US2389462A - Abrasive products and methods of manufacture - Google Patents

Description

concentrates in one part of the article.

Patented Nov. 20, 1945 ABRASIVE PRODUCTS AND METHODS OF ACTURE Robert L. Smith, Niagara Falls, N. Y., assignor to The Carborundum Company,

Niagara Falls,

N. Y., a corporation of Delaware No Drawing. Application April 17, 1940.

Serial No. 330,155

7 Claims.

This invention relates to abrasive products and methods of manufacturing the same. The invention is particularly concerned with abrasive products in which the binder comprises a prolamine of which zein, gliadin and hordein are examples. While my invention is particularly directed to the employment of prolamines as a binder for abrasives, I have found that they may be employed for other purposes as will hereinafter be described.

Abrasive articles are commonly divided into two general classes; one class comprising the bonded or molded articles wherein the individual abrasive grains are assembled into multilayered articles such as abrasive wheels and stones, the grains being joined together by means of a bond, and the other class comprising coated abrasives, an example of which is abrasive paper known as sandpaper. In this latter class of articles, the grains are customarily attached to a backing material, such as a sheet of paper or cloth, in a layer, as is obtained by distributing the abrasive grains over an adhesive coated surface, the abrasive coating being substantially one grain thick.

It is an object of the present invention to provide abrasive products and a method of manufacturing the same wherein a prolamine, and specifically the prolamine derived from corn known as zein, is employed as a binder. Another object of the invention is the provision of a relatively concentrated prolamine solution which is stable and non-gelling over reasonable periods of time. Another object of the invention is to provide a method of making bonded abrasive articles in which the bond comprises a substantial proportion of a prolamine.

In making bonded abrasive articles, it is necessary to'incorporate with the abrasive grains a bonding material in such a way that the bond is uniformly distributed throughout the mixture. The bond must also be capable of being fluxed so that it will attach itself to the abrasive grains and form the necessary bridge-work or bonding element between the individual grains. The bond, in order to insure uniformity in hardness which is the prime requisite of a satisfactory bonded abrasive article, must not move during the fluxing operation to the extent that it melts or flows and It is therefore another object of the invention to provide a method of fluxing the prolamine in the bonded abrasive article in order to insure the required bonding action between the abrasive grains.

Prolamines are one class of protein". Specifically they constitute vegetable proteins which have the common characteristic of being soluble in a mixture of alcohol and water containing -80% of alcohol and insoluble in absolute a1- cohol and in water. Since prolamines are mixtures of amino acids, they contain both amino groups and acid groups and, consequently, they react either as acids or bases. In fact, different constituents of the prolamines interact with each other under suitable conditions, as by heating or even allowing to stand in the presence of a sufficient proportion of water, to form more complex compositions which are insoluble and more brittle than the original compositions. Although I may use various prolamines, in describing my invention I will refer particularly to zein, it being understood, however, that other prolamines may be substituted in whole or in part for zein.

Zein is obtainable commercially under the trade-name Maizite" in the form of a powder which ordinarily contains from 5% to 8% free water. The powders are loose and free-flowing. Upon admixing with water and heating, they can be formed into a doughy mass, but water alone is not enough of a solvent to put the zein into solution. Water may be stated to plasticize the zein sufficiently to make it possible to mold the powder into a dough.

In making coated abrasive articles, which is one modification of my invention, it is necessary to liquefy the adhesive which is used to attach the abrasive grains to the backing, and to prepare the solutions in sufficient concentration that enough binder can be deposited in one coating operation to attach the grains strongly enough that they will not be displaced when they are given a second or sizing coating. Generally speaking, it is necessary to use solutions containing at least 40% of solids in order to satisfy this requirement.

One of the problems involved in the use of prolamines in connection with coated abrasive articles is the production of solutions which are concentrated enough to meet these above-mentioned requirements, and yet be sufiiciently stable that they do not thicken nor gel before they can be applied to the backing. It is a characteristic of the prolamines that their solutions tend to increase in viscosity and to gel unless the solutions are relatively dilute.

