CA1258182A - Foamed organopolysiloxane abrasive materials - Google Patents
Foamed organopolysiloxane abrasive materialsInfo
- Publication number
- CA1258182A CA1258182A CA000463820A CA463820A CA1258182A CA 1258182 A CA1258182 A CA 1258182A CA 000463820 A CA000463820 A CA 000463820A CA 463820 A CA463820 A CA 463820A CA 1258182 A CA1258182 A CA 1258182A
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- Canada
- Prior art keywords
- organopolysiloxane
- abrasive
- foam
- abrasive grit
- grit
- Prior art date
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Abstract
FOAMED ORGANOPOLYSILOXANE ABRASIVE MATERIALS
ABSTRACT OF THE DISCLOSURE
A foamed abrasive material having improved surface friction characteristics is described. The material is an organopolysiloxane foam having abrasive grit uniformly dispersed in the organopolysiloxane. The abrasive foam material having improved surface friction characteristics is prepared by mixing an abrasive grit in an organopolysiloxane having an organopolysiloxane foam-forming agent therein, to uniformly disperse the abrasive grit therein; allowing the mixture to foam; and curing the foam. In one embodiment, an article is formed of abrasive foam material by heating the abrasive grit-containing organopolysiloxane having an organopolysiloxane foam-forming agent therein at an elevated temperature in the presence of a catalyst in a mold, whereby gas formed in situ by the reaction of components in the filler and the organopolysiloxane form cells in the organopolysiloxane while simultaneously curing the organopolysiloxane in the mold at the elevated temperature.
ABSTRACT OF THE DISCLOSURE
A foamed abrasive material having improved surface friction characteristics is described. The material is an organopolysiloxane foam having abrasive grit uniformly dispersed in the organopolysiloxane. The abrasive foam material having improved surface friction characteristics is prepared by mixing an abrasive grit in an organopolysiloxane having an organopolysiloxane foam-forming agent therein, to uniformly disperse the abrasive grit therein; allowing the mixture to foam; and curing the foam. In one embodiment, an article is formed of abrasive foam material by heating the abrasive grit-containing organopolysiloxane having an organopolysiloxane foam-forming agent therein at an elevated temperature in the presence of a catalyst in a mold, whereby gas formed in situ by the reaction of components in the filler and the organopolysiloxane form cells in the organopolysiloxane while simultaneously curing the organopolysiloxane in the mold at the elevated temperature.
Description
~;~5818~
60-SI~ 457 FOAMED ORGANOPOLYSILOXANE ABRASIVE MATERIALS
.. _ . .. .
This invention relates generally to abrasive foam materials and a method of making foamed abrasive S materials, and more particularly, relates to foamed organopolyciloxane abrasive materials having abrasive grit uniformly dispersed throughout the organopolysiloxane.
A wide variety of materials is available for use in abrading and polishing surfaces, for stock removal and the like. The abrasive materials are generally classified into two types, namely, coated or bonded. A coated abrasive is one in which the particles of abrasive material, or alternatively, a polishing medium, identified herein as an abrasive material, are present as a thin coating on the surface of a body material which may be paper, cloth, netting, metal, resin, and the like, and are bonded to the body material by suitable adhesive or binder vehicle. A bonded abrasive is one in which the abrasive is dispersed within the bonding vehicle which is preformed into various solid shapes and cured or otherwise solidified for use in the solid form.
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While abrasive and polishing means of the coated and bonded types have been used for many years, they have not been entirely satisfactory for many applications. For example, the coated abrasives often wear of revealing the underlying body material, thereby providing a non-uniform abrading and polishing surface.
The bonded abrasives are generally dense, hard solids which become even harder in use. In many instances, because of localized temperature elevation in the vicinity of the working surface of the abrasive material, many of the polymeric materials used as binders and adhe~ives show some degree of thermal degradation resulting in smearing of the substrate being abraded or polished and in loss of cutting, abrasive or polishing action. Furthermore, because of the method o dispersing the abrasive in the binder in bonded abrasives, or because of the adhesive or binder vehicle used to adhere the abrasive to the surface of coated abrasive materials, there is poor accessability of the grit or grain surfaces to the surface undergoing abrasion, cutting, polishing and the like. Because of the foregoing, many of the prior art abrasive materials have to be resurfaced or refaced or discarded resulting in high costs due to downtime or due to the replacement of the material.
To overcome many of the foregoing deficiencies, it has been proposed to use abrasive foams wherein an abrasive grain is incorporated in foamable material prior to foaming with the resultant in situ production of a foam containing abrasive grain or grit substantially uniformly distributed throughout as >8~8'~
described in U.S. Patent No. 3,252,775, or wherein a pre-formed foam material in which the cells or voids in the foamed material, are impregnated with a slurry of abrasive and binder adhesive, dried and cured so that the voids or cells contain the abrasive substance bonded by the binder to the foamed material as described in U.S. Patent No. 3,653,859. By the latter method, the dispersion of the abrasive grit material is only as uniform as the distribution of voids or cells within the foamed material, and the integrity of the abrasive material is entirely dependent upon the binder adhesive utilized in the voids or cells. In most cases, these cellular or foamed grinding materials are made of phenolic resins and epoxy resins which can be foamed;
In many instances, the foams have such little integrity that they must be mounted or bound to more durable substrates to be effective as abrasive materials.
One type of abrasive wheel made of a soft, low-density polyurethane foam is described in U.S.
Patent No. 3,252,775, however, this type of abrasive material has poor strength and poor wearing properties and has not been successful commercially. It i5 for this reason that the art generally recognizes the necessity of employing highly dense and reinforced materials, such as a dense polyurethane composition cast around rein~orcing members as described in U.S.
Patent No. 4,150,955, to produce adequate abrasive and polishing members. Furthermore, the prior art teaches in U.S. ~atent No. 4,128,972 that the presence of foam in the final polishing wheel is unwanted. It is stated in U.S. Patent No. 4,128,972 that it is known that gas l'~S8~8~
60-SI-4s7 cells assist in cooling abrasive wheels through better heat ~ransfer, but void cells lessen the physical integrlty of the wheel, and distortion and ballooning are more often experienced, and the cohesive forces holding the unit abrasive grains in the tool and toqether are materially weakened. Thus, the prior art generally teaches that the presence of foaming agents in the adhesive elastomer bond are to be avoided.
Many prior art abras.ve and polishing materials have been made by incorporating the abrasive grit or polishing media in silicone resins or rubbers.
These are described, for example, in U.S. Patent No~
3,528,788, U.S. Patent No. 3,982,359, U.S. Patent No;
4 t 162,900 and U.S, Patent No. 4,307,544. In the foregoing patents ~hich utilize silicone rubber or elastomer as the binder medium, there is generally less localized temperature elevation in the vicinity of the working surface of the abrasive material at the interface with the part being abraded or polished where most organic polymers and even silicone resins show some degree of thermal degradation resulting in smearing and loss of cut or polishing action. The use of the silicone rubber or elastomer generally results in a much higher useable service temperature than the organic polymers and thereby provides higher stability and longer-lasting materials. However, there is still a certain degree of surface friction which results in localized temperature elevation and build up in the solid silicone rubbers.
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Summary of the _nvention In general, it is an object of ~he present invention to provide improved abrading and polishing materials which solve or substantially eliminate the foregoing problems, yet which are essentially cellular in structure.
It is another object of the present invention to provide an abrasive material having improved surface friction characteristics.
Another object of the present invention is to provide a method of preparing an abrasive material having improved surface friction characteristics.
Still another object of the present invention is to provide an article made of an abrasive material having improved surface friction characteristics.
Another object of the present invention is to provide an ahrasive material and method of making an abrasive material wherein there is improved accessability of the abrasive or grain material in the surface of the abrasive material.
These and other object of the invention are achieved by providing an organopolysiloxane foam having abrasive grit uniformly dispersed in the organopolysiloxane. Improved surface friction characteristics are realized by providing the voids or cells in the organopolysiloxane without sacrifice to the integrity of the material itself. Because of the properties and characteristics of the silicone rubber or lZS~3~8;~
60-SI_ 457 elastomer coupled with the void volume or cellular nature tnereof, there is reduced surface friction as well as improved heat dissipation resulting in reduced thermal degradation. This, in turn, improves the accessability of the abrasive or grain material at the surface. Furthermore, the use of the organopolysiloxane foam ha~ing abrasive grit uniformly dispersed in the organopolysiloxane, can be used at much higher service temperatures than the solid silicone rubbers or the organic polymeric foams or solids. The solid silicone rubbers or elastomers cause higher frictional heat leading to lower service life. The foamed organopolysiloxane elastomers of the present invention should operate at lower temperatures than the solid silicone elastomers. Thus, the foamed organopolysiloxane elastomers of the present invention having abrasive grit uniformly dispersed therein, will have an extended service life when compared with the service life of solid organopolysiloxane containing abrasive grit.
