US20030207659A1

US20030207659A1 - Abrasive product and method of making and using the same

Info

Publication number: US20030207659A1
Application number: US10/462,253
Authority: US
Inventors: Michael Annen; James Schutz
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2000-11-03
Filing date: 2003-06-16
Publication date: 2003-11-06

Abstract

The present invention relates to an abrasive article having a shaped abrasive coating on a shaped backing and to a method of making and using the flexible abrasive article. The flexible abrasive article includes a backing bearing separated, shaped non-abrasive structures having a distal end spaced from the backing which are coated with a shaped abrasive coating. The method comprises providing the backing, applying to one surface of the backing a plurality of separated, shaped non-abrasive structures with distal ends, coating the distal ends with a curable composition containing abrasive particles, imparting a shaped configuration to the uncured coating and curing the coating.

Description

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 10/033,391, filed Dec. 28, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/850,661, filed May 7, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/706,033, filed Nov. 3, 2000; and U.S. patent application Ser. No. 10/137,134, filed Apr. 30, 2002, which is a continuation-in-part of U.S. patent application Ser. No. 09/850,661, filed May 7, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/706,033, filed Nov. 3, 2000. Each of these prior applications is incorporated herein by reference.[0001]

FIELD OF THE INVENTION

The present invention relates generally to abrasive articles having a shaped abrasive coating on a non-abrasive shaped backing and to a method of making and using the abrasive article.

BACKGROUND OF THE INVENTION

In the abrasive industry there is a trend to finer and finer surface finish. Naturally, to achieve these finer surface finishes, smaller sized abrasive particles are employed in the abrasive article. In some instances the particle size of these small sized abrasive particles is less than 50 μm, typically less than 25 μm and sometimes less than 10 μm. In some instances loose abrasive slurries are employed rather than using fixed abrasive articles where the abrasive particles may be bonded together (to provide a bonded abrasive product) or to a backing (to provide a coated abrasive product). Many years ago, these loose abrasive slurries were capable of achieving surface finishes that were not previously obtainable with fixed abrasives. Over the last years, however, advances in fixed abrasives, especially coated abrasives, have enabled coated abrasives to effectively replace loose abrasive slurries in certain applications and thereby avoid the liquid handling equipment required for, and the waste disposal problems associated with, the use of slurries.

In many instances to achieve a fine surface finish, the polishing process is done in the presence of a fluid, typically water or some other type of lubricant. The fluid serves several purposes including minimizing heat build up and serving as a medium to remove the swarf or debris generated during polishing. If the swarf is not effectively removed during polishing, it is possible for the swarf to become re-deposited on the abrasive coating and thereby may cause coarse and undesirable scratches. Thus, it is imperative that the swarf be removed to provide efficient fluid flow at the interface between the abrasive coating and the workpiece surface being polished.

For all of the benefits of the fluid, there are sometimes drawbacks. For instance, with the very small abrasive particles, the resulting outer surface of the abrasive coating may be relatively smooth. The combination of the fluid and smooth abrasive coating has been known to create what is known in the industry as “stiction,” whereby the fluid will act like adhesive between the abrasive coating and the workpiece surface to cause these surfaces to stick together with unwanted results.

Stiction typically occurs in lapping type coated abrasive products. There are two common types of coated abrasive products. The first type has the abrasive particles bonded to the backing by means of a make coat. Overlying the abrasive grains is a size coat, which further reinforces the abrasive grains. In this first type, there is essentially one or two layers of abrasive particles. In the fine grades, the abrasive particles are so small that the resulting coated abrasive may exhibit a relatively short life. The second coated abrasive construction has the abrasive particles dispersed, typically uniformly dispersed, in the binder. This second construction is sometimes referred to as a “lapping film.” The lapping film may have longer life because there typically are multiple layers of abrasive particles as compared to the construction with the make and size coats. Likewise, the lapping film may produce a finer surface finish because the abrasive particles are more embedded in a binder. Conversely, lapping films tend to have lower cut rates since the first type construction tends to have more abrasive particles protruding.

Stiction tends to occur more frequently with lapping-type construction because the abrasive particles are embedded in the binder to provide a smooth surface. Various lapping type products have been provided with an abrasive coating which is shaped or structured, i.e., having raised portions and recessed portions. These products are sold by 3M Company under the trade designation “TRIZACT™” abrasive products. They are generally described in U.S. Pat. No. 5,152,917 (Pieper, et al.). Other lapping products are also described in U.S. Pat. No. 5,489,235 (Gagliardi, et al.).

Other Related Art

U.S. Pat. No. 2,115,897 (Wooddell et al.) teaches an abrasive article having a backing having attached thereto by an adhesive a plurality of bonded abrasive segments. These bonded abrasive segments can be adhesively secured to the backing in a specified pattern.

U.S. Pat. No. 2,242,877 (Albertson) teaches a method of making a compressed abrasive disc. Several layers of coated abrasive fibre discs are placed in a mold and then subjected to heat and pressure to form the compressed center disc. The mold has a specified pattern, which then transfers to the compressed center disc, thus rendering a pattern coated abrasive article.

U.S. Pat. No. 2,755,607 (Haywood) teaches a coated abrasive in which there are lands and grooves of abrasive portions. An adhesive coat is applied to the front surface of a backing and this adhesive coat is then combed to create peaks and valleys. Next abrasive grains are projected into the adhesive followed by solidification of the adhesive coat.

U.S. Pat. No. 3,048,482 (Hurst) discloses an abrasive article comprising a backing, a bond system and abrasive granules that are secured to the backing by the bond system. The abrasive granules are a composite of abrasive grains and a binder which is separate from the bond system. The abrasive granules are three dimensional and are preferably pyramidal in shape. To make this abrasive article, the abrasive granules are first made via a molding process. Next, a backing is placed in a mold, followed by the bond system and the abrasive granules. The mold has patterned cavities therein which result in the abrasive granules having a specified pattern on the backing.

U.S. Pat. No. 3,605,349 (Anthon) pertains to a lapping type abrasive article. Binder and abrasive grain are mixed together and then sprayed onto the backing through a grid. The presence of the grid results in a patterned abrasive coating.

U.S. Pat. No. 3,498,010 (Hagihara) describes a flexible grinding disc comprising an abrasive filled cured resin composite. The disc further comprises a structured surface formed by a molding process.

Great Britain Patent Application No. 2,094,824 (Moore) pertains to a patterned lapping film. The abrasive/binder resin slurry is prepared and the slurry is applied through a mask to form discrete islands. Next, the binder resin is cured. The mask may be a silk screen, stencil, wire or a mesh.

U.S. Pat. Nos. 4,644,703 (Kaczmarek et al.) and 4,773,920 (Chasman et al.) concern a lapping abrasive article comprising a backing and an abrasive coating adhered to the backing. The abrasive coating comprises a suspension of lapping size abrasive grains and a binder cured by free radical polymerization. The abrasive coating can be shaped into a pattern by a rotogravure roll.

Japanese Patent Application No. JP 62-238724A (Shigeharu, published Oct. 19, 1987) describes a method of forming a large number of intermittent protrusions on a substrate. Beads of pre-cured resin are extrusion molded simultaneously on both sides of the plate and subsequently cured.

U.S. Pat. No. 4,930,266 (Calhoun et al.) teaches a patterned abrasive sheeting in which the abrasive granules are strongly bonded and lie substantially in a plane at a predetermined lateral spacing. In this invention the abrasive granules are applied via an impingement technique so that each granule is essentially individually applied to the abrasive backing. This results in an abrasive sheeting having a precisely controlled spacing of the abrasive granules.

U.S. Pat. No. 5,014,468 (Ravipati et al.) pertains to a lapping film intended for ophthalmic applications. The lapping film comprises a patterned surface coating of abrasive grains dispersed in a radiation cured adhesive binder. To make the patterned surface an abrasive/curable binder slurry is shaped on the surface of a rotogravure roll, the shaped slurry removed from the roll surface and then subjected to radiation energy for curing.

U.S. Pat. No. 5,015,266 (Yamamoto) pertains to an abrasive sheet made by uniformly coating an abrasive/adhesive slurry over an embossed sheet to provide an abrasive coating which on curing has high and low abrasive portions formed by the surface tension of the slurry, corresponding to the irregularities of the base sheet.

U.S. Pat. No. 5,107,626 (Mucci) teaches a method of providing a patterned surface on a substrate by abrading with a coated abrasive containing a plurality of precisely shaped abrasive composites. The abrasive composites are in a non-random array and each composite comprises a plurality of abrasive grains dispersed in a binder.

Japanese Patent Application No. 02-083172 (Tsukada et al., published Mar. 23, 1990) teaches a method of a making a lapping film having a specified pattern. An abrasive/binder slurry is coated into indentations in a tool. A backing is then applied over the tool and the binder in the abrasive slurry is cured. Next, the resulting coated abrasive is removed from the tool. The binder can be cured by radiation energy or thermal energy.

Japanese Patent Application No. JP 4-159084 (Nishio et al., published Jun. 2, 1992) teaches a method of making a lapping tape. An abrasive slurry comprising abrasive grains and an electron beam curable resin is applied to the surface of an intaglio roll or indentation plate. Then, the abrasive slurry is exposed to an electron beam which cures the binder and the resulting lapping tape is removed from the roll.

U.S. Pat. No. 5,190,568 (Tselesin) describes a coated abrasive having a plurality of peaks and valleys. Abrasive particles are embedded in and on the surface of the composite structure.

U.S. Pat. No. 5,199,227 (Ohishi) describes a surface treating tape comprising a plurality of particulate filled resin protuberances on a substrate. The protuberances are closely spaced Bernard cells coated with a layer of premium abrasive particles.

U.S. Pat. No. 5,219,462 (Bruxvoort et al.), assigned to the same assignee as the present application, teaches a method for making an abrasive article. An abrasive/binder/expanding agent slurry is coated substantially only into the recesses of an embossed backing. After coating, the binder is cured and the expanding agent is activated. This causes the slurry to expand above the surface of the embossed backing.

U.S. Pat. No. 5,435,816 (Spurgeon et al.), assigned to the same assignee as the present application, teaches a method of making an abrasive article. In one aspect of this patent application, an abrasive/binder slurry is coated into recesses of an embossed substrate. Radiation energy is transmitted through the embossed substrate and into the abrasive slurry to cure the binder.

U.S. Pat. No. 5,437,754 (Calhoun), assigned to the same assignee as the present application, teaches a method of making an abrasive article. An abrasive slurry is coated into recesses of an embossed substrate. The resulting construction is laminated to a backing and the binder in the abrasive slurry is cured. The embossed substrate is removed and the abrasive slurry adheres to the backing.

U.S. Pat. No. 5,672,097 (Hoopman), assigned to the same assignee as the present application, teaches an abrasive article where the features are precisely shaped but vary among themselves.

European Patent No. 702,615 (Romero, published Oct. 22, 1997) describes an abrasive article having a patterned abrasive surface. The abrasive article has a plurality of raised and recessed portions comprising a thermoplastic material, the raised portions further comprising a layer of adhesive and abrasive material while the recessed portions are devoid of abrasive material.

U.S. Pat. No. 5,785,784 (Chesley et al.) pertains to an abrasive article having a first and a second, opposite, major surface. A mechanical fastener is formed on one surface and precisely shaped abrasive composites are applied via a production tool on the opposite major surface.

U.S. Pat. No. 6,299,508 (Gagliardi et al.) describes an abrasive article having a plurality of grinding-aid containing protrusions integrally molded to the surface of a backing. The protrusions are contoured so as to define a plurality of peaks and valleys, wherein abrasive particles cover at least a portion of the peaks and valleys.

What is desired in the industry is an abrasive article that minimizes any swarf or debris build up at the abrading interface; quickly generates fine surface finish; has long life; and minimizes stiction.

