WO2001043919A1

WO2001043919A1 - Abrasive article, abrasive slurries and method of making an abrasive article

Info

Publication number: WO2001043919A1
Application number: PCT/US2000/031907
Authority: WO
Inventors: John T. Wallace; Scott R. Culler
Original assignee: 3M Innovative Properties Company
Priority date: 1999-12-15
Filing date: 2000-11-20
Publication date: 2001-06-21
Also published as: AU1783801A

Abstract

The present invention relates to abrasive articles having an abrasive coating comprised of a binder, abrasive particles having a Mohs' hardness of 7 or greater and non-abrasive particles having a Mohs' hardness less than about 6, wherein the non-abrasive particles have a particle size that is greater than the particle size of the abrasive particles. The abrasive slurries that are used to make the abrasive coating of the present invention may be used in both coated, structured and nonwoven abrasive articles as well as in making composite particles. The invention also relates to methods of making coated and non-woven abrasive articles and methods of making composite particles.

Description

ABRASIVE ARTICLE, ABRASIVE SLURRIES AND METHOD OF MAKING AN ABRASIVE ARTICLE

BACKGROUND This invention relates to abrasive slurries, abrasive articles made employing these abrasive slurries, and to methods of making abrasive articles.

Abrasive articles are used to abrade a wide range of substrates including metal, wood, wood like materials, painted surfaces, glass, ceramics, plastics and the like. Abrading metal is a substantial market opportunity and is a critical process in the metal working industry. There afe^" many different types of metals abraded including carbon steels, aluminum, stainless steel, titanium, high nickel alloys, tool steel and the like.

In high stock removal applications, coated abrasives and bonded abrasives are commonly used. U.S. Patent No. 5,152,917 (Pieper et al.) discloses a structured abrasive article that provides both a high rate of cut and consistent surface finish on the workpiece surface. The structured abrasive coating comprises abrasive composites having a plurality of abrasive particles dispersed in a binder that are bonded to a backing. U.S. Patent No. 5,378,251 (Culler et al.) discloses an abrasive article comprising a backing having an abrasive coating bonded to the front surface of the backing. The abrasive coating comprises a mixture of abrasive particles, binder and halide salt grinding aid particles. U.S. Patent No. 5,942,015 (Culler et al.) discloses an abrasive article that provides a long abrading life and generates a fine surface finish. This abrasive article is made from an abrasive slurry that comprises two different grades of abrasives particles (i.e., a first larger grade and a second smaller grade) dispersed in a binder precursor.

Over the past decade, uses of titanium have increased because titanium is relatively strong, lightweight metal. Metalworking processes, such as casting titanium, typically result in excess titanium that is necessary to remove later, generally in an abrading process. Nevertheless, titanium in some instances may be a difficult material to abrade. Abrading inherently generates heat; titanium grinding is known to generate a fair amount of heat. If this heat is transferred into the titanium, it may cause degradation of the titanium's physical properties, which is undesirable Thus, titanium abrading processes are generally designed to minimize any substantial heat build up. Abrasive articles incorporating fused alumina based abrasive particles have been used in grinding titanium with some success. Fused alumina based abrasive particles are relatively inexpensive, provide high cut rates and long useful product life. However, fused alumina based abrasive particles may generate excessive heat and for this reason they are not exclusively used in titanium grinding. Abrasive articles incorporating silicon carbide abrasive particles have also been used in grinding titanium. In some applications, silicon carbide abrasive particle may generate less heat than fused alumina abrasive particles. Nonetheless, silicon carbide abrasive particles are not exclusively used because in general silicon carbide abrasive particles are more expensive and provide a shorter useful product life than the corresponding fused alumina based abrasive particles. Thus current titanium grinding processes generally use a combination of abrasive articles having either fused alumina based or silicon carbide abrasive particles to provide the optimum combination of low cost, low heat generation, high cut rates and long useful product life.

What is desired in the grinding industry, preferably titanium grinding industry, is an abrasive article that provides an optimum combination of low abrasive article cost, low heat generation, high cut rates and long useful product life.

SUMMARY OF THE INVENTION

The present invention provides abrasive slurries, abrasive articles made from the abrasive slurries, and suitable methods of making the abrasive articles slurries.

In one embodiment, the present invention provides an abrasive slurry suitable for use to make either an abrasive coating of an abrasive article or to make composite particles. The abrasive slurry comprises a binder precursor, a plurality of abrasive particles having a Mohs' hardness of 7 or greater dispersed in the binder precursor and a plurality of non-abrasive particles having a Mohs' hardness less than about 6 dispersed in the binder precursor; wherein the non-abrasive particles have a particle size greater than a particle size of the abrasive particles. In a specific embodiment of this invention the non-abrasive particles further comprise a first (larger) particle size distribution of non-abrasive particles having a first median particle size; and a second (smaller) particle size distribution of non-abrasive particles having a second median particle size; wherein the median particle size ratio is about 2 or greater. Suitable non-abrasive particles larger than the abrasive particles generally have a particle size greater than about 105 micrometers, preferably greater than 110 micrometers, more preferably greater than about 115 micrometers and most preferably greater than about 120 micrometers. One preferred non-abrasive particle is a grinding aid particle made of potassium tetrafluoroborate.

In a second embodiment, the present invention provides an abrasive article having an abrasive coating made from the present abrasive slurry. Suitable abrasive articles include coated, structured and nonwoven abrasive articles.

In another embodiment, the present invention provides a method of making an abrasive article utilizing an abrasive slurry of the present invention. The method comprises the steps of: (a) coating a backing sheet with an abrasive slurry of the present invention; and

(b) subjecting the abrasive slurry to conditions sufficient to at least partially solidify the binder precursor.

This invention also provides one preferred method of making an abrasive article comprising the steps of:

(a) providing a production tool having a major surface with a plurality of shaped recesses formed therein;

(b) filling the recesses with an abrasive slurry of the present invention;

(c) providing a backing having a front surface and a back surface; laminating the front surface of the backing to the surface of the production tool so that at least a portion of the front surface of the backing is in direct contact with the surface of the production tool;

(e) subjecting the abrasive slurry to conditions sufficient to at least partially cure the binder precursor; and (f) separating the backing from the production tool.

Another method of this invention provides composite particles made by the steps of:

(a) providing a production tool having a major surface with a plurality of precisely shaped recesses formed therein; (b) filling the precisely shaped recesses with an abrasive slurry comprising: a binder precursor, a plurality of abrasive particles having a Mohs' hardness of 7 or greater randomly dispersed in said binder precursor, a plurality of non-abrasive particles having a Mohs' hardness less than about 6 dispersed in the binder precursor; wherein the non-abrasive particles have a particle size greater than a particle size of the abrasive particles,

(c) subjecting the abrasive slurry to conditions sufficient to at least partially cure the binder precursor to form precisely shaped composite particles; and

(d) removing the precisely shaped composite particles from the precisely shaped recesses of the production tool.

The composite particles made by this method may also be used in a variety of abrasive articles, such as coated and nonwoven abrasive articles.

Other advantages and aspects of the invention will be described in the description of preferred embodiments, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a typical abrasive particle size distribution for an abrasive slurry or an abrasive article of the present invention.

FIG. 2 is a side view in cross-section of one embodiment of an abrasive article of the present invention.

FIG. 3 is a side view in cross-section of another embodiment of an abrasive article of the present invention.

FIG. 4 is a side view in cross-section of another embodiment of an abrasive article of the present invention. FIG. 5 is a side view in cross-section of another embodiment of an abrasive article of the present invention.

FIG. 6 is a schematic of a process for making precisely shaped composite particles.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention pertains to abrasive slurries, abrasive articles made utilizing the abrasive slurries, and to methods of making the abrasive articles. Abrasive Slurries

The abrasive slurry of the present invention further comprises abrasive particles having a Mohs' hardness of greater than 7. As used herein "Mohs' hardness" refers to a scale, which indicates the relative hardness of a material. The Mohs' hardness scale ranges from 1 to 10, with 1 being the softest, and 10 being the hardest. Examples of abrasive particles having a Mohs' hardness greater than 7 include fused aluminum oxide, ceramic aluminum oxide, silicon carbide, diamond, cubic boron nitride and the like.