In accordance with at least some of the objects of the present invention, there is also provided a method of preparing an abrasive material having improved surface friction characteristics comprising mixing an abrasive grit or polishing media in an organopolysiloxane having an organopolysiloxane foam-forming agent therein until the abrasive grit is substantially uniformlv dispersed therein; allowing the mixture to foam and curing the foam. Furthermore, in accordance with at least some of the objects of the present invention, the abrasive grit-containing l'~S8;~8~
organopolysiloxane having an organopolysiloxane foam forming agent and a catalyst therein are placed in a mold and heated at an elevated temperature to foam and cure the organopolysiloxane to produce a molded article. Thus, in certain embodiments~ an article is formed of abrasive foam material by heating the abrasive yrit-containing organopolysiloxane having an organopolysiloxane foam-forming agent therein at an elevated temperature in the presence of a catalyst in a mold, whereby gas formed in situ by the reaction of components in the filler and the organopolysiloxane, form cells in the organopolysiloxane while simultaneously curing the organopolysiloxane in the mold at the elevated temperature.
These and various other objects, features and advantages of the invention can be best understood from the following detailed description.
Detailed Description of the Invention .
In the present invention, the abrasive materials having improved surface friction characteristics must have a binder or matrix material of a sponged or foamed silicone elastomer or rubber, that is, an organopolysiloxane foam or sponge rubber having an abrasive or polishing ~aterial substantially uniformly dispersed therein. In order to achieve at least some of the objects of the present invention, the organopolysiloxane foam or sponge rubber having the abrasive or polishing material dispersed in the :~ZS8~8'~
organopolysiloxane material itself must be one which results in reduced surface friction, thereby leading to lower stock temperatures with improved accessability of the abrasive or polishing surfaces to the body being 5 worked. The composite formed by the present invention must contain substantially.uniformly dispersed abrasive grit or polishing material in the organopolysiloxane foam such that the resultant cured composite abrasive material exhibits hoth cellular and abrasive characteristics.
The organopolysiloxane foams are especially adaptable to molding to zny shape, without great heat or pressure and can be simply and inexpensively handled during molding. In preferred embodiments, the organopolys:iloxane foams are those which are curable at elevated temperatures so that the organopolysiloxane having an organopolysiloxane foam-forming agent therein can be easily handled, for example, so that the abrasive material or polishing material and other additives can be substantially uniformly dispersed therein, prior to placing in a mold and curing.
The Eormulation of the organopolysiloxane foams of the present invention can be carefully controlled to provide foamed binder or matrix material of desired essential characteristics, including desired cell sizes, that is, cells ranqing from about 0.001 cm. to about 0.30 cm.; a desired proportion of void or cell space to the total volume of the body, that is, a void space ranging from about 15% to about 85~ of the organopolysiloxane in the foam material and more l'~S8~8~
_g_ preferably, from about 15~ to about 25~ of th2 organopolysiloxane in the foam material; essential toughness or hardness for use in particular operations;
and adaptability to receive inert fillers to increase S heat resistance, lubricating characteristics and the like, as well as to receive the abrasive or polishing materials, and the like.
Any organopolysiloxane material can be suitably ~oamed to provide the organopolysiloxane foam which may be used to form the abrasive material of the pres~nt invention. Typical organopolysiloxane foam-forming materials and methods and typical foamable organopolysiloxanes are well-known in the art. One typical organopolysiloxane foam-forming material is described and claimed in U.S. Patent No- 3,379,659, issued April 23,-1968. In United States Patent No.
3,379r659t there is disclosed and claimed a room temperature vulcanizing organopolysiloxane foam-forming composition and a method for making organopolysiloxane foams which utilize a silicon hydride and an aminoxy-substituted organosilicon material. Foaming in U.S. Patent No. 3,3?9,659 is achieved by the liberation of hydrogen gas from the silicon when the foam-forming composition is contacted with hydroxylated material, such as, atmospheric moisture. In one preferred embodiment o the present invention, a hydrated filler material, such as hydrated silica is incorporated in the organopolysiloxane rubber or elastomer to provide the moisture which is liberated from the hydrated silica upon heating at an appropriate elevated temperature which also simultaneously cures the composition in the :~'Z58~8~
presence of a catalyst, to form a cured material. The moisture reacts with a foam-forming agent in the organopolysiloxane elastomer to form a gas which foams the organopolysiloxane rubber or elastomer. This can be carried out in any mold to form a desired molded article. In one molding technique known in the art, a layer of fabric or cloth is placed between the platen and side retaining wall of the mold. This aids in the dissipation of the sponging gas or gases and is readily adaptable to molding techniques which utilize low molding pressures.
Another typical foamable organopolysiloxane composition is described and claimed in U.S. Patent. No.
3,425,967, issued February 4, 1969. In United States Patent No. 3,425,967, the foamable composition comprises a vinyl chain~stoped polysiloxane having a specified formula, an organopolysiloxane copolymer comprising (R")3SiOo 5 units and SiO2 units in which from about 2.5 to about 10 mole percent of the silicon atoms contain silicon-bonded vinyl groups; an inorganic fibrous material; a finely divided filler; an amount of a liquid organohydrogenpolysiloxane having a specified formula; and a blowing agent.
Still another typical silicone foam is described and claimed in United States P~tent Number 3,62~i,010, issued November 30, 1971, wherein organopolysiloxane foam is made by mixing a carboxyalkylpolysiloxane, a diisocyanate and a tertiary amine; allowing the composition to foam; then curing the foamed composition. Carbon dioxide generated during the 125~8~8'~
reaction of the components in U.S. Patent No. 3,524,010, causes foaming of the product during the curing reaction, and, thus, causes foam formation. Heating o the product in U.S. Patent No. 3,S24,010 at a temperature of from about 100C to about 120C results in a cured, foamed organopolysiloxane product.
Still other typical organopolysiloxane foams well known in the art may be used in the present invention. For example, other typical organopolysiloxane foams which may be used in the present invention, are the peroxide-cured organopolysiloxanes containing a conventional blowing agent, such as, benæenesulfonyl hydrazide (BSH). Other conventional blowing agents include, for example, toluenesulfonyl hydrazide (TSH), 4,4'-oxybis(benzenesulfonyl hydrazide) (OBSH) and azobisformamide (ABFA) also known as azodicarbonamide.
A sufficient amount of heat is applied to cause the formation of gas from the blowing agent while simultaneously curing the rubber or elastomer undergoing "foaming" by the action of the gas. Other typical organopolysiloxane foams are the addition-cured organopolysiloxane rubbers or elastomers, such as, those containing a silicon hydride which releases hydrogen gas (the foaming agent) in the presence of moisture, such as, the water contained in a water-containing filler dispersed in the organopolysiloxane material, the water in the water-containing filler being released when the organopolysiloxane containing the water-containing filler is heated at an elevated temperature. As indicated above, in this preferred embodiment, the 1~58~
heating of the organopolysiloxane rubber or elastomer to release the water in the hydrated filler, such as hydrated silica, also simultaneously cures the organopolysiloxane while the hydrogen gas is released during the heating to form the cells or voids in the organopolysiloxane rubber or elastomer. Thus, in preferred embodiments of the present invention, the organopolysiloxane foam is one which is curable at elevated temperatures because it not only affects the cure by forming crosslinks between vinyl groups on the polymer with hydrogen on the methyl hydrogen on the silicon hydride (methyl silicon hydride) crosslinking a~ent which is catalyzed by platinum, but because it also affects the foaming by releasing the water of hydration contained in the filler in the organopolysiloxane material. The water reacts with silicon hydride also incorporated in the organopolysiloxane rubber or elastomer to release hydrogen gas and cause the void formation in the organopolysiloxane material. Thus, when the organopolysiloxane foam is an addition cured organopolysiloxane and contains a typical addition-curing or crosslinklng agent, such as, a silicon hydride tfor example, methyl silicon hydride), it is cured at an elevated temperature in the presence of an addition catalyst, preferably, a class of typical platinum derivative catalysts well-known in the art, while hydrogen gas is simultaneously released to form the voids or cells in the organopolysiloxane foam which also contains the abrasive material or polishing material uniformly dispersed therein.