SUMMARY OF THE INVENTION

The invention provides an abrasive product, a method of making the same and a method of using the same. The novel abrasive product has a shaped abrasive coating on a shaped backing that provides a surface which has depressed areas which permit accumulated debris to collect without disturbing the raised abrasive portions of the abrasive product. Compared to a planar backing, the shaped backing transfers higher grinding pressure to the workpiece, thereby increasing the rate of finish refinement.

In one aspect, the invention provides an abrasive article comprising:

a. a backing having a first major surface and an opposite second major surface;

b. a plurality of separated, shaped non-abrasive structures, each structure having an attachment end attached to said first major surface and a distal end spaced from said first major surface with said shaped structures comprising distal ends being aligned generally in the same plane;

c. a shaped abrasive coating comprised of abrasive particles in a bond system having raised areas and depressed areas coated over at least said distal ends.

The invention further provides a method of making an abrasive article. The method comprises:

a. providing a backing having a first major surface and an opposite second major surface;

b. applying a plurality of separated, shaped non-abrasive structures to said first major surface, each of said structures having an attachment end attached to said first major surface and a distal end spaced from said first major surface with shaped structures comprising distal ends aligned generally in the same plane;

c. coating at least said distal ends with a coating composition comprising abrasive particles in a curable composition which will cure to provide a bond system for the abrasive particles;

d. imparting a shaped configuration to the coating composition to provide on curing a shaped abrasive coating having raised areas and depressed areas; and

e. curing the curable composition.

The invention further provides a method of finishing a surface of a substrate, the method comprising:

a. contacting a surface of a workpiece with an abrasive article comprising:

(1) a backing having a first major surface and an opposite second major surface;

(2) a plurality of separated, shaped non-abrasive structures, each structure having an attachment end attached to said first major surface and a distal end spaced from said first major surface with said shaped structures comprising distal ends being aligned generally in the same plane; and

(3) a shaped abrasive coating comprised of abrasive particles in a bond system having raised areas and depressed areas coated over at least said distal ends; and

b. relatively moving the abrasive article and/or said workpiece to modify the surface of the workpiece.

Typically, in use a liquid such as water is applied to the working surface of the coated abrasive product to facilitate removal of swarf and grinding debris.

The abrasive product of the present invention is characterized by having a backing which preferably includes on one surface thereof a plurality of separated, shaped structures. Each structure has an attachment end attached to the surface of the backing and a distal end spaced from the surface of the backing with the distal ends being generally aligned in the same plane. A shaped or structured abrasive coating comprised of abrasive particles in a bond system is coated over at least the distal ends of the shaped structures.

Definition of Terms

The term “backing” shall mean a shaped, preferably flexible backing onto which shaped features and shaped abrasive composites are to be subsequently added.

The term “shaped non-abrasive structures” shall mean structures composed of materials which do not include abrasive particles.

The term “shaped abrasive coating” shall mean a coating of a cured binder and abrasive material that has an exposed or working surface which includes raised portions and recessed portions.

The term “at least partially cured” means “part” or “all” of the curable binder precursor material has been cured to such a degree that it is handleable and collectable. The term “at least partially cured” does not mean that part or all of the curable binder precursor is always fully cured, but that it is sufficiently cured, after being at least partially cured, to be handleable and collectable.

As used herein, the expression “handleable and collectable” refers to material that will not substantially flow or experience a substantial change in shape if subjected to an applied force that tends to strain or deform a body.

The phrase “fully cured” shall mean the binder precursor is sufficiently cured so that the resulting product will function as an abrasive article, e.g. a coated abrasive article.

The term “separated, shaped structures” shall mean bodies which individually have a height and a volume contained within an area defined either by its distal or attachment end in any regular or irregular configuration which may include a cylindrical shape having a round distal end or attachment end, a box-shape which may include a square or rectangular distal or attachment end, a truncated three-side or four-sided pyramidal shape, or an irregular shape.

The term “separated” when referring to “shaped structures” shall mean that adjacent structures in the same abrasive product will have a gap therebetween and includes adjacent structures separated by a gap which may touch and be a part of one another either at touching corners of a box-shaped structure or touching sides of a cylindrical shaped structure.

The phrase “said distal ends being aligned generally in the same plane” shall mean that a substantial portion of the distal ends of the shaped structures lie mainly in the same plane although the surface may include additional shaped structures which have distal ends which fall short of lying in such a plane.

The term “applying a plurality of separated, shaped structures to the first surface” shall include physically attaching bodies to one surface of the backing of a composition which is not the same as that of the backing or by molding a backing in a mold which creates the structures and the backing at the same time with the appropriate shapes for the structures. The term “applying” also includes embossing a backing to provide an undulated surface which includes embossed raised portions wherein the height of the shaped structure would be defined by a wall derived from the backing being imparted with an embossed configuration and a distal end which, likewise, originates from the embossed backing.

The term “bearing area” shall mean the cumulative area of the abrasive coating on the distal ends in the same plane.

The term “percent bearing area” shall mean the total bearing area as defined above as compared to the total backing area on which the separated, shaped structures are applied X 100.

The abrasive product of the present invention has a long useful life because of the existence of spaces between the shaped bodies which provides a collection area for swarf and debris generated during finishing. Thus, the abrasive product can use very fine abrasive grains to provide extremely fine surface finishes to any of a variety of workpiece surfaces. The product of the invention provides a viable replacement for utilizing loose abrasive slurries and obviates the need for liquid handling equipment normally associated with slurries and the need for finding appropriate disposal sites for used slurries. The presence of the recessed areas between the shaped bodies that are coated with shaped abrasive coatings provides for efficient fluid flow at the working face of the abrasive product of the invention without undesirable “stiction” which is normally encountered in smooth-surfaced lapping films on smooth-surfaced workpiece surfaces. Compared to a planar backing, the shaped backing transfers higher grinding pressure to the workpiece, thereby increasing the rate of finish refinement. The products of the invention, having a shaped-surface, provide for controlled breakdown of the abrasive layer which provides for a constant cut rate and extended use life of the abrasive coating. The products of the invention also provide for reduced heat generation in use because the abrasive surface is not continuous. They further provide better conformance to short range (e.g., orange peel) and long range (e.g., auto body contours) surface textures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged schematic cross-sectional drawn representation of a portion of an abrasive product according to the present invention. [0065]
FIG. 2 is a schematic representation of one process for making an abrasive article according to the present invention. [0066]
FIG. 3 is a photomicrograph taken at a magnification of 10 X of the top surface of a coated abrasive product made in accordance with the present invention. [0067]
FIG. 4 is a photomicrograph taken at a magnification of 10 X of the top surface of a coated abrasive product made in accordance with the present invention. [0068]
FIG. 5 is a top plane view of a roller for making a production tool useful for making the shaped abrasive layer of articles according to the present invention. [0069]
FIG. 6 is an enlarged sectional view of one segment of the roll depicted in FIG. 5 taken at line [0070] 6-6 to show surface detail.
FIG. 7 is an enlarged sectional view of another segment of the patterned surface of the roll depicted in FIG. 5, taken at line [0071] 7-7.
FIGS. 8 and 9 are an enlarged drawn plane view representations of a pattern used to make tooling for Examples 1-16[0072]

