Shaped abrasive particles, methods of manufacture, and articles comprising the same

Abstract

A multi-phase abrasive particle precursor is disclosed. The precursor includes a first phase of a first material, where the first material has a substantially constant first composition throughout the first phase. The precursor also includes a second phase of a second material, where the second material has a substantially constant composition throughout the second phase. The precursor includes an interface between the first phase and the second phase. The multi-phase abrasive particle precursor is a shaped abrasive particle precursor.

Description

BACKGROUND

[0001] Abrasive particles and abrasive articles including abrasive particles can be used in product manufacturing processes to abrade, polish, or grind a variety of materials and surfaces. Thus, there is an ongoing need for improvements in the cost, performance, or longevity of abrasive particles or abrasive articles. SUMMARY

[0002] Various embodiments disclosed herein relate to a multi-phase abrasive particle precursor. The precursor includes a first phase of a first material, where the first material has a substantially constant first composition throughout the first phase. The precursor also includes a second phase of a second material, where the second material has a substantially constant composition throughout the second phase. The precursor includes an interface between the first phase and the second phase. The multi-phase abrasive particle precursor is a shaped abrasive particle precursor.

[0003] Curved shaped abrasive particles can provide significant advantages over other flat shaped abrasive particles. Curved abrasive particles can allow the particles to better adhere within an abrasive article structure. Improved adhesion can result in reduced delamination as compared to flat shaped particles or 2D polygonal shaped particles. Curved abrasive particles can better align, i.e., be more easily oriented or self-orient, within an abrasive article structure. The open structure of curved abrasive particles provides better load resistance than comparative intact particles. In the sandpaper industry, the term "load" is used to refer to a product that can become clogged or stuck with small particles of the material being sanded by the sandpaper that fill the spaces between the abrasive particles due to residue, making the sandpaper work harder or even destroying the sandpaper (ending useful life). Another feature of curved shaped abrasive particles is that the empty interior space can be filled with a grinding aid, such as a lubricant. BRIEF DESCRIPTION OF DRAWINGS

[0004] The drawings generally illustrate by way of example, and not by way of limitation, various embodiments discussed in this document.

[0005] Figures 1A-1C A shaped abrasive particle having a multiphase according to embodiments herein is shown.

[0006] Figure 2 A method of making a multi-phase shaped abrasive particle according to embodiments herein is shown.

[0007] Figure 3 An embodiment of a coated abrasive article is shown in which embodiments disclosed herein can be useful.

[0008] Figures 4A-4F A curved polyhedral shaped abrasive particle according to embodiments herein is shown.

[0009] Figure 5A curved polyhedral shaped abrasive particle precisely placed on a surface in one embodiment herein is shown.

[0010] Figure 6A and Figure 6B A method of making a curved shaped abrasive particle in an embodiment herein is shown.

[0011] Figure 7 A method of making a curved shaped abrasive particle in an embodiment herein is shown.

[0012] Figures 8A-8D Twisted abrasive particles and abrasive articles are shown where they can be useful.

[0013] Figures 9A-9E Embodiments of multi-phase abrasive particles are shown.

[0014] FIGS. 10 through Figure 13 Embodiments of curved abrasive particles and comparative results are shown.

[0015] FIGS. 14 and 15 show embodiments of twisted abrasive particles. DETAILED DESCRIPTION

[0016] Reference will now be made in detail to specific embodiments of the subject innovation, examples of which are illustrated in the accompanying drawings. While the subject innovation will be described in conjunction with the enumerated claims, it will be understood that the exemplary subject matter is not intended to limit the claims to the

[0017] Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not only the explicitly recited values and ranges of about 0.1% to about 5%, but also include individual values and sub-ranges within the indicated range, for example, 1%, 2%, 3%, and 4% and sub-ranges like 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%, etc. Unless otherwise indicated, the statement of a range "from about X to Y" has the same meaning as "from about X to about Y." Likewise, unless otherwise indicated, the statement of a range "from about X, Y, or about Z" has the same meaning as "from about X, about Y, or about Z."

[0018] In this document, the terms“a,”“an,” or“the” are used to include one or more than one unless the context clearly dictates otherwise. The term“or” is used in the inclusive sense of“and / or” unless the context clearly dictates otherwise. The expression“at least one of A and B” has the same meaning as“A, B, or A and B.” Additionally, it should be understood that the words referred to herein and not otherwise defined should be understood to have a meaning that is consistent with their meaning in the context of this document and unless otherwise defined. Any use of section headings is intended to aid reading of the document and should not be interpreted as limiting; information that is relevant to a section heading can occur within or outside of that particular section.

[0019] In the methods described herein, various acts can be carried out in any order without departing from the principles of the invention unless expressly provided otherwise. Moreover, specified acts can be conducted concurrently where appropriate, unless expressly provided otherwise. For example, performing a claimed act of X and performing a claimed act of Y can be performed concurrently in a single operation, and the resulting process would fall within the literal scope of the claimed process.

[0020] As used herein, the term“about” can allow for a degree of variability in, for example, a value or a range, for example within 10%, or 5%, or 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0021] As used herein, the term“substantially” refers to a majority of or mostly, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%.

[0022] As used herein, the term“shaped abrasive particle” means an abrasive particle in which at least a portion of the abrasive particle has a predetermined shape that is replicated from a mold cavity used to form a shaped precursor abrasive particle. Except in the case of abrasive fragments (e.g., as described in U.S. Patent Application Publication Nos. 2009 / 0169816 and 2009 / 0165394), shaped abrasive particles will typically have a predetermined geometry that substantially replicates the mold cavity used to form the shaped abrasive particle. As used herein, shaped abrasive particles do not include abrasive particles obtained by mechanical crushing operations.

[0023] For the purposes of the present invention, geometry is also intended to include regular or irregular polygons or stars, where one or more sides (peripheral portions of faces) can be arcuate (towards the interior or towards the exterior, with the first alternative being preferred). Thus, for the purposes of the present invention, triangular shapes also include three-sided polygons where one or more sides (peripheral portions of faces) can be arcuate, i.e., the definition of triangle is extended to spherical triangles, and the definition of quadrilateral is extended to super-ellipses. The second side can have (and preferably is) a second face. The second face can have edges of a second geometry.

[0024] Figures 1A-1C Shaped abrasive particles having multiple phases are shown in accordance with embodiments herein. Figures 1A-1C Three shaped abrasive particles 100, 130, 160 are shown, each of which includes a different composition of multiple phases. As shown, Figure 1A One multiple phase shaped abrasive particle includes a first layer 110 and a second layer 120, with an interface 115 extending between the first layer 110, the second layer 120. In one embodiment, the shaped abrasive particles 100, 130, and 160 are formed by filling a mold cavity with a first composition, and then with a second composition. In Figure 1A In embodiments, the mold cavity is triangularly shaped, and the materials forming the first layer 110 and the second layer 120 are deposited in order, forming a triangularly shaped first layer 110 and second layer 120. In one embodiment, the interface 115 is a distinct interface extending across the entire triangular surface. In another embodiment, the interface 115 is characterized by at least some intermixing between the compositions of the first layer 110, the second layer 120. In some embodiments, some time can pass between depositing the first layer 110 and the second layer 120, such that at least some drying occurs. In one embodiment, the two compositions can be dispensed as slurries, or in another embodiment, as gels, or in a third embodiment, as one slurry and one gel.

[0025] In contrast to the shaped abrasive particle 100, the shaped abrasive particle 130 is formed by dispensing a first material 140 in a first portion of a triangularly shaped mold cavity, and a second material 150 in a second portion of the triangularly shaped mold cavity. During dispensing of the two compounds, an interface 145 is formed when the two compositions meet. In one embodiment, the two compositions are dispensed substantially simultaneously. In one embodiment, the two compositions can be dispensed as slurries, or in another embodiment, as gels, or in a third embodiment, as one slurry and one gel.

[0026] Notably, the two compositions remain substantially constant during dispensing into the mold. For example, one composition is not provided as a dopant to the other composition. The composition of the first layer 140 remains substantially constant from the dispensing source to the mold cavity. Similarly, the composition of the second layer 150 remains substantially constant. An interface 145 is formed where the first composition 140 and the second composition 150 meet within the cavity.

[0027] Like shaped abrasive particles 130, shaped abrasive particles 160 are also formed by dispensing a first material 170 in a first portion of a mold cavity and a second material 180 in a second portion of the mold cavity. An interface 175 is formed when the compositions 170, 180 meet within the mold cavity. In one embodiment, the two compositions are dispensed substantially simultaneously. In one embodiment, the two compositions can be dispensed as a slurry, or in another embodiment, as a gel, or in a third embodiment, as one slurry and one gel.

[0028] As shown in FIG. 1, when two or more compositions are deposited in a mold cavity, an interface is formed. While only two compositions are shown in FIG. 1, it is contemplated that any number of compositions can be deposited in the mold cavity. In some embodiments, some mixing can occur at the interface, such that there are three phases, the first composition, the second composition, and the interface composition. In some embodiments, the interface substantially bisects the base of the shaped abrasive particle, as shown in FIG. 2, thereby forming two portions. In another embodiment, the interface is substantially parallel to the base of the triangle. Figures 1A-1C Figures 1A-1C As shown in FIG. 1, when two or more compositions are deposited in a mold cavity, an interface is formed. While only two compositions are shown in FIG. 1, it is contemplated that any number of compositions can be deposited in the mold cavity. In some embodiments, some mixing can occur at the interface, such that there are three phases, the first composition, the second composition, and the interface composition. In some embodiments, the interface substantially bisects the base of the shaped abrasive particle, as shown in FIG. 2, thereby forming two portions. In another embodiment, the interface is substantially parallel to the base of the triangle. Figure 1C

[0029] In one embodiment, the first composition and the second composition are alpha alumina and zirconia alumina. Alumina doped with zirconia is known to provide better abrasive performance, however abrasive particles composed of zirconia alumina can be considerably more expensive. Previous attempts in the art to obtain the benefits of zirconia alumina have included doping alpha alumina particles in certain portions or throughout the particle with zirconia particles. For example, U.S. Provisional Patent Application Publication 2013 / 0283705 to VSM describes a method of making zirconia-enhanced alumina particles that include zirconia precipitates in the alumina structure.

[0030] ​​In contrast, it is contemplated herein that there are two separate compositions separated by different interfaces. For example, one composition can be a zirconia-doped alumina slurry or gel, while the other is a slurry or gel that does not contain zirconia. Alternatively, one composition can be a zirconia alumina gel or slurry. Embodiments of abrasive particles composed of two or more compositions can include any combination of inorganic / inorganic materials, such as alumina / silica; inorganic / organic combinations, such as ceramic / polymer; or combinations of the same material with different crystalline phases, such as crystalline / amorphous. A suitable embodiment is a combination of alumina with alpha-alumina / gamma-alumina.

[0031] Other suitable abrasive compounds are also expressly contemplated, including other ceramic compounds, as discussed in more detail herein.

[0032] While shown in Figures 1A-1C is a substantially 50:50 mixture of the two compositions, it is expressly contemplated that one compound can be present in a higher amount than the other. For example, the minor composition can comprise at least 15% by volume of the particle body. In some embodiments, at least 30% by volume of the particle body is composed of the minor composition in each particle. In some embodiments, 50% to 90% by volume of the particle body is composed of zirconia alumina.

[0033] Figure 2 A method of making a multi-phase shaped abrasive particle according to embodiments herein is shown. Method 200 can be used to make Figures 1A-1C the particles shown. Additionally, method 200 can be adapted to make other shaped abrasive particles.

[0034] In block 210, a mold cavity is partially filled with a material having a first composition. The material can be a sol-gel or slurry. The material is a precursor material for the abrasive particle. The mold cavity has a shape 202 and a depth 204. In some embodiments, the cavity is smooth, in other embodiments it includes a texture 206. In one embodiment, partially filling the mold cavity with the first material can include dispensing the first material in the form of a layer 212 that can extend along the entire bottom surface of the cavity, forming the shape 202. Partially filling can also include dispensing the material in only a portion 214 of the mold cavity, for example by positioning a dispenser in a corner, along an edge, or otherwise near the perimeter of the mold cavity. Other arrangements are possible, as indicated in block 216. For example, the first material can be dispensed so that it creates only a partial layer that covers only a portion of the shape 202.