lZS8~8'~
When the organopolysiloxane foam is one which is formed from an addition cured organopolysiloxane, the gas which forms the voids or cells in the organopolysiloxane, is derived from a reaction from 5 $illers and materials incorporated in the organopolysiloxane. For example, a water-bearing filler, such as a hydrated filler, for example, hydrated silica, can be dispersed or mixed in the organopolysiloxane as is well-known in the art. An agent compatible with the organopolysiloxane and which releases a gas in the presence of water, can be incorporated in the organopolysiloxane by mixing. When the water in the filler is released, the gas forms from the reaction wi~h the agent in the organopolysiloxane rubber or elastomer which agent forms a gas in the presence of water, and the cells or voids are formed in the organopolysiloxane by the gas. For example, one typical agent is a silicon hydride, such as, a methyl silicon hydride which reacts with water to form hydrogen gas. Thus, in one of the preferred embodiments o the present invention, hydrated silica is incorporated in the organopolysiloxane rubber as a filler, and a silicon hydride is incorporated in the organopolysiloxane rubber as a crosslinking agent, and at an elevated temperature, the water of hydration is released from the hydrated silica, reacts with the silicon hydride and f~rms hydrogen gas. The elevated temperature used in this instance is about 50C to about 300C, and more preferably, about 150C to about 200C.
When a typical catalyst is incorporated therein, such as a platinum catalyst, the organopolysiloxane rubber l'~S8~8'~
simultaneously cures while the hydrogen gas foams the organopol~siloxane rubber. Thus, the elevated temperature must be sufficient to cause the liberation of hydrogen when water in the hydrated silica reacts with the silicon hydride, whereby the hydrogen causes the formation of cells within the organopolysiloxane rubber, as well as to cause the curing.
The abrasive grit or polishing material, generally referred to herein as abrasive grit, may be any well-known abrasive or polishing material, for example, it can be silicon carbide, finely-divided aluminum oxide, synthetic alumina, diamond, cubic crystal boron nitride, synthetic mullites and other natural and synthetic materials generally well-known in the art for their abrasive character or their polishing character or both.
As indicated above, in certain preferred embodiments of the present invention, the abrasive material comprising the organopolysiloxane foam having abrasive grit uniformly dispersed in the organopolysiloxane, may be treated with an organosilane or equivalent agent to promote the bonding of the abrasive or polishing material to the organopolysiloxane foam binder or matrix. In accordance with the present invention, the preferred organosilanes may be vinyltriethoxy silane, 2-13,4-epoxycyclohexyl)ethyl-trimethoxy silane, phenyltriethoxy silane, methacryloxypropyltrimethoxy silane, gamma-aminopropyltriethoxy silane and saliciaminde of aminosilane. Methods and compositions for pre-treating -~2581,8'~
60-SI- 4~7 the abrasive or polishing material prior to dispersing the material in the organopolysiloxane is deseribed and claimed in U.S. Patent No. 3,489,541, issued January 13, 1970 and U.S. Patent No. 3,904,391, issued September 9, 1975 In essence, these referen~e disclose at least washing the abrasive or polishing material with the specified organosilane, preferably after treating the abrasive or polishing material with a suitable agent, such as, an alkali metal hydroxide or other etching agent. Methods and solutions for treating the abrasive or polishing material are well defined in the foregoing references.
The amount of abrasive grit or polishing material incorporated in the organoplysiloxane foam is generally critical in order to avoid large islands of non-grit-containing areas in the organopolysiloxane foam. Thus, the minimum amount is that amount which must be incorporated into the organopolysiloxane foam in order to provide a sufficient amount of abrasive or polishing material substantially uniformly dispersed in the organopolysiloxane. The maximum amount of abrasive or polishing material is that amount which does not destroy or compromise the integrity of the oranopolysiloxane foam rubber or elastomer in which it is uniformly dispersed. In most embodiments, the minimum amount required to avoid areas or islands of non-grit-containing material, is at least about 53% by weight, based on the weight of the organopolysiloxane.
Generally, in most embodiments, the abrasive grit or polishing material is incorporated in the organopolysiloxane foam rubber in an amount ranging from about 53 percent ~o abou. 80 weight percent, based on the weight of the organoQolysiloxane rubber.
The abrasive grit or polishing material must be su~stantially uniformly dispersed within the organopolysiloxane prior to foaming the organopolysiloxane in order to provide the improved surface friction characteristics. This is generally accomplished by thoroughly blending, mixing or otherwise distributing the abrasive grit or polishing material in the organopolysiloxane rubber or elastomer prior to foaming, and it may be carried out simultaneously with the dispersion of other materials therein, for example, fillers, blowing agents, such as, organopolysiloxane lS foam-forming agents, whether blowing agents or gas forming agents, such as, silicon hydride. The organopolysiloxane rubber or elastomer which is - subjected to foaming is generally a gum, however, in certain instances, the organopolysiloxane may be a liquid. Liquids may be utilized, however, it is more difficult to maintain the abrasive grit on polishing material in uniform dispersion therein until the organopolysiloxane liquid is cured. In any event, the abrasive material or polishing material as well as the other materials, such as, fillers and organopolysiloxane foam-forming agents, are incorporated in the organopolysiloxane rubber or elastomer by thoroughly mixing with a suitable mixing device, such as, a Waring blender, a ball mlll, a rubber mill, a ~anbury mixer, or any other suitable stirring or mixing device.
Various reinforcing fillers can also be incorporated in the organopolysiloxane foams of the 8'~
60-SI-~57 present invention. Reinforcing inorganic fillers, such as, calcium carbonate, titanium dioxide, silica, fumed silica, hydrated silica as indicated above to provide water for the reaction with silicon hydride to produce hydrogen gas for foaming, and the like.
Kaolinite clays, aluminum silicate clays and silica, as well as carbon black, can be added to provide desirable results by one skilled in the art. In general, the reinforcing fillers or additives can be used singly or in combination and serve to strengthen the organopolysiloxane matrix and to increase the Shore hardness of the finished products. The proportion of the abrasive grit or polishing material can also be employed to vary the hardness, making it possible to proportion the respective amounts of abrasive or polishiny material and reinforcing filler to achieve a desired hardness as well-known in the art, as well as the desired polishing or abrasive action. Generally, in accordance with the present invention, the amount of reinforcing and other fillers or fillers may be used up to about 50% by weight of the organopolysiloxane.
Naturally, as discussed above, the organopolypolysiloxanes of the present invention also contain an organopolysiloxane foam-forming agent, which may be a gas, or which may be an agent which forms a gas in the presence of moisture, heat, chemical additives, and the like, and combinations thereof. The amount of foam-forming agent in the organopolysiloxane of the present invention is that amount which forms the desired degree of porosity or proportion of gas cells or voids within the foam, more specifically, that amo~nt which l~S8~8~
60-SI~57 provides void spaces within the cellular body up to about 85~ of .he total volume of the organopolysiloxane body. Generally, between about 15% and about 85% of the total volume of the organopolysiloxane body is void volume, and more preferably, about 15% to about 25~ of the total volume of the organopolysiloxane constitutes the gas célls or voids. Such void spaces can be in the form of substantially individualized cells or in the form of generally open or interconnecting cells. As indicated above, the cells or voids are generally formed by the realease of gases within the organopolysiloxane, for example, the release of hydrogen gas when silicon hydride or hydrazides react with water, or the release of carbon dioxide when diisocyanates operating as - 15 blowing agents release the carbon dioxide in the presence of heat. In most instances, in preferred embodiments of the present invention, the abrasive material, that is, the organopolysiloxane foam containing the abrasive grit or polishing material uniformly dispersed therein, has a density of about 60 pounds per cubic foot to about 95 pounds per cubic foot.
The degree of porosity and cell size of the organopolysiloxane foams of the present invention is controlled by the amount of blowing agent or other organopolysiloxane foam-forming agent incorporated in the organopolysiloxane. Also, various types and amounts of surfactants and non-ionic cell stabilizers well known in the art, may be employed to control porosity and cell size. In general, the greater the amount of surfactant or cell stabilizer, the ~iner and more uniform the cell.
The porosity and cell size within the organopolysiloxane 8~8;~
_1 9--foam can ~lso be cor.trolled to some extent by the degree of loading of the material in a mold, with respect either to the amount of organopolysiloxane employed or the amount of various fillers and additives. For example, the mold can be filled to any level, and when closed, can expand only to the extent of the mold left un-filled. Thus the control of the degree of porosity and cell size can be dependent upon mold filling, that is, the amount of organopolysiloxane material placed in the mold.
