1. Field of the Invention
The invention pertains to a transparent polyurethane coating layer, with self-repairing properties, for panes made of glass and/or plastic materials, with the coating layer according to the invention being prepared from a reactive mixture containing a plurifunctional, and specifically a trifunctional, isocyanate component and a plurifunctional polyalcohol component, possibly a reaction catalyst and other auxiliary substances.
2. Background of the Prior Art
Polyurethane coating layers with self-repairing properties are utilized especially as anti-shattering coatings for silicate glass panes, for example, in automobile windshields. This application, is described, for example, in French patent publications Nos. 2 187 719 and 2 251 608. These layers, which are placed on the surface of the window which faces inward, prevent direct contact with the sharp edges of the glass fragments in case the window breaks. In this configuration, the coating layers are protected against direct atmospheric influences by the layer(s) of glass.
Coatings of this type are also utilized as coating layers for transparent plastic materials. German patent publications Nos. 2 058 504, 2 634 816, 3 201 849 describe such an application. In this case, these polyurethane layers serve to improve the scratch resistance of plastic material. The aforementioned polyurethane coatings in fact have the characteristic of being self-repairing, i.e., superficial deformations in these layers disappear after a certain period of time, with the duration of this disappearance generally depending on the temperature.
Such self-repairing polyurethane coating layers can also find applications as coatings for surfaces of panes made of glass and/or plastic materials, which are exposed to the external atmosphere, either to improve the resistance of the plastic materials to scratching, or to improve the resistance of glass to abrasion. It is in fact known that these soft coating layers are also highly suitable to significantly improve the resistance of glass to abrasion, for example, during periods in which they are exposed to contact with sand.
Known polyurethane coating layers have remarkable properties, not only in the area of scratch resistance and other usage properties, but also, especially, in the area of the long-term durability of these properties, as long as these layers are not exposed simultaneously to the influence of light, heat and humidity, i.e., as long as they are not directly exposed to the open atmosphere, namely, direct sunlight and simultaneous exposure to humidity and rain. It was found that, during such exposure to the elements, apparently, due to the effects of light and the simultaneous hydrolytic attack by water, the surface of the coating layers becomes damaged over time. After a certain period of time, this surface deterioration is visible to the naked eye and continues uninterrupted. Consequently, coating layers of known formulas are not appropriate in the long term for use on the external surface of a pane, i.e. which is directly exposed to the outside atmosphere and a continued need for the same is presented.