Henrik Behm

Surface pre-treatment for barrier coatings on polyethylene terephthalate

Polymers have favourable properties such as light weight, flexibility and transparency. Consequently, this makes them suitable for food packaging, organic light-emitting diodes and flexible solar cells. Nonetheless, raw plastics do not possess sufficient barrier functionality against oxygen and water vapour, which is of paramount importance for most applications. A widespread solution is to deposit thin silicon oxide layers using plasma processes. However, silicon oxide layers do not always fulfil the requirements concerning adhesion and barrier performance when deposited on films. Thus, plasma pre-treatment is often necessary. To analyse the influence of a plasma-based pre-treatment on barrier performance, different plasma pre-treatments on three reactor setups were applied to a very smooth polyethylene terephthalate film before depositing a silicon oxide barrier layer. In this paper, the influence of oxygen and argon plasma pre-treatments towards the barrier performance is discussed examining the chemical and topological change of the film.It was observed that a short one-to-ten-second plasma treatment can reduce the oxygen transmission rate by a factor of five. The surface chemistry and the surface topography change significantly for these short treatment times, leading to an increased surface energy. The surface roughness rises slowly due to the development of small spots in the nanometre range. For very long treatment times, surface roughness of the order of the barrier layers thickness results in a complete loss of barrier properties. During plasma pre-treatment, the trade-off between surface activation and roughening of the surface has to be carefully considered.

Influence of layer type and order on barrier properties of multilayer PECVD barrier coatings

Due to their macromolecular structure, plastics are limited in their scope of application whenever high barrier functionality against oxygen and water vapour permeation is required. One solution is the deposition of thin silicon oxide coatings in plasma-enhanced chemical vapour deposition (PECVD) processes. A way to improve performance of barrier coatings is the use of multilayer structures built from dyad layers, which combine an inorganic barrier layer and an organic intermediate layer. In order to investigate the influence of type and number of dyads on the barrier performance of coated 23 µm PET films, different dyad setups are chosen. The setups include SiOCH interlayers and SiOx-barrier layers deposited using the precursor hexamethyldisiloxane (HMDSO). A single reactor setup driven in pulsed microwave plasma (MW) mode as well as capacitively coupled plasma (CCP) mode is chosen. In this paper the effects of a variation in intermediate layer recipe and stacking order using dyad setups on the oxygen barrier properties of multilayer coatings are discussed with regard to the chemical structure, morphology and activation energy of the permeation process.Changes in surface nano-morphology of intermediate layers have a strong impact on the barrier properties of subsequent glass-like coatings. Even a complete failure of the barrier is observed. Therefore, when depositing multilayer barrier coatings, stacking order has to be considered.

The effect of UV radiation from oxygen and argon plasma on the adhesion of organosilicon coatings on polypropylene

The influence of ultraviolet (UV) radiation from oxygen and argon pretreatment plasmas on a plastic substrate has not been fully understood yet. In particular, its influence on the adhesion properties has not been sufficiently researched so far. This paper addresses this issue by comparing the bond strength of a plasmapolymerized silicon organic coating (SiO x C y H z ) on polypropylene (PP) after oxygen and argon plasma pretreatment and pretreatment by UV radiation emitted by the same plasmas. The UV radiation is isolated from the other species from the plasma by means of a magnesium fluoride (MgF2) optical filter. It could be shown that UV radiation originating from an oxygen plasma has a significant impact on both substrate surface chemistry and coating adhesion. The same maximum bond strength enhancement can be reached by pretreating the polypropylene surface either with pulsed oxygen plasma, or with only the UV radiation from this oxygen plasma. Also, similar surface chemistry and topography modifications are induced. For argon plasma no significant influence of its UV radiation on the substrate could be observed in this study.