Generally, in preparing the abrasive materials having improved surface friction characteristics in accordance with the present invention, the abrasive or polishing material is mixed with the organopolysiloxane having an organopolysiloxane foam-forming agent therein until the abrasive or polishing material is substantially unîformly ~ispersed therein. After the mixing is complete and all of the ingredients are uniformly dispersed therein, including any fillers, catalysts, foam-forming agents, polishing or abrasive materials, and the like, are uniformly dispersed therein, the mixture is allowed to foam and cure. As discussed above, the curing may be accomplished simultaneously with ~he foaming. The order in which the fillers, foam-forming agents catalysts and any other materials are incorporated in the organopolysiloxane, is not critical as long as they are uniformly dispersed in the organopolysiloxane by appropriate mixing.
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Appropriate catalysts, such as organoperoxides, platinum or platinum derivatives and any of the other well-known catalysts for organopolysiloxanes, may also be mixed in an effective catalytic amount into the organopolysiloxane along wi~h the organopolysiloxane foam-forming agent, crosslinking agent or agents~ such as, silicon hydride, fillers, abrasive or polishing materials and the like.
Generally, the amount of catalyst can be easily adjusted by one skilled in the art without undue experimentation.
Curing time can also be easily controlled, depending upon the desired amount of cure, by one skilled in the art.
After the mixing of the ingredients is complete, and the abrasive grit or polishing material are substantially uniformly dispersed throughout the organopolysiloxane gum or fluidr the mixture is foamed and cured by heating the abrasive grit-containing organopolysiloxane having the organopolysiloxane foam-forming agent therein at an elevated temperature in the presence of an effective catalytic amount of catalyst to cure the organopolysiloxane. In most instances, the elevated temperature is a temperature of about 50C to abouto 300C, and more preferably from about 150C to about 200C. The length of time of heating may be that amount of time required to effect the desired cure~ such as, for example, from less than about 1 minute up to 5 hours or more. After curing is complete, generally in a mold, the cured foam containing ~'~S8~L8'~
the abrasive grit or ~olishing material is cooled to room temperature and removed from the mold.
In general, the organopolysiloxane foams having abrasive qrit or polishing material uniformly dispersed in the organopolysiloxane, can be molded or formed in virtually any shape and size desired.
Well-known molded and shaped abrasive and polishing articles are known, such as abrasive wheels and polishing wheels. Belts and sheets of the organopolysiloxane foams having abrasive grit or polishing material uniformly dispersed therein can also be made or formed from the materials of the present invention, and they can be formed onto a backing or reinforcing material which may be fibrous or non-fibrous. The organopolysiloxane foams having the abrasive grit uniformly dispersed therein in accordance with the present invention can be formed into continuous belts or sheets following standard practices. The flexible, cellular organopolysiloxane foams of the present invention, when formed into abrasive or polishing articles as described above, can be suitably reinforced with fibers, fabrics, and the like.
Generally, there is also improved accessability of grain surfaces yielding more aggressive cuts or greater polishing ability and shorter grinding or polishing times.
In one preferred embodiment of the present invention, molded articles are formed by mixing the abrasive grit or polishing material in an organopolysiloxane gum or liquid having an lZS13~8~
organopolysiloxane foam-forming agent therein, until the abrasive grit is substantially uniformly dispersed therein; placing the mixture in a mold, the mixture containing a crosslinking agent and a catalyst to promote cross-linking or curing of the mixture; allowing the mixture to foam; and curing the foam. The mixture may be heated as desired at an elevated temperature in the mold to promote the foaming and/or curing of the organopolysiloxane rubber or elastomer. Naturally, when the organopolysiloxane foam-forming agent is silicon hydride which reacts with water from water-containing filler or fillers in the organopolysiloxane, the cells in the organopolysiloxane rubber or elastomer are formed by the release of hydrogen gas when the mixture is heated at an elevated temperature, generally, between about 150~C. to about 200C.
The following examples further illustrate the practice of the invention, and they are meant to be exemplary only and are not to be construed as limiting the invention in any way.
EXAMPLE I
Sponging was accomplished by combining a hydrated silica reinforced silicone rubber compound with methyl hydride oil and a platinum catalyst. The ~ilicone rubber was 68.8 parts by weight polydimethylmethylvinyl siloxane and contained 29 parts by weight hydrated silica, 1.9 parts by weight silanol stopped polydimethylsiloxane fluid, 0.4 parts by weight vinyl tris(2-ethoxymethoxy)silane and 0.1 part by weigh~
~Z~ 8~
60-SI_4s7 -~3-of a typical heat age additive. The formulation contained 47 parts by weight of the above reinforced organopolysiloxane, 53 parts by weight of a 60 grit silicon carbide abrasive material, 1 part by weight methyl hydride oil and 1 part by weight platinum catalyst. The ingredients were uniformly mixed in a conventional rubber mill so that the abrasive grit was uniformly dispersed throughout the mixture. The mixture as prepared in the rubber mill, was placed in a mold 15.24 cm. (6 inches) x 15.24 cm. (6 inches) x 1.27 cm.
(0.5 inch). The mold was underfilled to allow room for expansion during the release of the hydrogen gas. At the elevated molding temperature, the hydride reacted with the water contained in the hydrated silica filler, and hydrogen gas was liberated to form the cells in the rubber. An open weave fabric was placed in the mold prior to placing the mixture therein to assist in the sponging operation by promoting the distribution of the hydrogen gas. The mold was heated at about 177C for abou~ 20 minutes. The slab of foamed organopolysiloxane having the silicon carbide abrasive therein, had a specific gravity of 1.42 compared with a specific gravity of 1.66 for the comparable non-foamed organopolysiloxane containing the same size and amount silicon carbide abrasive material. The blow ratio of the foamed organopolysiloxane containing the silicon carbide abrasive was 1.17. The abrasiveness of the compound was good, and the wear resistance of the slab compound as subjectively assessed, is good.
Abrasiveness was qualitatively determined by mounting a 5.08 cm. (~ inch) diameter by 1.27 cm. (0.5 inch) thick disk of the sponged composite on a portable 8~
electric drill which was then used to qrind various metal surfaces. The material displayed good abrasive and wear resistance properties.
EXAMPLE II
Sponging was accomplished by combining a fumed-silica reinforced silicone rubber compound with a blowing agent, organic peroxide catalyst and abrasive 1 n grit. The silicone rubber was 70.5 parts by weight polydimethylmethylvinyl siloxane and contained 1.0 part by weight of typical heat age and compression set additives, 5.4 parts by weight diatomaceous earth, 19.5 parts by weight of treated fumed silica, 0.2 parts by weight of vinyltriethoxy silane and 3.4 parts by weight methoxy stopp~d polydimethylsiloxane fluid. The formulation contained 47 parts by weight of the above fumed silica-reinforced silicone rubber, 53 parts by weight of an 80 mesh silicon carbide abrasive material, 0.4 parts by weight of benzenesulfonyl hydrazide blowing agent, 0.8 parts by weight of 2,4-dichlorobenzoyl peroxide and 2 parts by weight Verox powder, a 50
60-SI~ 457 FOAMED ORGANOPOLYSILOXANE ABRASIVE MATERIALS
.. _ . .. .
This invention relates generally to abrasive foam materials and a method of making foamed abrasive S materials, and more particularly, relates to foamed organopolyciloxane abrasive materials having abrasive grit uniformly dispersed throughout the organopolysiloxane.
A wide variety of materials is available for use in abrading and polishing surfaces, for stock removal and the like. The abrasive materials are generally classified into two types, namely, coated or bonded. A coated abrasive is one in which the particles of abrasive material, or alternatively, a polishing medium, identified herein as an abrasive material, are present as a thin coating on the surface of a body material which may be paper, cloth, netting, metal, resin, and the like, and are bonded to the body material by suitable adhesive or binder vehicle. A bonded abrasive is one in which the abrasive is dispersed within the bonding vehicle which is preformed into various solid shapes and cured or otherwise solidified for use in the solid form.
18~
While abrasive and polishing means of the coated and bonded types have been used for many years, they have not been entirely satisfactory for many applications. For example, the coated abrasives often wear of revealing the underlying body material, thereby providing a non-uniform abrading and polishing surface.
