RADIATION CURABLE SUPERSIZES

Abstract: Supersize formulations in which the binder medium is hydrophobic and radiation-polymerizable permits the use of larger quantities of supersize additives including additives that are water-soluble.

Description: RADIATION CURABLE SUPERSIZES Background to the Invention The present invention relates to the production of coated abrasives and particularly to the production of coated abrasives bearing a supersize coating. Supersize additives typically are chemicals that, under grinding conditions decompose to produce acid reacting materials such as halogens or halogen acids that react with a metal surface and make metal removal easier to accomplish. Typical additives are insoluble or very slightly soluble alkali metal salts of halo-acids and the most commonly encountered additives include potassium fluoroborate and cryolite. Other filler additives such as calcium carbonate or anti-loading or anti-static additives such as metallic stearates may also be incorporated into the supersize layer. The additive is dispersed in a binder medium that ensures that the additive is present at the coated abrasive surface in the vicinity of the abrasive grains where the heat generated during grinding is the greatest. Such coatings significantly enhance the grinding performance of coated abrasives by reducing the amount of heat generated, preventing glazing, extending the life of a coated abrasive material in addition to increasing the cut rate. They are particularly important in the grinding of difficult to grind materials such as stainless steel, titanium, nickel and aluminum. Clearly therefore the most preferred formulations contain the largest amount of the grinding aid that is feasible. Unfortunately when the binder medium is water-based as would be the case with a phenolic resin, epoxy or latex binder system for example, the amount of the grinding aid that can be incorporated is strictly limited because too much destabilizes the resin dispersion. In fact a typical supersize formulation incorporates only about 58% by weight of an additive such as potassium fluoroborate. In addition water soluble additives can not be used because they can cause rheology problems or because they precipitate out in the form of large crystals upon evaporation of the solvent. This is unfortunate since certain additives such as potassium fluoride, sodium fluoride, magnesium chloride and sodium nitrite would appear to be well suited to this application except for their high level of water solubility. It has now been discovered that a much wider range of additives can be used in larger amounts or in formulations with a much longer pot life if the binder medium is appropriately chosen. The formulation of the present invention provides such a composition which, in addition to permitting a wider range and concentration of additives, can be more readily cured such that the production process can be significantly shortened. Description of the Invention The present invention provides a supersize coating which comprises a supersize additive dispersed in a liquid, hydrophobic, radiation-curable binder medium. The invention also provides a coated abrasive incorporating such a supersize coating. Since the dispersion medium is the binder itself and since it is non-aqueous, the matter of destabilization of the formulation does not arise and supersize additives such as potassium fluoride that are not normally usable because of solubility concerns, can be employed. The liquid, hydrophobic radaition-curable binder is preferably one that is curable by UV radiation though other formulations with other radiation curable mechanisms such as electron beam radiation are also acceptable. The binders that are particularly preferred include acrylated epoxy oligomers, such as the resins sold by UCB Radcure Inc under the trade names Ebecryl 3200, 3201, 3500, 3600, 3700 and 3800; acrylated urethane oligomers such as the resins sold by UCB Radcure Inc. under the trade names Ebecryl 230, 244, 8301, 8402 and 8803; polyester/acrylate oligomers such as the resins sold by UCB Radcure Inc under the trade names Ebecryl 40, 80, 81, 140, 150, 657, 810, 830, 870, 1657 and 2047; and m addition mixtures of such oligomers with mono- acrylated monomers, diacrylated monomers and poly- acrylated monomers which are typically added to adjust the physical properties, viscosity and/or molecular weight of the final product. Typical such additives are 1, 6-hexanedιol diacrylate (HDODA) ; tπmethylolpropane ethoxy tπacrylate (TMPEOTA) ; tπmethylol propane tπacrylate (TMPTA) ; and octyl decyl acrylate (ODA) . Of these the most preferred include acrylated epoxy resms with a viscosity at ambient temperatures that makes it suitable for use as the carrier for a grinding aid. This generally implies a viscosity of at least 500 cps, and preferably from about 1500 to about 25,000 cps. As indicated above the viscosity can be adjusted by addition of acylated monomers. Ebecryl 3200 is an acrylated epoxy oligomer resin with a viscosity of from 1500 to 3000 cps. that has proved particularly effective in the formulations of the present invention. The supersize additives include those typically used With conventional binder media such as KBF 4 , cryolite, halohydrocarbons, iron sulfide and sodium fluorosilicate . However also included are those that have hitherto been considered unacceptable because of water solubility such as alkali metal halides and nitrites, magnesium halides, calcium hydrogen phosphate, as well as mixtures of two or more of any of the above additives. The amount of the supersize additive that might be incorporated into the supersize formulation can be from about 15 to about 65, and particularly from about 35 to about 50% by weight based on the total weight of the additive and the binder. The formulation can comprise other additives such as photoinitiators, (particularly where the binder is to be cured by UV radiation), free-radical generators, antistatic or anti-loading compounds, lubricants, colorants, fillers and the like without compromising the effectiveness or usefulness of the formulations of the invention. Description of Preferred Embodiments The invention is now described with reference to the following illustrative examples which are not intended to imply any necessary limitation on the essential scope of the present invention. Example 1 This Example compares the performance of various abrasive discs according to the invention with prior art discs using the Schieffer test. In this test a disc about 11.4cm in diameter is attached to a backup support pad using a ring-clamping device in a horizontal position. A cylindrical workpiece made of 304 stainless steel with an outside diameter of 2.54cm, wall thickness of 3.05mm and a length of 5.08cm is then moved into contact with the pad at a predetermined constant force and is rotated for a predetermined number of revolutions . In the present case the force chosen was 7 lbs (32 newtons) and the number of revolutions was set at 500. After this had been completed, the difference in weights of both the workpiece and the disc were measured and recorded. The test was carried out on discs prepared in identical ways except for the supersize coating. In the disc identified as C-l, no supersize application was used. In disc C-2 a conventional supersize coat comprising the maximum weight of potassium fluoroborate that could be used without destabilizing the formulation. This formulation contained 58% by weight but had a pot life of only about 6 hours. The additive was dispersed in a standard water-based phenolic resin was used. In discs I-l through 1-11 the same hydrophobic UV-curable Ebecryl 3200 acrylated epoxy oligonmer resin was used as the binder resin. In each case the amount of the indicated supersize additive was 40% by weight, based on the total weight of the binder plus additive. The formulation also contained 1.21 wt% of a photoinitiator, (Ciba 1173) . Three iterations were averaged for each disc and the results are reported in Table 1 below. TABLE 1 SAMPLE COMPOSITION/ TOTAL GM % CONTROL CUT (WT. PROPS CONTROL NONE 0.43 100% INV-1 KBF 4 (100%) 0.56 130% INV-2 FeS 2 /TMDS/MKCS 0.54 (45/5/50) 126% FeS 2 /MKCS/Zn INV-3 0 .84 (40/40/20) 195% INV-4 MoS 2 0 .67 156% INV-5 FeS 2 /CaHP0 4 /KCl 0 .72 167% (50/25/25) INV-6 FeS 2 /Mn0 2 /KCl 0 .62 144% (50/25/25) INV-7 TDMS/MKCS 0. .56 130% (50/50) INV-8 Na 2 SF 6 /MKCS 0. .55 128% (50/50) INV-9 FeS 2 /Na 3 AlF 6 0. .77 180% (50/50) INV-10 KBF 4 /KF 1. 24 288 ! INV-11 FeS 2 /K 3 P0 4 /KCl 0. 70 163% (50/25/25) In the above Table the abbreviations used (other than the conventional chemical formulae) have the following meanings: TMDS .... tetramethylthiuram disulfide (available from Aldrich Chemical Co. ) MKC-S....is a complex of potassium and manganese chlorides, (available from BBU Chemie GmbH, Austria) As will be seen from the above Table, the supersize formulations of the invention performed extremely well in increasing the amount of metal removed. Grinding aids such as potassium chloride and potassium phosphate are very soluble in water and cannot be used in an aqueous medium. However as will be observed, they are components of the most effective grinding aid formulations.

