Abrasive articles have been utilized to abrade and finish workpieces surfaces for well over a hundred years. These applications have ranged from high stock removal, high pressure metal grinding processes to fine polishing, such as of ophthalmic lenses. In general, abrasive articles are made of a plurality of abrasive particles bonded either together (e.g., a bonded abrasive or grinding wheel) or to a backing (e.g., a coated abrasive). For a coated abrasive there is typically a single layer, or sometimes two layers, of abrasive particles. Once these abrasive particles are worn, the coated abrasive is essentially worn out and is typically discarded.
One solution to this single layer of abrasive particles is described U.S. Pat. No. 4,652,275 (Bloecher et al.); U.S. Pat. No. 4,799,939 (Bloecher et al.) and U.S. Pat. No. 5,039,311 (Bloecher). The coated abrasive articles that are disclosed in these references have a plurality of abrasive agglomerates bonded to a backing. The abrasive agglomerate is a shaped mass comprising abrasive particles, a binder, optionally a grinding aid, and optionally other additives. These abrasive agglomerates essentially result in a three dimensional coating of abrasive particles forming the abrasive article.
Another three dimensional coating of abrasive particles is an abrasive lapping film. A lapping film, like that disclosed in U.S. Pat. No. 4,644,703 (Kaczmarek et al.), U.S. Pat. No. 4,773,920
Another three dimensional coating of abrasive particles is an abrasive lapping film. A lapping film, like that disclosed in U.S. Pat. No. 4,644,703 (Kaczmarek et al.), U.S. Pat. No. 4,773,920 (Chasman et al.) and U.S. Pat. No. 5,015,266 (Yamamoto), is made from an abrasive slurry comprising abrasive particles and a binder, which is bonded to a backing. Although these lapping films have had wide commercial success in polishing applications where a fine surface finish on a workpiece is desired, these lapping films do not always have the desired rate of cut for many other applications.
A more recent development in three dimensional coatings of abrasive particles has provided abrasive articles often referred to as “structured abrasives”. Various constructions of structured abrasive articles are disclosed, for example, in U.S. Pat. No. 5,152,917 (Pieper et al.). Pieper teaches a structured abrasive that results in a relatively high rate of cut and a relatively fine surface finish on the workpiece surface. The structured abrasive comprises non-random, precisely shaped abrasive composites that are bonded to a backing. Other references directed to structured abrasive articles and methods of making them include U.S. Pat. No. 5,855,632 (Stoetzel et al.), U.S. Pat. No. 5,681,217 (Hoopman et al.), U.S. Pat. No. 5,435,816 (Spurgeon et al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S. Pat. No. 5,304,223 (Pieper et al.), and U.S. Pat. No. 5,014,468 (Ravipati et al.). Pieper, and the other structure abrasive patents, are a significant advancement in the abrasives art, however there is always room for improvement for large stock removal and extended life.