ESSENTIAL ELEMENTS FOR INKJET PRINTING

R.B.CHAVANDept. of Textile Technology

Indian Institute of TechnologyHauz-Khas, New Delhi 110016

COMPUTER

• Computer system essential for data processing

• CPU Pentium IV 600Hz x2 or above • OS Windows NT4SP4 • Memory 256 MB or above • Hard disk 9.1 GB or above • CD-ROM 40 x or above  • Color display (Monitor) 17 inch 

SOFTWARE

• Raster Image Processing (RIP)

• Colour Management System

• Convert scanned design into electronic signals.

• Allows editing of design

• Give command to the inkjet printer for faithful printing of scanned/edited design.

DIGITAL PRINTER

• Mainly DOD printers used for textile printing• Choice• Thermal or bubble jet printer• Piezo printer• Piezo preferred • wide choice inks• Reliability• Durable print heads

TEXTILE SUBSTRATE

• In digital world known as “ media “• Fabric to be printed

FABRIC PRE-TREATMENT

• Conventional printing• Bleached fabric without any pre-treatment is used

for conventional printing• Chemicals and auxiliaries necessary for print

fixation like thickener, urea, alkali, acid, defoaming agents etc. are incorporated in the print paste

• Viscous print paste. No danger of print spreading • Digital printing• Printing chemicals/auxiliaries can not in

incorporated in printing ink.• They are incorporated in fabric in the form of fabric

pre-treatment.

FABRIC PRE-TREATMENT

• Such pre-treatments help to maximize the absorbency and reactivity of the textile substrate towards the inks.

• Minimize ink spreading to prevent loss of definition and colour intensity.

• Many patented and proprietary formulations exist,• ranging from simple formulations of soda ash,

alginate and urea • to more sophisticated combinations of cationic

agents, softeners, polymers and inorganic particulates such as fumed silica.

• Many of these have been aimed at fashion fabrics such as cotton, silk, nylon and wool.

• 3P InkJet Textiles (Germany) is marketing pretreated fabrics ready for inkjet printing.

Fabric pre-coat machine

Fabric Feeding System

Fabric feeding

Fabric Exit

ensures perfect registration and alignment throughout, even for delicate and unstable fabrics such as knits or fine silks. If required, this machine may also pre-heat, dry or set the printed fabric, before finally rolling-up the output smoothly and with even tension.

Ichinose-unit: conveyor belt and dryer

Ichinose uses a conveyor belt to transport and align the textile substrate.

The conveyor belt carrying the fabric gently moves ahead for inkjet printing operation. The print head nozzles are set up right above the carrier belt, and the cloth printed with the inks sprayed from the head nozzles. This can prevent the inks from bleeding onto the cloth. After printing operation the cloth at the exit end is released from the conveyor belt. The conveyor belt can be cleaned whenever necessary

Requirement of ink for paper printing

• All papers are cellulose in nature• Ink held on paper mainly by adhesive

forces• Most suitable inks are pigments or any

water soluble dye • Adhesion of ink to paper is through simple

adhesives like PVA or poly vinyl acetate.• paper is not subjected to washing, rubbing

and various other agencies to which fabric is subjected.

• Only requirement is good light fastness

Ink requirement for textiles

• Fibres of different nature are available correspondingly different classes of suitable dyes for each fibre

• During use textile material is subjected to various agencies like washing, rubbing, chlorine water (Swimming), light, perspiration etc

• Fastness requirement in case of textiles is more stringent compared to paper

• Adhesive forces are not adequate to give the desired fastness properties to printed textiles

• ink (dye, Pigment) must be held by means of interactive forces between dye and fibre.

Ink requirement for textiles

• The interactive forces will vary depending on the nature of fibre and dye class e.g.

• Reactive dye:Cellulose Covalent bond• Acid dye:Silk Electrostatic force • Disperse dye :Polyester H bonding, entrapment

in compact fibre structure• Textiles are stretchable, flexible, often have

highly porous and textured surface• Textiles, being porous, and absorbent, require

greater volume of ink to produce same shade compared to paper.

