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: [email protected]
•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.