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Introduction to Ink Design

Introduction to Ink Design

• Critical aspects of Ink jet ink design• Ink properties• Ink types

– Aqueous– Oil-based– Solvent-based– Phase change– UV curable

Inkjet ink design

Complexity

Ingredients

High

Up to 10

High

Up to 15

High

Up to 10

Med

~ 6

Med

~ 4

ApplicationFunctionality Med High High Med Low

Purity

Filtered Inkper micron

High

<0.5

Med

<3.0

Med

<1.0

Med

<1.0

High

<0.2

Reliability

Ink dropsper nozzle

High

> 1010

High

> 1011

High

> 1010

High

> 109

High

> 109

CIJ OfficeTIJ

Officepiezo

CIJ Multi DODPiezo

Ink Property Binary deflection

Ink jet ink requirements

CIJ Valve jet

OfficeTIJ

Officepiezo

CIJ Multi DODPiezo

Ink Property Binary deflection

Viscosity/cP ~ 1.5 3 - 8 8 - 12 < 2 ~ 1.5 ~ 1.5

Surface Tension/ dynes/cm

> 35 25 - 40 > 32 > 24 > 35 > 35

Max. size

/ microns

1 3 1 5 1 0.2

Conductivitymicro siemens

Yes> 500

Yes> 1000

No No No No

Salt levelsChlorides/ppm

< 100 < 100 < 100 < 100 < 10 < 10

Ink jet ink requirements

• Viscosity and Surface Tension properties dominate droplet formation

– Dynamic properties are most important– Dynamic properties are very different in the nozzles

region• Laboratory measurements are not key for design

– These measurements characterise low shear properties of an ink

– During the nozzle region ink experience high shear conditions

Droplet formation and jet stability

Image quality & durability

Wetting of capillary channels

Flow through the nozzle

Understanding the inkjet process

High Speed IJ Technology

Printhead Development

App

aren

t Res

olut

ion

Low

High

Speed

Low High

Industrial Printheads

Desktop Printheads 600 - 1200 dpi180 m /min

Printhead Developments: Resolution - Drop Volume

• Ink droplet volume: limits definition of printed features (in absence of substrate modification)

• Most Industrial Printheads not achieved <6pl

2pl 20pl 80pl

16μ 34μ 53μ

Resolution: High Low

Printhead Developments: Speed

Variable Droplet Size

Higher frequency

Higher Nozzle Density

Page wide array

P (Image Quality)

Line

Spe

ed m

/min

Cactus SeedCactus Seed

200+

100

50

25

64800 180000 720000

9 734 72 456 34

Text and Barcode

CIJ DOD

P (Image Quality)

Line

Spe

ed m

/min

Cactus SeedCactus SeedCactus SeedCactus Seed

200+

100

50

25

64800 180000 720000

9 734 72 456 34

Text and Barcode

9 734 72 456 34

Text and Barcode

CIJ DOD

P = (resolution)2 * No. of greyscale levels

Printhead

Maintenance Station

Scanning

Page Wide Array

Scanning vs. Fixed Head IJ Printing

IJ Productivity: Full Colour Printing

Sca

nnin

g

Hea

dsFi

xed

Hea

d11 m2/hr of Printed output

120m2/hr

940m2/hr

Role Of Ink in High Speed PrintingInk Formulation challenges

1. Ink Jet Stage - Ultra high reliability

2. Ink behaviour on substrate 3. Performance Properties of image post ink

evaporation, absorption, reaction

•All aspects of the printing process need to be optimised to deliver a satisfactory process

For example, for a 30 min job @ 24m/min:• each nozzle must deliver reproducibly up to 10 million

ink droplets without interruption

What do we mean by Ultra High Reliability?

Extremely high jetting stability - “Turn it on & it works”

Delivering Ink Reliability:

Needs consider ink design, chemical and process technology to optimise performance in head of choice

•Basic ink operating window

•Component Design

•Operability testing and waveform matching

•Ink Path Issues

Component Design: Some key factors

Drop Regularity:

Ultra Stable Pigment dispersion with tight particle size control (<200nm) for drop regularity.

Also requires understanding of how to control dynamic surface tension, wetting and visco-elastic properties.

>10μm<200nm

IJ vs Typical Analogue Dispersion

20-30μm

Ink Component Design: Some key factors

Open time :

Ink components must be designed not to clog nozzles

0 500 1000 1500

Minutes

Aqueous Desktop

Solvent

Aqueous Industrial

Oil

UVIn

k C

lass

Ink Jet Open Time

Typical Open Time

Acceptable Open Time for Single Pass Printing

Important aspects of ink design- ink flow through the print head

• Ink flow through the print head– Wetting of different materials throughout the

head– Wetting capillary channels effectively

• Minimise sensitivities of air– Entrapped air– Pressure differences

Ink ReservoirInk Manifold Multiple printheads

Important aspects of ink design- ink flow through the print head

• Creating a stable meniscus

– Wetting / non-wetting faceplates• Aid to maintenance systems

– Balance surface tension forces of the meniscus and gravity feed from ink supply

Range of ink jet ink types

• Common characterisation of ink type is by carrier base

• Commercial Inks:– Water based inks – Solvent based inks – “Oil” based inks – Phase change inks – UV curable based inks

Printhead Technologies and Ink Types

Aqueous

Solvents

Hot Melt

UVCurables

CIJ OfficeTIJ

Officepiezo

CIJ Multi DODPiezo

DODShared

wall

Ink TypeBinary deflection

Inkjet Ink Formulations

Ingredients• Liquid carriers

– water, solvents, oils• Binders

– polymers• Colorants

– dyes & pigments• Additives

– surfactants– conductivity salts

Critical Materials• Colorants• Binders

Influence– jet performance– reliability– stability– application

performance