiki ( Japan ) ColorSpan (USA) Piezo Drop on Demand Technology Seiren ViscoTex System Mimaki SJ1300/JV Series TX 1600/TX2 Series Konica Nassenger KS System DPS 65 ( Magic Print Heads from Aprion ) Dupont( Vutek ) Spectra Print Heads Leggett and Platt ( Spectra Print Heads ) There is on going trend in the last 2 years at adapting wide format graphic printers to textile printing systems and producing individual printed articles for sale to the retailer / consumer. The majority of these systems are developing ink formulations based on dye systems rather than pigments with the aim of obtaining fixation and consequently wider shade gamut, improved handle and excellent colour fastness properties. The development of reliable ink systems for textiles is only a recent introduction. Also the challenges of obtaining reliable print systems for Disperse dye inks ( both for transfer and direct printing ) is only just being realised. As cellulose printing (cotton, viscose rayon) and blends with cellulose accounts for nearly 70% of all textile printing consequently considerable research has been aimed at developing stable ink formulations based on reactive dyes. A further reason for developing ink formulations based on reactive dyes is the inherent higher price of the finished print with consequent higher margins for the printer. Reactive Dyes in Textile Ink Jet Reactive dyes were first introduced in 1956 (13) These dyes have suitable groups capable of forming a covalent link between the dye and the hydroxyl in the cellulose. In textile printing two essential types have developed; (i) monohalogenotriazine types which react by a nucleophilic substitution mechanism, and (ii) groups which react by the addition of the nucleophilic group of the substrate to a C=C double bond on the reactive group (the most common of this class are sulphuric acid esters of ß-hydroxyethylsulphones which form vinyl sulphone groups under alkaline conditions). Due to the differing reactivities of the two types and the need for long term stability in conventional printing the first type - the monohalogenetriazine types are the most popular in textile printing, accounting for approximately 85% of conventional textile printing on cellulosic fabrics. 6 6

7 The reactive scheme for a typical monochloro-s-triazinyl dye is shown in Figure 3. The reaction takes place under alkaline conditions and heat (normally steam fixation at 102 C for 10 minutes) together with other additives such as urea. REACTION SCHEME FOR REACTIVE DYE (MONOCHLORO-S-TRIAZINE) WITH CELLULOSE Figure 3 Reactive Scheme for Reactive Dye Monochloro-s-triazinyl type) with Cellulose There are many factors which must be taken into effect when developing dyes, dye formulations and the ink systems for the wide range of head technologies being researched today.figure 4 highlights some of the factors which must be taken into consideration when designing ink systems for specific print head and substrate combinations. The development of specific ink systems is very complex undertaking and is very much a comprise situation, balancing the properties of the ink vehicle with performance criteria set by the print head technology and at the same time taking in the requirements of the media/substrate (17 ). In conventional textile printing the reactive dye is applied to the textile with alkali and all the necessary additional chemicals in the form of a print paste. The print is then normally steamed to fix the dye to the hydroxyl groups within the cellulose and subsequently washed to remove any unreacted colour, chemicals and the thickener. A much more complex process than conventional ink jet printing on paper. This requirement for extra chemicals to fix the reactive dye, the reactivity of the dye itself under alkaline conditions and the relative small amount of ink formulation applied has led to the modification of conventional print technology and the introduction of chemical pre-treatments (2) (5). 7 7

8 Textile Substrate Pre Treatment Technology With ink jet textile print systems that use dyes, the chemicals required for fixation of the dyes have to be applied by a padding or coating application prior to ink jet printing. However, even with the application of the conventional print chemicals colour yield is still not comparable to that achieved by conventional printing processes. This in the main is due to the very much smaller amount of ink formulation applied by the print head.it must also be noted that different print head technologies apply also differing amounts of ink ( ink jet volumes are measured using picolitre units ). This is in contrast to conventional printing where the amount of print formulation applied can be up to 200 gm/sq. metre or more (dependent on the actual weight/sq. metre of the textile) with ink jet the amount of ink formulation applied can be as small as 20mls/square metre. Actual amounts applied by the various print technologies differ depending on the actual print head principle,nozzle size( drop volume ), frequency rate ( which determines the number of drops /second ). Also with ink jet printing on textiles the amount of ink applied is constant for a specific head technology. With these considerable extra constraints an integral part of any successful ink jet textile system is the pre-treatment technology. For an textile ink jet application to be successful,the dye chemists(or textile chemists) and the media must work in a close relationship with the systems integrator ( and the print head developer). These pre treatment chemical and process methods must be developed for specific dye types and substrate combinations. Application Areas of Current Ink Jet Printers The major application areas of jet printing have been in the pre-printing (proofing and sample print areas), small run on demand printing ( sometimes referred to as Agile Manufacturing Model ). Ink Jet Printing has also been used to produce colour catalogues and the easier communication of colour information (16 ). 8 8

