Oct 17th 2005 AIMCAL 2005 1

OXFORD UNIVERSITY

A Review of Transparent Barrier Coatings.

B.M.Henry. Department of Materials, University of Oxford, Parks Road,

Oxford, OX1 3PH UK

Oct 17th 2005 AIMCAL 2005 2

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Talk Outline

• Introduction • Background• Different barrier technologies:

Nanotechnology,Ormocers,PECVD,PML,Ion assisted Sputtering,Reactive PVD,

• Summary

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Introduction

l Gas barrier films are of interest for many applications including packaging and the display industry.

l For over two decades numerous methods have been used to manufacture transparent barrier coatings with varying degrees of success.

l An overview will be presented of the barrier performance of transparent coatings fabricated by a wide range of techniques as reported in the literature.

l To reflect the current trend, emphasises is placed on films which display very high gas barrier properties.

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Barrier properties of polymeric materials

COC PLA

PET

PE-HD

PE-LDPS

PVC-PPP PC

PVC-U

PA 6

CellulosePVDC

PENPAN

BOPP

0,01

0,1

1

10

100

1000

10000

0,01 0,1 1 10 100 1000

Water vapour permeability / g / m2 d at 23°C, 85% r.h.

Ox

yg

en

perm

eab

ilit

y a

t 23

°C

/ c

m3 /

m2d

ba

r

Oxygen and water vapor permeability for various technical polymers, for 100 mm material thickness at a temperature of 23°C

Polymers are permeable towards diffusion of O2 with considerable differences depending on their physical interaction.

Some polymers can provide decent barriers to O2 but then faced with other problematic issues.

Permeation through Polymers

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Barrier Materials

10 - 1000 nm

12 - 100 mm

AlSiOx

AlOx

ITOSiNx

AlOxNy

Polymer substrate

OPP, PET, PENSurface pre-treated.

E-Beam Evaporation, Reactive Sputtering, PECVD

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Permeation through Barriers Films

Barrier Material Thickness OxygenTransmission

[ccm/m2/day/atm]

Water VapourTransmission

[g/m2/day/atm]

DepositionProcess

FilmCompo-

sition

PET / Blank 12.00 mm 100 64.64

PVDC 24.00 mm 8 0.3

EVOH 24.00 mm 0.16 - 1.86 * N/A

m-OPA 15.00 mm 30

Aluminized PET(single)

~ 30nm 0.31 - 1.55 0.31 - 1.55 Evaporation Al

Aluminized PET(double)

~ 30nmeach

0.03 N/A Evaporation Al

Aluminum on PE 7mm Al 0.001 N/A Laminated Al

SiOx on PET 10 - 80 nm 0.35 - 10** 0.46 - 1.24 Evaporation SiOx

SiOx on PET 10 - 80 nm 0.08 - 1.55 0.5 - 5.0 PECVD SiOx

Al2O3 on PET 20 nm 1.5 5.0 Evaporation,Reactive

Evaporation

Al2O3

Al2O3/SiO x on PET 50 nm 2.0 - 3.0 1.0 Evaporation Al 2O3/

SiO x

Diamond-likeCarbon on PET

20 nm 2 1.50 PECVD Diamond

* depending on relative humidity and ethylene content** depending on used process

• Permeation can be reduced when an inorganic barrier layer is deposited.

• The gas transmission rates are improved and can fulfil the demands for packaging.

• These films are not ideal for applications such as displays etc.

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Permeation through Barriers: Defects!

•• The low barrier performance is due to a defective The low barrier performance is due to a defective barrier coating on the polymer substratebarrier coating on the polymer substrate

5 mm

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Barrier Materials

l Single layer coatings on polymer films provide modest barrier structures.

l Multilayer coatings can provide better barrier performance.

l Separate the inorganic layers with thin organic coatings.

l Organic interlayers applied either in vacuum (monomer evaporation + curing) or by a wet coat process.

10 -6 10 -4 10 -2 10 0 10 210 -6

10 -4

10 -2

100

102

water vapour permeability / g / m2 d

oxyg

en

perm

eab

ilit

y / c

m3/

m2

d b

ar

Enhanced layers and Multilayer barrier coatings,

Standard: 1 inorg. layer

Single polymers

Standard 2 inorg. layers

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Nanotechnology Barrier Films

l Pioneered by InMat® Inc., NanolokTM

coatings start as aqueous suspensions of nanodispersed silicates in a polymer matrix.

l Can be applied via gravure coating processes to polymer substrates.

