Patent Description:
Bonded abrasive particles include abrasive particles retained in a binder matrix that can be resinous or vitreous. Examples include, grindstones, cutoff wheels, hones, and whetstones.

Alignment and orientation of abrasive particles in abrasive articles such as, for example, coated abrasive articles and bonded abrasive articles has been a source of continuous interest for many years.

For example, coated abrasive articles have been made using techniques such as electrostatic coating of abrasive particles have been used to align crushed abrasive particles with the longitudinal axes perpendicular to the backing. Likewise, shaped abrasive particles have been aligned by mechanical methods as disclosed in <CIT>).

Precise placement and orientation of abrasive particles in bonded abrasive articles has been described in the patent literature. For example, <CIT>) describes the use of magnetic flux to orient abrasive grain having a thin coating of iron dust in bonded abrasive articles. Likewise, British (<CIT>) describes the use of a magnetic field to orient abrasive grain having a thin coating of iron or steel dust to orient the abrasive grain in bonded abrasive articles. Using this technique, abrasive particles were radially oriented in bonded wheels.

<CIT>) discloses equipment for making abrasive particles in even distribution, array pattern, and preferred orientation. Using electric current to form a magnetic field causing acicular soft magnetic metallic sticks to absorb or release abrasive particles plated with soft magnetic materials.

The use of an electrostatic field to apply abrasive grains to a coated backing of an abrasive article is well known. For example, <CIT> issued to Minnesota Mining and Manufacturing Company in <NUM> discloses the use of an electrostatic field for affecting the orientation of abrasive grains such that each abrasive grain's elongated dimension is substantially erect (standing up) with respect to the backing's surface <CIT> forms the basis of the preamble of the independent claims and discloses a method for applying abrasive grains to a substrate using two electrodes and an electrostatic field.

A method of aligning abrasive particles on a substrate. The method comprises providing a substrate. The method also comprises providing abrasive particles. The method also comprises generating a modulated electrostatic field. The modulated electrostatic field is configured to have a first effective direction at a first time and a second effective direction at a second time. The electrostatic field is configured to cause the abrasive particles to align rotationally in both a z-direction and a y-direct.

As used herein, forms of the words "comprise", "have", and "include" are legally equivalent and open-ended. Therefore, additional non-recited elements, functions, steps or limitations may be present in addition to the recited elements, functions, steps, or limitations.

As used in this Specification, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., <NUM> to <NUM> includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and the like).

The terms "about" or "approximately" with reference to a numerical value or a shape means +/- five percent of the numerical value or property or characteristic, but also expressly includes any narrow range within the +/- five percent of the numerical value or property or characteristic as well as the exact numerical value. For example, a temperature of "about" <NUM> refers to a temperature from <NUM> to <NUM>, but also expressly includes any narrower range of temperature or even a single temperature within that range, including, for example, a temperature of exactly <NUM>. For example, a viscosity of "about" <NUM> Pa-sec refers to a viscosity from <NUM> to <NUM> Pa-sec, but also expressly includes a viscosity of exactly <NUM> Pa-sec. Similarly, a perimeter that is "substantially square" is intended to describe a geometric shape having four lateral edges in which each lateral edge has a length which is from <NUM>% to <NUM>% of the length of another lateral edge, but which also includes a geometric shape in which each lateral edge has exactly the same length.

The term "substantially" with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited. For example, a substrate that is "substantially" transparent refers to a substrate that transmits more radiation (e.g. visible light) than it fails to transmit (e.g. absorbs and reflects). Thus, a substrate that transmits more than <NUM>% of the visible light incident upon its surface is substantially transparent, but a substrate that transmits <NUM>% or less of the visible light incident upon its surface is not substantially transparent.

The term "length" refers to the longest outer surface-to-outer surface dimension of an object.

The term "width" refers to the longest dimension of an object that is perpendicular to its length.

The term "thickness" refers to the longest dimension of an object that is perpendicular to both of its length and width.

The term "aspect ratio" is defined as largest dimension divided by the largest dimension present along an axis defined by the largest dimension.

The term "modulated electrostatic field" refers to an electrostatic field that changes in direction and optionally magnitude. The change can be continuous or discrete, e.g. an electrode changing from a positive to negative charge.

The suffix "(s)" indicates that the modified word can be singular or plural.

The term "monodisperse" describes a size distribution in which all the particles are approximately the same size.

The terms "a", "an", and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a material containing "a compound" includes a mixture of two or more compounds.

The term "ceramic" refers to any of various hard, brittle, heat- and corrosion-resistant materials made of at least one metallic element (which may include silicon) combined with oxygen, carbon, nitrogen, or sulfur. Ceramics may be crystalline or polycrystalline, for example.

The ceramic particles may be shaped (e.g., precisely-shaped) or random (e.g., crushed and/or platey). Shaped ceramic particles and precisely-shaped ceramic particles may be prepared by a molding process using sol-gel technology as described, for example, in <CIT>), <CIT>(<CIT>)), <CIT>), <CIT>), and <CIT>).

Exemplary shapes of ceramic particles include crushed, pyramids (e.g., <NUM>-, <NUM>-, <NUM>-, or <NUM>-sided pyramids), truncated pyramids (e.g., <NUM>-, <NUM>-, <NUM>-, or <NUM>-sided truncated pyramids), cones, truncated cones, rods (e.g., cylindrical, vermiform), and prisms (e.g., <NUM>-, <NUM>-, <NUM>-, or <NUM>-sided prisms). In some embodiments (e.g., truncated pyramids and prisms), the ceramic particles respectively comprise platelets having two opposed major facets connected to each other by a plurality of side facets.