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an enlarged schematic cross-sectional drawn representation of a portion of an [0073] abrasive product 10 according to the present invention. Abrasive product 10 includes backing 11 having a first major surface 14 and an opposite major surface 15. A plurality of separated, shaped structures 12 are attached to first major surface 14. Alternatively, the shaped structures may be unitarily formed from the backing, as herein described. Each shaped structure 12 includes an attachment end 16 which is attached to first major surface 14 and a distal end 17 which is spaced from first major surface 14 by the height 20 of the shaped structure. A shaped abrasive layer 13 is coated over at least distal ends 17 of separated shaped structures 12. Shaped abrasive layer 13 is characterized by including abrasive particles 21 in a suitable bond system 22 and includes raised portions 18 and depressed portions 19.
As shown in the photomicrograph of FIG. 3, viewed from above, shaped [0074] structures 12 may have a circular configuration, or a square configuration as depicted in the photomicrograph of FIG. 4. Alternatively, when viewed from above, the shaped structure may have a hexagonal configuration or the configuration of an annulus. The shaped structures need not all have the same structure or the same shape. For example, a product having circular shapes varying in diameter from 10 mm to 100 mm may be provided with smaller diameter shapes being located between larger diameter shapes.
The shaped structures may be randomly positioned on backing [0075] 11 or they may be aligned in rows in at least one direction, but preferably they are aligned in rows in at least two directions. When aligned in rows, a channel is provided by the space between rows. The channel is preferably free of any abrasive coating, although it may be coated with abrasive, if desired.
Preferred materials for forming shaped [0076] structures 12 include polymeric materials which may be solid or may comprise a foam.
Distal ends [0077] 17 of shaped structures 12 are preferably flat, although they may include other configurations which may be embossed with a pattern, curved, domed or otherwise configured.
The spacing from the backing surface of the distal ends of the shaped structures may be any convenient spacing, but preferably is at least about 0.05 mm and typically about 0.25 to about 20 mm. [0078]
[0079] Backing 11 may be any conventional backing material described hereinafter useful as a coated abrasive backing. Preferred backing materials include polymeric films and foamed sheet materials.
[0080] Backing 11 may be coated with an abrasive composition according to the methods described in U.S. Pat. No. 5,435,816 (Spurgeon et al.) and U.S. Pat. No. 5,667,541 (Klun et al.), incorporated herein by reference.
The [0081] backing 11 may further comprise a laminate having one part of a two part attachment system onto which is laminated (on the smooth side of the attachment system layer) a second layer. The lamination of backing 11 may serve as a means of improving dimensional stability during coating and subsequent use, as described in U.S. patent application Ser. No. 09/850,661 (Schutz et al.) filed May 7, 2001, which is incorporated herein by reference.
Each abrasive composite layer includes components important to surface modification characteristics and the durability of an abrasive article. The components of the abrasive composite layers and other embodiments of the invention are discussed in the following sections of the patent application. [0082]
Shaped Backing [0083]
There are numerous means to make the backing with the shaped structures. In one aspect, the shaped structures may be laminated or adhered to the first major surface of the backing. Any suitable lamination technique or adhesive may be employed. In another aspect, the shaped structures are formed on the first major surface of the backing. There are numerous methods to achieve this. [0084]
In the first method, the shaped structure is formed by a continuous molding process. In this process, it is generally preferred that the shaped structures be made from an acrylate and/or epoxy resin that is capable of being crosslinked into an acrylate and/or epoxy polymer. Additional details on acrylate resins and epoxy resin may be found in the binder section of this patent application. FIG. 2 illustrates an [0085] apparatus 23 for applying a shaped coating to the first major surface of the backing. A production tool 24 is in the form of a belt having a cavity-bearing contacting a surface 30, an opposite backing surface 38 and appropriately sized cavities within contacting surface 30. Backing 25 having a first major surface 26 and a second major surface 27 is unwound from roll 28. At the same time backing 25 is unwound from roll 28, the production tool 24 is unwound from roll 29. The contacting surface 30 of production tool 24 is coated with a mixture of precursor material that will form the shaped structure at coating station 31. The mixture can be heated to lower the viscosity thereof prior to the coating step. The coating station 31 can comprise any conventional coating means, such as knife coater, drop die coater, curtain coater, vacuum die coater, roll coater or an extrusion die coater. After the contacting surface 30 of production tool 24 is coated, the backing 25 and the production tool 24 are brought together such that the mixture wets the first major surface 26 of the backing 25. In FIG. 2, the mixture is forced into contact with the backing 25 by means of a contact nip roll 33, which also forces the production tool/mixture/backing construction against a support drum 35. Next, a sufficient dose of radiation energy is transmitted by a source of radiation energy 37 through the back surface 38 of production tool 24 and into the mixture to at least partially cure the binder precursor, thereby forming a shaped, handleable structure 39. The production tool 24 is then separated from the shaped, handleable structure 39. Separation of the production tool 24 from the shaped handleable structure 39 occurs at roller 40. The angle α between the shaped, handleable structure 39 and the production tool 24 immediately after passing over roller 40 is preferably steep, e.g., in excess of 30°, in order to bring about clean separation of the shaped, handleable structure 39 from the production tool 24. The production tool 24 is rewound as roll 41 so that it can be reused. Shaped, handleable structure 39 is wound as roll 43. If the binder precursor has not been fully cured, it can then be fully cured by exposure to an additional energy source, such as a source of thermal energy or an additional source of radiation energy, to form the backing with the shaped structures. Alternatively, full cure may eventually result without the use of an additional energy source to form the coated abrasive article. As used herein, the phrase “full cure” and the like means that the binder precursor is sufficiently cured so that the resulting product will function as a backing for a coated abrasive article.
Typically the production tool is used to provide a polymeric composite layer with an array of either precisely or irregularly shaped structures. The production tool has a surface containing a plurality of cavities. These cavities are essentially the inverse shape of the polymeric structures and are responsible for generating the shape and placement of the polymeric structures. These cavities may have any geometric shape that is the inverse shape to the geometric shapes suitable for the shaped structures onto which the abrasive layer is coated. Preferably, the shape of the cavities is selected such that the surface area of the shaped structure decreases away from the backing. The production tool can be a belt, a sheet, a continuous sheet or web, a coating roll such as a rotogravure roll, a sleeve mounted on a coating roll, or die. Additional details on production tools may be found in the section for “Making Abrasive Coating.”[0086]
In another method of making a shaped backing, the curable resin can be coated onto the surface of a rotogravure roll. The backing comes into contact with the rotogravure roll and the curable resin wets the backing. The rotogravure roll then imparts a pattern or texture into the curable resin. Next, the resin/backing combination is removed from the rotogravure roll and the resulting construction is exposed to conditions to cure the precursor polymer subunits such that shaped polymer features are formed. A variation of this process is to coat the curable resin onto the backing and bring the backing into contact with the rotogravure roll. [0087]
The rotogravure roll may impart desired patterns such as a hexagonal array, truncated ridges, lattices, spheres, truncated pyramids, cubes, blocks, or rods. The rotogravure roll may also impart a pattern such that there is a land area between adjacent polymeric features. Alternatively, the rotogravure roll can impart a pattern such that the backing is exposed between adjacent polymeric shapes. Similarly, the rotogravure roll can impart a pattern such that there is a mixture of polymeric shapes. [0088]
In still another method is to spray or coat the curable resin layer through a screen to generate a pattern in the curable resin layer. Then the precursor polymer subunits are cured to form the polymeric structures. The screen can impart any desired pattern such as a hexagonal array, truncated ridges, lattices, spheres, pyramids, truncated pyramids, cubes, blocks, or rods. The screen may also impart a pattern such that there is a land area between adjacent polymeric structures. Alternatively, the screen may impart a pattern such that the backing is exposed between adjacent polymeric structures. Similarly, the screen may impart a pattern such that there is a mixture of polymeric shapes. [0089]
Another method of making a shaped backing is to laminate a textured, shaped or embossed layer onto the first major surface of the backing. The resulting shaped laminate can then be used as the backing onto which a shaped abrasive layer is coated onto the textured, shaped or embossed layer. This textured, shaped or embossed layer can include, for example, scrims or screens. [0090]
Yet another alternative method for making a shaped backing is to pattern-coat a curable resin onto a generally planar backing, wherein the resin contains a component that can subsequently be expanded such that the dimensions of the pattern-coated resin features increase after expansion. This expansion preferably takes place before curing of the resin, but can also take place after curing. Examples of components that can be expanded upon changes in process conditions include expandable microspheres, such as available under the MICROPEARL tradename from Pierce-Stevens Corp, Buffalo, N.Y. A modification to this method is that the polymer microspheres are expanded prior to adding to the curable resin. The curable resin is pattern-coated into structures that are of sufficient height, and subsequently cured, yielding a shaped backing with features comprised of polymeric foam. [0091]
A backing consisting of shaped structures can also be formed by the continuous coating of a layer of curable resin wherein the resin contains a component that can subsequently be expanded in a pattern by local irradiation with specific wavelength range of electromagnetic radiation, e.g. infrared. Preferably, the curable resin layer is cured subsequent to the patterned expansion of the expandable component. [0092]
In yet another method, the backing is embossed to create the shaped structures. For example, thermoplastic films or foams such as nylon, propylene, polyester, polyethylene and the like, may be thermally embossed. The embossing tool has essentially the inverse of the desired shape and dimensions of the shaped structures. [0093]
The particular type and construction of the backing and/or shaped structures will depend upon many factors and mainly upon the desired properties of the final abrasive article for the intended polishing application. For example where a flexible abrasive article is desired, a foam backing and foam structures may be desirable. Alternatively where high cut rates are desired, a stiffer backing may be preferred. One skilled in the art will be able to formulate a backing and shaped structures that exhibit the appropriate properties. [0094]
Abrasive Particles [0095]
An abrasive article of the present invention typically comprises at least one abrasive composite layer that includes a plurality of abrasive particles dispersed in precursor polymer subunits. The binder is formed from a binder precursor comprising precursor polymer subunits. The abrasive particles may be uniformly dispersed in a binder or alternatively the abrasive particles may be non-uniformly dispersed therein. It is preferred that the abrasive particles are uniformly dispersed in the binder so that the resulting abrasive article has a more consistent cutting ability. [0096]
The average particle size of the abrasive particles can range from about 0.01 to 1500 micrometers, typically between 0.01 and 500 micrometers, and most generally between 1 and 100 micrometers. The size of the abrasive particle is typically specified to be the longest dimension of the abrasive particle. In most cases there will be a range distribution of particle sizes. In some instances it is preferred that the particle size distribution be tightly controlled such that the resulting abrasive article provides a consistent surface finish on the workpiece being abraded. [0097]
Examples of conventional hard abrasive particles include fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, black silicon carbide, green silicon carbide, titanium diboride, boron carbide, tungsten carbide, titanium carbide, diamond (both natural and synthetic), silica, iron oxide, chromia, ceria, zirconia, titania, silicates, tin oxide, cubic boron nitride, garnet, fused alumina zirconia, sol gel abrasive particles and the like. Examples of sol gel abrasive particles can be found in U.S. Pat. Nos. 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 (Wood et al.), all incorporated hereinafter by reference. [0098]
The term abrasive particle, as used herein, also encompasses single abrasive particles bonded together with a polymer to form an abrasive agglomerate. Abrasive agglomerates are further described in U.S. Pat. Nos. 4,311,489 (Kressner); 4,652,275 (Bloecher et al.); 4,799,939 (Bloecher et al.), and 5,500,273 (Holmes et al.). Alternatively, the abrasive particles may be bonded together by inter particle attractive forces. [0099]
The abrasive particle may also have a shape associated with it. Examples of such shapes include rods, triangles, pyramids, cones, solid spheres, hollow spheres and the like. Alternatively, the abrasive particle may be randomly shaped. [0100]
Abrasive particles can be coated with materials to provide the particles with desired characteristics. For example, materials applied to the surface of an abrasive particle have been shown to improve the adhesion between the abrasive particle and the polymer. Additionally, a material applied to the surface of an abrasive particle may improve the dispersibility of the abrasive particles in the precursor polymer subunits. Alternatively, surface coatings can alter and improve the cutting characteristics of the resulting abrasive particle. Such surface coatings are described, for example, in U.S. Pat. Nos. 5,011,508 (Wald et al.); 3,041,156 (Rowse et al.); 5,009,675 (Kunz et al.); 4,997,461 (Markhoff-Matheny et al.); 5,213,591 (Celikkaya et al.); 5,085,671 (Martin et al.) and 5,042,991 (Kunz et al.), the disclosures of which are incorporated herein by reference. [0101]
Fillers [0102]
