Abrasive product coated with agglomerated particles formed in situ and method of making the same

Abstract

The present invention relates to a coated abrasive article containing abrasive agglomerates based on target cores that provide an extended surface. Target cores are defined as geometric shapes, e.g., spherical, rectangular, tetrahedral, conical, cylindrical, pyramidal or combinations and mixtures thereof. The preferred cores are porous structures with their own abrasive capacity as a grinding aid element. They are bonded on substrates, e.g., textile fabrics, plastic films, saturated or no treated papers, vulcanized fibers, non-wovens and mixtures thereof to produce extended surfaces on which are deposited the working abrasive particles, e.g., aluminum oxide, silicon carbide, zirconia alumina, ceramic aluminum oxide and mixtures thereof, through an electrostatic field to improve performance capabilities. The electrostatic field promotes orientation of the deposited grains around the cores with exposed sharp edges over the extended area, causing as a secondary effect the compacting of the abrasive grains. The abrasive grains are agglomerated in situ via nucleation of the surface of the target cores during the coated abrasive manufacturing process. Incorporation of the abrasive particles on the interstices between target cores also produces increased life of the coated abrasive article. The invention includes the method of manufacturing the abrasive article by forming the agglomerated particles in situ during the manufacturing process.

Claims

1. A coated abrasive article, comprising: a backing having a major surface; a plurality of agglomerates adhered to said major surface, said agglomerates formed in situ on said backing during the process of manufacturing said coated abrasive article by nucleation of a plurality of abrasive particles on a plurality of target cores previously adhered to said major surface of said backing, said target cores being porous structures having an abrasive capacity as a grinding aid element; and a pre-make, a make and a size coat, each said coat comprising an organic resin, wherein said pre-make and make coats bind said target cores to said working surface of said backing and wherein said make and size coats bind said abrasive particles to said target cores to form said agglomerates.

2. The coated abrasive article of claim 1 further comprising a top coat over said size coat.

3. The coated abrasive article of claim 1 wherein said target cores range is size from about 50 to about 5000 microns, said abrasive particles range is size from about 3 to about 2000 microns and the size ratio of said target cores to said abrasive particles is about 1-3:1.

4. The coated abrasive article of claim 1 wherein said target cores are in the form of shaped structures selected from the group consisting of spheres, cylinders, cubes, pyramids, tetrahedrons and other polyhedral shapes.

5. The coated abrasive article of claim 1 wherein said target cores are selected from the group consisting of alpha alumina with different percentages of alpha alumina between about 95% to about 99.9%, alumina zirconia, silica, titanium dioxide, glass, micro natural stones, polyethylene, polypropylene, polystyrene, other polymers and materials having a hardness of at least about 4 on Mohs scale and mixtures thereof.

6. The coated abrasive article of claim 1 wherein said abrasive particles are selected from the group consisting of fused brown and white aluminum oxide, heat treated aluminum oxide, silicon carbide, zirconia alumina, ceramic aluminum oxide, cubic boron nitride, garnet, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, glass bubbles, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, diatomaceous earths, materials having a hardness of at least about 7 on Mohs scale and mixtures thereof.

7. The coated abrasive article of claim 1 wherein said agglomerates are distributed on said backing in regular cell patterns forming shapes selected from the group consisting of circles, ellipses, triangles, squares, rectangles, rhombuses, other polygonal shapes and combinations thereof.

8. The coated abrasive article of claim 1 wherein said pre-make, make and size coats are selected from the group consisting of phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, epoxy resins, acrylic resins, urethane resins, alkyd resins and mixtures thereof and may be the same or different.

9. The coated abrasive article of claim 1 wherein: said backing is selected from the group consisting of treated textile fabrics made from natural and synthetic yarns, vulcanized fibers, non-wovens, papers, saturated papers, polymeric extruded films, polymeric foams, paper/cloth combinations, mesh, stitch-bonded and combinations thereof; said target cores are selected from the group consisting of alpha alumina with different percentages of alpha alumina between about 95% to about 99.9%, alumina zirconia, silica, titanium dioxide, glass, micro natural stones, polyethylene, polypropylene, polystyrene, other polymers and materials having a hardness of at least about 4 on Mohs scale and mixtures thereof; and said abrasive particles are selected from the group consisting of fused brown and white aluminum oxide, heat treated aluminum oxide, silicon carbide, zirconia alumina, ceramic aluminum oxide, cubic boron nitride, garnet, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, glass bubbles, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, diatomaceous earths, other materials having a hardness of at least about 7 on Mohs scale and mixtures thereof; and said pre-make, make and size coats are each selected from the group consisting of phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, epoxy resins, acrylic resins, urethane resins, alkyd resins and mixtures thereof and may be the same or different, wherein said pre-make and make coats bind said target cores to said working surface of said backing and wherein said make and size coats bind said abrasive particles to said target cores to form said agglomerates.

10. A method for manufacturing a coated abrasive article, comprising: selecting a backing having a first surface; applying to said first surface a pre-make coat comprising an organic resin; depositing a plurality of target cores onto said resin-coated first surface; at least partially curing said pre-make coat to adhere said target cores to said backing; applying a make coat comprising an organic resin over said at least partially cured pre-make coat, said target cores and said backing; depositing a plurality of abrasive particles onto said make coat; at least partially curing said make coat to form a plurality of agglomerates in situ on said first surface of said backing by nucleation of said abrasive particles on said target cores previously adhered to said backing; applying a size coat comprising an organic resin over said at least partially cured make coat and agglomerates; and curing said size, make and pre-make coats.

11. The method of claim 10 further comprising applying a top coat over said size coat and curing said top coat.

12. The method of claim 10 wherein said target cores are in the form of shaped structures selected from the group consisting of spheres, cylinders, cubes, pyramids, tetrahedrons and other polyhedral shapes.

