Patent Description:
Coated abrasive discs made from triangular abrasive platelets are useful for abrading, finishing, or grinding a wide variety of materials and surfaces in the manufacturing of goods. In particular, highpressure off-hand grinding of carbon steel by off-hand abrading with a handheld right-angle grinder is an important application for coated abrasive discs. In view of the above, there continues to be a need for improving the cost, performance, and/or life of the coated abrasive discs.

Coated abrasive articles having rotationally aligned triangular abrasive platelets are disclosed in <CIT>), or also in document <CIT>. The coated abrasive articles have a plurality of triangular abrasive platelets each having a surface feature. The plurality of triangular abrasive platelets is attached to a flexible backing by a make coat comprising a resinous adhesive forming an abrasive layer. The surface features have a specified Z-axis rotational orientation that occurs more frequently in the abrasive layer than would occur by a random Z-axis rotational orientation of the surface feature.

According to claim <NUM>, the present invention , provides a coated abrasive disc comprising:.

Advantageously, coated abrasive discs according to the present disclosure are useful for highpressure off-hand abrading of carbon steel, where they exhibit superior performance as compared to previous similar discs.

According to claim <NUM>, the present invention provides a method of abrading a workpiece, the method comprising frictionally contacting a portion of the abrasive layer of a coated abrasive disc according to the device claims with a workpiece, and moving at least one of the workpiece and the coated abrasive disc relative to the other to abrade the workpiece.

According to claim <NUM>, the present invention provides a method of making a coated abrasive disc, the method comprising:.

As used herein:
The term "mild steel" refers to a carbon-based steel alloy containing less than about <NUM> percent by weight of carbon.

The term "offhand abrading" means abrading where the operator manually urges the disc/wheel against a workpiece or vice versa.

The term "proximate" means very near or next to (e.g., contacting or embedded in a binder layer contacting).

The term "spiral" refers to a spiral which is planar. In some preferred embodiments, the spiral may be an arithmetic spiral, also known as an "Archimedean spiral". An arithmetic spiral has the property that any ray from the origin intersects successive turnings of the spiral in points with a constant separation distance.

The term "workpiece" refers to a thing being abraded.

As used herein, the term "triangular abrasive platelet", means a ceramic abrasive particle with at least a portion of the abrasive particle having a predetermined shape that is replicated from a mold cavity used to form the shaped precursor abrasive particle. Except in the case of abrasive shards (e.g., as described in <CIT>), the triangular abrasive platelet will generally have a predetermined geometric shape that substantially replicates the mold cavity that was used to form the triangular abrasive platelet. Triangular abrasive platelet as used herein excludes randomly sized abrasive particles obtained by a mechanical crushing operation.

As used herein, "Z-axis rotational orientation" refers to the angular rotation, about a Z-axis perpendicular to the major surface of the disc backing, of the longitudinal dimension the triangular abrasive platelet sidewall that most faces the disc backing.

Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.

<FIG> shows an exemplary coated abrasive disc <NUM> according to the present disclosure, wherein triangular abrasive platelets <NUM> are secured at precise locations and Z-axis orientations to a disc backing <NUM>.

Referring now to <FIG> and <FIG>, abrasive layer <NUM> disposed on a major surface <NUM> of disc backing <NUM>. Abrasive layer <NUM> comprises triangular abrasive platelets <NUM> secured to major surface <NUM> of disc backing <NUM> by at least one binder material (shown as make layer <NUM> and size layer <NUM>). Optional supersize layer <NUM> overlays size layer <NUM>. Triangular abrasive platelets <NUM> are disposed at regularly-spaced points <NUM> along an arithmetic spiral pattern <NUM> extending outwardly toward outer circumference <NUM>. On a respective basis, one sidewall of at least <NUM> percent of each of the triangular abrasive platelets <NUM> disposed facing and proximate to the disc backing is lengthwise aligned within <NUM> degrees of being tangent to the arithmetic spiral pattern <NUM> at the corresponding points <NUM>. In this regard, collinear and parallel configurations are to be considered as being aligned at zero degrees relative to the tangent.

The disc backing may comprise any known coated abrasive backing, for example. In some embodiments, the disc backing comprises a continuous uninterrupted disc, while in others it may have a central arbor hole for mounting. Likewise, the disc backing may be flat or it may have a depressed central hub, for example, a Type <NUM> depressed center disc. The disc backing may be rigid, semi-rigid, or flexible. In some embodiments, the backing has a mechanical fastener, or adhesive fastener securely attached to a major surface opposite the abrasive layer. Suitable materials for the substrate include polymeric films, metal foils, woven fabrics, knitted fabrics, paper, vulcanized fiber, nonwovens, foams, screens, laminates, combinations thereof, and treated versions thereof. For off-hand grinding applications where stiffness and cost are concerns, vulcanized fiber backings are typically preferred. For applications where stiffness of the backing is desired, a flexible backing may also be used by affixing it to a rigid backup pad mounted to the grinding tool.

The disc backing is generally circular and preferably rotationally symmetric around its center. Preferably it has a circular perimeter, but it may have additional features along the perimeter such as, for example, in the case of a scalloped perimeter.

