Atomic Layer Deposition in Food Packaging and Barrier Coatings

Cost Workshop 16th September2011, EspooDr. Pirjo HeikkiläVTT Technical Research Centre of Finland

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Outline of the Presentation

Food packaging

Barrier properties of food packaging

Atomic layer deposition - ALD

Barrier properties of ALD coatings

Literature examples

Summary

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Food Packaging

Purposes of food packaging Protect the product from the surroundings Maintain quality of food Communication, legal and commercial demands

Deteriorative reactions of food include Enzymatic Chemical Physical Microbiological changes

Important properties of packaging Mechanical properties Barrier properties Depend on individual food product

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Barrier Properties of Food Packaging

Typical packaging materials with enhanced barrier properties Coated papers and papersboards Polymer films

Typical polymeric materials used in food packaging Polyethylene PE Polypropylene PP Polystyrene PS Polyvinylchloride PVC Polyethylene terephtalate PET Biobased materials More and more also biodegradable synthetic polymers

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Barrier Properties of Food Packaging

Barrier property of polymers depends on the inherent permeability to gases (oxygen, carbon dioxide) and vapours (water vapour). PET – good gas and moisture barrier Biopolymers – high water vapor permeability.

Barrier properties can be enhanced using Aluminium foil Coatings with high barrier material Multilayered materials Nanocomposites

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Atomic layer deposition - ALD

Preparation of solid thin films using gaseous reactants

Reactions used in cycles Surface controlled Self-terminated One monolayer at a time –

no reactions in gas phase

Process steps for binarycompound (e.g. Metal oxide)

1. One reactant (metal)2. Purge 3. Second reactant (oxygen)4. Purge

Figure George S.M. et al., Acc. Chem. Res., 42(4)2009, 498–508

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Atomic layer deposition - ALD

Thickness of the coating is controlled by the amount of cycles

Low pressure processing in temperatures between 50 °C – 500 °C

Requirements for reactants: Volatility and thermal stability in operating temperatures Self-terminating reactions

In some cases other reactant can be replaced by surface activation

Typical example in barrier coatings – Al2O3

Trimethylaluminiun (TMA) + H2O – thickness 0.1 nm/cycle TMA + O3

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Atomic layer deposition - ALD

Figure Puurunen R., J. Appl. Phys. 97 2005, 121301

Materials grown by ALD: Oxides.

Nitrides.

Sulphides.

Selenides.

Tellurides

Pure elements.

Other compounds.

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Barrier Properties of ALD coatings

Gas permeation through a single inorganic layers is dominated by the defect size and density in the film.

Properties of ALD coating favourable to barrier properties: Thickness in nanometer range possible

Flexibility Reduced cracking probability

Conformality High quality coatings

Optimally pinhole free Fixed thickness

Figure Puurunen R., J. Appl. Phys. 97 2005, 121301

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Barrier Properties of ALD coatings

Challenges of ALD coating method in barrier applications

Chemical functionality of substrate essential for initial growth mechanism. Sometimes pretreatments

of surface is needed.

Best quality (film density and level of impurities) is obtained in high temperatures, but polymer substrates require relative low processing temperature. Use of thermally more resistive substrate

Figure Puurunen R., J. Appl. Phys. 97 2005, 121301

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Barrier Properties of ALD coatings

Challenges of ALD coating method in barrier applications

Conventionally ALD is batch process (time and cost). Continuous roll-to-roll processing is coming.

Ceramic coatings are brittle and, thus, susceptible to cracking. Tendency decreases with decreasing coating thicknesses

Safety issues of nanocoating materials!?

Figure Kääriäinen T.O.et al.,. Thin Solid Films, 2011, 519, 10, 3146-3154

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Literature ExamplesBarrier properties of Al2O3 coatings, comparison of coating methods– Hirvikorpi et al.

Comparison of aluminum oxide coatings obtained using ALD, electron beam evaporation, magnetron sputtering and a sol–gel methods Base: low-density polyethylene (LDPE) coated (15 g/m2) board Barrier performance improved, ALD was most efficient

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Literature ExamplesALD coatings (TiO2 and Al2O3) on polymer coated paperboards -

Kääriäinen et al.

Base LDPE extrusion coatedpaper Between 15 and 30 nm ALD

film thickness the diffusion resistance starts rising rapidly(see figure). WV barrier optimum at approx.

100 nm thickness. Film becomes less resistant to

stress with increasing ALD film thickness.

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Literature ExamplesWater vapor barrier of ALD coated biopolymer film – Hirvikorpi et al.

Water vapour transmission rate of coated paperboard depends on • ALD coating

• Thickness25 nm or 50 nm

• MaterialAl2O3 or SiO2

• Property of the base material• Treatments

untreated or corona pre-treated• Material

PE or PLA

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Literature ExamplesGas diffusion barriers on polymers using Al2O3 – George et al.

Base flexible polyethylene naphthalate and Kapton® polyimide to beused organic flexible displays and electronics OTR values of ~5*10−3 cc/m2/day (Al2O3 ≥ 5 nm)

Such low values have reported earlier for such thin single-layer coatings on polymers OTR of PECVD grown SiO2(100 nm) on PET have 0.4 cc/m2/day

WVRT values of ~1*10−3 g/m2/day (Al2O3 ~26 nm)

Tritiated water HTO as a radioactive tracer

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Summary

Protection provided by food packaging depends mainly on its mechanical properties and barrier properties Typical barrier packaging materials are coated papers and

papersboards and polymer films. ALD method produces thin coatings layers used in enhancing of

barrier properties+ Thin, flexible, low amount of defects? Brittle, quality depends of substrate and coating temperature,

processing costs Oxygen and water vapour barrier materials obtained by ALD has

been reporter in literature.

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Literature

Arora A., Padua G.W., Review: Nanocomposites in food packaging, Journal of Food Science 75(1)2010, 43-49

Petersen K., Nielsen P.V., Bertelsen G., Lawther M., Olsen M.B., Nilsson N.H., Mortensen G., Potentialof biobased materials for food packaging, Food Science and Technology 10 1999, 52-68

Puurunen, R. Surface chemistry of atomic layer deposition: A case study for the trimethylaluminium/water process Journal of Applied Physics 97, 2005, 121301-1 -52

George, S.M.; Yoon, B.; Dameron, A.A. Surface Chemistry for Molecular Layer Deposition of Organic and Hybrid Organic-Inorganic Polymers Accounts of Chemical Research

Hirvikorpi T., Vähä-Nissi M., Harlin A., Karppinen M., Comparison of some coating techniques to fabricate barrier layers on packaging materials, Thin Solid Films, 518(19)2010, 5463-5466

KääriäinenT.O., Maydannik P., Cameron D.C., Lahtinen K., Johansson P., Kuusipalo J., Atomic layerdeposition on polymer based flexible packaging materials: Growth characteristics and diffusion barrierproperties. Thin Solid Films, 2011, 519, 10, 3146-3154

Hirvikorpi T., Vähä-Nissi M., Harlin A., Merles J., Miikkulainen V., Karppinen M., Effect of corona pre-treatment on the performance of gas barrier layers applied by atomic layer deposition onto polymer-coated paperboard, Applied Surface Science 257 (2010) 736–740

Groner,M.D.; George,S.M.; McLean,R.S.; Carcia,P.F. Gas diffusion barriers on polymers using Al2O3 atomic layer deposition. Appl. Phys. Lett., 2006, 88, 5, 051907/1-051907/3

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