Coated abrasive having a coating of an epoxy resin coatable from water

Abstract: This invention relates to a coated abrasive having a plurality of abrasive grains bonded to a backing by means of one or more binders, in particular a binder formed from an epoxy resin that is coatable from water. Coated abrasives comprise a backing having abrasive grains bonded thereto by one or more binders. These binders typically comprise a glutinous or resinous adhesive, and may optionally contain one or more additives. Binders are typically applied by coating from an organic solvent. In recent years, however, there has been a need to coat these resins exclusively from water on account of increasingly stringent pollution legislation. Accordingly, it is desired to provide a coated abrasive article having an overcoating containing an epoxy resin and a grinding aid, wherein the epoxy resin can be coated from water. This invention provides a coated abrasive article having a coating comprising a composition formed from an epoxy resin that is capable of being coated from water, a curing agent, and optionally a grinding aid dispersed in the epoxy resin. It is preferred that the coat containing the epoxy resin and the grinding aid be the outermost coat of the coated abrasive article, e.g. the size coat or supersize coat, in order to position the grinding aid in direct contact with the workpiece being abraded.

Description: This invention relates to a coated abrasive having a plurality of abrasive grains bonded to a backing by means of one or more binders, in particular a binder formed from an epoxy resin that is coatable from water. Coated abrasives comprise a backing having abrasive grains bonded thereto by one or more binders. These binders typically comprise a glutinous or resinous adhesive, and may optionally contain one or more additives. Examples of resinous adhesives include epoxy resins, phenolic resins, urethane resins, acrylate resins, and aminoplast resins. Examples of additives include fillers, grinding aids, wetting agents, dispersing agents, pigments, coupling agents, and dyes. In some applications, a grinding aid is included in the binder to improve the abrading characteristics of the coated abrasive. It is believed that the grinding aid has a significant effect on the chemical and physical processes of abrading, thereby providing improved performance. For example, Minnesota Mining and Manufacturing Company of St. Paul, Minnesota has manufactured Regalite Polycut (Trade Name) coated abrasives that contain an overcoating of an epoxy resin with a potassium tetrafluoroborate grinding aid dispersed in the epoxy resin. The binders previously referred to are typically applied by coating from an organic solvent. There are several advantages in coating a resinous binder from an organic solvent, rather than from water. The lower surface tension of organic solvents typically provides better wetting and better adhesion, lower viscosities, and better dispersions of the additives. However, increasingly stringent pollution legislation makes use of solvents more difficult. U.S. Patent No. 4,396,657 discloses a saturant for impregnating the multifilament yarns of a stitchbonded coated abrasive backing comprising an epoxy resin, a dicyandiamide, blocked isocyanates, and/or imidazole curing agents. The epoxy resin is capable of being coated from water. U.S. Patent No. 3,615,303 discloses a treatment for the backing of a coated abrasive. The treatment, referred to as an intermediate layer, comprises an epoxide resin mixture based on (a) 4,4'-dihydroxydiphenyl1-2, 2-propane (Bisphenol A), (b) an epoxide resin based on Bisphenol A internally plasticized by a reaction with castor oil, (c) carbamic acid alkyl esters, and (d) a curing agent. This epoxide resin is capable of being coated from water. EP-A-486,308 (of the same applicant as the present application), priority date November 14th, 1990, published May 20th, 1992 (Article 54(3)) discloses a coated abrasive wherein a size coat must contain an epoxy resin coatable from water and a grinding aid. The make coat is preferably a phenolic resin but there is incidental reference to possible use of an epoxy resin coatable from water without specification of the nature of such resin. According to the invention there is provided a coated abrasive article comprising: a. a backing; b. a cured make coat overlying said backing; c. a plurality of abrasive grains supported on and adherently bonded to said backing by means of said make coat; and d. a cured size coat overlying said abrasive grains and said make coat, wherein at least one of said make coat or said size