An abrasive article of this invention may comprise an abrasive coating which further comprises a filler. A filler is a particulate material with an average particle size range between 0.1 to 50 micrometers, typically between 1 to 30 micrometers. Examples of useful fillers for this invention include metal carbonates (such as calcium carbonate, calcium magnesium carbonate, sodium carbonate, magnesium carbonate), silica (such as quartz, glass beads, glass bubbles and glass fibers), silicates (such as talc, clays, montmorillonite, feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate), metal sulfates (such as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate), gypsum, vermiculite, sugar, wood flour, aluminum trihydrate, carbon black, metal oxides (such as calcium oxide, aluminum oxide, tin oxide, titanium dioxide), metal sulfites (such as calcium sulfite), thermoplastic particles (such as polycarbonate, polyetherimide, polyester, polyethylene, polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, polypropylene, acetal polymers, polyurethanes, nylon particles) and thermosetting particles (such as phenolic bubbles, phenolic beads, polyurethane foam particles and the like). The filler may also be a salt such as a halide salt. Examples of halide salts include sodium chloride, potassium cryolite, sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, silicon fluorides, potassium chloride, magnesium chloride. Examples of metal fillers include, tin, lead, bismuth, cobalt, antimony, cadmium, iron titanium. Other miscellaneous fillers include sulfur, organic sulfur compounds, graphite and metallic sulfides and suspending agents. [0103]
An example of a suspending agent is an amorphous silica particle having a surface area less than 150 meters square/gram that is commercially available from DeGussa Corp., Rheinfelden, Germany, under the tradename “OX-50.” The addition of the suspending agent can lower the overall viscosity of the abrasive slurry. The use of suspending agents is further described in U.S. Pat. No. 5,368,619 (Culler) incorporated hereinafter by reference. [0104]
Abrasive Composite Binders [0105]
The abrasive coating of this invention is formed from a curable abrasive composite layer that comprise a mixture of abrasive particles and precursor polymer subunits. The curable abrasive composite layer preferably comprises organic precursor polymer subunits. The precursor polymer subunits preferably are capable of flowing sufficiently so as to be able to coat a surface. Solidification of the precursor polymer subunits may be achieved by curing (e.g., polymerization and/or cross-linking), by drying (e.g., driving off a liquid) and/or simply by cooling. The precursor polymer subunits may be an organic solvent borne, a water-borne, or a 100% solids (i.e., a substantially solvent-free) composition. Both thermoplastic and/or thermosetting polymers, or materials, as well as combinations thereof, maybe used as precursor polymer subunits. Upon the curing of the precursor polymer subunits, the curable abrasive composite is converted into the cured abrasive composite. The preferred precursor polymer subunits can be either a condensation curable resin or an addition polymerizable resin. The addition polymerizable resins can be ethylenically unsaturated monomers and/or oligomers. Examples of useable crosslinkable materials include phenolic resins, bismaleimide binders, vinyl ether resins, aminoplast resins having pendant alpha, beta unsaturated carbonyl groups, urethane resins, epoxy resins, acrylate resins, acrylated isocyanurate resins, urea-formaldehyde resins, isocyanurate resins, acrylated urethane resins, acrylated epoxy resins, or mixtures thereof. [0106]
An abrasive composite layer may comprise by weight between about 1 part abrasive particles to 90 parts abrasive particles and 10 parts precursor polymer subunits to 99 parts precursor polymer subunits. Preferably, an abrasive composite layer may comprise about 30 to 85 parts abrasive particles and about 15 to 70 parts precursor polymer subunits. More preferably an abrasive composite layer may comprise about 40 to 70 parts abrasive particles and about 30 to 60 parts precursor polymer subunits. [0107]
The precursor polymer subunits are preferably a curable organic material (i.e., a polymer subunit or material capable of polymerizing and/or crosslinking upon exposure to heat and/or other sources of energy, such as electron beam, ultraviolet light, visible light, etc., or with time upon the addition of a chemical catalyst, moisture, or other agent which cause the polymer to cure or polymerize). Precursor polymer subunits examples include amino polymers or aminoplast polymers such as alkylated urea-formaldehyde polymers, melamine-formaldehyde polymers, and alkylated benzoguanamine-formaldehyde polymer, acrylate polymers including acrylates and methacrylates alkyl acrylates, acrylated epoxies, acrylated urethanes, acrylated polyesters, acrylated polyethers, vinyl ethers, acrylated oils, and acrylated silicones, alkyd polymers such as urethane alkyd polymers, polyester polymers, reactive urethane polymers, phenolic polymers such as resole and novolac polymers, phenolic/latex polymers, epoxy polymers such as bisphenol epoxy polymers, isocyanates, isocyanurates, polysiloxane polymers including alkylalkoxysilane polymers, or reactive vinyl polymers. The resulting binder may be in the form of monomers, oligomers, polymers, or combinations thereof. [0108]
The aminoplast precursor polymer subunits have at least one pendant alpha, beta-unsaturated carbonyl group per molecule or oligomer. These polymer materials are further described in U.S. Pat. Nos. 4,903,440 (Larson et al.) and 5,236,472 (Kirk et al.), both incorporated herein by reference. [0109]
Preferred cured abrasive composites are generated from free radical curable precursor polymer subunits. These precursor polymer subunits are capable of polymerizing rapidly upon an exposure to thermal energy and/or radiation energy. One preferred subset of free radical curable precursor polymer subunits include ethylenically unsaturated precursor polymer subunits. Examples of such ethylenically unsaturated precursor polymer subunits include aminoplast monomers or oligomers having pendant alpha, beta unsaturated carbonyl groups, ethylenically unsaturated monomers or oligomers, acrylated isocyanurate monomers, acrylated urethane oligomers, acrylated epoxy monomers or oligomers, ethylenically unsaturated monomers or diluents, acrylate dispersions, and mixtures thereof. The term acrylate includes both acrylates and methacrylates. [0110]
Ethylenically unsaturated precursor polymer subunits include both monomeric and polymeric compounds that contain atoms of carbon, hydrogen and oxygen, and optionally, nitrogen and the halogens. Oxygen or nitrogen atoms or both are generally present in the form of ether, ester, urethane, amide, and urea groups. The ethylenically unsaturated monomers may be monofunctional, difunctional, trifunctional, tetrafunctional or even higher functionality, and include both acrylate and methacrylate-based monomers. Suitable ethylenically unsaturated compounds are preferably esters made from the reaction of compounds containing aliphatic monohydroxy groups or aliphatic polyhydroxy groups and unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, or maleic acid. Representative examples of ethylenically unsaturated monomers include methyl methacrylate, ethyl methacrylate, styrene, divinylbenzene, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxy propyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, lauryl acrylate, octyl acrylate, caprolactone acrylate, caprolactone methacrylate, tetrahydrofurfuryl methacrylate, cyclohexyl acrylate, stearyl acrylate, [0111] 2 -phenoxyethyl acrylate, isooctyl acrylate, isobomyl acrylate, isodecyl acrylate, polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, vinyl toluene, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, hexanediol diacrylate, triethylene glycol diacrylate, 2-(2-ethoxyethoxy) ethyl acrylate, propoxylated trimethylol propane triacrylate, trimethylolpropane triacrylate, glycerol triacrylate, pentaerthyitol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate and pentaerythritol tetramethacrylate. Other ethylenically unsaturated materials include monoallyl, polyallyl, or polymethallyl esters and amides of carboxylic acids, such as diallyl phthalate, diallyl adipate, or N,N-diallyladipamide. Still other nitrogen containing ethylenically unsaturated monomers include tris(2-acryloxyethyl) isocyanurate, 1,3,5-tri(2-methyacryloxyethyl)-s-triazine, acrylamide, methylacrylamide, N-methyl-acrylamide, N,N-dimethylacrylamide, N-vinylpyrrolidone, or N-vinyl-piperidone.
A preferred precursor polymer subunits contains a blend of two or more acrylate monomers. For example, the precursor polymer subunits may be a blend of trifunctional acrylate and a monofunctional acrylate monomers. An example of one precursor polymer subunits is a blend of propoxylated trimethylol propane triacrylate and 2-(2-ethoxyethoxy) ethyl acrylate. The weight ratios of multifunctional acrylate and monofunctional acrylate polymers may range from about 1 part to about 90 parts multifunctional acrylate to about 10 parts to about 99 parts monofunctional acrylate. [0112]
It is also feasible to formulate a precursor polymer subunits from a mixture of an acrylate and an epoxy polymer, e.g., as described in U.S. Pat. No. 4,751,138 (Tumey et al.), incorporated herein by reference. [0113]
Other precursor polymer subunits include isocyanurate derivatives having at least one pendant acrylate group and isocyanate derivatives having at least one pendant acrylate group are further described in U.S. Pat. No. 4,652,274 (Boettcher et al.), incorporated herein by reference. The preferred isocyanurate material is a triacrylate of tris(hydroxyethyl) isocyanurate. [0114]
Still other precursor polymer subunits include diacrylate urethane esters as well as polyacrylate or polymethacrylate urethane esters of hydroxy terminated isocyanate extended polyesters or polyethers. Examples of commercially available acrylated urethanes include those under the tradename “UVITHANE 782,” available from Morton Chemical, Moss Point, Miss.; “CMD 6600,” “CMD 8400,” and “CMD 8805,” available from UCB Radcure Specialties, Smyrna, Ga.; “PHOTOMER” resins (e.g., PHOTOMER 6010) from Henkel Corp., Hoboken, N.J.; “EBECRYL 220” (hexafunctional aromatic urethane acrylate), “EBECRYL 284” (aliphatic urethane diacrylate of 1200 diluted with 1,6-hexanediol diacrylate), “EBECRYL 4827” (aromatic urethane diacrylate), “EBECRYL 4830” (aliphatic urethane diacrylate diluted with tetraethylene glycol diacrylate), “EBECRYL 6602” (trifunctional aromatic urethane acrylate diluted with trimethylolpropane ethoxy triacrylate), “EBECRYL 840” (aliphatic urethane diacrylate), and “EBECRYL 8402” (aliphatic urethane diacrylate) from UCB Radcure Specialties; and “SARTOMER” resins (e.g., “SARTOMER” 9635, 9645, 9655, 963-B80, 966-A80, CN980M50, etc.) from Sartomer Co., Exton, Pa. [0115]
Yet other precursor polymer subunits include diacrylate epoxy esters as well as polyacrylate or poly methacrylate epoxy ester such as the diacrylate esters of bisphenol A epoxy polymer. Examples of commercially available acrylated epoxies include those under the tradename “CMD 3500,” “CMD 3600,” and “CMD 3700,” available from UCB Radcure Specialties. [0116]
Other precursor polymer subunits may also be acrylated polyester polymers. Acrylated polyesters are the reaction products of acrylic acid with a dibasic acid/aliphatic diol-based polyester. Examples of commercially available acrylated polyesters include those known by the trade designations “PHOTOMER 5007” (hexafunctional acrylate), and “PHOTOMER 5018” (tetrafunctional tetracrylate) from Henkel Corp.; and “EBECRYL 80” (tetrafunctional modified polyester acrylate), “EBECRYL 450” (fatty acid modified polyester hexaacrylate) and “EBECRYL 830” (hexafunctional polyester acrylate) from UCB Radcure Specialties. [0117]
Another preferred precursor polymer subunits is a blend of ethylenically unsaturated oligomer and monomers. For example the precursor polymer subunits may comprise a blend of an acrylate functional urethane oligomer and one or more monofunctional acrylate monomers. This acrylate monomer may be a pentafunctional acrylate, tetrafunctional acrylate, trifunctional acrylate, difunctional acrylate, monofunctional acrylate polymer, or combinations thereof. [0118]
The precursor polymer subunits may also be an acrylate dispersion like that described in U.S. Pat. No. 5,378,252 (Follensbee), incorporated herein by reference. [0119]
In addition to thermosetting polymers, thermoplastic binders may also be used. Examples of suitable thermoplastic polymers include polyamides, polyethylene, polypropylene, polyesters, polyurethanes, polyetherimide, polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, acetal polymers, polyvinyl chloride and combinations thereof. [0120]
Water-soluble precursor polymer subunits optionally blended with a thermosetting resin may be used. Examples of water-soluble precursor polymer subunits include polyvinyl alcohol, hide glue, or water-soluble cellulose ethers such as hydroxypropylmethyl cellulose, methyl cellulose or hydroxyethylmethyl cellulose. These binders are reported in U.S. Pat. No. 4,255,164 (Butkze et al.), incorporated herein by reference. [0121]
Initiators [0122]
In the case of precursor polymer subunits containing ethylenically unsaturated monomers and oligomers, polymerization initiators may be used. Examples include organic peroxides, azo compounds, quinones, nitroso compounds, acyl halides, hydrazones, mercapto compounds, pyrylium compounds, imidazoles, chlorotriazines, benzoin, benzoin alkyl ethers, diketones, phenones, or mixtures thereof. Examples of suitable commercially available, ultraviolet-activated photoinitiators have tradenames such as “IRGACURE 651,” “IRGACURE 184,” and “DAROCUR 1173” commercially available from Ciba Specialty Chemicals, Tarrytown, N.Y. Another visible light-activated photoinitiator has the trade name “IRGACURE 369” commercially available from Ciba Geigy Company. Examples of suitable visible light-activated initiators are reported in U.S. Pat. Nos. 4,735,632 (Oxman et al.) and 5,674,122 (Krech et al.). [0123]
A suitable initiator system may include a photosensitizer. Representative photosensitizers may have carbonyl groups or tertiary amino groups or mixtures thereof. Preferred photosensitizers having carbonyl groups are benzophenone, acetophenone, benzil, benzaldehyde, o-chlorobenzaldehyde, xanthone, thioxanthone, 9,10-anthraquinone, or other aromatic ketones. Preferred photosensitizers having tertiary amines are methyldiethanolamine, ethyldiethanolamine, triethanolamine, phenylmethyl-ethanolamine, or dimethylaminoethylbenzoate. Commercially available photosensitizers include “QUANTICURE ITX,” “QUANTICURE QTX,” “QUANTICURE PTX,” “QUANTICURE EPD” from Biddle Sawyer Corp., New York, N.Y. [0124]
In general, the amount of photosensitizer or photoinitiator system may vary from about 0.01 to 10% by weight, more preferably from 0.25 to 4.0% by weight of the components of the precursor polymer subunits. [0125]
Additionally, it is preferred to disperse (preferably uniformly) the initiator in the precursor polymer subunits before addition of any particulate material, such as the abrasive particles and/or filler particles. [0126]
In general, it is preferred that the precursor polymer subunits be exposed to radiation energy, preferably ultraviolet light or visible light, to cure or polymerize the precursor polymer subunits. In some instances, certain abrasive particles and/or certain additives will absorb ultraviolet and visible light, which may hinder proper cure of the precursor polymer subunits. This occurs, for example, with ceria abrasive particles. The use of phosphate containing photoinitiators, in particular acylphosphine oxide containing photoinitiators, may minimize this problem. An example of such an acylphosphate oxide is 2,4,6-trimethylbenzoyldiphenylphosphine oxide, which is commercially available from BASF Corporation, Ludwigshafen, Germany, under the trade designation “LUCIRIN TPO-L.” Other examples of commercially available acylphosphine oxides include “DAROCUR 4263” and “DAROCUR 4265” commercially available from Ciba Specialty Chemicals. [0127]
