Abrasive Suspension Systems and Methods of Making the Same

The invention relates to abrasives and more particularly to abrasive compositions comprised of particles in a liquid medium.

Abrasive compositions used for finishing processes, including polishing and lapping, generally have consisted of particles dispersed in a liquid. Diamonds have long been used as the abrasive particles in such compositions because of their hardness. Generally, the abrasive compositions have been in the form of slurries wherein the diamonds formed a discontinuous phase and, e.g., a hydrocarbon-based liquid, formed the continuous phase. For example, a common abrasive material such as that generally described above consists of diamonds, naptha, mineral oil, ethylene glycol, coolants or machine oil, and water.

The problem with the above-identified compositions is that the diamonds and/or abrasive particles tend to settle out of the liquid base and form cakes. This "caking" is often in the form of an agglomeration of particles which may scratch the pieces on which the abrasive material is later applied. Consequently, in order to avoid this problem, these abrasive materials must be constantly stirred and/or mixed when in use. In addition, another disadvantage of the above-identified compositions is the fact that these abrasive compositions generally utilize liquid bases containing hydrocarbons, which are by nature insoluble in water and may be hazardous materials and/or at least require special disposal procedures.

The present invention solves the above-identified problems by utilizing a water soluble liquid base as the continuous phase and the uniformly dispersed abrasive particles as the discontinuous phase. More importantly, the abrasive particles in the present invention do not fall out of suspension and thus, do not agglomerate. As a result, the present invention can be applied to equipment and/or other surfaces requiring polishing or lapping by spray, pump, or even gravity delivery systems with no mixing or stirring of any kind. Further, due to the durable suspension of the particles, consumers can purchase the product and store it for extended periods of time without having the abrasive particles cake at the bottom of the container and thus without the need to mix or stir the abrasive prior to use.

Moreover, since the present invention is water soluble, work pieces and any equipment used in finishing processes can be cleaned with soap and water and operators are subjected to fewer health hazards since the present invention, which has a MSDS rating of 1, contains no hydrocarbons or hazardous materials. Due to the fact that the present invention utilizes a water soluble liquid base and/or continuous phase, recovery of the abrasive particles after use of the abrasive composition is enhanced. The present invention also results in a more efficient abrasive composition which results in a savings of time and money.

The invention is directed to an abrasive composition comprising: from about 5% by weight to about 96% by weight water; from about 3% by weight to about 94% by weight of a polyhydric alcohol ether compound; from about 0.00075% by weight to about 0.25% by weight surfactant; from about 0.0015% by weight to about 1% by weight polymer; and from about 0.001% by weight to about 50% by weight abrasives.

The invention is also directed to an abrasive composition comprising: from about 50% by weight to about 79% by weight water; from about 20% by weight to about 50% by weight of a polyhydric alcohol ether compound; from about 0.0015% by weight to about 0.2% by weight surfactant; from about 0.005% by weight to about 0.2% by weight polymer; and from about 0.005% by weight to about 30% by weight abrasives.

The invention is further directed to a liquid base component for an abrasive composition comprising: from about 5% to about 96% by weight water; from about 3% to about 94% by weight of a polyhydric alcohol ether compound; and from about 0.0015% to about 1% by weight polymer.

Moreover, the invention is directed to a method of making an abrasive composition having an abrasive component and a liquid base component comprising: (a) preparation of the abrasive component by (i) mixing abrasives with a caustic solution to form a mixture; (ii) optionally, heating the mixture; (iii) adjusting the pH to about 5 to about 10; (iv) adding a polymeric acid salt to the mixture; (v) adding a surfactant in a sufficient amount to adjust the pH of the mixture to about 5 to about 10; (b) preparation of the liquid base component by mixing a polymer with a polyhydric alcohol ether compound solution; and (c) mixing the abrasive and liquid base components together to form the abrasive composition. As used herein, "abrasive composition" excludes dentrifices.

The invention is directed to abrasive suspension systems or compositions for finishing processes including polishing and lapping. The present invention utilizes particles or abrasives durably suspended in a liquid base comprised of water, an alcohol ether compound, and a polymer.