coat is formed from a composition comprising an epoxy resin coatable from water, an emulsifier for said epoxy resin, a curing agent, and water, provided: a. if only said make coat is formed from said epoxy resin, then said epoxy resin has an epoxy equivalent weight of from 160 to 500; or b. if only said size coat contains said epoxy resin, said size coat is free of grinding aid; or c. if both said make coat and said size coat contain said epoxy resin, either said epoxy resin has an epoxy equivalent weight of from 160 to 500, or said size coat is free of grinding aid. There is further provided a method of preparing the coated abrasive article of the invention comprising the steps of (1) providing a backing; (2) applying a make coat over said backing; (3) applying a plurality of abrasive grains onto said make coat; (4) at least partially curing said make coat; (5) applying over said make coat and said abrasive grains a size coat, and (6) curing said size coat, wherein at least one of said make coat or said size coat as applied is formed from a composition comprising an epoxy resin coatable from water, an emulsifier for said epoxy resin, a curing agent, and water, provided: a. if only said make coat is formed from said epoxy resin, then said epoxy resin has an epoxy equivalent weight of from 160 to 500; or b. if only said size coat contains said epoxy resin, said size coat is free of grinding aid; or c. if both said make coat and said size coat contain said epoxy resin, either said epoxy resin has an epoxy equivalent weight of from 160 to 500, or said size coat is free of grinding aid. There is also provided a method for preparing a coated abrasive article comprising a supersize coating overlying said size coat which method comprises the steps of: (1) providing a backing; (2) applying a make coat over said backing; (3) applying a plurality of abrasive grains onto said make coat; (4) at least partially curing said make coat; (5) applying a size coat over said make coat and abrasive grains; (6) at least partially curing said make coat and said size coat; (7) applying over said make coat, abrasive grains and size coat a supersize coat, and (8) curing said supersize coat, wherein said make coat as applied is formed from a composition comprising an epoxy resin coatable from water, said epoxy resin having an epoxy equivalent weight of from 160 to about 500, an emulsifier for said epoxy resin, a curing agent, and water. When the epoxy resin is incorporated into the make coat, it is required that the epoxy resin have an epoxy equivalent weight of preferably in the range of 165 to 350 and most preferably in the range of 180 to 250. Epoxy equivalent weight (EEW) is the average molecular weight of the resin divided by the average number of epoxy functional groups per molecule. The purpose of the curing agent is to initiate polymerization of the epoxy resin, which is the resinous adhesive in the binder. The purpose of the grinding aid is to improve the abrading characteristics of the coated abrasive. Examples of typical grinding aids include potassium tetrafluoroborate and cryolite. In some cases, it may be beneficial to incorporate a dispersing agent into the compositions containing the epoxy resin coatable from water and the grinding aid to reduce the viscosity of these compositions prior to application. The weight ratio of the epoxy resin to the grinding aid ranges from 10 to 85 parts epoxy resin to 15 to 85 parts grinding aid. It is preferred that the coat containing the epoxy resin and the grinding aid be the outermost coat of the coated abrasive article in order to position the grinding aid in direct contact with the workpiece being abraded. Brief Description of the Drawings FIG. 1 is a side view of a coated abrasive made according to the present invention. FIG. 2 is a side view of a coated abrasive made according to the present invention. Detailed Description As used herein, the term "epoxy resin" refers to epoxy resins capable of being coated from water unless indicated otherwise; the term "epoxy dispersion" refers to a dispersion containing an epoxy resin, an emulsifier for the epoxy resin, a curing agent for the epoxy resin, and water. FIGS. 1 and 2 depict embodiments subject to the limitation in the claims wherein at least one of the make coat, size coat, or optional supersize coat is formed from a composition comprising an epoxy resin, an emulsifier for the epoxy resin, a curing agent, and water. Subject to the limitations specified in the claims, it is also acceptable for the make coat and size coat; make coat and supersize coat; size coat and supersize coat; or make coat, size coat