[0035] The shape 202 can be any suitable abrasive shape. Figures 1A-1CAn equilateral triangular prism is shown. However, other triangular shaped particles are also possible, including particles having an oblique angle, such as those described in WO 2019 / 207423 published October 31, 2019, or those described in WO 2019 / 207417 published October 31, 2019, or those described in PCT Application Serial No. IB 2019 / 059112 filed October 24, 2019.

[0036] As used herein, the term "length" when referring to a triangular shaped abrasive particle refers to the largest dimension of the triangular shaped abrasive particle. "Width" refers to the largest dimension of the triangular shaped abrasive particle perpendicular to the length. The term "thickness" or "height" refers to the dimension of the triangular shaped abrasive particle perpendicular to the length and width. For abrasive particles that are not triangular in shape, length refers to the longest dimension, and width refers to the largest dimension perpendicular to the length, while thickness refers to the dimension perpendicular to the length and width.

[0037] For shaped abrasive particles herein, other polygonal shapes are also contemplated, including acute triangular, obtuse triangular, right triangular, isosceles triangular, or scalene triangular. Quadrilateral prisms are also contemplated, including rectangular prisms, kite prisms, rhombic prisms, square prisms, or cubic prisms. Other polygonal shapes are also contemplated, such as pentagonal prisms, hexagonal prisms, and the like.

[0038] Shaped abrasive particles can have an elongated shape, such as those described in U.S. Provisional Application 2019 / 0106362 published April 11, 2019, or those described in WO 2019 / 069157 published April 11, 2019. The elongated shape can be triangular prism shaped, rod shaped, or otherwise include one or more vertices along the perimeter.

[0039] Shaped abrasive particles can have a variable cross-sectional area along the length of the particle, such as those described in U.S. Provisional Application 2019 / 0249051. For example, the shaped abrasive particle can be dog bone shaped, or otherwise have a cross-sectional area that varies from a first end to a second end.

[0040] Shaped abrasive particles can have a tetrahedral shape, such as those described in WO 2018 / 207145 published November 15, 2018, or those described in U.S. Patent 9,573,250 issued February 21, 2017.

[0041] Shaped abrasive particles can also have concave or convex portions, or can be defined as having one or more acute interior angles, such as those described in U.S. Patent 10,301,518 issued May 28, 2019.

[0042] The shaped abrasive particles can also include shape-on-shape particles, such as plate-on-plate shaped particles as described in 8,728,185, published May 20, 2014.

[0043] The shaped abrasive particles can also include shaped abrasive particles having irregular polygonal shapes as described in U.S. Provisional Patent Application 62 / 924956, filed October 23, 2019.

[0044] The shaped abrasive particles can also be shaped as free standing abrasive particles such that the cutting portion is more likely to embed into the make layer, for example, in an orientation away from the backing, such as those described in PCT Application Serial No. IB 2019 / 060457, filed December 4, 2019.

[0045] The shaped abrasive particles can also have cavities. The shaped abrasive particles can also include porosities, such as described in U.S. Patent 8,142,532, published March 27, 2012, which is incorporated herein by reference.

[0046] The shaped abrasive particles can also have a low sphericity. Methods for making shaped abrasive particles having a low sphericity are described, for example, in U.S. Patent Application Publication 2010 / 0319269.

[0047] The shaped abrasive particles can have a second apex on the second side, as described in U.S. Patent 9,447,311, published September 16, 2016. Methods for making abrasive particles in which the second side is an apex (e.g., a double wedge shaped abrasive particle) or a ridge line (e.g., a roof shaped particle) are described, for example, in U.S. Provisional Application 2012 / 022733, published September 13, 2012.

[0048] The shaped abrasive particles can be formed to have a sharp tip, such as those described in U.S. Provisional Application 2019 / 0233693, published August 1, 2019, or U.S. Provisional Application Serial No. 62 / 877443, filed July 23, 2019.

[0049] The shaped abrasive particles can also be formed to have a precisely shaped portion and a non-shaped portion, for example, a crushed portion, as described in U.S. Provisional Patent Application 62 / 833865, filed April 15, 2019.

[0050] The shaped abrasive particles can also have a combination of one or more of the shape features discussed herein, including a beveled sidewall, a groove, a recess, a facet, a fractured surface, a cavity, more than one apex, a sharp edge, a non-shaped portion, a notch, an angle of inclination, and / or a low sphericity.

[0051] In block 220, the mold cavity is partially filled with a second material. For example, a second material can be dispensed in a second layer 222 on the first layer 212. The second material can be dispensed to occupy a portion 224 of the mold cavity. In some embodiments, this can be accomplished by dispensing the second material concurrently with the first material. However, in other embodiments, the second material is dispensed after the first material. Other arrangements 226 are also suitable. For example, the second material can be dispensed into the first material, causing the first material to disperse toward the edges of the mold cavity, thereby making room for the second material to be dispensed.

[0052] In one embodiment, the first material can be at least 10% of the total volume of material dispensed into the mold cavity, or at least 15%, or at least 20%, or at least 30%, or at least 35%, or at least 40%, or at least 45%, or at least 50%, or at least 55%, or at least 60%, or at least 65%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90% of the total volume of material dispensed into the mold cavity.

[0053] Embodiments and embodiments discussed herein relate to shaped abrasive particles having only two materials forming the composition of the abrasive particles. However, it is expressly contemplated that additional materials can be dispensed or present within the mold cavity. Additionally, in some embodiments, one of the first and second materials can be doped or otherwise include particles of a third composition.

[0054] As discussed below, the dispensed materials can have different solvent compositions, which can result in different drying rates, as described below. The initial dispensing ratio can be different than the final volume ratio between the dispensed materials, as the solvent is evaporated or otherwise removed from the abrasive particles during further processing.

[0055] In block 230, in some embodiments, the abrasive particle composition in the mold cavity undergoes an initial drying of the two materials, as shown in block 234. In some embodiments, if the first and second materials are dispensed sequentially, this can be in addition to an initial drying between dispensing the first and second materials, as shown in block 232. Additional drying steps or other processing steps, such as evaporation, can be performed, as shown in block 236.

[0056] In block 240, the abrasive particles undergo a firing or sintering process, as discussed in more detail below. Depending on the coating used, the firing can be performed before or after the particle coating process.

[0057] In block 250, the abrasive particles are used to form an abrasive article, such as a coated abrasive article, a bonded abrasive article, a nonwoven abrasive article, an abrasive brush, or can be used in other ways for abrasive or finishing operations.

[0058] The shaped abrasive particles can be formed from a variety of suitable materials or combinations of materials. For example, the polygonal shaped abrasive particles can include ceramic materials or polymeric materials. The ceramic materials can include alpha alumina, alpha alumina derived from a sol-gel process, or mixtures thereof. Other suitable materials include fused alumina, heat treated alumina, ceramic alumina, sintered alumina, silicon carbide materials, titanium diboride, boron carbide, tungsten carbide, titanium carbide, diamond, cubic boron nitride, garnet, fused alumina-zirconia, ceria, zirconia, titania, or combinations thereof.

[0059] Embodiments of abrasive particle compositions suitable for use in the abrasive particles herein include: fused alumina; heat treated alumina; white fused alumina; ceramic alumina materials such as those commercially available under the trade designation 3M CERAMIC ABRASIVE GRAIN from 3M Company, St. Paul, MN; brown alumina; blue alumina; 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; chromium oxide; zirconia; titania; tin oxide; quartz; feldspar; flint; corundum; sol-gel prepared abrasive particles; and combinations thereof. Of these materials, molded alpha alumina abrasive particles derived from a sol-gel process are preferred in many embodiments. Abrasive materials that cannot be processed by a sol-gel process can be molded with temporary or permanent binders to form shaped precursor particles, which are then sintered to form abrasive particles, for example, as disclosed in U.S. Patent Application Publication No. 2016 / 0068729 Al (Erickson et al.).

[0060] Examples of sol-gel prepared abrasive particles and methods of making the same can be found in U.S. Patents 4,314,827 (Leitheiser et al.), 4,623,364 (Cottringer et al.), 4,744,802 (Schwabel), 4,770,671 (Monroe et al.), and 4,881,951 (Monroe et al.). It is also contemplated that the abrasive particles can include abrasive agglomerates such as, for example, those described in U.S. Patents 4,652,275 (Bloecher et al.) or 4,799,939 (Bloecher et al.). In some embodiments, the first and / or abrasive particles can be surface treated with a coupling agent (e.g., an organosilane coupling agent) or otherwise physically treated (e.g., oxidized iron or titanium oxide) to enhance the adhesion of the abrasive particles to the bond (e.g., the make layer and / or size layer). The abrasive particles can be treated prior to their incorporation with the corresponding bond precursor, or they can be surface treated in situ by including the coupling agent into the bond.

[0061] Preferably, the abrasive particles described herein are ceramic abrasive particles such as, for example, sol-gel prepared polycrystalline alpha alumina particles. Sol-gel alpha alumina particle precursors can be used to make abrasive particles comprised of crystallites of alpha alumina, magnesium aluminate spinel, and rare earth hexaaluminate according to, for example, the methods described in U.S. Patent 5,213,591 (Celikkaya et al.) as well as U.S. Patent Application Publications 2009 / 0165394 Al (Culler et al.) and 2009 / 0169816 Al (Erickson et al.).

[0062] Alpha alumina based shaped abrasive particles can be made according to well known multi-step processes. Briefly, the method includes the following steps: making a seeded or unseeded sol-gel alpha-alumina precursor dispersion that is convertible to alpha-alumina; filling one or more mold cavities having a desired outer shape with the sol-gel to form precursor shaped abrasive particles, drying the sol-gel to form precursor triangular abrasive particles; removing the precursor abrasive particles from the mold cavities; calcining the precursor abrasive particles to form calcined precursor abrasive particles, and then sintering the calcined precursor abrasive particles to form the first and / or second group of abrasive particles.

[0063] Further details regarding methods of making sol-gel derived abrasive particles can be found, for example, in U.S. Patents 4,314,827 (Leitheiser), 5,152,917 (Pieper et al.), 5,435,816 (Spurgeon et al.), 5,672,097 (Hoopman et al.) 5,946,991 (Hoopman et al.) 5,975,987 (Hoopman et al.) and 6,129,540 (Hoopman et al.), and U.S. Published Patent Application 2009 / 0165394 Al (Culler et al.).

[0064] In some preferred embodiments, the abrasive particles are precision shaped, with individual abrasive particles having a shape that is substantially that of a portion of a cavity of a mold or production tool in which the particle precursor was dried prior to optional calcination and sintering.

[0065] The abrasive particles used in the present disclosure can generally be made using a tool (i.e., a mold) and cut using precision machining, providing higher feature definition than other fabrication alternatives, such as, for example, stamping or punching.

[0066] Examples of alpha alumina (i.e., ceramic) abrasive particles from sol-gel processes can be found in U.S. Patents 5,201,916 (Berg), 5,366,523 (Rowenhorst (Re 35,570)) and 5,984,988 (Berg). Details regarding such abrasive particles and methods of making them can be found, for example, in U.S. Patents 8,142,531 (Adefris et al.), 8,142,891 (Culler et al.); and 8,142,532 (Erickson et al.); and U.S. Patent Application Publications 2012 / 0227333 (Adefris et al.), 2013 / 0040537 (Schwabel et al.) and 2013 / 0125477 (Adefris).

[0067] Examples of slurry-prepared alpha alumina abrasive particles can be found in WO 2014 / 070468, published May 8, 2014. Slurry-prepared particles can be formed from a powder precursor, such as an alumina powder. The slurry process can be advantageous for larger particles that are difficult to make using sol-gel techniques.

[0068] The abrasive particles can undergo a sintering process, such as, for example, the process described in U.S. Patent 1,040,0146, published September 3, 2019. However, other treatment techniques are expressly contemplated.