The term "essentially free of" means containing less than <NUM> percent by weight (e.g., less than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or even less than <NUM> percent by weight, or even completely free) of, based on the total weight of the object being referred to.

The terms "precisely-shaped abrasive particle" refers to an abrasive particle wherein at least a portion of the abrasive particle has a predetermined shape that is replicated from a mold cavity used to form a precursor precisely-shaped abrasive particle that is sintered to form the precisely-shaped abrasive particle. A precisely-shaped abrasive particle will generally have a predetermined geometric shape that substantially replicates the mold cavity that was used to form the abrasive particle.

As used herein, "substantially horizontal" means within ± <NUM>, ± <NUM>, or ± <NUM> degrees of perfectly horizontal. As used herein, "substantially vertical" means within ± <NUM>, ± <NUM>, or ± <NUM> degrees of perfectly vertical. As used herein, "substantially orthogonal" means within ± <NUM>, ± <NUM>, ± <NUM>, or ± <NUM> degrees of <NUM> degrees.

As used herein, "z-direction rotational orientation" refers to the particle's angular rotation about its longitudinal axis. As used herein, "y-direction rotation orientation" refers to the particle's angular rotation about its latitudinal axis. The latitudinal axis of the particle is aligned with the electrostatic field as the particle is translated through the air by the electrostatic force.

In conventional electrostatic systems, abrasive particles can be applied to coated backings by conveying the abrasive particles horizontally under the coated backing traveling parallel to and above the abrasive particles on the conveyer belt. The conveyor belt and coated backing pass through a region that is electrostatically charged by a bottom plate connected to a voltage potential and a grounded upper plate. The abrasive particles then travel substantially vertically under the force of the electrostatic field, and against gravity, attaching to the coated backing and achieving an erect orientation with respect to the coated backing. A significant number of the abrasive particles align their longitudinal axis parallel to the electrostatic field prior to attaching to the coated backing.

Additionally, electrostatic deposition of abrasive particles onto a curable layer (e.g., a make coat) is well-known in the abrasive art (e.g., see <CIT>) and <CIT>)), and analogous technique wherein the slurry layer is substituted for the curable layer is effective for accomplishing electrostatic deposition of abrasive particles. And it has been possible to orient particles by controlling the z-directional rotation (<CIT>)). However, it is desired to be able to also control y-directional rotational direction of the abrasive particles. For example, it is known that abrasive particles can have better cutting efficiency when rotationally oriented properly. For example, if tips or edges of particles can be rotationally oriented with respect to a direction of use of an abrasive article, the plurality of tips or edges can have greater abrading efficiency. Previous efforts have focused on a static, parallel plate system to create a charge on abrasive particles, causing them to orient in the z-direction. Embodiments described herein utilize a dynamic electrostatic system that modulates the direction of charge experienced by abrasive particles, causing them to generally orient with respect to the backing but also rotationally orient with respect to a proposed direction of use.

The embodiments described herein are described with respect to abrasive particles, particularly with respect to abrasive particles being applied to a backing. However, it is expressly contemplated that the embodiments described herein are also applicable to other applications. For example, any application that positions particulates on a substrate, where rotational orientation and / or alignment of the particulates can affect the performance of the resulting product.

Alignment of abrasive particles on a backing is possible by applying a magnetic coating and using a magnetic field. However, this requires a magnetic coating on the abrasive particles. This coating can require an extra process step and associated cost. Iron, a common metal used in magnetic coating, can present concerns for contamination in certain applications. Therefore, a process is desired that can align abrasive particles on or within an abrasive article without requiring a magnetic coating.

<FIG> illustrates an electrostatic system for applying particles to a substrate in an embodiment of the invention. System <NUM> is illustrated and described with respect to applying abrasive particles <NUM> onto a backing <NUM>. However, system <NUM> may also have other applications for other technology areas. <FIG> illustrates one example particle which could be aligned on a backing using electrostatic system <NUM>. However, while a triangular particle <NUM> is illustrated for explanatory purposes, it is expressly contemplated that systems and methods described herein can be used to align a variety of particles including other precision shaped particles, other formed particles, platey or crushed particles.

Particle <NUM> can be understood as having a length <NUM>, a width <NUM>, and a thickness <NUM>. It also has an aspect ratio, which is defined as the ratio of length <NUM> to width <NUM>. As illustrated in <FIG>, it may be possible to align a particle <NUM> on a substrate in any of the x, y or z directions. A substrate may be located, for example, in or below the X-Y plane. As discussed in detail in <CIT>, rotational orientation of abrasive particles on a backing can have a significant effect on performance of an abrasive article.

Particle <NUM> may be oriented along any of axes x, y or z using systems and methods described herein. Orientation with respect to the X-axis can be controlled based on how frequently, and where, particles <NUM> are dispensed with respect to a substrate. As illustrated in <CIT>, rotational orientation with respect to the Z-axis can improve abrasive cutting effectiveness. Systems and methods herein allow for rotational orientation with respect to the Y-axis, e.g. with respect to an edge of a substrate. It may be possible to achieve better abrading efficiency when width <NUM> is parallel to, or substantially parallel to, an edge of a substrate to which particles will be fixed.