and supersize coat;to be formed from the epoxy composition. In some instances, it is preferred that the size coat or supersize coat or both coats contain, in addition to the epoxy resin, the emulsifier for the epoxy resins, and the curing agent, a grinding aid. Grinding aids are particularly useful in coarse grade abrasives that are used for abrading metals. In the embodiment shown in FIG. 1, coated abrasive 10 comprises a backing 12 and a plurality of abrasive grains 14 supported by and adherently bonded to backing 12 by means of a binder 16, hereafter referred to as the make coat. Overlying abrasive grains 14 and make coat 16 is a binder 18, hereafter referred to as the size coat. Size coat 18 further secures abrasive grains 14 to backing 12. The size coat subject to the limitations in the claims can be prepared from a composition comprising an epoxy resin, an emulsifier for the epoxy resin, a curing agent, a grinding aid, and water. In this particular embodiment, the size coat is the outermost coating of the coated abrasive, and it can directly contact the workpiece being abraded. In the embodiment shown in FIG. 2, coated abrasive 20 comprises a backing 22 and a plurality of abrasive grains 24 supported by and adherently bonded to backing 22 by means of a binder 26, hereafter referred to as the make coat. Overlying the abrasive grains 24 and make coat 26 is a binder 28, hereinafter referred to as the size coat. Coated abrasive 20 further comprises supersize coat 30 overlying size coat 28. Subject to the limitations in the claims supersize coat 30 can be formed from a composition comprising an epoxy resin, an emulsifier for the epoxy resin, a curing agent, a grinding aid, and water. In this particular embodiment, the supersize coat is the outermost coating of the coated abrasive, and it can directly contact the workpiece being abraded. It is also acceptable for both size coat 28 and supersize coat 30 to be formed from a composition comprising an epoxy resin, an emulsifier for the epoxy resin, a curing agent, a grinding aid, and water. Backings 12 and 22 are preferably selected from materials that can be formed into sheets, such as paper, cloth, polymers, nonwoven materials, e.g., an open, porous non-woven web, vulcanized fibre, combinations thereof, and treated versions thereof. Abrasive grains 14 and 24 are preferably selected from such abrasive materials as silicon carbide, fused aluminum oxide, heat-treated aluminum oxide, garnet, alumina zirconia, ceramic aluminum oxide, diamond, cubic boron nitride, and combinations thereof. Make coats, size coats, and supersize coats not formed from the epoxy dispersion can be formed from a glutinous or resinous adhesive, and they may also contain other additives. Examples of resinous adhesives suitable for preparing make coats, size coats, and supersize coats include phenolic resins, urea formaldehyde resins, epoxy resins not coatable from water, urethane resins, acrylate resins, aminoplast resins, melamine resins, and mixtures thereof. Additives suitable for make coats, size coats, and supersize coats include wetting agents, grinding aids, fillers, coupling agents, dyes, pigments, antistatic agents, and combinations thereof. An epoxy resin contains an oxirane ring, i.e., The epoxy resin is polymerized or cured by means of a ring opening mechanism. Epoxy resins suitable for this invention must be coatable from water. Epoxy resins suitable for this invention include both monomeric epoxy compounds and polymeric epoxy compounds. The epoxy resins may vary greatly in the nature of their backbones and their substituent groups; for example, their backbones can be aliphatic, cycloaliphatic, or aromatic. A representative example of an aliphatic epoxy resin is diglycidyl ether of a polyoxyalkylene glycol. Representative examples of cycloaliphatic epoxy resins include epoxycyclohexanecarboxylates, e.g., 3,4-epoxy-2-methylcyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, and 3,4-epoxy-2-methylcyclohexylmethyl 3,4-epoxy-2-methylcyclohexanecarboxylate. Representative examples of aromatic epoxy resins include 3,3-bis[4-(2,3-epoxypropoxy)-phenyl]propane (diglycidyl ether of bisphenol A), N,N,N,N'-tetraglycidyl-4,4'-diaminodiphenylmethane, and triglycidyl-p-aminophenol. The backbone of the epoxy resin can be modified with organic substituents, such as, for example, a urethane epoxy resin. The addition of the urethane group to the epoxy backbone can increase the flexibility of the resulting cured binder. In some instances, e.g., with respect to fine grade coated abrasive products, flexibility provides some advantages. The preferred epoxy resin