The abrasive layer may comprise a single binder layer having abrasive particles retained therein, or more typically, a multilayer construction having make and size layers. Coated abrasive discs according to the present disclosure may include additional layers such as, for example, an optional supersize layer that is superimposed on the abrasive layer, or a backing antistatic treatment layer may also be included, if desired. Exemplary suitable binders can be prepared from thermally curable resins, radiation-curable resins, and combinations thereof.

The make layer can be formed by coating a curable make layer precursor onto a major surface of the backing. The make layer precursor may comprise, for example, glue, phenolic resin, aminoplast resin, urea-formaldehyde resin, melamine-formaldehyde resin, urethane resin, free-radically polymerizable polyfunctional (meth)acrylate (e.g., aminoplast resin having pendant α,β-unsaturated groups, acrylated urethane, acrylated epoxy, acrylated isocyanurate), epoxy resin (including bis-maleimide and fluorene-modified epoxy resins), isocyanurate resin, and mixtures thereof. Of these, phenolic resins are preferred, especially when used in combination with a vulcanized fiber backing.

Phenolic resins are generally formed by condensation of phenol and formaldehyde, and are usually categorized as resole or novolac phenolic resins. Novolac phenolic resins are acid-catalyzed and have a molar ratio of formaldehyde to phenol of less than <NUM>:<NUM>. Resole (also resol) phenolic resins can be catalyzed by alkaline catalysts, and the molar ratio of formaldehyde to phenol is greater than or equal to one, typically between <NUM> and <NUM>, thus presenting pendant methylol groups. Alkaline catalysts suitable for catalyzing the reaction between aldehyde and phenolic components of resole phenolic resins include sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide, organic amines, and sodium carbonate, all as solutions of the catalyst dissolved in water.

Resole phenolic resins are typically coated as a solution with water and/or organic solvent (e.g., alcohol). Typically, the solution includes about <NUM> percent to about <NUM> percent solids by weight, although other concentrations may be used. If the solids content is very low, then more energy is required to remove the water and/or solvent. If the solids content is very high, then the viscosity of the resulting phenolic resin is too high which typically leads to processing problems.

Phenolic resins are well-known and readily available from commercial sources. Examples of commercially available resole phenolic resins useful in practice of the present disclosure include those marketed by Durez Corporation under the trade designation VARCUM (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>); those marketed by Ashland Chemical Co. of Bartow, Florida under the trade designation AEROFENE (e.g., AEROFENE <NUM>); and those marketed by Kangnam Chemical Company Ltd. of Seoul, South Korea under the trade designation PHENOLITE (e.g., PHENOLITE TD-<NUM>).

The make layer precursor may be applied by any known coating method for applying a make layer to a backing such as, for example, including roll coating, extrusion die coating, curtain coating, knife coating, gravure coating, and spray coating.

The basis weight of the make layer utilized may depend, for example, on the intended use(s), type(s) of abrasive particles, and nature of the coated abrasive disc being prepared, but typically will be in the range of from <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> grams per square meter (gsm) to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or even <NUM> gsm. The make layer may be applied by any known coating method for applying a make layer (e.g., a make coat) to a backing, including, for example, roll coating, extrusion die coating, curtain coating, knife coating, gravure coating, and spray coating.

Once the make layer precursor is coated on the backing, the triangular abrasive platelets are applied to and embedded in the make layer precursor. The triangular abrasive platelets are applied nominally according to a predetermined pattern and Z-axis rotational orientation onto the make layer precursor.

Triangular abrasive platelets are disposed at regularly-spaced (i.e., spaced apart at a constant interval) points along the arithmetic spiral pattern extending outwardly toward the outer circumference. At least <NUM> percent (e.g., at least <NUM> percent or at least <NUM> percent or even at least <NUM> percent) of the points <NUM> have one of the triangular abrasive platelets disposed thereat. The arithmetic spiral pattern may cover a portion of the major surface of the disc backing or the entire backing.

Referring now to <FIG>, each one of triangular abrasive platelets <NUM> has respective top and bottom surfaces (<NUM>,<NUM>) connected to each other, and separated, by three sidewalls 166a, 166b, 166c.

One sidewall 166a of at least <NUM> percent (e.g., at least <NUM> percent, at least <NUM> percent or even <NUM> percent) of the triangular abrasive platelets <NUM> is disposed facing (and preferably proximate to) disc backing <NUM> (see <FIG>). Further, each sidewall <NUM> that is disposed facing disc backing <NUM> has a horizontal Z-axis <NUM> rotational orientation Θ that is within <NUM> degrees (preferably within <NUM> degrees, and more preferably within <NUM> degrees) of the tangent <NUM> to the arithmetic spiral pattern at the respective point <NUM> where it is disposed.

<FIG> show another embodiment of a useful triangular abrasive platelets <NUM>, triangular abrasive platelet <NUM> has respective top and bottom surfaces (<NUM>, <NUM>) connected to each other, and separated by, three sloping sidewalls (<NUM>).

In this regard, the horizontal Z-axis rotational direction is considered to be within <NUM> degrees of the tangent at a point on the spiral pattern if its Z-axis projection onto the arithmetic spiral pattern <NUM> (which is planar) intersects the tangent line at an angle of <NUM> degrees or less. Collinear and parallel configurations are considered to intersect the tangent line at an angle of <NUM> degrees.