Referring back to <FIG>, a particle source <NUM> provides abrasive particles <NUM> to system <NUM>. Abrasive particles <NUM> may, for example, be precision shaped particles, formed particles, platey or crushed particles. Particle source <NUM> could be, for example, a conveyor belt, a ramp, or other conveyance mechanism. Additionally, particle source <NUM> may also providing a screening function, such that particles <NUM> are all similarly sized.

A substrate <NUM> is also provided that is not initially in contact with provided particles <NUM>. Substrate <NUM> may have a binder precursor material on it or may be free of binding material. Substrate <NUM> may be a non-woven, flexible, or stiff backing material.

A modulating electrostatic field generator <NUM> is provided. The modulating electrostatic field generator <NUM> is positioned opposite a plate <NUM>. When actuated, modulating electrostatic field generator <NUM> creates an electrostatic field that draws particles <NUM> away from plate <NUM> and toward backing <NUM> through field <NUM>. Electrostatic field generator <NUM> modulates a generated electrostatic field as it rotates back and forth, as indicated by arrows <NUM>. The rotation causes an effective electric field experienced by a particle to change as generator <NUM> moves between a first and a second position and, optionally, back again. Modulation refers to the changing of experienced electrostatic field on an abrasive particle over time. Modulating may refer to a continuous change, for example caused by rotation of field generator <NUM>, or may refer to a discrete change, for example caused by plate <NUM> changing magnitude or direction without going through intermediate values.

Generator <NUM> and plate <NUM> are differently charged. For example, generator <NUM> may be positively charged and plate <NUM> may be a ground. Generator <NUM> may be positively charged and plate <NUM> may be negatively charged. Other configurations are also possible and contemplated herein such that, when actuated, particles <NUM> are moved away from a source <NUM> and toward a backing <NUM>. The modulating electrostatic field generator can use either a direct current or an alternating current source to create a modulated electrostatic field. Additionally, voltage-based sources may also be used to create a modulated electrostatic field, in some embodiments.

In one embodiment, modulated field generator <NUM> is configured to rotate either clockwise or counterclockwise, as indicated by arrows <NUM>. In one embodiment, modulated field generator <NUM> is configured to, as it rotates, change directionality of field <NUM>. Prior art alignment systems that focused on a parallel plate architecture were only able to achieve alignment of particles in the z-direction. However, modulating an experienced electric field using generator <NUM>, it is possible to improve alignment of particles on a substrate in the y-direction as well. In the system illustrated in <FIG>, modulation occurs by rotating electrostatic field generator <NUM> with respect to the particle, which may cause the particle to `wiggle' as it is translated and positioned on backing <NUM> until a preferred alignment is obtained.

Aligned particles <NUM> may be adhered to backing <NUM> during or after an alignment process. For example, backing <NUM> may comprise a binder that receives aligned particles <NUM>, in one embodiment. However, in another embodiment, a binder is applied to aligned particles <NUM> after the alignment process is complete.

A preferred alignment may be illustrated in <FIG>. In one embodiment, it is desired for an abrasive particle <NUM> to be aligned substantially parallel to the edges of a backing <NUM>. Preferred orientations of abrasive particles <NUM> are represented by angle ranges <NUM>. Suboptimal orientations are represented by angle ranges <NUM>. A preferred rotational orientation of abrasive particles <NUM>, in one embodiment, has abrasive particles rotationally aligned with between about <NUM>° and <NUM>° degrees of rotation with respect to edges of a backing <NUM>. Outside of that range, abrasive particles experience fracturing of larger scrap portions, which reduces the life of the particle as it keeps each active sharp tip for less time prior to fracturing and loses more mass with each experienced fracture. However, in other embodiments, other abrasive articles, and for other abrasive particle shapes, other rotational orientations may be desired.

Additionally, while <FIG> illustrates a system <NUM> that relies on a horizontally provided source <NUM> to provide particles <NUM> that are sufficiently charged to defy gravity to contact backing <NUM>, it is also expressly contemplated that other embodiments are possible. For example, plate <NUM> could also be a second modulating field generator configured to rotate in the same, or opposite, direction from field generator <NUM>. Additionally, the position of plate <NUM> and field generator <NUM> could be switched, such that particles <NUM> fall onto backing <NUM> through field <NUM>. This may allow for a weaker field to be used, as particles <NUM> would not have to defy gravity during orientation.

While <FIG> illustrates a simpler electrostatic field generation system <NUM>, which applies an electrostatic field <NUM> over the diameter of field generation system <NUM>, it is envisioned that, in other embodiments, abrasive particles may experience an electrostatic field over a longer distance. As a conveyance mechanism moves abrasive particles through an electrostatic field, it may cause them to increasingly change alignment with respect to a substrate, causing a greater percentage of abrasive particles to achieve an alignment within a rotational orientation within a specific angle range.

<FIG> illustrate a system for aligning particles on a backing in an embodiment of the invention. A substrate may move in the direction indicated by arrow <NUM>, such that a given particle <NUM> is exposed to a modulating electrostatic field as substrate moves in direction <NUM>. However, in another embodiment, a substrate remains stationary during an alignment process. In one embodiment, a modulated electrostatic field is provided through an electrode array. Each electrode in the array can be controlled, and charged, by a voltage controller. For example, each electrode can be charged to a significant positive voltage, negative voltage, or substantially no voltage. For example, a voltage of +/-5kV may be applied, or a voltage of +/-10kV, or a voltage of +/-15kV, or a voltage of +/-20kV, or a voltage of +/-25kV, or a voltage of +/-30kV.

