| 摘要 |
PURPOSE:To prevent generation of crack upon bending with a large curvature, by using tetraol having an average molecular weight less than a specific value, which is alkylene oxide addition polymer of ethylenediamine, as a polyol component of polyurethane. CONSTITUTION:A transparent synthetic resin layer 2 is formed on the upper surface of a base 1 by potting a polyurethane material thereon. Polyurethane is a reaction product from a polyether polyol component and an aliphatic isocyanate component. As the polyol component, used is tetraol having an average molecular weight less than 1,100, which is an alkylene oxide addition polymer of ethylenediamine. A compounding ratio of the polyol component and the isocyanate component is normally set to 1>OH/NCO>1/1.3. |