Cationic initiators may be used to initiate polymerization when the binder is based upon an epoxy or vinyl ether. Examples of cationic initiators include salts of onium cations, such as arylsulfonium salts, as well as organometallic salts such as ion arene systems. Other examples are reported in U.S. Pat. Nos. 4,751,138 (Tumey et al.); 5,256,170 (Harmer et al.); 4,985,340 (Palazotto); and 4,950,696, all incorporated herein by reference. [0128]
Dual-cure and hybrid-cure photoinitiator systems may also be used. In dual-cure photoiniator systems, curing or polymerization occurs in two separate stages, via either the same or different reaction mechanisms. In hybrid-cure photoinitiator systems, two curing mechanisms occur at the same time upon exposure to ultraviolet/visible or electron-beam radiation. [0129]
Backing [0130]
A variety of backing materials are suitable for the abrasive article of the present invention, including both flexible backings and backings that are more rigid. Examples of typical flexible abrasive backings include polymeric film, primed polymeric film, metal foil, cloth, paper, vulcanized fiber, nonwovens and treated versions thereof and combinations thereof. The thickness of a backing generally ranges between about 20 to 5000 micrometers and preferably between 50 to 2500 micrometers. [0131]
Alternatively, the backing may be fabricated from a porous material such as a foam, including open and closed cell foam. [0132]
Examples of more rigid backings include metal plates, ceramic plates, and the like. Another example of a suitable backing is described in U.S. Pat. No. 5,417,726 (Stout et al.) incorporated herein by reference. The backing may also consist of two or more backings laminated together, as well as reinforcing fibers engulfed in a polymeric material as disclosed in U.S. Pat. No. 5,573,619 (Benedict et al.). [0133]
The backing may be a sheet like structure that was previously considered in the art to be an attachment system. For example the backing may be a loop fabric, having engaging loops on the opposite second major surface and a relatively smooth first major surface. The shaped structures are adhered to the first major surface. Examples of loop fabrics include stitched loop, Tricot loops and the like. Additional information on suitable loop fabrics may be found in U.S. Pat. Nos. 4,609,581 (Ott) and 5,254,194 (Ott) both incorporated herein after by reference. Alternatively the backing may be a sheet like structure having engaging hooks protruding from the opposite second major surface and a relatively smooth first major surface. The shaped structures are adhered to the first major surface. Examples of such sheet like structures with engaging hooks may be found in U.S. Pat. Nos. 5,505,747 (Chesley), 5,667,540 (Chesley), 5,672,186 (Chesley) and 6,197,076 (Braunschweig) all incorporated herein after by reference. During use, the engaging loops or hooks are designed to interconnect with the appropriate hooks or loops of a support structure such as a back up pad. [0134]
Shaped Structures [0135]
The shaped structures may be fabricated out of any suitable material, including: nonwovens, foam (open and closed cell foam), polymeric film, polymeric material (both thermosetting and thermoplastic polymers). Examples of thermosetting polymers include: phenolic, epoxy, acrylate, urethane, urea-formaldehyde, melamine-formaldehyde and the like. Examples of thermoplastic polymers include: polyurethane, nylon, polypropylene, polyethylene, polyester, acyrnonitrile butadiene stryene, stryene, and the like. [0136]
Heights of backing raised portions may range from about 0.05 millimeters to about 20 millimeters, typically about 0.1 to about 10 millimeters and preferably about 0.25 to about 5 millimeters. Heights of abrasive coating raised portions range from about 5 micrometers (μm) to about 1000 μm, typically about 25 μm to about 500 μm and preferably about 25 μm to about 250 μm. [0137]
Ratio of backing height raised portions to abrasive coating raised portions may be in the range of about 1:1 to 1000:1, typically about 2:1 to 500:1 and preferably about 5:1 to 100:1. [0138]
The shaped structures may be bonded to the backing or alternatively the shaped structures may be unitary with the backing. [0139]
An Abrasive Composite Layer [0140]
An abrasive composite layer of this invention typically comprises a plurality of abrasive particles fixed and dispersed in precursor polymer subunits, but may include other additives such as coupling agents, fillers, expanding agents, fibers, antistatic agents, initiators, suspending agents, photosensitizers, lubricants, wetting agents, surfactants, pigments, dyes, UV stabilizers and suspending agents. The amounts of these additives are selected to provide the properties desired. [0141]
The abrasive composite may optionally include a plasticizer. In general, the addition of the plasticizer will increase the credibility of the abrasive composite and soften the overall binder composition. In some instances, the plasticizer will act as a diluent for the precursor polymer subunits. The plasticizer is preferably compatible with the precursor polymer subunits to minimize phase separation. Examples of suitable plasticizers include polyethylene glycol, polyvinyl chloride, dibutyl phthalate, alkyl benzyl phthalate, polyvinyl acetate, polyvinyl alcohol, cellulose esters, silicone oils, adipate and sebacate esters, polyols, polyols derivatives, t-butylphenyl diphenyl phosphate, tricresyl phosphate, castor oil, or combinations thereof. Phthalate derivatives are one type of preferred plasticizers. [0142]
The abrasive particle, or abrasive coating, may further comprise surface modification additives include wetting agents (also sometimes referred to as surfactants) and coupling agents. A coupling agent can provide an association bridge between the precursor polymer subunits and the abrasive particles. Additionally, the coupling agent can provide an association bridge between the binder and the filler particles. Examples of coupling agents include silanes, titanates, and zircoaluminates. [0143]
In addition, water and/or organic solvent may be incorporated into the abrasive composite. The amount of water and/or organic solvent is selected to achieve the desired coating viscosity of precursor polymer subunits and abrasive particles. In general, the water and/or organic solvent should be compatible with the precursor polymer subunits. The water and/or solvent may be removed following polymerization of the precursor, or it may remain with the abrasive composite. Suitable water soluble and/or water sensitive additives include polyvinyl alcohol, polyvinyl acetate, or cellulosic based particles. [0144]
Examples of ethylenically unsaturated diluents or monomers can be found in U.S. Pat. No. 5,236,472 (Kirk et al.), incorporated herein by reference. In some instances these ethylenically unsaturated diluents are useful because they tend to be compatible with water. Additional reactive diluents are disclosed in U.S. Pat. No. 5,178,646 (Barber et al.), incorporated herein by reference. [0145]
Abrasive Composite Structure Configuration [0146]
An abrasive article of this invention contains an abrasive coating with at least one abrasive composite layer that includes plurality of shaped, preferably precisely shaped, abrasive composite structures. The term “shaped” in combination with the term “abrasive composite structure” refers to both “precisely shaped” and “irregularly shaped” abrasive composite structures. An abrasive article of this invention may contain a plurality of such shaped abrasive composite structures in a predetermined array on a backing. Alternatively, the shaped abrasive composites may be in a random shape or an irregular placement on the backings. An abrasive composite structure can be formed, for example, by curing the precursor polymer subunits while being borne on the backing and in the cavities of the production tool. [0147]
The shape of the abrasive composites structures may be any of a variety of geometric configurations. Typically the base of the shape in contact with the backing has a larger surface area than the distal end of the composite structure. The shape of the abrasive composite structure may be selected from among a number of geometric solids such as a cubic, cylindrical, prismatic, parallelepiped, pyramidal, truncated pyramidal, conical, hemispherical, truncated conical, or posts having any cross section. Generally, shaped composites having a pyramidal structure have three, four, five or six sides, not including the base. The cross-sectional shape of the abrasive composite structure at the base may differ from the cross-sectional shape at the distal end. The transition between these shapes may be smooth and continuous or may occur in discrete steps. The abrasive composite structures may also have a mixture of different shapes. The abrasive composite structures may be arranged in rows, spiral, helix, or lattice fashion, or may be randomly placed. [0148]
The sides forming the abrasive composite structures may be perpendicular relative to the backing, tilted relative to the backing or tapered with diminishing width toward the distal end. An abrasive composite structure with a cross section that is larger at the distal end than at the back may also be used, although fabrication may be more difficult. [0149]
The height of each abrasive composite structure is preferably the same, but it is possible to have composite structures of varying heights in a single fixed abrasive article. The height of the composite structures generally may be less than about 2000 micrometers, and more particularly in the range of about 25 to 1000 micrometers. The diameter or cross sectional width of the abrasive composite structure can range from about 5 to 500 micrometers, and typically between about 10 to 250 micrometers. [0150]
The base of the abrasive composite structures may abut one another or, alternatively, the bases of adjacent abrasive composites may be separated from one another by some specified distance. [0151]
The linear spacing of the abrasive composite structures may range from about 1 to 24,000 composites/cm[0152] ²and preferably at least about 50 to 15,000 abrasive composite structures/cm². The linear spacing may be varied such that the concentration of composite structures is greater in one location than in another. The area spacing of composite structures ranges from about 1 abrasive composite structure per linear cm to about 100 abrasive composite structures per linear cm and preferably between about 5 abrasive composite structures per linear cm to about 80 abrasive composites per linear cm.
The percentage bearing area may range from about 5 to about 95%, typically about 10% to about 80%, preferably about 25% to about 75% and more preferably about 30% to about 70%. [0153]
The shaped abrasive composite structures are preferably set out on a backing, or a previously cured abrasive composite layer, in a predetermined pattern. Generally, the predetermined pattern of the abrasive composite structures will correspond to the pattern of the cavities on the production tool. The pattern is thus reproducible from article to article. [0154]
In one embodiment, an abrasive article of the present invention may contain abrasive composite structures in an array. With respect to a single abrasive composite layer, a regular array refers to aligned rows and columns of abrasive composite structures. In another embodiment, the abrasive composite structures may be set out in a “random” array or pattern. By this it is meant that the abrasive composite structures are not aligned in specific rows and columns. For example, the abrasive composite structures may be set out in a manner as described U.S. Pat. No. 5,681,217 (Hoopman et al.). It is understood, however, that this “random” array is a predetermined pattern in that the location of the composites is predetermined and corresponds to the location of the cavities in the production tool used to make the abrasive article. The term “array” refers to both “random” and “regular” arrays. [0155]
Production Tool [0156]
FIG. 5 shows a roller that was used to make [0157] production tool 24 as depicted in FIG. 2. The following specific embodiment of roller 50 was used to make production tool 24 which was then used to make the abrasive composite structure of the present invention. Roller 50 has a shaft 51 and an axis of rotation 52. In this case the patterned surface includes a first set 53 of adjacent circumferential grooves around the roller and a second set 54 of equally spaced grooves deployed at an angle of 30° with respect to the axis of rotation 52.
FIG. 6 shows an enlarged cross sectional view of a segment of the patterned surface of [0158] roller 50 taken at line 6-6 in FIG. 5 perpendicular to the grooves in set 53. FIG. 6 shows the patterned surface has peaks spaced by distance x which is 54.8 μm apart peak to peak and a peak height, y, from valley to peak of 55 μm, with an angle z which is 53°. FIG. 7 shows an enlarged cross sectional view of a segment of the patterned surface of roller 50 taken at line 7-7 in FIG. 5 perpendicular to the grooves in set 54. FIG. 7 shows grooves 55 having an angle w which is a 99.5° angle between adjacent peak slopes and valleys separated by a distance t which is 250 μm and a valley depth s which is 55 μm.
[0159] Roller 50 may also be used to make a production tool for forming the shaped structures 12, according to the method described in U.S. Pat. No. 5,435,816 (Spurgeon et al.), which is incorporated herein by reference. FIG. 8 shows a plan view of exemplary square shaped structures having post and bearing areas defined by the dimensions a and b. Likewise, FIG. 9 depicts a plan view of exemplary circular shaped structures having post and bearing areas defined by the dimensions c and d.
A production tool is used to provide an abrasive composite layer with an array of either precisely or irregularly shaped abrasive composite structures. A production tool has a surface containing a plurality of cavities. These cavities are essentially the inverse shape of the abrasive composite structures and are responsible for generating the shape and placement of the abrasive composite structures. These cavities may have any geometric shape that is the inverse shape to the geometric shapes suitable for the abrasive composites. Preferably, the shape of the cavities is selected such that the surface area of the abrasive composite structure decreases away from the backing. [0160]
The production tool can be a belt, a sheet, a continuous sheet or web, a coating roll such as a rotogravure roll, a sleeve mounted on a coating roll, or die. The production tool can be composed of metal, (e.g., nickel), metal alloys, or plastic. The metal production tool can be fabricated by any conventional technique such as photolithography, knurling, engraving, hobbing, electroforming, diamond turning, and the like. Preferred methods of making metal master tools are described in U.S. Pat. No. 5,975,987 (Hoopman et al.). [0161]
A thermoplastic tool can be replicated off a metal master tool. The master tool will have the inverse pattern desired for the production tool. The master tool is preferably made out of metal,. e.g., a nickel-plated metal such as aluminum, copper or bronze. A thermoplastic sheet material optionally can be heated along with the master tool such that the thermoplastic material is embossed with the master tool pattern by pressing the two together. The thermoplastic material can also be extruded or cast onto the master tool and then pressed. The thermoplastic material is cooled to a nonflowable state and then separated from the master tool to produce a production tool. The production tool may also contain a release coating to permit easier release of the abrasive article from the production tool. Examples of such release coatings include silicones and fluorochemicals. [0162]
