coated abrasive binders made from a photocurable addition - polymerizable composition containing a free - radically - polymerizable monomer and a photoinitiator system containing an arylidonium salt , a sensitizing compound , and an electron donor having an oxidation potential that is greater than zero and less than or equal to that of p - dimethoxybenzene . the binders cure rapidly and deeply under ultraviolet or visible light , even when filled with large amounts of mineral grain or with coarse grades of minerals .