13. The method of claim 10 wherein said target cores are selected from the group consisting of alpha alumina with different percentages of alpha alumina between about 95% to about 99.9%, alumina zirconia, silica, titanium dioxide, glass, micro natural stones, polyethylene, polypropylene, polystyrene, other polymers and materials having a hardness of at least about 4 on Mohs scale and mixtures thereof and wherein said target cores range in size from about 50 to about 5000 microns.

14. The method of claim 13 wherein said abrasive particles are selected from the group consisting of fused brown and white aluminum oxide, heat treated aluminum oxide, silicon carbide, zirconia alumina, ceramic aluminum oxide, cubic boron nitride, garnet, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, glass bubbles, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, diatomaceous earths, materials having a hardness of at least about 7 on Mohs scale and mixtures thereof and wherein said abrasive particles range is size from about 3 to about 2000 microns and the size ratio of said target cores to said abrasive particles is about 1-3:1.

15. The method of claim 14 wherein said pre-make, make and size coats are selected from the group consisting of phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, epoxy resins, acrylic resins, urethane resins, alkyd resins and mixtures thereof and may be the same or different.

16. The method of claim 10 wherein said target cores and said abrasive particles are deposited using a method selected from the group consisting of gravity and electrostatic deposition methods and may be the same or different.

17. The method of claim 10 wherein said agglomerates are distributed on said backing in regular cell patterns forming shapes selected from the group consisting of circles, ellipses, triangles, squares, rectangles, rhombuses, other polygonal shapes and combinations thereof.

18. The method of claim 10 wherein said pre-make, make and size coats are applied by a technique selected from the group consisting of spray coating, roll coating, die coating, powder coating, curtain coating and knife coating.

19. The method of claim 10 wherein said curing is achieve by subjecting said abrasive article to an energy source selected from the group comprising heat transfer, ultraviolet light or an electron beam.

20. The method of claim 19 wherein said curing is achieved by heating to a temperature of about 60 C. to about 150 C.

21. A coated abrasive article made by a process, comprising: selecting a backing having a first surface; applying to said first surface a pre-make coat comprising an organic resin; depositing a plurality of target cores onto said resin-coated first surface; at least partially curing said pre-make coat to adhere said target cores to said backing; applying a make coat comprising an organic resin over said at least partially cured pre-make coat, said target cores and said backing; depositing a plurality of abrasive particles onto said make coat; at least partially curing said make coat to form a plurality of agglomerates in situ on said first surface of said backing by nucleation of said abrasive particles on said target cores previously adhered to said backing; applying a size coat comprising an organic resin over said at least partially cured make coat and agglomerates; and curing said size, make and pre-make coats.

22. The coated abrasive article of claim 21 wherein said process further comprises applying a top coat over said size coat and curing said top coat.

23. The coated abrasive article of claim 21 wherein said target cores range is size from about 50 to about 5000 microns, said abrasive particles range is size from about 3 to about 2000 microns and the size ratio of said target cores to said abrasive particles is about 1-3:1.

24. The coated abrasive article of claim 21 wherein said target cores are in the form of shaped structures selected from the group consisting of spheres, cylinders, cubes, pyramids, tetrahedrons and other polyhedral shapes.

25. The coated abrasive article of claim 21 wherein said target cores are selected from the group consisting of alpha alumina with different percentages of alpha alumina between about 95% to about 99.9%, alumina zirconia, silica, titanium dioxide, glass, micro natural stones, polyethylene, polypropylene, polystyrene, other polymers and materials having a hardness of at least about 4 on Mohs scale and mixtures thereof and wherein said target cores range in size from about 50 to about 5000 micronsw.

26. The coated abrasive article of claim 25 wherein said abrasive particles are selected from the group consisting of fused brown and white aluminum oxide, heat treated aluminum oxide, silicon carbide, zirconia alumina, ceramic aluminum oxide, cubic boron nitride, garnet, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, glass bubbles, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, diatomaceous earths, materials having a hardness of at least about 7 on Mohs scale and mixtures thereof and wherein said abrasive particles range is size from about 3 to about 2000 microns and the size ratio of said target cores to said abrasive particles is about 1-3:1.

27. The coated abrasive article of claim 26 wherein said pre-make, make and size coats are selected from the group consisting of phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, epoxy resins, acrylic resins, urethane resins, alkyd resins and mixtures thereof and may be the same or different.

28. The coated abrasive article of claim 21 wherein said target cores and said abrasive particles are deposited using a method selected from the group consisting of gravity and electrostatic deposition methods and may be the same or different.

29. The coated abrasive article of claim 21 wherein said agglomerates are distributed on said backing in regular cell patterns forming shapes selected from the group consisting of circles, ellipses, triangles, squares, rectangles, rhombuses, other polygonal shapes and combinations thereof.

30. The coated abrasive article of claim 21 wherein said pre-make, make and size coats are applied by a technique selected from the group consisting of spray coating, roll coating, die coating, powder coating, curtain coating and knife coating.

31. The coated abrasive article of claim 21 wherein said curing is achieve by subjecting said abrasive article to an energy source selected from the group comprising heat transfer, ultraviolet light or an electron beam.

32. The coated abrasive article of claim 31 wherein said curing is achieved by heating to a temperature of about 60 C. to about 150 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and intended advantages of the present invention will be more readily apparent by references to the following detailed description in connection with the accompanying drawings wherein:

(2) FIG. 1 is a cross-sectional view of a coated abrasive of the present invention.

(3) FIG. 2 is an optical photomicrograph profile showing a coated abrasive article of the present invention with agglomerated abrasive particles made by nucleation of the target cores, both partially and fully covered, and also showing the porous center core.

(4) FIG. 3 is an optical photomicrograph profile showing an example of target core particles used in the present invention.

(5) FIG. 4 is an enlarged optical photomicrograph profile representing the different parts comprising a coated abrasive of the present invention.

(6) FIG. 5 is an optical photomicrograph showing target cores deposited on a textile backing and adhered by synthetic resins and agglomerated abrasive particles.