In some preferred embodiments, the spacing between the respective points on the arithmetic spiral pattern is from <NUM> to <NUM> times, more preferably <NUM> to <NUM> times, and even more preferably <NUM> to <NUM> times the average length of the sidewalls of the triangular abrasive platelets that are facing the fiber disc backing, although other spacings may also be used.

It is permissible that some of the regularly-spaced points along the arithmetic spiral may not have a triangular abrasive platelet disposed at that location. In preferred embodiments, at least <NUM> percent (preferably at least <NUM> percent, more preferably at least <NUM> percent, and more preferably at least <NUM> percent) of contiguous regularly-spaced points adjacent to points occupied by a triangular abrasive platelet also have a triangular abrasive platelet disposed thereat.

In some embodiments, the triangular abrasive platelets are shaped as thin triangular prisms, while in other embodiments, the triangular abrasive platelets are shaped as truncated triangular pyramids (preferably with a taper angle of about <NUM> degrees). The triangular abrasive platelets may have different side lengths, but are preferably equilateral on their largest face.

The triangular abrasive platelets have sufficient hardness to function as abrasive particles in abrading processes. Preferably, the triangular abrasive platelets have a Mohs hardness of at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, or even at least δ. Preferably, they comprise alpha alumina.

Crushed abrasive or non-abrasive particles may be included in the abrasive layer between the abrasive elements and/or abrasive platelets, preferably in sufficient quantity to form a closed coat (i.e., substantially the maximum possible number of particles of nominal specified grade(s) that can be retained in the abrasive layer).

Examples of suitable abrasive particles include: fused aluminum oxide; heat-treated aluminum oxide; white fused aluminum oxide; ceramic aluminum oxide materials such as those commercially available under the trade designation <NUM> CERAMIC ABRASIVE GRAIN from <NUM> Company, St. Paul, MN; brown aluminum oxide; blue aluminum oxide; silicon carbide (including green silicon carbide); titanium diboride; boron carbide; tungsten carbide; garnet; titanium carbide; diamond; cubic boron nitride; garnet; fused alumina zirconia; iron oxide; chromia; zirconia; titania; tin oxide; quartz; feldspar; flint; emery; sol-gel-derived abrasive particles; and combinations thereof. Of these, molded sol-gel derived alpha alumina triangular abrasive platelets are preferred in many embodiments. Abrasive material that cannot be processed by a sol-gel route may be molded with a temporary or permanent binder to form shaped precursor particles which are then sintered to form triangular abrasive platelets, for example, as described in <CIT>).

Examples of sol-gel-derived abrasive particles and methods for their preparation can be found in <CIT>); <CIT>); <CIT>), <CIT>); and <CIT>). It is also contemplated that the abrasive particles could comprise abrasive agglomerates such, for example, as those described in<CIT>) or <CIT>). In some embodiments, the triangular abrasive platelets may be surface-treated with a coupling agent (e.g., an organosilane coupling agent) or other physical treatment (e.g., iron oxide or titanium oxide) to enhance adhesion of the abrasive particles to the binder (e.g., make and/or size layer). The abrasive particles may be treated before combining them with the corresponding binder precursor, or they may be surface treated in situ by including a coupling agent to the binder.

Preferably, the triangular abrasive platelets comprise ceramic abrasive particles such as, for example, sol-gel-derived polycrystalline alpha alumina particles. Triangular abrasive platelets composed of crystallites of alpha alumina, magnesium alumina spinel, and a rare earth hexagonal aluminate may be prepared using sol-gel precursor alpha alumina particles according to methods described in, for example, <CIT>) and <CIT>) and <CIT>).

Alpha alumina-based triangular abrasive platelets can be made according to well-known multistep processes. Briefly, the method comprises the steps of making either a seeded or non-seeded sol-gel alpha alumina precursor dispersion that can be converted into alpha alumina; filling one or more mold cavities having the desired outer shape of the triangular abrasive platelet with the sol-gel, drying the sol-gel to form precursor triangular abrasive platelets; removing the precursor triangular abrasive platelets from the mold cavities; calcining the precursor triangular abrasive platelets to form calcined, precursor triangular abrasive platelets, and then sintering the calcined, precursor triangular abrasive platelets to form triangular abrasive platelets. The process will now be described in greater detail.

Further details concerning methods of making sol-gel-derived abrasive particles can be found in, for example, <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); and <CIT>); and in <CIT>).

The triangular abrasive platelets may include a single kind of triangular abrasive platelets or a blend of two or more sizes and/or compositions of triangular abrasive platelets. In some preferred embodiments, the triangular abrasive platelets are precisely-shaped in that individual triangular abrasive platelets will have a shape that is essentially the shape of the portion of the cavity of a mold or production tool in which the particle precursor was dried, prior to optional calcining and sintering.

Triangular abrasive platelets used in the present disclosure can typically be made using tools (i.e., molds) cut using precision machining, which provides higher feature definition than other fabrication alternatives such as, for example, stamping or punching. Typically, the cavities in the tool surface have planar faces that meet along sharp edges, and form the sides and top of a truncated pyramid. The resultant triangular abrasive platelets have a respective nominal average shape that corresponds to the shape of cavities (e.g., truncated pyramid) in the tool surface; however, variations (e.g., random variations) from the nominal average shape may occur during manufacture, and triangular abrasive platelets exhibiting such variations are included within the definition of triangular abrasive platelets as used herein.