A single repeatable electrostatic system element <NUM> is illustrated in <FIG>. However, system <NUM> may be repeated along a manufacturing line as needed. For example, different sizes and shapes of abrasive particles may require longer dwell times within an electrostatic field to achieve alignment within a preferred rotational orientation range, requiring more, or fewer, passes through electrostatic system element <NUM> than other shaped / sized particles. Higher line-speeds may require a longer electrostatic system to achieve the desired dwell time of a particle within the electrostatic field.

In the example of <FIG>, the web is simulated as about <NUM> (<NUM>") above the lower electrodes. These electrodes were modeled and simulated as an array of <NUM> copper wires, <NUM> (<NUM>") diameter, vertically spaced <NUM> (<NUM>"), and spaced <NUM> (<NUM>") horizontally. The wires are shown with an exaggerated diameter for clarity.

As illustrated in <FIG>, system <NUM> comprises a plurality of first electrodes 210A-E, and a plurality of second electrodes 210F-J. While five sets of electrodes are illustrated, in other embodiments more, or fewer, electrode pairs are present. For example, while <FIG> illustrated an embodiment with a single pair of electrodes, two pairs, three pairs, four pairs or more than five pairs may be present within a repeatable system <NUM>.

Additionally, while illustrated as pairs of electrodes, it is expressly contemplated that some embodiments have other electrode configurations. For example, the top electrodes may be more closely spaced than the bottom electrodes. Additionally, an electrode on the top does not need to align, or be associated with, an electrode on the bottom. Further, electrodes on the top (or bottom) may not be equally spaced, from each other. Different physical configurations may require different voltage sequencing.

Each of electrodes 210A-E and 210F-J, in one embodiment, is in a fixed position, with modulation of an experienced electrostatic field occurring as particles <NUM> on a backing <NUM>, moves through the generated electric field in the direction indicated by arrow <NUM>. The modulated electric field causes the abrasive particles to 'wiggle' or shift position with respect to substrate <NUM>. In addition to causing particles <NUM> to orient themselves rotationally in the z-direction, e.g. such that a length of a given particle <NUM> is substantially perpendicular to substrate <NUM>, the modulated electric field causes a particle <NUM> to orient itself in the y-direction such that a width is substantially parallel to the edges of substrate <NUM>. In another embodiment, different charges are applied to electrodes 210A-E and / or 210F-J while backing <NUM> remains stationary, causing modulation of the electrostatic field experienced by each of particles <NUM>. However, in some embodiments it is expressly contemplated that, in the z-direction, particles <NUM> may be rotationally oriented at an angle with respect to the backing.

<FIG> and <FIG> illustrate the electric field experienced by a particle <NUM> on substrate <NUM> at a given time. <FIG> illustrates one example sequence of charges on electrodes 210A-E and 210F-J at different time steps. The time step sequence of <FIG> shows one complete revolution of the electric field. For time step T1, electrodes 210A and 210F are charged to -5kV, electrodes 220E and 220J are charged to +5kV, and all other electrodes are not driven to a specific voltage but are left floating. In <FIG> and <FIG>, the electrodes undergo <NUM> different configurations before repeating (e.g. T19 is identical to T1). <FIG> illustrates field diagrams of the electric field experienced by a particle at position <NUM>. A wide range of timesteps may be appropriate, depending on the particle size and the strength of the electrostatic field. For example, the timesteps may be as on the order of about <NUM>, or <NUM>, or <NUM>, or <NUM> or <NUM>.

<FIG> illustrate another system for aligning particles on a backing in an embodiment of the invention. System <NUM> has nine pairs of electrodes, with first electrodes 310A-I opposing electrodes 310J-310R. However, while nine pairs of electrodes are present in <FIG>, systems in other embodiments may have fewer, e.g. six pairs, seven pairs, eight pairs, or additional pairs, e.g. ten, eleven or more. Additionally, while illustrated as pairs of electrodes, it is expressly contemplated that some embodiments have other electrode configurations. For example, the top electrodes may be more closely spaced than the bottom electrodes. Additionally, an electrode on the top does not need to align, or be associated with, an electrode on the bottom. Further, electrodes on the top (or bottom) may not be equally spaced, from each other. Different physical configurations may require different voltage sequencing.

Electrodes 310A-I and 310J-R were modeled and simulated as an array of <NUM> copper wires, <NUM> (<NUM>") diameter, vertically spaced <NUM> (<NUM>"), and spaced <NUM> (<NUM>") horizontally. The wires are shown with an exaggerated diameter for clarity. Particle <NUM> indicates the point in space where the simulation analysis begins at time T1. The web may or may-not be moving in direction <NUM>; the simulation and analysis is the same either way. However, it may be of use to move the web at the same speed as the rotating field travels, enabling a particle to remain in a rotating field that does not appear to be traveling, when viewed from the perspective of a particle on the moving web.