Improvement of bonding properties of laser transmission welded, dissimilar thermoplastics by plasma surface treatment

Compared to different welding methods such as ultrasonic welding, laser transmission welding is a relatively new technology to join thermoplastic parts. The most significant advantages over other methods are the contactless energy input which can be controlled very precisely and the low mechanical loads on the welded parts. Therefore, laser transmission welding is used in various areas of application, for example in medical technology or for assembling headlights in the automotive sector. However, there are several challenges in welding dissimilar thermoplastics. This may be due to different melting points on the one hand and different polarities on the other hand. So far these problems are faced with the intermediate layer technique. In this process a layer bonding together the two components is placed between the components. This means that an additional step in the production is needed to apply the extra layer. To avoid this additional step, different ways of joining dissimilar thermoplastics are inves...

A novel approach for an in-line atmospheric plasma-treatment of polymers and reinforcements during extrusion

A novel approach for an in-line atmospheric plasma-treatment of composites or blends during extrusion processing using a twin screw extruder is reported. The atmospheric plasma-treatment takes place in a partially filled zone of the twin screw extruder. Exemplarily, a glass fibre-reinforced polypropylene (PP) composite and a polypropylene-polyamide 6-blend (PP-PA6-blend) are processed using the in-line atmospheric plasma treatment process. For both systems a slight increase of Young’s modulus and a slight decrease of the elongation at break are observed, while the tensile strength and the notched impact strength of the glass fibre reinforced polypropylene composites are barely affected. The Charpy notched impact strength of the PP-PA6-blend is improved by almost 43 % from 22.5 kJ/m2 to 32.1 kJ/m2 by applying the in-line atmospheric plasma-treatment process.

Erhöhung der Flexibilität von Barrierebeschichtungen

A ihrer Verarbeitungsbedingungen und der geringen Materialdicke stellen Kunststo folien besondere Anforderungen an eine Veredelung im Plasma. In vielen Fällen soll dabei die durch die makromolekulare Struktur des Kunststo s bedingte, hohe Durchlässigkeit der Folien gegenüber üchtigen Medien, wie zum Beispiel Sauersto oder Wasserdampf, verringert werden. Der Einsatzbereich plasmapolymerer Barrierebeschichtungen zur Verringerung der Permeation wird jedoch zumeist durch die hohe Flexibilität der Kunststofffolie beschränkt. Die Entstehung dehnungsinduzierter Risse in der Beschichtung ist für verschiedene plasmapolymere Schichten unter Belastung untersucht und beschrieben worden [ALF03, HMGW09, YHRG01]. Abgeschieden auf Polyethylenterephthalat (PET) verlieren silizium-basierte Sperrschichten (SiOx) zumeist ab einer geringen Substratdehnung von circa 2 % ihre Sperrwirkung. Kohlenwasserstoffbasierte (a-C:H) beziehungsweise siliziumorganische (SiOCH) Schichtsysteme ertragen Dehnungen > 4 %. Der Ansatz ist daher, durch Kombination der verschiedenen Schichtarten unterschiedlicher Sprödheit plasmapolymere Mehrschichtsysteme zu entwickeln, welche bei Dehnungen von 4 % noch eine deutliche Barrierewirkung aufweisen. In alternierend aufgebauten Mehrschichtsystemen sollen spröde, anorganische SiOx-artige Schichten die Barrierefunktion übernehmen sowie weiche, organische Schichten die Flexibilität des Verbundes sicherstellen. Hierzu werden an den zwei Standorten verschiedene Niederdruck-Anlagen zur plasmagestützten Beschichtung von PET-Folien (Hostaphan RN36, Dicke: 36 μm, OTR: circa 45 cm3/(m2 day bar)) der Firma Mitsubishi Polyester Films GmbH, Wiesbaden, eingesetzt. Die Anlagen erlauben die Beschichtung von Folien im Rollezu-Rolle-Verfahren mit Hilfe von Radiofrequenz(RF, IFAM) beziehungsweise Mikrowellen-Plasmen (MW, IKV). Im Hinblick auf eine mögliche spätere industrielle Umsetzung des Verfahrens soll durch den Vergleich der Ergebnisse der Ein uss der Anregungsart auf die Eigenscha en der Beschichtung untersucht werden.