Towards Roll‐to‐Roll Deposition of High Quality Moisture Barrier Films on Polymers by Atmospheric Pressure Plasma Assisted Process

Abstract

An atmospheric pressure dielectric barrier discharge (DBD) was applied for the deposition of silica-like moisture barrier films on polyethylene 2,6 naphthalate foil. The diffuse plasma was sustained between two cylindrical drum electrodes in N 2 /O 2 /Ar gas flow with the addition of tetraethyl orthosilicate. The chemical composition, morphology and water vapour transmission rate of the moisture permeation barrier layers were studied as a function of the dynamic deposition rate and substrate temperature. It was demonstrated that dense silica-like layers of 100 nm thick with a good permeation barrier of �1.8 � 10À 3 g � m À 2 � day (at 40 8C, 90% RH), corresponding to three orders of magnitude barrier improvement with respect to the pristine polymer, can be deposited in an atmospheric pressure process.

The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films

“…The experimental roll-to-roll reactor for thin film deposition was already described in detail elsewhere [5]. In brief, the system consisted of cylindrical electrodes in a bi-axial geometry, a gas injector and an independent foil transport system.…”

“…The dielectric barrier discharge (DBD) reactor type, widely employed in surface treatment applications [1] is nowadays subject of intense research for the synthesis of functional thin films either in a plane parallel or in a cylindrical electrode geometry [2][3][4][5][6][7][8][9]. In the DBD reactor with the gas mixture injected parallel to the electrodes and operating in precursor deficiency regime, the precursor depletion results in a non-uniform deposition rate profile along the gas flow [10,11].…”

“…In a recent study [11] the gradient film properties of films deposited on static substrate in an AP-PECVD reactor were investigated using spatially resolved ATR-FITR analysis. As ATR-FTIR has proved to be a valuable technique to study the intrinsic microstructure of amorphous silica films, with a focus on the relative content of hydroxyl (eOH) impurities [5,6,[29][30][31][32]. A clear variation in the film microstructure has been observed within the discharge region.…”

“…From a practical point of view this provides new insight in the possibility to scale the reactor throughput and to increase the production of high quality barrier film. Considering that the energy delivered per precursor molecule [5] should remain constant (in analogy to the similarity defined by the Yasuda parameter [34]), an increase in the throughput means an increase in reactive gas flow rates with proportional increase in power dissipated in the plasma. However, in practice this straightforward approach has limitations such as the dependency of the DBD regime on the dissipated power density, thermal sensitivity of the polymeric substrates and a limited length of the reactive plasma zone.…”

“…However, in practice this straightforward approach has limitations such as the dependency of the DBD regime on the dissipated power density, thermal sensitivity of the polymeric substrates and a limited length of the reactive plasma zone. At the same time both the dynamic deposition rate and specific energy spent per precursor molecule, as discussed in [5], represents averaged values in the PECVD reactor. Hence, the local deposition rate as well as the local plasma chemical kinetics significantly varies along the gas flow direction due to the precursor depletion.…”