(7) FIG. 6 is an optical photomicrograph showing cell patterns in such a way that the target cores and agglomerated abrasive particles will form shapes.

(8) FIG. 7 is a schematic diagram of a method for manufacturing a coated abrasive article of the present invention.

(9) FIG. 8 is a graph of total cut in grams with respect to lifetime of the coated abrasive of Examples 1 and 2.

(10) FIG. 9 is a graph of the cut profile with respect to time of the coated abrasive of Examples 1 and 2.

(11) FIG. 10 is a graph of the roughness profile with respect to time of the coated abrasive of Examples 1 and 2.

(12) FIG. 11 is a graph of total cut in grams with respect to lifetime of the coated abrasive of Examples 3, 4 and 5.

(13) FIG. 12 is a graph of the cut profile with respect to time of the coated abrasive of Examples 3, 4 and 5.

(14) FIG. 13 is a graph of the roughness profile with respect to time of the coated abrasive of Examples 3, 4 and 5.

(15) FIG. 14 is a graph of total cut in grams with respect to lifetime of the coated abrasive of Examples 6, 7 and 8.

(16) FIG. 15 is a graph of the cut profile with respect to time of the coated abrasive of Examples 6, 7 and 8.

(17) FIG. 16 is a graph of total cut in grams with respect to lifetime of the coated abrasive of Example 6 and Control C in 4 kg of pressure.

(18) FIG. 17 is a graph of the cut profile with respect to time of the coated abrasive Examples 6 and Control C in 4 kg of pressure.

(19) While the invention will be described in connection with the presently preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included in the spirit of the invention as defined in the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Abrasive Article

(20) The abrasive products manufactured based on this invention have an extended or longer working life than conventional single-grain, layer-coated abrasives as a result of the use of multi-grains exposed on extended areas. The extended abrasion life is the result of three main features: (1) extended areas (target cores) where the abrasive particles have been set; (2) increased numbers of abrasive particles that have been agglomerated by over exposition time of those target cores in the electrostatic field; and (3) increased core abrasion capacity of the target cores.

(21) According to the present invention, the coated abrasive comprises porous cores providing extended areas whose walls form the bases for the abrasive particles. Resin binders promote proper adhesion to support and give the product resistance during the grinding process. When first used, the agglomerated cores with the abrasive particles begin their grinding action with the outer, top, sharp edges. Over time wear exposes more fresh cutting edges. Thus, coated abrasive articles of the present invention exhibit an extended lifetime at least two or three times longer than a conventional coated abrasive, as a result of the construction methods of the present invention which are described below.

DEFINITIONS

(22) Target cores refers to particles with defined geometric shapes, e.g., spherical, cubical, rectangular, tetrahedral, conical, cylindrical, pyramidal or combinations and mixtures thereof. These particles may also be porous structures with their own abrasive capacity.

(23) Extended surface defines the area gained from the addition of the target cores on the backing.

(24) In situ means that the agglomerate particles are formed during and as part of the manufacturing process of the coated abrasive.

(25) Nucleation refers to the process by which the abrasive particles are deposited on the surface of the target cores causing the agglomeration of the abrasive particles.

(26) Binder precursor is defined as the resinous-type material that has not been totally polymerized and may comprise one or more additives.

(27) Curing and polymerization are used interchangeably and defined as the increase in molecular weight of the modified thermosetting binder so that the modified thermosetting binder forms a network.

Backing

(28) The backing in the present invention may be selected based on the final use or application of the coated abrasive product. The backing is selected from conventional backings well known to those skilled in the art. The backing may be selected from treated textile fabrics of different flexibilities, thickness and smoothness. The backing may be made from natural or synthetic yarns like cotton, polyester cotton, polyester, nylon, rayon or blends thereof. Other suitable backings include vulcanized fibers, non-wovens, papers, saturated papers, polymeric extruded films, polymeric foams, paper/cloth combinations, mesh, stitch-bonded and combinations thereof.

(29) In most of the cases the textile fabrics have been treated with acrylic latexes and synthetic resins. Treatments are intended to seal the fabric and improve its physical properties, e.g., tensile strength, smoothness, porosity, elongation resistance, flexibility, stiffness or thickness. These treatments are well known to those skilled in the art. Examples are described in U.S. Pat. No. 3,787,273 (Okrepkie et al.) and U.S. Pat. No. 5,700,302 (Stoetzel et al.).

(30) Finished cloth backings are also available in the market from companies like Gustav Ernstmeier Gmbh or AG Cilander.

Pre-Make, Make and Size Coats

(31) The pre-make coat is intended to affix the target cores on the backing. The make coat is used to affix the abrasive particles on the target cores. And the size coat promotes the proper adhesion to all agglomerated particles.

(32) The supersize or top coat, when used, is applied over the size coat in order to improve grinding capacity and heat release, particularly when the coated abrasive will be used to abrade stainless steel or heat sensitive alloys. This optional layer contains active fillers which are well known to those skilled in the art, e.g., those fillers broadly described in U.S. Pat. No. 5,221,295 (Zador) and U.S. Pat. No. 5,507,850 (Helmin).

(33) The top coat may be comprised of non-active fillers used as anti-loading components. These fillers are also well known to those skilled in the art such as the fillers disclosed in the U.S. Pat. No. 4,988,554 (Peterson et al.).

(34) The compositions of the pre-make coat, make coat, size coat and supersize coats comprise a liquid binder precursor based on either thermoset resins or radiation-curable resins. The preferred resins in this case are polymerizable organic structures that may include phenolic resins, urea formaldehyde resins, melamine formaldehyde resins, bis phenol epoxy resins, isocyanate extended polyesters and polyethers, moisture curable urethane resins, vinyl ethers and mixtures thereof.