The bonded abrasives are generally dense, hard solids which become even harder in use. In many instances, because of localized temperature elevation in the vicinity of the working surface of the abrasive material, many of the polymeric materials used as binders and adhe~ives show some degree of thermal degradation resulting in smearing of the substrate being abraded or polished and in loss of cutting, abrasive or polishing action. Furthermore, because of the method o dispersing the abrasive in the binder in bonded abrasives, or because of the adhesive or binder vehicle used to adhere the abrasive to the surface of coated abrasive materials, there is poor accessability of the grit or grain surfaces to the surface undergoing abrasion, cutting, polishing and the like. Because of the foregoing, many of the prior art abrasive materials have to be resurfaced or refaced or discarded resulting in high costs due to downtime or due to the replacement of the material.
To overcome many of the foregoing deficiencies, it has been proposed to use abrasive foams wherein an abrasive grain is incorporated in foamable material prior to foaming with the resultant in situ production of a foam containing abrasive grain or grit substantially uniformly distributed throughout as >8~8'~
described in U.S. Patent No. 3,252,775, or wherein a pre-formed foam material in which the cells or voids in the foamed material, are impregnated with a slurry of abrasive and binder adhesive, dried and cured so that the voids or cells contain the abrasive substance bonded by the binder to the foamed material as described in U.S. Patent No. 3,653,859. By the latter method, the dispersion of the abrasive grit material is only as uniform as the distribution of voids or cells within the foamed material, and the integrity of the abrasive material is entirely dependent upon the binder adhesive utilized in the voids or cells. In most cases, these cellular or foamed grinding materials are made of phenolic resins and epoxy resins which can be foamed;
In many instances, the foams have such little integrity that they must be mounted or bound to more durable substrates to be effective as abrasive materials.
One type of abrasive wheel made of a soft, low-density polyurethane foam is described in U.S.
Patent No. 3,252,775, however, this type of abrasive material has poor strength and poor wearing properties and has not been successful commercially. It i5 for this reason that the art generally recognizes the necessity of employing highly dense and reinforced materials, such as a dense polyurethane composition cast around rein~orcing members as described in U.S.
Patent No. 4,150,955, to produce adequate abrasive and polishing members. Furthermore, the prior art teaches in U.S. ~atent No. 4,128,972 that the presence of foam in the final polishing wheel is unwanted. It is stated in U.S. Patent No. 4,128,972 that it is known that gas l'~S8~8~
60-SI-4s7 cells assist in cooling abrasive wheels through better heat ~ransfer, but void cells lessen the physical integrlty of the wheel, and distortion and ballooning are more often experienced, and the cohesive forces holding the unit abrasive grains in the tool and toqether are materially weakened. Thus, the prior art generally teaches that the presence of foaming agents in the adhesive elastomer bond are to be avoided.
Many prior art abras.ve and polishing materials have been made by incorporating the abrasive grit or polishing media in silicone resins or rubbers.
These are described, for example, in U.S. Patent No~
3,528,788, U.S. Patent No. 3,982,359, U.S. Patent No;
4 t 162,900 and U.S, Patent No. 4,307,544. In the foregoing patents ~hich utilize silicone rubber or elastomer as the binder medium, there is generally less localized temperature elevation in the vicinity of the working surface of the abrasive material at the interface with the part being abraded or polished where most organic polymers and even silicone resins show some degree of thermal degradation resulting in smearing and loss of cut or polishing action. The use of the silicone rubber or elastomer generally results in a much higher useable service temperature than the organic polymers and thereby provides higher stability and longer-lasting materials. However, there is still a certain degree of surface friction which results in localized temperature elevation and build up in the solid silicone rubbers.
~81~
Summary of the _nvention In general, it is an object of ~he present invention to provide improved abrading and polishing materials which solve or substantially eliminate the foregoing problems, yet which are essentially cellular in structure.
It is another object of the present invention to provide an abrasive material having improved surface friction characteristics.
Another object of the present invention is to provide a method of preparing an abrasive material having improved surface friction characteristics.
Still another object of the present invention is to provide an article made of an abrasive material having improved surface friction characteristics.
Another object of the present invention is to provide an ahrasive material and method of making an abrasive material wherein there is improved accessability of the abrasive or grain material in the surface of the abrasive material.
These and other object of the invention are achieved by providing an organopolysiloxane foam having abrasive grit uniformly dispersed in the organopolysiloxane. Improved surface friction characteristics are realized by providing the voids or cells in the organopolysiloxane without sacrifice to the integrity of the material itself. Because of the properties and characteristics of the silicone rubber or lZS~3~8;~
60-SI_ 457 elastomer coupled with the void volume or cellular nature tnereof, there is reduced surface friction as well as improved heat dissipation resulting in reduced thermal degradation. This, in turn, improves the accessability of the abrasive or grain material at the surface. Furthermore, the use of the organopolysiloxane foam ha~ing abrasive grit uniformly dispersed in the organopolysiloxane, can be used at much higher service temperatures than the solid silicone rubbers or the organic polymeric foams or solids. The solid silicone rubbers or elastomers cause higher frictional heat leading to lower service life. The foamed organopolysiloxane elastomers of the present invention should operate at lower temperatures than the solid silicone elastomers. Thus, the foamed organopolysiloxane elastomers of the present invention having abrasive grit uniformly dispersed therein, will have an extended service life when compared with the service life of solid organopolysiloxane containing abrasive grit.
In accordance with at least some of the objects of the present invention, there is also provided a method of preparing an abrasive material having improved surface friction characteristics comprising mixing an abrasive grit or polishing media in an organopolysiloxane having an organopolysiloxane foam-forming agent therein until the abrasive grit is substantially uniformlv dispersed therein; allowing the mixture to foam and curing the foam. Furthermore, in accordance with at least some of the objects of the present invention, the abrasive grit-containing l'~S8;~8~
organopolysiloxane having an organopolysiloxane foam forming agent and a catalyst therein are placed in a mold and heated at an elevated temperature to foam and cure the organopolysiloxane to produce a molded article. Thus, in certain embodiments~ an article is formed of abrasive foam material by heating the abrasive yrit-containing organopolysiloxane having an organopolysiloxane foam-forming agent therein at an elevated temperature in the presence of a catalyst in a mold, whereby gas formed in situ by the reaction of components in the filler and the organopolysiloxane, form cells in the organopolysiloxane while simultaneously curing the organopolysiloxane in the mold at the elevated temperature.
These and various other objects, features and advantages of the invention can be best understood from the following detailed description.
Detailed Description of the Invention .
In the present invention, the abrasive materials having improved surface friction characteristics must have a binder or matrix material of a sponged or foamed silicone elastomer or rubber, that is, an organopolysiloxane foam or sponge rubber having an abrasive or polishing ~aterial substantially uniformly dispersed therein. In order to achieve at least some of the objects of the present invention, the organopolysiloxane foam or sponge rubber having the abrasive or polishing material dispersed in the :~ZS8~8'~
organopolysiloxane material itself must be one which results in reduced surface friction, thereby leading to lower stock temperatures with improved accessability of the abrasive or polishing surfaces to the body being 5 worked. The composite formed by the present invention must contain substantially.uniformly dispersed abrasive grit or polishing material in the organopolysiloxane foam such that the resultant cured composite abrasive material exhibits hoth cellular and abrasive characteristics.
The organopolysiloxane foams are especially adaptable to molding to zny shape, without great heat or pressure and can be simply and inexpensively handled during molding. In preferred embodiments, the organopolys:iloxane foams are those which are curable at elevated temperatures so that the organopolysiloxane having an organopolysiloxane foam-forming agent therein can be easily handled, for example, so that the abrasive material or polishing material and other additives can be substantially uniformly dispersed therein, prior to placing in a mold and curing.
The Eormulation of the organopolysiloxane foams of the present invention can be carefully controlled to provide foamed binder or matrix material of desired essential characteristics, including desired cell sizes, that is, cells ranqing from about 0.001 cm. to about 0.30 cm.; a desired proportion of void or cell space to the total volume of the body, that is, a void space ranging from about 15% to about 85~ of the organopolysiloxane in the foam material and more l'~S8~8~
_g_ preferably, from about 15~ to about 25~ of th2 organopolysiloxane in the foam material; essential toughness or hardness for use in particular operations;
and adaptability to receive inert fillers to increase S heat resistance, lubricating characteristics and the like, as well as to receive the abrasive or polishing materials, and the like.