In the practice of the present invention, any known abrasives and/or particles may be utilized as long as the abrasives and/or abrasive particles remain durably suspended in the liquid base of the present invention. For example, diamond, boron nitride, boron carbide, aluminum oxide, and silicon carbide abrasives may be used in the practice of the present invention. It has been found that generally diamonds are the preferred abrasive for use in the practice of the present invention. The present invention may be used with, e.g., diamonds having a diameter of 0.001 to 80 microns and/or a U.S. Sieve Series 20 to 400. Likewise, boron nitride, boron carbide, aluminum oxide, and silicon carbide particles having a diameter of 0.001 to 80 microns or U.S. Sieve Series 20 to 400 can also be used in the practice of the present invention.

In the practice of the present invention, the abrasives are suspended in a liquid base or continuous phase. The liquid base is preferably comprised of water, an alcohol ether compound, and a polymer. Preferably, the water of the liquid base is deionized and has a resistivity of at least 6 megohms and most preferably has a resistivity of at least 18 megohms.

The alcohol ether compound of the liquid base is preferably a polyhydric alcohol ether compound and includes polyalkylene glycols such as ethylene glycol, propylene glycol, and di- and tri- propylene and ethylene glycols. Surprisingly, it has been found that the addition of an ether functionality to the polyhydric alcohol compounds, results in improved systems which utilize abrasive particles below about 1 micron in diameter. Specifically preferred compounds include, but are not limited to, ethylene glycol n-butyl ether, ethylene glycol methyl ether, ethylene glycol propyl ether, diethylene glycol n-butyl ether, diethylene glycol methyl ether, diethylene glycol propyl ether, triethylene glycol n-butyl ether, triethylene glycol methyl ether, triethylene glycol propyl ether, propylene glycol n-butyl ether, propylene glycol methyl ether, propylene glycol propyl ether, dipropylene glycol n-butyl ether, dipropylene glycol methyl ether, dipropylene glycol propyl ether, tripropylene glycol n-butyl ether, tripropylene glycol methyl ether, tripropylene glycol propyl ether and mixtures thereof.

The liquid base of the present invention also includes a polymer. Preferably, the polymer is an acrylic polymer selected from the group consisting of polymers or copolymers of acrylic acid, e.g., methacrylic acid, acrylic acid esters, methacrylic acid esters, or acrylonitrile. Preferably, the polymers useful in the practice of the present invention are crosslinked. It has been found that the acrylic polymer sold under the trade name "CARBOPOL EZ-1 RESIN" (Lot No. ZC054N4) manufactured and sold by the BFGoodrich Company's Specialty and Chemicals Division, is preferred when utilizing diamonds as the abrasive. The "CARBOPOL EZ-1 RESIN" is an acrylic polymer containing residual acrylic acid and powder/dust of polymer.

Generally, depending upon the application, the present invention comprises from about 0.001% to about 50% by weight abrasive particles, preferably diamonds, of the total abrasive composition. Preferably, the diamond particles comprise from about 0.01% to about 20% by weight of the abrasive composition of the present invention. The same is true when utilizing boron nitride, boron carbide, aluminum oxide or silicon carbide particles. Water comprises from about 5% to about 94% by weight of the abrasive composition of the present invention. Preferably, water comprises from about 40% to about 79% of the total abrasive material. The alcohol ether component of the present invention comprises from about 5% to about 94% by weight of the total abrasive composition and preferably comprises from about 20% to about 59% by weight when utilizing diamond particles. Generally, when utilizing "CARBOPOL EZ-1 RESIN," the abrasive material of the present invention comprises from about 0.0015% to about 1% by weight polymer of the total abrasive composition. Preferably, the invention comprises from about 0.005% to about 0.2% by weight polymer of the total abrasive composition.