In some embodiments, the base and the top of the triangular abrasive platelets are substantially parallel, resulting in prismatic or truncated pyramidal shapes, although this is not a requirement. In some embodiments, the sides of a truncated trigonal pyramid have equal dimensions and form dihedral angles with the base of about <NUM> degrees. However, it will be recognized that other dihedral angles (including <NUM> degrees) may also be used. For example, the dihedral angle between the base and each of the sides may independently range from <NUM> to <NUM> degrees, typically <NUM> to <NUM> degrees, more typically <NUM> to <NUM> degrees.

As used herein in referring to triangular abrasive platelets, the term "length" refers to the maximum dimension of a triangular abrasive platelet. "Width" refers to the maximum dimension of the triangular abrasive platelet that is perpendicular to the length. The terms "thickness" or "height" refer to the dimension of the triangular abrasive platelet that is perpendicular to the length and width.

Examples of sol-gel-derived triangular alpha alumina (i.e., ceramic) abrasive particles can be found in <CIT>); <CIT>(<CIT>)); and <CIT>). Details concerning such abrasive particles and methods for their preparation can be found, for example, in <CIT>); <CIT>); and <CIT>); and in <CIT>. ); and <CIT>).

The triangular abrasive platelets are typically selected to have a length in a range of from <NUM> micron to <NUM> microns, more typically <NUM> microns to about <NUM> microns, and still more typically from <NUM> to <NUM> microns, although other lengths may also be used.

Triangular abrasive platelets are typically selected to have a width in a range of from <NUM> micron to <NUM> microns, more typically <NUM> microns to <NUM> microns, and more typically <NUM> microns to <NUM> microns, although other lengths may also be used.

Triangular abrasive platelets are typically selected to have a thickness in a range of from <NUM> micron to <NUM> microns, more typically from <NUM> micron to <NUM> microns, although other thicknesses may be used.

In some embodiments, triangular abrasive platelets may have an aspect ratio (length to thickness) of at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or more.

Surface coatings on the triangular abrasive platelets may be used to improve the adhesion between the triangular abrasive platelets and a binder in coated abrasive discs, or can be used to aid in electrostatic deposition of the triangular abrasive platelets. In one embodiment, surface coatings as described in <CIT>) in an amount of <NUM> to <NUM> percent surface coating to triangular abrasive platelet weight may be used. Such surface coatings are described in <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); and <CIT>). Additionally, the surface coating may prevent the triangular abrasive platelet from capping. Capping is the term to describe the phenomenon where metal particles from the workpiece being abraded become welded to the tops of the triangular abrasive platelets. Surface coatings to perform the above functions are known to those of skill in the art.

The abrasive particles may be independently sized according to an abrasives industry recognized specified nominal grade. Exemplary abrasive industry recognized grading standards include those promulgated by ANSI (American National Standards Institute), FEPA (Federation of European Producers of Abrasives), and JIS (Japanese Industrial Standard). ANSI grade designations (i.e., specified nominal grades) include, for example: ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, and ANSI <NUM>. FEPA grade designations include F4, F5, F6, F7, F8, F10, F12, F14, F16, F16, F20, F22, F24, F30, F36, F40, F'<NUM>, F54, F60, F70, F80, F90, F100, F120, F150, F180, F220, F230, F240, F280, F320, F360, F400, F500, F600, F800, F1000, F12. <NUM>, F1500, and F2000. JIS grade designations include JIS8, JIS12, JIS16, JIS24, JIS36, JIS46, JIS54, JIS60, J1S80, JIS100, JIS150, JIS180, JIS220, JIS240, JIS280, JIS320, JIS360, JIS400, JIS600, JIS800, J1S1000, JIS1500, JIS2500, JIS4000, JIS6000, JIS8000, and JIS10000. According to one embodiment of the present disclosure, the average diameter of the abrasive particles may be within a range of from <NUM> to <NUM> microns in accordance with FEPA grades F60 to F24.

Alternatively, the abrasive particles can be graded to a nominal screened grade using U. Standard Test Sieves conforming to ASTM E-<NUM> "Standard Specification for Wire Cloth and Sieves for Testing Purposes". ASTM E-<NUM> prescribes the requirements for the design and construction of testing sieves using a medium of woven wire cloth mounted in a frame for the classification of materials according to a designated particle size. A typical designation may be represented as -<NUM>+<NUM> meaning that the abrasive particles pass through a test sieve meeting ASTM E-<NUM> specifications for the number <NUM> sieve and are retained on a test sieve meeting ASTM E-<NUM> specifications for the number <NUM> sieve. In one embodiment, the abrasive particles have a particle size such that most of the particles pass through an <NUM> mesh test sieve and can be retained on a <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> mesh test sieve. In various embodiments, the abrasive particles can have a nominal screened grade of: -<NUM>+<NUM>, -<NUM>/+<NUM>, -<NUM>+<NUM>, - <NUM>+<NUM>, -<NUM>+<NUM>. <NUM> -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>/+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, - <NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, -<NUM>+<NUM>, or -<NUM>+<NUM>. Alternatively, a custom mesh size can be used such as -<NUM>+<NUM>.