As illustrated in <FIG>, electrodes 310A-I and 310J-R undergo a sequence of charges at sixteen different time steps before repeating (e.g. T17 is identical to T1). However, in other embodiments, more or fewer charge configurations may be present in different time steps before the sequence repeats. For example, one embodiment includes only two charge configurations, such that modulation comprises switching from a first configuration to a second configuration, and back to the first configuration. <FIG> illustrates field diagrams of the electric field experienced by a particle at position <NUM> as it moves through the electrode pairs in the direction <NUM>.

Several different systems of applying a modulated electrostatic field have been discussed. In some embodiments, methods of use discussed below apply to the systems described above. However, the methods described below may be useful with other system designs.

<FIG> illustrates a method for aligning particles on a substrate in an embodiment of the invention. Method <NUM> may be useful for aligning abrasive particles on a backing, for example.

In step <NUM>, a substrate is provided. In the example of abrasives, the substrate may be a nonwoven or other suitable backing material. An abrasive article substrate may be flexible or stiff, depending on an application need. In some embodiments, the substrate is provided with a binder precursor already applied, such that the abrasive particles embed themselves into the binder precursor layer in response to an experienced electric field. However, in other embodiments there is no binder precursor applied to a substrate prior to particle alignment. Additionally, in some embodiments, a binder precursor may be applied to the particles such that the precursor can be activated once the particles are aligned in a desired orientation. For example, abrasive particles may comprise a hot-melt coating that can be heat-activated once the particles are aligned on a backing. Additionally, coatings that improve static charge or static control could also be used in order to improve alignment.

In step <NUM>, particles are provided. In one embodiment, particles are provided to an electrostatic field on a conveyance mechanism. However, in another embodiment, particles are provided through a size-limiting screen such that only similarly sized particles are received for alignment. However, other suitable methods for providing particles are also envisioned.

In step <NUM>, the particles are aligned on the substrate. Alignment may take place in a batch or a continuous process. For example, the system illustrated in <FIG> could receive a batch of particles at a given time for alignment on a substrate, or it could receive a continuous stream of particles and a continuous supply of backing material. The systems in <FIG> and <FIG> can be configured to receive particles continuously, for example from a conveyor belt, at a regular rate through a screen, etc. Alignment takes place, in one embodiment, by modulating the experienced electrostatic field on a particle. For example, a single electrostatic field generator may rotate, causing a directionality of a generated electric field to shift as it rotates. In another embodiment, multiple electrodes may be present and may rotate or otherwise change an experienced electrostatic field. The changing experienced electrostatic field may cause a particle to wobble, or shift, into a preferred alignment position with respect to the substrate. In one embodiment, alignment comprises more particles aligned within a preferred orientation range than would occur randomly. In one embodiment, the acceptable orientation range is with respect to an edge of the backing such that oriented particles are substantially parallel to an edge of the backing.

In step <NUM>, the particles are bound to the substrate. In an example of a coated abrasive article, this may be accomplished by adding a make coat to the substrate in step <NUM> and allowing the make coat to cure in step <NUM>. In a nonwoven abrasive article example a resin-based or other binder may be applied to the substrate and aligned abrasive particles in step <NUM> to hold the abrasive particles in place. Additionally, in some embodiments, a binder precursor may be applied and later activated once particles are aligned. These and / or other suitable binders and methods of fixing particles to a backing are also envisioned. While steps <NUM> and <NUM> are described separately, in some embodiment they occur substantially concurrently. For example, the binder resin could include a pressure sensitive adhesive that binds the particles to the substrate during alignment. Alternatively, the binder could comprise a resin that cures in the atmospheric conditions under which alignment takes place.

<FIG> illustrate example processes for applying particles to a substrate in an embodiment of the invention. <FIG> illustrates an embodiment where particles <NUM> are provided for attachment through a screen <NUM>, while <FIG> illustrates particles <NUM> being provided on a conveyance mechanism <NUM>. However, it is expressly contemplated that other conveyance mechanism and arrangements are also possible. For example, use of a conveyance mechanism <NUM> may allow for a modulating field generator <NUM> to be located above incoming particles <NUM>, instead of below, such that particles <NUM> are pulled against gravity to affix to a backing.

As illustrated in the embodiment of <FIG>, system <NUM> can receive a plurality of particles <NUM> for attachment to a substrate <NUM>. Particles <NUM> can be provided on through a screen that can prevent particles above a maximum size from passing through. 5A illustrates a conveyor and a screen positioned such that particles <NUM> fall through a field <NUM> onto a substrate, it is also expressly envisioned that, in other embodiments, particles <NUM> are provided such that they are transported against gravity to a substrate. For example, while an electrostatic field generator <NUM> is illustrated in <FIG> as being located below backing <NUM>, it is also envisioned that field generator <NUM> can be located above substrate <NUM>, with screen <NUM> located below substrate, such that particles are pulled, against gravity, toward substrate <NUM>.

In one embodiment, substrate <NUM> moves in a direction as indicated by arrow <NUM>, such that a particle deposition and alignment occur in a continuous process. However, batch deposition and alignment is also contemplated in other embodiments.

Electrostatic field generator <NUM> is configured to provide a modulated electrostatic field with an opposing stationary plate, which also serves as screen <NUM>. While a single plate <NUM> is illustrated, it is also contemplated that an array of stationary electrodes <NUM> is also envisioned. Additionally, electrodes <NUM> may have a fixed charge or a charge sequence that is configured to change in unison with the rotation of field generator <NUM>.