Suitable thermoplastic production tools are reported in U.S. Pat. No. 5,435,816 (Spurgeon et al.), incorporated herein by reference. Examples of thermoplastic materials useful to form the production tool include polyesters, polypropylene, polyethylene, polyamides, polyurethanes, polycarbonates, or combinations thereof. It is preferred that the thermoplastic production tool contain additives such as anti-oxidants and/or UV stabilizers. These additives may extend the useful life of the production tool. [0163]
Method for Making An Abrasive Article [0164]
There are a number of methods to make the abrasive article of this invention. In one aspect the abrasive coating comprises a plurality of precisely shaped abrasive composites. In another aspect the abrasive coating comprises non-precisely shaped abrasive composites, sometimes referred to as irregularly shaped abrasive composites. A preferred method for making an abrasive article with one abrasive composite layer having precisely shaped abrasive composite structures is described in U.S. Pat. Nos. 5,152,917 (Pieper et al) and 5,435,816 (Spurgeon et al.), both incorporated herein by reference. Other descriptions of suitable methods are reported in U.S. Pat. Nos.: 5,454,844 (Hibbard et al.); 5,437,754 (Calhoun); and 5,304,223 (Pieper et al.), all incorporated herein by reference. [0165]
A suitable method for preparing an abrasive composite layer having a plurality of shaped abrasive composite structures includes preparing a curable abrasive composite layer comprising abrasive particles, precursor polymer subunits and optional additives; providing a production tool having a front surface; introducing the curable abrasive composite layer into the cavities of a production tool having a plurality of cavities; introducing a backing or previously cured abrasive composite layer of an abrasive article to the curable abrasive composite layer; and curing the curable abrasive composite layer before the article departs from the cavities of the production tool to form a cured abrasive composite layer comprising abrasive composite structures. The curable abrasive composite is applied to the production tool so that the thickness of the curable abrasive composite layer is less than or equal to its practical thickness limit. [0166]
An abrasive composite layer that is substantially free of a plurality of precisely shaped abrasive composite structures is made by placing a curable abrasive composite layer on a backing, or previously cured abrasive composite layers, independently of a production tool, and curing the abrasive composite layer to form a cured abrasive composite layer. The curable abrasive composite layer is applied to a surface so that the thickness of the abrasive composite layer is less than or equal to its practical thickness limit. Additional abrasive composite layers may be added to an abrasive article by repeating the above steps. [0167]
The curable abrasive composite layer is made by combining together by any suitable mixing technique the precursor polymer subunits, the abrasive particles and the optional additives. Examples of mixing techniques include low shear and high shear mixing, with high shear mixing being preferred. Ultrasonic energy may also be utilized in combination with the mixing step to lower the curable abrasive composite viscosity (the viscosity being important in the manufacture of the abrasive article) and/or affect the rheology of the resulting curable abrasive composite layer. Alternatively, the curable abrasive composite layer may be heated in the range of 30° C. to 70° C., microfluidized or ball milled in order to mix the curable abrasive composite. [0168]
Typically, the abrasive particles are gradually added into the precursor polymer subunits. It is preferred that the curable abrasive composite layer be a homogeneous mixture of precursor polymer subunits, abrasive particles and optional additives. If necessary, water and/or solvent is added to lower the viscosity. The formation of air bubbles may be minimized by pulling a vacuum either during or after the mixing step. [0169]
The coating station can be any conventional coating means such as drop die coater, knife coater, curtain coater, roll coater, vacuum die coater or a die coater. A preferred coating technique is a vacuum fluid bearing die reported in U.S. Pat. Nos. 3,594,865; 4,959,265 (Wood); and 5,077,870 (Melbye), which are incorporated herein by reference. During coating, the formation of air bubbles is preferably minimized. [0170]
In another variation, both the shaped portion of the shaped, flexible backing and the shaped abrasive composite may be molded from a single tooling using one or two sequential coating operations. The tooling may contain the mirror image of the combination of the shaped backing features [0171] 12 and shaped abrasive composite features 13 shown in FIG. 1. This production tool may be completely filled with the abrasive slurry in a single coating step. Alternatively, the production tool may be filled in two sequential coating steps, the first of which only partially fills the tool with the abrasive slurry and the second of which fills the remainder of the tool with a second resin or slurry. As with the shape of the shaped features of the backing, and with the abrasive slurry of the first coating, this second resin or slurry may be tailored to optimize the performance of the resulting abrasive article. In a two-step coating operation, the first coating operation is preferably accomplished by means of the aforementioned vacuum fluid bearing die method or slide die coating method reported in U.S. Pat. No. 5,741,549 (Maier et al.).
After the production tool is coated, the backing, or previously cured abrasive composite layer of an abrasive article, and the next layer of curable abrasive composite is brought into contact by any means such that the next layer of curable abrasive composite wets a surface of the backing or previously cured abrasive composite layer. The curable abrasive composite layer is brought into contact with the backing or the previously cured abrasive composite layer by contacting the nip roll which forces the resulting construction together. The nip roll may be made from any material; however, the nip roll is preferably made from a structural material such as metal, metal alloys, rubber or ceramics. The hardness of the nip roll may vary from about 30 to 120 durometer, preferably about 60 to 100 durometer, and more preferably about 90 durometer. [0172]
Next, energy is transmitted into the curable abrasive composite layer by an energy source to at least partially cure the precursor polymer subunits. The selection of the energy source will depend in part upon the chemistry of the precursor polymer subunits, the type of production tool as well as other processing conditions. The energy source should not appreciably degrade the production tool or backing. Partial cure of the precursor polymer subunits means that the precursor polymer subunits is polymerized to such a state that the curable abrasive composite layer does not flow when inverted in the production tool. If needed, the precursor polymer subunits may be fully cured after it is removed from the production tool using conventional energy sources. [0173]
After at least partial cure of the precursor polymer subunits, the production tool and abrasive article are separated. If the precursor polymer subunits are not essentially fully cured, the precursor polymer subunits can then be essentially fully cured by either time and/or exposure to an energy source. Finally, the production tool is rewound on a mandrel so that the production tool can be reused again and the fixed abrasive article is wound on another mandrel. [0174]
In another variation of this first method, the curable abrasive composite layer is coated onto the backing and not into the cavities of the production tool. The curable abrasive composite layer coated backing is then brought into contact with the production tool such that the slurry flows into the cavities of the production tool. The remaining steps to make the abrasive article are the same as detailed above. [0175]
It is preferred that the precursor polymer subunits are cured by radiation energy. The radiation energy may be transmitted through the backing or through the production tool. The backing or production tool should not appreciably absorb the radiation energy. Additionally, the radiation energy source should not appreciably degrade the backing or production tool. For instance, ultraviolet light can be transmitted through a polyester backing. Alternatively, if the production tool is made from certain thermoplastic materials, such as polyethylene, polypropylene, polyester, polycarbonate, poly(ether sulfone), poly(methyl methacrylate), polyurethanes, polyvinylchloride, or combinations thereof, ultraviolet or visible light may be transmitted through the production tool and into the slurry. For thermoplastic based production tools, the operating conditions for making the fixed abrasive article should be set such that excessive heat is not generated. If excessive heat is generated, this may distort or melt the thermoplastic tooling. [0176]
The energy source may be a source of thermal energy or radiation energy, such as electron beam, ultraviolet light, or visible light. The amount of energy required depends on the chemical nature of the reactive groups in the precursor polymer subunits, as well as upon the thickness and density of the binder slurry. For thermal energy, an oven temperature of from about 50° C. to about 250° C. effect on shaped structure and/or backing, and a duration of from about 15 minutes to about 16 hours are generally sufficient. Electron beam radiation or ionizing radiation may be used at an energy level of about 0.1 to about 10 Mrad, preferably at an energy level of about 1 to about 10 Mrad. Ultraviolet radiation includes radiation having a wavelength within a range of about 200 to about 400 nanometers, preferably within a range of about 250 to 400 nanometers. Visible radiation includes radiation having a wavelength within a range of about 400 to about 800 nanometers, preferably in a range of about 400 to about 550 nanometers. [0177]
The resulting cured abrasive composite layer will have the inverse pattern of the production tool. By at least partially curing or curing on the production tool, the abrasive composite layer has a precise and predetermined pattern. [0178]
There are many methods for making abrasive composites having irregularly shaped abrasive composites. While being irregularly shaped, these abrasive composites may nonetheless be set out in a predetermined pattern, in that the location of the composites is predetermined. In one method, curable abrasive composite is coated so that the thickness of the abrasive composite layer is within the practical thickness limits of the composite, into cavities of a production tool to generate the abrasive composites. The production tool may be the same production tool as described above in the case of precisely shaped composites. However, the curable abrasive composite layer is removed from the production tool before the precursor polymer subunits is cured sufficiently for it to substantially retain its shape upon removal from the production tool. Subsequent to this, the precursor polymer subunits are cured. Since the precursor polymer subunits are not cured while in the cavities of the production tool, this results in the curable abrasive composite layer flowing and distorting the abrasive composite shape. [0179]
In another method of making irregularly shaped composites, the curable abrasive composite can be coated onto the surface of a rotogravure roll. The backing comes into contact with the rotogravure roll and the curable abrasive composite wets the backing. The rotogravure roll then imparts a pattern or texture into the curable abrasive composite. Next, the slurry/backing combination is removed from the rotogravure roll and the resulting construction is exposed to conditions to cure the precursor polymer subunits such that an abrasive composite is formed. A variation of this process is to coat the curable abrasive composite onto the backing and bring the backing into contact with the rotogravure roll. [0180]
The rotogravure roll may impart desired patterns such as a hexagonal array, ridges, lattices, spheres, pyramids, truncated pyramids, cones, cubes, blocks, or rods. The rotogravure roll may also impart a pattern such that there is a land area between adjacent abrasive composites. This land area can comprise a mixture of abrasive particles and binder. Alternatively, the rotogravure roll can impart a pattern such that the backing is exposed between adjacent abrasive composite shapes. Similarly, the rotogravure roll can impart a pattern such that there is a mixture of abrasive composite shapes. [0181]
Another method is to spray or coat the curable abrasive composite layer through a screen to generate a pattern and the abrasive composites. Then the precursor polymer subunits are cured to form the abrasive composite structures. The screen can impart any desired pattern such as a hexagonal array, ridges, lattices, spheres, pyramids, truncated pyramids, cones, cubes, blocks, or rods. The screen may also impart a pattern such that there is a land area between adjacent abrasive composite structures. This land area can comprise a mixture of abrasive particles and binder. Alternatively, the screen may impart a pattern such that the backing is exposed between adjacent abrasive composite structures. Similarly, the screen may impart a pattern such that there is a mixture of abrasive composite shapes. This process is reported in U.S. Pat. No. 3,605,349 (Anthon), incorporated herein by reference. [0182]
Attachment System [0183]
The abrasive article of the invention may be secured to a support structure, commonly referred to as a backup pad. The abrasive article may be secured by means of a pressure sensitive adhesive, hook and loop attachment or some mechanical means. [0184]
The pressure sensitive adhesive must have sufficient adhesive strength to secure the coated abrasive to a support pad during use. For example, a typical coated abrasive disc/support pad composite may rotate as many as 6,000 revolutions per minute. Representative examples of pressure sensitive adhesives suitable for this invention include latex crepe, rosin, acrylic polymers and copolymers e.g., polybutylacrylate, polyacrylate ester, vinyl ethers, e.g., polyvinyl n-butyl ether, vinyl acetate adhesives, alkyd adhesives, rubber adhesives, e.g., natural rubber, synthetic rubber, chlorinated rubber, and mixtures thereof. One preferred pressure sensitive adhesive is an isooctylacrylate:acrylic acid copolymer. The pressure sensitive adhesive may be coated out of organic solvent, water or be coated as a hot melt adhesive. [0185]
The back side of the abrasive article may contain a loop substrate. The purpose of the loop substrate is to provide a means that the abrasive article can be securely engaged with hooks from a support pad. The loop substrate may be laminated to the coated abrasive backing by any conventional means. The loop substrate may be laminated prior to the application of the make coat precursor or alternatively, the loop substrate may be laminated after the application of the make coat precursor. In another aspect, the loop substrate may in essence be the coated abrasive backing. The loop substrate may be a chenille stitched loop, a stitchbonded loop substrate or a brushed loop substrate (e.g., brushed nylon). Examples of typical loop backings are further described in U.S. Pat. Nos. 4,609,581 and 5,254,194 all incorporated herein after by reference. The loop substrate may also contain a sealing coat to seal the loop substrate and prevent subsequent coatings from penetrating into the loop substrate. [0186]
Likewise, the back side of the abrasive article may contain a plurality of hooks; these hooks are typically in the form of sheet like substrate having a plurality of hooks protruding therefrom. These hooks will then provide the engagement between the coated abrasive article and a support pad that contains a loop fabric. This hook substrate may be laminated to the coated abrasive backing by any conventional means. [0187]

