Development of Conductive Inks for Flexography.

Gwent Electronic Materials Company History

• Formed in 1988• Formed in 1988• Manufacture of passive electronic

materialsmaterials• Contract Research• Toll Manufacture• Biosensor materials developed 1994• AET acquired in 2001q• Development of handheld water

quality testing system 2004

Products and Services

• Supply of custom inks for electronics• Supply of custom inks for electronics• Supply of custom inks for electro

ceramicsceramics• Supply of custom inks for biosensors• Supply of custom inks for sensors• Supply of custom inks for sensors• Contract research on ink formulations

Supply electrochemical base electrodes• Supply electrochemical base electrodes• Supply biosensors for environmental and

agri food market sectorsagri-food market sectors

An Approach to Developing C d i I kConductive Inks

• Selection of Raw Material based onSelection of Raw Material based on printing requirements.

• Manufacture of intermediates and final• Manufacture of intermediates and final inks.Di i f P d• Dispersion of Powders

• Rheological Measurement• Electrical Conductivity Measurement

Selection of Raw Materials

Solvents and the roles they play in the formulation.

Polymer types and considerations.

Functional Phases Conductive powdersFunctional Phases, Conductive powders.

Function of Solvents/DiluentsFunction of Solvents/Diluents

• Dissolve the selected resin systemDissolve the selected resin system.• Maintain printability.

C t l d i t• Control drying rate.

Formulation Considerations for S l tSolvents.

• Resin must remain fully dissolvedResin must remain fully dissolved during printing and drying process.

• Generally several solvents are used• Generally several solvents are used with different boiling points and evaporation ratesevaporation rates.

• Direct effect on the drying of the i t d filprinted films.

Solvent Properties to C idConsider

• Solvents and diluent can be used.Solvents and diluent can be used.• Solvents dissolve the resin, diluents do

not.not.• Solvents must remain in the ink

formulation during drying process toformulation during drying process to maintain resin solubility.

• Combining solvents to give a blendCombining solvents to give a blend gives the best drying properties to a printed ink.p

• Drying is a “wicking” process that draws solvent from the printed ink film.

Function of the ResinFunction of the Resin

• Binder system to hold the particulatesBinder system to hold the particulates together.

• Gives the final dried film strength and• Gives the final dried film strength and adhesion to a given substrate.T f f h t l t• Transfer process from photopolymer to the substrate.

Formulation Considerations f R ifor Resins.

• Many types of resins can be used.y yp• Resin type depends on the substrate and adhesion

required.• Resin must prefer to adhere to the substrate rather• Resin must prefer to adhere to the substrate rather

than the photopolymer, otherwise no transfer will take place.R i t d ill l d d th t f• Resin type used will also depend on the types of solvents that can be used to dissolve it.

• Dielectric effect of the resin used will affect the electrical conductivity of the dried film.

• Shrinkage of the resin on drying will have an effect on the electrical conductivity.on the electrical conductivity.

• Solvent release of the resin on drying.

Functional ComponentsFunctional Components

• Silver PowdersSilver Powders• Silver Flakes

C b P d• Carbon Powders• Graphite Powders• Silver Complexes• Silver Metallo-OrganicsSilver Metallo Organics

Function of Conductive P dPowders

• Give final dried print electricalGive final dried print electrical conductivity.

• Particle size will also determine the• Particle size will also determine the rheology of the final ink.

Formulation Considerations f C d i P dfor Conductive Powders

• Particle sizeParticle size.• Particle size distribution.

T d it• Tap density.• Surface area.

Manufacturing of Silver P dPowders

• Chemical PrecipitationChemical Precipitation.• Coating of Powders.

P i f P d• Processing of Powders.• Manufacture of Flakes.

Effect of Silver Powder C tiCoating

• Coatings are used to preventCoatings are used to prevent agglomeration of the silver powder.