In one embodiment, modulation of the electrostatic field is accomplished by rotation of field generator <NUM>, as indicated by arrows <NUM>. However, electrostatic field generator <NUM> may also provide a modulated electrostatic field by moving back and fourth with respect to a stationary backing <NUM>. Additionally, while only one electrostatic field generator <NUM> is illustrated in <FIG>, it is expressly contemplated that a modulated electrostatic field can be produced using multiple sets of electrodes present above and / or below the backing web.

In <FIG>, conveyance mechanism <NUM> provides particles <NUM> using a ramp. However, in other embodiments, conveyance mechanism is a conveyor belt that travels horizontally without an angle. However, a ramp configuration may reduce the strength of field required to translate particles <NUM> against gravity, in embodiments where field generator <NUM> is located above substrate <NUM>. Additionally, while only one field generator <NUM> is illustrated in <FIG>, opposite a charged plate <NUM>, <NUM>, respectively, it is expressly contemplated that a second modulating field generator may be present in other embodiments.

The methods and systems described herein are useful for applying particles to a substrate in a preferred alignment. Such systems and methods are especially applicable in the abrasives industry. Abrasive particles, particularly shaped abrasive particles, can achieve higher working efficiency and / or longer useful life when aligned properly. Additionally, some shaped abrasive particles are designed to have a different abrading efficiency in a first direction than in a second direction. It is important, therefore, to be able to align a plurality of particles within an abrasive article such that they rotationally oriented within a preferred angle range with respect to the backing of the abrasive article. In some embodiments, it is preferred that the abrasive particles are aligned such that a width is parallel, or substantially parallel, to the edges of the backing.

<FIG> illustrate abrasive articles in embodiments of the invention. <FIG> are illustrated for simplicity, for example without a make coat, size coat or other binder layer present to hold abrasive particles <NUM>, <NUM> and <NUM> in place. The abrasive particles illustrated in <FIG> are triangular prisms. However, while triangular prisms are presented as an example, many other shapes are also possible. It is noted that, from a top view, as well as from up or down web, a properly placed triangular prism appears to be a rectangle.

<FIG> illustrates a side view of an abrasive article <NUM> with a plurality of abrasive particles <NUM> on a backing <NUM>. In one embodiment, it is preferred that particles <NUM> align such that the bottom edge of each triangular prism particle <NUM> is in contact with backing <NUM> and is parallel to the edges of backing <NUM>.

<FIG> illustrates a top-down view of an abrasive article <NUM> with a plurality of abrasive particles <NUM> on a backing <NUM>. Only two rows of abrasive particles <NUM> is illustrated for ease of understanding. However, in some embodiments many more rows of abrasive particles <NUM> are present. Additionally, in some embodiments abrasive particles <NUM> will not align with respect to each other. Instead, each individual abrasive particle <NUM> will align within a modulated electrostatic field with respect to backing <NUM>.

While <FIG> illustrate embodiments where a preferred alignment is an abrasive particle substantially parallel to an edge of a substrate, as illustrated by abrasive article <NUM> in <FIG>, in other embodiments the preferred alignment is different. As illustrated in <FIG>, a preferred alignment can be a particle <NUM> at an angle <NUM> with respect to an edge of backing <NUM>. Angle <NUM> can be set by the placement of substrate <NUM> with respect to the electrostatic field generated.

Further details concerning the manufacture of coated abrasive articles according to the present disclosure can be found in, for example, <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), and <CIT>).

Nonwoven abrasive articles typically include a porous (e.g., a lofty open porous) polymer filament structure having abrasive particles bonded thereto by a binder. Further details concerning the manufacture of nonwoven abrasive articles according to the present disclosure can be found in, for example, <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), and <CIT>).

The abrasive particles described with respect to abrasive articles and methods of manufacture herein can be particles of any abrasive material. Useful abrasive materials that can be used include, for example, fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, ceramic aluminum oxide materials such as those commercially available as <NUM> CERAMIC ABRASIVE GRAIN from <NUM> Company of St. Paul, Minnesota, black silicon carbide, green silicon carbide, titanium diboride, boron carbide, tungsten carbide, titanium carbide, cubic boron nitride, garnet, fused alumina zirconia, sol-gel derived ceramics (e.g., alumina ceramics doped with chromia, ceria, zirconia, titania, silica, and/or tin oxide), silica (e.g., quartz, glass beads, glass bubbles and glass fibers), feldspar, or flint. Examples of sol-gel derived crushed ceramic particles can be found in <CIT>), <CIT>); <CIT>), <CIT>); and <CIT>). Further details concerning methods of making sol-gel-derived abrasive particles can be found in, for example, <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT><CIT>), and <CIT>), and in U. <CIT>) and<CIT>).

The abrasive particles may be shaped (e.g., precisely-shaped) or random (e.g., crushed and/or platey). Shaped abrasive particles and precisely-shaped abrasive particles may be prepared by a molding process using sol-gel technology as described, for example, in <CIT>), <CIT> (<CIT>)), <CIT>), <CIT>), and <CIT>).

<CIT>) describes alumina particles that have been formed in a specific shape, then crushed to form shards that retain a portion of their original shape features. In some embodiments, the abrasive particles are precisely-shaped (i.e., the abrasive particles have shapes that are at least partially determined by the shapes of cavities in a production tool used to make them).