The abrasive slurry further comprises non-abrasive particles. These non-abrasive particles have a Mohs' hardness less than about 6, preferably less than about 5. There are two suitable main classes of non-abrasive particles: filler particles and grinding aid particles.

Filler particles are generally inorganic particulates. Fillers may serve to reinforce the abrasive coating or abrasive bond and/or may reduce cost. Typical examples of fillers include calcium metasilicate, silica, calcium carbonate, feldspar, gypsum, sodium silicate and the like.

Grinding aid particles are paniculate materials that interact beneficially at the workpiece/abrasive article interface during abrading. In particular, grinding aid particles may either (1) decrease the friction between the abrasive particles and the workpiece being abraded, (2) prevent the abrasive particles from "capping" (i.e., prevent metal particles from becoming welded to the tops of the abrasive particles), (3) decrease the interface temperature between the abrasive particles and the workpiece, or (4) decrease the required grinding force. Common classes of grinding aid particles include halide salts, organic compounds with halide moieties, sulfur based compounds, metal particles, phosphate compounds, and combinations thereof. The abrasive slurry of the present invention may further comprise at least two distinct particle size distributions (i.e., grades) of non-abrasive particles (e.g., filler or grinding aid particles) (i.e., a first larger particle size distribution, and a second smaller particle size distribution). As used herein "particle size distribution" refers to a specific distribution of non-abrasive particles wherein the allowable weight fraction (or weight percentage) of each of several non-abrasive particle size ranges contained in the particle size distribution are specified. One measurement of the size of a sample of non-abrasive particles is the median particle size or D(50). As used herein "median particle size" or "D(50)" for a sample of non-abrasive particle is equal to the non-abrasive particle size (typically specified as a diameter) for which 50% of the volume of the sample comprises non-abrasive particles which are smaller than the median volume particle size. As used herein "median particle size ratio" or "D50 ratio" refers to the median particle size of the larger particle size distribution of non-abrasive particles in the slurry divided by the median particle size of any smaller grade of non-abrasive particles in the slurry. For example, in an abrasive slurry comprising first and second non-abrasive particle grades having median particle sizes of 100 micrometer and 50 micrometers, respectively, the median particle size ratio or D(50) ratio is equal to 2. In some embodiments of an abrasive slurry of the present invention, the median particle size ratio may be about 2 or greater, preferably about 3 or greater, most preferably about 5 or greater, and most preferably about 7 or greater. It is also within the scope of the present invention to have more than two non-abrasive particle size distributions in the abrasive article. For example, the non-abrasive particle size distribution may contain three distinct particle size distributions of non-abrasive particles. Further, the abrasive slurry may comprise a first particle size distribution of grinding aid particles and a second particle size distribution of filler particles.

Abrasive slurries of the present invention may remain as slurries (i.e., substantially free from settling) for days rather than hours thereby allowing the slurries to be stored for long periods of time. An advantage of utilizing a mixture of at least two particle size distributions of non-abrasive particle is that the presence of the smaller particle size distribution of non-abrasive particles reduces the sedimentation rate. An abrasive slurry of the present invention may have little or no compaction of particles on the bottom of the container for over one day. This eliminates the need for constant agitation to coat the abrasive slurries. In many previously known slurries, as soon as agitation is stopped, the larger particles begin to settle and eventually become compacted at the bottom of the container. The compacted particles must be redispersed before the slurry may be used for the production of abrasive articles, a process, which may be difficult and/or inconvenient.

The abrasive slurry typically comprises by weight about 5% to 50% binder precursor, about 5% to 90% abrasive particles and about 5% to 45% non-abrasive particles. In a preferred embodiment, the abrasive slurry comprises by weight about 10% to 40%) binder precursor, about 25% to 85% abrasive particles and about 5% to 35% non-abrasive particles. In a more preferred embodiment, the abrasive slurry comprises by weight about 10% to 30% binder precursor, about 40%) to 80% abrasive particles and about 10% to 30%) non-abrasive particles. In a most preferred embodiment, the abrasive slurry comprises by weight about 12% to 20% binder precursor, about 55% to 73% abrasive particles and about 15% to 25%) non-abrasive particles.

In general based only on the non-abrasive particles, there will be between about 10% to about 90% by weight of the first non-abrasive particles and from about 10% to about 90%) by weight of the second non-abrasive particles. It is preferred that there be about 25% to about 75% by weight of the first non-abrasive particles and from about 25% to about 75%) by weight of the second non-abrasive particles. It is more preferred that there be about 30% to about 70% by weight of the first non-abrasive particles and from about 30%) to about 70% by weight of the second non-abrasive particles.

Binder Precursors The abrasive slurry comprises a binder precursor. As used herein "binder precursor" refers to a flowable or unsolidified material, which can be converted to a solid binder. Conversion of the binder precursor to a binder involves a curing or solidification process. As used herein "curing" refers to a polymerization, crosslinking, drying, and/or gelling process. Binder precursors are typically provided in a liquid or flowable form to allow an abrasive slurry containing the binder precursor to be coated. During the manufacture of the abrasive article, the binder precursor is exposed to the appropriate energy source to convert (i.e., at least partially cure or solidify) the binder precursor into a solid binder. Conversion of a flowable or liquid binder precursor to a solid binder is typically the result of a curing or solidification process such as, for example, polymerization, crosslinking, gelling, or evaporation of a liquid from a binder dissolved or dispersed in the liquid (e.g., a polymer dissolved in a solvent). Mixtures of polymerizable binder precursors, crosslinkable binder precursors, and binders dissolved or dispersed in a liquid are also possible. Preferred binders precursors can be either condensation curable resins or addition polymerizable resins. The addition polymerizable resins can be ethylenically unsaturated monomers and/or oligomers. Examples of useable crosslinkable materials include phenolic resins, bismaleimide binders, vinyl ether resins, aminoplast resins having pendant alpha, beta unsaturated carbonyl groups, urethane resins, epoxy resins, acrylate resins, acrylated isocyanurate resins, urea-formaldehyde resins, isocyanurate resins, acrylated urethane resins, acrylated epoxy resins, or mixtures thereof. Aminoplast monomer or oligomer binder precursors have at least one pendant alpha, beta-unsaturated carbonyl group per molecule, or per oligomer. These materials are described in U.S. Pat. Nos. 4,903,440 and 5,236,472.

Ethylenically unsaturated monomers or oligomers may be monofunctional, difunctional, trifunctional, tetrafunctional, or may have greater functionality. Representative examples of ethylenically unsaturated monomers include methyl methacrylate, ethyl methacrylate, styrene, divinylbenzene, hydroxy ethyl acrylate, hydroxy ethyl methacrylate, hydroxy propyl acrylate, hydroxy propyl methacrylate, hydroxy butyl acrylate, hydroxy butyl methacrylate, vinyl toluene, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, hexanediol diacrylate, triethylene glycol diacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, hexanediol diacrylate, triethylene glycol diacrylate, trimethylolpropane triacrylate, glycerol triacrylate, pentaerthyitol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, or pentaerythritol tetramethacrylate, methyl methacrylate, trimethylolpropane triacrylate, glycerol triacrylate, pentaerthyitol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate and pentaerythritol tetramethacrylate.

Other ethylenically unsaturated resins include monoallyl, polyallyl, and polymethallyl esters, and amides of carboxylic acids, such as diallyl phthalate, diallyl adipate, and N,N-diallyladipamide. Still other nitrogen containing compounds include tris(2-acryl-oxyethyl)isocyanurate, l,3,5-tri(2-methyacryloxyethyl)-s-triazine, acrylamide, methylacrylamide, N-methyl-acrylamide, N,N-dimethylacrylamide, N-vinyl-pyrrolidone, and N-vinyl-piperidone. Isocyanurate derivatives having at least one pendant acrylate group and isocyanate derivatives having at least one pendant acrylate group are further described in U.S. Pat. No. 4,652,274. The preferred isocyanurate material is a triacrylate of tris(hydroxy ethyl) isocyanurate.

