Presentation on Flexographic Printing

Techniques.At:-

by:-Leslie D. Embury

January 2010

TheGwent Group of

CompaniesSuppliers to Major Multinational

Companies in :-

The Automotive Industry.The Fuel Cell Industry.

The Electro-ceramics Industry.The Pharmaceutical Industry.

The Bio Science Industry.The Electronic Display Industry.

andGeneral Electronics.

Large Area Printing

• The Application of Flexography for the Volume Printing of Electronics.

SynopsisFlexography is an additive printing process that has the potential toachieve the necessary resolution and precision for volume printing ofplastic electronics and OLED lighting. The Technology Strategy boardfunded the “Accuflex” project, this project is developing a flexographicprinting system for volume production of high resolution plasticelectronics, achieving fine line registration within large areas oncontinuous webs. This will require improved control of the printingprocess, particularly the plate (image carrier) technology; web handlingand drying to create accurate fine line and precise features with therequisite inter layer registration that is essential for the use of theseprocesses for the manufacture of sophisticated flexible displays, RFID,intelligent packaging, bio sensors, disposable electronics and intelligenttextiles. The initial target products for Accuflex are large area lighting andconducting tracks for packaging, e.g. on tablet or blister packs.

Accuflex• A UK government funded project.• The Gwent Group.: Formulation of improved conducting inks.• Timsons Ltd.: Press development include precision digital

drive system on their T-Flex press.• Tectonic Ltd.:– On line inter unit registration measurement and

full web inspection.• Millennium Lasers Ltd.: on-line trimming.• Asahi plc.: Flexographic plate technology.• Innovia Ltd.: Substrate technology, including biodegradable

films.• WCPC, Swansea University: Fundamental research in

flexography, particularly on contoured and textured plates to address the demands of feature resolution and quality.

Areas of Technology to be addressed.

• Machine registration.• Ink formulation.• Printing geometry.• Substrate stability & surface parameters.• Transfer plate development.• Optical registration.• Laser trim.

Flexographic Printing

Flexographic Printing

Flexoprinting 10-60 meters per minute

Flexographic Printing

• The TFlex 508 flexographic printing press is being used as a basic platform for Accuflex project due to its robust construction, high specification drive elements and adaptability

Flexographic Printing

Flexographic Printing

Flexographic Printing

Current Printing Techniques.

• The process of choice currently for deposition of conductive inks isscreen printing, which are typically demands high viscosity materialsproducing a thick film which have prolonged drying and curing times.

• A variation being Stencil printing.• There are significant challenges in formulating materials for

flexographic printing.• Additionally, the system must compete with alterative possibilities.• Direct Gravure.• Ink Jet• Direct Write.• Subtractive Technologies.

Screen PrintingFig 1 The basic screen print process

SqueegeePaste

Screen frame

Screen mesh

Emulsion

Nest

Substrate

Screen Printing

Printing speed: 60 -1500 sheets per hour

High Definition Screens

Screen with 500 meshcalendared fabricwire diameter 8 µmline/space 20 µm/20 µm

Material agglomerationThree particle agglomerate limits maximum particle size of powder to 12-15μm (assuming aperture of 45 μm)

Print Limitations300SDS 40µm 400UT 40µm V330 40µm

C2090903R3 76% Pt

Stencil Printing

Electroformed apertures

Positive advantage since no threads to reduce open area.

Negative one direction only, without a dotting process.

Stencils

• 20 micron lines and spaces

• Speed of printing 60-1500 sheets per hour

Ink Jet

Piezo-Electric DepositionUp to 24 meters/min for digital printing

Ink Jet

• Nano silvers printed 50 micron lines• Using Current technology 30–50 µm lines

Ink Jet

Glucose Biosensor responseSEM of Ink Jetted GOX layer

Ink Dispersion Equipment for flexo Ink

Ink Requirements for Flexographic Printing

• The process demands low viscosity inks, the films deposited arethinner

• The solvents in the ink must be compatible with the plates.• Increased flexibility is required and the drying times are significantly

shorter.• The initial demands are for conductive inks, this process

requirement mean a fundamental rethink in formulation in terms of:-• Particle size.• Particle shape• Solvent and Resin systems that can be used.• Their development had led to a conductive ink which is capable of

being printed by flexography

Flexographic Printing InksRaw Materials Selection

• Solvents and the roles they play in the formulation.

• Polymer types and considerations.• Functional Phases, Conductive

powders.