• Fabrics with neps and pile leave lint on print head causing nozzle clogging

INKJET INKS

• High purity• Dyes• Pigments• Milled to very fine particle size and particle size

distribution• Ink formulation• Precise viscosity and surface tension• Good shelf life, no settling• High colour strength• Good colour build up on fabric.• Good fastness properties

Typical operating parameters for ink-jet engines

Print Head Viscosity cps Drop volume Pico litre pl

Continuous 1-10 400

Thermal 1-3 200

Piezo 5-30 100

The average particle size of disperse ink must be approx. 0,5 micro meter or lower in order to avoid clogging of the nozzles. Electrostatic deflection systems also require that the ink is electrically conducting which is difficult to achieve in organic solvent based systems.

REACTIVE AND ACID DYES

• Reactive dyes are suited to cotton, viscose and other cellulosic materials

• acid dyes are used for wool, silk and nylon. • Both are fully water soluble and relatively easy to

formulate for a wide range of inkjet heads.• especially the widely installed thermal drop on

demand jet types.

PIGMENT COLOURS AND DISPERSE DYES

• Both exist in water as dispersion of small particles. • These inks must be prepared with high degree of

expertise so that the particles will not settle or agglomerate (flocculate).

• The particle size must have an average of 0.5 micrometer and the particle size distribution must be very narrow with more than 99% of the particles smaller than 1 micrometer in order to avoid clogging of the nozzles.

PIGMENT COLOURS

• pigment printing accounts for over 50% of all conventional textile printing.

• they offer excellent wash and light fastness and have the great advantage of universal application to almost all fibres.

• after treatments are limited to a dry fixation process.

• Research is going on to develop UV-curable pigment inks in- stead of thermal curable inks.

BINDER APPLICATION

• major problem with use of pigments in inkjet system is how best to formulate and apply the resins binder which is required to bond the pigment particles to the fabric surface.

• Several different approaches, from spraying binder through a separate jet head to screen printing binder over an inkjet printed colour have been suggested.

• In the long run, improved binder technology seems likely to prevail, allowing trouble- free formulation and printing from a single inkjet head for each colour.

Supplier Trade name Type

Dyestar HelizarineBafixanReactive

Pigment Disperse (Transfer)Reactive (MCT)

Ciba Terasil (D)Terasil (T)Irgaphor TBICibacronLanaset

DisperseDisperse 9Transfer)HC Pigment + binderReactive MCTAcid

Dohmenn Dorasyn Acid

Dupont Artistry 1000Artistry 500

Pigment (CMYK)Pigment + Binder

Colorspan Colorspan Reactive

Commercial water-based inks

Fibre Colorant Aftertreatment (Fixation)

After wash

Cotton, Viscose

Reactive Steam Yes

Silk, wool, Polyamide

Reactive/Acid

Steam Yes

Polyester Disperse HT steam Yes

All fibres Pigment PolymerizationThermal, UV curing

No

Digital printing inks for different substrates

Component Content %

Water < 80

Solvent (EthyleneGlycol*

30 Max

Additives (Wetting and Antifoaming agents Dye

10

Upto 10

Ink formulation

*Avoids drying out of the nozzles

SPOT COLOURS

• Inks used in conventional (Analog) printing are known as spot colours.

• required shade is prepared by mixing appropriate colours before printing.

• It is a skilled job, • It allows matching the desired shade as

closely as possible.

• This gives an extremely large colour gamut, less variation in colour in solid areas, and a cleaner brighter shades.

Process Colours

• The inks used in inkjet printing are known as process colours.

• The desired shade is produced on fabric itself during printing operation by blending the primaries -cyan, magenta, yellow and black (CMYK) drop by drop sequentially over a small area rather than being premixed in an ink kitchen prior to printing

• Each primary must be transparent to produce compound shades using CMYK.