[0069] Incomplete polygonal shaped abrasive particles comprising a polymeric material can be characterized as soft abrasive particles. The soft shaped abrasive particles described herein can comprise any suitable material or combination of materials. For example, the soft shaped abrasive particles can comprise a reaction product of a polymerizable mixture comprising one or more polymerizable resins. The one or more polymerizable resins are selected from phenolic resins, urea-formaldehyde resins, urethane resins, melamine resins, epoxy resins, bismaleimide resins, vinyl ether resins, aminoplast resins (which can include pendant alpha, beta unsaturated carbonyl groups), acrylate resins, acrylated isocyanurate resins, isocyanurate resins, acrylated polyurethane resins, acryl-modified epoxy resins, alkyl resins, polyester resins, drying oils, or mixtures thereof. The polymerizable mixture can include additional components such as plasticizers, acid catalysts, crosslinking agents, surfactants, mild abrasives, pigments, catalysts, and antibacterial agents. Softer PSG particles having a Mohs hardness between 2.0 and 5.0 can be made according to the method described in WO 2019 / 215539 published on November 14, 2019, which can be used for scratch-free applications.

[0070] In the case of a plurality of components present in the polymerizable mixture, the components can comprise any suitable weight percent of the mixture. For example, the polymerizable resin can be in a range of about 35 wt% to about 99.9 wt%, about 40 wt% to about 95 wt% of the polymerizable mixture, or less than, equal to, or greater than about 35 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, or about 99.9 wt% of the polymerizable mixture.

[0071] If present, the crosslinking agent can be in a range of about 2 wt% to about 60 wt%, about 5 wt% to about 10 wt% of the polymerizable mixture, or can be less than, equal to, or greater than about 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or about 15 wt%. Examples of suitable crosslinking agents include a crosslinking agent available from Allnex USA Inc., Alpharetta, Georgia, USA under the trade designation CYMEL 303LF; or a crosslinking agent available from Allnex USA Inc., Alpharetta, Georgia, USA under the trade designation CYMEL 385.

[0072] If present, the mild abrasive can be in a range of about 5 wt% to about 65 wt%, about 10 wt% to about 20 wt% of the polymerizable mixture, or can be less than, equal to, or greater than about 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, or about 65 wt%. Examples of suitable mild abrasives include a mild abrasive available under the trade designation MINSTRON 353 TALC from Imerys Talc America, Inc., Three Forks, Montana, USA; a mild abrasive available under the trade designation USG TERRA ALBA NO. 1 CALCIUM SULFATE from USG Corporation, Chicago, Illinois, USA; recycled glass (40-70 grit), silica, calcite, nepheline, syenite, calcium carbonate, or mixtures thereof available from ESCA Industries, Ltd., Hatfield, Pennsylvania, USA.

[0073] If present, the plasticizer can be in a range of about 5 wt% to about 40 wt%, about 10 wt% to about 15 wt% of the polymerizable mixture, or less than, equal to, or greater than about 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, or 40 wt%. Examples of suitable plasticizers include acrylic resins or styrene butadiene resins. Examples of acrylic resins include acrylic resins available under the trade designation RHOPLEX GL-618 from DOW Chemical Company, Midland, Michigan, USA; acrylic resins available under the trade designation HYCAR 2679 from Lubrizol Corporation, Wickliffe, Ohio, USA; acrylic resins available under the trade designation HYCAR 26796 from Lubrizol Corporation, Wickliffe, Ohio, USA; polyether polyols available under the trade designation ARCOL LG-650 from DOW Chemical Company, Midland, Michigan, USA; or acrylic resins available under the trade designation HYCAR 26315 from Lubrizol Corporation, Wickliffe, Ohio, USA. Examples of styrene butadiene resins include resins available under the trade designation ROVENE 5900 from Mallard Creek Polymers, Inc., Charlotte, North Carolina, USA.

[0074] If present, the acid catalyst can be in a range of 1 wt% to about 20 wt%, about 5 wt% to about 10 wt% of the polymerizable mixture, or less than, equal to, or greater than about 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or about 20 wt%. Examples of suitable acid catalysts include aluminum chloride solutions or ammonium chloride solutions.

[0075] If present, the surfactant can be in a range of about 0.001 wt% to about 15 wt%, about 5 wt% to about 10 wt% of the polymerizable mixture, or can be less than, equal to, or greater than about 0.001 wt%, 0.01 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or about 15 wt% of the polymerizable mixture. Examples of suitable surfactants include surfactants available under the trade designation GEMTEX SC-85-P from Innospec Performance Chemicals, Salisbury, North Carolina, USA; surfactants available under the trade designation DYNOL 604 from Air Products and Chemicals, Inc., Allentown, Pennsylvania, USA; surfactants available under the trade designation ACRYSOL RM-8W from Dow Chemical Company, Midland, Michigan, USA; or surfactants available under the trade designation XIAMETER AFE 1520 from Dow Chemical Company, Midland, Michigan, USA.

[0076] If present, the antimicrobial agent can be in a range of 0.5 wt% to about 20 wt%, about 10 wt% to about 15 wt% of the polymerizable mixture, or can be less than, equal to, or greater than about 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or about 20 wt% of the polymerizable mixture. An example of a suitable antimicrobial agent includes zinc pyrithione.

[0077] If present, the pigment can be in a range of about 0.1 wt% to about 10 wt%, about 3 wt% to about 5 wt% of the polymerizable mixture, or can be less than, equal to, or greater than about 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, or 10 wt%. Examples of suitable pigments include pigment dispersions available under the trade designation SUNSPERSE BLUE 15 from Sun Chemical Corporation, Parsippany, New Jersey, USA; pigment dispersions available under the trade designation SUNSPERSE VIOLET 23 from Sun Chemical Corporation, Parsippany, New Jersey, USA; pigment dispersions available under the trade designation SUN BLACK from Sun Chemical Corporation, Parsippany, New Jersey, USA; or pigment dispersions available under the trade designation BLUE PIGMENT B2G from Clariant Ltd., Charlotte, North Carolina, USA.

[0078] In addition to the materials already described, at least one magnetic material can be included within or coated onto the incomplete polygonal shaped abrasive particles. Examples of magnetic materials include iron; cobalt; nickel; various alloys of nickel and iron sold as various grades of Permalloy; various alloys of iron, nickel, and cobalt sold as Fernico, Kovar, Fernico I, or Fernico II; various alloys of iron, aluminum, nickel, cobalt, and (sometimes) copper and / or titanium sold as various grades of Alnico; an alloy of iron, silicon, and aluminum (about 85:9:6 by weight) sold as iron-aluminum-silicon alloy; a Heusler alloy (e.g., Cu2MnSn); a manganese bismuthide (also known as Bismanol); a rare earth magnetizable material such as an alloy of gadolinium, dysprosium, holmium, europium oxide, neodymium, iron, and boron (e.g., Nd2Fe 14 B) and an alloy of samarium and cobalt (e.g., SmCo5); MnSb; MnOFe2O3; Y3Fe5O 12CrO2; MnAs; ferrites such as ferrite, magnetite; zinc ferrite; nickel ferrite; cobalt ferrite, magnesium ferrite, barium ferrite, and strontium ferrite; yttrium iron garnet; and combinations of the foregoing. In some embodiments, the magnetizable material is an alloy containing 8 to 12 weight percent aluminum, 15 to 26 weight percent nickel, 5 to 24 weight percent cobalt, up to 6 weight percent copper, up to 1 weight percent titanium, with the balance of the material totaling 100 weight percent being iron. In some other embodiments, a magnetizable coating can be deposited on the shaped abrasive particles 100 using a vapor deposition technique such as, for example, physical vapor deposition (PVD), including magnetron sputtering.

[0079] Inclusion of these magnetizable materials can cause the incomplete polygonal shaped abrasive particles to respond to a magnetic field. Any of the incomplete polygonal shaped abrasive particles can include the same material or include different materials.

[0080] Alignment of the abrasive particles can be accomplished using electrostatic coatings or magnetic coatings, as described in the following applications: PCT Patent Application Publication WO 2018 / 080703 (Nelson et al.), WO 2018 / 080756 (Eckel et al.), WO 2018 / 080704 (Eckel et al.), WO 2018 / 080705 (Adefris et al.), WO 2018 / 080765 (Nelson et al.), WO 2018 / 080784 (Eckel et al.), WO 2018 / 136271 (Eckel et al.), WO 2018 / 134732 (Nienaber et al.), WO 2018 / 080755 (Martinez et al.), WO 2018 / 080799 (Nienaber et al.), WO 2018 / 136269 (Nienaber et al.), WO 2018 / 136268 (Jesme et al.), WO 2019 / 207415 (Nienaber et al.), WO 2019 / 207417 (Eckel et al.), WO 2019 / 207416 (Nienaber et al.), U.S. Provisional Application 62 / 914,778, filed October 14, 2019, and U.S. Provisional Application 62 / 875,700, filed July 18, 2019, and U.S. Provisional Application 62 / 924,956, filed October 23, 2019.

[0081] The incomplete polygonal shaped abrasive particles are monolithic abrasive particles. As shown, the incomplete polygonal shaped abrasive particles do not contain a binder and are not an agglomeration of abrasive particles held together by a binder or other adhesive material.

[0082] Incomplete polygonal shaped abrasive particles can be formed in a number of suitable ways, for example, incomplete polygonal shaped abrasive particles can be prepared according to a multi-operation process. The method can be performed using any material or precursor dispersion material. Briefly, for embodiments in which the incomplete polygonal shaped abrasive particles are monolithic ceramic particles, the process can include the following operations: preparing a seeded or unseeded precursor dispersion that can be converted to a corresponding ceramic (e.g., a boehmite sol-gel that can be converted to alpha alumina); filling one or more mold cavities having a desired outer shape of the incomplete polygonal shaped abrasive particles with the precursor dispersion; drying the precursor dispersion to form a precursor shaped abrasive particle; removing the precursor incomplete polygonal shaped abrasive particle from the mold cavity; calcining the precursor incomplete polygonal shaped abrasive particle to form a calcined precursor incomplete polygonal shaped abrasive particle; and then sintering the calcined precursor incomplete polygonal shaped abrasive particle to form the incomplete polygonal shaped abrasive particle. The process will now be described in more detail in the context of incomplete polygonal shaped abrasive particles comprising alpha-alumina. In other embodiments, the mold cavities can be filled with melamine to form melamine shaped abrasive particles.

[0083] The method can include an operation of providing a seeded or unseeded precursor dispersion that can be converted to a ceramic. In examples in which the precursor is seeded, the precursor can be introduced with a seed iron oxide (e.g., FeO). The precursor dispersion can include a liquid as a volatile component. In one example, the volatile component is water. The dispersion can include a sufficient amount of liquid to make the viscosity of the dispersion low enough to be able to fill the mold cavities and replicate the mold surface, but not so much that the cost of subsequently removing the liquid from the mold cavities is prohibitive. In one example, the precursor dispersion includes 2 to 90 percent by weight of particles that can be converted to a ceramic, such as aluminum oxide monohydrate (boehmite) particles, and at least 10 percent by weight, or 50 to 70 percent by weight, or 50 to 60 percent by weight of a volatile component such as water. Conversely, in some embodiments, the precursor dispersion includes 30 to 50 percent by weight, or 40 to 50 percent by weight of solids.

[0084] Examples of suitable precursor dispersions include zirconia sols, vanadia sols, ceria sols, alumina sols, and combinations thereof. Suitable alumina dispersions include, for example, boehmite dispersions and other alumina hydrate dispersions. Boehmite can be prepared by known techniques or can be commercially obtained. Examples of commercially available boehmite include products sold under the trade designations "DISPERAL" and "DISPAL" both available from Sasol North America, Inc., or under the trade designation "HIQ-40" available from BASF Corporation. These aluminum monohydrate are relatively pure; that is, they contain relatively little, if any, other hydrate phases in addition to the monohydrate, and have a high surface area.

[0085] The physical properties of the resulting polygonal shaped abrasive particles can generally depend on the type of materials used in the first and second precursor dispersions dispensed in block 210, block 220. As used herein, a "gel" is a three-dimensional network of solids dispersed in a liquid.