Flexographic Printing InksFunction and Selection of

solvents• Dissolve the selected resin system.• Maintain printability.• Control drying rate.• Resin must remain fully dissolved during printing and

drying process.• Generally several solvents are used with different boiling

points and evaporation rates.• Direct effect on the drying of the printed films.

Flexographic Printing InksSolvent Properties to

Consider• Solvents and diluent can be used.• Solvents dissolve the resin, diluents do not.• Solvents must remain in the ink formulation during

drying process to maintain resin solubility.• Combining solvents to give a blend gives the best drying

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

printed ink film.

Flexographic Printing InksFunction of the Resin

• Binder system to hold the particulates together.

• Gives the final dried film strength and adhesion to a given substrate.

• Transfer process from photopolymer to the substrate.

Flexographic Printing InksFormulation

Considerations for Resins.• Many types of resins can be used.• Resin type depends on the substrate and adhesion required.• Resin must prefer to adhere to the substrate rather than the

photopolymer, otherwise no transfer will take place.• 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.

• Solvent release of the resin on drying.

Flexographic Printing InksFunctional Components

• Silver Powders• Silver Flakes• Carbon Powders• Graphite Powders• Silver Complexes• Silver Metallo-Organics

Flexographic Printing InksFunction of Conductive

Powders• Give final dried print electrical conductivity.• Particle size will also determine the rheology of the

final ink.

Flexographic Printing Inks Formulation Considerations

for Conductive Powders

• Particle size.• Particle size distribution.• Tap density.• Surface area.

Flexographic Printing Inks Manufacturing of Silver

Powders

• Chemical Precipitation.• Coating of Powders.• Processing of Powders.• Manufacture of Flakes.

Flexographic Printing Inks Effect of Silver Powder

Coating• Coatings are used to prevent

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

conductivity.• Solvents must be capable of removing

the silver coating.

Flexographic Printing Inks Selecting Silver Powder or

Flake• Powders

• Particle Size Distribution

Flexographic Printing Inks Selecting Powder or Flake

• Typical Flake• Particle Size

Distribution

Flexographic Printing Inks Nano-Silver Powder

• 30nm mono dispersed powder (25 -45nm)• Organic content minimised.• No surfactants or dispersants added.• Powder supplied “wet” in a solvent.• Easier to disperse.• PSD (SEM)• D10 10nm• D50 30nm• D90 50nm

Flexographic Printing Inks Selection of Silver Powder

or Flake• Powders are spherical.• Have less particle to

particle contact.• Generally give low

conductivity in polymer systems.

• Can be added to improve conductivity of flake formulations

• Flakes are flat platelets.• Have greater overlap of

particles when printed.• Generally give higher

conductivity in polymer formulations.

• Wide range of flake sizes.

Functional Conductive Flexographic Inks

Property Silver Ink C2080815D1

Carbon Ink C2090424D2

Ink Type Solvent Based Solvent Based

Drying Requirement Forced air 60 – 70°c Forced air 60 – 70°c

Viscosity @ 50s-1(typically) 0.8 Pa s 0.5 Pa s

Volume Resistance Ohms/cm*

5.2475x10-5 2.07x10-2

Maximum Print Speed** 30m/min 30m/min

Flexographic Printing Inks Rheology of Conductive

Flexographic Inks.

Silver Flexo InkC2080815D1#2090115.08

0.0000

0.1000

0.2000

0.3000

0.4000

0.5000

0.6000

0.7000

0 50 100 150 200 250 300 350 400

Shear Rate s-1

Visc

oaity

Pa

s

Carbon Flexo Ink C2080529D7 #2080618.25

0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200 250 300 350 400

Shear Rate s-1

Visc

osity

Pa

s

Trial Formulations• All Silver powders and flakes have differing Tap

Densities, and Surface areas.• Silver Flakes range from 1.5 – 6.0 g/cm3• Silver Powders range from 0.8 – 4.9 g /cm3• Surface Area range from 0.2 – 3.6 m2/g• Require a Model formulation to be able to

assess different Silver Powders and Flakes.• Allows comparisons to be made between the

performance of flakes and powders within the formulations.

Volumetric Ratio’s

• Allows the same volume of Silver to be added to the same volume of Resin in the formulation.

• Eliminates differences between the Tap Densities of different powders and flakes.