Acrylated urethanes are acrylate esters (typically diacrylate esters) of hydroxy terminated isocyanate extended polyesters or polyethers. Examples of acrylated urethanes include those commercially available under the trade designations "UNITHANE 782" (available from Morton Thiokol Chemical), "CMD 6600", "CMD 8400", or "CMD 8805" (available from UCB Radcure Specialties). Acrylated epoxies are acrylate esters (typically diacrylate esters) of epoxy resins such as, for example, the diacrylate esters of bisphenol A epoxy resin. Examples of acrylated epoxies include those commercially available under the trade designations "CMD 3500", "CMD 3600", or "CMD 3700" (available from UCB Radcure Specialties).

Epoxide binder precursors have an oxirane (epoxide) ring and are polymerized by ring opening. Examples of preferred epoxy resins lacking ethylenically unsaturated groups include 2,2-bis[4-(2,3-epoxypropoxy)-phenyl] propane (also known as diglycidyl ether of bisphenol A), and those commercially available under the trade designations "EPON 828", "EPON 1004", or "EPON 1001F" (available from Shell Chemical Co.) and "DER-331", "DER-332", or "DER-334" (available from Dow Chemical Co.). Other suitable epoxy resins include glycidyl ethers of phenol formaldehyde novolak resins commercially available under the trade designations "DEN-431" and "DEN-438" (available from Dow Chemical Co.).

Abrasive Particles

Abrasive particles may be selected from those commonly used in abrasive articles, however, the abrasive particle size and composition will be chosen with the application of the abrasive article in mind. It is preferred that abrasive particles used in abrasive slurries or abrasive articles of the present invention have a Mohs' hardness of at least about 7, preferably at least about 7.5, more preferably at least about 8, and most preferably at least about 8.5. Examples of suitable abrasive particles include boron carbide, cubic boron nitride, fused aluminum oxide, ceramic aluminum oxide, heat treated aluminum oxide, alumina zirconia, silicon carbide, iron oxides, tantalum carbide, cerium oxide, garnet, titanium carbide, synthetic and natural diamond, zirconium oxide, silicon nitride, or combinations thereof. The ceramic aluminum oxide particles may be made according to a sol gel process such as described in U.S. Pat. Nos. 4,314,827; 4,623,364; 5,090,968; 5,201,916 (Berg et al.) and 4,881,951.

One preferred abrasive particle for titanium grinding is silicon carbide. Another preferred abrasive particle for titanium grinding is aluminum oxide. The aluminum oxide may be fused aluminum oxide, heat treated fused aluminum oxide or a ceramic aluminum oxide.

Abrasive particles of the present invention typically have a median particle size from about 0.1 to about 1500 micrometers, preferably from about 0.1 to about 700 micrometers, more preferably from about 1 to about 250 micrometers, and most preferably from about 1 to about 150 micrometers. Abrasive particles suitable for abrasive slurries of the present invention should be size graded to meet a desired or predetermined particle size distribution.

The median particle size of the abrasive particles may be larger than the largest median particle size of the non-abrasive particles. Alternatively, the median particle size of the abrasive particles may be smaller than the largest median particle size of the non- abrasive particles, but the abrasive particle median size may be larger than the smallest median particle size of the non-abrasive particles. Conversely, the median particle size of the abrasive particles may be smaller than both the largest and smallest median particle sizes of the non-abrasive particles.

Abrasive particles may also include agglomerates of individual abrasive particles. An abrasive agglomerate is formed when a plurality of abrasive particles is bonded together with a binder to form a larger abrasive particle, which may have a specific paniculate structure. The plurality of particles which form the abrasive agglomerate may comprise more than one type of abrasive particle. The abrasive slurries of this invention may be employed to make abrasive agglomerate particles.

Non-Abrasive Particles

Non-abrasive particles for use in the present invention have a Mohs' hardness less than about 6, preferably less than about 5. There are two major classes of non-abrasive particles, fillers and grinding aid particles.

Filler particles are generally inert during grinding. There are several reasons to incorporate filler particles such as reduce overall cost, increase bond hardness and/or to strengthen the abrasive coating (or abrasive bond). Examples of useful filler particles for this invention include metal carbonates such as calcium carbonate (e.g., chalk, calcite, marl, travertine, marble and limestone), calcium magnesium carbonate, sodium carbonate, or magnesium carbonate. Other examples include silica (e.g., quartz, glass beads, glass bubbles, glass fibers), silicates (e.g., talc, clays, montmorillonite, feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate), metal sulfates (e.g., calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate), gypsum, vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides (e.g., calcium oxide (lime), aluminum oxide, tin oxide (stannic oxide), titanium dioxide), metal sulfites (e.g., calcium sulfite), thermoplastic particles (e.g., particles of polycarbonate, polyetherimide, polyester, polyethylene, polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, polypropylene, acetal polymers, polyurethanes, nylon), or thermosetting particles (e.g., phenolic bubbles, phenolic beads, polyurethane foam particles).

Grinding aid particles may interact beneficially at the workpiece/abrasive article interface during use of the abrasive article. Grinding aid particles may either (1) decrease the friction between the abrasive particles and the workpiece being abraded, (2) prevent the abrasive particle from "capping" (i.e., prevent metal particles from becoming welded to the tops of the abrasive particles), (3) decrease the interface temperature between the abrasive particles and the workpiece, or (4) decrease the required grinding force. Grinding aids encompass a wide variety of different materials and maybe inorganic or organic based. Examples of grinding aid particles useful in this invention include waxes, organic halides, halide salts, metals, or metal alloys. The organic halide particles will typically break down during abrading and release a halogen acid or a gaseous halide compound. Examples of such particles include chlorinated waxes like tetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride. Examples of halide salts include sodium chloride, potassium cryolite, sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, silicon fluorides, potassium chloride, or magnesium chloride. Examples of metals include tin, lead, bismuth, cobalt, antimony, cadmium, iron, or titanium. Other grinding aid particles include sulfur, organic sulfur compounds, graphite, phosphate compounds or metallic sulfides. It is also within the scope of this invention to use a combination of different grinding aid particles which may, in some instances, produce a synergistic effect. The exemplified grinding aid particles are only a representative list.

In one embodiment of this invention, the median particle size of the non-abrasive particles will be less than or equal to the median particle size of the abrasive particles. In other embodiments, the median particle size of the non-abrasive particles may be larger than the median particle size of the abrasive particles. For example, the median particle size of the non-abrasive particles may be anywhere from about at least 5% larger to over 100% larger in particle size than the abrasive particles. This percentage increase in particle size will depend in part on the median particle size of the abrasive particles. For example, the median particle size of the abrasive particles may be about 30 micrometers or less, whereas the median particle size of the non-abrasive particles may be about 105 micrometers. Alternatively, the median particle size of the abrasive particles may be about 100 micrometers or less, whereas the median particle size of the non-abrasive particles may be about 105 micrometers Thus it is within the scope of this invention that the non-abrasive particles have a median particle size greater than about 100 micrometers, greater than about 105 micrometers, greater than about 110 micrometers, greater than about 115 micrometers or greater than about 120 micrometers Such non-abrasive particles that have a larger particle size than the abrasive particles may provide high cut rates and long life. A preferred non-abrasive particle is a potassium tetrafluoroborate grinding aid particle.

Non-abrasive particles typically have a Gaussian-like, or bell-shaped distribution, when particle size is plotted against the number of particles having a given particle size (i.e., particle size is plotted along the x-axis and the number of particles is plotted along the y-axis of a Cartesian coordinate system). A key aspect of this invention is that there are at least two distinct particle size distributions of non-abrasive particles (i.e., a first larger grade, and a second smaller grade).

Various methods of measuring the size of non-abrasive particles are known to those skilled in the art. Any of the standard methods, such as screening, sedimentation, laser measurements, etc. could be used to measure the size of non-abrasive particles useful for the present invention. One method that is particularly suitable is based upon an instrument using the Fraunhofer-Mie method of calculation which determines particle size based on diffraction angles of two different light wavelengths passed through a circulating suspension of particles. This technique can be performed by commercially manufactured instruments, such as a Horiba LA-910 manufactured by Horiba Instruments, Inc. of Irvine, CA. This technique measures particle size on a volume basis, meaning that the particle sizes determined by two-dimensional diffraction results are extrapolated to a three-dimensional volume output.