for the size coat or supersize coat is a diglycidyl ether of bisphenol A. The value of n can range from 0 to 10, but it preferably ranges from 1 to 4. As the value of n increases, the viscosity of the resin also increases. If the viscosity of the resin is too high, it will be difficult to apply as a coating. Another type of epoxy resin is a novolac resin, which is illustrated below. n' can range from 0 to 4, preferably from 0.2 to 2. The higher values of n' result in a more viscous resin. The epoxide equivalent weight (EEW) can range from 160 to 700. For the make coat, it is required that this equivalent weight be 160 to 500, preferably in the range of 165 to 350 and most preferably in the range of 180 to 250. Higher EEW can be utilized for the make coat; however, in many instances, special care or even additional processing steps must be undertaken during the making of the coated abrasive. A make coat that is formed from an epoxy composition having a higher EEW tends to solidify too fast. Excessively rapid solidification tends to result in poor adhesion of the abrasive grains to the make coat. To minimize adhesion problems, the make coat formed from the epoxy dispersion having the higher EEW has to be heated prior to the application of the abrasive grains to inhibit solidification of the make coat. Alternatively, steam can be applied to the surface of the make coat to resoften the surface to inhibit solidification of the make coat to allow the abrasive grains to adhere properly. The preferred EEW for a size coat or supersize coat formed from an epoxy dispersion is typically in the range of 200 to 700. The pH of the epoxy resin, by itself, can range from 3 to 8.5, preferably from 3.5 to 8. Examples of commercially available epoxy resins suitable for this invention include the CMD series or "EPI-REZ" (Trade Mark) series epoxy resins from Rhone-Poulenc, Louisville, Kentucky. In order to form the coatable composition for preparing a make coat, a size coat, or a supersize coat, the epoxy resin is dispersed in water with the aid of an emulsifier to form a dispersion, hereafter referred to as "epoxy dispersion". The epoxy dispersion will contain from 30 to 90% solids, preferably 45% to 75% solids. Emulsifiers that are suitable for preparing the epoxy dispersion include cationic, anionic, and nonionic emulsifiers. Cationic dispersions result in a positive charge on the resin particle or on the emulsifier, whereas anionic dispersions provide negative charges. Nonionic dispersions do not have charges associated with them. Nonionic emulsifiers are preferred. Representative examples of emulsifiers suitable for this invention include sodium dioctyl sulfosuccinate, alcohol ethoxylates, and alcohol alkoxylates. A curing agent can then be added to the epoxy dispersion. The purpose of the curing agent is to initiate the polymerization of the epoxy resin after the composition has been coated so that a thermosetting, chemical resistant polymer will be formed. Typically, the epoxy dispersion contains from 0.01 to 30% by weight curing agent, preferably 1 to 5% by weight curing agent, based upon the weight of the epoxy resin. Representative examples of curing agents suitable for the epoxy resins of this invention include amines, such as polyamidoamines and tertiary amines, amides such as dicyandiamide, mercaptans, and imidazoles, such as 2-methyl imidazole, 2-phenyl imidazole, and 2-ethyl-4-methylimidazole. The preferred curing agent is 2-ethyl-4-methylimidazole, commercially available from Air Products Company under the trade designation "EMI-24". It is also preferred that the curing agent be dispersed in water prior to being added to the epoxy dispersion. Other useful curing agents for the epoxy resin include urea-formaldehyde resins and melamine formaldehyde resins. Examples of commercially available urea-formaldehyde resins include "DURITE AL 8401" and "DURITE AL 8405" (Trade Marks) resins, available from the Borden Chemical Co. The weight ratio of epoxy resin to urea-formaldehyde resin typically ranges from 40 to 80 parts epoxy resin to 20 to 60 parts urea-formaldehyde resin. Subject to the limitations in the claims in addition to the epoxy resin, the emulsifier, the curing agent, and water, an epoxy dispersion for preparing the size coat or supersize coat may also contain a grinding aid, particularly for coated abrasives containing coarse to medium grade abrasive grains. As used herein, "grinding aids" are particulate materials, the addition of which to a coated abrasive article enhances the abrading performance of the coated abrasive article. It is believed that the grinding aid exercises a