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United States Patent  [ii] Patent Number: 4,751,138
Tumey et al.  Date of Patent: Jun. 14,1988
 COATED ABRASIVE HAVING RADIATION CURABLE BINDER
 Inventors: Michael L. Tumey, St. Paul; Donna W. Bange, Eagan; Aida F. Robbins, Maplewood, all of Minn.
 Assignee: Minnesota Mining and
Manufacturing Company, St. Paul,
 Appl. No.: 895,315
 Filed: Aug. 11, 1986
 Int. Q." B32B 5/16; B05D 3/06
 U.S. CI 428/323; 428/328;
428/413; 427/44; 427/54.1; 51/298; 51/295
 Field of Search 428/323, 328, 413;
427/44, 54.1; 51/298
 References Cited
U.S. PATENT DOCUMENTS
4,047,903 9/1977 Hesse et al 51/298
4,130,690 12/1978 Lien et al 428/413
4,156,035 5/1979 Tsao et al 427/44
4,250,053 2/1981 Smith 252/426
4,428,807 1/1984 Lee et al 204/159.14
4,457,766 7/1984 Caul 51/298
4,588,419 5/1986 Caul et al 51/295
4,617,194 10/1986 Scott et al 427/44
Coated abrasive product and a process for producing same. The coated abrasive product comprises a backing, a make coat, and a size coat, and may contain an optional saturant coat, an optional presize coat, an optional backsize coat, or any combination of said optional coats, in which at least one coat is formed from a composition curable by electromagnetic radiation comprising:
(A) a curable portion containing both ethylenically unsaturated groups and 1,2-epoxide groups, which groups can be in the same compound or in different compounds, and
(B) a photoinitiator portion.
The photoinitiator portion activates both free-radical and cationic curing mechanisms.
17 Claims, 1 Drawing Sheet
COATED ABRASIVE HAVING RADIATION
BACKGROUND OF THE INVENTION 5
This invention relates to coated abrasive products, and, in particular, to coated abrasive products having a radiation curable binder.
Coated abrasives generally comprise a backing and abrasive granules supported thereby and adhered 10 thereto. The backing may be paper, cloth, polymeric, film, vulcanized fiber, etc. or a combination of two or more of these materials. The abrasive granules may be formed of flint, garnet, aluminum oxide, alumina-zirconia, diamond, silicon carbide, etc. Binders for the 15 purpose of adhering the granules to the backing include phenolic resins, hide glue, varnish, epoxy resins, ureaformaldehyde resins, and polyurethane resins.
The coated abrasive may employ a "make" coat of resinous binder material which is utilized to secure the 20 ends of the abrasive granules onto the backing as the granules are oriented and a "size" coat of resinous binder material over the make coat which provides for firm adherent bonding of the abrasive granules. The size coat resin may be of the same material as the make coat 25 resin or it may be of a different resinous material.
In the manufacture of conventional coated abrasives, the make coat resinous binder is first applied to the backing, the abrasive granules are then applied, the make coat is partially cured, the size coat resinous 30 binder is then applied, and finally, the construction is fully cured. Generally, thermally curable binders provide coated abrasives having excellent properties, e.g. heat resistance. Thermally curable binders include phenolic resins, epoxy resins, and alkyd resins. With back- 35 ings formed of polyester or cellulose, however, curing temperatures are limited to a maximum of about 130° C. At this temperature, cure times are sufficiently long to necessitate the use of festoon curing areas. Festoon curing areas are disadvantageous in that they result in 40 formation of defects at the suspension rods, inconsistent cure due to temperature variations in the large festoon ovens, sagging of the binder, and shifting of abrasive granules. Furthermore, festoon curing areas require large amounts of space and large amounts of energy. 45 Accordingly, it would be desirable to develop a resin that does not require a great deal of heat to effect cure. Radiation curable resins are known in the art. Offenlegungsschrift No. 1,956,810 discloses the use of radiation for the curing of unsaturated polyester resins, acid 50 hardenable urea resins, and other synthetic resins, especially in mixtures with styrene as binder for abrasives. U.S. Pat. No. 4,047,903 discloses a radiation curable binder comprising a resin prepared by at least partial reaction of (a) epoxy resins having at least 2 epoxy 55 groups, e.g. from diphenylolpropane and epichlorohydrin, with (b) unsaturated monocarboxylic acids, and (c) optionally polycarboxylic acid anhydride. U.S. Pat. No. 4,457,766 discloses the use of acrylated epoxy resins, which are designated therein "epoxy acrylates", 60 such as the diacrylate esters of bisphenol A epoxy resins, as a radiation curable binder for coated abrasives.