Referring now to FIG. 1, a graph of a typical particle size distribution for an abrasive slurry of the present invention is shown. Non-abrasive particle size is plotted along the x-axis of the coordinate system using a logarithmic scale. Frequency, which is proportional to the number of non-abrasive particles, is plotted along the y-axis of the coordinate system. The histogram-style plot represents the distribution of non-abrasive particles. The height of each histogram column is proportional to the number of non- abrasive particles in the size range designated on the x-axis. As shown in FIG. 1, the distribution of non-abrasive particle sizes has two distinct Gaussian-like or bell-shaped curves, the centers of which are designated as 10 and 12. The bell-shaped curve centered at 10 is due primarily to the smaller of the two non-abrasive particle grades in the abrasive slurry. The bell-shaped curve centered at 12 is due primarily to the larger of the non- abrasive particle grades in the abrasive slurry. The distance between the centers of the bell-shaped curves is proportional to the difference in median particle size of the two abrasive grades. Hence, the distance between the centers of the bell-shaped distributions 10 and 12 would be expected to increase as the median particle size ratio increases. The height (distance from the x-axis) of the bell-shaped curves is proportional to the number of non-abrasive particles. Therefore, as the amount of a non-abrasive particle grade in the abrasive slurry is increased, the bell-shaped curve corresponding to the non-abrasive particle grade will similarly increase in height.

It should be noted that although the median particle size ratio for any two non- abrasive particles must be about 2 or greater, this does not preclude having non-abrasive particles of the same size in each particle size distribution. Since each non-abrasive particle grade comprises a distribution of non-abrasive particle sizes, overlap of the distributions is not precluded.

Non-abrasive particles of the present invention typically have a particle size from about 0.01 to about 250 micrometers, preferably from about 0.1 to about 200 micrometers, more preferably from about 1 to about 150 micrometers, and most preferably from about 5 to about 125 micrometers.

In abrasive slurries of the present invention the different particle size distributions should be provided in sufficient relative amounts in order to provide the potential for at least one improved property, such as, for example, a reduced slurry sedimentation rate, a longer abrasive article useful product life, and/or higher cut rates.

The present invention allows using higher weights of abrasive particles or increased mineral loading without adversely affecting coating viscosity. In general, lower viscosity abrasive slurries are sometimes used due to the relative ease of coating and/or processing. In general as the abrasive particle weight ratio is increased, then the resulting abrasive slurry generally becomes more viscous. The present invention provides a means to achieve relatively high abrasive particle weight ratios in the abrasive slurry, i.e., greater than 55%), most preferably greater than about 60%. The abrasive slurry has a reasonable and coatable viscosity.

Curing Agents

Abrasive slurries of the present invention may further comprise a curing agent. A curing agent is a material that functions to initiate and complete a polymerization or crosslinking process, such that the initially flowable binder precursor is converted into a cured or solid binder. The term curing agent encompasses initiators, photoinitiators, catalysts and activators. Polymerization of the preferred ethylenically unsaturated monomers or oligomers occurs via a free-radical addition polymerization mechanism. Free radical polymerization may be initiated by an electron beam source, an ultraviolet radiation source, a visible radiation source, or a thermal source (i.e., heat). If an electron beam source is used, the electron beam directly generates free-radicals in the binder precursor thereby initiating polymerization without need for a chemical initiator. However, it is possible to use chemical initiators even if the binder precursor is exposed to an electron beam. If the energy source is heat, ultraviolet light, or visible light, a chemical initiator may be preferred in order to generate free-radicals to initiate the polymerization. Examples of chemical initiators that generate free-radicals upon exposure to ultraviolet light or heat include, but are not limited to, organic peroxides, azo compounds, quinones, nitroso compounds, acyl halides, hydrazones, mercapto compounds, pyrylium compounds, imidazoles, chlorotriazines, benzoin, benzoin alkyl ethers, diketones, phenones, or mixtures thereof. Examples of commercially available photoinitiators that generate free radicals upon exposure to ultraviolet light include those commercially available under the trade designation "IRGACURE 651", or "IRGACURE 184" (available from Ciba Geigy Company), and the photoinitiator available under the trade designation "DAROCUR

1173" (available from from Merck). Typically, chemical initiators are used in amounts from about 0.1% to about 10%, preferably from about 0.25% to about 1% by weight, based on the weight of the binder precursor.

Additives

Abrasive slurries of the present invention may further comprise optional additives such as plasticizers, abrasive particle surface modification additives, coupling agents, expanding agents, fibers, antistatic agents, initiators, suspending agents, photosensitizers, lubricants, wetting agents, surfactants, pigments, dyes, fragrances, UV stabilizers, or suspending agents. The amounts of these materials are selected to provide the properties desired.

Abrasive slurries of the present invention may further comprise surface modification additives such as wetting agents and coupling agents. A coupling agent may provide a bridge between the binder and the abrasive particles. Likewise, the coupling agent may provide a bridge between the binder and the filler particles. Examples of coupling agents include silanes, titanates, and zircoaluminates.

Abrasive slurries of the present invention may further comprise suspending agents.

An example of a suspending agent is an amorphous silica particle commercially available from DeGussa Corp., under the trade designation "OX-50". The use of suspending agents is further described in U.S. Pat. No. 5,368,619.

Preparing an Abrasive Slurry

An abrasive slurry of the present invention may be prepared by combining together a binder precursor, abrasive particles, non-abrasive particles and any optional ingredients, using any suitable mixing technique. It is generally preferred that the resulting abrasive slurry be a homogeneous mixture or dispersion. To prepare the dispersion, it is generally preferred to charge the mixing vessel first with the binder precursor. Next, abrasive particles and non-abrasive particles are gradually added to the binder precursor as the resulting dispersion is continuously mixed. It is preferred that the rate of addition should be such that there is an essentially uniform dispersion. Any suitable mixing technique may be employed such as both low shear and high shear mixing, with high shear mixing being preferred. There are many different types of high shear mixers; one such example has a scraper that continuously scraps the sidewalls of the mixing vessel. In some instances, the mixing vessel may be chilled to prevent excess heat generation. This heat generation may prematurely initiate the polymerization of the binder precursor. Thus the mixing vessel may be chilled to a temperature less than 50°C, preferably less than 25°C and more preferably less than 20°C.

If necessary, ultrasonic energy may also be utilized in combination with the mixing step to lower the viscosity of the abrasive slurry. In some instances it is preferred to heat the abrasive slurry to lower the viscosity.

Abrasive Articles

The present invention provides not only abrasive slurries but also provides abrasive articles made from these abrasive slurries. Abrasive articles of the present invention may be coated abrasive articles or nonwoven abrasive articles.

In one embodiment of the invention, the abrasive coating is provided as a continuous coating. The abrasive coating may have any desired surface topography such as, for example, a smooth surface, a textured surface, a structured surface, or a surface comprising a plurality of composite particles. As used herein "textured" means a surface topography comprising a plurality of protuberances (i.e., ridges, peaks, mesas, and the like) or indentations. The plurality of protuberances and/or indentations may be regular or irregular in size, shape, orientation, and spacing. A textured surface may be formed, for example, by a gravure coating technique which may produce a sinusoidal-like topography comprising a plurality of irregularly shaped, regularly repeating raised ridges or pyramids. Coated abrasive articles of the present invention comprise a backing having an abrasive coating adhered to the front surface thereof. The abrasive coating comprises an abrasive slurry of the present invention, which has been cured or solidified. This type of abrasive coating is sometimes referred to as an abrasive lapping film or abrasive tape.