9 Other uses of textile ink jet include, At the colouring and design stage. Samples on fabric can be obtained quickly in a choice of colour ways without having to make films, screens or print paste so customers can make the "Go/NoGo" decision for a particular design in a particular colour combination. Correlation of the print produced for the sample print by ink jet must subsequently be reproduced in the production using screen technology.methods have been developed to achieve this Match to Print (MTP ) capability (16 ). Ink Jet printers can be used as a method of producing small-scale production prints of exclusive designs (for example for ties, scarves and pocket handkerchiefs) within a very short time compared to any procedure involving an engraving stage. This on demand printing to the 100metre length produced by ink jet will become of increasing important The introduction of the Canon WonderPrint bubble jet printing system, which was announced at the Vienna 17 th IFVTCC Congress in June 1996, which is capable of printing 100square metres /hour will lead to further developments for ink jet print machines in this production scale area. Similarly one-off sample prints for use in garments for selection purposes by a retailer, photographing for mail-order catalogues or publicity material in advance of bulk production can be produced. Since the introduction of this approach customers can submit a new design (or could submit digital information produced from his own CAD system) to the textile printer. 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 generate digital information to drive the jet printer and produce a sample print. The subsequent jet printed sample follows the normal post printing operations of steaming and washing-off. This enables the production of realistic small samples in a short time without the requirement of engraving screens or producing conventional sample prints. Only when firm decisions have been made would screens be engraved and a conventional sample printed for final approval prior to bulk production. In addition production of colour atlases that can be ink jet printed onto cloth opens up new possibilities in the specification and communication of colours. Easy translation of ink jet sample prints into bulk production recipes could also be made easier by the use of colour atlases. These recipes can be transmitted electronically to automatic dispensing colour systems for production of colours for production printing. This then gives the capability of 'integrating' the total textile print production process. The potential of integrating sample and production using digital systems and ink jet print technology has been recently described (16). 9 9

10 Recent Developments As discussed in the introduction,conventional textile printing uses a separate screen for each of the colours required. The conventional textile printer has therefore the complete range of colours to choose from when producing a design. For example, if a customer requires a bright orange colour he can choose a bright orange dye to satisfy the customer. With ink jet printing technology ('continuous' and 'drop-on-demand' ink jet print heads ) colours are normally produced using 4 colours only (Cyan, Magenta, Yellow and Black), therefore to produce a bright orange the yellow and magenta are used. Therefore, using the CMYK process colour approach it was soon realised that only 70 percent of the colour gamut of the total available gamut to the textile printer could be achieved. Canon also with their WonderPrint bubble jet printer have added extra colours, besides the CMYK set, they have added two extra colours ( orange and a blue ), together with two dilute inks. This trend to extra colours,in addition to the standard CMYK set, to satisfy the textile printer will see increasing developments over the next few years.machines are now available with both 6 and 8 colour systems The use of spot colours ( pre mixed colours ),using the ink jet printer to apply the design only is also an area of interesting debate. It is known that some projects have taken this approach. Also the combination of ink jet digital printing with conventional analogue printing to produce hybrid prints is also another concept under investigation. The development of new colorants with increased colour value and solubility will also be an increasing trend as the concentration of colour in an textile ink jet formulation is far higher than conventional paper ink jet. This requirement for extra dye in an ink formulation for textiles obviously can effect the life time of the print head which can be a significant extra cost. An obvious challenge would be to develop a radical new approach with a coloration system which gives 100 percent fixation with no wash off, giving the possibilities of taking digital printing further down stream to the retailer or even the consumer. The whole area of textile ink jet is under considerable research activity at the moment. Just taking patents related to dyes/applications (not machinery developments) in the textile ink jet area we have seen over 150 in the last 4 years alone ( 92 percent originating from Japan ) 10 10

