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ties, and obtain defect free coatings, solvent is commonly added to the uncured resins.
When polyester or cellulose backings or lofty fibrous mats of such fibers are used, curing temperature is 5 sometimes limited to about 130° C. At this temperature, the long cure time along with solvent removal necessitate the use of festoon curing areas. Disadvantages of festoon curing areas include the emission of volatile organic compounds (VOC) such as organic solvents, 10 unreacted resin precursors such as phenol and formaldehyde, and the like.
Of the many thermally curable resins, including phenolic resins, urea-aldehyde resins, urethane resins, melamine resins, epoxy resins, and alkyd resins, phenolic resins are used extensively to manufacture abrasive articles because of their thermal properties, availability, low cost, and ease of handling. Although phenolic resins are discussed herein, it should be appreciated by those skilled in the art that the principles discussed 20 herein are applicable to other thermally curable resins, such as those previously named. The monomers currently used in greatest volume to produce phenolic resins are phenol and formaldehyde. Other important phenolic starting materials are the alkyl-substituted 25 phenols, including cresols, xylenols, p-tert-butylphenol, p-phenylphenol, and nonylphenol. Diphenols, e.g., resorcinol (1,3-benzenediol) and bisphenol-A (bis-A or 2,2-bis(4-hydroxyphenyl) propane), are employed in smaller quantities for applications requiring
COATABLE THERMALLY CURABLE BINDER
PRESURSOR SOLUTIONS MODIFIED WITH A
REACTIVE DILUENT, ABRASIVE ARTICLES
INCORPORATING SAME, AND METHODS OF
MAKING SAID ABRASIVE ARTICLES
This application is a continuation-in-part of parent application Ser. No. 07/823,998, filed Jan. 22,1992, now abandoned and is related to application Ser. No. 07/823,861, filed concurrently with the parent of this application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to abrasive articles utilizing a binder which secures abrasive grains to a backing sheet, on fibers of a fibrous mat, or in a shaped mass, and to methods of making such articles utilizing a binder precursor solution including a reactive diluent. The reactive diluent reduces emissions of volatile organic compounds from the binder precursor solutions and, in some embodiments, renders the cured binder more flexible.
2. Discussion of the Art
Abrasive articles may be categorized as coated, bonded, and nonwoven abrasives. Coated abrasives generally comprise a flexible backing upon which an abrasive coating comprising abrasive grains and a binder is attached. The backing can be selected from
paper, cloth, film, vulcanized fiber, etc. or a combina- 30 special properties, tion of one or more of these materials, or treated ver- There are two basic types of phenolic resins: resole sions thereof. The abrasive grains can be formed of flint, and novolak phenolic resins. Molecular weight adgarnet, aluminum oxide, alumina zirconia, ceramic alu- vancement and curing of resole phenolic resins are minum oxide, diamond, silicon carbide, etc. Binders catalyzed by alkaline catalysts. The molar ratio of aldecommonly comprise cured versions of hide glue or 35 hyde to phenolic is greater than or equal to 1.0, typivarnish, or one or more resins such as phenolic, urea- cally between 1.0 and 3.0. In the production of adhesive formaldehyde, melamine-formaldehyde, urethane, ep- coatings for nonwoven and coated abrasives, one stanoxy, and acrylic resins. Phenolic resins include those of the phenol-aldehyde type.
dard starting phenolic resin composition is a 70% solids condensate of a 1.96:1.0 formaldehyde:phenol mixture
Nonwoven abrasive articles typically comprise a 40 with 2% potassium hydroxide catalyst added based on
fibrous mat of fibers which have on at least a portion of their surface an abrasive coating comprising abrasive grains and a binder. The fibers can be formed from various polymers, including polyamides, polyesters,
weight of phenol. The phenolic resin composition is typically 25-28% water and 3-5% propylene glycol ether, which are required to reduce viscosity of the resin. Before this resin is used as a component of a make
polypropylene, polyethylene, and various copolymers. 45 or size coating, i.e., to make it coatable, further viscosity
Naturally occurring fibers such as cotton, wool, bast fibers and various animal hairs may also be suitable.
