ESSENTIAL ELEMENTS FOR INKJET PRINTING

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ESSENTIAL ELEMENTS FOR INKJET PRINTING

• R.B.CHAVAN
• Dept. of Textile Technology
• Indian Institute of Technology
• Hauz-Khas, New Delhi 110016

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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 

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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.

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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

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TEXTILE SUBSTRATE

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

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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.

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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.

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Fabric pre-coat machine
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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.
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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
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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

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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.

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Ink requirement for textiles

• The interactive forces will vary depending on the
  nature of fibre and dye class e.g.
• Reactive dyeCellulose Covalent bond
• Acid dyeSilk 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

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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

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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.
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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.

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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.

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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.

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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.

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Commercial water-based inks
Supplier Trade name Type
Dyestar Helizarine Bafixan Reactive Pigment Disperse (Transfer) Reactive (MCT)
Ciba Terasil (D) Terasil (T) Irgaphor TBI Cibacron Lanaset Disperse Disperse 9Transfer) HC Pigment binder Reactive MCT Acid
Dohmenn Dorasyn Acid
Dupont Artistry 1000 Artistry 500 Pigment (CMYK) Pigment Binder
Colorspan Colorspan Reactive
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Digital printing inks for different substrates
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 Polymerization Thermal, UV curing No
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Ink formulation
Component Content
Water lt 80
Solvent (Ethylene Glycol 30 Max
Additives (Wetting and Antifoaming agents Dye 10 Upto 10
Avoids drying out of the nozzles
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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.

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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.

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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.

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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

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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

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CMYK
Colour gamut with 4 and 6 inks outside
Hexachrome gamut Inside CMYK gamut
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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.

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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.

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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.

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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.

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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)

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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.

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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.