11 Finally, the overall cost equation has to be taken into consideration ( including all stages i.e. cost of engraving, sampling, etc ).Currently the use of textile ink jet is only economic for sample prints or when the production is under 50 metres when detailed comparison are taken with the conventional methods ( including the cost of engraving ) With the increased research activity this figure will increase but it will be some years before actual production figures that some analysts predict will be realised in practise. Conclusions The availability of textile ink jet systems for the sample and proofing market is now established, which has led to significant benefits to the textile printer. In particular the reduction of lead times, reducing stock levels, responding to fashion changes quickly will make the European, American and Japanese printer more competitive. The next stage in the development will be the availability of short run ink jet machines capable of printing up to the 100 square metre production area. This will lead to the development of a new type of printer closer to the retailer ( the so called Agile Manufacturing model). Full production ink jet printing still has a number of major technical barriers to overcome, not least is the cost equation. However the race is on to develop production systems; currently there is no clear print head technology winner. There are a number of competing head technologies,each probably developing into their own market segments. The key parameter for a production textile ink jet printer is the cost and reliability of the ink head under production conditions and the availability of innovative chemical solutions to colour, ink formulations and pre treatment technologies. The success of any textile Ink jet project is the development of partnerships between machinery makers(print head manufacturers ), specialist chemical manufacturers to bring dye synthesis expertise and pre treatment chemistry,together with the forward looking textile printer. For those players, head manufacturers, systems integrators, chemical manufacturers and importantly the textile printer (end users), who get the equation right the potential rewards will be significant. References (1) J R Provost, 'Dynamic Response in Textile Printing', Textile Chemist & Colorist, June 1995, Vol 27, No. 6, p11. (2) T L Dawson, 'Jet Printing', Rev. Progress in Coloration, 22 (1992) 22. (3) K Dunkerley, 'Developments in Carpet Printing', Rev. Progress in Coloration, 11 (1981) 74. (4) T L Dawson, B Roberts, 'Dyeing and Printing Method for the Coloration of Carpet Yarn and Carpet Piece by Jet Impregnation', JSDC 93 (1977)

12 (5) S O Aston, J R Provost, H Masselink, 'Jet Printing with Reactive Dyes', JSDC 109 (1993) 147. (6) C H Hertz, 'Ink Jet Printing', Advances in Electronics and Electron Physics vol 65 (1985) 91 (Academic Press) (7) C H Hertz, B A Samuelson, 'Ink Jet Printing of High Quality Images', J Imaging Tech 15 (1989) 141. (8) Eureka Project, EU796. (9) Brite-Euram Project, BRE2-CT (10) Graham, L, 'Ink Jet Systems for Dyeing and Printing of Textiles, Textile Chemist & Colorist 21 (1989) No. 6, p27. (11) Anon., Kanebo and Canon Jointly Develop Bubble Jet Printing System, Japan Textile News, March 1993, p90. (12) Kanebo/Toshin, U.S. Patent, (17th September 1994). (13) A Johnson (Ed.), 'The Theory of Coloration of Textiles' (2nd Edition), Society of Dyers and Colourists 1989, p (14) J R Provost, 'Ink Jet Printing on Textiles', Surface Coating International (JOCCA) 77 (1994) 36. (15) Zeneca, European Patent Application 534,660 A1 (14th September 1992). (16) J.R.Provost, R.J.M.Kool, J.V. Lammeren, Integrated Digital Approach to Color Management In Textile Printing, Textile Chemist and Colorist, 28( 1996 ) No 8 p71-75 (17) A.J.Lavery,J.R.. Provost Color Media Interactions in Ink Jet Printing 13 th International Conference on Digital Printing Technologies, I. S. and T pages

13 COLOR-TEXTILE INTERACTIONS IN INK JET PRINTING TEXTILE/INK INTERACTION Drying time Spreading/wicking Water fastness Light fastness Colour value/yield Chroma (colour quality) Rub fastness TEXTILE PRINT HEAD TECHNOLOGIES COLOUR/INK FORMULATIONS PERFORMANCE: Drop performance Ink/Material compatibility Nozzle clogging Nozzle crusting Biological growth Contamination Long-term operability PROPERTY: Surface tension Viscosity Specific gravity ph Conductivity Dye purity Dye purity/solubility Toxicological properties Particle size Stability Accoustic properties Shelf life Figure 4 Ink/Print Head/Media Interaction in Ink Jet Printing 13 13

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