significant effect on the chemical and physical processes encountered during abrading, thereby providing improved performance. In particular, it is believed that the grinding aid will carry out one or more of the following: (1) decrease friction between the abrasive grains and the workpiece being abraded, (2) prevent abrasive grains from "capping", i.e., prevent metal particles from becoming welded to the tops of the abrasive grains, or (3) decrease interface temperature between the abrasive grains and the workpiece. Furthermore, the addition of grinding aids typically increases the useful life of the coated abrasive. Representative examples of classes of grinding aids suitable for this invention include waxes, organic halide compounds, halide salts, metals, and alloys of metals. Organic halide compounds typically break down during abrading and release a halogen acid or a gaseous halide compound. Examples of organic halides include chlorinated waxes, such as tetrachloronaphthalene, pentachloronaphthalene; and polyvinyl chloride. Chlorinated waxes can also be considered to be waxes. Examples of halide salts include sodium chloride (NaCl), potassium chloride (KCl), potassium fluoroborate (KBF 4 ), ammonium cryolite (NH 4 ) 3 AlF 6 , cryolite (Na 3 AlF 6 ), and magnesium chloride (MgCl 2 ). Examples of metals include tin, lead, bismuth, cobalt, antimony, cadmium, iron, and titanium. Other grinding aids include sulfur and organic sulfur compounds, graphite, and metallic sulfides. Combinations of grinding aids can be used, and in some instances may produce a synergistic effect. The preferred grinding aid for stainless steel is potassium tetrafluoroborate. The preferred grinding aid for mild steel is cryolite. The ratio of epoxy resin to grinding aid preferably ranges from 10 to 85, preferably 15 to 60, parts by weight epoxy resin to 15 to 85, preferably 40 to 85, parts by weight grinding aid. In some instances, it is preferred to add a dispersing agent to the epoxy dispersion. For example, if potassium tetrafluoroborate is used as a grinding aid, it is preferred to add a dispersing agent to the epoxy dispersion to lower its viscosity. However, if cryolite is used as a grinding aid, it is not always necessary to add a dispersing agent to the epoxy dispersion. Representative examples of commercially available dispersing agents suitable for this invention include fluorosurfactants having the trademarks of "FLUORAD", available from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, and "AEROSOL OT", available from Rohm & Haas Company. Typically, the concentration of the dispersing agent is less than 2%, based on the weight of the epoxy resin. In general, the viscosity of the composition containing epoxy resin, emulsifier, curing agent, and water should be less than 10000 mPa (10,000 centipoises), preferably less than 5000 mPa (5,000 centipoises). If the viscosity is greater than 30000 mPa (30,000 centipoises), it is difficult to process the composition in the manufacture of a coated abrasive. Other types of resins can also be included in the epoxy dispersion. For example phenolic resins, which can co-react with the epoxy resin, can be included. Additionally, urethanes and rubber compounds can be added to the dispersion in order to improve the toughness of the cured epoxy resin. Latexes can be added to the epoxy dispersion to increase the flexibility of the cured binder. Other additives, such as dyes, defoamers, pigments, fillers, and coupling agents, can be used in the composition for preparing the size coat or supersize coat of this invention. When particular grinding aids are employed, it may be necessary to utilize a defoamer to remove unwanted air bubbles. It should be noted that make coats 16 and 26 can also be prepared from compositions comprising an epoxy resin coatable from water, an emulsifier for the epoxy resin, a curing agent, a grinding aid, and water. Once the epoxy dispersion has been applied to the coated abrasive article, it can be heated to bring about polymerization of the epoxy resin. Heating is typically conducted for a period of from 10 to 250 minutes, preferably from 20 to 50 minutes, at temperatures from 80 to 130°C, preferably from 105 to 115°C. Surprisingly, it has been found that the abrading performance of a coated abrasive containing an epoxy resin of this invention is significantly improved over that of a coated abrasive containing an epoxy resin coated from an organic solvent, with everything else being equal. Furthermore, it has been found that the performance of the coated abrasive containing the epoxy resin of this invention does not decrease over time