VACUUM COATINGS FOR BARRIER PERFORMANCE: PROBLEMS & SOLUTIONS

Professor Nadir Ahmed Idvac Ltd.

Greenheys, Manchester Science Park Pencroft Way, Manchester M15 6JJ, England

Tel: +44(0)161 868 0088 Email: idvac@aol.com

•Privately owned company. •Strong links with UK top universities. •Develops cost effective vacuum coating processes. •Supplies evaporation source retrofits to convert standard Aluminium metallisers to other coatings. •Provides the industry with a contract consultancy service. •Introduces customers to new worldwide markets and applications. •Provides Analytical services. •Vacuum Training courses, Patent search,etc.

Roll to roll vacuum metallisation for barrier applications.

• Packaging.

Aluminium: by far the largest vacuum deposited thin film

to provide barrier properties

Clear Barriers: increasing demand for food packaging

•Solar film

• Solar Cells

• Transparent electrodes

Electroluminescent lamps

Touch panels

•High barrier

Flexible LCDs.

•Ultra-barrier

Flexible substrates and encapsulation for OLEDs.

Advantages of Vacuum Metallisation

Clean Coating Film Outgassing Environmentally Friendly

High Quality Durable Coating Dry Coating

Control of Physical Properties Longer Lifetime Effluent Free

High Line Speed

Standard aluminium metallisation for packaging

Al: High pressure; poor Oxygen & Water barrier

Al: Low pressure; good Oxygen & Water barrier

1

7

13

19

25

31

37

22

15

8

1-202468

1012141618202224262830323436384042

7 Boats Simultaneously @ 165 cm/min for 10s (026)40-4238-4036-3834-3632-3430-3228-3026-2824-2622-2420-2218-2016-1814-1612-1410-128-106-84-62-40-2-2-0

Typical uniformity during aluminium metallisation

Transparent Barrier Coating SiO, SiOx, SiO2, Al2O3, Others

Thermal Evaporation

&

Electron Beam)

Sputtering PECVD

Slow, expensive Medium line speed

High quality

Clear, Good Oxygen

and Water barrier Good quality

Light colour/transparent

Fast, Cost effective

Good Oxygen & Water Barrier

Not very transparent

Good properties when

laminated

Stand alone

no lamination required

Lamination may or

may not required

Vacuum deposited clear barrier packaging coatings.

PVD

• RESISTANCE HEATED

•Non- Reactive SiOx

•Reactive SiO +O2

•Reactive Al + O2

• ELECTRON BEAM HEATED

• Reactive SiO + O2

• Reactive Al + O2

• Mixed Reactive SiO + Al + O2

• Mixed Non-Reactive SiO2 + Al2O3

• ‘Low cost’ reactive ‘ ‘SiO’ + O2

PECVD

• Medium frequency, RF, Micro-wave. Silicon based

coatings

• Micro-wave. Carbon based coatings

1 2 3 4 5 6 7 8 9

0

5

10

15

20

25

30

35

40

45

WV

TR

/OT

R

Sample Number

OTR

WTR

Variation of Aluminium Oxide barrier properties for different batches

OTR: cc/m2 day

WVTR: g/m2 day

Tropical test

Uncoated

BOPP(arbitrary

value)

Metallized BOPP

SiOx on BOPP

SiOx/Al

0

20

40

60

80

100

120

140

160

180

200

OT

R,c

c/m

2 d

ay

Thermally evaporated 15nm SiOx on 20micron BOPP

Water Barrier: g/m2 day

Oxygen Barrier:cc/m2 day

Uncoated BOPPMetallised

BOPP SiOxSiOx/Al

0

1

2

3

4

5

6

7

8

9

WV

TR

: g

/m2 d

ay

100% RH, 38 deg C, tropical test

SiOx on 20 BOPP;200m/min SiOx on metallised BOPP;

200m/min

Structure of 15nm SiOx on metallised and un- metallised BOPP film

Contradictions to Barrier Pinholes Theory

Films treated at different levels with same OD and defect density show different barrier properties.

EB metallization vs. Thermal or Free Span at same OD and defect density show different barrier properties.

Laminated metallised films with adhesive coatings or extrusion lamination show different barrier properties.

