Coated abrasive articles generally comprise a backing layer to which a multiplicity of abrasive particles are bonded. In one form, the abrasive particles are bonded to the backing by a first binder, commonly called a make coat. A second binder, commonly called a size coat, is then applied over the make coat and the abrasive particles to reinforce the particles. In a second form, commonly called a slurry coated abrasive coating, the abrasive particles are dispersed throughout a cured binder which bonds the abrasive coating to the backing.
Backings for coated abrasives have been made from a variety of materials, depending upon the product requirements. For example, paper, nonwoven webs, cloth, vulcanized fibers, polymeric film, and combinations thereof have all been used as coated abrasive backings. The choice of a particular backing material for an abrasive article typically involves balancing factors such as cost, strength, tear resistance, adhesion of abrasive coatings, surface finish of the backing, water resistance, and the like in order to select the backing material having the best balance of properties for the desired application.
For example, an advantageous feature in some abrasive articles is easy tearability. Preferred tearable abrasive articles can be torn in straight fashion either in the down-web or cross-web direction thereby allowing the user to tear a sheet of coated abrasive to the desired size without the need for a cutting instrument. Woven cloth backings have typically been used when tearability is desired since the woven nature of the cloth results in a backing which can be torn in straight fashion.
Another advantageous feature in some abrasive articles is a water resistant construction. As used herein xe2x80x9cwater resistantxe2x80x9d means that the performance of the abrasive article is not substantially reduced when the abrasive article is wet or is used to abrade a wet surface. Woven cloth backings typically require expensive treatment coatings in order to produce an abrasive article which is water resistant.
Accordingly, there is a need for a more cost effective water resistant tearable abrasive article.
The present invention provides an abrasive article comprising a backing and an abrasive coating. The backing comprises a polymer film and a scrim which is partially embedded into the polymer film.
The scrim comprises a plurality of generally parallel warp elements which extend in a first (down-web) direction and a plurality of generally parallel weft elements which extend in a second (cross-web) direction. The second direction is perpendicular from the first direction. As used herein xe2x80x9cwarp elementxe2x80x9d refers to an element which extends in the down-web direction in a scrim. As used herein xe2x80x9cweft elementxe2x80x9d refers to an element which extends in the cross-web direction in a scrim. The warp and weft elements may be combined by weaving, stichbonding, or adhesive bonding. The warp and weft elements may be fibers, filaments, threads, yarns or a combination thereof. In a preferred embodiment, the warp and weft elements are yarns which are woven together in a one-over-one weave.
The scrim is partially embedded in the polymer film. As used herein xe2x80x9cpartially embeddedxe2x80x9d means that the scrim is embedded in the polymer film but is not completely encased or surrounded by the polymer film. The polymer film is made of a melt processable polymer including thermoplastics, thermoplastic elastomers, elastomers, and blends thereof. Preferably, the polymer is polyethylene since it is inexpensive and is water resistant.
Bonded to at least one side of the backing is an abrasive coating including a binder and a plurality of abrasive particles. The abrasive coating may be a conventional abrasive coating (i.e., having a make coat and a size coat which bond the abrasive particles to the backing) or the abrasive coating may be formed from a slurry. The abrasive coating may be bonded to either the first side or the second side of the backing. In a preferred embodiment, the abrasive coating is bonded to the first side of the backing over the scrim and the polymer film.
The preferred binders are radiation curable because they may be cured on heat sensitive backings (e.g., polyethylene) without damaging the backing and because they may provide an abrasive coating having water resistance. A particularly preferred abrasive coating includes a radiation curable hot melt make coating including an epoxy resin, a polyester component, a polyfunctional acrylate, and a curing agent.
Abrasive articles of the present invention are tearable along a substantially straight line in the first direction and in the second direction. As used herein xe2x80x9ctearablexe2x80x9d means that the article can be pulled apart or ripped into pieces using hand generated force. The warp and weft elements of the scrim provide directional control to the tear. That is, the abrasive article will typically tear in a direction which is substantially parallel to a warp or weft element.