Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-04-06
2003-10-21
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S424000, C525S427000, C525S428000, C525S429000
Reexamination Certificate
active
06635719
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to coating compositions for abrasive backings and particularly to those compositions containing an aminoplast resin and a thermoplastic resin.
Coated abrasives generally comprise a flexible backing upon which a binder holds and supports a coating of abrasive grains. The backing can be selected from paper, cloth, film, vulcanized fiber, etc., or a combination of one or more of these materials. The abrasive grains can be formed of flint, garnet, aluminum oxide, alumina-zirconia, ceramic aluminum oxide, diamond, silicon carbide, and the like. Binders are commonly selected from phenolic resins, hide glue, urea-formaldehyde resins, urethane resins, epoxy resins, and varnish. Phenolic resins include those of the phenol-aldehyde type.
Coated abrasives may employ a make coat of resinous binder material in order to secure the abrasive grains to the backing, and a size coat of resinous binder material can be applied over the make coat and abrasive grains in order to more firmly bond the abrasive grains to the backing. The resinous material of the make and size coats may be the same material or may be different materials. A common resinous material used for both make and size coatings is generically referred to as phenolic resin. Phenolic resins are a class of materials made from the reaction of phenol with various aldehydes.
Phenolic resins are commonly used in coated abrasive articles because of their high adhesive strength to abrasive particles, durability, and high thermal stability. There are two types of phenolic resins, resole and novolac. Resole phenolic resins have a molar ratio of formaldehyde to phenol greater than or equal to one to one, typically between 1.5:1.0 to 3.0:1.0. Novolac resins have a molar ratio of formaldehyde to phenol less than one to one.
The phenolic resins contain about 70 percent to about 85 percent solids, and preferably contain about 72 percent to about 82 percent solids. If the percent solids is very low, then more energy is required to remove the water and/or solvent. If the percent solids is very high, then the viscosity of the resulting phenolic resin is too high which leads to processing problems. The remainder of the phenolic resin is preferably water with substantially no organic solvent due to environmental concerns with the manufacturing of substantially no organic solvent due to environmental concerns with the manufacturing of abrasive articles. Examples of commercially available phenolic resins include those known under the trade designations VARCUM and DUREZ, available from Occidental Chemical Corp., Tonawanda, N.Y.; AROFENE and AROTAP, available from Ashland Chemical Company, Columbus, Ohio; RESINOX, available from Monsanto, St. Louis, Mo.; and BAKELITE, available from Union Carbide, Danbury, Conn.
Although phenolic resins are widely used in the coated abrasives industry, phenolic resins do not adhere well to some types of backing materials. Poor adhesion may cause the phenolic binder to peel away or shear off prematurely as the abrasive article is subjected to normal use. This lack of adhesion limits the types of backings that can be used in coated abrasive articles that use phenolic resin binders.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a treated substrate for an abrasive article. The treatment coat, also called a “presize” is made from a binder precursor or curable composition comprising an oligomeric aminoplast resin having on average at least one pendant &agr;,&bgr;-unsaturated carbonyl group per oligomeric unit, a thermoplastic polyamide, and a catalyst for crosslinking or curing the &agr;,&bgr;-unsaturated functionality of the aminoplast resin.
In another aspect, the invention provides a substrate for an abrasive article comprising a) a backing; and b) a crosslinked treatment coat on said backing, said treatment coat is formed from a curable precursor composition comprising a mixture of i) from about 30 to about 60 weight percent of an oligomeric aminoplast resin having on average at least one pendant &agr;,&bgr;-unsaturated carbonyl group per oligomeric unit, ii) from about 70 to about 40 weight percent of a thermoplastic polyamide miscible in said aminoplast resin, the weight percents being based on the total resin content, and iii) a sufficient amount of a catalyst for the curable oligomeric aminoplast resin having on average at least one pendant &agr;,&bgr;-unsaturated carbonyl group per oligomeric unit, said catalyst being stable at the temperature of mixing of the components.
In another aspect, the invention provides a curable precursor composition comprising a) from about 30 to about 60 weight percent of an oligomeric aminoplast resin having on average at least one pendant &agr;,&bgr;-unsaturated carbonyl group per oligomeric unit; b) from about 70 to about 40 weight percent of a thermoplastic polyamide miscible in said aminoplast resin, the weight percents being based on the total resin content; and c) a sufficient amount of a catalyst for the curable oligomeric aminoplast resin having on average at least one pendant &agr;,&bgr;-unsaturated carbonyl group per oligomeric unit, said catalyst being stable at temperature of mixing of the components.
The cured composition is also useful as a make coat, a size coat for coated abrasives, and as a laminating adhesive for multi-layer backing substrates.
In another aspect, the invention provides a treated substrate comprising a substrate which comprises a hydroenhanced cloth and a treatment coat on the substrate. “Hydroenhanced” means that the substrate is treated using high pressure water to increase the surface area of the yarns. An example of this treatment is described in U.S. Pat. No. 4,976,456. The treatment coat may be selected from a variety of compositions suitable for use in abrasive articles.
The term “precursor” means the binder is uncured and not crosslinked. The term “crosslinked” means a material having polymeric sections that are interconnected through chemical bonds (that is, interchain links) to form a three-dimensional molecular network. Thus, the binder precursor is in an uncured state when applied to the backing.
In general, the aminoplast resin/polyamide treatment coat comprises a semi-interpenetrating polymer network of a cured or crosslinked thermosetting polymer and a thermoplastic polymer. As used herein, a “semi-interpenetrating polymer network (semi-IPN)” is defined as a polymer network of two or more polymers wherein at least one polymer is crosslinked and at least one is uncrosslinked.
For purposes of this application, “cured,” “crosslinked,” and “polymerized” can be used interchangeably. For purposes of this invention, a binder precursor is “energy-curable” in the sense that it can crosslink (that is, cure) upon exposure to radiation; for example, actinic radiation, electron beam radiation, and/or thermal radiation. A binder precursor may be in the form of a molten mixture or may be a solid at room temperature. For instance, a binder precursor may be a solid film that is transfer coated to the backing. Upon heating to elevated temperatures, this binder precursor is capable of flowing, increasing the tack of the hot melt binder precursor, and allowing the hot melt binder precursor to penetrate and bond intimately with the backing substrate. Alternatively, for instance, if the resin is solvent-borne (organic or water), (<100 percent solids) or blended with low molecular weight reactive diluents (100 percent solids), the binder precursor may be liquid at room temperature.
As used herein, a “hot melt”composition refers to a composition that is a solid at room temperature (about 20 to 22° C.) but which, upon heating, melts to a viscous liquid that can be readily applied to a backing. A “melt processable” composition refers to a composition that can transform, for example, by heat and/or pressure, from a solid to a viscous liquid by melting, at which point it can be readily applied to a backing.
Desirably, the aminoplast resin/polyamide binder precursors of the invention can be formula
Dahlke Gregg D.
DeVoe Robert J.
3M Innovative Properties Company
Bardell Scott A.
Woodward Ana
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