So There is Inconsistency

Factors Affecting Diffusion in Solids

Degree of Crystallisation

Porosity Interaction with Gas/Water Polarity of Gas/Water

Lattice Defects

Fine Cracks

Flow through Pinholes

(Depending on Size&Number)

No Reaction: Random Diffusion

Through Inteerstices Water is Reactive & Bi-Polar

Cryastalline: Slow Diffusion

Semi Crystalline: fast Diffusion

Grain Boundaries

Prferential Paths

Reaction: Dense or Porous

Oxide

Attractive Interaction

(Hydrolysis)

PINHOLES

Crystallization of

Condensed Coating Vaporization of

Solvent/ Water

Film Roughness

Due to Anti-blocks

Fine Cracks<1μ Film Properties

Low Pumping Speed Surface Treatment

Film Temperature

Spitting

Dust particles

Coating Thickness

Line Speed

Vacuum Level Surface Charges/ Breakdown

Factors Affecting Barrier in Metallised Films

Surface Coating Coating/Film Interface

(Oxide?)

Polymer Film

Permeation of O2, CO2, H2O

From Film backside

Type of Film

Quality of Film

Reaction with O2 centres

In Polymeric Film

Surface Chemistry

Corona; Other treatments

Coating Method:

Thermal, EB, Sputtering

Coating Thickness

Coating Structure:

Dense/Porous

Vacuum Level

Radiant Heat

Winding Mechanism

Line Speed

AlOxCyHz

OPP: Hydrocarbon

PET: Carboyl

Morphology

Chemical Structure

Morphology

Film temperature

During Metallization

Moisture/ Solvent Retention

Developments in Vacuum Metallising

Vacuum Technology Winding Mechanism Evaporation Sources Process Control

Efficient Pumps Tension Control New Design Feedback Control

Vacuum Monitors Efficient Drives Different Materials User Friendly

S N S N

Magnets Water inlet

N N S N

Film

Water cooled back plate

Plasma

Schematic of Plasma Treatment Source

Water Outlet

Coating without plasma treatment Coating with plasma treatment

Effect of plasma treatment on coating structure

PECVD Barrier Process.

Plasma He + O2 + Ar + monomer Clear barrier coating

MF electrical power

By product gasses

(H2O, CO, CO2, HC)

Monomer: e.g. HMDSO (Hexamethyldisiloxane)

CH

3 H3C Si O

CH

3

Si

CH

3

CH

3

CH

3

Non-toxic

Non-pyrophoric

Considered safe

Courtesy of General Vacuum Equipment Ltd.

PECVD Process Module.

Magnetically enhanced plasma

Clear barrier coating

5 x 10-2 mbar

Chilled Process Drum

Monomer + Process Gases

Exhaust Gases

U/W R/W

40 KHz power supply

GPE

Courtesy of General Vacuum Equipment Ltd.

GPE: Gas Purge Electrode

ULTRA-BARRIER COATINGS Some coating requirements:

• Reduce defect numbers.

• Dense Structure.

• Reduce grain boundaries – Semi-crystalline to amorphous?

• Reduce nano-defects.

• Reduce chemical effects.

• Multilayered coatings?

• Perfect layers?!

• Smooth surfaces, prevent shorts and defected devices.

- Example: planarisation layer

Polymer Multi-Layer (PML) process for the flash evaporation of

monomer liquids (acrylates).

Sigma Technologies, Batelle North Western, 3M, General Electric.

ULTRA-BARRIER COATINGS on POLYMERS.

• Undercoats and Overcoats for environmentally sensitive devices, OLEDs.

• Polymer substrates ‘high’ permeation rates.

• For >10,000hr operation OLED structures require very low permeation levels,

reaction with low work function cathode metals (Ca, Mg, Li, LiF etc.)

< 10-2 cc/m2/day < 10-5 – 10-6 g/m2/day

For robust plastic and flexible displays.

Barix TM - Example of engineered ultra-barrier flexible substrate. • All vacuum deposited layers.

• Acrylate flash evaporated, electron beam or UV cured, around 1um thick.

• Acrylate flows to form flat surface, pin hole free.

• Acrylate burys imperfections.

• Inorganic layer sputtered, e.g. Al2O3, 10-20 nm thick.

- Flash evaporation difficult to control, can become unstable, variable thickness.

- Anything better or simpler? Single layer?

Barix TM - Example of engineered ultra-barrier flexible substrate. VITEX SYSTEMS,

CA, USA

Few –

10’s of

layers

ACRYLATE

INORGANIC

HARDCOAT

POLYMER

HARDCOAT

Conclusions Aluminium metallising is by far the largest vacuum deposited thin

film to provide barrier properties for packaging industry.

Requirement for better improved barrier properties resulted in

advanced control of aluminium metallisation process.

Pasma Pre-treatment is extensively utilised for enhanced barrier and

adhesion on polymer webs at speeds approaching 1000m/min.

Clear barrier coatings for packaging deposited by PVD, plasma

assisted reactive evaporation and plasma enhanced CVD are gaining in

importance.

Extensive work to develop extra barrier properties for special

markets.