(35) The resol or novolac phenolic resins are well known as one of the best selections, because of their outstanding thermal properties and economical cost. Resol phenolic resins may have a molar formaldehyde to phenol ratio between about 1.0-2.5 to 1. Their choice will be a function of the desired molecular weight structure. Novolac phenolic resins may have a formaldehyde/phenol ratio from about 0.5-0.9 to 1. Examples of commercially available resins in the market with their suppliers include Fibrex or other types from Masisa Resins, several types of resins from Fenoresinas, Durez and Varcum from Occidental Chemicals Corp, Resinox from Monsanto Chemicals, Aerofenet & Aerotap from Ashland Chemicals and Ruthapen from Bakelite AG.

(36) Urea formaldehyde and melamine formaldehyde resins may be used in the present invention. Such resins are well known to those skilled in the art and are commercially available in the market. Examples include Fibers 550 from Masnova Resinas and Ureic resins from Fenoresinas.

(37) Melamine formaldehyde resins may be used in the present invention as methylated or partially methylated waterborne melamine resins such as Cymel 328-385-373 from Cytec Industries.

(38) Epoxy resins based on bis phenol A or F and commercially available in the market may be used in the present invention. Examples include DER 331-332-334, DEN 428 from Dow Checmical Co, Epon 828-1004-1001 F from Shell Chemical Co, CHS 520 from Spolchemie.

(39) Isocyanate extended polyesters and polyethers may also be used. Examples of commercially available resins in this category include CMD 6600-8400-8805 from Radcure Specialties.

(40) Moisture curable liquid or hot melt urethane resins with 100% solids such as those available from Henkel or HB Fuller may be used in the present invention.

Target Cores

(41) Target cores refers to the species which have defined geometric shapes, e.g., spherical, cylindrical, cubic, conical, rectangular, tetrahedral and other polyhedral structures and which have a porous structure with their own abrasive capacity to act as a grinding aid element. Target cores may also have different chemical composition, e.g., a-alumina or with different zirconia contents and mixtures thereof. The choice of the chemical composition and the type and size of the target core depends on the end use for the coated abrasive article. Examples of different types of target cores are shown in Table 1.

(42) TABLE-US-00001 TABLE 1 Type of Type of target operation core Chemical composition Heavy Rectangular, Zirconia (93%), -alumina (98%) cut conical, purity and mixtures thereof cylindrical, pyramidal, mixtures thereof Medium Rectangular, Zirconia (93%), -alumina (98%) cut conical, purity and mixtures thereof cylindrical, pyramidal, mixtures thereof Finishing Spherical, -alumina (99%) purity conical mixtures thereof Polishing Spherical -alumina 99% of purity, polyethylene, polypropylene, polystyrene, another polymer and mixtures thereof Micro Spherical polyethylene, polypropylene, polystyrene Finishing another polymer and mixtures thereof

(43) The previous table is only for illustration and is not meant to be limiting in any way. Other target cores which might be used include those with different purity or composition of zirconia and alumina or with different chemical composition, e.g., silica, titanium dioxide, glass, micro natural stones, materials having a hardness of at least about 4 on Mohs scale and mixtures thereof.

(44) Hollow alpha-alumina cores used in this invention are the preferred material, because they are lightweight, are heat and compression resistant, have a low thermal conductivity and have a high abrasion capacity when the agglomerated cores are broken by the sanding process itself. Examples of suitable target cores include commercially available Alodur KKW, KKW Special and KKLS bubble alumina from Treibacher Schleifmittel Company. Other suitable examples include Duralum AB, Duralum AB LS and Durazon CSB from Washington Mills Company.

(45) The agglomerated cores of the present invention wear very uniformly in the grinding process at heavy or moderate loads without breaking into large lumps. Thus, each agglomerated core will have an extended life. The breakage of the cores during use exposes new abrasive grains which are located at the periphery of the target and in the valleys, further improving the life of the product.

(46) The layout of the agglomerated cores produces enough space between adjacent cores (valley to peak height) to promote in a more efficient way the use of liquid lubricants or coolants to avoid or reduce clogging during the sanding process of soft metals like aluminum and other soft metal alloys. Other dry lubricants like zinc, calcium or lithium stearates may be used in an anti-clogging layer, if the coated abrasive will be used to remove old paints, enamel coatings, polyester resin coatings, acrylic resin coatings or any other polymeric coatings.

(47) The spaces between agglomerated target cores in a semi-open coat distribution allow the use of heat-release chemicals or grinding aids called Top Coats, like potassium fluoroborate, cryolite or other active fillers. The use of these substances produces a cooler sanding process mostly for heat sensitive metals like stainless steel, titanium and others.

(48) The target cores range in size from about 50 to about 5000 microns, more preferably from about 100 to about 2500 microns. The specific size will be selected based on the final product requirements. The size must also be selected based on the abrasive grain particle to be deposited and must always be larger than the abrasive particles. The size distribution should be as uniform as possible in order to optimize the final finish of the sanded material.

Abrasive Particles

(49) Abrasive grains that are used in the present invention include: fused brown and white aluminum oxide, heat-treated aluminum oxide, silicon carbide, zirconia alumina, ceramic aluminum oxide, cubic boron nitride, garnet, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, glass bubbles, gypsum, talc, calcium oxide, aluminum oxide, calcium silicate, diatomaceous earths, materials having a hardness at least about 7 on Mohs scale and combinations thereof. High quality abrasive grains are available from Treibacher Schleifmittel GmbH, Washington Mills and many other producers.

Distribution and Patterns of Agglomerated Abrasive Particles

(50) The abrasive products manufactured in accord with this invention have either a closed or an open coat distribution which is selected based upon their intended final use. If the pre-make coat is applied by gravure roll, the selected tool may have a variety of engraved cell patterns and bias angles in such way that the target cores and agglomerated abrasive particles will form shapes, e.g., replicated triangles, squares, polygons, circles, rhombuses and the like. The layout arrangement of particles also may be either random or specifically designed based upon the intended use of the abrasive article.

