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
Printing chemicals/auxiliaries can not in incorporated in printing ink.
They are incorporated in fabric in the form of 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
Milled to very fine particle size and particle size distribution
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 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. 100 5-30 Piezo 200 1-3 Thermal 400 1-10 Continuous Drop volume Pico litre pl Viscosity cps Print Head
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 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.
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.
Digital printing inks for different substrates No Polymerization Thermal, UV curing Pigment All fibres Yes HT steam Disperse Polyester Yes Steam Reactive/ Acid Silk, wool, Polyamide Yes Steam Reactive Cotton, Viscose After wash Aftertreatment (Fixation) Colorant Fibre
Ink formulation *Avoids drying out of the nozzles 10 Upto 10 Additives (Wetting and Antifoaming agents Dye 30 Max Solvent (Ethylene Glycol* < 80 Water Content % Component
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.
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.
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.
inability of any given set of CMYK process colours to generate a full colour gamut suitable for textile industry.
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 inks outside: Hexachrome gamut Inside: 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.
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.
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)
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.
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.