By: Aravin Prince. P
Department Of Textile Technology,
Rvs College of Engg & Tech,
Digital printing, the most advanced technology in textile printing is an emerging new technique. This paper deals with various types of ink jet printing and usage of inks for the latest developments in inkjet printing. It also deals about the fabric pretreatment and after treatment for digital printing. The future of the digital printing is very bright due to its special nature like sample production competitive nature to normal print etc. The one and only demerits of this printing is costlier to apply. This paper will review digital ink-jet printing on textiles and their developments it offers to textile industry and consumers in comparison with conventional printing.
KEY WORDS: Digital Printing, Ink-jet Printer, Textiles
� INK JET PRINTING
� FABRIC PRE -TREATMENT
� INKS CONSUMPTION
� DEVELOPMENTS AND FIXATION
� AFTER TREATMENTS
� DEVELOPMENTS IN DIGITAL PRINTING
� DEVELOPMENTS IN DESIGN MAKING PROCESS
� DEVELOPMENTS IN INKS
The first pigment ink to produce wash-resistant and rub-fast textiles.
Helizarin� EVO P 100 does away with the time-consuming and cost-intensive intermediate drying stage and the application of binder
The new solution for pigmented ink-jet printing-
� For virtually any fabric
� Rich colors
� Greater brilliance
� Sharp outlines
� Wash-resistant colors
The rapidly evolving world of digitalized textiles is a reflection of several unique and contrasting business models that create challenges, treats and opportunities to the future of the textile printing market. One of the important issues associated with digital printing on textiles is speed & reliability as this has commercial implication for the industry, so time saving and energy saving. Ink jet printing has demerits such as high cost, lower production speed, limited color space and etc.So, now these techniques are more essential and have to be improved with more research & developments.
1. Digital Printing � Trends and techniques by Arun k. patra / Colorage Annual 2005.
2. Digital inkjet printing � I Holme / Colorage April 2006.
3. Digital Creativity � Journal of textile & Apparel Technology & Management / Volume 4 / Issue 1 / summer 2004.
4. Advantage of Digital printing- Journal of textile & apparel, Technology & Management / Volume4, Issue 3 / Spring 2005.
5. Digital printing / B Chavan / Asian Dyer, Nov-Dec 2005
6. The future of digital textile printing / International Textile Bulletin 1/2001
7. Printing of textiles- Future prospects / colourage Dec 1995
Aravin Prince.P is final year student of B. Tech, Textile Technology, Department of Textile Technology, RVS College of Engg & Tech, Dindigul, Tamilnadu. He can be contacted at email@example.com
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The digital printing is introduced in 1950 for paper printing. But this printing technique used to textiles at 1970 onwards only.
Digital printing in simple terms is the process of creating prints generated and designed from a computer, as opposed to analog printing, which requires printing screens. Among the various approaches for digital printing including electro photography, ink jet has gained a very significant place in the field of innovative printing techniques.
This technique is more related to those used in reprographics industry than textile printing. For eg reference is made to toners and inks rather than dyes, pigments and printing pastes.
Similarly, print resolution and speed are defined in �drops per inch� (DPI) and �Characters per second� (CPS), rather than in mesh/raster and yards/meter per minute.
From the roller printing technology of the fifties through screen-printing to today�s state �of- the art inkjet printing technology by using digital CAD system have evolved in stages of developments.
In digital inkjet printing, print heads, containing banks of fine nozzles, fire fine droplets of individual colored inks on to a pre treated fabrics. The print design is created digitally and the ink droplets are mixed together on the fabric surface to create final color, so called spot color.
The print design concept is manipulated digitally the set-up time to produce short runs, sampling, or proofing is dramatically decreased. All the costs that are generated due to screen engraving, past making, strike offs, down time and wastage are also completely eliminated.
The dyes are supplied in color cartridges by the dye maker and, ones connected in the printer, are ready for instant use. Ink jet printing is a low water consumption and low energy consumption process compared with conventional printing process.
PRINCIPLE OF INK JET PRINTING:
Directing minute droplet of ink, from a nozzle, onto the printing substrate. A common feature of droplet formation is computer control of droplet position on the substrate by their response to high frequency digital electronic signals. The droplet formation involves the application of controlled pressure on the liquid ink in its reservoir; as it streams into the printing nozzles, the ink stream is broken into droplets.