Fillers

(51) Fillers to be used in the present invention include inorganic and organic materials that will improve the coating toughness, hardness, reduce backing porosity, increase binders solid contents, improve grinding capacity or optimize the abrasive coat. Fillers may be either non-active or active fillers.

(52) Examples of non-active fillers include calcium carbonate, wolastonite, clays, gypsum, talc, calcium oxide, calcium silicate, limestone, silicas, glass fibers, feldspar, calcium sulfates, vermiculite, titanium dioxide and the like.

(53) Examples of active fillers or inorganic grinding aids include potassium fluoroborate, cryolite, polyvinyl halides, polyvinyliden halide disclosed in U.S. Pat. No. 3,616,580 (Duwell et al.), chlorinated waxes disclosed in U.S. Pat. No. 3,676,092 (Halsey), polytrifluorochloroethylene disclosed in U.S. Pat. No. 3,869,834 (Mullin et al.) inorganic sulfur, cupric sulfide, molybdenum sulfide, potassium sulfate disclosed in U.S. Pat. No. 3,833,346 (Wirth); U.S. Pat. No. 3,868,232 (Sioui et al.); and U.S. Pat. No. 4,475,926 (Hickory).

Other Additives

(54) Other additives may be used as part of the formulations in the present invention including colorants, lubricants, defoamers, anti-settling agents, wetting agents, dispersing agents and organic solvents. These components are used to adjust desired characteristics, e.g., viscosity, wetting and liquid mixtures flowability and to the coating resin mixes.

(55) Defoamers that may be used with the present invention include BYK019 from BYK Chemie GmbH. Anti-settling and thickener agents may include OPTIGEL LX from Souther Clay Products Inc. Emulsifier agents may include ALKEST SP20 from Oxiteno-UNIVAR.

General Method of Manufacture

(56) Two processes are involved in the production of coated abrasives: coating and finishing.

Coating Method

(57) The manufacturing process is a continuous operation comprising the application of three (pre-make coat, make coat and size coat) or four (pre-make coat, make coat, size coat and super size coat) adhesive layers.

(58) A pre-make coat comprising a first organic-based binder precursor is applied to a backing by any technique known to those skilled in the art. Suitable techniques include spray coating, roll coating, die coating, powder coating or knife coating. The pre-make coat affixes the target cores on the backing. The target cores are distributed by either electrostatic or gravity methods which are well known to those skilled in art. The target cores are preferably uniformly distributed. The resulting structure is then exposed to a first energy source, e.g., a heat, ultra-violet or electron beam source, to at least partially cure the first binder precursor to form a solid pre-make coat that does not flow. For example, the resulting structure can be exposed to hot air at temperatures from about 60 C. to about 150 C., preferably from about 70 C. to about 130 C.

(59) After this first step a make coat comprising a second, organic-based binder precursor of the same or different composition from the first binder, is applied over the target cores by any conventional technique known to those skilled in the art, e.g., spray coating, roll coating, powder coating, slot die coating or curtain coating. After that the abrasive particles are electro-projected and/or applied by gravity and adhered in the make coat. In a presently preferred method, the abrasive grains can be passed into an electrostatic field where they become charged, one end of each grain becoming positive and the other negative. A negative electrode used in creating the electrostatic field attracts the positive end of the grain particle and repels the negative end, thus turning, aligning and applying the grain in an upright position on the backing to produce a uniform, sharp and aggressive abrasive surface. If a gravity system is selected instead of the electrostatic system, the abrasive grains fall in a controlled manner on the make-adhesive coated backing. The material thus processed can be coated in accord with the application needs in a closed or open coat.

(60) The resulting structure is then exposed to a second energy source, e.g., a heat, ultra-violet or electron beam source, to at least partially cure the second binder precursor to form a solid make coat that does not flow. Following this operation, a size coat comprising a third, organic-based binder precursor, which may be the same or different from the first and second binders, is applied over the target cores by any conventional technique known to those of skilled in the art, e.g., spray coating, roll coating, powder coating, die coating or curtain coating. Finally, the resulting abrasive construction is exposed to a third energy source, e.g., a heat, ultra-violet or electron beam source, which may be the same or different from the other two energy sources. The top coat (an optional layer) may be applied by any conventional technique known to those skilled in the art, e.g., spray coating or roll coating, and then curing by applying sufficient thermal or radiation energy. Complete polymerization is achieved by subjecting the resulting coated abrasive rolls (Jumbos) to temperature in stationary ovens.

Finishing or Converting

(61) As a result of the manufacturing process large size rolls of different widths and lengths called Jumbos are produced, on which the finishing process begins. These Jumbos are dried or cured before being conditioned to the proper moisture content for future processing into any required form. The Jumbo rolls are stored and then cut to final form, e.g., discs, rolls, belts and specialty forms.

EXAMPLES

Nomenclature

(62) 10 coated abrasive 11 valleys 12 peaks 20 backing 30 pre-make coat 40 target cores 41 porous center 50 make coat 60 abrasive particles 61 agglomerates 62 cell patterns 70 size coat 80 super size coat

(63) The following non-limiting examples will further illustrate the invention. The following abbreviations are used throughout:

(64) TABLE-US-00002 Designation Material RBAO regular brown fused aluminum oxide abrasive AZA aluminum zirconia abrasive BAO bluish grey aluminum oxide abrasive BSAO brown fused aluminum oxide abrasive, semi-friable WAO white fused aluminum oxide abrasive SiC silicon carbide abrasive CAO sintered aluminum ceramic abrasive KBF.sub.4 potassium tetrafluoroborate (98% pure) RF phenolic resin CaCO.sub.3 calcium carbonate CRY cryolite IO red iron oxide AL sorbitan monolaurate (Alkest SP20) SAA spherical hollow alpha alumina

Specific Procedure for Making an Abrasive Article of the Present Invention

(65) Backing 20 is coated with pre-make coat 30. Target cores 40 are then drop-coated by gravity onto pre-make coat 30 and precured. Make coat 50 is applied over target cores 40, followed by deposit of abrasive particles 60 over the make coat. The resulting abrasive article 10 is then precured. Size coat 70 is applied over the abrasive grains and the partially cured make coat and pre-make coat, after which the pre-make coat, make coat and size coat are fully cured. Optionally, supersize coat 80 is applied over size coat 70, and then cured to produce a finally cured abrasive article 10. The abrasive article is then flexed.