Test Procedures

The following test procedures were used to evaluate resin compositions and coated abrasive articles of the present invention. [0188]
Wet SCHIEFER Test [0189]
Abrasive coatings were laminated to a sheet-like backing bearing flattened engaging projections available from 3M Company under the trade designation HOOK-IT II™ backing and converted into 4-inch (10.16 cm.) discs. The back-up pad was secured to the driven plate of a SCHIEFER Abrasion Tester, available from Frazier Precision Company, Gaithersburg, Md., which had been plumbed for wet testing. Disc shaped acrylic plastic workpieces, 10.16 cm (4-inch) outside diameter by 1.27 cm (0.5-inch) thick, available under the trade designation “POLYCAST” acrylic plastic were obtained from Sielye Plastics, Bloomington, Minn. The water flow rate was set to 60 grams per minute. A 454 grams (one-pound) weight was placed on the abrasion tester weight platform and the mounted abrasive specimen lowered onto the workpiece and the machine turned on. The machine was set to run for 90 cycles in 30 cycle intervals. Surface finish values Rz were measured at four locations on the workpiece for each 30 cycle interval, with each test sample run in triplicate. [0190]
Panel Test [0191]
15.2 cm (6-inch) diameter circular specimens were cut from the abrasive test material and attached to a DYNABRADE model 56964 fine finish sander, available from Dynabrade Co., Clarence, N.Y. Abrasion tests were run for a total of one minute, in 10, 20 and 30 second intervals over three adjacent sections of the test panel, at an air pressure of 344 kPa (50 psi). The test panels were black base coat/clear coat painted cold rolled steel panels (E-coat: ED5000; Primer: 764-204; Base coat: 542AB921; Clear coat: RK8010A), obtained from ACT Laboratories, Inc., Hillsdale, Mich. Surface finish values Rz were measured at five points on each test panel section, with each test sample run in triplicate. [0192]
Surface Finish [0193]
Rz is the average individual roughness depths of a measuring length, where an individual roughness depth is the vertical distance between the highest point and the lowest point. [0194]
The surface finish of abraded workpieces by the Wet SCHIEFER Test and Panel Test were measured using a profilometer under the trade designation “PERTHOMETER MODEL M4P,” from Marh Corporation, Cincinnati, Ohio. [0195]

EXAMPLES

The following abbreviations are used in the examples. All parts, percentages and ratios in the examples are by weight unless stated otherwise: [0196]
CN973J75 urethane-acrylate resin from Sartomer, Inc., Exton, Pa. [0197]
F80 expandable polymeric microspheres, trade designation “MICROPEARL F80-SD1,” available from Pierce-Stevens Corp., Buffalo, N.Y. [0198]
SR339 2-phenoxyethyl acrylate from Sartomer, Inc., Exton, Pa. [0199]
SR351 trimethylolpropane triacrylate resin from Sartomer, Inc., Exton, Pa. [0200]
PD9000 anionic polyester dispersant, trade designation “ZEPHRYM PD 9000,” available from Uniqema, Wilmington, Del. [0201]
A-174 γ-methacryloxypropyltrimethoxy silane, trade designation “SILQUEST A-174,” available Crompton Corp., Friendly, W. Va. [0202]
TPO-L phosphine oxide, trade designation “LUCIRIN TPO-L,” available from BASF Chemicals, Ludwigshafen, Germany. [0203]
GC1000 green silicon carbide mineral, grade JIS1000, available from Fujimi Corp., Elmhurst, Ill. [0204]
GC1500 green silicon carbide mineral, grade JIS1500, available from Fujimi Corp., Elmhurst, Ill. [0205]
GC2000 green silicon carbide mineral, grade JIS2000, available from Fujimi Corp., Elmhurst, Ill. [0206]
GC2500 green silicon carbide mineral, grade JIS2500, available from Fujimi Corp., Elmhurst, Ill. [0207]
GC3000 green silicon carbide mineral, grade JIS3000, available from Fujimi Corp., Elmhurst, Ill. [0208]
GC4000 green silicon carbide mineral, grade JIS4000, available from Fujimi Corp., Elmhurst, Ill. [0209]
In all Examples, both the shaped backing features and shaped abrasive composite features were molded from polypropylene toolings that contained the mirror-image 3-dimensional pattern of the desired features. In all cases, the polypropylene tooling used to form the shaped abrasive composite was made according to U.S. Pat. No. 5,435,816 (Spurgeon et al.). Likewise, the shaped backing features in Examples 7 through 16, were also formed using tooling made according to U.S. Pat. No. 5,435,816. [0210]
In Examples 1 through 6, the shaped backing features were molded from polypropylene tooling sheets that were made from 48 cm×48 cm stainless steel master toolings. These master toolings were made via a masking/chemical etching process. From these master toolings, reverse-image polypropylene toolings were made using the following process: In a 135° C. heated press, a metal master tooling was placed on the bottom platen. On top of the tooling was placed a 0.8 mm thick sheet of polypropylene followed by a 3 mm thick aluminum plate. The composite was pressed at 618 kPa (90 psi) for 3 minutes and then removed. The mirror-image of the master tooling was molded into the polypropylene sheet. This molded polypropylene sheet was subsequently used as the tooling mold to produce the non-abrasive shaped structures on the backing. This process was repeated for each different tooling used in Examples 1 through 6. [0211]

Example 1

Pre-mix #1: 60.8 parts CN973J75, 36.4 parts SR339 and 2.8 parts TPO-L were combined using a mixer, available under the trade designation DISPERSATOR from Premier Mill Corp., Reading, Pa., at room temperature until air bubbles had dissipated. [0212]
Slurry #1: 3.4 parts of pre-expanded F80 was then added to 96.6 parts of Pre-mix #1 and formed into homogeneous slurry #1 using the DISPERSATOR mixer. F80 microspheres were pre-expanded at 160° C. for 60 minutes before use. [0213]
Slurry #1 was then applied, via hand spread, to a microreplicated tooling having square posts, 1.3 mm×1.3 mm×0.356 mm deep, with a 22% bearing area, as described in Table 3. The slurry filled tooling was then laminated face down to the smooth side of corona treated backing available from 3M Company under the trade designation 3M HOOK-IT II™ backing by passing through a set of rubber nip rolls at 26 cm/min. and a nip pressure of 275 kPa (40 psi). The slurry was then cured by passing twice through a UV processor, available from American Ultraviolet Company, Murray Hill, N.J., using two V-bulbs in sequence operating at 157.5 watts/cm (400 W/inch) and a web speed of 914 cm/min. The tooling was then removed to reveal a large scale 3-dimensional cured polymer foam structure having the mirror image of the tooling. [0214]
Pre-Mix #2: 33.6 parts SR339 was mixed by hand with 50.6 parts SR351, into which 8 parts PD 9000 was added and held at 60° C. until dissolved. The solution was cooled to room temperature. To this was added 2.8 parts TPO-L and 5 parts A-174 and the mixture again stirred until homogeneous. [0215]
Slurry #2: 61.5 parts GC2500 was incorporated into 38.5 parts of pre-mix #2 using the dispersator mixer to form homogeneous slurry #2. [0216]
The abrasive slurry was then applied, via hand spread, to a polypropylene microreplicated tooling, as depicted in FIGS. 6 and 7 wherein: s=55 μm; t=250 μm; w=99.53°; x=54.84 μm, y=55 μm; z=53.00°. The abrasive slurry filled tooling and was then laminated face down on the 3M HOOK-IT II™ backed large scale 3-dimensional coated structure by passing through a set of rubber nip rolls at 26 cm/min and a nip pressure of 275 kPa (40 psi). The slurry was then cured by passing twice through the UV Processor using two V-bulbs in sequence operating at 157.5 watts/cm (400 W/inch) and a web speed of 914 cm/min. On the first pass a 6 mm quartz plate was placed over the laminate in order to maintain pressure on the laminate. The tooling was then separated from the backing to reveal a cured 3-dimensional abrasive coating on top of a 3-dimensional foam structure. [0217]

Example 2

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 1, wherein slurry #1 was applied to a microreplicated tooling having the same square posts but with a 32% bearing area, as described in Table 3. [0218]

Example 3

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 1, wherein slurry #1 was applied to a microreplicated tooling having the same square posts but with a 42% bearing area, as described in Table 3. [0219]

Example 4

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 1, wherein slurry #1 was applied to a microreplicated tooling having the same square posts but with a 52% bearing area, as described in Table 3. [0220]

Example 5

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 1, wherein slurry #1 was applied to a microreplicated tooling having square posts, 10 mm×10 mm×0.533 mm deep, with a 90% bearing area, as described in Table 3. [0221]

Example 6

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 1, wherein slurry #1 was applied to a microreplicated tooling having round posts, 7 mm diameter×0.533 mm deep, with a 50% bearing area, as described in Table 3. [0222]

Example 7

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 1, wherein slurry #1 was applied to a microreplicated tooling having square posts, 2.6 mm×2.6 mm×0.533 mm deep, with a 42% bearing area, as described in Table 3. [0223]

Example 8

A double-sided adhesive coated {fraction (1/16)}-inch (1.6 mm) thick polyethylene foam tape, reference number 4496W, available from 3M Company, St. Paul, Minn., was laminated to the smooth side of the corona treated 3M HOOK-IT II™ backing. A 3-dimensional abrasive coating on top of 3-dimensional structure was then applied to this substrate as outlined in Example 7, wherein Slurry #1 was substituted with Premix #1. [0224]

Example 9

A sample was prepared as outlined in Example 8, wherein the 1.6 mm ({fraction (1/16)}-inch) thick polyethylene foam tape was replaced by 0.8 mm ({fraction (1/32)}-inch) thick material, reference 4492W, available from 3M Company, St. Paul, Minn. [0225]

Example 10

A 3-dimensional abrasive coating on top of 3-dimensional foam structure was prepared as outlined in Example 7, wherein the corona treated 3M HOOK-IT II™ backing was replaced by 76 μm (3 mil.) polyester film available under the trade designation “SCOTCHPAK” polyester film from 3M Company, St. Paul, Minn. [0226]
The following Examples 11-16 were made using a knife coater rather than handspread coating. [0227]