Another problem involved in the preparation of adhesive films in the manufacture of coated abrasive articles is the deposition of a dense strong solid film. If the prolamines are dissolved in a relatively low boiling solvent, such as the alcohoi and water mixtures customarily recommended for them, the rate of evaporation of the solvent is so great that the prolamines solidify on their upper surface and the removal of the remainder of the solvent in the body of the filnr results in the deposition of a porous, spongy him which is entirely unsuitable for attaching abrasive grains to the'backing.

I have found that prolamine solutions satisfactory for use in the manufacture of abrasive products, as well as for other coating and for impregnating purposes, canbe made in a mixture of certain organic solvents and water. In making such solutions it is desirable to use as large a proportion of water as possible for the obvious reasons that water is cheaper and involves no health or fire hazards. Furthermore, up to certain optimum conditions, mixtures containing higher percentages of water will dissolve more zein. Solvents which may be mixed with water to form solutions of my invention include furiural alcohol, diacetone alcohol and ethylene glycol mono-ethyl ether which is marketed under the trade name Cellosolve." However, such mixtures are not stable and it is necessary to add a small percentage of a stabilizer such as acetic acid with the more concentrated solutions containing relatively large proportions of water in order to prevent increase in viscosity and premature gelling. By suitably adjusting the proportion of the organic solvent and water and adding the stabilizer, it is possible to prepare solutions containing as much as 50% of zein which will be sufiiciently stable and non-gelling.

The films deposited from the solutions above described are characterized by relatively poor resistance to water. Films which are more resistant to the action of moisture can be prepared by dissolving the zein in solvents containing phenol condensation products such as are represented by the products sold under the trade name Bakelite." In preparing such solutions, it-is necessary to employ as the organic solvent a liquid which is a solvent for the phenolic resin. Such liquids include furan derivatives such as furfural or furfural alcohol, and mixtures of cresol with furfural. The phenolic resin is usually employed in the liquid A stage, which is the liquid obtained in the earlier stage of the condensation reaction between phenol and formaldehyde. By employing suitable proportions of the solvents, the liquid resin and the zein, it is possible to prepare solutions which will be satisfactory as the liquid adhesive in the manufacture of coated abrasives. Generally speaking, a relatively small proportion of the phenolic resin is suflicient to make the adhesive practically insoluble in water.

In making the bonded abrasives with the pro-. lamines it is particularly important to have the ultimate binder highly resistant to water. One method which I have used to bring this about comprises the employment of the liquid phenolic resins, preferably along with other resin solvents such as a mixture of cresol and iurfural, as a wetting agent, which is applied to the abrasive 65 grains. This is followed by mixing the liquidcoated grains with the powdered zein. Having prepared a mixture of this character, the articles are molded under pressure and after removal from the mold, they may be cured by suitable 7 heat treatment to develop the necessary strength and water-resistance in the final article,

I have given general directions for the preparation of adhesives for the manufacture oi coated abrasives and for preparing mixtures suitable for 75 to 125 F. with grams of a mixture of 70% molding into abrasive wheels and stones. I will now describe my invention with particular reference to a number of specific examples, it being understood that such examples are given for illustrative purposes only and are not limitative.

Example I 900 grams of #36 grit abrasive grain were wet with 50 grams of a mixture of 25 grams of liquid phenolic resin and 25 grams of 50/50 cresolfurfural. 100 grams or Maizite" were mixed therein to form an even coating about each individual abrasive grain. The mixture described above,which is a distributable type of mixture, was cold molded by pressing at about 1000 lb. per sq. in. pressure. After removing from the mold, a cure of 15 hours at'250-2'75 F. was found sumcient to flux the bond and form a composite abrasive article having satisfactory strength and exceptional grinding characteristics.

Example II 900 grams of #36 abrasive grain were wet with 50 grams of liquid phenolic resin. 100 grams of powdered zein were mixed therein to form an even coating about each individual abrasive grain. The coated abrasive grains were then molded and cured as in Example I.

Example III An adhesive suitable for making coated abrasives was prepared as follows: parts by weight of "Maizite" were stirred with 45 parts by weight of furfural alcohol to suspend the zein in the liquid. The "Maizite was put into solution by warming to 125 F. and by the addition of 30 parts by weight of H20. After cooling to about 75 F. the final coating solution was prepared by mixing in 5 parts by weight of a liquid phenolic resin. Such an adhesive mixture may be diluted by addition of equal parts of furfural alcohol and water.