Testing Procedures

Procedure for Testing Coated Abrasives (Belts)

(66) Belts were produced from production rolls after post-curing and flexing processes, cut into sizes of 2132 and installed upon a floor backstand sander with the following characteristics: contact wheel diameter 14, contact wheel slot angle 45, contact wheel hardness on surface 40 shore A for Examples 1 and 2 and Control A, contact wheel hardness on surface 90 shore A for Examples 3 to 8 and Controls B and C and sander speed 1740 rpm. Materials to be grinded: stainless steel and carbon steel work pieces of 1 diameter with a length of 1.0 meter. Pressure loads over the metal piece were 1.150 kg for Examples 1 and 2 and 2 kg for Examples 3 to 8.

(67) The abrasive belt cut efficiency or stock removal by abrading period is determined by weighing the work piece before and after each abrading period of 2.5 minutes to quantify the weight of metal that has been removed. The test is continued until there is no difference between the weight of the material before and after an abrading period at which point it is terminated. The abrasive belt life is determined by the sum of the number of periods achieved during the test.

(68) FIG. 1 is a cross-sectional side view of coated abrasive 10 of the present invention showing backing 20 with pre-make coat 30 linking target cores 40 with porous centers 41. Also seen is make coat 50 with abrasive particles 60 and agglomerates 61 produced in situ and covered with size coat 70 and supersize coat 80.

(69) FIG. 2 is an optical photomicrograph profile obtained from coated abrasive 10 of the present invention showing porous centers 41 of target cores 40, abrasive particles 60 deposited in valleys 11 and peaks 12 between each core 40, and agglomerates 61 produced in situ using conventional coated abrasive manufacturing equipment.

(70) FIG. 3 is an optical photomicrograph profile showing target cores 40, backing 20 and pre-make 30. Also seen are valleys 11 and peaks 12.

(71) FIG. 4 is a cross-sectional side view of coated abrasive 10 of the present invention showing agglomerates 61, backing 20, pre-make 30 joining target cores 40 having porous centers 41 with the backing and make 50 joining abrasive particles 60 with target cores 40 forming agglomerates 61.

(72) FIG. 5 is a top view of coated abrasive article 10 of the present invention before and after the abrasive grains have been deposited. Left picture (A) shows target core particles 40 deposited on backing 20 and pre-make 30. Also observed are valleys 11 between target cores 40. Meanwhile, right picture (B) shows abrasive particles 60 deposited by electro-projection on make coat 50 and valleys 11, and agglomerates 61 formed over target cores 40.

(73) FIG. 6 is a top view of coated abrasive article 10 of the present invention where the target cores 40 and agglomerated abrasive particles 61 form shapes displaying cell patterns of replicated rhombuses 62.

(74) FIG. 7 is a schematic flow diagram of the method of the present invention employing in situ agglomeration and illustrating the different steps in the process of the present invention for producing the agglomerates in situ.

(75) FIG. 8 is a graph illustrating the total cut in grams of Examples 1 and 2 of a coated abrasive article 10 of the present invention. FIG. 8 shows that the agglomerated abrasive has at least twice the cut efficiency of a conventional or mono-layer coated abrasive (Control A).

(76) FIG. 9 is a graph illustrating the rate of cut in grams of Examples 1 and 2 of a coated abrasive article 10 of the present invention. FIG. 9 shows that the agglomerated abrasive exhibits a more consistent level of cut throughout the test sequence than a conventional or mono-layer coated abrasive (Control A).

(77) FIG. 10 is a graph illustrating the roughness of the finished surface in microns (m) when using Examples 1 and 2 of a coated abrasive article 10 of the present invention. FIG. 10 shows that the agglomerated abrasives of the present invention have similar performance in finished surface to a conventional or mono-layer coated abrasive (Control A).

(78) FIG. 11 is a graph illustrating the total cut in grams of Examples 3, 4 and 5 of a coated abrasive article 10 of the present invention, of Control B and of a hollow-body agglomerate grain (U.S. Pat. No. 3,928,949). FIG. 11 shows that the agglomerated abrasives of the present invention have at least twice the cut efficiency of a conventional or mono-layer coated abrasive (Control B) or the hollow-body agglomerate grain of the '949 patent.

(79) FIG. 12 is a graph illustrating the rate of cut in grams of Examples 3, 4 and 5 of a coated abrasive article 10 of the present invention, of Control B and of a hollow-body agglomerate grain (U.S. Pat. No. 3,928,949). FIG. 12 shows that the agglomerated abrasives of the present invention exhibit a more consistent level of cut throughout the test sequence than the conventional or mono-layer coated abrasive (Control B) and the hollow-body agglomerate grain of the '949 patent.

(80) FIG. 13 is a graph illustrating the roughness of the finished surface in microns (m) when using Examples 3, 4 and 5 of a coated abrasive article 10 of the present invention, of Control B and of a hollow-body agglomerate grain (U.S. Pat. No. 3,928,949). FIG. 13 shows that the agglomerated abrasives of the present invention have similar performance in finished surface to the conventional or mono-layer coated abrasive (Control B) and the hollow body agglomerate grain of the '949 patent.

(81) FIG. 14 is a graph illustrating the total cut in grams of Examples 6, 7 and 8 of a coated abrasive article 10 of the present invention. FIG. 14 shows that the agglomerated abrasives of the present invention have at least twice the cut efficiency of a conventional or mono-layer coated abrasive (Control C).