The arithmetic spiral pattern can be characterized by its pitch (i.e., the regular separation between lines of the spiral pattern while traveling radially outward from the real or theoretical center of the spiral pattern. In some preferred embodiments, the arithmetic spiral pattern pitch is from <NUM> to <NUM> times, more preferably <NUM> to <NUM> times, and even more preferably <NUM> to <NUM> times the thickness of the triangular abrasive platelets, although this is not a requirement. Likewise, in some preferred embodiments, the regularly-spaced interval is from <NUM> to <NUM> times, more preferably from <NUM> to <NUM> times, and even more preferably <NUM> to <NUM> times the length of the triangular abrasive platelets, although this is not a requirement.

Coated abrasive discs according to the present disclosure can be made by a method in which the triangular abrasive platelets are precisely placed and oriented. The method generally involves the steps of filling the cavities in a production tool each with one or more triangular abrasive platelets (typically one or two), aligning the filled production tool and a make layer precursor-coated backing for transfer of the triangular abrasive platelets to the make layer precursor, transferring the abrasive particles from the cavities onto the make layer precursor-coated backing, and removing the production tool from the aligned position. Thereafter, the make layer precursor is at least partially cured (typically to a sufficient degree that the triangular abrasive platelets are securely adhered to the backing), a size layer precursor is then applied over the make layer precursor and abrasive particles, and at least partially cured to provide the coated abrasive disc. The process, which may be batch or continuous, can be practiced by hand or automated, e.g., using robotic equipment. It is not required to perform all steps or perform them in consecutive order, but they can be performed in the order listed or additional steps performed in between.

The triangular abrasive platelets can be placed in a desired rotational orientation (e.g., Z-axis rotational orientation) by first placing them in appropriately shaped cavities in a dispensing surface of a production tool arranged to have a complementary arithmetic spiral pattern.

An exemplary production tool <NUM> for making the coated abrasive disc <NUM> shown in <FIG> and <FIG>, formed by casting a thermoplastic sheet <NUM>, is shown in <FIG> and <FIG>. Referring now to <FIG> and <FIG>, production tool <NUM> has a dispensing surface <NUM> comprising an arithmetic spiral pattern <NUM> of cavities <NUM> sized and shaped to receive the triangular abrasive platelets. Cavities <NUM> are Z-axis rotationally aligned so that when filled with triangular abrasive platelets that when they are subsequently transferred they form the desired corresponding arithmetic spiral pattern and Z-axis rotational orientation in the resultant coated abrasive disc.

Once most, or all, of the cavities are filled with the desired number of triangular abrasive platelets the dispensing surface is brought into close proximity or contact with the make layer precursor layer on the disc backing thereby adhering (e.g., embedding and/or contacting) and transferring the triangular abrasive platelets from the production tool to the make layer precursor while nominally maintaining horizontal orientation. Of course, some unintended loss of orientation may occur, but it should generally be manageable within the ±<NUM> degrees or less tolerance.

In some embodiments, the depth of the cavities in the production tool is selected such that the triangular abrasive platelets fit entirely within the cavities. In some preferred embodiments, the triangular abrasive platelets extend slightly beyond the openings of the cavities. In this way, they can be transferred to the make layer precursor by direct contact with reduced chance of resin transfer to the to the production tool. In some preferred embodiments, the center of mass for each triangular abrasive platelet resides within a respective cavity of the production tool when the triangular abrasive platelet is fully inserted into the cavity. If the depth of the cavities becomes too short, with the triangular abrasive platelet's center of mass being located outside of the cavity, the triangular abrasive platelets are not readily retained within the cavities and may jump back out as the production tool is used in the apparatus.

In order to fill the cavities in the production tool, an excess of the triangular abrasive platelets is preferably applied to the dispensing surface of the production tool such that more triangular abrasive platelets are provided than the number of cavities. An excess of triangular abrasive platelets, which means that there are more triangular abrasive platelets present per unit length of the production tool than cavities present, helps to ensure that most cavities within the production tool are eventually filled with a triangular abrasive platelet as the triangular abrasive platelets accumulate onto the dispensing surface and are moved about either due to gravity or other mechanically applied forces to translate them into a cavity. Since the bearing area and spacing of the abrasive particles is often designed into the production tooling for the specific grinding application, it is generally desirable to not have too much variability in the number of unfilled cavities.

Preferably, a majority of the cavities in the dispensing surface are filled with a triangular abrasive platelet disposed in an individual cavity such that the sides of the cavity and platelet are at least approximately parallel. This can be accomplished by shaping the cavities slightly larger than the triangular abrasive platelets (or multiple thereof). To facilitate filling and release it may be desirable that the cavities have inwardly sloping sidewalls with increasing depth and/or have vacuum openings at the bottoms of the cavities, wherein the vacuum opening lead to a vacuum source. It is desirable to transfer the triangular abrasive platelets onto the make layer precursor-coated backing such that they stand up or are erectly applied. Therefore, the cavity shape is designed to hold the triangular abrasive platelet erectly.

In various embodiments, at least <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> percent of the cavities in the dispensing surface contain a triangular abrasive platelet. In some embodiments, gravity can be used to fill the cavities. In other embodiments, the production tool can be inverted and vacuum applied to hold the triangular abrasive platelets in the cavities. The triangular abrasive platelets can be applied by spray, fluidized bed (air or vibration), or electrostatic coating, for example. Removal of excess triangular abrasive platelets would be done by gravity as any abrasive particles not retained would fall back down. The triangular abrasive platelets can thereafter be transferred to the make layer precursor-coated disc backing by removing vacuum.