[0086] The precursor dispersion can include a modifying additive or a precursor of a modifying additive. The modifying additive can be used to enhance certain desired properties of the abrasive particles, or to improve the efficiency of a subsequent sintering step. The modifying additive or precursor of a modifying additive can be in the form of a soluble salt, such as a water-soluble salt. They can include a metal-containing compound, and can be a precursor of an oxide of magnesium, zinc, iron, silicon, cobalt, nickel, zirconium, hafnium, chromium, yttrium, praseodymium, samarium, ytterbium, neodymium, lanthanum, gadolinium, cerium, dysprosium, erbium, titanium, and mixtures thereof. The specific concentration of these additives that can be present in the precursor dispersion can vary.

[0087] The introduction of a modifying additive or a precursor of a modifying additive can cause the precursor dispersion to gel. The precursor dispersion can also be gelled by heating over a period of time, thereby reducing the liquid content of the dispersion by evaporation. The precursor dispersion can also include a nucleating agent. Suitable nucleating agents for use in the present disclosure can include fine particles of alpha alumina, alpha iron oxide or a precursor thereof, titanium dioxide and titanates, chromium oxide, or any other substance that causes the transformation to nucleate. If a nucleating agent is used, it should be in sufficient quantity to cause the transformation of alpha-alumina.

[0088] A peptizing agent can be added to the precursor dispersion to produce a more stable hydrosol or colloidal precursor dispersion. Suitable peptizing agents are monoprotic acids or acidic compounds such as acetic acid, hydrochloric acid, formic acid, and nitric acid. Multiprotic acids can also be used, but they can cause the precursor dispersion to gel rapidly, making it difficult to handle or to introduce additional components. Certain commercially sourced boehmites contain an acid titer (e.g., absorbed formic or nitric acid) that helps to form a stable precursor dispersion.

[0089] The precursor dispersion can be formed by any suitable means; for example, in the case of a sol-gel alumina precursor, it can be formed by simply mixing alumina monohydrate with water containing a peptizing agent, or by forming a slurry of alumina monohydrate to which a peptizing agent is added.

[0090] A defoamer or other suitable chemical can be added to reduce the tendency to form bubbles or entrain air when mixing. Other chemicals such as wetting agents, alcohols or coupling agents can be added if desired.

[0091] Further operations can include providing a mold having at least one mold cavity, or a plurality of cavities formed in at least one major surface of the mold. In some examples, the mold is formed as a production tool, which can be, for example, a coating roll such as a belt, a sheet, a continuous fiber web, a rotogravure roll, a sleeve mounted on a coating roll, or a die. In one example, the production tool can comprise a polymeric material. Examples of suitable polymeric materials include thermoplastics such as polyesters, polycarbonates, poly(ether sulfone), poly(methyl methacrylate), polyurethanes, polyvinyl chloride, polyolefins, polystyrene, polypropylene, polyethylene, or combinations thereof, or thermosetting materials. In one example, the entire mold is made of a polymeric or thermoplastic material. In another example, the surface of the mold that is in contact with the precursor dispersion when drying the precursor dispersion, such as the surface of the plurality of cavities, comprises a polymeric or thermoplastic material, and other portions of the mold can be made of other materials. By way of example, a suitable polymeric coating can be applied to a metal mold to change its surface tension properties.

[0092] A polymeric or thermoplastic production tool can be replicated from a metal master tool. The master tool can have the inverse pattern of the production tool required. The master tool can be made in the same way as the production tool. In one example, the master tool is made of metal, for example nickel, and is diamond turned. In one example, the master tool is formed at least in part using stereolithography. A polymeric sheet material can be heated together with the master tool so that the master tool pattern is imprinted on the polymeric material by pressing the two together. The polymeric or thermoplastic material can also be extruded or cast onto the master tool and then pressed. The thermoplastic material is cooled to harden it, thereby producing the production tool. If a thermoplastic production tool is utilized, care should be taken not to generate too much heat, which can distort the thermoplastic production tool, thereby limiting its lifetime.

[0093] Access to the cavities can be from either the top surface or the bottom surface of the mold. In some examples, the cavities can extend through the entire thickness of the mold. Alternatively, the cavities can extend only to a portion of the thickness of the mold. In one example, the top surface is substantially parallel to the bottom surface of the mold, with the cavities having a substantially uniform depth. At least one side of the mold, i.e., the side in which the cavities are formed, can remain exposed to the surrounding atmosphere during the step of removing the volatile component.

[0094] The cavities have a particular three-dimensional shape to produce shaped abrasive particles. The depth dimension is equal to the vertical distance from the top surface to the lowest point on the bottom surface. The depth of a given cavity can be uniform, or can vary along its length and / or width. The cavities of a given mold can have the same shape or different shapes.

[0095] An additional operation involves filling the cavities in the mold with the precursor dispersion (e.g., by conventional techniques). In some examples, a knife-over-roll coater or a vacuum slot die coater can be used. If desired, a release agent can be used to facilitate removal of the particles from the mold. Examples of release agents include oils (such as peanut or mineral oil, fish oil), silicones, polytetrafluoroethylene, zinc stearate, and graphite. Generally, a release agent such as peanut oil in a liquid such as water or an alcohol will be applied to the surface of the production mold that is in contact with the precursor dispersion, such that there is about 0.1 mg / in 2 (0.6 mg / cm 2 ) to about 3.0 mg / in 2 (20 mg / cm 2 ), or about 0.1 mg / in 2 (0.6 mg / cm 2 ) to about 5.0 mg / in 2 (30 mg / cm 2 ) of release agent per unit area of the mold. In some embodiments, the top surface of the mold is coated with the precursor dispersion. The precursor dispersion can be drawn onto the top surface.

[0096] In a further operation, a doctor blade or a squeegee can be used to fully press the precursor dispersion into the cavities of the mold. The remainder of the precursor dispersion that does not enter the cavities can be removed from the top surface of the mold and recycled. In some examples, a small amount of the precursor dispersion can remain on the top surface, and in other examples, the top surface is substantially free of dispersion. The pressure applied by the doctor blade or squeegee can be less than 100 psi (0.6 MPa), or less than 50 psi (0.3 MPa), or even less than 10 psi (60 kPa). In some examples, the exposed surface of the precursor dispersion does not substantially extend beyond the top surface.

[0097] Additional operations involve removing volatile components to dry the dispersion. The volatile components can be removed by a rapid evaporation rate. In some examples, removal of the volatile components by evaporation is conducted at a temperature above the boiling point of the volatile components. The upper limit of the drying temperature is generally dependent on the material from which the mold is made. In the case of a polypropylene mold, the temperature should be below the melting point of the plastic. In one example, in the case of an aqueous dispersion containing about 40% to 50% solids and a polypropylene mold, the drying temperature can be from about 90 °C to about 165 °C, or from about 105 °C to about 150 °C, or from about 105 °C to about 120 °C. Higher temperatures can result in improved production rates, but can also result in degradation of the polypropylene mold, limiting its useful life as a mold.

[0098] During drying, the precursor dispersion shrinks, often resulting in a retraction from the walls of the cavity. For example, if the cavity has flat walls, the resulting shaped abrasive particles can tend to have at least three concave major sides. It has now been found that by recessing the walls of the cavity (whereby the volume of the cavity is increased), it is possible to obtain an incomplete polygonal shaped abrasive particle having at least three substantially flat major sides. The degree of recessing is generally dependent on the solids content of the precursor dispersion.

[0099] Additional operations involve removing the resulting precursor incomplete polygonal shaped abrasive particles from the mold cavities. The shaped abrasive particle precursors can be removed from the cavities by using the following processes alone or in combination on the mold: gravity, vibration, ultrasonic vibration, vacuum, or pressurized air processes to remove the particles from the mold cavities.

[0100] The shaped abrasive particle precursors can be further dried outside the mold. This additional drying step is not necessary if the precursor dispersion is dried to the desired degree in the mold. However, in some cases, it can be economical to employ this additional drying step to minimize the residence time of the precursor dispersion in the mold. The polygonal shaped abrasive particles will be dried at a temperature of from 50 °C to 160 °C, or from 120 °C to 150 °C, for a time of from 10 minutes to 480 minutes, or from 120 minutes to 400 minutes.

[0101] Additional operations involve calcining the polygonal shaped abrasive particles. During calcination, substantially all of the volatile matter is removed, and the various components present in the precursor dispersion are converted to metal oxides. The polygonal shaped abrasive particles are typically heated to a temperature of from 400 °C to 800 °C, and held within this temperature range until free water and greater than 90% by weight of any bound volatile matter is removed. In an optional step, it can be desirable to introduce a modifying additive by an impregnation process. Water-soluble salts can be introduced by injecting them into the pores of the calcined shaped abrasive particle precursor. The polygonal shaped abrasive particles are then pre-fired again.

[0102] Additional operations can involve sintering the calcined shaped abrasive particles to form shaped abrasive particles 100. However, in some examples where the precursor includes a rare earth metal, sintering can not be necessary. Prior to sintering, the calcined shaped abrasive particles are not fully densified and thus lack the desired hardness for use as shaped abrasive particles. Sintering is performed by heating the calcined shaped abrasive particles to a temperature of 1000 °C to 1650 °C. The length of time the calcined shaped abrasive particles can be exposed to the sintering temperature to achieve this degree of conversion depends on a variety of factors, but five seconds to 48 hours are possible.

[0103] In another embodiment, the duration of the sintering step is in the range of one minute to 90 minutes. After sintering, the shaped abrasive particles 14 can have a Vickers hardness of 10 GPa (gigapascal), 16 GPa, 18 GPa, 20 GPa, or more.

[0104] Additional operations can be used to modify the method, such as rapidly heating the material from the calcining temperature to the sintering temperature, and centrifuging the precursor dispersion to remove sludge and / or waste. Furthermore, the method can be modified by combining two or more of these method steps, if desired.

[0105] To form soft shaped abrasive particles, the polymerizable mixture described herein can be deposited in a cavity. The cavity can have a shape corresponding to a negative impression of the desired incomplete polygon shaped abrasive particle. After the cavity is filled to a desired extent, the polymerizable mixture is allowed to cure in the cavity. Curing can occur at room temperature (e.g., about 25 °C) or at any temperature above room temperature. Curing can also be achieved by exposing the polymerizable mixture to a source of electromagnetic radiation or ultraviolet radiation.

[0106] The shaped abrasive particles can be independently sized according to the abrasive industry-recognized designations of nominal grade. Abrasive industry-recognized grading standards include those promulgated by ANSI (American National Standards Institute), FEPA (European Federation for Abrasive Materials), and JIS (Japanese Industrial Standards). ANSI grade designations (i.e., prescribed nominal grades) include, for example: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI 46, ANSI 54, ANSI 60, ANSI 70, ANSI 80, ANSI 90, ANSI 100, ANSI 120, ANSI 150, ANSI 180, ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, and ANSI 600. FEPA grade designations include F4, F5, F6, F7, F8, F10, F12, F14, F16, F18, F20, F22, F24, F30, F36, F40, F46, F54, F60, F70, F80, F90, F100, F120, F150, F180, F220, F230, F240, F280, F320, F360, F400, F500, F600, F800, F1000, F1200, F1500, and F2000. JIS grade designations include: JIS 8, JIS 12, JIS 16, JIS 24, JIS 36, JIS 46, JIS 54, JIS 60, JIS 80, JIS 100, JIS 150, JIS 180, JIS 220, JIS 240, JIS 280, JIS 320, JIS 360, JIS 400, JIS 600, JIS 800, JIS 1000, JIS 1500, JIS 2500, JIS 4000, JIS 6000, JIS 8000, and JIS 10,000.

[0107] Figure 3 Embodiments of coated abrasive articles are shown, in which embodiments disclosed herein can be useful. According to various embodiments of the present disclosure, a coated abrasive article is disclosed. The abrasive article can be selected from a number of different abrasive articles, such as an abrasive belt, an abrasive sheet, or an abrasive disc. However, although Figure 3 Coated abrasive articles are shown in the figures, other abrasive articles are also contemplated, such as bonded abrasive articles, bonded abrasive articles, or abrasive brushes.

