METHOD OF MAKING CERAMIC
AGGREGATE PARTICLES
This application is a continuation-in-part of the U.S. patent applications having U.S. Ser. Nos. 09/688,444, 5 09/688,484, and 09/688,486 filed Oct. 16, 2000, the disclosures of which are incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to methods of making 10 ceramic aggregate particles. More particularly, the present invention relates to methods of making ceramic aggregate particles comprising ceramic binder, and a plurality of solid particulates. The solid particulates may be abrasive particulates.
BACKGROUND
A variety of methods of making ceramic aggregate particles, for use in a variety of industries, exist. For 20 example, catalyst pellets used in the hydrogenation of toluene and heptane can be made by combining a metal alloy, a high molecular weight polymer, and optionally a plasticizer (i.e., a transient solvent) into a mixture, forming the mixture into a shape, extracting the plasticizer (e.g., by solvent 25 extraction), calcining the shaped mixture to remove the polymer, and then sintering the shaped mixture to provide catalyst pellets. Additional information can be found in U.S. Pat. Nos. 4,895,994 (Cheng et al.) and 4,900,698 (Lundsager). In the orthopedic and dental industry, hard, 30 shaped, ceramic bodies can be made by melting ceramic binder precursor, cooling the melt, and then crushing the cooled melt to provide ceramic bodies to be used in synthetic bone and dental composition. Additional information can be found in U.S. Pat. No. 5,914,356 (Erbe). In the abrasives 35 industry, ceramic aggregate particles can be made by forming a composition that includes a ceramic binder precursor and a temporary organic binder precursor, placing the composition into a mold, heating the composition in the mold to provide shaped particles, and sintering the shaped particles 40 to bum off the organic binder and provide ceramic aggregate particles. Additional information can be found in U.S. Pat. No. 5,975,988 (Christianson). Other uses for ceramic aggregate particles include, for example, roofing granules, filtration products, hard coatings, shot blast media, tumbling 45 media, brake linings, anti-slip and wear resistant coatings, retro-reflective sheeting and laminate composite structures.
While these conventional techniques are useful, there is always a need for other useful techniques which are less costly, require less labor, require less process space, or 50 require fewer steps than conventional techniques, or, that provide ceramic aggregate particles having similar or improved properties over those made by conventional techniques. For example, techniques for forming ceramic aggregate particles which do not require a molding step may 55 provide a less expensive process. Additionally, techniques which do not require the use of solvents (e.g., toluene or heptane) may be desirable.
A need also exists for a method to produce ceramic aggregate particles which have relatively consistent shapes 60 and sizes in order to provide greater consistency of performance to articles made with such ceramic aggregate particles. Regarding particularly abrasive articles, for example, there continues to be a need for abrasive particles which can provide abrasive surfaces with sustained consistent cut rates 65 for, preferably, extended life times, with consistent work piece finish.
SUMMARY OF THE INVENTION
The present invention provides methods of making ceramic aggregate particles. One method according to the present invention comprises:
forming a plurality of ceramic aggregate precursor particles from a composition comprising curable binder precursor material, and ceramic binder precursor material, and a plurality of solid particulates, by forcing the composition through a perforated substrate;
at least partially curing the ceramic aggregate precursor particles;
separating the aggregate precursor particles from the perforated substrate; and
heating the ceramic aggregate precursor particles to provide ceramic aggregate particles, wherein the solid particulates are bonded together by the ceramic binder
In one aspect, the present invention may further comprise the step of combining at least a portion of the ceramic aggregate particles with abrasive article binder material and abrasive material to provide an abrasive article. Alternatively, at least a portion of the ceramic aggregate particles comprise abrasive particles.
Typically, the composition is essentially free of solvent. In one embodiment of methods according to the present invention, the mixture of components may further comprise a plurality of solid particulates. The plurality of solid particulates typically have an average particle size in the range from about 0.5 micrometers to about 1500 micrometers. Typically, the mixture of components further comprises photoinitiator. In one embodiment, the at least partially curing step may comprise thermal curing, radiation curing, or combinations thereof. During the heating step, heating is typically conducted at a temperature in the range from about 500° C. to about 1500° C.
As used herein, the expression "curable binder precursor material" refers to any material that is deformable or can be made to be deformed by heat or pressure or both and can be at least partially cured to provide material, such as, for example, ceramic aggregate precursor particles, that are handleable and collectable. As used herein with respect to curable binder precursor material, the expression "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 expression "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. Ceramic aggregate precursor particles and ceramic aggregate particles that are handleable and collectable tend to remain intact if subjected to an applied force that tends to strain or deform a body. Ceramic aggregate precursor particles and ceramic aggregate particles that are not handleable and collectable tend not to remain intact if subjected to an applied force that tends to strain or deform a body.
As used herein, the expression "ceramic binder precursor material" refers to particulate additives which, when heated to a temperature sufficient to bum out organic materials present in the ceramic aggregate precursor particle, may subsequently bond together to form a rigid ceramic phase bonding the ceramic aggregate particle together and to provide a ceramic aggregate particle. Ceramic binder precursor material may include crystalline or non-crystalline
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ceramic material. Hereinafter, "ceramic aggregate precursor particle" means the ceramic binder precursor material has not yet bonded together sufficiently to provide a particle that is handleable and collectable. Hereinafter, "ceramic aggregate particle" means the ceramic binder precursor material 5 has sufficiently bonded together to provide a particle that is handleable and collectable. Typically, methods according to the present invention provide at least a portion of the ceramic aggregate particles having an aspect ratio greater than one. 10
As used herein, the word "ceramic" means inorganic, non-metallic material that may include a crystalline phase, a noncrystalline phase (e.g., glass), or a combination of both a crystalline phase and a non-crystalline phase (e.g., porcelain, glass-ceramic). 15
Hereinafter, "essentially free of solvents" means the composition used to make ceramic aggregate precursor particles contains less than 10% solvent.