As mentioned above, excess triangular abrasive platelets may be supplied than cavities such that some will remain on the dispensing surface after the desired number of cavities have been filled. These excess triangular abrasive platelets can often be blown, wiped, or otherwise removed from the dispensing surface. For example, a vacuum or other force could be applied to hold the triangular abrasive platelets in the cavities and the dispensing surface inverted to clear it of the remaining fraction of the excess triangular abrasive platelets.

In preferred embodiments, the production tool is formed of a thermoplastic polymer such as, for example, polyethylene, polypropylene, polyester, or polycarbonate from a metal master tool. Fabrication methods of production tools, and of master tooling used in their manufacture, can be found in, for example, <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); and <CIT>); and <CIT>) and <CIT>).

In preferred embodiments, the production tool is produced by additive manufacturing or "<NUM>-D printing", of a suitable thermoplastic, thermoset or radiation curable resin.

Once the triangular abrasive platelets have been embedded in the make layer precursor, it is at least partially cured in order to preserve orientation of the mineral during application of the size layer precursor. Typically, this involves B-staging the make layer precursor, but more advanced cures may also be used if desired. B-staging may be accomplished, for example, using heat and/or light and/or use of a curative, depending on the nature of the make layer precursor selected.

Next, the size layer precursor is applied over the at least partially cured make layer precursor and triangular abrasive platelets. The size layer can be formed by coating a curable size layer precursor onto a major surface of the backing. The size layer precursor may comprise, for example, glue, phenolic resin, aminoplast resin, urea-formaldehyde resin, melamine-formaldehyde resin, urethane resin, free-radically polymerizable polyfunctional (meth)acrylate (e.g., aminoplast resin having pendant α,β-unsaturated groups, acrylated urethane, acrylated epoxy, acrylated isocyanurate), epoxy resin (including bis-maleimide and fluorene-modified epoxy resins), isocyanurate resin, and mixtures thereof. If phenolic resin is used to form the make layer, it is likewise preferably used to form the size layer. The size layer precursor may be applied by any known coating method for applying a size layer to a backing, including roll coating, extrusion die coating, curtain coating, knife coating, gravure coating, spray coating, and the like. If desired, a presize layer precursor or make layer precursor according to the present disclosure may be also used as the size layer precursor.

The basis weight of the size layer will also necessarily vary depending on the intended use(s), type(s) of abrasive particles, and nature of the coated abrasive disc being prepared, but generally will be in the range of from <NUM> or <NUM> gsm to <NUM>, <NUM>, or even <NUM> gsm, or more. The size layer precursor may be applied by any known coating method for applying a size layer precursor (e.g., a size coat) to a backing including, for example, roll coating, extrusion die coating, curtain coating, and spray coating.

Once applied, the size layer precursor, and typically the partially cured make layer precursor, are sufficiently cured to provide a usable coated abrasive disc. In general, this curing step involves thermal energy, although other forms of energy such as, for example, radiation curing may also be used. Useful forms of thermal energy include, for example, heat and infrared radiation. Exemplary sources of thermal energy include ovens (e.g., festoon ovens), heated rolls, hot air blowers, infrared lamps, and combinations thereof.

In addition to other components, binder precursors, if present in the make layer precursor and/or presize layer precursor of coated abrasive discs according to the present disclosure may optionally contain catalysts (e.g., thermally activated catalysts or photocatalysts), free-radical initiators (e.g., thermal initiators or photoinitiators), curing agents to facilitate cure. Such catalysts (e.g., thermally activated catalysts or photocatalysts), free-radical initiators (e.g., thermal initiators or photoinitiators), and/or curing agents may be of any type known for use in coated abrasive discs including, for example, those described herein.

In addition to other components, the make and size layer precursors may further contain optional additives, for example, to modify performance and/or appearance. Exemplary additives include grinding aids, fillers, plasticizers, wetting agents, surfactants, pigments, coupling agents, fibers, lubricants, thixotropic materials, antistatic agents, suspending agents, and/or dyes.

Exemplary grinding aids, which may be organic or inorganic, include waxes, halogenated organic compounds such as chlorinated waxes like tetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride; halide salts such as sodium chloride, potassium cryolite, sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, silicon fluorides, potassium chloride, magnesium chloride; and metals and their alloys such as tin, lead, bismuth, cobalt, antimony, cadmium, iron, and titanium. Examples of other grinding aids include sulfur, organic sulfur compounds, graphite, and metallic sulfides. A combination of different grinding aids can be used.

Exemplary antistatic agents include electrically conductive material such as vanadium pentoxide (e.g., dispersed in a sulfonated polyester), humectants, carbon black and/or graphite in a binder.

Examples of useful fillers for this disclosure include silica such as quartz, glass beads, glass bubbles and glass fibers; silicates such as talc, clays, (montmorillonite) feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate, metal sulfates such as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate; gypsum; vermiculite; wood flour; aluminum trihydrate; carbon black; aluminum oxide; titanium dioxide; cryolite; chiolite; and metal sulfites such as calcium sulfite.