as rapidly as does that of a coated abrasive containing an epoxy resin coated from an organic solvent. The advantages of utilizing the epoxy resin of this invention rather than epoxy resins coated from an organic solvent include reduction of pollution, greater ease of cleaning from the coating station, and greater ease of roll coating onto the surface of the coated abrasive. The following non-limiting examples will further illustrate the invention. All ratios are based upon weight unless indicated otherwise. The following material designations will be used. Epoxy resin PFAW: A nonionic aqueous dispersion of a polyfunctional aromatic epoxy resin having an average functionality of three. This dispersion was commercially available from Rhone-Poulenc under the trade designation "EPI-REZ W55-5003". The epoxy equivalent weight ranged from 180 to 205. Curing Agent AA: Amine adduct curing agent that was purchased from Rhone-Poulenc Company under the trade designation "EPI-CURE 826". Examples 1, 2 and Comparative Examples A-C For Examples 1 and 2, the make and size coats were formed from an epoxy dispersion. The coated abrasives made according to these examples were tested according to the Schiefer Test and the test results can be found in Table I. Schiefer Test The coated abrasive article was converted into a 10.2 cm diameter disc and secured to a foam back up pad by means of a pressure-sensitive adhesive. The coated abrasive disc and back up pad assembly were installed on a Schiefer testing machine and the coated abrasive disc was used to abrade a workpiece made of polymethyl methacrylate ("PLEXIGLASS"). The load was 4.5 kg. All of the testing was done under conditions of a water flood. The cut was the total amount of polymethyl methacrylate removed during 500 rotations of the coated abrasive disc. Additionally, the cut data represented an average for two coated abrasive discs. Example 1 A make coat that consisted of 65.7 g of PFAW, 8.08 g of AA, and 26.22 g of water was prepared. The percentage of solids was 45%. The make coat was knife coated onto a waterproof A weight paper at a dry weight of approximately 4 g/m 2 . The make coat was dried in air for about three minutes. Then, grade P320 silicon carbide was electrostatically projected into the make coat at a weight of approximately 40 g/m 2 . The resulting construction was cured for five minutes at a temperature of 100°C. Next, a size coat was applied over the abrasive grains at a weight of about 36 g/m 2 . The size coat was of the same composition as the make coat, except that the percentage of solids was 40%. The resulting construction was cured for about 20 minutes at a temperature of 100°C. Example 2 The coated abrasive article for Example 1 was made in the same manner as was used in Example 1 , except that the weight of the size coat was 44 g/m 2 . Comparative Example A The coated abrasive article for Comparative Example A was a grade 320 "3M 413Q IMPERIAL WETORDRY" A weight paper commercially available from the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. The abrasive grains were silicon carbide. Comparative Example B The coated abrasive article for Comparative Example B was a grade 320 "3M 213Q IMPERIAL WETORDRY" A weight paper commercially available from the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. The abrasive grains were aluminum oxide. Comparative Example C The coated abrasive article for Comparative Example C was a grade 320 coated abrasive article that employed a waterproof A weight paper, and was commercially available from the Komatsubara Company, Japan. The abrasive grains were silicon carbide. Example Cut (g) 1 1.74 2 1.88 Comparative A 1.37 Comparative B 1.72 Comparative C 1.75 The article of Example 2 performed better than the articles of Comparative Examples A, B and C. Examples 3-4 and Comparative Examples D-H The coated abrasive article in Example 3 used a make coat and a size coat that were formed from an epoxy dispersion. All of the coated abrasive articles in this set of examples were tested according to the Schiefer Test, and the test results are set forth in Table II. In addition, for this set of examples, the surface finish of the workpiece was measured at the end of the 500 cycles by a Type M4P Perthometer. Ra is the arithmetic mean of the departures of the profile from the mean line in nm (microinches) and Rtm is the mean of the maximum peak-to-valley values from each of five consecutive sampling lengths in nm (microinches). Example 3 A make coat precursor that consisted of PFAW (1,005 g) of AA (1,230 g), silicone surfactant (15 g) and water (3,990 g) was prepared. PFAW had a pH