The abrasive coating may also comprise a plurality of composite particles adhered to a backing by a make coat. The composite particles comprise an abrasive slurry of the present invention, which has been cured to form distinct, free-flowing, individual particles. The composite particles may have precise shapes (i.e., cone, triangular prism, cylinder, pyramid, and cube) or they may have irregular shapes. As used herein "make coat" refers to a coating, which is applied to the backing for the purpose of adhering abrasive particles thereto. Optionally, additional coatings such as a size coat or supersize coat may be applied to further bond the abrasive composites to the backing. Nonwoven abrasive articles comprise an open, lofty, three-dimensional web of fibers bound together at points of mutual contact by a binder. The binder of such a construction may comprise a slurry of the present invention. In addition, abrasive composite particles of the present invention may be adhered to the fibers of a nonwoven web to provide a nonwoven abrasive article. Methods of making nonwoven abrasive articles are described in U.S. Pat. Nos. 2,958,593 (Hoover) and 4,227,350 (Fitzer).

It is generally preferred that the non-abrasive particles be grinding aid particles and that there be two distinct particle size distributions of grinding aid particles. The preferred grinding aid particles are halide salts, more preferably potassium tetrafluoroborate and cryolite. One preferred embodiment of the invention comprises an acrylate binder, alumina (more preferably heat treated fused alumina) abrasive particles and two distinct particle size distributions KBF₄ grinding aid particles. In this one embodiment, the first distribution has a median particle size (or D50) of about 100 micrometers; the second distribution has a median particle size of about 10 micrometers. Thus in this one embodiment there is a 10 to 1 ratio between the two particle size distributions of the grind aid particles.

Referring to FIG. 2, a first embodiment of an abrasive article according to the present invention is illustrated. Abrasive article 20 comprises backing 22 having on its front surface abrasive coating 23. Abrasive coating 23 comprises a plurality of abrasive particles dispersed in a binder 24. Abrasive coating 23 is formed by curing or solidifying an abrasive slurry of the present invention. In this embodiment, binder 24 bonds the abrasive coating 23 to backing 22. According to the present invention the abrasive particles comprise a mixture binder 24, abrasive particles 26, non-abrasive particles 28. The non-abrasive particles have at least two distinct particle size distributions.

Abrasive coating 23 may have any desired surface topography. The surface topography of abrasive coating 23 may be controlled by factors such as, for example, the coating technique used to apply the abrasive slurry, the rheology of the abrasive slurry, and the time period between coating and cure or solidification of the abrasive slurry. In FIG. 2, abrasive coating 23 has a textured sinusoidal-like surface topography comprising a plurality of raised shaped, regularly repeating ridges. A sinusoidal-like surface topography may be formed, for example, by gravure coating an abrasive slurry of the present invention onto a backing. Additional details on the manufacture of abrasive coating may be found in U.S. Pat. Nos. 4,644,703; 4,773,920; 5,199,227; 5,833,724 and 5,863,306. Alternatively, abrasive coating 23 may have a smooth surface topography, formed, for example, by knife coating or die coating an abrasive slurry of the present invention onto a backing.

Referring now to FIG. 3, a second embodiment of an abrasive article of the present invention is shown is illustrated. Abrasive article 30 is a structured abrasive article comprising a plurality of shaped abrasive composites each composite having a predetermined shape and being disposed on a backing in a predetermined array. Abrasive article 30 comprises a backing 32 having on its front surface a plurality of shaped abrasive composites 35. Abrasive composites 35 have a discernible precise shape (i.e., pyramidal) and comprise a plurality of abrasive particles dispersed in a binder 39. In this embodiment, binder 39 bonds abrasive composites 35 to backing 32. The abrasive composites 35 are formed by curing or solidifying an abrasive slurry of the present invention. Therefore, the abrasive composites comprise binder 39, abrasive particles 38, and non-abrasive particles 36. There are at least two distinct particle size distributions of non-abrasive particles.

Structured abrasive articles may be produced by at least partially curing or solidifying an abrasive slurry of the present invention while the abrasive slurry is being held within precisely shaped recesses of a production tool. The precisely shaped recesses of the production tool function to mold the abrasive slurry to the desired precise shape. The binder precursor of the abrasive slurry must be at least partially cured or solidified while being held in the precisely shaped recesses so that that the abrasive slurry is set, and does not substantially deform from its precise shape upon removal from the production tool.

Referring now to FIGS. 4 and 5, third and fourth embodiments of an abrasive article according to the present invention are shown. Abrasive article 40 comprises backing 42 having bonded thereto a plurality of composite particles 44. Composite particles 44 comprise a plurality of abrasive particles dispersed in a binder. The composite particles are formed by curing or solidifying an abrasive slurry of the present invention in the form of individual particles. Composite particles 44 comprise binder 52 having dispersed therein abrasive particles 54, non-abrasive particles 55. The non-abrasive particles comprise a mixture of at least two distinct particle size distributions, a first larger median particle size and a second smaller median particle size distribution.

Composite particles 44 may be precisely shape or may be irregularly shaped. Precisely shaped composite particles may be formed by at least partially curing or solidifying an abrasive slurry of the present invention while the slurry is held within the precisely shaped recesses of a production tool. Irregularly shaped composite particles may be formed, for example, by crushing a cured or solidified abrasive slurry thereby forming individual irregularly shaped and sized composite particles. In this embodiment, precisely shaped composite particles 44 are bonded to backing 42 by two coatings. Coating 46, commonly referred to as a make coat, is applied over backing 42 and bonds composite particles 44 to backing 42. Coating 48, commonly referred to as a size coat, is applied over composite particles 44 and reinforces composite particles 44. Optionally, a third coating 50, commonly referred to as a supersize coat, may be applied over the size coat 48. In alternative embodiments, additional abrasive particles may be included in the make, size or supersize coatings. The composite particles may be applied to the backing by conventional techniques, such as drop coating or electrostatic coating. Depending upon the coating method, the composite particles may be oriented with respect to the backing in a non-random manner (see FIG. 4), or they may be oriented in a random manner with respect to the backing (see FIG. 5).

Backing Materials for Abrasive Articles The backing for an abrasive article according to the present invention may be any number of conventionally used backings, such as paper, cloth, film, vulcanized fiber, woven and nonwoven materials, and the like, or a combination of two or more of these materials, or treated versions thereof. The choice of backing material will depend on the intended application of the abrasive article. In the case of a woven backing, it is sometimes preferable to fill the interstices of the backing with at least one coating before the application of an abrasive slurry. Coatings used for this purpose are called saturant, back or presize coatings, depending on how and to what surface of the backing the coating is applied. Additional details on backing treatments can be found in U.S. Pat. No. 5,700,302.

Method of Making Abrasive Articles and Structured Abrasive Articles The present invention further provides methods for making abrasive articles of the present invention. A first method of making an abrasive article is provided which comprises the steps of (a) coating a backing with an abrasive slurry of the present invention; and (b) subjecting the abrasive slurry to conditions sufficient to at least partially cure the binder precursor. An abrasive slurry may be coated onto the front surface of a backing by any conventional coating method, such as, for example, roll coating, transfer coating, spraying, die coating, curtain coating, knife coating, and rotogravure coating. The abrasive coating may be have any desired surface topography. For example, the surface may be smooth, textured, or structured. The surface topography may be controlled by the coating technique used to coat the abrasive slurry (i.e., a sinusoidal-like topography may be provided by a rotogravure cylinder), or the surface topography may be produced by a separate texturing process.

Once coated, the binder precursor of the abrasive slurry is typically exposed to an energy source in order to convert the binder precursor to a binder. Conversion of the binder precursor to the binder is typically the result of a polymerization, crosslinking, gelling, or drying process. The energy source may be a source of thermal energy, or radiation energy, such as, electron beam, ultraviolet light, or visible light. The total amount of energy required to convert the binder precursor into a binder is dependent upon the chemical structure of the binder precursor, and the thickness and optical density of the abrasive slurry. When thermal energy is used, the oven temperature will typically range from about 50°C to about 250°C, and the exposure time will typically range from about 15 minutes to about 16 hours. For binder precursors solidified by free radical polymerization, the UV or visible radiation energy level (in the absence of heating) should be at least about 100 milliJoules/cm², more preferably from about 100 to about 700 milliJoules/cm², and particularly preferably from about 400 to about 600 milliJoules/cm². Ultraviolet radiation refers to electromagnetic radiation having a wavelength in the range of about 200 to about 400 nanometers, preferably within the range of about 250 to 400 nanometers. Visible radiation refers to electromagnetic radiation having a wavelength in the range of about 400 to about 800 nanometers, and preferably in the range of about 400 to about 550 nanometers. Electron beam irradiation, a form of ionizing radiation, can be used at an energy level of about 0.1 to about 10 Mrad, preferably at an energy level of about 1 to about 10 Mrad, at an accelerating potential ranging from about 150 to about 300 kiloelectron volts.