Ceramic aggregate particles made by the present invention can be used in products such as, for example, abrasives, 20 roofing granules, filtration products, hard coatings, shot blast media, tumbling media, brake linings, anti-slip and wear resistant coatings, synthetic bone, dental compositions, retro-reflective sheeting and laminate composite structures.
In one embodiment, methods according to the present 25 invention involve combining at least a portion of the cured ceramic aggregate particles with abrasive article binder material and abrasive material to provide an abrasive article. Suitable abrasive articles include coated abrasive articles (including nonwoven abrasive articles) and bonded abrasive 30 articles.
The method of the present invention provides ceramic aggregate particles where a major portion of the particles have a substantially uniform cross-sectional shape. By "major portion" it is meant that at least 50 percent, prefer- 35 ably about 90 percent, of the particles have a substantially uniform cross-sectional shape. Such uniform particles provide articles into which they are incorporated with more consistent performance characteristics. For example, abrasive ceramic aggregate made according to the present inven- 40 tion have consistently high cut rates and consistent surface finish for longer life times than do abrasive aggregates prepared by conventional methods.
The method of forming the aggregates of the invention described above are generally less costly, and require fewer 45 steps, and less space and labor than conventional means of making ceramic aggregate particles, such as molding.
The ceramic aggregates produced by the methods of this invention are described in Applicant's U.S. Ser. No. 09/971, 899 (filed on the same date as this application and incorpo- 50 rated herein).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view in elevation of an exemplary ceramic aggregate particle made according to a 5J method of the present invention.
FIG. 2 is a printed, digitized image of an exemplary ceramic aggregate particle made according to a method of the present invention.
FIG. 3 is a schematic side view illustrating a device for 60 practicing a method of the present invention.
FIG. 4 is a perspective view of a portion of a device for practicing a method of the present invention, with a front portion of the device cut away to expose a portion of the interior of the device. 65
FIG. 5 is a perspective view of a portion of the screen used in the device shown in FIG. 4.
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FIG. 6 is a fragmentary cross-sectional schematic view of a coated abrasive article including abrasive ceramic aggregate particles according to the present invention.
FIG. 7 is a perspective view of a bonded abrasive article including abrasive ceramic aggregate particles according to the present invention.
FIG. 8 is an enlarged schematic view of a nonwoven abrasive article including abrasive ceramic aggregate particles according to the present invention.
DESCRIPTION
In one embodiment, a method according to the present invention utilizes a composition comprising a mixture of components comprising curable binder precursor material, ceramic binder precursor material, and a plurality of solid particulates to make ceramic aggregate precursor particles. Optionally an initiator and/or other modifying additives may be included in the mixture. In one embodiment at least a portion of the solid particulates are abrasive grits or particles.
Curable Binder Precursor
Curable binder precursor can be cured by radiation energy or thermal energy. Typically, radiation curable binder precursor material comprises at least one of epoxy resin, acrylated urethane resin, acrylated epoxy resin, ethylenically unsaturated resin, aminoplast resin having at least one pendant unsaturated carbonyl group, isocyanurate derivatives having at least one pendant acrylate group, isocyanate derivatives having at least one pendant acrylate group, or combinations thereof. Other useful radiation curable binder precursor material includes vinyl ethers.
Epoxies have an oxirane ring and are polymerized by the ring opening via a cationic mechanism. Useful epoxy resins include monomeric epoxy resins and polymeric epoxy resins. These resins can vary greatly in the nature of their backbones and substituent groups. For example, the backbone may be of any type normally associated with epoxy resins and substituent groups thereon can be any group free of an active hydrogen atom that is reactive with an oxirane ring at room temperature. Representative examples of substituent groups for epoxy resins include halogens, ester groups, ether groups, sulfonate groups, siloxane groups, nitro groups, and phosphate groups. Examples of some epoxy resins useful in this invention include 2,2-bis[4-(2,3epoxypropyloxy)phenyl]propane (diglycidyl ether of bisphenol A) and materials under the trade designation "EPON 828", "EPON 1004" and "EPON 1001F", commercially available from Shell Chemical Co., Houston, Tex., "DER-331", "DER-332" and "DER-334", commercially available from Dow Chemical Co., Freeport, Tex., Other suitable epoxy resins include glycidyl ethers of phenol formaldehyde novolac (e.g., "DEN-431" and "DEN-428", commercially available from Dow Chemical Co.). The epoxy resins used in the invention can polymerize via a cationic mechanism with the addition of appropriate photoinitiator(s). These resins are further described in U.S. Pat. Nos. 4,318,766 and 4,751,138, which are incorporated by reference.
Exemplary acrylated urethane resin includes a diacrylate ester of a hydroxy terminated isocyanate extended polyester or polyether. Examples of commercially available acrylated urethane resin include "UVITHANE 782" and "UVITHANE 783," both available from Morton Thiokol Chemical, Moss Point, Miss., and "CMD 6600", "CMD 8400", and "CMD 8805", all available from Radcure Specialties, Pampa, Tex.
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