Any organopolysiloxane material can be suitably ~oamed to provide the organopolysiloxane foam which may be used to form the abrasive material of the pres~nt invention. Typical organopolysiloxane foam-forming materials and methods and typical foamable organopolysiloxanes are well-known in the art. One typical organopolysiloxane foam-forming material is described and claimed in U.S. Patent No- 3,379,659, issued April 23,-1968. In United States Patent No.
3,379r659t there is disclosed and claimed a room temperature vulcanizing organopolysiloxane foam-forming composition and a method for making organopolysiloxane foams which utilize a silicon hydride and an aminoxy-substituted organosilicon material. Foaming in U.S. Patent No. 3,3?9,659 is achieved by the liberation of hydrogen gas from the silicon when the foam-forming composition is contacted with hydroxylated material, such as, atmospheric moisture. In one preferred embodiment o the present invention, a hydrated filler material, such as hydrated silica is incorporated in the organopolysiloxane rubber or elastomer to provide the moisture which is liberated from the hydrated silica upon heating at an appropriate elevated temperature which also simultaneously cures the composition in the :~'Z58~8~
presence of a catalyst, to form a cured material. The moisture reacts with a foam-forming agent in the organopolysiloxane elastomer to form a gas which foams the organopolysiloxane rubber or elastomer. This can be carried out in any mold to form a desired molded article. In one molding technique known in the art, a layer of fabric or cloth is placed between the platen and side retaining wall of the mold. This aids in the dissipation of the sponging gas or gases and is readily adaptable to molding techniques which utilize low molding pressures.
Another typical foamable organopolysiloxane composition is described and claimed in U.S. Patent. No.
3,425,967, issued February 4, 1969. In United States Patent No. 3,425,967, the foamable composition comprises a vinyl chain~stoped polysiloxane having a specified formula, an organopolysiloxane copolymer comprising (R")3SiOo 5 units and SiO2 units in which from about 2.5 to about 10 mole percent of the silicon atoms contain silicon-bonded vinyl groups; an inorganic fibrous material; a finely divided filler; an amount of a liquid organohydrogenpolysiloxane having a specified formula; and a blowing agent.
Still another typical silicone foam is described and claimed in United States P~tent Number 3,62~i,010, issued November 30, 1971, wherein organopolysiloxane foam is made by mixing a carboxyalkylpolysiloxane, a diisocyanate and a tertiary amine; allowing the composition to foam; then curing the foamed composition. Carbon dioxide generated during the 125~8~8'~
reaction of the components in U.S. Patent No. 3,524,010, causes foaming of the product during the curing reaction, and, thus, causes foam formation. Heating o the product in U.S. Patent No. 3,S24,010 at a temperature of from about 100C to about 120C results in a cured, foamed organopolysiloxane product.
Still other typical organopolysiloxane foams well known in the art may be used in the present invention. For example, other typical organopolysiloxane foams which may be used in the present invention, are the peroxide-cured organopolysiloxanes containing a conventional blowing agent, such as, benæenesulfonyl hydrazide (BSH). Other conventional blowing agents include, for example, toluenesulfonyl hydrazide (TSH), 4,4'-oxybis(benzenesulfonyl hydrazide) (OBSH) and azobisformamide (ABFA) also known as azodicarbonamide.
A sufficient amount of heat is applied to cause the formation of gas from the blowing agent while simultaneously curing the rubber or elastomer undergoing "foaming" by the action of the gas. Other typical organopolysiloxane foams are the addition-cured organopolysiloxane rubbers or elastomers, such as, those containing a silicon hydride which releases hydrogen gas (the foaming agent) in the presence of moisture, such as, the water contained in a water-containing filler dispersed in the organopolysiloxane material, the water in the water-containing filler being released when the organopolysiloxane containing the water-containing filler is heated at an elevated temperature. As indicated above, in this preferred embodiment, the 1~58~
heating of the organopolysiloxane rubber or elastomer to release the water in the hydrated filler, such as hydrated silica, also simultaneously cures the organopolysiloxane while the hydrogen gas is released during the heating to form the cells or voids in the organopolysiloxane rubber or elastomer. Thus, in preferred embodiments of the present invention, the organopolysiloxane foam is one which is curable at elevated temperatures because it not only affects the cure by forming crosslinks between vinyl groups on the polymer with hydrogen on the methyl hydrogen on the silicon hydride (methyl silicon hydride) crosslinking a~ent which is catalyzed by platinum, but because it also affects the foaming by releasing the water of hydration contained in the filler in the organopolysiloxane material. The water reacts with silicon hydride also incorporated in the organopolysiloxane rubber or elastomer to release hydrogen gas and cause the void formation in the organopolysiloxane material. Thus, when the organopolysiloxane foam is an addition cured organopolysiloxane and contains a typical addition-curing or crosslinklng agent, such as, a silicon hydride tfor example, methyl silicon hydride), it is cured at an elevated temperature in the presence of an addition catalyst, preferably, a class of typical platinum derivative catalysts well-known in the art, while hydrogen gas is simultaneously released to form the voids or cells in the organopolysiloxane foam which also contains the abrasive material or polishing material uniformly dispersed therein.
lZS8~8'~
When the organopolysiloxane foam is one which is formed from an addition cured organopolysiloxane, the gas which forms the voids or cells in the organopolysiloxane, is derived from a reaction from 5 $illers and materials incorporated in the organopolysiloxane. For example, a water-bearing filler, such as a hydrated filler, for example, hydrated silica, can be dispersed or mixed in the organopolysiloxane as is well-known in the art. An agent compatible with the organopolysiloxane and which releases a gas in the presence of water, can be incorporated in the organopolysiloxane by mixing. When the water in the filler is released, the gas forms from the reaction wi~h the agent in the organopolysiloxane rubber or elastomer which agent forms a gas in the presence of water, and the cells or voids are formed in the organopolysiloxane by the gas. For example, one typical agent is a silicon hydride, such as, a methyl silicon hydride which reacts with water to form hydrogen gas. Thus, in one of the preferred embodiments o the present invention, hydrated silica is incorporated in the organopolysiloxane rubber as a filler, and a silicon hydride is incorporated in the organopolysiloxane rubber as a crosslinking agent, and at an elevated temperature, the water of hydration is released from the hydrated silica, reacts with the silicon hydride and f~rms hydrogen gas. The elevated temperature used in this instance is about 50C to about 300C, and more preferably, about 150C to about 200C.
When a typical catalyst is incorporated therein, such as a platinum catalyst, the organopolysiloxane rubber l'~S8~8'~
simultaneously cures while the hydrogen gas foams the organopol~siloxane rubber. Thus, the elevated temperature must be sufficient to cause the liberation of hydrogen when water in the hydrated silica reacts with the silicon hydride, whereby the hydrogen causes the formation of cells within the organopolysiloxane rubber, as well as to cause the curing.
The abrasive grit or polishing material, generally referred to herein as abrasive grit, may be any well-known abrasive or polishing material, for example, it can be silicon carbide, finely-divided aluminum oxide, synthetic alumina, diamond, cubic crystal boron nitride, synthetic mullites and other natural and synthetic materials generally well-known in the art for their abrasive character or their polishing character or both.
As indicated above, in certain preferred embodiments of the present invention, the abrasive material comprising the organopolysiloxane foam having abrasive grit uniformly dispersed in the organopolysiloxane, may be treated with an organosilane or equivalent agent to promote the bonding of the abrasive or polishing material to the organopolysiloxane foam binder or matrix. In accordance with the present invention, the preferred organosilanes may be vinyltriethoxy silane, 2-13,4-epoxycyclohexyl)ethyl-trimethoxy silane, phenyltriethoxy silane, methacryloxypropyltrimethoxy silane, gamma-aminopropyltriethoxy silane and saliciaminde of aminosilane. Methods and compositions for pre-treating -~2581,8'~
60-SI- 4~7 the abrasive or polishing material prior to dispersing the material in the organopolysiloxane is deseribed and claimed in U.S. Patent No. 3,489,541, issued January 13, 1970 and U.S. Patent No. 3,904,391, issued September 9, 1975 In essence, these referen~e disclose at least washing the abrasive or polishing material with the specified organosilane, preferably after treating the abrasive or polishing material with a suitable agent, such as, an alkali metal hydroxide or other etching agent. Methods and solutions for treating the abrasive or polishing material are well defined in the foregoing references.
