CCMX, Neuchâtel, CSEM, March 26th, 2009 Barrier coating for food packaging Pierre Fayet Tetra Pak (Suisse) SA, Romont pierre.fayet@tetrapak.com Outlook: 1. Barrier coating technology 2. Mechanical characterization 3. Toughening of SiOx barrier coating 4. Conclusion
Application of Silica-based barrier coatings 10 3 PP LDPE HDPE BioPolymers Flexible solar cells Anti-reflective coatings OTR (100 um; cm3/m2/day/bar) 10 1 10-1 10-3 10-5 Flexible displays Solar modules LCP PET PEN PVDC Food products PA6 Cellulose 10-7 courtesy of LTC-EPFL 10-7 10-5 10-3 10-1 10 1 10 3 Gas-barrier coatings WVTR (100 um; g/m2/day)
Vacuum Technologies for Metal Oxide Coatings (AlOx, SiOx) Reactive Evaporation EB Evaporation PECVD Electron Beam Source Disiloxane & Oxygen Chill Drum Chill Drum Chill Drum Evaporation Source Oxygen Oxide Material Plasma 400-800 m/min 400-800m/min 100-400 m/min 50 200 nm 50 200 nm 10 20 nm (*) 3 cm 3 /m 2 /day/atm (*) 3 cm 3 /m 2 /day/atm (*) 3 cm 3 /m 2 /day/ atm Low mechanical resist Low mechanical resist. High mechanical resist. High heat input High heat input Low heat input (*) On standard PET film substrates
Oxide toughness vs. coating technology PECVD EB Evaporation Reactive Evaporation Oxides AlOx/PET SiOx/PET SiOx/BoPA 0 1 2 3 4 5 6 7 Nominal Strain
Uniaxial fragmentation tests Cohesive failure Adhesive failure Adhesion Cohesion Cohesive strength Coating toughness σ max 1/ α l 1 () l = β Γ 1+ l0 α G c = 2 σ π E c a Interfacial shear strength σ ( ) max lc IFSS = 2 hc l c W. WEIBULL. J. Appl. Mech. 18, 293-7 (1951). A. KELLY and W. R. TYSON. J. Mech. Phys. Sol. 13, 329-50 (1965). Y. Leterrier, Prog. Mater. Sci., 48, 1-55 (2003)
Tests de fragmentation: SiOx deposited on PE & PET films Leterrier Y., Rochat G., Månson J.-A.E., Fayet P., Proc. 44th Ann. Conf. Soc. Vacuum Coaters, Boston, MA, April 18-23 (1998)
What before fragmentation? AFM allows to see what has been up-to-now hidden be the other used methods Buckling 3% strained 10 nm SiOx / RDO12 Buckling patterns patterns no no cracks! cracks! SiOx Buckling might be due to energy transfer at the interface between PET substrate and SiOx coating. This effect is reversible!
What before fragmentation? The density of wrinkles increases before the initiation of fragmentation, and then decreases until it vanishes 1.40 1.20 1.00 Density [1/mu] 0.80 0.60 0.40 0.20 Crack Density Wrinkles Density 0.00 0.00 5.00 10.00 15.00 20.00 25.00 Nominal Strain [%] 10 nm SiOx / RDO12 G. Rochat, A. David, F. Sommer, P. Fayet, Proceedings AIMCAL Technical Fall conference 2007 G. Rochat, A. David, F. Sommer, P. Fayet, Vacuum Tech. & Coating, June 2008, 73-77
Healing of SiOx by UV-curable silane top-coating Oxide layer Microdefects Polymer substrate Nanodefects UV-Crosslinked polysiloxane layer Polymer substrate Organosilane layer deposition Polymer substrate Patent appl. WO2008/122293A1 Submitted to Surf. Coat. Technol. Y. Leterrier, B. Singh, J. Bouchet, J.-A.E. Månson, G. Rochat, P. Fayet
Barrier improvement SiOx 50 nm Oxygen Transmission Rate [cm 3 /(m 2.day.bar)] 2.5 2 1.5 1 0.5 0 VTS (2%PI-2)/SiO 2-48/PET MPMS (2%PI-2)/SiO 2-48/PET 0 5 10 15 20 CH 3 Vinyltrimethoxysilane (VST) H 2 C O Si O O CH 3 CH 3 CH 3 γ-methacryloxypropyltriethoxysilane (MPMS) O OEt Silane concentration [%] CH 2 C C O (CH 2 ) 3 Si OEt OEt
Strain effect on SiOx and Silane coated SiOx 100 SiOx 10 nm/pet VS/10 nm SiOx/PET 100 SiOx 50 nm VS 369-av. 50 nm SiOx (8 samples) OTR (cm 3 /m 2 /day/bar) 10 OTR (cm 3 /m 2 /day/bar) 10 1 1-0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08-0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Strain Strain Critical strain: 4.2 5.2% Critical strain: 1.5 5.1% Toughness: 11.3 17.3 J/m 2 Toughness: 6.9 80.0 J/m 2 the microstructure and defect population of the hybrid silane-silica coating, which control the toughness of the material, are very different for the two considered
Conclusion Plasma produced barrier coatings have been applied for large throughput, low cost production in food packaging AFM coupled with a micro-tensile stage is a versatile nondestructive technique allowing to: follow in situ cracks initiation and crack growth in inorganic coatings deposited on polymer substrates determine mechanical properties and surface morphology The modification of SiOx coatings with UV-curable silanes resulted in combined improvement of oxygen barrier and critical failure strain The key factor, which controls the property improvement of the hybrid UV-curable silane-silica coatings is the chemical conversion state of the silane
Thanks for your attention Fragmentation test Yves Leterrier Jan-Anders E. Månson Plasma technology Christoph Hollenstein Surface analysis/ AFM Biophy Research, France