Optionally a supersize layer may be applied to at least a portion of the size layer. If present, the supersize typically includes grinding aids and/or anti-loading materials. The optional supersize layer may serve to prevent or reduce the accumulation of swarf (the material abraded from a workpiece) between abrasive particles, which can dramatically reduce the cutting ability of the coated abrasive disc. Useful supersize layers typically include a grinding aid (e.g., potassium tetrafluoroborate), metal salts of fatty acids (e.g., zinc stearate or calcium stearate), salts of phosphate esters (e.g., potassium behenyl phosphate), phosphate esters, urea-formaldehyde resins, mineral oils, crosslinked silanes, crosslinked silicones, and/or fluorochemicals. Useful supersize materials are further described, for example, in <CIT>). Typically, the amount of grinding aid incorporated into coated abrasive products is about <NUM> to about <NUM> gsm, more typically about <NUM> to about <NUM> gsm. The supersize may contain a binder such as for example, those used to prepare the size or make layer, but it need not have any binder.

Further details concerning coated abrasive discs comprising an abrasive layer secured to a backing, wherein the abrasive layer comprises abrasive particles and make, size, and optional supersize layers are well known, and may be found, for example, in <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); <CIT>); and <CIT>).

Coated abrasive discs according to the present disclosure are useful for abrading a workpiece; for example, by off-hand abrading with a handheld right-angle grinder. Preferred workpieces include welding beads (e.g., especially mild steel welds), flash, gates, and risers off castings.

Unless otherwise noted, all reagents were obtained, or are available from chemical vendors such as, for example, Sigma-Aldrich Company, St. Louis, Missouri, or may be synthesized by known methods. Abrasive particles used in the Examples are reported in Table <NUM>, below.

A <NUM>-inch (<NUM>-mm) circular plastic transfer tool consisting of an array of triangular cavities, having geometries such as those described in <CIT>), was prepared by <NUM>-D printing. The transfer tool pattern was a continuous spiral from center to edge where all of the cavity openings were oriented substantially edgewise with respect to the grinding direction of the rotating coated abrasive disc as shown in <FIG> and <FIG>. The cavity spacing down the length of the spiral was approximately <NUM> per inch (<NUM> per centimeter) and the spiral pitch was approximately <NUM> rows per inch (<NUM> rows per centimeter). The total number of cavities on the disc was approximately <NUM>. The transfer tool was treated with a molybdenum sulfide spray lubricant (obtained under the trade designation MOLYCOAT from the Dow Coming Corporation, Midland, Michigan) to assist abrasive grain release.

An excess of abrasive grain AP1 was applied to the surface of the transfer tool having the cavity openings and the tooling was shaken from side to side by hand. The transfer tooling cavities were soon filled with AP1 grains held in a vertex down and base up orientation and aligned along the cavity long axis. Additional AP1 was applied and the process repeated until greater than <NUM> percent of the transfer tooling cavities were filled by AP1 grain. Excess grain was removed from the surface of the transfer tool leaving only the grains contained within the cavities.

A make resin was prepared by mixing <NUM> parts resole phenolic resin (based-catalyzed condensate from <NUM>:<NUM> to <NUM>:<NUM> molar ratio of formaldehyde:phenol), <NUM> parts of calcium carbonate (HUBERCARB, Huber Engineered Materials, Quincy, Illinois) and <NUM> parts of water. <NUM> grams of make resin was applied via a brush to a <NUM>-inch (<NUM>-cm) diameter × <NUM> thick vulcanized fiber web (DYNOS VULCANIZED FIBER, DYNOS GmbH, Troisdorf, Germany) having a <NUM>-inch (<NUM>-cm) center hole.

The AP1 filled transfer tool was placed cavity side up on a <NUM>-inch by <NUM>-inch (<NUM>-cm × <NUM>-cm) square wooden board. The make resin coated surface of the vulcanized fiber disc was brought into contact with the filled transfer tool and another <NUM>-inch by <NUM>-inch (<NUM>-cm × <NUM>-cm) square wooden board was placed on top. The resulting assembly was inverted while being held in rigid contact and gently tapped to dislodge the AP1 grains from the transfer tool so as to fall base first onto the make resin surface. The vulcanized fiber disc backing was then allowed to fall away from the now substantially grain-free transfer tool resulting in an AP1 coated vulcanized fiber disc replicating the transfer tooling pattern.

A drop-coated filler grain consisting of AP2 was applied in excess to the wet make resin and agitated until the entire exposed make resin surface was filled to capacity with AP2. The disc was inverted to remove excess AP2. The amount of AP2 addition was <NUM> +/- <NUM> grams.

The make resin was partially cured in an oven by heating for <NUM> minutes at <NUM>, followed by <NUM> minutes at <NUM>, followed by <NUM> hours at <NUM>. The disc was then coated with <NUM> +/- <NUM> grams of a conventional cryolite-containing phenolic size resin and cured for <NUM> minutes at <NUM>, followed by <NUM> minutes at <NUM>, followed by <NUM> hours at <NUM>. EXAMPLE <NUM> was used to grind AISI <NUM> steel tube using Grinding Test Method A. Grinding performance results are reported in Table <NUM>.