Coated and nonwoven abrasives may employ a "make" coating of binder precursor solution, which
reduction is often achieved using VOC. A binder precursor solution containing a phenolic resin which is used to produce a make coating may contain up to 40% of a VOC such as isopropyl alcohol to reduce viscosity
includes one or more of the above-named resins, in 50 and make the phenolic resin compatible with resin mod
order to secure the abrasive grains to the backing when the resin is cured as well as to orient the abrasive grains on the backing or throughout the lofty fibrous mat. A "size" coating of resinous binder material can be applied
ifiers (flexibilizers), while a binder precursor solution which is used to produce a size coating might contain up to 20% of a VOC such as diethylene glycol ethyl ether. Unreacted phenol and formaldehyde in the final,
over the make coating and abrasive grains in order to 55 cured resin also contribute to VOC. firmly bond the abrasive grains to the backing or fibrous In order to reduce emissions of VOC, efforts have mat. The resin of the size coating can be the same as the been made to increase the water compatibility of phenoresin of the make coating or a different material. lie resins. Fisher, in a review article without references
In the manufacture of coated and nonwoven abra- titled "Water Compatible Phenolic Resins" in Proceedsives, the make coating and abrasive grains are usually 60 ings of the American Chemical Society, Division of Polyfirst applied to the backing or lofty fibrous mats, the meric Material: Science and Engineering; 65 pp. 275-276 make coating partially cured, then the size coating is applied, and finally the make and size coatings are fully cured.
Generally, binders which include thermally cured 65 resins provide abrasive articles having excellent properties, e.g., heat resistance. In order to render the resin precursors coatable, obtain the proper coating viscosi
(1991), describes currently known methods of making "water compatible" phenolic resins, their benefits, and their shortcomings.
Unfortunately, the water tolerance of phenolic resins suffers in many of the formulations designed to reduce VOC. "Water tolerance" refers to the measurement of the maximum weight percent of distilled water, based
on initial resin weight, which can be added to a stirred, uncured phenolic resin via titration to begin causing visual phase separation (as evidenced by a milky appearance) of the resin/water mixture into aqueous and organic phases. As mentioned by Hoy et al, below, it is 5 imperative that during the drying stage, after a particular substrate has been covered with a layer of coating, that a single phase be maintained until the water has evaporated away leaving the now insoluble organic polymer deposit. Another problem with many water '0 compatible phenolic resins is that gel time is increased. "Gel time", as used herein, refers to the length of time at a given temperature that a phenolic resin transforms from a liquid to a gelled state. It is an indication of the rate of cure of a phenolic resin under established condi- 15 tions.
Phenolic resins suitable for use in the manufacture of abrasive articles may optionally contain plasticizers, crosslinking aids, or other modifiers. Modifiers have been used to overcome deficiencies of phenolic resins in certain applications such as brittleness in the cured state and lack of water tolerance in the uncured state. Modifiers have previously been used to adjust the physical properties of the finished product, such as hardness in a 2J wet environment, but many have required additional VOC for viscosity reduction.
It is known that nitroalkanes and urea react with formaldehyde, but these compounds have not been used as reactive diluents in the production of abrasive articles 3Q to the inventors' knowledge. It is also known that poly(oxyalkylene) amines react with phenolic resins, and there have been attempts by assignee to commercialize nonwoven abrasive articles employing poly(oxyalkylene) amines having molecular weight of 400 and above. 35 These attempts were largely unsuccessful. The high molecular weight poly(oxyalkylene) amines typically require an organic solvent to render coatable the binder precursor solution in which they are mixed.
U.S Pat. No. 4,571,413 to Dolden et al. describes the 40 use of polyethers [poly(oxyalkylene) diamines] in the preparation of modified phenolic resins for use in fiberreinforced composite materials and phenolic foams. Improved impact strength and flexural properties are noted. 2-45 parts of polyether per 100 parts aqueous 45 phenolic resin are suggested. All resole resins were acid catalyzed. There is no mention of base-catalysis, applicability to abrasive compositions, or lowering of VOC.
U.S. Pat. No. 4,786,683 to Schloman, Jr. et al. describes modified guayule resins containing poly(oxyalk- 50 alene) amines and phenolic resins for use as rubber modifiers.
