Surface modification of polyethylene terephthalate (PET) and oxide coated PET for adhesion improvement AIMCAL 2016 Dresden Juliane Fichtner Tobias Beck Frank Simon (IPF, Dresden) page 1
Motivation oxygen water vapor organic electronics permeation barrier system flexible solar cell organic electronics page 2 flexible OLED
Motivation varnish ZTO / SiOx varnish ZTO / SiOx varnish PET varnish ZTO / SiOx varnish ZTO / SiOx PET 10 µm 50 nm 75 µm sufficient wetting behavior and adhesion for good performance necessary page 3! BUT low surface energies and impurities! surface modification
Process parameter low pressure plasma treatment web width: 220 mm dual magnetron bipolar mode electrical power: 1 5 kw web speed: 1 5 m/min process pressure: 0.5 2.5 Pa page 4
Varnish layer manufacturing acrylic based varnish layer thickness: 10 µm curing dose: 25 kgy acceleration voltage: 150 kv electron current: 2 ma motion speed: 150 mm/s page 5
Characterization wetting behavior surface energy test inks if surface energy change < 5% samples removed dynamic advancing contact angle measurement analyzed by tangent method page 6
Characterization surface chemistry x-ray photoelectron spectroscopy (XPS) binding energy chemical bonding characteristics ATR FT-IR spectroscopy varnish adhesion pull-off test page 7
Sample comparison - activation intensity X i electrical power: 1 5 kw web speed: 1 5 m/min process pressure: 0.5 2.5 Pa influence on the absolut number of collisions of ions on the sample influences the electrical current X i = (I 1 + I 2 ) t page 8
Wetting behavior O 2 -plasma contact angle ZTO surface cleaning PET + SiO x contact angle page 9 surface modification
Surface modification - PET - O 2 -plasma Ph C E Sh D F C-atoms of phenyl ring C-atoms with one O-atom and CH 2 C-atoms carboxylic acid ester Peaks of π-electrons C-atoms of keto group C-atoms of carboxyl group page 10
Surface modification - PET - O 2 -plasma carboxylic acid ester + carboxyl groups carboxyl group decarboxylation page 11
Wetting behavior - SiO x - O 2 -plasma Hybrid SiO x enrichment with oxygen functional groups: hydroxy, keto and carbon acid groups polar character page 12
Varnish adhesion - O 2 -plasma adhesion on SiO x = Si-OH groups interact well with water by hydrogen bonds, but no effect on varnish adhesion PET: electron beam additional chemical bonding to the varnish page 13
Wetting behavior N 2 -plasma Contact angle similar for all substrates page 14
Surface modification - PET - N 2 -plasma atom fraction O:C (0,34 to 0,1) atom fraction N:C (0 to 0,46) carbon nitrides page 15
Surface modification - PET - N 2 -plasma atom fraction O:C (0,34 to 0,1) atom fraction N:C (0 to 0,46) carbon nitrides page 16
Surface modification - FTIR-ATR - N 2 -plasma C thin layer nitrogen-rich heterocycles 1,3-Diazabenzene or 1,4-Diazabenzene page 17
Varnish adhesion - N 2 -plasma max. adhesion: PET 2.3 MPa SiO x 1.5 MPa ZTO 1.2 MPa activation intensity nitrogen content adhesion page 18
Process gas mixtures - visual transmittance constant visual transmittance up to 80 v/v% nitrogen page 19
Process gas mixtures contact angle nitrogen content ZTO: contact angle + PET: contact angle page 20
Process gas mixtures varnish adhesion - ZTO max. adhesion of 0.8 MPa (nitrogen content of 70 v/v%) page 21
Atmospheric pressure electron beam radiation e- beam treatment lowers contact angle for all samples dose contact angle page 22
Surface modification - PET - N 2 -electron beam PET N 2 - electron beam no cracked or decomposed PET chains potentially carbon acid amides (C=C-NH-C) page 23 Binding Energy [ev]
Varnish adhesion - N 2 - electron beam max. adhesion: PET 2.1 MPa SiO x 1.7 MPa ZTO 0,7 MPa activation intensity nitrogen content adhesion page 24
Permeation rates plasma gas X i [As] WVTR [g/(m 2 *d)] OTR [cm 3 /(m 2 *d*bar)] non 0 0.067 0.25 N 2 172.8 0.069 0.2 O 2 184.8 0.076 0.3 Dose WVTR OTR atmosphere [kgy] [g/(m 2 *d)] [cm 3 /(m 2 *d*bar)] N 2 300 0,069 0,2 no influence of the plasma treatment and electron beam treatment on permeation barrier properties page 25
Conclusions low pressure plasma treatment Plasma gas composition varnish adhesion [MPa] PET SiO x ZTO non 0.7 0.5 no wettability 100 v/v% oxygen 2.7 0.7 no wettability 100 v/v% nitrogen 2.3 1.5 1.2 70 v/v% nitrogen 30 v/v% oxygen no value no value 0.8 increasing of varnish adhesion without impact on: transmittance permeation barrier properties page 26
Conclusions atmospheric pressure e-beam treatment Dose [kgy] varnish adhesion [MPa] PET SiO x ZTO non 0.7 0.5 no wettability 150 1.7 0.8 0.7 300 2.1 1.7 0.6 increasing of varnish adhesion without impact on: transmittance permeation barrier properties page 27
Thank you for your interest!! Contact: Dipl.-Ing. Juliane Fichtner Fraunhofer FEP Winterbergstr. 28 01277 Dresden, Germany Tel: +49 (351) 2586 145 juliane.fichtner@fep.fraunhofer.de www.fep.fraunhofer.de Parts of the results have been obtained within public funded research projects supported by the Free State of Saxony. page 28