of 7.0, contained 57% solids, and had an epoxy equivalent weight of approximately 205. In addition, AA contained about 100% solids. This make coat precursor was roll coated onto a waterproof A weight paper at a wet weight of approximately 4 g/m 2 . Then, grade 1200 silicon carbide was electrostatically projected into the make coat at a weight of approximately 11 g/m 2 . The resulting construction was cured for 10 minutes at a temperature of 120°C. Next, a size coat was applied over the abrasive grains at a weight of about 9 g/m 2 . The size coat was of the same material as the make coat. The resulting construction was cured for between 15 to 20 minutes at a temperature of 120°C. Example 4 The coated abrasive article of Example 4 was made in the same manner as was that of Example 3 except that the abrasive grain was a grade 600 silicon carbide. The weights of the make coat, abrasive grain, and size coat were about 2, 10 and 17 g/m 2 , respectively. Example 5 The coated abrasive article in Example 5 was made in the same manner as was that of Example 3 except that the abrasive grain was a grade 400 silicon carbide. The weight of the make coat, abrasive grain, and size coat were about 5, 18 and 15 g/m 2 , respectively. Comparative Example D The coated abrasive article for Comparative Example D was a grade 1200 "IMPERIAL MICROFINE" A weight paper commercially available from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. Comparative Example E The coated abrasive article for Comparative Example E was a grade 1200 waterproofed coated abrasive A weight paper commercially available from the Komatsubara Company, Japan under the trade designation "KOVAX". Comparative Example F The coated abrasive article for Comparative Example F was a grade 1200 coated abrasive that contained a waterproof A weight paper. Comparative Example L was commercially available from the Nikken Company, Japan. Comparative Example G The coated abrasive article for Comparative Example G was a grade 600 waterproofed coated abrasive A weight paper commercially available from the Komatsubara Company, Japan under the trade designation "KOVAX". Comparative Example H The coated abrasive article for Comparative Example H was a grade 400 waterproofed coated abrasive A weight paper commercially available from the Komatsubara Company, Japan under the trade designation "KOVAX". Example No. Cut (g) Ra Rtm nm µm nm µm 3 0.730 101.6 004 838.2 033 4 1.011 203.2 008 1676.2 066 5 1.098 330.2 013 2514.6 099 Comparative D 0.302 76.2 003 685.8 027 Comparative E 0.814 177.8 007 1397 055 Comparative F 0.636 127 005 1168.4 046 Comparative G 1.243 482.6 019 3175 125 Comparative H 1.433 533.4 021 3810 150 For this application, it is desired to have a high cut, with low Ra and Rtm values. In fine grade coated abrasive applications, cut and finish need to be balanced. The present invention provides this balance by providing a high cut with a low or fine surface finish.

Claims: A coated abrasive article comprising: a. a backing; b. a cured make coat overlying said backing; c. a plurality of abrasive grains supported on and adherently bonded to said backing by means of said make coat; and d. a cured size coat overlying said abrasive grains and said make coat, wherein at least one of said make coat or said size coat is formed from a composition comprising an epoxy resin coatable from water, an emulsifier for said epoxy resin, a curing agent, and water, provided: a. if only said make coat is formed from said epoxy resin, then said epoxy resin has an epoxy equivalent weight of from 160 to 500; or b. if only said size coat contains said epoxy resin, said size coat is free of grinding aid; or c. if both said make coat and said size coat contain said epoxy resin, either said epoxy resin has an epoxy equivalent weight of from 160 to 500, or said size coat is free of grinding aid. A coated abrasive article according to claim 1 further comprising a supersize coat overlying said size coat. A coated abrasive article according to claim 1 or claim 2, wherein said epoxy resin has an epoxy equivalent weight of less than 350. A coated abrasive article according to claim 1, wherein said size coat is formed from a composition comprising an epoxy resin coatable from water, an emulsifier for said epoxy resin, a curing agent, and water, said epoxy resin having an epoxy equivalent weight of from 160 to 700. A coated abrasive article according to any preceding claim, wherein said epoxy resin is a diglycidyl ether of bisphenol A. A coating abrasive article according to any preceding claim, wherein when said size coat comprises a resin other than an epoxy resin