Trial Formulations

Product Code C2080605R4 C2080605R3 C2080605R2 C2080609R2 C2080609R1 C2080603R10

Volumetric Ratio 12.5:1 10:1 7.5:1 7:1 6:1 5:1

In Dried Film

Weight % Silver 97.26 96.67 95.60 95.30 94.57 93.54

Weight % Resin 2.74 3.33 4.40 4.70 5.43 6.46

Conductivity (Ohms) 2.66 2.43 2.54 1.44 1.268 2.34

Volumetric Ratio Trial Results

Relationship between Resin Content and Conductivity for Conductive Flexographic Inks

0

1

2

3

4

5

6

7

12.5:1 10:1 7.5:1 7:1 6:1 5:1

Volumetric Ratio

Res

in C

onte

nt in

D

ried

Film

%

0

0.5

1

1.5

2

2.5

3

Con

duct

ivity

(Ohm

s)

of B

ar C

oate

d Fi

lms

% ResinConductivity

Mixing Silver Powder and Flake

Effect of Combining Silver Flake and Silver Powder on Conductivity (2:1)

00.5

11.5

22.5

33.5

10.56:1 10.56:1

Volumetric Ratio

Res

in C

onte

nt in

D

ried

Film

%

0123456

Con

duct

ivity

(O

hms)

of B

ar

Coa

ted

Film

s

% ResinConductivity

Modifying Resin Type

Effect of Changing Resin Type on Conductivity

0

1

2

3

4

5

7:1 7:1

Volumetric Ratio

Res

in C

on

ten

t in

D

ried

Fil

m %

00.20.40.60.811.21.41.6

Co

nd

uct

ivit

y (O

hm

s)

of

Bar

Co

ated

Fil

ms

% ResinConductivity

Trials

• Resin and Solvent type have significant effect on the print quality.

• Optimisation of Organic components in the ink to match surface energies of the film substrate being used.

• C2080609D1 (7:1)

Effect of Print Orientation to Print Quality

• 30 micron lines 45° orientation

• 30 micron lines (vertical)

• 30 micron lines (horizontal)

Effect of Print Orientation to Print Quality

• 100 micron lines 45° orientation

• 100 micron lines (vertical)

• 100 micron lines (horizontal)

Ink Rheology Problems

Ink Rheology Problems.

Carbon Only Inks

• Removal of Graphite to reduce PSD• Highest Conductivity Carbon Used

Resistance Results

• Carbon Only formulations have resistances that are x10 larger

Product Code C2090204R9 C2090204R10 C2090204R12 C2080529D7

Volume Resistance Ohm/cm 0.00564 0.00322 0.00520 0.0207

Carbon/Graphite C2090424D2

• Re-formulated to remove slow solvents.

• New formulation printed on Nilpeter press.

• Drying system.• Print Speeds.• Achieved 35m/min.• No set off.• 40m/min some set off.

9 nozzles per dryer

Nozzle air velocity >3000 FPM (600 m/min)

Air volume 340 CFM ( 9.6 m/min) per mpdule (2 stations)

Heater temperature 170 F. (77 C.)

Glucose Demostrator

• Trails using various carbon flexo inks were carried out on two substrates supplied by Innovia.

• Natureflex 45NVL and Natureflex 45NK.• Natureflex 45NK was found to give the

lowest Coefficient of Variance (CV%) .

Glucose Demonstrator• Three inks on total required for the glucose

demonstrator to be printed.• Electrode material, Carbon Flexo ink, used for

the working and pseudo reference electrode.• Insulation, used to isolate the tracks and define

working and pseudo electrode areas.• Hydrophobic Dielectric, used to channel sample

to electrode area.

Inks Used• Carbon Graphite formulation was modified to

give the lowest CV% when printed on Naturflex 45NK, C2091026D4 # 2091027.16.

• Insulation in Flint UV curable formulation,UVF00345-405#2090722.12 Flexo Overprint varnish.

• Hydrophobic Dielectric, solvent based flexo ink which was specially formulated to give good printing characteristics, D2091001D8 #2091031.02.

Bio-sensor Production

Possible Products

Possible Products

Possible Products

Conclusions

• High speed printing by Flexographic techniques is possible.

• Ink formulations can be produced to suit the majority of inks types that are needed.

• High cost machinery is offset by lower production costs.

• High volume production is obtainable.• Good electrical /electrochemical properties

can be obtained

Les EmburyManaging DirectorThe Gwent Group,Monmouth House,Mamhilad Park,Pontypool NP4 0HZ.United Kingdom.sales@gwent.orghttp://www.gwent.orgTel: +44 (0)1495 750505Fax: +44 (0) 1495 752121

The Gwent Group

Gwent Electronic Materials Ltd.Applied Enzyme Technology Ltd.Gwent Biotechnology Ltd.Gwent Sensors Ltd.LRH Ltd.