Claims: Claims l.A supersize coating formulation which consists essentially of a supersize additive dispersed in a liquid, hydrophobic, radiation-curable binder and optionally further additives selected from the group consisting of photoinitiators, free-radical generators, anti-static additives, anti-loadmg additives, lubricants and fillers . 2. A coating formulation according to Claim 1 wherein the binder consists essentially of a UV-curable liquid formulation. 3. A coating formulation according to Claim 1 wherein the binder comprises at least one UV-curable oligomer selected from the group consisting of acrylated epoxy oligomers, acrylated urethane oligomers and acrylated polyester oligomers and mixtures thereof. 4. A coating formulation according to Claim 1 wherein the supersize additive is present in an amount that is from about 25 to about 65% by weight, based on the total weight of the binder and the additive. 5. A coating formulation according to Claim 1 wherein the supersize additive is selected from the group consisting of acrylated epoxy oligomers and mixtures of such oligomers with acrylated monomers having a viscosity of from about 1000 to 3000 cps at 25°C. 6. A supersize coating formulation which comprises a supersize additive selected from the group consisting of potassium fluoroborate, sodium fluorosilicate, potassium fluoride, iron sulfide, potassium phosphate, molybdenum disulfide and calcium hydrogen phosphate dispersed in a liquid, hydrophobic, radiation-curable binder medium selected from the group consisting of acrylated epoxy oligomers and mixtures thereof with acrylated monmers . 7. A coated abrasive incorporating a supersize coating formulation according to Claim 1. 8. A coated abrasive incorporating a supersize coating formulation according to Claim 6.

Inventors: GAETA ANTHONY C, SWEI GWO SHIN, GAETA, ANTHONY, C., SWEI, GWO, SHIN
Applicants: NORTON CO, NORTON COMPANY
Application year: 1997
Main classification: C09K3
IPC codes: B24D3, B24D11, C09K3