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Nanotechnology Barrier Films

l The NanolokTM aqueous suspension is applied via a roll coating process onto a substrate.

l Once dry, a thin coating (0.25-2 microns) of NanolokTM forms on the substrate.

l This coating contains hundreds of nanodispersed platelets per micron of coating thickness. These platelets form a tortuous path for molecules such as oxygen, dramatically increasing the barrier properties of the substrate.

l NanolokTM coatings form an efficient barrier which can be 100’s of times less permeable than the uncoated substrate. In addition, these coatings are transparent.

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Ormocers®

l This technology, developed by the Fraunhofer Institute in Wurzburg, is inorganic organic hybrid polymers.

l These materials are produced through sol–gel chemistry and deposited as transparent coatings with micron-scale thickness.

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Ormocers®

l Can be used independently to obtain a modest barrier improvement or in combination with a metal oxide, in which case very high-barrier materials are

obtained.

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Ultra-High Barriers

l The following groups have all indicated that their films have WVTR below the sensitivity of the MOCON.

l General Electric- PECVD hybrid inorganic/organic ‘single layer’structure (WVTR ~10- 6 g/m2 /d)

l VITEX- AlOx-polyacrylate pairs (WVTR ~10- 5-10- 6 g/m2 /d)

l General Atomic- Single layer super sapphire; Ion assisted layer deposition (United States Patent Application 20040209126), (WVTR ~10- 5 g/m2 /d)

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GE: Barrier DevelopmentSingle layer glass-like barrier films provide insufficient barrier

Solution for barrier coating design

~ 100 defects/mm2

20x

~1mm

Defect Imaging w/ Acetone

0 20 40 60 80 1000

2

4

6

8

10

12

14

WV

TR

(g/m

2 /day

)

Thickness (nm)

Defect Limited Permeation

PC/SiNx

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GE: Graded Barrier Film

Single Layer Barrier:Graded Hybrid

Inorganic-OrganicBarrier Layer

Polymer Substrate

Promising WVTRGood Interfacial Adhesion

Graded ultra high barrier

FabricationPlasma Enhanced Chemical Vapor

Deposition

High Ion BombardmentLow T deposition

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XPS Spectrum of Graded UHB

GE’s Graded Ultra High Barrier

Inorganic Organiczone

GE: Graded Barrier Film

Cross-sectional TEM of Graded UHB

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GE: Graded Barrier Film

Noise reduced enabling improved detection limit

4 (± 2) x10-6

g/m2/day

Typical UHB (23C/50%RH):

Graded UHB in 10-6 g/m2/day range

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Vitex Barrier Film

l Based on repeated layers of organic/ inorganic pairs (dyads).

l Organic is deposited by a flash evaporation process either as a smoothing or intermediate layer.

l Organic layer is very smooth and has modest barrier properties.

l Inorganic layer deposited either by evaporation or sputtering.

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Vitex Barrier Films

l WVTR of about 10- 6 g/m2 /day at 25 °C and 40%RH, reported for five dyads (AlOx-polyacrylate pairs) on a PET substrate.

l This result does not strictly represent equilibrium permeation.

l Once the lag time is exceeded, the water vapor flux is expected to reach a steady-state value that is substantially higher, maybe 10- 3 to 10- 4 g/m2 /day, than the WVTR calculated during the transient period.

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General Atomics: “Super Sapphire”

l Polymer is pre-treated by an ion-gun-generated plasma under vacuum conditions in the presence of a partial oxygen pressure.

l Deposition of a transparent inorganic barrier layer on the pre-treated polymer layer using ion-assisted sputtering.

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Single Layer Super Sapphire – WVTR Single Layer versus Multilayer – WVTR

Radioactive TestTemp: 38°C, 100% RHArea: 86.5 cm2Measured Species: Tritiated Water (HTO)

General Atomics: “Super Sapphire”

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Symmorphix Barrier Technology

l Single layer: aluminosilicate

l Thin film (<200 nm)

l Reactive PVD process and pre-treatment

l Low temperature (<80oC)

l Flexible and scratch resistant

l Low cost

l Compatible with roll to roll process

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Symmorphix: Single Layer Barrier

• % transmission of barrier film on PEN equivalent to bare substrate.• Roughness of barrier coating is lower than bare substrate.• Novel pre-treatment improves barrier properties and coating smoothness.

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Symmorphix: Single Layer Barrier

l Single barrier layer (200nm) <6 x 10-6 g/m2

/day reported on PEN

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Summary

l A selection of the many different approaches to the fabrication of transparent barrier films has been presented.

l For packaging applications the modest barriers (~10- 1

g/m2 /d) displayed by thin single coatings deposited by conventional methods is sufficient.

l For more demanding barrier applications, such as displays, different strategies have been developed with the attainment of films claiming WVTR of around ~10- 6

g/m2 /d.

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