[0108] Figure 3is a cross-sectional view of a coated abrasive article 300. The coated abrasive article 300 includes a backing 350 defining a substantially planar major surface in the x-y direction. The backing 350 has a first layer of binder 340, which can be referred to as a make layer 340, applied on a first surface of the backing 350. A plurality of shaped abrasive particles are attached or partially embedded in the make layer 340, each having a first portion 310 and a second portion 315. A second layer of binder 330, hereinafter referred to as a size layer 330, is dispersed over the shaped abrasive particles. The coated abrasive article 300 can be formed into any suitable abrasive article.

[0109] The backing 350 can be flexible or rigid. Examples of suitable materials for forming a flexible backing include polymeric films, metal foils, woven fabrics, knitted fabrics, paper, vulcanized fibers, staple fibers, continuous fibers, nonwoven fabrics, foams, screens, laminates, and combinations thereof. The backing 350 can be shaped to allow the coated abrasive article 300 to be in the form of a sheet, a disc, a belt, a pad, or a roll. In some embodiments, the backing 350 can be flexible enough to allow the coated abrasive article 300 to be shaped into a loop to make an abrasive belt that can be run on a suitable grinding apparatus.

[0110] The make layer 340 secures the shaped abrasive particles to the backing 350, and the size layer 330 can help to consolidate the particles within the make size layer 340. The make layer 340 and / or the size layer 330 can include a resinous binder. The resinous binder can include one or more resins selected from the group consisting of phenolic resins, epoxy resins, urea-formaldehyde resins, acrylate resins, aminoplast resins, melamine resins, acryl-modified epoxy resins, urethane resins, and mixtures thereof.

[0111] What is shown herein are shaped abrasive particles that have a first portion 315 embedded within the make layer 340 and a second portion 310 that is substantially free of contact with the make layer 340. This can be beneficial if the first portion 315 is formed of a material that is more likely to bond with the make layer 340. The second portion 310 can have better cutting characteristics, or can be more expensive than the first portion 315, and thus can only occupy the volume of the shaped abrasive particle that can be used in an abrasive operation. However, although shaped abrasive particles having portions 310 and 315 are shown, other shaped abrasive particles, such as those in Figure 1A and Figure 1C may also be suitable.

[0112] Any abrasive article of the present disclosure can be manufactured using a variety of methods. For example, a coated abrasive article 300 can be formed by applying a make coat layer 340 on a backing 350. The make coat layer 340 can be applied by any suitable technique such as roll coating. Shaped abrasive particles can then be deposited on the make coat layer 340. Alternatively, the abrasive particles and make coat layer 340 formulation can be mixed to form a slurry, which is then applied to the backing 350. If the coated abrasive article 300 includes other shaped abrasive particles, crushed abrasive particles, and secondarily shaped abrasive particles, these particles can be applied as discrete groups sorted by particle type or together. The shaped abrasive particles 302 are deposited on the backing 350, the make coat layer 340 is cured at an elevated temperature or at room temperature for a set amount of time, and the shaped abrasive particles 302 adhere to the backing 350. A size coat layer 330 can then be optionally applied on the coated abrasive article 300.

[0113] The shaped abrasive particles 302 can be deposited on the backing 350 by any suitable technique. For example, the shaped abrasive particles 302 can be deposited on the backing 350 by a drop coating technique or an electrostatic coating technique. In drop coating, the shaped abrasive particles 302 are deposited in free form on the make coat layer 340. In embodiments of the electrostatic coating technique, a vibrating feeder that is electrically charged can be used to propel the shaped abrasive particles 302 from a feed surface toward a conductive member positioned behind the backing 350. In some embodiments, the feed surface is substantially horizontal and the coated backing can travel substantially vertically. The shaped abrasive particles 302 pick up an electrical charge from the feeder and are drawn toward the backing by the conductive member.

[0114] The shaped abrasive particles 302 can constitute 100 wt.% of the abrasive particles in any abrasive article. Alternatively, the shaped abrasive particles 302 can be part of a blend of abrasive particles distributed on the backing 350. If present as part of a blend, the shaped abrasive particles can be in a range of about 5 wt.% to about 95 wt.%, about 10 wt.% to about 80 wt.%, about 30 wt.% to about 50 wt.% of the blend, or less than, equal to, or greater than about 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, or about 95 wt.% of the blend. In the blend, the remainder of the abrasive particles can comprise conventional crushed abrasive particles. Crushed abrasive particles are typically formed by a mechanical crushing operation and do not have a replicated shape. The remainder of the abrasive particles can also comprise other shaped abrasive particles, which may, for example, include equilateral triangle shapes (e.g., flat triangle-shaped abrasive particles or tetrahedral shaped abrasive particles in which each face of the tetrahedron is an equilateral triangle).

[0115] The make layer, the size layer, or both can include any suitable resin, such as a phenolic resin, an epoxy resin, a urea-formaldehyde resin, an acrylate resin, an aminoplast resin, a melamine formaldehyde resin, an acrylic-modified epoxy resin, a urethane resin, or mixtures thereof. Additionally, the make layer, the size layer, or both can include a filler, a grinding aid, a wetting agent, a surfactant, a dye, a pigment, a coupling agent, an adhesion promoter, or mixtures thereof. Examples of fillers can include calcium carbonate, silica, talc, clay, calcium metasilicate, dolomite, aluminum sulfate, or mixtures thereof.

[0116] The dispensing tool can also be used to apply the shaped abrasive particles 302 to the backing 350. When the shaped abrasive particles 302 are adhered to the make layer, the dispensing tool including the shaped abrasive particles can remain in contact with the backing for any suitable amount of time. After a sufficient amount of time has passed to achieve good adhesion between the shaped abrasive particles and the make layer, the production tool is removed and optionally a size layer is disposed on the shaped abrasive particles.

[0117] The shaped abrasive particles described herein can also be used to form agglomerated particles. Agglomerated particles can include shaped abrasive particles in a vitreous bond matrix, as described, for example, in U.S. Provisional Application 2018 / 081246, published May 3, 2018. Agglomerated particles can also include shaped abrasive particles in a silicate bond, as described in WO 2019 / 167022, published September 6, 2019.

[0118] Alignment of abrasive particles can be accomplished using electrostatic coatings or magnetic coatings, as described in the following applications: PCT Patent Application Publication WO 2018 / 080703 (Nelson et al.), WO 2018 / 080756 (Eckel et al.), WO 2018 / 080704 (Eckel et al.), WO 2018 / 080705 (Adefris et al.), WO 2018 / 080765 (Nelson et al.), WO 2018 / 080784 (Eckel et al.), WO 2018 / 136271 (Eckel et al.), WO 2018 / 134732 (Nienaber et al.), WO 2018 / 080755 (Martinez et al.), WO 2018 / 080799 (Nienaber et al.), WO 2018 / 136269 (Nienaber et al.), WO 2018 / 136268 (Jesme et al.), WO 2019 / 207415 (Nienaber et al.), WO 2019 / 207417 (Eckel et al.), WO 2019 / 207416 (Nienaber et al.), and U.S. Provisional Application 62 / 914,778 filed October 14, 2019 and U.S. Provisional Application 62 / 875,700 filed July 18, 2019 and U.S. Provisional Application 62 / 924,956 filed October 23, 2019.

[0119] The magnetic coating can be applied prior to the firing process or after the firing process. The magnetic coating can cause the shaped abrasive particles to align in a magnetic field. The shaped abrasive particles can be aligned such that one of the apices points away from the backing. Once the magnetizable particles are coated onto the curable binder precursor, the curable binder precursor is at least partially cured at a first curing station (not shown) in order to securely hold the magnetizable particles in place. In some embodiments, additional magnetizable particles and / or non-magnetizable particles (e.g., filler abrasive particles and / or grinding aid particles) can be applied to the make coat precursor prior to curing.

[0120] In the case of coated abrasive articles, the curable binder precursor includes a make coat precursor and the magnetizable particles include magnetizable abrasive particles. A size coat precursor can be applied to the at least partially cured make coat precursor and magnetizable abrasive particles, although this is not required. If a size coat precursor is present, it is at least partially cured at a second curing station, optionally further curing the at least partially cured make coat precursor. In some embodiments, a top coat 320 is disposed on the at least partially cured size coat precursor.

[0121] Figures 4A-4F Curved polyhedral shaped abrasive particles according to embodiments herein are shown. While FIGS. 1 toFigure 3 Shaped abrasive particles having a first portion and a second portion that remain in contact through particle formation, article manufacture, and abrasive use are shown, but it is expressly contemplated that multiphase shaped abrasive particles can also be configured such that the phases are separable at the interface.

[0122] Figures 4A-4F Shaped abrasive particles according to embodiments herein are shown. Figures 4A-4F Shaped abrasive particles are shown that are curved polyhedral particles made using a mold having flat surfaces. However, other shapes are possible using molds having other interior surfaces. Additionally, although smooth edges are shown, grooves or other textures can also be created on any surface of the abrasive particle that contacts the mold surface during drying or other processing.

[0123] Figure 4A and Figure 4B Curved abrasive particles 410 and 410a are shown that differ by the presence or absence of a void 415 that can extend partially or completely through the thickness 418. Curved abrasive particles 410 and 410a are formed from a layer of abrasive particle precursors having a thickness 418 that has been caused to partially curl into a curved shape during drying such that the surface area of the inner side 414 is less than the outer surface area of the outer side 416. The inner side 414 and the outer side 416 are substantially parallel to each other. The shaped abrasive particles can also have at least one concave (or recessed) face or facet; at least one face or facet that is outwardly shaped (or convex). Methods for making dished abrasive particles are described, for example, in U.S. Patent Application Publications 2010 / 0151195 and 2009 / 0165394. Additionally, the shaped abrasive particles can also have a faceted surface as described in U.S. Patent 10,150,900, published December 11, 2018.

[0124] Curved abrasive particles 410 and 410a each include one or more abrasive tips 412. In some embodiments, as shown, the abrasive tips 412 (or 422) are all on the flat inner. Figures 4A-4D

[0125] The amount of curvature of the abrasive particle can be determined by the amount of contraction and different rates of contraction of the inner side 414 relative to the outer side 416. The degree of curvature of the abrasive particle can also be determined by the thickness of the precursor particle. For example, if the precursor particle has a non-uniform thickness, the thinner portions will curve more than the thicker portions due to less resistance from the particle body. This also allows for the design of abrasive particles with desired curved structures.

[0126] Figure 4C and Figure 4D ​Bent abrasive particles 420 and 420a are shown, which differ by the presence of a void 425, which can extend partially or completely through the thickness 428. Bent abrasive particles 420 and 420a include a plurality of abrasive tips 422. Bent abrasive particles 420 and 420a also include an inner surface 424 and an outer surface 426. The outer surface 426 has a greater surface area than the surface 424, which can be caused by different shrinkage rates of the surfaces 424, 426 during drying.

[0127] Figure 4E and Figure 4F Bent abrasive particles 430 and 430a are shown, which differ by the presence of a void 435, which can extend partially or completely through the thickness 638. Bent abrasive particles 430 and 430a each have four abrasive tips 432, two (432a) of which are substantially planar with the void 435, and two of which are present on the curved region of the bent abrasive particles 430, 430a. Bent abrasive particles 430 and 430a have a thickness 438 that is substantially uniform along their region. The inner surface 434 has an area that is less than the area of the outer surface 436, which is caused by a change in shrinkage rate between the surfaces 434, 436 during drying.

[0128] Figure 5 Bent polyhedral shaped abrasive particles precisely placed on a surface in one embodiment herein are shown. While bent abrasive particle 502 is shown to be similar to particle 400, other bent shapes are also contemplated, including those in Figures 4B-4F .

[0129] Abrasive article 500 can include a substrate 510 having a plurality of bent abrasive particles 502 positioned thereon. Bent abrasive particles 502 each have a plurality of abrasive tips 504, each of which is oriented toward an inner surface 506 of the bent abrasive particle 502. For each bent abrasive particle 502, the inner surface 506 can be substantially parallel to an outer surface 508.

