PURPOSE: To obtain the titled coating material maintaining its flexibility even when allowed to stand at a high temp. over a long term and capable of further improving the transmission characteristics, by using hydrogenated 1,4-polybutadine as a part or all of a base.

CONSTITUTION: The titled coating material contains hydrogenated 1,4-polybutadiene (A) having two or more functional groups in one molecule such as a compound obtd. by hydrogenating 1,4-polybutadiene having two or more hydroxyl groups, isocyanate groups or carboxyl groups in one molecule, a mixture (B) of the component A with unhydrogenated 1,4-polybutadiene having two or more functional groups in one molecule, or modified polybutadiene (C) derived from the component A or B and having introduced polymerizable C-C double bends different from C-C double bonds which may remain in the component A or are contained in the component B such as polybutadiene modified with butyl triethylene glycol acrylate.