The coated abrasives described in the foregoing patents exhibit the shortcoming of poor adhesion of abrasive granules to the backing because the binder does not 65 cure in areas where the granules screen out radiation, unless high dosages of ionizing radiation are employed. High dosages of radiation can adversely affect the back
ing. The poor adhesion of the abrasive granules results in a large loss of abrasive granules, i.e. "shelling", from the backing upon flexing and grinding. Attempts to improve the adhesion of the abrasive granules by curing by ionizing radiation, e.g., electron beam, through the backside of the backing often leads to degradation of the backing.
SUMMARY OF THE INVENTION
This invention involves a coated abrasive product and a process for producing this abrasive product. The coated abrasive product comprises a backing, a make coat, a layer of abrasive grains, a size coat, and, optionally, a saturant coat, or a presize coat, or a backsize coat, or any combination of these optional coats, wherein at least one coat is formed from a composition curable by electromagnetic radiation. Surprisingly, this radiation curable composition is curable by electromagnetic radiation even in areas where abrasive granules screen out radiation. The use of the radiation curable composition of this invention overcomes the problem of poor adhesion of abrasive granules resulting from incomplete cure of the binder by combining a cationic curing mechanism with a free-radical curing mechanism. Another significant advantage of this invention is that the radiation curable binder can be cured relatively quickly to firmly anchor the deposited abrasive granules. When a heat curable phenolic resin is used as the binder for the make coat, its relatively long curing time provides ample opportunity for the abrasive granules to shift from their orientation at deposition.
The radiation curable composition suitable for use in this invention comprises a resin portion comprising ethylenically-unsaturated groups and 1,2-epoxide groups, and a photoinitiator portion, in an amount sufficient to cure the radiation curable composition, comprising at least one polymerization photoinitiator selected from the group consisting of:
(1) salts having an onium cation and a halogen-containing complex anion of a metal or metalloid, e.g., diphenyliodonium hexafluoroantimonate, and
(2) a mixture of (a) at least one salt having an organometallic complex cation and a halogen-containing complex anion of a metal or metalloid, e.g., (i75-cyclopentadienyl)tricarbonyliron(l +) hexafluoroantimonate, and (b) at least one free-radical polymerization initiator.
It is generally preferred to use a free-radical polymerization initiator in conjunction with the photoinitiator salts of the aforementioned group (1). Optionally, the photoinitiator can also contain one or more thermally activated cationic or free-radical initiators. In addition, the photoinitiator can optionally contain photosensitizers to sensitize the composition to visible light.
Preferably, the curable portion is selected from the group consisting of:
(A) at least one bireactive compound containing at least one ethylenically-unsaturated group and at least one 1,2-epoxide group,
(B) at least one ethylenically-unsaturated compound and at least one compound containing at least one 1,2-epoxide group,
(C) at least one bireactive compound containing at least one ethylenically-unsaturated group and at least one 1,2-epoxide group, and at least one ethylenicallyunsaturated compound,
(D) at least one bireactive compound containing at least one ethylenically-unsaturated group and at least one
1,2-epoxide group, and at least one compound containing at least one 1,2-epoxide group, and (E) at least one bireactive compound containing at least one ethylenically-unsaturated group and at least one 1,2-epoxide group, at least one ethylenically- 5 unsaturated compound, and at least one compound containing at least one 1,2-epoxide group. It is within the scope of the present invention to utilize various combinations of radiation curable resin systems with conventional heat curable resin systems. For in- 10 stance, the backsize coat of a cloth substrate could be formed using radiation curable resin, and then the make and size coats formed utilizing conventional heat curable resin systems. In another case, the make coat may be formed by a radiation curable resin, while the size 15 coat may be of a conventional heat curable resin. Thus, the radiation curing resin systems of the present invention are compatible with, and may be utilized in various combinations with conventional heat curable resins.
BRIEF DESCRIPTION OF THE DRAWINGS 20
FIG. 1 illustrates in cross-section a coated abrasive on a cloth backing material.