According to one method, a production tool having a plurality of precisely shaped recesses is coated with an abrasive slurry of the present invention in order to fill the precisely shaped recesses. The front surface of a backing is then brought into contact with the abrasive slurry. While in contact, the abrasive slurry is exposed to conditions sufficient to at least partially cure or solidify the binder precursor of the abrasive slurry. Finally, the backing having the abrasive coating bonded thereon is removed from the shaped surface of the production tool to yield a structured abrasive article.

Alternatively, an abrasive slurry of the present invention may be coated on the front surface of a backing. The slurry-coated front surface of the backing is then brought into contact with a production tool such that the slurry fills the precisely shaped recesses of the production tool. While in contact, the abrasive slurry is exposed to conditions sufficient to at least partially cure or solidify the binder precursor of the abrasive slurry. Finally, the backing having the abrasive coating bonded thereon is removed from the precisely shaped surface of the production tool to yield a structured abrasive article.

One preferred method of making an abrasive article of the present invention is provided which comprises the steps of: (a) providing a production tool having a major surface said major surface having a plurality of shaped recesses formed therein; (b) filling said precisely shaped recesses with an abrasive slurry of the present invention; (c) providing a backing having a front and a back surface; (d) laminating the front surface of a backing to the surface of the production tool so that at least a portion of the front surface of the backing is in direct contact with the surface of the production tool; (e) subjecting the abrasive slurry to conditions sufficient to at least partially cure the binder precursor; and (f) separating the backing from the production tool. In an alternative method, the abrasive slurry is coated onto the front surface of the backing and then the production tool is brought into coated with the abrasive slurry coated backing. The remaining steps to form the abrasive article are as those described above. The production tool of step (a) has a surface (defining a main plane) which contains a plurality of recesses distending as indentations from the main plane. These recesses define the inverse shape of the abrasive composite and are responsible for generating the shape and placement of the abrasive composites. The recesses can be provided in any geometric shape that is the inverse of a geometric shape which is suitable for an abrasive composite, such as, for example, cubic, cylindrical, prismatic, hemispheric, pyramidal, truncated pyramidal, conical, truncated conical, or post-like with a flat top surface.

One preferred shape comprises a plurality of pyramidal recesses, the pyramids have different shapes and dimensions associated with them. This type of pattern is further described in U.S. Pat. Nos. 5,672,097 and 5,946,991. Another type of pattern comprises a series of ridges, these ridges are placed at angle relative to the working direction of the abrasive belt. The ridge pattern may have between 1 to 50 ridges/cm and preferably about 5 to 25 ridges/cm. One preferred ridge pattern consists of a series of repeating ridges, each ridge has a different included angle. There may be between 2 to 50 ridges of different included angles, typically between 3 and 10 ridges of different included angles. The included angles may range from 40 to 90 degrees, typically 50 to 90 degrees. One pattern consists of a series of four different ridges that repeat, these ridges having included angles of 60, 70, 80 and 90 degrees. Measured dimensions of topographies used in suitable production tools are listed below.

The production tool can take the form of a belt, sheet, continuous sheet or web, coating roll such as a rotogravure roll, sleeve mounted on a coating roll, or die. The production tool may be composed of metal, (e.g., nickel), metal alloys, or thermoplastic material. The master tool is preferably made of a nickel-plated metal, such as nickel-plated aluminum, nickel-plated copper, or nickel-plated bronze. The metal production tool can be fabricated by any conventional technique including but not limited to photolithography, knurling, engraving, hobbing, electroforming, or diamond turning.

A production tool made of thermoplastic material may be replicated from a master tool. When a production tool is replicated from a master tool, the master tool is provided with the inverse of the pattern, which is desired, for the production tool. A production tool can be replicated from a master tool by pressing a sheet of thermoplastic material against the master tool while heating the master tool and/or the thermoplastic sheet such that the thermoplastic material is embossed with the master tool pattern. The thermoplastic material is then cooled to a solid state and is then separated from the master tool to produce a production tool.

Additional details on producing master tools and/or production tools may found in U.S. Pat. Nos. 5,435,816; 5,658,184; 5,672,097; 5,946,991 and WO 97/12727 and WO 99/11434.

Abrasive slurries of this invention may be coated using conventional techniques. These coating techniques include roll coating, transfer coating, spraying, die coating, vacuum die coating, knife coating, curtain coating, and rotogravure coating. Pressure may be applied by a nip roll or other suitable technique in order to force the abrasive slurry to flow in and fill the recesses of the production tool.

In a variation of the method, the slurry-coated backing may be separated from the production tool prior to curing or solidifying the binder precursor. Separation from the production tool may distort the surface topography of the abrasive slurry. Once separated from the production tool, the abrasive slurry is then cured or solidified.

Method of Making Abrasive Articles with Composite Particles According to the present invention, abrasive articles may be produced by first producing abrasive composite particles, and then bonding the abrasive composite particles to the front surface of a backing with a coating (i.e., a make coating), or series of coatings (i.e., a make coat and size coat). Composite particles are distinct, free-flowing, individual particles comprising a cured or solidified abrasive slurry of the present invention. Composite particles may be formed in any desired shape and/or size and may be precisely-shaped or irregularly shaped. A typical manufacturing process for producing precisely shaped abrasive composite particles using an abrasive slurry of the present invention is illustrated in FIG. 6. Apparatus 70 comprises a carrier web 72 which is fed from an unwind station 74. Unwind station 74 is in the form of a roll. The carrier web 72 can be made of a material such as paper, cloth, polymeric film (e.g., polyester film), or treated versions thereof. In FIG. 6, the carrier web 72 is transparent to radiation. An abrasive slurry of the present invention 76 is fed by gravity from a hopper 78 onto a major surface of the carrier web 72. The major surface of the carrier web 72 containing the abrasive slurry 76 is forced against the surface of a production tool 80 by means of a nip roll 82. Suitable production tools may be a patterned mandrel or patterned transparent web. The surface of the production tool 80 that contacts the carrier web contains shaped recesses. The shaped recesses shape or mold the shaped composite particles. The nip roll 82 also aids in forcing the abrasive slurry 76 into the recesses of the production tool 80. The abrasive slurry 76 then travels through a curing zone 83 where it is exposed to an energy source 84 to at least partially cure or solidify the binder precursor to form a binder. Next, the carrier web 72 containing the solidified binder is passed over a nip roll 86. There must be sufficient adhesion between the carrier web 72 and the solidified binder in order to allow for subsequent removal of the binder from the cavities of the production tool 80. The composite particles are removed from the carrier web 72 and collected in a container 90. External means 91 (e.g., ultrasonic energy) can be used to help release the composite particles 88 from the carrier web 72. The carrier web 72 is then recovered at rewind station 92 so that it can be reused. Rewind station 92 is in the form of a roll. Other methods for the production of precisely shaped abrasive composite particles are reported in U.S. Pat. No. 5,500,273 (Holmes et al.).

It is preferred that the size of the shaped abrasive composite particles range from about 25 to about 2500 micrometers, preferably from about 100 to about 1500 micrometers. The particle shape can be any geometrical shape, such as, for example, a cone, triangular prism, cylinder, pyramid, hemisphere, and a body having two opposed polygonal faces separated by a constant or varying distance (i.e., a polygonal platelet). It is also within the scope of this invention to produce irregularly shaped composite particles. A coated abrasive article utilizing individual abrasive particles or composite abrasive particles may be made according to the following procedure. A backing having a front surface and a back surface is provided. The front surface of the backing is coated with a first curable coating, commonly referred to as a make coat. The individual abrasive particles and/or abrasive composite particles are then coated or applied into the first curable coating. These abrasive particles may be drop coated or electrostatic coated. This make coat coating is then solidified or at least partially cured to adhere the particles to the backing. Optionally, a second curable coating, usually referred to as a size coating, may be applied over the individual abrasive particles or composite abrasive particles. This size coating is then solidified or at least partially cured. The size coat further bonds the abrasive particles to the backing. Optionally, additional coatings, such as a supersize coat can be applied over the individual abrasive particles or composite abrasive particles and size coat. Preferred methods of making coated abrasive products are described, for example, in U.S. Pat. Nos. 4,734,104 (Broberg), 4,737,163 (Larkey), 5,203,884 (Buchanan et al.), 5,378,251 (Culler et al.), 5,417,726 (Stout et al.), 5,436,063 (Follett et al.), 5,496,386 (Broberg et al.), and 5,520,711 (Helmin).