(82) FIG. 15 is a graph illustrating the rate of cut in grams of Examples 6, 7 and 8 of a coated abrasive article 10 of the present invention. FIG. 15 shows that the agglomerated abrasives of the present invention exhibit a more consistent level of cut throughout the test sequence than a conventional or mono-layer coated abrasive (Control C).

(83) FIG. 16 is a graph illustrating the total cut in grams of Example 6 of a coated abrasive article 10 of the present invention using a higher work pressure (4 kg instead of 2 kg). FIG. 16 shows the effect of glassing on the agglomerated abrasive of the present invention at 2 kg of work pressure.

(84) FIG. 17 is a graph illustrating the rate of cut in grams of Example 6 and Control C showing that the agglomerated abrasive 10 of the present invention exhibits a more consistent level of cut throughout the test sequence than the conventional or mono-layer coated abrasive (Control C).

Examples 1-8

(85) Examples 1 to 8 of abrasive articles of the present invention were manufactured in accordance with the Specific Procedure for Making Coated Abrasives described above. These examples were tested in accordance with the Procedure for Testing Coated Abrasives (Belts) with the test results set forth in Table 2.

(86) TABLE-US-00003 TABLE 2 PREMAKE COAT TARGET CORES MAKE COAT ABRASIVE PARTICLES SIZE COAT DESIG- BACKING Wt Wt Wt Wt Wt NATION Type Comp (g/m.sup.2) Type (g/m.sup.2) Comp (g/m.sup.2) Type (g/m.sup.2) Comp (g/m.sup.2) Example 1 Polycotton 92% RF 140 SAA 0.2 mm 100 92% RF 70 Grade 240 BSAO 170 66% RF 80 2 1 Cloth 01% IO 01% IO 02% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 28% CRY 03% H.sub.2O Example 2 Polycotton 92% RF 140 SAA 0.2 mm 100 92% RF 70 Grade 240 BAO 170 66% RF 80 2 1 Cloth 01% IO 01% IO 02% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 28% CRY 03% H.sub.2O Example 3 Polycotton 92% RF 270 SAA 0.9 mm 178 92% RF 150 N/A N/A 66% RF 137 2 1 Cloth 01% IO 01% IO 02% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 28% CRY 03% H.sub.2O Example 4 Polycotton 92% RF 270 SAA 0.9 mm 178 92% RF 150 Grade 120 CAO 550 66% RF 137 2 1 Cloth 01% IO 01% IO 02% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 28% CRY 03% H.sub.2O Example 5 Polycotton 92% RF 270 SAA 0.9 mm 178 92% RF 150 Grade 120 BAO 550 66% RF 137 2 1 Cloth 01% IO 01% IO 02% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 28% CRY 03% H.sub.2O Example 6 Polyester 55% RF 400 SAA 1.8 mm 510 55% RF 400 Grade 050 RBAO 850 55% RF 300 4 1 Cloth 37% CaCO.sub.3 37% CaCO.sub.3 37% CaCO.sub.3 01% IO 01% IO 01% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 06% H.sub.2O Example 7 Polyester 55% RF 400 SAA 1.8 mm 510 55% RF 400 Grade 050 AZA 850 55% RF 300 4 1 Cloth 37% CaCO.sub.3 37% CaCO.sub.3 37% CaCO.sub.3 01% IO 01% IO 01% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 06% H.sub.2O Example 8 Polyester 55% RF 400 SAA 1.8 mm 510 55% RF 400 Grade 050 BAO 850 55% RF 300 4 1 Cloth 37% CaCO.sub.3 37% CaCO.sub.3 37% CaCO.sub.3 01% IO 01% IO 01% IO 01% AL 01% AL 01% AL 06% H.sub.2O 06% H.sub.2O 06% H.sub.2O

Comparison of Examples 1 to 8 with Controls A to C

(87) The abrasive articles of the comparative examples (Controls A to C) are conventional, coated abrasive belts commercially available from Fabrica Nacional de Lija S. A de C. V (Fandeli) under the designation R-88 in grade P240, P120 and 050, respectively. The coated abrasives prepared in Examples 1 through 8 were tested according to the procedure for testing coated abrasive in belt form outlined above.

(88) Table 3 below displays the results of durability testing of Control A (R-88 P240) and Examples 1 and 2 and shows the sum of the number of periods achieved during the tests. Durability can also be measured by the total amount of metal removed.

(89) TABLE-US-00004 TABLE 3 DURABILITY Abrasive Abrading % of Article Periods Control Control A 34 100 Example 1 90 265 Example 2 18 53

(90) An abrasive article of the present invention with target cores having agglomerates prepared in situ (Example 1) was more than twice as durable as a conventional abrasive article as shown in Table 3 and FIGS. 8 and 9. The abrasive article with target cores having agglomerates prepared in situ was able to abrade the work piece during many more periods than the conventional abrasive article. Example 2 was less durable than Control A, because Example 2 exhibited a premature glassing at these conditions due to the toughness of the abrasive employed in producing the agglomeration.

(91) Table 4 displays the total cut and surface roughness values produced with Control Sample A and Examples 1 and 2.

(92) TABLE-US-00005 TABLE 4 Abrasive Initial Total % of Initial Ra Final Ra Article Cut (g) Cut (g) Control (m) (m) Control A 28.7 1182.1 100 0.65 0.31 Example 1 18.2 894 76 0.72 0.33 Example 2 12.9 1473.2 125 0.72 0.36

(93) Abrasive products made by the present invention improve the consistency of the cut and finish performance when compared to conventional abrasive articles. Control A provides a high level of initial cut, but decreases in cut as the product is used. See FIG. 9. In contrast, Example 1 exhibits a more consistent level of cut throughout the test sequence, while Example 2 again clearly shows premature glassing. Both examples exhibit the same type of finish as the conventional abrasive (Control A). Thus, the agglomeration of the present invention does not affect the quality of the finished product as shown in FIG. 10.

(94) Durability of Control B (R-88 P120) and Examples 3 to 5 are displayed in Table 5 which shows the sum of the number of periods achieved during the test. Durability can also be measured by the total amount of metal removed.