Process Colours

• With screen-printing the inks may be dried between colours,

• with ink-jet all colours are printed simultaneously, wet on wet.

• The colour gamut obtainable with spot colours is larger than with process colours.

• limitations

• inability of any given set of CMYK process colours to generate a full colour gamut suitable for textile industry.

Process Colours

• Theoretically one may be able to produce 16.7 million colours;

• however, only 1.5 million might be useful for most textile printing

• out of this 1 million colours may be outside the colour space possible from this system.

• In order to improve the colour gamut and to obtain extremely fine images special colour systems are developed. Hexachrome® (Pantone Inc.) is a 6-color process consisting of the four basic colours plus orange and green inks. This approach results in more brilliant continuous-tone images and in almost twice the number of colours that can be obtained using CMYK

Extended Process colours

• In order to improve the colour gamut special colour systems are developed.

• Hexachrome® (Pantone Inc.) is a 6 Process colour system consisting of the four basic colours (CMYK) plus orange and green inks.

• This approach results in more brilliant continuous-tone images

• Almost twice the number of colours that can be obtained using CMYK

Colour gamut with 4 and 6 inksoutside: Hexachrome gamutInside: CMYK gamut

CMYK

Extended Process colours

• Introduction of 6, 7, 8, and even 12-color digital printers into the market,

• these systems come closer to achieving the results obtained using analog printing. .

• However, this increasing number of colours in the design of systems for ink-jet printing of textiles is problematical.

• Each additional colour head increases the problems of data handling rate and nozzle failure.

• It also significantly reduces the fraction of the printer that is not actively printing at any given moment,

• thus significantly reducing machine efficiency.

Fabric post Treatments

• Post treatments similar to analog printing

• Steaming, curing for dye/pigment fixation

• Washing to remove unfixed colour and chemicals, thickener.

• Finishing: Water repellant, fire retardant, soil release etc.

Slow adoption of inkjet printing

• The existing speeds adequate for sample printing but not for bulk production

• Availability of printing inks at reasonable cost• Colour matching problems in flat colours• Reproducibility of results from one printer to

another printer.• Migration of manufacturing capacity to Asia where

labour intensive processes prevail.• Main stream textile printers are geared to low cost

mass production business model and long response time

• Niche market has to be build up from scratch• Educating the consumers about the potentialities of

digital printing.

Future Vision• Sampling: This is the traditional application area and

this may be expected to continue with modest growth.

• Bulk production for batches less than 1000 metres. • This is the vision of many • Mass-customization: The creation of new niche

markets for small-medium batches of printed textiles for specific customers.

• It may be possible that garment makers decide to buy a digital printer and attach it to a laser cutting table.

• After printing, the fabric could be cut single ply using a computerized system and then converted to made-ups.

Future Vision

• Major inkjet manufacturers are working to resolve the issue of production speed and it is hoped that inkjet printers will be available with a speed to compete with rotary screen printing.

• The ITMA 2003 exhibition in Birmingham, UK, was a significant milestone for digital printing,

• 27 companies offering textile digital printing equipment.

• Many of the machines shown were said to print at over 50 m2 per hour,

• Reggiani printer was said to print at 150m2/hour.

• However this far less than rotary screen printing (3600 meters/hour)

Future Vision

• The other possibility is that inkjet printing technology may be used as weaving technology

• where printers may have large number of inkjet printers like looms to carry out the printing production.

• In Bangkok a printing unit has 25 Stork Sapphire machines run much like a traditional weaving department.

Conclusion

• Digital printing provides an opportunity to meet the present day market trends of mass customization.

• It has established as an acceptable technology for sample production.

• Among other technology problems speed of printing is the main hurdle in commercialization of technology.

• Attempts are being made to achieve commercially acceptable printing speeds.

• Till then the practice of combination of digital printing for sampling and rotary screen printing for production will continue.

• What now seems certain is that there is sufficient industrial investment and commitment by manufacturers to ensure that commercial ink jet textile printing will become a reality.