CLASSIFICATION OF INKJET PRINTERS:
Initially, Inkjet Technology can be classified into
� Coarse resolution type
� Fine resolution type
I. COARSE RESOLUTION TYPE:
It is based on valve control technology. It has maximum resolution of 40Dpi.It is used in carpet industry.
II. FINER RESOLUTION TYPE:
It has the fine resolution up to 300Dpi. The most important features of this inkjet printer are the printing head & nozzles. Numerous nozzles are used to each color. These nozzles are 10 to 1000� in diameter. It can be subdivided into
1. Continuous stream printing
2. Drop-on demand
CONTINUOUS STEAM PRINTING:
In this system, ink is forced at a high pressure & high frequency through a nozzle. The emerging stream of ink is broken into small droplets. These droplets can be selectively charged and deflected by pasting through high voltage plates. Drop selection is achieved by deflecting the desired drops for the image to the substrate and collecting the unwanted for recycling. In this system, ink is electrically conductive & as the ink passes through the charged plates, current flows in the column.
Two possible method of obtaining a design by this process, they are
� Raster scan method
� Binary continuous inkjet system
RASTER SCAN METHOD:
In this method charged droplets are deflected onto the substrate in a predetermined manner & the uncharged droplets are collected in a feedback and then it is recycled.
BINARY CONTINUOUS INK JET SYSTEM:
In this method the uncharged droplets will be unaffected by the deflection plates which carry a charge opposite that of the charging plates. The undeflected drops then strike the substrate to form the image. Drops carrying a charge are deflected to a gutter by the deflection plates for recycle.
Besides these the multi-deflection continuous inkjet has also been used for textile printing. This differs from the binary system in that the dye drops are given a variable charge that gives different deflections as the drops pass through the deflection plates. This allows multiple positions on the substrate (up to 30) to be printed from a single jet. This technology found application in printers for industrial marketing and served as the basis for t-shirt printers.
DROP ON DEMAND:
The impulse or drop on demand inkjet is a system of fundamental simplicity. This technology, as the name suggests produces an ink droplet when required and fires this on to the substrate. It differs from continuous inkjet systems in two aspects
I. The image forming ink droplets are not charged, so no deflection device is involved
II. Electrical signals are normally used to control the moment when an individual droplet is needed.
The DOD printers are of the following types:
� Bubble jet/ thermal jet
� Electrostatic ink jet
Majority of the DOD printers currently in use, are of this type. In this technology, the printer depends on a thermal pulse to generate the ink drop. In fact, computer signal heats a resister to a high temperature, which creates a vapour bubble in a volatile component in the printing ink and this vapour bubble causes a drop of ink to be ejected from the nozzle. The vapour bubble must then cool and collapse allowing the ink chamber to refill from a reservoir. Cycle time is limited about 10,000 drops per second and volume per drop of ink is in the range of 150-200 Picoliters (1�10-12 ). Thus, single thermal inkjet can deliver about 0.1ml of ink per minute.
The biggest problem with the thermal inkjet is the high rate of nozzle failure. High temperature (>3500C) required for rapid drop ejection, cause decomposition of ink components on the resister, leading to poor heat transfer and / or nozzle clogging. Resister failure resulting from rapid thermal cycling is also a major problem. But, the main advantage of thermal inkjet/ bubble jet technology is the low cost of nozzle fabrication. Thus, thermal inkjets offer low cost print heads but suffer from reliability and speed.
The piezo inkjet uses a piezoelectric transducer for ejecting ink droplets. These transducers may be of different forms but all work on the principle that when a varying voltage is applied across them, they expand and contract proportionally to the applied voltage. In a typical piezoelectric printer, the computer imposes an electrical potential across a piezoelectric material, which causes a contraction in the direction of a electric field and an expansion in the perpendicular direction. On removal of the potential, the piezoelectric returns to its normal dimensions and the ink chamber is filled from an ink reservoir by capillary action. The cycle time of the piezo based printers is limited by the ink replenishment rate and can be somewhat higher (14,000 cycles per second) than the thermal inkjet, but drop volumes are relatively smaller (as low as a few picolitres). The small drop size allows the piezo based printers to produce very high resolution prints (2880 Dpi is commercially available). These printers also have the advantage of much greater print head life than the thermal based system.