This invention also pertains to a bond system for coated abrasive or nonwoven abrasive articles. This bond system may be a make coat, size coat, supersize coat or combinations thereof. The bond system comprises a plurality of non-abrasive particles distributed in a binder, preferably there are two distinct particle size distributions of the non-abrasive particles. The preferred non-abrasive particles are filler particles or grinding aid particles, with the grinding aid particles being most preferred. A preferred median particle size ratio (i.e., median particle size of larger particle size distribution is divided by median particle size of smaller particle size distribution) is about 2 or greater. More preferably, the median particle size ratio is about 3 or greater, about 5 or greater, or about 7 or greater.

This invention also pertains to a method of abrading workpieces, preferably metal workpieces. Examples of typical metal workpieces include: aluminum, carbon steels, mild steels, tool steels, stainless steel, hardened steel, titanium and the like. The abrasive article made according to this invention works exceptionally well in abrading titanium. Titanium is used in a wide variety of objects such as golf clubs, shafts, bearing surfaces, jet blades and the like. The titanium grinding may be done dry or in combination with a lubricant or water. The abrasive belt speed may range from 2000 to 10000 surface feet per minute. The applied force may range from 1 to 100 kilograms, typically 1 to 10 kilograms. The present invention provides abrasive articles, which may have an improved useful product life as compared with prior art abrasive articles or may provide an improved surface finish on a workpiece. The abrasive article is especially useful in abrading titanium; in titanium grinding the abrasive article of the present invention may be capable of generating less heat. The abrasive article of the present invention is capable of providing high cut rates and/or long product life in titanium grinding applications.

Reducing the rate of erosion of the coarse grade abrasive coating can provide an improved useful life. A reduced rate of erosion is particularly important for coarse grade abrasive articles with large particle size distribution which are prone to excessive erosion under severe grinding (abrading) conditions. The addition of the smaller particle size distribution non-abrasive particles provides increased bonding area between the binder and the non-abrasive particles thereby resulting in an abrasive composite which is stronger and less prone to erosion under severe grinding conditions.

An improved useful life may be provided by increased the rate of erosion of the fine grade abrasive coating. A increased rate of erosion is particularly important for fine grade abrasive articles with small particle size distribution which are prone to minimal erosion due to the light pressing generally employed. The addition of the larger particle size distribution non-abrasive particles provides for a means to increase the erodibility of the abrasive article under reduced pressure. It is within one skilled in the abrasive art to formulate the abrasive coating to have the desired rate of erodability. The following non-limiting examples will further illustrate the invention. All parts, percentages, ratios, etc., in the examples are by weight unless otherwise indicated. The following abbreviations and trade designations are used throughout:

FSX-120 fused aluminum oxide abrasive particles, grade P-120, commercially available from Triebacher under the trade designation "FSX P-120";

FSX-180 fused aluminum oxide abrasive particles, grade P-180, commercially available from Triebacher under the trade designation "FSX P-180"; FSX-2000 fused aluminum oxide abrasive particles, grade P-2000, commercially available from Triebacher under the trade designation "FSX P-2000";

OX-50 amorphous silica filler, commercially available from DeGussa Corp. under the trade designation "OX-50";

KBF4-1 potassium tetrafluoroborate with 90% of the particles passing through a US standard mesh 200 sieve, commercially available from Atotech, Rock Hill,

SC, under the trade designation "Spec 102";

KBF4-2 potassium tetrafluoroborate with 75% of the particles not passing through a

US standard mesh 200 sieve, commercially available from Atotech, Rock

Hill, SC, under the trade designation "Spec 104";

IRG369 2-benzyl-2-N,N-dimethylamino- 1 -(4-morpholinophenyl)- 1 -butanone, commercially available from Ciba Geigy Corp. under the trade designation "IRGACURE 369";

A- 174 silane coupling agent, 3-methacryloxypropyl-trimethoxysilane, commercially available from Union Carbide under the trade designation

"A-174";

SR368 triacrylate of tris(hydroxy ethyl)isocyanurate, commercially available from

Sartomer Co., under the trade designation "SR368";

SR351 trimefhylol propane triacrylate, commercially available from Sartomer Co., under the trade designation "SR351";

PER cumene peroxide, commercially available from Aldrich Chemical Co.,

Milwaukee, WI.

The abrasive articles produced and used in the examples below were made according to one of the procedures for preparing abrasive articles described below, and the abrasive articles were tested according to the test procedures described below. Table 1 The Base Abrasive Slurry Formulation

Table 2

The Formulations and Process Conditions of

Comparative Examples A-B and Examples 1-5

AP - Abutting Pyramids SP - Spaced Pyramids

The formulations from Table 2 show that using the KBF4-2 in the formulation increased the mineral loading. The use of the KBF4-2 in the slurry formulation allows for a significant increase in the mineral loading of these formulations. Even though the mineral loading is increased the resulting slurry viscosity is well within the range that may easily be coated in the process described to make the abrasive samples. Table 3 The Rocker Drum Test Results of Comparative Examples A-B and Examples 1-5

The data in Table 3 indicates that the addition of the KBF4-2 does not adversely affect the cut in the formulations studied. In all formulations except Ex. 5 the cut as measured by the rocker drum test was improved. This is most likely due to the increased mineral loading in the formulations. The erodability of the structured product as measured by the caliper loss after the rocker drum test was run indicates that the combination of increased mineral loading, addition of KBF4-2 and topography all improved the erodability of the abrasive structure.

Table 4 The Formulations and Production Tool Type of Comparative Examples C-D and Examples 6-10

AP - Abutting Pyramids TR - Triangular Ridges

The Formulations in Table 4 were run to see if the use of the KBF4-2 could be used with larger sized mineral than the formulations in Table 2. A similar result was obtained in that the mineral was increased through the use of the KBF4-2 and the viscosity was still coatable using the process described to make the coated abrasive article. Two 20 mil high topographies were coated to study the effect of the increased mineral loaded formulations. Ex. 8-10 were prepared to determined the use of a thermal cure additive in addition to the radiation cure initiator would impact the performance of the coated slurry. Table 5 shows the rocker drum data at 4# weight. The data indicates that the life of the product is affected by topography and the life of the 20 TR topography can be greatly improved through the additional use of the thermal cure initiator. This allowed for the cure of the slurry even though the mineral loading was increased.

Table 5

The Rocker Drum Test Results of

As with the fine grade examples of Table 3, the breakdown of the abrasive slurry was improved by having increased mineral loading and better cure. Ex. 9 and 10 were coated thicker than the other samples by about 3 mils in caliper. The combination of better cure and improved slurry formulation allowed the continuous land area under the define topography to continue cutting and to erode away to the backing. Table 6 The Rocker Drum Test results of Examples C-D and Examples 6-10 at 8# weight

Table 6 shows the results of cut and caliper loss for the slurry formulations of Table 4 when the grinding force is increased by increasing the weight on the workpiece. The amount of metal removed in more than doubles at 500 cycles compared to the 4# results in Table 5. The caliper loss in much greater at the higher pressures as can be seen by the caliper loss values in Table 6 at 500 cycles compared to those in Table 5 after the cut rate had dropped of significantly. The same trend in increased erodability of the abrasive slurry is found at the higher grinding pressures as was seen through the 4-pound data in Table 5.

General Procedure for Preparing Examples 1-5 and Comparative Examples A-B The following general procedure was used to make the structured abrasive articles reported in Examples 1-5 and Comparative Examples A-B. Either an abutting pyramid production tool or a spaced pyramid production tool was used, according to

Table 2.