[0130] As shown in Figure 5 , abrasive particles can be placed precisely in a first orientation 520 or a second orientation 530. However, other orientations are also possible. In some embodiments, an abrasive article includes abrasive particles oriented in a single orientation exclusively. In another embodiment, abrasive particles can include abrasive particles in various orientations. However, as described herein, abrasive particles can be magnetically coated, or otherwise configured to align in precise locations on the substrate 510.

[0131] The mechanism for forming convex-concave surfaces is that when more release agent or excess release agent is present on the mold surface that contacts the sol-gel, the precursor shaped abrasive particles tend to detach from the bottom surface of the mold during drying, thereby forming convex-concave surfaces on the disc-shaped abrasive particles.

[0132] The disclosed mechanism for forming curved PSGs is different from the mechanisms described in the prior art (e.g., U.S. Patent 8,142,891, published March 27, 2012) because the articles described herein are formed by controlling the gradient volume shrinkage of the gel particles during drying.

[0133] Figure 6A and Figure 6B A method of making curved polyhedral shaped abrasive particles in the embodiments herein is shown. The method 600 allows for the making of curved precision shaped abrasive particles with well-controlled curvature. In one embodiment, a process is shown that allows for the making of two different PSG particles through one path. The methods described herein can allow for thinner abrasive particles than would otherwise be readily made in a mold.

[0134] In block 610, the mold cavity is filled with a first precursor material. The precursor material can be dispensed into the mold such that it covers the bottom surface of the mold, but does not completely fill the mold.

[0135] In block 620, the mold cavity is filled with a second precursor material. The second precursor material can have the same composition as the first layer, or can have a different composition 622 than the first material. For example, the first material can be alpha alumina, and the second material is zirconia alumina. Other compositions, doped compositions, or mixtures are expressly contemplated. The second precursor material can also be another material that is not intended for abrasive use 624, such as a polymer or to facilitate the bending of other materials during drying.

[0136] In some embodiments, the second precursor material is selected such that minimal mixing will occur at the interface between the two layers, such that the two layers can be separated, for example in block 640. However, in some embodiments, some mixing, fusing, or other bonding occurs such that the layers are not easily separable.

[0137] In block 630, a curvature is induced in the abrasive particle. As indicated in block 632, the curvature can be induced by drying the particle such that one of the first and second layers dries faster than the other, causing the edge to curl. As indicated in block 634, heat is also applied. Other methods are also contemplated as indicated in block 636.

[0138] In block 640, in some embodiments, the first and second layers are separated. In some embodiments, only one layer will be used to form the abrasive article, so when the abrasive grain precursor is removed from the mold cavity, it needs to be separated into the portion that will be incorporated into the abrasive article and the portion that will be discarded. The physical separation of the first and second layers from each other can occur easily during removal from the mold, or can require some force 642. For example, the mold can be subjected to vibration to cause the layers to separate from each other. This also helps to separate the portion to be retained and the portion to be discarded. The layers can also be separated by a weight 644 or using another mechanism 646.

[0139] In block 650, the curved abrasive grains are further processed. The processing can include preparing the curved abrasive grains for incorporation into an abrasive article. For example, the curved abrasive grains can be further dried or fired as indicated in block 652. The abrasive grains can also undergo a coating step as indicated in block 654. For example, coating the abrasive grains with a magnetically responsive coating can enable precise alignment on a backing or other substrate. Other processing can also be performed as indicated in block 656.

[0140] Figure 6B A schematic 670 is shown that illustrates the formation of curved abrasive grains 692 and a discarded layer 694. However, although the top layer is shown as the discarded layer 694 in Figure 6B other embodiments, it can be the abrasive grains 892 that are discarded. For example, a sacrificial precursor layer can be more easily removed from the mold, so it is used as the mold contact layer.

[0141] The mold is first filled with a first layer of precursor material 672, and then filled with a second layer of precursor material 674. An interface 676 can exist between the first layer 672 and the second layer 674.

[0142] The drying step results in two layers curling due to the difference in drying rate of the bottom layer 682 versus the top layer 684. The convex-concave formation of the bottom layer 682, top layer 684 is due to the gradient volume shrinkage during gel drying. For example, if the surface layer of the gel dries faster than the interior of a portion of the gel particle, and it shrinks more in volume than the interior portion of the gel particle, then the formation of a convex-concave surface results. The gradient volume shrinkage can be achieved by a gradient solid, a gradient temperature, or by using a gel / slurry precursor mixture with different drying rates or volume shrinkage. The top layer can be a temporary sacrificial layer or the same composition as the interior gel layer. In one embodiment, a temporary top layer 684 is used. In another embodiment, a precursor slurry with two different solids contents generates a gradient drying / shrinkage to form the convex-concave structure.

[0143] When drying is complete, the two layers separate at the interface 886 to form the curved abrasive particle 692 and the discard layer 694. The discard layer 694 and the curved abrasive particle 692 can both comprise a ceramic material, or in other embodiments, the sacrificial portion can comprise a polymer or other softer material. Suitable temporary sacrificial layers are combustible materials or soluble materials that can be removed after the particle is prepared. A common method of eliminating the temporary sacrificial layer is to burn the layer off during pre-firing, firing, or sintering. Typical temporary sacrificial layers are polymer layers such as starch, polyvinyl alcohol, cellulose, and gelatin. In one embodiment, a polyvinyl alcohol (PVA) solution (5% to 10% by weight) is used as a typical temporary sacrificial layer.

[0144] The particle 670 has an edge length 678. The edge length 678 is similar to the edge length of the curved abrasive particle 692, the discard layer 694, with some variation due to the curvature. The thickness 693, 695, respectively, is substantially constant throughout the area of the curved abrasive particle 692, the discard layer 694.

[0145] Figure 6B The formation of curved polyhedral abrasive particles is shown. While a curved triangular shaped particle is shown, it is expressly contemplated that other shaped molds cavities can be used to produce other curved shapes. For example, a quadrilateral shaped mold cavity can be used to form a curved particle having four corners that are curved upward, similar to the illustration of Figures 4A-4F Similarly, pentagonal, hexagonal, heptagonal, octagonal, nonagonal, or other suitable polygon shaped mold cavities can be used to produce particles having any number of curved points.

[0146] Similarly, the methods described herein can be used to cause rod shaped shaped particles or other elongated shaped particles to be curved. Elongated abrasive particles can be used, for example, in abrasive wheels, particularly for heavy duty grinding operations. International Patent Publication WO 2019 / 069157, published April 11, 2019, discloses a method of making elongated abrasive particles having precisely controlled linear longitudinal shapes. Disclosed herein is a method of making curved elongated shaped abrasive particles. The particles described herein have a curvature on both the inner and outer sides, and in some embodiments, the curvature on the inner and outer surfaces is substantially similar, resulting in a substantially constant thickness along the length of the particle.

[0147] Figure 7 A schematic 700 is shown that illustrates the formation of a first abrasive particle layer 740 having abrasive edges 742 and a second abrasive particle layer 730 having abrasive edges 732. In some embodiments, the second abrasive particle layer 730 is added only to cause the abrasive particles 742 to be curved, and is discarded after formation. However, while the second precursor material layer 712 is shown as being removed after the first abrasive particle layer 740 is formed, it is expressly contemplated that the second precursor material layer 712 can be removed before the first abrasive particle layer 740 is formed. Figure 7The middle is shown as a discarded layer, but in other embodiments it can be a first precursor material layer 714 of the mold that is discarded. For example, the sacrificial precursor layer can be more easily removed from the mold and thus used as a mold contact layer. For example, the second abrasive particle layer 730 can be a slurry and the first abrasive particle layer 740 is a boehmite gel.

[0148] The mold 710 is first filled with a first precursor material layer 714 and then filled with a second precursor material layer 712. An interface 716 can exist between the first precursor material layer 714 and the second precursor material layer 712.

[0149] The drying step results in two layers curling, which is due to the different drying rates of the bottom layer 726 versus the top layer 722. The convexity of the top layer 722, bottom layer 726 is due to the gradient volume shrinkage during gel drying. As discussed above, in some embodiments one of the top layer 722, bottom layer 726 is a sacrificial layer. The sacrificial layer can be formed of an abrasive particle material, another ceramic material, or a non-ceramic material such as a polymeric material or a plastic material. When drying is complete, the two layers are separated at the interface 724 to form the second abrasive particle layer 730, first abrasive particle layer 740.

[0150] The second precursor material layer 712 and the first precursor material layer 714 have a length 718 when in the mold. The length 718 can be similar to the length of the top layer 722 and the bottom layer 726. Each of the second abrasive particle layer 730, first abrasive particle layer 740 also has a final particle thickness 734, 744.

[0151] Figures 8A-8D Abrasive particles and abrasive articles are shown that are twisted, where they can be useful. FIGS. 1 to Figure 7 Abrasive particles are shown having multiple sharp tips or edges that all point in substantially the same direction after the drying step and thus there is only one concavity.

[0152] In contrast, Figures 8A-8D Abrasive particles are shown having a twisted shape due to drying such that when placed on a backing, as shown in Figure 8C only two abrasive tips are facing away from the backing and two are used as stabilizing features.

[0153] As Figure 8AAs shown, in one embodiment, the square shaped abrasive particle precursors can self-align into free standing abrasive particles with the cutting tip pointing upwards in the standing position. Precursor particles with a twisted structure can be achieved by using more than two phases. In one embodiment, a sacrificial layer is applied to both surfaces of the alumina precursor gel particles to form a sandwich structure. When the sample is placed in an oven for drying, the two sides of the precursor gel particle dry differently: the side exposed to air dries faster than the side at the bottom of the cavity. The particle bends towards the surface exposed to air. Once the precursor particle is demolded from the tool, the side facing the tool starts to dry and the particle bends accordingly. Thus, the dried precursor gel becomes a twisted particle. A first layer 810 can be deposited on a second layer 812 and during the drying step, have different drying rates, which results in a bend that creates a first surface 814 and a second surface 816. The thickness between the first surface 814 and the second surface 816 is substantially the same across the surface 814. The first layer 810 can be a ceramic layer or a polymer layer.

[0154] Figures 8B-8D Such particles are shown how they can be used in abrasive articles, such as bonded abrasive articles 820, coated abrasive articles 830, and nonwoven abrasive articles 840. Such particles can be particularly useful in abrasive articles because for nonwoven articles, the additional surface area can result in greater bonding area between the particles 842 and the nonwoven fibers 844. In bonded abrasive articles, such particles can increase the availability of abrasive tips during abrasive operations of various wheel designs. Also, for coated abrasive articles, such shapes can self-orient on the backing.

[0155] The shaped abrasive particles are typically selected to have a length in the range of 0.001 mm to 26 mm, more typically 0.1 mm to 10 mm, and more typically 0.5 mm to 5 mm, although other lengths can be used.

[0156] According to various embodiments, methods of using an abrasive article, such as an abrasive belt or an abrasive disc, include contacting an incomplete polygonal shaped abrasive particle with a workpiece or substrate. The workpiece or substrate can comprise many different materials, such as steel, steel alloys, aluminum, plastics, wood, or combinations thereof. Upon contact, one of the abrasive article and the workpiece is moved relative to the other in a direction of use, and a portion of the workpiece is removed.

[0157] The present invention relates to a method for abrading a workpiece, the method comprising bringing at least a portion of an abrasive article according to the present invention into frictional contact with a surface of the workpiece; and moving (upon contact) at least one of the workpiece or the abrasive article to abrade at least a portion of the surface of the workpiece.

[0158] During use, the abrasive article can be used for dry or wet grinding. During wet grinding, the abrasive article is typically used in conjunction with a grinding fluid, which may, for example, include water or a commercially available lubricant (also referred to as coolant). During wet grinding, the lubricant is typically used to cool the workpiece and the abrasive article, lubricate the interface, remove swarf (debris), and clean the abrasive article. The lubricant is typically applied directly to the grinding area to ensure that the fluid is not carried away by the abrasive article. One advantage of using an incomplete polygonal abrasive particle is that it is able to incorporate and retain lubricant in the void spaces of its structure.