Exemplary shapes of abrasive particles include crushed, pyramids (e.g., <NUM>-, <NUM>-, <NUM>-, or <NUM>-sided pyramids), truncated pyramids (e.g., <NUM>-, <NUM>-, <NUM>-, or <NUM>-sided truncated pyramids), cones, truncated cones, rods (e.g., cylindrical, vermiform), and prisms (e.g., <NUM>-, <NUM>-, <NUM>-, or <NUM>-sided prisms). In some embodiments (e.g., truncated pyramids and prisms), the abrasive particles respectively comprise platelets having two opposed major facets connected to each other by a plurality of side facets.

In some embodiments, the abrasive particles and/or magnetizable abrasive particles have an aspect ratio of at least <NUM>, at least <NUM>, at least <NUM>, or even at least <NUM>, although this is not a requirement.

Preferably, abrasive particles used in practice of the present disclosure have a Mohs hardness of at least <NUM>, at least <NUM>, or at least <NUM>, although other hardnesses can also be used.

Further details concerning abrasive particles and methods for their preparation can be found, for example, in <CIT>), <CIT>), and <CIT>), and in <CIT>), <CIT>), and <CIT>).

The abrasive particles are typically selected to correspond to abrasives' industry accepted nominal grades such as, for example, the American National Standards Institute, Inc. (ANSI) standards, Federation of European Producers of Abrasive Products (FEPA) standards, and Japanese Industrial Standard (JIS) standards. Exemplary ANSI grade designations (i.e., specified nominal grades) include: ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, ANSI <NUM>, and ANSI <NUM>. Exemplary FEPA grade designations include: P8, P12, P16, P24, P36, P40, P50, P60, P80, P100, P120, P180, P220, P320, P400, P500, <NUM>, P800, P1000, and P1200. Exemplary JIS grade designations include: JIS8, JIS12, JIS16, JIS24, JIS36, JIS46, JIS54, JIS60, JIS80, JIS100, JIS150, JIS180, JIS220, JIS240, JIS280, JIS320, JIS360, JIS400, JIS400, JIS600, JIS800, JIS1000, JIS1500, JIS2500, JIS4000, JIS6000, JIS8000, and JIS <NUM>,<NUM>.

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

Electrostatic systems and methods described herein can also be used to apply filler particles to the coated backing. Useful filler particles include silica such as quartz, glass beads, glass bubbles and glass fibers; silicates such as talc, clays (e.g., montmorillonite), feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate; metal sulfates such as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate; gypsum; vermiculite; wood flour; aluminum trihydrate; carbon black; aluminum oxide; titanium dioxide; cryolite; chiolite; and metal sulfites such as calcium sulfite.

The new electrostatic system can be used to apply grinding aid particles to the coated backing. Exemplary grinding aids, which may be organic or inorganic, include waxes, halogenated organic compounds such as chlorinated waxes like tetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride; halide salts such as sodium chloride, potassium cryolite, sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, silicon fluorides, potassium chloride, magnesium chloride; and metals and their alloys such as tin, lead, bismuth, cobalt, antimony, cadmium, iron, and titanium; and the like. Examples of other grinding aids include sulfur, organic sulfur compounds, graphite, and metallic sulfides. A combination of different grinding aids can be used. The grinding aid may be formed into particles or particles having a specific shape as disclosed in U. S <NUM>,<NUM>,<NUM>.

Abrasive articles according to the present disclosure are useful for abrading a workpiece. Methods of abrading range from snagging (i.e., high pressure high stock removal) to polishing (e.g., polishing medical implants with coated abrasive belts), wherein the latter is typically done with finer grades of abrasive particles. One such method includes the step of frictionally contacting an abrasive article (e.g., a coated abrasive article, a nonwoven abrasive article, or a bonded abrasive article) with a surface of the workpiece, and moving at least one of the abrasive article or the workpiece relative to the other to abrade at least a portion of the surface.

Examples of workpiece materials include metal, metal alloys, exotic metal alloys, ceramics, glass, wood, wood-like materials, composites, painted surfaces, plastics, reinforced plastics, stone, and/or combinations thereof. The workpiece may be flat or have a shape or contour associated with it. Exemplary workpieces include metal components, plastic components, particleboard, camshafts, crankshafts, furniture, and turbine blades.

Abrasive articles according to the present disclosure may be used by hand and/or used in combination with a machine. At least one of the abrasive article and the workpiece is moved relative to the other when abrading. Abrading may be conducted under wet or dry conditions. Exemplary liquids for wet abrading include water, water containing conventional rust inhibiting compounds, lubricant, oil, soap, and cutting fluid. The liquid may also contain defoamers, degreasers, for example.

Objects and advantages of this invention are further illustrated by the following non-limiting examples.

A rotating cylinder was used to modulate electrostatic fields. The cylinder dimensions were <NUM> inches in diameter by <NUM> inch wide and was rotated at <NUM> rpm. The ends of the cylinder tapered down to a one-inch shaft to allow for mounting to a DC motor with a coupling on one end and a pillow block bearing on the other. The cylinder was hollow and had <NUM> inch thick walls throughout. The cylinder was created via a viper SLA 3D printer with a clear polymer resin. Copper conductive paths were taped on the cylinder to create cross-web ribs as illustrated in <FIG>. The traces were <NUM> inch wide and had <NUM> inch spacing between each. At the edge of the cylinder, a piece of copper tape was wrapped all the way around such that all copper traces were in contact with each other. An additional copper trace was put on the shaft such that a charged wired could drag against it and keep constant contact while the cylinder was spinning. The copper traces were all charged to <NUM> kv with <NUM> milliamps.