The amount of abrasive grit or polishing material incorporated in the organoplysiloxane foam is generally critical in order to avoid large islands of non-grit-containing areas in the organopolysiloxane foam. Thus, the minimum amount is that amount which must be incorporated into the organopolysiloxane foam in order to provide a sufficient amount of abrasive or polishing material substantially uniformly dispersed in the organopolysiloxane. The maximum amount of abrasive or polishing material is that amount which does not destroy or compromise the integrity of the oranopolysiloxane foam rubber or elastomer in which it is uniformly dispersed. In most embodiments, the minimum amount required to avoid areas or islands of non-grit-containing material, is at least about 53% by weight, based on the weight of the organopolysiloxane.
Generally, in most embodiments, the abrasive grit or polishing material is incorporated in the organopolysiloxane foam rubber in an amount ranging from about 53 percent ~o abou. 80 weight percent, based on the weight of the organoQolysiloxane rubber.
The abrasive grit or polishing material must be su~stantially uniformly dispersed within the organopolysiloxane prior to foaming the organopolysiloxane in order to provide the improved surface friction characteristics. This is generally accomplished by thoroughly blending, mixing or otherwise distributing the abrasive grit or polishing material in the organopolysiloxane rubber or elastomer prior to foaming, and it may be carried out simultaneously with the dispersion of other materials therein, for example, fillers, blowing agents, such as, organopolysiloxane lS foam-forming agents, whether blowing agents or gas forming agents, such as, silicon hydride. The organopolysiloxane rubber or elastomer which is - subjected to foaming is generally a gum, however, in certain instances, the organopolysiloxane may be a liquid. Liquids may be utilized, however, it is more difficult to maintain the abrasive grit on polishing material in uniform dispersion therein until the organopolysiloxane liquid is cured. In any event, the abrasive material or polishing material as well as the other materials, such as, fillers and organopolysiloxane foam-forming agents, are incorporated in the organopolysiloxane rubber or elastomer by thoroughly mixing with a suitable mixing device, such as, a Waring blender, a ball mlll, a rubber mill, a ~anbury mixer, or any other suitable stirring or mixing device.
Various reinforcing fillers can also be incorporated in the organopolysiloxane foams of the 8'~
60-SI-~57 present invention. Reinforcing inorganic fillers, such as, calcium carbonate, titanium dioxide, silica, fumed silica, hydrated silica as indicated above to provide water for the reaction with silicon hydride to produce hydrogen gas for foaming, and the like.
Kaolinite clays, aluminum silicate clays and silica, as well as carbon black, can be added to provide desirable results by one skilled in the art. In general, the reinforcing fillers or additives can be used singly or in combination and serve to strengthen the organopolysiloxane matrix and to increase the Shore hardness of the finished products. The proportion of the abrasive grit or polishing material can also be employed to vary the hardness, making it possible to proportion the respective amounts of abrasive or polishiny material and reinforcing filler to achieve a desired hardness as well-known in the art, as well as the desired polishing or abrasive action. Generally, in accordance with the present invention, the amount of reinforcing and other fillers or fillers may be used up to about 50% by weight of the organopolysiloxane.
Naturally, as discussed above, the organopolypolysiloxanes of the present invention also contain an organopolysiloxane foam-forming agent, which may be a gas, or which may be an agent which forms a gas in the presence of moisture, heat, chemical additives, and the like, and combinations thereof. The amount of foam-forming agent in the organopolysiloxane of the present invention is that amount which forms the desired degree of porosity or proportion of gas cells or voids within the foam, more specifically, that amo~nt which l~S8~8~
60-SI~57 provides void spaces within the cellular body up to about 85~ of .he total volume of the organopolysiloxane body. Generally, between about 15% and about 85% of the total volume of the organopolysiloxane body is void volume, and more preferably, about 15% to about 25~ of the total volume of the organopolysiloxane constitutes the gas célls or voids. Such void spaces can be in the form of substantially individualized cells or in the form of generally open or interconnecting cells. As indicated above, the cells or voids are generally formed by the realease of gases within the organopolysiloxane, for example, the release of hydrogen gas when silicon hydride or hydrazides react with water, or the release of carbon dioxide when diisocyanates operating as - 15 blowing agents release the carbon dioxide in the presence of heat. In most instances, in preferred embodiments of the present invention, the abrasive material, that is, the organopolysiloxane foam containing the abrasive grit or polishing material uniformly dispersed therein, has a density of about 60 pounds per cubic foot to about 95 pounds per cubic foot.
The degree of porosity and cell size of the organopolysiloxane foams of the present invention is controlled by the amount of blowing agent or other organopolysiloxane foam-forming agent incorporated in the organopolysiloxane. Also, various types and amounts of surfactants and non-ionic cell stabilizers well known in the art, may be employed to control porosity and cell size. In general, the greater the amount of surfactant or cell stabilizer, the ~iner and more uniform the cell.
The porosity and cell size within the organopolysiloxane 8~8;~
_1 9--foam can ~lso be cor.trolled to some extent by the degree of loading of the material in a mold, with respect either to the amount of organopolysiloxane employed or the amount of various fillers and additives. For example, the mold can be filled to any level, and when closed, can expand only to the extent of the mold left un-filled. Thus the control of the degree of porosity and cell size can be dependent upon mold filling, that is, the amount of organopolysiloxane material placed in the mold.
Generally, in preparing the abrasive materials having improved surface friction characteristics in accordance with the present invention, the abrasive or polishing material is mixed with the organopolysiloxane having an organopolysiloxane foam-forming agent therein until the abrasive or polishing material is substantially unîformly ~ispersed therein. After the mixing is complete and all of the ingredients are uniformly dispersed therein, including any fillers, catalysts, foam-forming agents, polishing or abrasive materials, and the like, are uniformly dispersed therein, the mixture is allowed to foam and cure. As discussed above, the curing may be accomplished simultaneously with ~he foaming. The order in which the fillers, foam-forming agents catalysts and any other materials are incorporated in the organopolysiloxane, is not critical as long as they are uniformly dispersed in the organopolysiloxane by appropriate mixing.
8'~
Appropriate catalysts, such as organoperoxides, platinum or platinum derivatives and any of the other well-known catalysts for organopolysiloxanes, may also be mixed in an effective catalytic amount into the organopolysiloxane along wi~h the organopolysiloxane foam-forming agent, crosslinking agent or agents~ such as, silicon hydride, fillers, abrasive or polishing materials and the like.
Generally, the amount of catalyst can be easily adjusted by one skilled in the art without undue experimentation.
Curing time can also be easily controlled, depending upon the desired amount of cure, by one skilled in the art.
After the mixing of the ingredients is complete, and the abrasive grit or polishing material are substantially uniformly dispersed throughout the organopolysiloxane gum or fluidr the mixture is foamed and cured by heating the abrasive grit-containing organopolysiloxane having the organopolysiloxane foam-forming agent therein at an elevated temperature in the presence of an effective catalytic amount of catalyst to cure the organopolysiloxane. In most instances, the elevated temperature is a temperature of about 50C to abouto 300C, and more preferably from about 150C to about 200C. The length of time of heating may be that amount of time required to effect the desired cure~ such as, for example, from less than about 1 minute up to 5 hours or more. After curing is complete, generally in a mold, the cured foam containing ~'~S8~L8'~
the abrasive grit or ~olishing material is cooled to room temperature and removed from the mold.
In general, the organopolysiloxane foams having abrasive qrit or polishing material uniformly dispersed in the organopolysiloxane, can be molded or formed in virtually any shape and size desired.
Well-known molded and shaped abrasive and polishing articles are known, such as abrasive wheels and polishing wheels. Belts and sheets of the organopolysiloxane foams having abrasive grit or polishing material uniformly dispersed therein can also be made or formed from the materials of the present invention, and they can be formed onto a backing or reinforcing material which may be fibrous or non-fibrous. The organopolysiloxane foams having the abrasive grit uniformly dispersed therein in accordance with the present invention can be formed into continuous belts or sheets following standard practices. The flexible, cellular organopolysiloxane foams of the present invention, when formed into abrasive or polishing articles as described above, can be suitably reinforced with fibers, fabrics, and the like.
Generally, there is also improved accessability of grain surfaces yielding more aggressive cuts or greater polishing ability and shorter grinding or polishing times.
