Atomic Layer Deposition in Food Packaging and Barrier Coatings

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1 Atomic Layer Deposition in Food Packaging and Barrier Coatings Cost Workshop 16 th September2011, Espoo Dr. Pirjo Heikkilä VTT Technical Research Centre of Finland

2 2 Outline of the Presentation Food packaging Barrier properties of food packaging Atomic layer deposition - ALD Barrier properties of ALD coatings Literature examples Summary

3 3 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

4 4 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

5 5 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

6 6 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 binary compound (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,

7 7 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 Al 2 O 3 Trimethylaluminiun (TMA) + H 2 O thickness 0.1 nm/cycle TMA + O 3

8 8 Atomic layer deposition - ALD Materials grown by ALD: Oxides. Nitrides. Sulphides. Selenides. Tellurides Pure elements. Other compounds. Figure Puurunen R., J. Appl. Phys ,

9 9 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 ,

10 10 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 ,

11 11 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,

12 12 Literature Examples Barrier properties of Al 2 O 3 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/m 2 ) board Barrier performance improved, ALD was most efficient

13 13 Literature Examples ALD coatings (TiO 2 and Al 2 O 3 ) on polymer coated paperboards - Kääriäinen et al. Base LDPE extrusion coated paper 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.

14 14 Literature Examples Water vapor barrier of ALD coated biopolymer film Hirvikorpi et al. Water vapour transmission rate of coated paperboard depends on ALD coating Thickness 25 nm or 50 nm Material Al 2 O 3 or SiO 2 Property of the base material Treatments untreated or corona pre-treated Material PE or PLA

15 15 Literature Examples Gas diffusion barriers on polymers using Al 2 O 3 George et al. Base flexible polyethylene naphthalate and Kapton polyimide to be used organic flexible displays and electronics OTR values of ~5*10 3 cc/m 2 /day (Al 2 O 3 5 nm) Such low values have reported earlier for such thin single-layer coatings on polymers OTR of PECVD grown SiO 2 (100 nm) on PET have 0.4 cc/m 2 /day WVRT values of ~1*10 3 g/m 2 /day (Al 2 O 3 ~26 nm) Tritiated water HTO as a radioactive tracer

16 16 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.

17 17 Literature Arora A., Padua G.W., Review: Nanocomposites in food packaging, Journal of Food Science 75(1)2010, Petersen K., Nielsen P.V., Bertelsen G., Lawther M., Olsen M.B., Nilsson N.H., Mortensen G., Potential of biobased materials for food packaging, Food Science and Technology , Puurunen, R. Surface chemistry of atomic layer deposition: A case study for the trimethylaluminium/water process Journal of Applied Physics 97, 2005, 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, KääriäinenT.O., Maydannik P., Cameron D.C., Lahtinen K., Johansson P., Kuusipalo J., Atomic layer deposition on polymer based flexible packaging materials: Growth characteristics and diffusion barrier properties. Thin Solid Films, 2011, 519, 10, Hirvikorpi T., Vähä-Nissi M., Harlin A., Merles J., Miikkulainen V., Karppinen M., Effect of corona pretreatment on the performance of gas barrier layers applied by atomic layer deposition onto polymercoated paperboard, Applied Surface Science 257 (2010) Groner,M.D.; George,S.M.; McLean,R.S.; Carcia,P.F. Gas diffusion barriers on polymers using Al 2 O 3 atomic layer deposition. Appl. Phys. Lett., 2006, 88, 5, / /3

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