Equilateral triangle shaped ceramic particles and precisely-shaped ceramic particles were prepared by a molding process using sol-gel technology as described, for example, in <CIT>), <CIT>(<CIT>)), <CIT>), <CIT>), and <CIT>). The equilateral triangular shaped ceramic abrasive particles had an edge length of <NUM> microns and a thickness of <NUM> microns were placed on a grounded plate a <NUM> inches below the center of the cylinder. A length of two-inch wide <NUM> vinyl tape was placed in between the cylinder and the ground plate with the adhesive coated side down to serve as the coated web (setup is shown in <FIG>).

An electric motor was used to get the cylinder to a speed of <NUM> rpm and then the <NUM> kV charge was turned on. Voltage was supplied by an electrostatic power supply. The PSG particles jumped upward toward the charged cylinder and adhered to the tacky portion of the vinyl tape. <NUM>% of particles were in an optimal orientation and <NUM>% were in a sub-optimal orientation.

The same method was used except that the cylinder had <NUM>" wide rib of copper and there was no speed to the cylinder applied. <NUM>% of particles were in an optimal orientation, and <NUM>% of particles were in a sub-optimal position.

8A illustrates a web that can move down-web in the direction of the arrow. A portion of the web length has electrodes A-I above the web, and electrodes J-R below the web. In this example the web is about midway between the upper and lower electrodes. These electrodes were modeled and simulated as an array of <NUM> copper wires, <NUM>" diameter, vertically spaced <NUM>", and spaced <NUM>" horizontally. The wires are shown with an exaggerated diameter for clarity in this figure. The green cube indicates the point in space where the simulation analysis begins at time T1. The web may or may-not be moving in the direction of the purple arrow; the simulation and analysis is the same either way. However, it may be of use to move the web at the same speed as the rotating field travels, enabling a particle to remain in a rotating field that does not appear to be traveling, when viewed from the perspective of a particle on the moving web. To create a rotating electric field, the electrodes of <FIG> can be charged by a controller.

<FIG> shows a time sequence of voltages to be applied to the electrodes of <FIG> using a controller to create a rotating electric field starting at the position of the green cube of <FIG>. There is a cycle of <NUM> time steps shown in <FIG>. This cycle is repeated 2⅛ times in <FIG> and in 8D. Time step T9 begins the second loop thru the <NUM> time step cycle. This <NUM> step cycle can be repeated forever. Or this sequence can be reversed to generate an electric filed that rotates in the opposite direction and travels in the opposite direction. Other time step sequences can be used to generate other dynamic electric fields. In this table, a "+" symbol indicates that the Voltage Controller will deliver a large positive voltage (e.g., +5kV) to the appropriate electrode for any given time step, and a "-" symbol indicates that the Voltage Controller will deliver a large negative voltage (e.g., -5kV) to the appropriate electrode for that time step. The locations in this table that have no symbol indicate that the associated electrodes will be left floating for the associated time step.

<FIG> shows the electric field simulation for the first time step T1. In this time step, electrodes C and L are charged to -5kV, electrodes G and P are charged to +5kV, and all other electrodes are not driven to a specific voltage but are left floating. The arrow indicates the direction of the electric field in the location of the box of <FIG>.

Claim 1:
A method of orienting abrasive particles on a substrate, the method comprising:
providing a substrate (<NUM>);
providing abrasive particles (<NUM>); and
generating a modulated electrostatic field (<NUM>), wherein the modulated electrostatic field (<NUM>) is configured to have a first effective direction at a first time and a second effective direction at a second time;
wherein the electrostatic field (<NUM>) is configured to cause the abrasive particles (<NUM>) to align rotationally in both a z-direction and a y-direction;
wherein the generated electrostatic field (<NUM>) is generated by a first electrode (210A-E, 310A-I, <NUM>, A-I) and a second electrode (210F-J, 310J-R, <NUM>, <NUM>, J-R) wherein the substrate (<NUM>) is provided between the first and second electrode, and wherein the abrasive particles (<NUM>) are drawn toward the substrate (<NUM>); characterized in that
A) the first electrode (210A-E, 310A-I, <NUM>, A-<NUM>) provides a modulated electrostatic field by changing the effective direction of the electrostatic field over time, and the second electrode (210F-J, 310J-R, <NUM>, <NUM>, J-R) provides a modulated electrostatic field by changing the effective direction of the electrostatic field over time; or
B) the first electrode is a set of first electrodes (210A-E, 310A-I, <NUM>, A-I) and the second electrode is a set of second electrodes (210F-J, 310J-R, <NUM>, <NUM>, J-R), and the substrate is configured to pass between the first set of electrodes and the second set of electrodes; or
C) the first electrode (210A-E, 310A-I, <NUM>, A-<NUM>) provides a modulated electrostatic field by changing the effective direction of the electrostatic field over time, and the second electrode (210F-J, 310J-R, <NUM>, <NUM>, J-R) provides a modulated electrostatic field by changing the effective direction of the electrostatic field over time, and the first electrode is a set of first electrodes (210A-E, 310A-I, <NUM>, A-I) and the second electrode is a set of second electrodes (210F-J, 310J-R, <NUM>, <NUM>, J-R), and the substrate is configured to pass between the first set of electrodes and the second set of electrodes.