[0159] Common lubricants can be classified based on their ability to mix with water. A first class of lubricants suitable for use in the present application includes oils, such as mineral oil (typically petroleum-based oil) and vegetable oil. A second class suitable for use in the present application includes emulsions of lubricants (e.g., mineral oil-based lubricants; vegetable oil-based lubricants and semi-synthetic lubricants) and solutions of lubricants (typically semi-synthetic and synthetic lubricants) with water.

[0160] Compared to other shaped abrasive particles, curved abrasive particles can provide significant advantages. Curved abrasive particles can allow the particles to better adhere within an abrasive article structure. Improved adhesion can result in reduced delamination as compared to flat shaped particles or 2D polygonal shaped particles. Curved abrasive particles can better align within an abrasive article structure, i.e., be more easily oriented or self-orient. The open structure of curved abrasive particles provides better load carrying performance than comparative complete particles. In the sandpaper industry, the term “load” is used to refer to a product that can become clogged or stuck with small particles of material that the sandpaper has been polishing due to residue filling the gaps between abrasive particles, making the sandpaper work harder or even destroying the sandpaper (ending useful life). Another feature of curved shaped abrasive particles is that the empty interior space can be filled with an abrasive aid, such as a lubricant.

[0161] A multiphase abrasive particle precursor is presented. The particle includes a first phase composed of a first material. The first material has a first composition that is substantially constant throughout the first phase. The particle also includes a second phase composed of a second material. The second material has a second composition that is substantially constant throughout the second phase. The particle also includes an interface between the first phase and the second phase. The multiphase abrasive particle precursor is a shaped abrasive particle precursor.

[0162] The multiphase abrasive particle precursor can be implemented such that the first material is a first abrasive material.

[0163] The multi-phase abrasive particle precursor can be implemented such that the first abrasive material comprises alpha alumina, alpha alumina from a sol-gel process, fused alumina, heat treated alumina, ceramic alumina, sintered alumina, silicon carbide material, titanium diboride, boron carbide, tungsten carbide, titanium carbide, diamond, cubic boron nitride, garnet, fused alumina-zirconia, cerium oxide, zirconium oxide, titanium oxide, or a combination thereof.

[0164] The multi-phase abrasive particle precursor can be implemented such that the second material is a second abrasive material different from the first abrasive material.

[0165] The multi-phase abrasive particle precursor can be implemented such that the second material is a ceramic material.

[0166] The multi-phase abrasive particle precursor can be implemented such that the second material is a polymeric material.

[0167] The multi-phase abrasive particle precursor can be implemented such that the second material is a sacrificial material.

[0168] The multi-phase abrasive particle precursor can be implemented such that the interface has a shape substantially the same as a shape of the shaped abrasive particle precursor.

[0169] The multi-phase abrasive particle precursor can be implemented such that the shaped abrasive particle comprises a first shaped surface opposite a second shaped surface, the first shaped surface and the second shaped surface separated by a thickness. The interface extends from the first shaped surface to the second shaped surface.

[0170] The multi-phase abrasive particle precursor can be implemented such that the first material and the second material have different drying rates such that, during a drying step, the first phase and the second phase dry into first and second curved layers.

[0171] The multi-phase abrasive particle precursor can be implemented such that the first material and the second material, when dried, separate at the interface into a first abrasive precursor particle and a second abrasive precursor particle.

[0172] The multi-phase abrasive particle can be implemented such that the first abrasive particle has a first shape, the second abrasive precursor particle has a second shape, and the first shape and the second shape are the same.

[0173] The multi-phase abrasive particle can be implemented such that the first shape is a polygon.

[0174] The multi-phase abrasive particle can be implemented such that the first shape is an elongated shape.

[0175] The multi-phase abrasive particle can be implemented such that the first shape comprises a first corner and a second corner, and the first corner and the second corner curve in the same direction.

[0176] The multi-phase abrasive particle can be implemented such that a first curvature of the first corner is different than a second curvature of the second corner.

[0177] The multi-phase abrasive particle can be implemented such that the first shape includes a first corner and a second corner. The first corner and the second corner curve in different directions.

[0178] A method of making a multi-phase abrasive particle is presented. The method includes dispensing a first material in a mold cavity having a mold shape. The mold shape includes a shaped perimeter and a depth. The method also includes dispensing a second material in the mold cavity. An interface is formed between the first material and the second material. The method also includes drying the dispensed first material and second material in the mold cavity. After drying, a first portion of the multi-phase abrasive particle includes the first material. A second portion of the multi-phase abrasive particle includes the second material.

[0179] The method can be implemented such that the first material has a substantially constant composition across the first portion. The second material has a substantially constant composition across the second portion.

[0180] The method can be implemented such that the depth is substantially constant across a surface area of the mold cavity.

[0181] The method can be implemented such that at least one surface of the mold cavity includes a texture.

[0182] The method can be implemented such that dispensing includes leveling the first material or the second material relative to a mold surface prior to drying.

[0183] The method can be implemented such that it further includes dispensing a release agent into the mold cavity.

[0184] The method can be implemented such that dispensing the first material and dispensing the second material occur substantially simultaneously.

[0185] The method can be implemented such that the first material is dispensed as a first layer within the mold cavity.

[0186] The method can be implemented such that the second material is dispensed as a second layer covering the first layer.

[0187] The method can be implemented such that the second material is dispensed into the first layer, causing a displacement of first material such that a portion of the second material contacts a bottom surface of the mold cavity.

[0188] The method can be implemented such that dispensing the first material and the second material causes a first mold feature of the mold cavity to include only the first material and causes a second mold feature to include only the second material. The first mold feature and the second mold feature include an edge, a corner, or an interior surface.

[0189] The method can be implemented such that drying includes causing the first layer and the second layer to bend.

[0190] The method can be implemented such that the mold shape includes a first angle and a second angle. Causing to bend includes the first angle and the second angle curling in the same direction.

[0191] The method can be implemented such that the first angle and the second angle have different degrees of bending.

[0192] The method can be implemented such that the mold shape includes a first angle and a second angle. Causing to bend includes the first angle and the second angle curling in different directions.

[0193] The method can be implemented such that it further includes separating the first layer and the second layer at the interface.

[0194] The method can be implemented such that dispensing the first material includes dispensing a slurry or sol-gel including the first material.

[0195] The method can be implemented such that dispensing the second material includes dispensing a slurry or sol-gel including the second material.

[0196] The method can be implemented such that it further includes sintering the dried abrasive particles at a sintering temperature.

[0197] The method can be implemented such that one of the first material and the second material is destroyed when heated to the sintering temperature.

[0198] Example

[0199] The objects and advantages of the disclosure will be further illustrated by the following non-limiting examples, but the specific materials and amounts thereof, as well as other conditions and details, recited in these examples should not be construed to unduly limit this disclosure. All parts, percentages, ratios, etc. in the examples and throughout the specification are by weight unless otherwise specified.

[0200] All other reagents are obtained or purchased from fine chemical suppliers such as Sigma-Aldrich Company, St. Louis, Missouri, or can be synthesized by known methods, unless otherwise specified.

[0201] Abbreviations for units used in the examples:

[0202] °C: degrees Celsius

[0203] cm: centimeters

[0204] g: grams

[0205] g / m 2 : grams per square meter

[0206] rpm: revolutions per minute

[0207] mm: millimeters

[0208] wt. %: weight percent

[0209] The materials used in the examples are described in Table 1 below.

[0210] Table 1

[0211]

[0212]

[0213] Figures 9-10 illustrate embodiments of multi-phase abrasive particles.

[0214] Example 1 used a two-phase material to produce triangular shaped abrasive particles.

[0215] In this embodiment, a Zr-Al-sol-gel precursor premix was used as the phase 1 material and an Al-sol-gel precursor premix was used as the phase 2 material. A one-piece molding production tool having triangular shaped cavities was used. The production tool had a plurality of triangular shaped cavities having a depth of 28 mils and a side of 110 mils, wherein the angled sidewall had a pre-set angle of the punch slope and was located between the sidewall and the mold floor.

[0216] The mold was coated with a release agent (0.2% peanut oil in methanol) wherein approximately 0.5 mg / in^(0.08 mg / cm^) of peanut oil was applied to the mold. Excess methanol was removed by placing the mold sheet in an air convection oven at 45 °C for 5 minutes prior to use.

[0217] In the first step, two vertices of the triangular shaped cavities were filled with the phase 1 material. This was accomplished by placing the Zr-Al-sol-gel precursor premix on the surface of the molding production tool with a putty knife, followed by pushing the putty knife to move in one direction on the surface of the production tool. The phase 1 material was forced to fill the two vertices of the cavities.

[0218] In the second step, the phase-2 material, an Al-sol-gel precursor premix, was applied to the molding production tool with a putty knife and then the Al-sol-gel precursor premix was forced to completely fill the remaining cavities of the production tool with the putty knife.

[0219] The mold production tool filled with the precursor pre-mix was placed in an air convection oven at 45 °C for at least 45 minutes to dry. The precursor shaped abrasive particles were removed from the mold by passing them over an ultrasonic energy concentrator. The precursor shaped abrasive particles were dried at about 140 °C for 10 minutes. Figure 9A An image of a precisely shaped precursor particle comprising two phase materials is shown. By using the same process, triangular shaped precursor particles comprising two phase materials can be achieved. Figure 9B An image of a triangular shaped precursor particle comprising two phase materials is presented, and only one vertex of the triangle is filled with phase-1 material, and the rest of the triangle is filled with phase-2 material. Figure 9C An embodiment of a triangular shaped precursor particle comprising two phase materials is shown, and half of the triangular precursor particle is made of phase-1 material, and the other half of the triangular precursor particle is made of phase-2 material.

[0220] The precursor particles are further converted to abrasive particles by pre-firing at 750 °C for about 10 minutes, and then sintering at about 1400 °C for 15 minutes. The microstructure of the final abrasive particles is observed under SEM. Figure 9D A cross-sectional view of the boundary between phase-1 material and phase-2 material in the sintered shaped abrasive particles prepared in Example 1 is shown. The boundary between the phases can be clearly seen, and it is clearly indicated that the phase-1 material and phase-2 material have significantly different microstructures. In Figure 9D In the presented magnified image, the microstructure of phase 1 material is shown, the crystallites of alumina have very uniform size, and form a close-packed matrix.

[0221] FIGS. 11-14 show embodiments of curved abrasive particles.

[0222] Example-2 Making precisely shaped curved abrasive particles

[0223] The same mold production tool and process as in Example-1 were used, except that the Al-sol-gel precursor pre-mix was used as phase-1 material, and the slurry precursor pre-mix was used as phase-2 material.

[0224] In the first step, the Al-sol-gel precursor pre-mix was applied to the surface of the mold production tool with a putty knife, and forced to fill about 2 / 3 volume of each triangular shaped cavity.

[0225] In the second step, the slurry precursor pre-mix was placed on the surface of the mold production tool with a putty knife, and forced to fill the remaining space in each cavity.

[0226] The mold production tool filled with the precursor pre-mix was placed in an air convection oven at 45 °C for at least 45 minutes to perform the drying. Due to the dehydration, the volume of the Al-sol-gel precursor pre-mix shrinks significantly during the drying (the Al-sol-gel precursor pre-mix has about 60 wt% water), and the volume of the slurry precursor pre-mix shrinks almost not due to its high solid content (78 wt% or higher). Therefore, the precursor particles gradually bend as the drying proceeds due to the internal forces between the two-phase materials. Due to the weak affinity between the Al-sol-gel precursor and the slurry precursor pre-mix, the two-phase materials separate from each other after drying, forming two bent precursor particles.

[0227] Optionally, the precursor particles can be further doped with rare earth elements according to the methods described in, for example, U.S. Patent 5,213,591 (Celikkaya et al.) and U.S. Patent Publications 2009 / 0165394A1 (Culler et al.) and 2009 / 0169816A1 (Erickson et al.). The precursor particles are further converted to abrasive particles by pre-firing at 750 °C for about 10 minutes, and then sintering at about 1400 °C for 15 minutes. Figure 11A An image showing a side view of a bent Phase 1 shaped abrasive particle is shown. Figure 11B An image showing a bent Phase 2 shaped abrasive particle is shown. Figure 12A and Figure 12B An image showing a bent Phase 1 shaped abrasive particle at different viewing angles is shown.