The micro jet technology is a further development of the piezoelectric inkjet in which piezo ceramic walls of the inkjet channels vibrate to eject ink droplets. The advantages with this are high resolution and potential to economically produce wide nozzle arrays. Also, piezotype systems are suited for both aqueous and solvent based inks, as well as for hot melt or phase change inks in many non-textile applications
As the name suggests, this involves the use of valves. Solenoid valves are used in it, to control the flow of ink in an air stream that carries the drops to the substrate. Resolution is limited to 25Psi and thus not quite suitable for apparels. However, these machines have been used.
FABRIC PRE-TREATMENT FOR INK JET PRINTING:
In the case of inkjet printing, a highly effective pre-treatment is necessary. Fabric must be singed to remove surface hairs that could lower the fabric printing quality and also prevent the risk of flaws being generated by surface fibers touching the print head and blocking the nozzles. Desizing, Scouring and Bleaching to remove impurities and to provide a fabric of uniform absorbency and whiteness are essential. In inkjet printing the colors depth obtainable is an important limiting factor, and fabric mercerization can be used to increase the apparent color depth of the print.
The type of fabric pre-treatment will vary with the dyes used in the inks. For inkjet printing of reactive dyes on to cellulosic fabrics the pad liquor applied the fabric may contain alginates for penetration control, urea to increase color depth and alkali which is essential for the formation of a covalent bond between the dye and the fiber.
Digital printing techniques make new demands on the colorants and formulations used. While in screen printing colors are applied in the form of high viscosity pastes. In inkjet printing the requirement is for very thin ink formulations, moreover the colors or dyes to be used for inkjet printing should have small particle size and over sized particles block the jets. The average particle size of the inks must therefore be negligible compared to the nozzle orifices and then only smooth ink flow can be guaranteed. Besides these the choice of auxiliary system is crucial for the stability of ink formulations.
Basically inkjet printing ink is classified into two types, they are
� Water based inks
� Solvent based inks
FIXATION & DEVELOPMENTS OF PRINTS:
Fixation/ Development of the digitally printed fabric is of paramount importance. Unless the prints are properly fixed, the demands of the roller retailers and consumers print of view of wash fastness, rubbing fastness, light fastness cannot be fulfilled.
Logically based on the type of dyes used in ink formulations, the same fixation method that level been successfully practiced in normal printing methods such as Curing, Chemical padding can be used.
In the inks based can reactive dyes the following formulations is suggested.
Cotton: Steam 102c for 8min, or thermo fixation at 140-150c for 5min, or high temp steaming at 120c for 1-4min.
Viscose: Steam at 102c for 8min
RECENT DEVELOPMENTS IN INK JET PRINTING:
One of the most innovative digital inkjet printers is the �Reggiani DReAM� machine which uses scitex Aprion print heads and Ciba speciality chemical inks. Pretreated cotton fabric 160cm wide was printed at 150m2 /h with six colors, the spot mixing giving a very high definition print design containing eighteen final colors at 600Dpi. The Cibacron RAC reactive dye inks used were printed and can be fixed in steam, washed off and dried as normal. The DReAM ink jet printing machine incorporates a continuous-blanket washing system and an online drying unit. This high speed inkjet printer is designed for printing short to medium print runs, and opens up many opportunities in the latter field.
The Monna Lisa ink jet printer on the Robustelli stand has been designed for printing high quality print designs, as well as sampling printing, and has generated interest among Italian printers. The printing speed is claimed to be about 28m2/h at 720Dpi and 78m2/h at 360Dpi. The Monna Lisa uses Epson print heads and reactive and acid dye inks developed by Epson.
The Dupont Artistri 2020 digital inkjet printer incorporates Dupont Artistri software and ink and is based on a piezo print head system. Sixteen print heads are incorporated on two carriage rolls and four types of Artistri inks in the 700 series are used, namely acid, disperse, reactive, and pigment inks. The Dupont Artistri 2020 is capable of printing at 30-50m2/h.
