Sabine Amberg-Schwab

Barrier Properties OF Inorganic-Organic Polymers: Influence of Starting Compounds, Curing Conditions and Storage-Scaling-Up to Industrial Application—

With a new kind of barrier coating material, namely inorganic-organic polymers, it is possible to obtain high-barrier properties for oxygen, water vapor, and flavor permeation. These hybrid polymers can be synthesized by the sol-gel technique. Network forming reactions and degrees of condensation in the coating sols as well as in the cured coating materials were characterized using 29Si, 13C-NMR and FT-Raman spectroscopy. The oxygen barrier properties of the hybrid polymers were found to be strongly influenced by the inorganic and also by the organic network density. In order to scale-up the excellent laboratory results to pilot plant and production dimensions additional efforts were necessary. For optimization of the barrier coating compositions the influence of the starting compounds on the resulting barrier properties had to be investigated. A constant quality of the coating sols during the industrial processing had to be guaranteed so as to obtain reproducible barrier properties. The influence of storage conditions on chemical reactions in the coating sols, indicated by changes of viscosity, was investigated. Since the curing times of the laboratory system were not transferable to the high speed of the production roll coating process more effective curing methods had to be found. The influence of the storage time of the cured coating materials on the oxygen barrier properties was investigated. Even by storing at ambient temperature further improvement of the oxygen barrier properties was obtained. Only by optimizing all of the above mentioned parameters can the excellent barrier properties result in marketable products.

Inorganic-Organic Polymers as Migration Barriers Against Liquid and Volatile Compounds

In addition to the barrier properties against water vapor and oxygen, inorganic-organic polymers can also function as protection layers against unwanted migration of chemical substances in two ways. First, hybrid polymers prevent components from migrating out of polymer substrates. This is of special interest for polymeric materials containing substances like plasticizing agents, unreacted monomers or catalysts. Thus the olfactory nuisance and the toxicological emission are decreased. The plastics are also prevented from becoming prematurely brittle. Second, the coated materials are also protected against the interaction of dyes or dirt staining the material.These functions can be achieved by thermally or UV curable coating materials, synthesized by the sol-gel technique. Since several polymer materials show only a low heat resistance (e.g. PVC, polyolefines), this publication is focussed on the development of new migration barriers based on photochemically curable sols.Another advantage of the UV process in comparison to thermal treatments are the short curing times and low power consumption which make this process even more attractive for industrial applications. The coatings were characterized by IR and solid state NMR spectroscopy. The migration barrier properties were tested according to industrial standards.Due to the choice of specific functional groups, these hybrid polymers can be further modified in order to combine the migration barrier function with additional properties: scratch and abrasion resistance, hydrophobicity, antistatic effects. Examples of feasible combinations of properties are also given.

Multilayer coatings for flexible high-barrier materials

A multilayer, flexible, and transparent high-barrier system based on flexible plastic foils, polyethyleneterephthalate (PET) and ethylene-tetrafluoroethylene-copolymer (ETFE), combined with vacuum-deposited, inorganic SiOx layers and hybrid ORMOCER® varnish layers were prepared in different orders on a semiproduction level. Barrier properties of prepared systems, as water vapour transmission (WVTR) and oxygen transmission (OTR), were measured and studied in connection with surface energy, surface topography, and water vapour adsorption properties. Correlations among layers sequence, barrier properties, and other parameters are presented, including some basic principles of permeation of substances through multilayer barrier systems. A combination of several inorganic and hybrid varnish layers is necessary to achieve the technological demands from a barrier standpoint. It is easier to suppress the oxygen transport than the water transport, due to the additional active penetration of water through hydrogen bonds and silanol creations at oxide interfaces, capillary condensation, and swelling with high internal pressure, leading to new defects.