An abrasive composition of the invention can be made by preparing an abrasive component like a diamond abrasive mixture containing diamonds ranging from about 0.001 microns to about 80 microns and then mixing it into the liquid base of the invention. To prepare the abrasive component, one may select any volume of diamond abrasive and mix it with a caustic, such as sodium hydroxide, at a ratio of about 1 part diamond abrasive to about 5 parts caustic. An equal volume of water is then added, and the entire mixture is optionally heated to boiling. After boiling for about 15 minutes, the mixture is removed from the heat and allowed to cool. The mixture is then decanted and rinsed repeatedly until approximately neutral pH is achieved. The resulting diamond mixture should not be dried. Once neutral pH is reached, deionized water, in an amount equal to about 5% of the total volume of the desired abrasive composition, is added to the diamond mixture. For example, for 1 liter of abrasive composition, 50 ml of deionized water may be added. In order to eliminate the agglomeration and flocculation of particles that may otherwise occur in the abrasive composition, a surfactant/dispersant in an amount equal to about 0.1% of the total weight of the desired abrasive composition to be produced is then added to the diamond mixture and mixed until thoroughly dispersed. In preparing the novel abrasive component of the present invention, a salt of a polymeric acid may be utilized, e.g., "Tamol 731N" (Lot No. 0044C36B) available from Rohm and Haas Company in Philadelphia, Pa., may be used. The "Tamol 731N" contains about 24-26% sodium salt of polymeric carboxylic acid, about 74-76% water, and less than 0.1% individual residual monomers. To complete preparation of the abrasive component, a surfactant in an amount equal to about 0.015% of the total amount of the desired abrasive composition, or in an amount necessary to bring the pH of the total abrasive component to 7, is added to the component. The preferred surfactant is an ethanolamine, like triethanolamine, but, monoethanolamine and diethanolamine may also be utilized. Upon reaching a pH of 7, the abrasive component is complete. Generally, ethanolamine is added in an amount from about 0.00075% to about 0.5% by weight of the total abrasive composition.

To prepare the liquid base component of the present invention, deionized water is mixed with an alcohol ether compound, like a polyhydric alcohol ether compound. Generally, water and the alcohol ether compound are mixed at a ratio to achieve the desired lubricating qualities for the desired application. Then the polymer, such as "CARBOPOL EZ-1 RESIN" described above, in an amount from about 0.01% to about 0.15% of the total weight of desired abrasive composition to be produced is sprinkled evenly across the top of the liquid base component prepared thus far. At this point, the liquid base component with the polymer should represent the weight of desired abrasive composition to be produced less the weight of the prepared abrasive component. Once the polymer is saturated and has formed a clear gel, the liquid base component should be mixed at 60 rpm until the liquid base component is a homogeneous mixture.

Once both the abrasive component and the liquid base component are properly prepared, the abrasive component is washed into the liquid base component utilizing a deionized water spray. Once the resulting mixture has thickened, it should be mixed at approximately 200 rpm for approximately 2 minutes until completely blended. The material formed by this method results in a novel composition having abrasives durably suspended in a liquid water soluble base which meets all objects of the invention.

The following are examples of specific compositions of the present invention for (1) ceramic and (2) polycrystalline diamond lapping. However, the percentages of components change depending upon a number of variable factors including but not limited to: (1) pressure set of machine; (2) feed rate; (3) rpm of table; (4) finish requirements; (5) stock removal; (6) time of cycle; and (7) type of material processed, etc.

A ceramic lapping composition of the present invention was made comprising 79.1% by weight water, 20% by weight polyhydric alcohol ether compound, 0.03% by weight diamond particles ranging from 20 to 28 microns in diameter, 0.03% by weight of a 50% solution of triethanolamine, and 0.03% by weight acrylic polymer.

A polycrystalline diamond lapping composition of the present invention was made comprising 29.82% by weight water, 50% by weight polyhydric alcohol ether compound, 20% by weight diamond (100-170 U.S. Sieve), 0.03% by weight of a 50% solution of triethanolamine, and 0.15% by weight acrylic polymer.

While the present invention has been described with reference to preferred embodiments, various modifications known to those skilled in the art, may be made without departing from the invention as recited in the several claims appended hereto.