• Coating isolate each silver particle• Coating isolate each silver particle.• Poor removal of the coating reduces

d ti itconductivity.• Solvents must be capable of removing

the silver coating.

Selecting Silver Powder or FlakeSelecting Silver Powder or Flake

• Powders • Particle SizePowders Particle Size Distribution

Selecting Powder or FlakeSelecting Powder or Flake

• Typical Flake • Particle SizeTypical Flake Particle Size Distribution

Selection of Silver Powder or Fl kFlake

• Powders are • Flakes are flat spherical.

• Have less particle to ti l t t

platelets.• Have greater

l f ti lparticle contact.• Generally give low

conductivity in

overlap of particles when printed.

• Generally giveconductivity in polymer systems.

• Can be added to

• Generally give higher conductivity in polymer Ca be added to

improve conductivity of flake formulations

formulations.• Wide range of flake

sizesformulations sizes.

Manufacture of InksManufacture of Inks

• Dissolve Resin to • aDissolve Resin to produce a carrier system

a

system.• Add Powders to

produce a preproduce a pre-mix.Di• Disperse powders.

• Adjust to Viscosity

Dispersion TechniquesDispersion Techniques

• Triple Roll MillingTriple Roll Milling

Dispersion TechniquesDispersion Techniques

• Bead MillingBead Milling

Dispersion TechniquesDispersion Techniques

• ToursmillToursmill• High Shear Mixer

and Basket Mill

Typical Constituents of aFunctional Product

Weight (%)Functional Phase 27 - 70Organic Binder 9 - 3Organic Binder 9 - 3Organic Solvents 64 - 27

Shrinkage of filmWet Ink layerWet Ink layer25 microns

Dried Ink Layer 12 microns

Rheological MeasurementRheological Measurement

• Cone and PlateCone and Plate• Haake VT 550

• Ford Cup No 4

• Brookfield RVT• With RVT Spindles• With RVT Spindles

Rheology of Conductive Fl hi I kFlexographic Inks.

Silver Flexo InkC2080815D1#2090115.08

0 4000

0.5000

0.6000

0.7000

Pa s

0 0000

0.1000

0.2000

0.3000

0.4000

Visc

oaity

P

Carbon Flexo Ink C2080529D7 #2080618.25

0.30.0000

0 50 100 150 200 250 300 350 400

Shear Rate s-1

0.15

0.2

0.25

Visc

osity

Pa

s

0

0.05

0.1

0 50 100 150 200 250 300 350 400

Shear Rate s-1

V

Electrical Resistance

Why is the resistance of printed metal films higher than theoretical figures?

Resistivityy

Units ohms meters

Measure a cube of material

Volume ResistivityVolume Resistivity• Volume resistivity is defined as the ratio of the y

dc voltage drop per unit thickness to the amount of current per unit area passing through the materialmaterial.

• A basic material property, volume resistivity indicates how readily a material conductsindicates how readily a material conducts electricity through the bulk of the material.

• Volume resistivity is expressed in ohm-centimeters (Ω-cm).

Measurement of Volume R i i iResistivity

• 4 Point probes4 Point probes.• Current applied, at a known voltage

though two outer probesthough two outer probes.• Voltage drop is measured, by a second set

f bof probes.• Resistance is calculated.• Volume resistance is calculated based on

the sample test area and thickness.p

Sheet Resistance

Printed Circuits. With known dimensions so that number of squares can be calculated.

Measure Resistance, and thickness.

Calculate to give resistance per squareCalculate to give resistance per square

Units ohms/square/thickness

Gwent Electronic Materials LtdGwent Electronic Materials Ltd

Monmouth HouseMamhilad ParkPontypoolTorfaenTorfaenNP4 0HZUnited Kingdom

Tel: 00 44 (0) 1495 750505F 00 44 (0) 1495 752121Fax: 00 44 (0) 1495 752121Email: gem@gwent.orgWebsite www.gwent.orgg g