[0228] Example-3 Making precisely shaped curved abrasive particles using a temporary sacrificial layer

[0229] The same mold production tool and process as in Example 2 were used, except that the slurry precursor pre-mix was used as the Phase 1 material, and the PVA polymer was used as the Phase 2 material. Figure 12C An image showing bent Phase 1 abrasive particles precisely placed on a fibrous backing is shown. Figure 12D An image showing bent Phase 1 abrasive particles randomly coated on a fibrous backing is shown.

[0230] Making experimental abrasive disks

[0231] A vulcanized fiber disc blank material was used as the abrasive substrate, which had a diameter of 7 inches (17.8 cm), with a central hole of 7 / 8 inch (2.2 cm) diameter and a thickness of 0.83 mm (33 mils). The vulcanized fiber was obtained from DYNOS GmbH, Trostorf, Germany as Dynos Vulcanized Fibre. The primer resin 1 was applied to the fiber disc blank material with a brush until an added weight of 3.0 grams - 3.1 grams was reached.

[0232] A coated pan was weighed and the abrasive particles prepared in the illustrated embodiment were applied using an electrostatic coater. The abrasive coated pan was removed and weighed to determine the amount of coated abrasive particles. In this embodiment, 15.0 g - 15.1 g of the curved abrasive particles prepared in Example-2 of P36 grade were used. The pan was pre-cured at 90°C for 1 hour and then pre-cured at 103°C for 3 hours.

[0233] The pre-cured pan was then coated with a size resin by brush. Excess size resin was removed with a dry brush until the submerged shiny appearance was reduced to a matte appearance. The size pan was weighed to determine the size resin weight. The amount of size resin added depends on the mineral composition and weight, but is typically between 12 grams / pan and 28 grams / pan. In this embodiment, 11.5 g - 13.0 g of size was used. The pan was cured by heat at 90°C for 90 minutes and then at 103°C for 16 hours. The cured pan was orthogonally flexed on a 1.5 inch (3.8 cm) diameter roller. The pan was allowed to equilibrate with ambient humidity for 1 week before testing.

[0234] Comparative abrasive disks

[0235] A 7 inch (17.8 cm) abrasive fiber pan from 3M Company, Cubitron II Fibre Disc 982C, was used as a comparative abrasive embodiment. The comparative abrasive pan had a similar construction to the experimental abrasive pans, except that it was coated with P36 grade flat triangular shaped abrasive particles.

[0236] Grinding performance testing

[0237] This test was designed to measure the effectiveness of abrasive pan constructions to remove metal from a workpiece by measuring how the cut rate changes over time and the total amount of metal effectively removed over the life of the abrasive pan. The coated abrasive pan was mounted on an inclined aluminum backing pad and driven at a speed of 5500 rpm. A portion of the pan covering the sloped edge of the backing pad was brought into contact with the surface of a 1.25 cm x 18 cm 1018 soft steel workpiece at an approximate 6 kg load. Each pan was used to grind a separate workpiece for a total of 20 minutes at one minute intervals, or until the pan failed or the cut rate dropped below 20 grams / minute. The amount of metal removed from each workpiece was recorded. The initial cut amount was recorded as the amount of metal removed during the first one minute interval. The final cut amount was recorded as the amount of metal removed during the final one minute interval. The total cut amount was the cumulative amount of metal removed from the workpiece over the life of the abrasive pan, or 20 one minute intervals, whichever came first. The cut amount data was recorded in Table 1 in grams of workpiece metal removed. Figure 13 The experimental fiber pans coated with curved abrasive particles showed higher initial cut amounts than the comparative abrasive pan due to the more acute vertices exposed on the surface of the abrasive surface. The results are shown in Table 1.Figure 13 Images of the two-phase, dry, curved rod-shaped precursor particles on the surface of the production tool are shown.

[0238] Example 4

[0239] The same procedure as Example-2 was used, except that a different molding production tool was used. A polypropylene tool containing parallel linear grooves (width 1.15 mm at top, depth 1.00 mm, width 0.15 mm at bottom) interrupted by barriers (i.e., 0.917 mm height walls) spaced at regular intervals of 2.75 mm was used to make curved rod-shaped precursor particles. Figure 14A Images of the two-phase, dry, curved rod-shaped precursor particles on the surface of the production tool are shown. Figure 14B Images of the Phase 1 curved rod-shaped precursor particles are shown, and Figure 14C Images of the Phase 2 curved rod-shaped precursor particles are shown.

[0240] Figure 15 shows an example of twisted abrasive particles made according to Example 5.

[0241] Example-5 Making twisted abrasive particles

[0242] The same procedure as Example-4 was used, except that PVA was used as the Phase-1 material, an Al-sol-gel precursor pre-mix was used as the Phase-2 material, and then another layer of PVA was used as the Phase-3 material.

[0243] Flaky precursor particles were made using a polypropylene tool containing parallel linear rectangles (width 2.0 mm at top, depth 1.00 mm, width 1.90 mm at bottom) interrupted by barriers (i.e., 0.917 mm height walls) spaced at regular intervals of 3.25 mm. The production tool was pre-treated with RA before use.

[0244] In the first step, a PVA solution (8 wt% aqueous solution) was applied to the molding production tool with a brush. The production tool was placed in air for 5-10 minutes to let the PVA solution solidify on the production tool and fill the bottom of the cavities. The sample was then dried in an air convection oven at 45 °C for 5 minutes.

[0245] In the second step, an Al-sol-gel precursor pre-mix was applied to the production tool with a putty knife to fill the space of the cavities.

[0246] In the third step, a PVA solution (8 wt% aqueous solution) was applied to the surface of the production tool filled with the Al-sol-gel precursor pre-mix with a brush, and then the sample was dried at 75 °C for 10 minutes. The dried precursor particles were de-molded from the production tool by passing them over the top of an ultrasonic horn. The de-molded precursor particles were pre-fired at 650 °C for 20 minutes to burn off the PVA layer.

[0247] Optionally, the precursor particles can be further doped with rare earth elements according to the methods described in, for example, U.S. Patent 5,213,591 (Celikkaya et al.) and U.S. Patent Publications 2009 / 0165394A1 (Culler et al.) and 2009 / 0169816A1 (Erickson et al.). The precursor particles are further converted to abrasive particles by pre-firing at 750°C for about 10 minutes, and then sintering at about 1400°C for 15 minutes. Figures 15A-15C Images of the final fired twisted platelet abrasive particles are shown.

Claims

1. A multi-phase abrasive particle precursor, the precursor comprising: a first phase comprising a first material, wherein the first material has a substantially constant first composition throughout the first phase; a second phase comprising a second material, wherein the second material has a substantially constant second composition throughout the second phase; an interface between the first phase and the second phase; wherein the multi-phase abrasive particle precursor is a shaped abrasive particle precursor; and wherein the first material and the second material have different drying rates, such that during a drying step, the first phase and the second phase are capable of drying into a first curved layer and a second curved layer.

2. The multi-phase abrasive particle precursor of claim 1, wherein the first material is a first abrasive material.

3. The multi-phase abrasive particle precursor of claim 2, wherein the first abrasive material comprises: alpha alumina, alpha alumina from sol-gel, fused alumina, heat treated alumina, ceramic alumina, sintered alumina, silicon carbide material, titanium diboride, boron carbide, tungsten carbide, titanium carbide, diamond, cubic boron nitride, garnet, fused alumina-zirconia, cerium oxide, zirconium oxide, titanium oxide, or combinations thereof.

4. The multi-phase abrasive particle precursor of claim 3, wherein the second material is a second abrasive material different from the first abrasive material.

5. The multi-phase abrasive particle precursor of claim 3, wherein the second material is a ceramic material.

6. The multi-phase abrasive particle precursor of claim 3, wherein the second material is a polymeric material.

7. The multi-phase abrasive particle precursor of claim 3, wherein the second material is a sacrificial material.

8. The multi-phase abrasive particle precursor of any one of claims 1 to 7, wherein the interface has substantially the same shape as a shape of the shaped abrasive particle precursor.

9. The multi-phase abrasive particle precursor of any one of claims 1 to 7, wherein the shaped abrasive particle precursor comprises a first shaped surface opposite a second shaped surface, the first shaped surface and the second shaped surface separated by a thickness, and wherein the interface extends from the first shaped surface to the second shaped surface.

10. The multi-phase abrasive particle precursor of claim 1, wherein the first material and the second material are capable of separating into a first abrasive precursor particle and a second abrasive precursor particle at the interface upon drying.

11. The multi-phase abrasive particle precursor of claim 10, wherein the first abrasive precursor particle has a first shape, the second abrasive precursor particle has a second shape, and wherein the first shape and the second shape are the same.

12. The multi-phase abrasive particle precursor of claim 11, wherein the first shape is a polygonal shape.

13. The multi-phase abrasive particle precursor of claim 11, wherein the first shape is an elongated shape.

14. The multi-phase abrasive particle precursor of claim 11, wherein the first shape comprises a first corner and a second corner, and wherein the first corner and the second corner are curved in the same direction.

15. The multi-phase abrasive particle precursor of claim 14, wherein a first curvature of the first corner is different than a second curvature of the second corner.

16. The multi-phase abrasive particle precursor of claim 11, wherein the first shape includes a first corner and a second corner, and wherein the first corner and the second corner are curved in different directions.

17. A method of making a multi-phase abrasive particle using the multi-phase abrasive particle precursor of claim 1, the method comprising: dispensing a first material in a mold cavity having a mold shape, wherein the mold shape includes a shaped perimeter and a depth; dispensing a second material in the mold cavity, wherein an interface is formed between the first material and the second material; drying the dispensed first and second materials in the mold cavity, wherein after drying, a first portion of a multi-phase abrasive particle includes the first material, and wherein a second portion of the multi-phase abrasive particle includes the second material, wherein drying includes causing the first and second layers to curve when the first and second phases are capable of drying into the first and second curved layers.

18. The method of claim 17, wherein the first material has a substantially constant composition across the first portion, and wherein the second material has a substantially constant composition across the second portion.

19. The method of claim 17 or 18, wherein the depth is substantially constant across a surface area of the mold cavity.

20. The method of claim 17 or 18, wherein at least one surface of the mold cavity includes a texture.

21. The method of claim 17 or 18, wherein dispensing includes tending the first material or the second material to level with respect to a mold surface prior to drying.

22. The method of claim 17 or 18, and further comprising dispensing a release agent into the mold cavity.

23. The method of claim 17 or 18, wherein dispensing the first material and dispensing the second material occur substantially simultaneously.

24. The method of claim 17 or 18, wherein the first material is dispensed as a first layer within the mold cavity.

25. The method of claim 24, wherein the second material is dispensed as a second layer, covering the first layer.

26. The method of claim 24, wherein the second material is dispensed into the first layer, causing a displacement of first material such that a portion of the second material contacts a bottom surface of the mold cavity.

27. The method of claim 17 or 18, wherein the first material and the second material are dispensed such that a first mold feature of the mold cavity includes only the first material, and such that a second mold feature includes only the second material, and wherein the first and second mold features include an edge, a corner, or an interior surface.

28. The method of claim 17, wherein the mold shape includes a first corner and a second corner, and wherein causing the curving includes the first corner and the second corner curling in the same direction.

29. The method of claim 28, wherein the first and second corners have different degrees of curvature.

30. The method of claim 17, wherein the mold shape includes a first corner and a second corner, and wherein causing bending includes curling the first and second corners in different directions.

31. The method of claim 28, and further comprising: separating the first and second layers at the interface.

32. The method of claim 17 or 18, wherein dispensing the first material includes dispensing a slurry or sol-gel including the first material.

33. The method of claim 17 or 18, wherein dispensing the second material includes dispensing a slurry or sol-gel including the second material.

34. The method of claim 17 or 18, and further comprising: sintering the dried abrasive particles at a sintering temperature.

35. The method of claim 34, wherein one of the first and second materials is destroyed when heated to the sintering temperature.

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