Example 11

A 3-dimensional abrasive coating on top of 3-dimensional structure was prepared by knife coating pre-mix #1 to a polypropylene tooling having microreplicated tooling having square posts, 2.6 mm×2.6 mm×0.533 mm deep, with a 42% bearing area, as described in Table 3. The coated tooling was then applied to a 76 μm (3-mil.) polyester film backing so that contact was established between the backing and the slurry. The laminated tooling was given a single pass in the UV processor using a D-bulb at 236 W/cm (600 W/inch) exposure, at a web speed of 9.1 m/min. (30 ft./min.) and a nip pressure of 344 kPa (50 psi), after which the tooling was removed. Slurry #2 was knife coated onto a polypropylene tool having a small-feature as depicted in FIGS. 6 and 7 wherein: s=55 μm; t=250 μm; w=99.53°; x=54.84 μm, y=55 μm; z=53.00°. The coated tool was then laminated to the large-feature structure and exposed under the same conditions in the UV processor and the tooling then removed. [0228]

Example 12

A 3-dimensional abrasive coating on top of 3-dimensional structure was prepared as outlined in Example 11, wherein the ratio of Pre-mix #2: GC 2500 was changed from 38.5:61.5 to 34.5:65.5 Pre-mix #2:GC1000 respectively. [0229]

Example 13

A 3-dimensional abrasive coating on top of 3-dimensional structure was prepared as outlined in Example 11, wherein the ratio of Pre-mix #2:GC 2500 was changed from 38.5:61.5 to 36.5:63.5 Pre-mix #2:GC1500 respectively. [0230]

Example 14

A 3-dimensional abrasive coating on top of 3-dimensional structure was prepared as outlined in Example 11, wherein the ratio of Pre-mix #2:GC 2500 was changed from 38.5:61.5 to 36.5:63.5 Pre-mix #2:GC2000 respectively. [0231]

Example 15

A 3-dimensional abrasive coating on top of 3-dimensional structure was prepared as outlined in Example 11, wherein the mineral GC 2500 was replaced by GC3000. [0232]

Example 16

A 3-dimensional abrasive coating on top of 3-dimensional structure was prepared as outlined in Example 11, wherein the ratio of Pre-mix #2:GC 2500 was changed from 38.5:61.5 to 40.5:59.5 Pre-mix #2:GC4000, respectively. [0233]

Comparative Sample

A coated abrasive foam disc, grade P3000, available under the trade designation TRIZACT HOOKIT II™, from 3M Company, St Paul, Minn. [0234]
Abrasion Tests [0235]

Results of Wet Schiefer and Panel tests are listed in Table 1 and Table 2 respectively.

TABLE 1


Wet Schiefer Test

	Rz-Initial	Rz @ 30 Cycles	Rz @ 60 Cycles	Rz @ 90 Cycles
Example	μm (μ-inches)	μm (82 -inches)	μm (μ-inches)	μm (μ-inches)

Comparative Sample	1.79 (70.3)	0.76 (30.0)	0.71 (27.9)	0.70 (27.5)
1	1.67 (65.8)	0.77 (30.1)	0.58 (23.0)	0.51 (19.9)
2	1.78 (69.9)	0.88 (34.8)	0.69 (27.0)	0.64 (25.3)
3	1.68 (66.3)	0.69 (27.2)	(0.58) (22.7)	0.54 (21.3)
5¹	1.71 (67.4)	0.82 (32.1)	0.51 (20.0)	0.53 (21.0)
6	1.75 (69.0)	0.73 (28.8)	0.59 (23.3)	0.49 (19.3)
7	1.75 (68.9)	0.74 (29.1)	0.63 (24.9)	0.57 (22.3)
11	1.78 (70.2)	0.63 (24.9)	(0.52) (20.3)	0.47 (18.5)
12	1.79 (70.4)	1.03 (40.6)	0.97 (38.3)	0.92 (36.2)
13	1.73 (68.1)	0.77 (30.2)	0.74 (29.0)	0.71 (28.0)
14	1.82 (71.8)	0.69 (27.2)	0.67 (26.4)	0.64 (25.2)
15	1.81 (71.2)	0.72 (28.2)	0.45 (17.8)	0.38 (14.9)
16	1.77 (69.6)	0.84 (32.9)	0.51 (20.1)	0.31 (12.2)

Examples 4 and 10 were not tested.

TABLE 2


Panel Test

	Rz-Initial	Rz @ 10 secs.	Rz @ 30 secs.	Rz @ 60 secs.
Example	μm (μ-inches)	μm (μ-inches)	μm (μ-inches)	μm (μ-inches)	Stiction

Comparative	1.49 (58.2)	0.74 (29.1)	0.65 (25.5)	0.65 (25.5)	No
Sample
8	1.52 (59.8)	0.62 (24.2)	0.59 (23.1)	0.62 (24.5)	No
9	1.51 (59.3)	0.63 (24.9)	0.57 (22.5)	0.58 (22.7)	No
11	1.45 (57.1)	0.56 (21.9)	0.50 (19.7)	0.56 (21.9)	No
12	1.44 (56.6)	0.97 (38.3)	0.80 (31.3)	0.74 (29.0)	No
13	1.44 (56.5)	0.76 (29.9	0.62 (24.2)	0.61 (23.9)	No
16	1.42 (56.0)	0.74 (29.0)	0.66 (25.8)	0.64 (25.2)	No

Table 3, read in conjunction with FIGS. 8 and 9, sets forth the tooling dimensions for Examples 1-16.

TABLE 3


	Tooling Dimensions	Bearing Area	Reference
Example	(mm)	(%)	Figure

1	a = 1.3, b = 1.5,	22	8
	height = 0.356
2	a = 1.3, b = 1.0,	32	8
	height = 0.356
3	a = 1.3, b = 0.7,	42	8
	height = 0.356
4	a = 1.3, b = 0.5,	52	8
	height = 0.356
5	a = 10.0, b = 0.5,	90	8
	height = 0.533
6	c = 7.0,d = 1.8,	50	9
	height = 0.0.533
7 through 16	a = 2.6, b = 1.4,	42	8
	height = 0.533

In comparing the Comparative Sample to Examples 1 through 11, it is apparent that, after sanding, all finishes were significantly refined in a short period of time. However, the Examples of the present invention provided a finer finish in an even shorter time. Moreover, these results were essentially independent of bearing area in the range from 22% to 90% bearing area. In analyzing the testing results for Examples 11 through 16, it is apparent that the final surface finish becomes rougher as the grade of abrasive mineral becomes coarser. However, within this trend, Example 14 of Table 1 (made with JIS2000 SiC) provided a finer surface finish at all sanding times than the Comparative Sample (graded as P3000, which is finer than JIS2000). These Examples also demonstrate that the present invention may readily employ a range mineral grades. [0239]
The present invention has now been described with reference to several embodiments thereof. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the exact details and structures described herein, but rather by the structures described by the language of the claims, and the equivalents of those structures. [0240]

Claims

What is claimed is:

1. An abrasive article comprising:

a. a backing having a first major surface and an opposite second major surface;

b. a plurality of separated shaped non-abrasive structures, each structure having an attachment end attached to said first major surface and a distal end spaced from said first major surface with said shaped structures comprising distal ends being aligned generally in the same plane; and

2. The abrasive article of claim 1 wherein shaped structures viewed from above are square.

3. The abrasive article of claim 1 wherein said shaped structures viewed from above are round or hexagonal.

4. The abrasive article of claim 1 wherein said shaped structures are aligned in rows in at least one direction.

5. The abrasive article of claim 1 wherein said shaped structures are aligned in rows in two directions.

6. The abrasive article of claim 4 wherein the aligned rows of shaped structures are separated by a channel defined by the space between rows.

7. The abrasive article of claim 6 wherein said channel is free of any abrasive coating.

8. The abrasive article of claim 1 wherein said shaped structures comprise a polymeric material.

9. The abrasive article of claim 1 wherein said shaped structures are unitary with said backing.

10. The abrasive article of claim 1 wherein said shaped structures comprise a foam.

11. The abrasive article of claim 1 wherein said distal ends have a flat surface.

12. The abrasive article of claim 1 wherein said backing is a polymeric film.

13. The abrasive article of claim 1 wherein said abrasive coating comprises precisely shaped abrasive composites.

14. The abrasive article of claim 1 wherein said abrasive particles have an average particle size less than about 60 μm.

15. The abrasive article of claim 1 wherein said distal ends are spaced from said first major surface by at least about 0.05 mm.

16. The abrasive article of claim 1 wherein said distal ends are spaced from said first major surface by about 0.05 mm to about 20 mm.

17. The abrasive article of claim 1 wherein said backing is flexible.

18. A method of making an abrasive article, said method comprising:

b. applying a plurality of separated, shaped non-abrasive structures to said first major surface, each of said structures having an attachment end attached to said first major surface and a distal end spaced from said first major surface with said shaped structures comprising distal ends aligned generally in the same plane;

e. curing the curable composition.

19. The method of claim 18 wherein said plurality of separated, shaped structures are applied by embossing said backing.

20. The method of claim 18 wherein said plurality of separated, shaped structures are applied by filling cavities in a production tool with a curable composition, contacting the first major surface of the backing with the curable composition contained within the cavities in the production tool at least partially curing the curable composition and separating the production tool from the shaped structures on the backing.

21. The method of claim 18 wherein said backing is flexible.

22. The method of claim 18 wherein said backing comprises a polymeric film.

23. The method of claim 18 wherein said shaped structures viewed from above are round.

24. The method of claim 18 wherein said shaped structures viewed from above are square.

25. The method of claim 18 wherein said shaped structures are aligned in rows in at least one direction.

26. The method of claim 18 wherein said shaped structures are aligned in rows in two directions.

27. The method of claim 25 wherein the aligned rows of shaped structures are separated by a channel defined by the space between rows.

28. The method of claim 27 wherein said channel is free of any abrasive coating.

29. The method of claim 18 wherein said shaped structures comprise a polymeric material

30. The method of claim 18 wherein said shaped structures comprise a foam.

31. The method of claim 18 wherein said shaped structures are provided by molding a curable material having a mold cavity corresponding to the shape of the backing and the shaped structures and at least partially curing the curable composition and removing the backing having the shaped structures from the mold.

32. The method of claim 18 wherein said abrasive coating is provided filling cavities of a production tool having cavities corresponding to the shaped configuration with a mixture comprising a curable binder composition containing abrasive particles, applying the mixture contained in the cavities to at least the distal ends, at least partially curing the binder composition while the production tool is in contact with the mixture and removing the production tool after said curing.

33. The method of claim 18 wherein said abrasive coating is provided by filling cavities of a production tool having cavities corresponding to the shaped configuration with a mixture comprising a curable binder composition containing abrasive particles, applying the mixture contained in the cavities to at least the distal ends, removing the production tool and at least partially curing the curable composition.

34. The method of claim 18 wherein the coating and imparting are accomplished by use of a rotogravure roll.

35. The method of claim 18 wherein said abrasive particles have an average particle size less than about 60 μm.

36. The method of claim 18 wherein said distal ends are spaced from said first major surface by at least about 0.05 mm.

37. The method of claim 18 wherein said distal ends are spaced from said first major surface by about 0.05 mm to about 20 mm.

38. A method of finishing a surface of a substrate, the method comprising:

a. contacting a surface of a workpiece with an abrasive article comprising:

(2) a plurality of separated shaped non-abrasive structures, each structure having an attachment end attached to said first major surface and a distal end spaced from said first major surface with said shaped structures comprising distal ends being aligned generally in the same plane;

b. relatively moving the abrasive article and/or the workpiece to modify the surface of the workpiece.

39. The method of claim 38 wherein said workpiece surface is painted.

40. The method of claim 38 further comprising introducing a fluid to the contacting surface of the workpiece and the abrasive article.

41. The method of claim 38 wherein said fluid is water.

42. The method of claim 38 wherein said abrasive article moving is a random orbital moving.