(95) TABLE-US-00006 TABLE 5 DURABILITY Abrasive Abrading % of Article Periods Control Control B 13 100 Example 3 35 269 Example 4 77 592 Example 5 190 1462 Hollow Body 34 262 (U.S. Pat. No. 3,928,949)

(96) Abrasive articles of the present invention with target cores and agglomerates prepared in situ (Examples 3, 4 and 5) were more than twice as durable as a conventional abrasive article as shown in Table 5 and FIGS. 11 and 12. Example 3 confirms the abrading capacity of the target cores. Examples 3, 4 and 5 were able to abrade the work piece for many more periods than the conventional abrasive article (Control B). Examples 4 and 5 displayed more than 5 times the abrading capacity of the control. Comparison with another agglomerate grain (the hollow body of U.S. Pat. No. 3,928,949) shows that the examples of the present invention were at least twice as durable as those prepared using the technology of the prior art '949 patent.

(97) Table 6 displays the total cut and surface roughness values produced from Control B and Examples 3, 4 and 5.

(98) TABLE-US-00007 TABLE 6 Abrasive Initial Total % of Initial Ra Final Ra Article Cut (g) Cut (g) Control (m) (m) Control B 19.6 100.9 100.00 1.53 1.61 Example 3 4.5 73.6 72.94 4.06 1.28 Example 4 14.5 224.5 222.50 2.23 0.96 Example 5 16.1 630.6 624.98 2.27 1.5 Hollow Body 6 133 131.81 1.37 1.06 (U.S. Pat. No. 3,928,949)

(99) The abrasive products of the present invention improve the consistency of the cut and finish performance, when compared with conventional abrasive articles such as Control B and those prepared using the hollow body technology of the '949 patent.

(100) Control B produces a high level of initial cut, but decreases in cut as the product is used. See FIG. 12. In contrast, Examples 4 and 5 exhibit a more consistent level of cut throughout the test sequence. Example 4 was less durable than Example 5, because at the test conditions the ceramic grain is fouled due to glassing, so this kind of particle needs more work pressure to show a better performance. Comparison with another agglomerate grain (the hollow body of U.S. Pat. No. 3,928,949) shows that the examples of the present invention were more than twice as durable as those prepared using the technology of the '949 patent. All of the examples produce similar finishes when compared to the conventional abrasive of Control B, demonstrating that the in situ agglomeration of the present invention does not affect the quality of the final finish as shown in FIG. 13.

(101) The results of durability testing of Control C (R-88 050) and Examples 6, 7 and 8 are displayed in Table 7 which shows the sum of the number of periods achieved during the tests. Durability can also be measured by the total amount of metal removed.

(102) TABLE-US-00008 TABLE 7 DURABILITY Abrasive Abrading % of Article Periods Control Control C 145 100 Example 6 192 132 Example 7 281 194 Example 8 320 221

(103) An abrasive article of the present invention with target cores and agglomerates formed in situ (Examples 6, 7 and 8) were more than twice as durable as a conventional abrasive article as shown in Table 7 and FIGS. 14 and 15. Examples 6, 7 and 8 were able to abrade the work piece for many more periods than a conventional abrasive article (Control C).

(104) Table 8 displays the total cut and surface roughness values obtained from Control C and Examples 6, 7 and 8.

(105) TABLE-US-00009 TABLE 8 Abrasive Initial Total % of Article Cut (g) Cut (g) Control Control C 28.7 1182.1 100 Example 6 18.2 894 76 Example 7 12.9 1473.2 125 Example 8 17.2 1901.5 161

(106) The results demonstrate that abrasive products of the present invention improve the consistency of the cut and finish performance, when compared to conventional abrasive articles. Only Example 6 was less durable than Control C, because the abrasive particle exhibited glassing.

(107) Control C shows a high level of initial cut, but decreases in cut as the product is used (See FIG. 15.), while Examples 6, 7 and 8 exhibit a more consistent level of cut throughout the test sequence. Example 6 was less durable than the other examples and Control C, because at the test conditions the brown grain is fouled by glassing. Accordingly, this kind of particle needs more work pressure to exhibit a better performance.

(108) To demonstrate that the brown grain needs more work pressure, the procedure for testing coated abrasives in belt form was modified to increase the work pressure from 2 kg to 4 kg. Table 9 displays the durability results of Control C and Example 6 by the number of abrading periods achieved during the tests. Durability can also be measured by the total amount of metal removed.

(109) TABLE-US-00010 TABLE 9 DURABILITY Abrasive Abrading % of Article Periods Control Control C 11 100 Example 6 62 564

(110) Example 6 shows significantly improved performance with the higher work pressure resulting in its durability being at least 5 times the durability of Control C. See also FIG. 16. Table 10 displays the total cut values obtained by Control C and Example 6 with the 4 kg work pressure.

(111) TABLE-US-00011 TABLE 10 Abrasive Initial Total % of Article Cut (g) Cut (g) Control Control C 56.1 110.6 100 Example 6 27.4 317 286

(112) As shown in Table 10, Example 6 was more than twice as durable as and more efficient than a conventional abrasive article (Control C). While Control C demonstrates a high level of initial cut, the rate of cut decreases as the product is used (See FIG. 17.), while Example 6 exhibits a more consistent level of cut throughout the test sequence.

(113) The foregoing description has been directed in primary part to a particular preferred embodiment in accord with the requirements of the Patent Statutes and for purposes of explanation and illustration. It will be apparent, however, to those skilled in the art that many modifications and changes in the specifically described abrasive articles and methods of making the same with in situ formation of the agglomerates may be made without departing from the true scope and spirit of the invention. For example, while the invention has been described using gravity-dispersed target cores, in an alternative method electrostatic methods may be used to better align the target cores. Because many such variations can be made, the invention is not restricted to the preferred embodiments described and illustrated but covers all modifications which may fall within the scope of the following claims.