FIG. 2 illustrates in cross-section a coated abrasive on a paper backing material. 25
Coated abrasives that may be produced by the resin systems of the invention are illustrated in FIGS. 1 and 2. As illustrated in FIG. 1, the coated abrasive generally 30 indicated as 10 is cloth backed. Cloth 12 has been treated with an optional backsize coat 14 and an optional presize coat 16. Overlaying the presize coat is a make coat 18 in which are embedded abrasive granules 20 such as silicon carbide or aluminum oxide. A size 35 coat 22 has been placed over the make coat 18 and the abrasive granules 20. There is no clear line of demarcation between the backsize coat and the presize coat which meet in the interior of the cloth backing which is saturated as much as possible with the resins of these 40 coats.
In FIG. 2 there is illustrated a coated abrasive generally indicated as 30 which is formed on a paper backing 32. Paper backing is treated with a backsize coat 34 and presize coat 36. The presize coat is overcoated with a 45 make coat 38 in which are embedded abrasive granules 40. The abrasive granules 40 and make coat 38 are overcoated with a size coat 42 which aids in holding the abrasive granules 40 onto the backing during utilization and further may contain cutting aids. 50
As used herein the term, "electromagnetic radiation" means non-particulate radiation having a wavelength within the range of 200 to 700 nanometers. "Bireactive compounds" are those which contain at least one ethylenically-unsaturated group and at least one 1,2- 55 epoxide group.
Ethylenically-unsaturated compounds that can be used in the polymerizable mixture of this invention include monomelic or polymeric compounds that contain atoms of carbon, hydrogen, and oxygen, and op- 60 tionally, nitrogen and the halogens. Oxygen and nitrogen atoms are generally present in ether, ester, urethane, amide, and urea groups. The compounds preferably have a molecular weight of less than about 4000 and are preferably esters of aliphatic monohydroxy and 65 polyhydroxy group-containing compounds and unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, ma
leic acid, and the like. Representative examples of preferred ethylenically-unsaturated compounds include methyl methacrylate, ethyl methacrylate, styrene, divinylbenzene, vinyl toluene, ethylene glycol diacrylate and methacrylate, hexanediol diacrylate, triethylene glycol diacrylate and methacrylate, trimethylolpropane triacrylate, glycerol triacrylate, pentaerythritol triacrylate and methacrylate, pentaerythritol tetraacrylate and methacrylate, dipentaerythritol pentaacrylate, sorbitol triacrylate, sorbital hexaacrylate, bisphenol A diacrylate, and ethoxylated bisphenol A diacrylate. Other examples of ethylenically-unsaturated compounds include ethylene glycol diitaconate, 1,4-butanediol diitaconate, propylene glycol dicrotonate, dimethyl maleate, and the like. Other ethylenically-unsaturated compounds include monoallyl, polyallyl, and polymethallyl esters and amides of carboxylic acids, such as diallyl phthalate, diallyl adipate and, N,N-diallyladipamide. Still other nitrogen-containing compounds include tris(2-acryloyloxyethyl)isocyanurate, l,3,5-tri(2-methacryloxyethyl)-s-triazine, acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, Nvinylpyrrolidone, and N-vinylpiperidone. It is preferred that the ethylenically unsaturated compounds be acrylic compounds because of their ready availability and high speed of cure.
Polymeric ethylenically-unsaturated compounds that can be used include the reaction products of acrylic or methacrylic acid or an isocyanato-alkyl acrylate or methacrylate with a polymeric polyether or polyester polyol. Representative examples of polymeric polyols include the polyoxyalkylene polyols, i.e., the diols, triols, and tetrols, the polyester diols, triols, and tetrols formed by the reaction of organic dicarboxylic acids with polyhydric alcohols, and the polylactone diols, triols, and tetrols. Examples of polymeric polyols that are commerically available include polyoxyethylene diols, triols and tetrols, such as the Carbowax ® polyols available from Union Carbide, the polyoxytetramethylenediols, such as Polymeg (§) polyols available from Quaker Oats Company, the polyester polyols such as the Multron® poly(ethyleneadipate)polyols available from Mobay Chemical Company, the polycaprolactone polyols such as the PCP polyols available from Union Carbide, and the urethane acrylates such as "C-9504" available from ARCO Chemicals.
The 1,2-epoxide group-containing compounds that can be used in the polymerizable mixture of this invention have an oxirane ring, i.e.,