U.S. Pat. No. 4,163,030 to Banucci et al. describes blends of polyetheramide-imide compounds and phenolic resins. Applicability to solventless dry powder coat- 55 ings and electrical insulation is noted.
U.S. Pat. No. 3,734,965 to Becker describes poly(oxyalkalene) compounds with aldehydes and substituted phenols as curatives for epoxy resins.
U.S. Pat. No. 4,226,971 to Waddill e al. describes an 60 epoxy curing agent derived from the phenol-aldehyde condensation product with the aminoalkylene derivative of a poly(oxyalkalene) polyamine.
U.S. Pat. No. 3,933,936 to Smith et al. describes aziridine-modified phenolic resins with good bond to wood, 65 metal, ceramics, and plastics, and which have fast cure. There is no mention of abrasive applications, poly(oxyalkalene) compounds, or reduction of VOC.
U.S. Pat. No. 4,650,838 to Das et al. describes aromatic phthalocyanine compounds as modifiers for phenolic resins. Improved thermal stability and applicability to friction materials are noted. Novolaks or resolated novolaks are the focus.
U.S. Pat. No. 5,041,481 to Sugimori et al. describes amino compound adhesion promoters for curable compositions such as paints, adhesives, or sealing compounds.
U.S. Pat. No. 4,102,866 to Speranza et al. describes poly(oxyalkalene) compounds as a curative for epoxynovolak resins.
U.S. Pat. No. 4,164,520 to Waddill et al. describes a process employing poly(oxyalkalene) compounds to accelerate the cure of epoxy resins.
British Patent No. 1,501,331 to Minnesota Mining and Manufacturing Company describes the use of poly(oxyalkalene) compounds with epoxy resins to manufacture friction materials.
U.S. Pat. No. 4,906,774 to Speranza et al. describes the preparation of urea-linked diamine product from poly(oxyalkalene) diamines and diisocyanates.
U.S. Pat. No. 4,154,724 to Schulze describes the preparation of ureido-functional poly(oxyalkalene) compounds.
U.S. Pat. No. 5,039,759 (Hoy, et al.) discloses the use of reactive urea, thiourea, and carbamate derivatives as cosolvents and reactive diluents for modifying water dispersible resins including polyester alkyd resins, carboxylated hydroxyl-containing epoxy fatty acid esters, carboxylated polyesters, carboxylated alkyd resins, carboxylated acrylic interpolymers free of amide groups, and carboxylated vinyl interpolymers. While utility in these systems is disclosed, there is no suggestion of the use of reactive urea, thiourea, or carbamate derivatives as reactive diluents in phenolic or urea-aldehyde resin systems.
U.S. Pat. No. 3,862,060 (Anderson) descibes stable emulsions containing high concentrations of thermosettable phenol-formaldehyde resole resins as the dispersed phase. The emulsions exhibit a water tolerance of less than 40 percent, and are stabilized with a proteinaceous compound. The resole resins are prepared with amine catalysts and are preferably modified with melamine. The emulsions optionally contain urea or dicyandiamide, which act to reduce the free formaldehyde.
U.S. Pat. No. 5,008,336 (Richey, Jr., et al.) describes tri-substituted amino oxides having at least two reactive hydroxyls useful as reactive diluents in polyol polymercontaining coating compositions.
U.S. Pat. No. 4,903,440 (Larson, et al.) describes a modified resole phenolic resin for use in abrasive articles containing a binder having at least 1.1 pendant alpha, beta-unsaturated carbonyl groups per molecule but does not suggest the storage life benefits of the compositions described herein, nor the compositions themselves.
U.S. Pat. No. 3,817,976 (Bakul, et al.) discloses the use of a butadiene-nitrile rubber as a modifier, but requires the use of additional organic solvents.
U.S. Pat. No. 4,505,712 (Floyd, et al.) and U.S. Pat. Nos. 4,345,063; 4,285,690; 4,332,586; and 4,284,758 (North) describe the use of cyclic urea derivatives for treating textile fabrics and paper in the absence of formaldehyde, but likewise requires organic solvent additions.
U.S. Pat. No. 4,927,431 (Buchanan, et al.) describes a modified phenolic resin binder for use in abrasive arti