capable of being coated from water, said size coat further includes a grinding aid. A coated abrasive article according to claim 6, wherein said grinding aid is potassium fluoroborate. A coated abrasive article according to any preceding claim, wherein said curing agent is selected from the group consisting of amines, amides, imidazoles, and urea-formaldehyde. A coated abrasive article according to any one of claims 1 to 8 wherein said epoxy coatable from water further comprises a dispersing agent. A coated abrasive according to claim 9 wherein said dispersing agent is a fluorosurfactant. Method of preparing the coated abrasive article of claim 1, comprising the steps of: (1) providing a backing; (2) applying a make coat over said backing; (3) applying a plurality of abrasive grains onto said make coat; (4) at least partially curing said make coat; (5) applying over said make coat and said abrasive grains a size coat, and (6) curing said size coat, wherein at least one of said make coat or said size coat as applied is formed from a composition comprising an epoxy resin coatable from water, an emulsifier for said epoxy resin, a curing agent, and water, provided: a. if only said make coat is formed from said epoxy resin, then said epoxy resin has an epoxy equivalent weight of from 160 to 500; or b. if only said size coat contains said epoxy resin, said size coat is free of grinding aid; or c. if both said make coat and said size coat contain said epoxy resin, either said epoxy resin has an epoxy equivalent weight of from 160 to 500, or said size coat is free of grinding aid. The method of claim 11, wherein when said size coat of step (5) comprises a resin other than an epoxy resin capable of being coated from water, said size coat further includes a grinding aid dispersed in said epoxy resin. Method of preparing the coated abrasive article of claim 2, comprising the steps of: (1) providing a backing; (2) applying a make coat over said backing; (3) applying a plurality of abrasive grains onto said make coat; (4) at least partially curing said make coat; (5) applying a size coat over said make coat and abrasive grains; (6) at least partially curing said make coat and said size coat; (7) applying over said make coat, abrasive grains and size coat a supersize coat, and (8) curing said supersize coat, wherein said make coat as applied is formed from a composition comprising an epoxy resin coatable from water, said epoxy resin having an epoxy equivalent weight of from 160 to about 500, an emulsifier for said epoxy resin, a curing agent, and water. The method of claim 13, wherein the supersize coat of step (7) further includes a grinding aid dispersed in said epoxy resin. Method according to claim 11 of preparing the coated abrasive article of claim 1 further comprising the step of inhibiting solidification of said make coat, said make coat being formed from a composition comprising: (a) said epoxy resin coatable from water (b) an emulsifier for said epoxy resin (c) a curing agent, and (d) water. The method of claim 15, wherein inhibition of solidification of said make coat is effected by applying heat to said make coat prior to applying said abrasive grains. The method of claim 15, wherein inhibition of solidification of said make coat is effected by applying steam to the surface of said make coat to resoften said surface of said make coat prior to applying said abrasive grains. Method according to claim 13 of preparing the coated abrasive article of claim 2 further comprising the step of inhibiting solidification of said make coat wherein said make coat is formed from a composition comprising: (a) an epoxy resin coatable from water (b) an emulsifier for said epoxy resin (c) a curing agent, and (d) water. The method of claim 18, wherein inhibition of solidification of said make coat is effected by applying heat to said make coat prior to applying said abrasive grains. The method of claim 18, wherein inhibition of solidification of said make coat is effected by applying steam to the surface of said make coat to resoften said surface of said make coat prior to applying said abrasive grains. A coated abrasive article according to any of claims 1 to 10, wherein said backing is selected from the group consisting of paper, cloth, polymers, non-woven materials, vulcanized fibre, combinations thereof, and treated versions thereof.

Inventors: BUCHANAN SCOTT J, LEE CHONG SOO, BUCHANAN, SCOTT J., LEE, CHONG SOO, BUCHANAN, SCOTT J., C/O MINNESOTA MINING AND, Lee, Chong Soo, c/o Minnesota Mining and
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1992
Main classification: B24D3
IPC codes: B24D3