Dupont announced at ITMA 2003 that the Rimslow Pvt Ltd�s Steam-X steamer was a marketing partner for this printer. The Rimslow Steam-X steamer is a compact steaming unit for print fixation and is fitted in line after inkjet printing. The unit has a fabric path length of six maters on the steamer, which is sufficient at normal ink jet printing speeds to fix acid, reactive, and disperse dyes.
The Colorwings Texjet 254 in-line digital inkjet printer operates with eight print heads at production rates of up to 50m2/h. The eight color disperse print system is heat-fixed by sublimation and a vacuum system is used to ensure that double-sided prints can be obtained that are suitable for flags. Pigment, reactive and acid inks can also be printed, and a number of the Colorwing Texjet 254 printers can be networked to provide a flexible manufacturing process.
Mimaki showed their TX3-1600 piezo DOD printer with eight print heads capable of printing at 360-720Dpi and suitable for short run production and sampling. A novel printer was the Mimaki GP0604 printer for printing cotton T-shirts and other garments using Mimaki pigment inks.
Leggett and Platt Digital Technologies Inc. of the USA exhibited their virtu RS printer on the Spuhl stand. This uses Virtue-Hue V pigment inks which can be applied to polyester and polyester-rich fabrics. The print image is cold-cured using ultraviolet radiation and then the print image is passed in to a thermal fixation zone in which the disperse dyes sublime and are absorbed by the polyester. The Virtue RS printer has UV-protective shielding and is manufactured 2.5 or 3.5ٰ meters wide. The printing speed is claimed to be up to 125m2/h or about 35m2/h on a six-color print.
DEVELOPMENT PROCESS IN DESIGN MAKING:
Thus the process illustrated by Fig. 1, the role of inkjet printing is limited to
Creating a sample of the design.
CAD, and while the role of CAD finishes here, in the process shown in Fig. 2, the CAD data itself can be used in the small-lot production of diverse design
The price of a single high-quality inkjet-printing machine for use with textiles is very high, and so to make them economical, individual machines must have a high print speed. Groups taking up this challenge include those of Kyoto Municipal Textile Research Institute et al, of Toshin Kogyo and Dupont, and of Ciba Specialty Chemicals, Reggiani and Aprion, and with this, the application of inkjet printing will become like that shown in Fig. 2. An important feature of the process as shown in Fig. 2 is that the following sequence of operations has become a direct line.
Image design →CAD→inkjet printing operations and production
Textile printing in three days with roller, rotary or flat-screen printing is inconceivable; it is simply not humanly possible. There is no way to work this miracle other than through the use of high-speed inkjet printing (according to an industry source). In meeting these expectations, the introduction of 2nd generation inkjet machinery cannot be overemphasized.
DEVELOPMENTS IN INKS
To meet increasing demand, new ink jet inks are being developed for the textile market. BASF has introduced Bafixan disperse dye inks and Helizarin pigment inks and has introduced a new pretreatment system, Luprejet HD. Ciba Specialty Chemicals has designed a range of reactive inks, Cibacron RAC, for cellulose fabrics, chemical reaction with the fibers ensuring high application performance and bright shades. Further ink ranges for other fibers are being developed, including acid inks for high fashion and sports wear fabrics of silk and polyamide/Lycra blends, pigmented inks especially designed for home furnishing of all fibers and disperse inks for polyester. These high-tech inks must be of the right consistency to pass through the heads at very high speed and dry immediately on the fabric.
In addition, Ciba Specialty Chemicals has designed a special chemical recipe for fabric preparation suitable for Cibacron RAC inks. The system, which comprises the inks, the preparation recipe and the printer with its special printing heads, provides customers with a complete integrated ink jet textile printing solution.
MULTI FUNCTIONAL AGENT:
Use Helizarin� EVO P 100 in the digital ink-jet process to achieve printing results which you have experienced up to now only with traditional pigment printing. The properties of the low-viscosity ink eliminate the need for subsequent application of binder.
The ink formulation involving the newly developed Multi Functional Agent consigns the typical problems of ink-jet pigment printing to history. The textiles retain their pleasant handle.