In one preferred embodiment of the present invention, molded articles are formed by mixing the abrasive grit or polishing material in an organopolysiloxane gum or liquid having an lZS13~8~
organopolysiloxane foam-forming agent therein, until the abrasive grit is substantially uniformly dispersed therein; placing the mixture in a mold, the mixture containing a crosslinking agent and a catalyst to promote cross-linking or curing of the mixture; allowing the mixture to foam; and curing the foam. The mixture may be heated as desired at an elevated temperature in the mold to promote the foaming and/or curing of the organopolysiloxane rubber or elastomer. Naturally, when the organopolysiloxane foam-forming agent is silicon hydride which reacts with water from water-containing filler or fillers in the organopolysiloxane, the cells in the organopolysiloxane rubber or elastomer are formed by the release of hydrogen gas when the mixture is heated at an elevated temperature, generally, between about 150~C. to about 200C.
The following examples further illustrate the practice of the invention, and they are meant to be exemplary only and are not to be construed as limiting the invention in any way.
EXAMPLE I
Sponging was accomplished by combining a hydrated silica reinforced silicone rubber compound with methyl hydride oil and a platinum catalyst. The ~ilicone rubber was 68.8 parts by weight polydimethylmethylvinyl siloxane and contained 29 parts by weight hydrated silica, 1.9 parts by weight silanol stopped polydimethylsiloxane fluid, 0.4 parts by weight vinyl tris(2-ethoxymethoxy)silane and 0.1 part by weigh~
~Z~ 8~
60-SI_4s7 -~3-of a typical heat age additive. The formulation contained 47 parts by weight of the above reinforced organopolysiloxane, 53 parts by weight of a 60 grit silicon carbide abrasive material, 1 part by weight methyl hydride oil and 1 part by weight platinum catalyst. The ingredients were uniformly mixed in a conventional rubber mill so that the abrasive grit was uniformly dispersed throughout the mixture. The mixture as prepared in the rubber mill, was placed in a mold 15.24 cm. (6 inches) x 15.24 cm. (6 inches) x 1.27 cm.
(0.5 inch). The mold was underfilled to allow room for expansion during the release of the hydrogen gas. At the elevated molding temperature, the hydride reacted with the water contained in the hydrated silica filler, and hydrogen gas was liberated to form the cells in the rubber. An open weave fabric was placed in the mold prior to placing the mixture therein to assist in the sponging operation by promoting the distribution of the hydrogen gas. The mold was heated at about 177C for abou~ 20 minutes. The slab of foamed organopolysiloxane having the silicon carbide abrasive therein, had a specific gravity of 1.42 compared with a specific gravity of 1.66 for the comparable non-foamed organopolysiloxane containing the same size and amount silicon carbide abrasive material. The blow ratio of the foamed organopolysiloxane containing the silicon carbide abrasive was 1.17. The abrasiveness of the compound was good, and the wear resistance of the slab compound as subjectively assessed, is good.
Abrasiveness was qualitatively determined by mounting a 5.08 cm. (~ inch) diameter by 1.27 cm. (0.5 inch) thick disk of the sponged composite on a portable 8~
electric drill which was then used to qrind various metal surfaces. The material displayed good abrasive and wear resistance properties.
EXAMPLE II
Sponging was accomplished by combining a fumed-silica reinforced silicone rubber compound with a blowing agent, organic peroxide catalyst and abrasive 1 n grit. The silicone rubber was 70.5 parts by weight polydimethylmethylvinyl siloxane and contained 1.0 part by weight of typical heat age and compression set additives, 5.4 parts by weight diatomaceous earth, 19.5 parts by weight of treated fumed silica, 0.2 parts by weight of vinyltriethoxy silane and 3.4 parts by weight methoxy stopp~d polydimethylsiloxane fluid. The formulation contained 47 parts by weight of the above fumed silica-reinforced silicone rubber, 53 parts by weight of an 80 mesh silicon carbide abrasive material, 0.4 parts by weight of benzenesulfonyl hydrazide blowing agent, 0.8 parts by weight of 2,4-dichlorobenzoyl peroxide and 2 parts by weight Verox powder, a 50
2,5-dimethyl-2,5-bis(t-butylperoxy~ hexane. The formulation was mixed and molded as described in Example I. The slab of foamed, cured organopolysiloxane having the silicon carbide abrasive therein, had a specific gravity of 1.24 compared with a specific gravity of 1.66 for the comparable non-foamed organopolysiloxane. The blow ratio of the foamed organopolysiloxane containing the silicon carbide abrasive was 1.34. Abrasiveness of the compound was excellent.
8~
While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such modifications as may be embraced within the following claims.
8~
While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such modifications as may be embraced within the following claims.
Claims (13)
1. An abrasive material having improved surface friction characteristics comprising:
a) an organopolysiloxane foam having cells therein which comprises from 15% to 85% by volume of the organopolysiloxane and being of a size ranging from about 0.001 cm to about 0.30 cm and b) an abrasive grit having a density of from about 60 pounds per cubic foot to about 95 pounds per cubic foot uniformly dispersed in said cells.
a) an organopolysiloxane foam having cells therein which comprises from 15% to 85% by volume of the organopolysiloxane and being of a size ranging from about 0.001 cm to about 0.30 cm and b) an abrasive grit having a density of from about 60 pounds per cubic foot to about 95 pounds per cubic foot uniformly dispersed in said cells.
2. An abrasive material as claimed in claim 1 wherein said abrasive grit is at least one selected from silicon carbide, finely-divided aluminum oxide, synthetic alumina, diamond, cubic crystal boron nitride and synthetic mullites.
3. An abrasive material as claimed in claim 2 wherein the organopolysiloxane is an addition cured organopolysiloxane.
4. An abrasive material as claimed in claim 3 wherein said addition cured organopolysiloxane is a hydrated silica-filled organopolysiloxane containing a silicon hydride.
5. An abrasive material as claimed in claim 2 wherein the organopolysiloxane is an organoperoxide cured organopolysiloxane foamed with a blowing agent.
6. A method of preparing an abrasive material comprising mixing an abrasive grit in an organopolysiloxane having an organopolysiloxane foam-forming agent there until the abrasive grit is substantially uniformly dispersed therein; heating the abrasive grit-containing organopolysiloxane at a temperature of about 50°C to about 300°C in the presence of a catalyst to foam and cure said organopolysiloxane.
7. The method of claim 6 comprising heating the organopolysiloxane having an organopolysiloxane foam-forming agent therein at a temperature of about 150°C to about 200°C.
8. The method of claim 6 wherein the organopolysiloxane is a hydrated silica-filled organopolysiloxane and a silicon hydride.
9. The method of claim 8 wherein the organopolysiloxane foam-forming agent is the silicon hydride and water in the hydrated silica filler, and hydrogen gas is released by the reaction of the silicon hydride and the water at elevated temperatures, thereby forming cells in the organopolysiloxane and foaming the organopolysiloxane containing the abrasive grit dispersed therein.
10. The method of claim 9 wherein the organopolysiloxane is simultaneously foamed and cured at the elevated temperature in the presence of a platinum catalyst.
11. The method of claim 6 wherein about 10 weight percent to about 70 weight percent abrasive grit (based on the weight of the organopolysiloxane) is incorporated in the organopolysiloxane.
12. The method of claim 6 wherein the cells formed in the organopolysiloxane containing the abrasive grit range in size from about 0.001 cm. to about 0.30 cm.
13. The method of claim 6 wherein the organopolysiloxane foam having the abrasive grit therein has a density of about 60 pounds per cubic foot to about 95 pounds per cubic foot.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US53829383A | 1983-10-03 | 1983-10-03 | |
| US538,293 | 1995-10-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1258182A true CA1258182A (en) | 1989-08-08 |
Family
ID=24146288
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000463820A Expired CA1258182A (en) | 1983-10-03 | 1984-09-21 | Foamed organopolysiloxane abrasive materials |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH0613696B2 (en) |
| CA (1) | CA1258182A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5849052A (en) * | 1995-04-28 | 1998-12-15 | Minnesota Mining And Manufacturing Company | Abrasive article having a bond system comprising a polysiloxane |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101160064B1 (en) * | 2006-07-14 | 2012-06-26 | 생-고벵 아브라시프 | Backingless abrasive article and a method of repairing optical media |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS48101694A (en) * | 1972-04-06 | 1973-12-21 |
-
1984
- 1984-09-21 CA CA000463820A patent/CA1258182A/en not_active Expired
- 1984-10-03 JP JP59206442A patent/JPH0613696B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5849052A (en) * | 1995-04-28 | 1998-12-15 | Minnesota Mining And Manufacturing Company | Abrasive article having a bond system comprising a polysiloxane |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60104654A (en) | 1985-06-10 |
| JPH0613696B2 (en) | 1994-02-23 |
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