EXAMPLE <NUM> was prepared as described in EXAMPLE <NUM>. The amount of AP2 drop coated secondary grain was <NUM> +/- <NUM> grams and the amount of cryolite size resin was <NUM> +/- <NUM> grams. EXAMPLE <NUM> was used to grind AISI <NUM> mild steel using Grinding Test Method B. AISI <NUM> mild steel has the composition, on a weight basis: <NUM> percent carbon, <NUM>-<NUM> percent manganese, <NUM> percent (max) phosphorus, <NUM> percent (max) of sulfur, and <NUM>-<NUM> percent iron. Grinding performance results are reported in Table <NUM>.

COMPARATIVE EXAMPLE A was a commercially available electro-coated vulcanized fiber disc (obtained under the trade designation 982C grade <NUM>+, <NUM> Company, Saint Paul, Minnesota). COMPARATIVE EXAMPLE A was used to grind AISI <NUM> mild steel using Grinding Test Method B. Grinding performance results are reported in Table <NUM>.

COMPARATIVE EXAMPLE B was prepared as described in EXAMPLE <NUM> with the exception as follows: The transfer tool cavities were arranged in a rectangular array pattern as described in Example <NUM> in<CIT>). The cavity array was <NUM> per inch (<NUM> per centimeter) in both horizontal and vertical directions for a total cavity density of <NUM> per square inch (<NUM> per square centimeter) or approximately <NUM> cavities for the entire tool. The transfer tool was filled with AP1 grain. The make resin amount was <NUM> +/- <NUM> grams. The drop coated secondary grain was <NUM> +/- <NUM> grams of AP2. The cryolite size resin level was <NUM> +/- <NUM> grams. COMPARATIVE EXAMPLE B was used to grind AISI <NUM> steel tube using Grinding Test Method A. Grinding performance results are reported in Table <NUM>.

COMPARATIVE EXAMPLE C was prepared as described in COMPARATIVE EXAMPLE B. The transfer tool was filled with AP1 grain. The make resin amount was <NUM> grams. The drop coated secondary grain was <NUM> grams of AP2. The cryolite size resin level was <NUM> grams. COMPARATIVE EXAMPLE C was used to grind <NUM> mild steel using Grinding Test Method B. Grinding performance results are reported in Table <NUM>.

The grinding performance of the various discs was evaluated by grinding <NUM> mild carbon steel tubes using the following procedure. Seven-inch (<NUM>-cm) diameter coated abrasive discs for evaluation were attached to a drive motor running at a constant rotational speed of <NUM> rpm and fitted with a <NUM>-inch (<NUM>) ribbed disc pad face plate (obtained as <NUM> EXTRA HARD RED RIBBED from <NUM> Company, St. Paul, Minnesota). The grinder was activated and urged against an end face of a <NUM> inch (<NUM>) diameter, <NUM> inch (<NUM>) wall thickness pre-weighed <NUM> steel tube under a controlled force of <NUM> pounds. The workpiece was abraded under these conditions for <NUM>-second grinding intervals (passes). Following each <NUM>-second interval, the workpiece was cooled to room temperature and weighed to determine the cut of the abrasive operation. The test end point was determined when the cut fell below <NUM> grams per cycle. Test results were reported as the incremental cut (g/cycle) for each interval and the total stock removed (g).

The grinding performance of the various discs was evaluated by grinding <NUM> mild carbon steel bars using the following procedure. Seven-inch (<NUM>-cm) diameter coated abrasive discs for evaluation were attached to a drive motor running at a constant rotational speed of <NUM> rpm and fitted with a <NUM>-inch (<NUM>) ribbed disc pad face plate (obtained as <NUM> EXTRA HARD RED RIBBED from <NUM> Company, St. Paul, Minnesota). The grinder was activated and urged against an end face of a <NUM> × <NUM> in (<NUM> × <NUM>) pre-weighed <NUM> steel bar under a controlled force. The workpiece was abraded under these conditions for <NUM>-second grinding intervals (passes). Following each <NUM>-second interval, the workpiece was cooled to room temperature and weighed to determine the cut of the abrasive operation. The test endpoint was determined when the cut fell below <NUM> grams per cycle. Test results were reported as the incremental cut (g/cycle) for each interval and the total stock removed (g).

Results reported in Table <NUM> (below) were obtained according to the Grinding Tests.

Claim 1:
A coated abrasive disc (<NUM>) comprising:
a disc backing (<NUM>) having an outer circumference (<NUM>);
an abrasive layer (<NUM>) disposed on the disc backing (<NUM>), wherein the abrasive layer (<NUM>) comprises triangular abrasive platelets (<NUM>) secured to a major surface (<NUM>) of the disc backing (<NUM>) by at least one binder material, wherein the triangular abrasive platelets (<NUM>) are disposed at least <NUM> percent of regularly-spaced points (<NUM>) along an arithmetic spiral pattern (<NUM>) extending outwardly toward the outer circumference (<NUM>),
wherein each one of the triangular abrasive platelets (<NUM>) has respective top and bottom (<NUM>, <NUM>) surfaces connected to each other, and separated by, three sidewalls (<NUM>), and
wherein, on a respective basis, one sidewall (<NUM>) of at least <NUM> percent of each of the triangular abrasive platelets (<NUM>) is disposed facing and proximate to the disc backing (<NUM>), and is lengthwise aligned within <NUM> degrees of being tangent to the arithmetic spiral pattern (<NUM>).