Examination of universal microhardness of liard reaction layers resulting from reactions of organic polymers with container glass surfaces and their use for low-friction protective layers

Abstract

Clear, highly alkaline and wear-resistant hard reaction layers are formed by direct alkaline coupling of organic polymers with functional groups, particularly high-molecular polyols, to siliceous glass surfaces having container glass compositions. As compared with untreated glass these are characterized by an increased universal hardness and an excellent scratch resistance. Formation of these layers requires a highly alkahne reaction medium, e.g. 2% NaOH, 85°C, according to the conditions of the alkaline washing process of returnable beverage bottles in the bottling plants. It can be assumed that the formation of the reaction layer is associated with the formation of highly molecular ionic polymers with 5-coordinated silicon. Results of universal microhardness measurements of the hard reaction layers which were formed with aqueous polymer dispersions (epoxy resin microdispersion; low-molecular oxidized polyethylene) are presented. The increase of plastic universal hardness in comparison with untreated glass demonstrates the enhanced wear resistance of these layers. So far layer thicknesses up to 0.3 µm could be achieved. These results suggest new approaches to develop highly efficient low-friction protective layers for returnable bottles, and after increasing the thickness of the hard reaction layer up to several micrometers, they could possibly be applied also to lightweight bottles under enhanced internal pressure as used for carbonated beverages. Universal microhardness measurements are a very useful tool in the development and most effective improvement of such novel low-friction protective coatings for container glass.