First, a base abrasive slurry, comprising a binder precursor, was prepared by thoroughly mixing the raw materials of the premix as listed in Table 1 with a

Morehouse-Cowles Visco-Max high shear mixer from Trident Process, Inc., Bloomington,

MN. Then FSX-2000 and KBF4-1 were added to the mixer in amounts according to

Table-2. The operative conditions of the mixer for each sample is listed also in Table 2.

The abrasive slurry was coated directly onto an J-weight rayon cloth backing (having a latex phenolic backing treatment and a one mil SR368/SR351 tie coat ) at a speed of about

15 meters/ minute or 30 meters/ minute (50 or 100 ft/min) with a knife coater using a gap of 50 or 253 micrometers (2 or 10 mils).

Next, the production tooling was pressed against the slurry with the force of a rubber nip roll so that the slurry filled the recesses of the production tool. UV/visible radiation, at a dosage of about 236 Watts/cm (600 Watts/inch) produced by 2 "D" bulbs available from Fusion Systems, was transmitted through the tooling and into the abrasive slurry. The UV/visible radiation initiated the polymerization of the binder precursor and resulted in the abrasive slurry forming abrasive composites which were adhered to the cloth substrate. The coated abrasive product was post cured 12 hours at 115°C (240°F) to cure the backing treatment.

General Procedure for Preparing Examples 6-10 and Comparative Examples C-D

Examples 6-10 and Comparative Examples C-D were prepared according to the procedure above for Example 1-5, except FSX-2000 was replaced by FSX-180 and FSX- 120 and a 20 mil abutting pyramid or triangular ridge production tool was used. The formulations are listed in Table 4.

All the examples prepared above were tested using a rocking drum test. A 6 cm by 23 cm strip of abrasive article was placed on a drum having a 30.5 cm (12 inch) diameter and 3.6 kg (8 lbs) force pressed a 0.476 cm by 0.476 cm by 15.24 cm (3/16 inch by 3/16 inch by 6 inch) 1018 mild steel workpiece onto and against the abrasive article. The abrasive article was oscillated for 500 cycles at a rate of one cycle per second over a total distance of 25 cm (10 inches) per cycle. The amount of thickness lost by the abrasive composites was measured with a micrometer and the results are reported in Table 3, the thickness of the abrasive article was measured in 4 places before testing and then again after the 500 cycles and the difference was calculated. The testing results are listed in the Tables.

Claims

1. An abrasive article having an abrasive coating bonded to a front surface of a backing, the abrasive coating comprising: a) a binder; b) a plurality of abrasive particles having a Mohs' hardness of 7 or greater dispersed in said binder, and c) a plurality of non-abrasive particles, having a Mohs' hardness less than about 6 dispersed in the binder, wherein the non-abrasive particles have a particle size greater than a particle size of the abrasive particles.

2. An abrasive article according to claim 1 wherein the plurality of non-abrasive particles are selected from the group consisting of filler particles and grinding aid particles.

3. An abrasive article according to claim 2 wherein the non-abrasive particles are halide salt grinding aid particles.

4. An abrasive article according to claim 1 wherein the abrasive coating is a textured coating.

5. An abrasive article according to claim 1 wherein the abrasive coating is a smooth coating.

6. An abrasive article according to claim 1 wherein the abrasive coating is a structured coating comprising an array of precisely shaped abrasive composites.

7. An abrasive article according to claim 6 wherein the array is random.

8. An abrasive article according to claim 6 wherein the array is patterned.

9. An abrasive article according to claim 1, wherein a first distribution of non-abrasive particles have a mean particle size greater than 105 micrometers.

10. An abrasive article according to claim 9, wherein a second distribution of non-abrasive particles have a mean particle size less than 30 micrometers.

11. An abrasive article according to claim 1 wherein the non-abrasive particles comprise: a first particle size distribution having a first median particle size; and a second particle size distribution having a second median particle size; wherein a ratio of the first non-abrasive particle size distribution to the second non-abrasive particle size distribution is about 2 or greater.

12. An abrasive article according to claim 1 1 wherein the ratio is about 3 or greater.

13. An abrasive article according to claim 11 wherein the ratio is about 5 or greater.

14. An abrasive article according to claim 1 1 wherein the ratio is about 7 or greater.

15. An abrasive slurry comprising: a) a binder precursor; b) plurality of abrasive particles having a Mohs' hardness of 7 or greater dispersed in the binder precursor; and c) a plurality of non-abrasive particles having a Mohs' hardness less than about 6 dispersed in the binder precursor; wherein the non-abrasive particles have a median particle size greater than a median particle size of the abrasive particles.

16. An abrasive slurry according to claim 15, wherein a first distribution of non-abrasive particles have a mean particle size greater than 105 micrometers.

17. An abrasive slurry according to claim 15, wherein a second distribution of non-abrasive particles have a mean particle size less than 30 micrometers.

18. An abrasive slurry according to claim 15 wherein the non-abrasive particles comprise: a first particle size distribution having a first median particle size; and a second particle size distribution having a second median particle size; wherein the ratio of the first non-abrasive particle size distribution to the second non-abrasive particle size distribution is about 2 or greater.

19. An abrasive slurry according to claim 18 wherein the ratio is about 3 or greater.

20. An abrasive slurry according to claim 18 wherein the ratio is about 5 or greater.

21. An abrasive slurry according to claim 18 wherein the ratio is about 7 or greater.

22. A method of making an abrasive article comprising the steps of:

(a) coating a backing with an abrasive slurry comprising: a binder precursor; a plurality of abrasive particles having a Mohs' hardness of 7 or greater dispersed in the binder precursor; a plurality of non-abrasive particles having a Mohs' hardness less than about 6 dispersed in the binder precursor; wherein the non-abrasive particles have a particle size greater than the particle size of the abrasive particles,

(b) subjecting the abrasive slurry to conditions sufficient to at least partially cure said binder precursor.

23. A method of making an abrasive article comprising the steps of:

(a) providing a production tool having a major surface with a plurality of precisely shaped recesses formed therein;

(b) filling the precisely shaped recesses with an abrasive slurry comprising: a binder precursor; a plurality of abrasive particles having a Mohs' hardness of 7 or greater randomly dispersed in said binder precursor; and a plurality of non-abrasive particles having a Mohs' hardness less than about 6, wherein the non-abrasive particles have a particle size greater than a particle size of the abrasive particles.

(c) providing a backing having front and back surfaces;

(d) laminating the front surface of the backing to the filled surface of the production tool so that at least a portion of the front surface of the backing is in direct contact with the filled surface of the production tool;

(e) subjecting the abrasive slurry to conditions sufficient to at least partially cure the binder precursor; and

(f) separating the backing from said production tool.

24. A method of making an abrasive article according to claim 23 wherein step

(f) is performed before to step (e).

25. A method of making an abrasive article comprising the steps of:

(b) filling the precisely shaped recesses with an abrasive slurry comprising: a binder precursor, a plurality of abrasive particles having a Mohs' hardness of 7 or greater randomly dispersed in said binder precursor, a plurality of non-abrasive particles having a Mohs' hardness less than about 6 dispersed in the binder precursor; wherein the non-abrasive particles have a particle size greater than a particle size of the abrasive particles,

(c) subjecting the abrasive slurry to conditions sufficient to at least partially cure the binder precursor to form precisely shaped composite particles;

(d) removing the precisely shaped composite particles from the precisely shaped recesses of the production tool;

(e) providing a backing having a front surface; and

(f) adhering a plurality of the precisely shaped composite particles to the front surface of the backing with a make coat.

26. An abrasive article having a plurality of composite particles adhered to a backing with a make coat, wherein the composite particles comprise: a binder; a plurality of abrasive particles having a Mohs' hardness of 7 or greater dispersed in the binder; and a plurality of non-abrasive particles having a Mohs' hardness less than about 6 dispersed in the binder, wherein the non-abrasive particles have a particle size greater than the particle size of the abrasive particles.

27. An abrasive article according to claim 26 wherein the composite particles are precisely shaped.

28. An abrasive article according to claim 26 further comprising a size coat.