Organic modification of layered silicates for use as barrier pigments in coating systems

Functional coatings and the barrier pigments they contain are an indispensable part of corrosion or product protection. The frequently used layered silicates in their pure form often do not achieve a sufficient protection of the components or products. The barrier effect of the silicates can be significantly improved through targeted organic modification. The general use of commercial (unmodified) silicates leads to an improvement in the barrier of about 20 %. In contrast, the use of modified silicates achieves an improvement of up to 80 % [1], due to the extent of the diffusion path [2]. Decisive for the diffusion path and therefore for the subsequent functionality of the barrier is the exfoliation and orientation of the silicates, which depends on the compatibility with the coating system. Due to the large number of coating systems and the associated binder classes, the silicates should be specifically adapted to the respective polymer by being modified with reactive groups, which represents the main focus of this work. As a first polymer system an epoxy matrix was chosen. Thus, commercial silicates were modified by an epoxy-oligomer matrix based on 1,4-butanediol diglycidyl ether. The produced silicates were examined with the aid of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The expansion of the layers and the attachment of the organic molecules were investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS)

Freeze Drying of Organically Modified Layered Silicates as Key Step to Improve the Barrier Properties of Organic Coatings for High Power Electronics Protection

Abstract Organically modified layered silicates can be used as barrier pigments in organic coating systems to reduce the permeation of water vapor and gases, e.g., oxygen as well as harmful gases that promote corrosion. Unmodified layered silicates are not sufficient to reduce the permeation significantly. However, the arrangement and orientation of the particles have an enormous impact on the later performance in the barrier film. In organic solvents or non‐aqueous polymer matrices the non‐modified layered silicates cannot exfoliate adequately. The organic modification influences the layer spacing and the compatibility to organic solvents. Layered silicates are modified with dodecylamine to enhance the spacing layer. The spacing layer is enhanced by 55% caused by the organic modification as it is commonly known. In contrast to previous work freeze drying of the organically modified layered silicates improved the particle distribution and by this barrier properties significantly. The modified particles reduce the diffusion of water and oxygen by ≈99.6% and 97.2%, respectively. The corrosive gas test of electronic circuit boards shows no growth of dendrites and no failure of the electronics in contrast to protective coating without the layered silicates