Inkjet printing

Painettavan elektroniikan jatkokurssi – 15.11.2011Dr. Jukka HastPrincipal Scientist, Team leader, Adjunct ProfessorVTT Technical Research Centre of Finland

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Digital printing

Digital printing

Electrophotography Inkjet

Drop-on-demand Continuous

Thermal

Piezoelectric

Acoustic

Electrostatic

Binary

Greyscale

Binary deflection

Multiple deflection

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Benefits of inkjet printing

Digital printing variable information, customization, personalization

Non-contact printing substrate independent rigid and flexible, smooth and rough, 3D

surfaces

Additive layering of materials

Precise, high resolution and speed

Low material consumption

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Factors affecting inkjet print quality

SUBSTRATE PRINTHEAD

ENVIRONMENT

INK

-INK COMPOSITION:Colorants, solvents, additives

-INK PROPERTIES:Surface tension, viscosity, pH,

particle size

-PAPER vs. OTHER MATERIALS-COATING COMPOSITION:

coated vs. uncoated-HYDROPHOBIC vs. HYDROPHILIC

-SURFACE CHARGE

-DROP-ON-DEMAND vs. CONTINUOUS:Thermal DOD vs. piezoelectric DOD-NOZZLE DIAMETER

-Heating-Clogging tendency

-Impact-Spreading

-Wetting-Penetration

-Evaporation-Chemical bonding

-Distance

-MOISTURE-TEMPERATURE-ILLUMINATION

Dynamic paper-ink interactions

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Continuous inkjet (CIJ)

Drop generator Chargeelectrode

High-voltagedeflection plate Gutter

Substrate

Continuous ink-jet

Binary deflection Multi deflection

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Drop-on-demand inkjet (DOD)

Orifice

Pressurechamber

Heater

Ink

Drop-on-demand ink-jet

Piezo-electric Thermal (TIJ)

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Inkjet technologies for printed electronics

Continuous Inkjet Thermal Inkjet Piezoelectric Inkjet

Principle Continuous drop formation. Electrodes guide image forming drops to substrate and other drops for re-circulation.

Drop-on-demand: drops generated only when needed. Heater generates a bubble that forces an ink drop out of the nozzle orifice.

Drop-on-demand. Piezoelectric crystal generates a pressure pulse that forces an ink drop out of the nozzle orifice.

Benefits High speed. Only acoustic pressure affecting ink during drop formation choice of ink chemistries. Durable printheads.

Drawbacks Ink re-circulation not preferred with often sensitive and expensive inks ink waste. Large drops low resolution.

Ink sedimentation. Low speed. Short printhead lifetime. Ink exposed to high temperature (even 300oC) during drop formation.

Nozzle drying.

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Printhead technologies versus ink types

Printhead technology Water-based inks

Solvent-based inks Hot Melt inks UV-curable

inks

CIJ Binary X X

CIJ Multi deflection X X X

DOD Piezo X X X X

Office piezo X X X

Office TIJ X X

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Inkjet ink requirements depending on the printhead technology

Ink property CIJ BinaryCIJ Multi-

deflection

DOD Piezo

Office piezo Office TIJ

Viscosity (cP) ~1,5 3-8 8-12 ~1,5 ~1,5

Surface tension (mN/m) >35 25-40 >32 >35 >35

Particle size max. (mm) 1 3 1 1 0,2

Conductivity (mSiemens) >500 >1000 No No No

Salt levels Chlorides (ppm) <100 <100 <100 <10 <10

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Typical inkjet ink

Component Purpose (%)

Main solvent Carrier 60 – 90

Co-solvent Controls viscosity 5 – 30

Colorant / functional ingredient Functionality / colour 1 – 10

Surfactant Wetting, penetration 0.1 – 10

Bioside Prevents biological growth 0.05 – 1

Buffer pH control 0.1 – 0.5

Other additives Anti-foaming, chelating agent etc. > 1

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Dynamic interactions

Impact Spreading Wetting, penetration Dry

Evaporation

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Application areas for inkjet

GRAPHIC ARTSCoding, markingDocument printingPhotograph printingWide-format printingTextile printingPublication printingDecoration of 2D and 3D surfacesPackage printing

MANUFACTURINGElectronicsMEMSDisplaysRFIDSolar cellsOpticsDiagnosticsMedical scienceCTP plate makingSmell generation

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