Example IV 2000 grams of Maizite were dissolved by stirring at -'75 F. with 2400 grams of a 65 "Cellosolve-35 water mixture. After the solids had gone into solution, 200 grams of concentrated NI-IrOH solution were added to give increased stability to the coating solution. Such an adhesive may be further diluted by addition of a solvent mixture containing equal parts of "Cellosolve and water.

Emample V A coating adhesive suitable for making abrasive papers was prepared as follows: '70 parts by weight of Maizite were dissolved by stirring at 125 F. with 70 parts by weight of a mixture of 50 parts phenol and 20 parts water. After complete solution had taken place, 10 parts by weight of a liquid phenolic resin were added and the solution cooled to -60 F. at which temperature it is ready for use.

Example VI 50 grams of Maizi were dissolved by heating Cellosolve" and 30% E20. After solution, 25 grams of a liquid phenolic resin were added and the mixture cooled to 15 B. About 10 grams of a 5% caustic solution were stirred in to stabilize the solution and increase its resistance toward gel formation.

Example VII 40 parts by weight of "Maizlte" were dissolved in 60 by weight of a mixture of 70% butyl Carbitol and 30% water by warming to 125' 1'. Such a solution when cooled to 75-80 F. was found suitable as a coating adhesive.

Example VIII 1400 grams of "Maizite" were dissolved in 1800 grams of the following solvent mixture: 1400 grams of .90 ethyl alcohol-10 water and 400 grams of 90 diacetone alcohol-l water solution.

The mixture was warmed until complete solution had taken place. After cooling to 75 F., 70 grams of glacial acetic acid were added as a stabilizer against gelation.

Exam le us Example I Abrasive P per was prepared with the adhesive of Example IX by coating 9. paper backing with the adhesive in an amount sufilcient to leave 3 to 3.5 pounds of solids per sandpaper makers ream of 480 sheets 9" x 11". 80 grit fused alumina abrasivegrain was applied to the adhesive to the extent of 22 pound per ream, the adhesive was dried, and a sizing coat, made by diluting the making coat with equal parts of a mixture of equal parts of Cellosolve" and water, was coated over the abrasive grains in an amount suincient to leave 2.5 to 3 pounds per ream of solids. The coated article was then air dried for 2'hours and heat treated at 225 F. for 3 to 4 hours. The resulting product was an excellent wood-working abrasive paper".

aasases As stated hereinabove, I have also found that the prolamines, when suitably combined with solvents, can be used for other purposes than for the manufacture of abrasive products. For example, by forming solutions of the general character described above, protective film may be formed by painting, spraying, rolling, or otherwise applying a layer of the solution which upon removal of the solvents deposits a strongly adherent and tough film which is resistant to oils and greases and, particularly when modified by the inclusion of phenolic condensation products,

is resistant also to moisture. Another particular use to which I have put the solution is the preparation of backing materials by impregnating or saturating a fabric, such as cheese-cloth, with the solution to' form a continuous film of the prolamine composition carrying the fabric reinforcement embedded in it. Such products are adapted for a number of purposes such as wrappings, for backings for abrasive products, or for adhesive tapes such as those made with a permanently tacky and pressure sensitive type of adhesive. An example of this modification of my invention is as follows:

Example XI A flexible backing material was made by coating onto a cheese cloth as a carrier base the following mixture: 70 grams of "Maizite," 70 grams of fine kaolin, 140 grams of a solvent containing 75% "Cellosolve" and 25% E20, and 35 grams of triethanolamine. The above mixture was applied to the cheese cloth base in such a manner as to perties of the ultimate film form. when dry. a continuous sheet of resinous material.

The-solutions of my invention may be also employed for impregnating purposes such as the impregnation of for abrasive articles or the impre nation of very p rous sheets of fibrous material such as are obtained by felting cellulose fibres. Examples of this application of the solutions are as follows:

Example XII -urea formaldehyde impregnating composition was" prepared as A Maizi and moldin follows:

25 parts by weight of "Maizite" were added to parts by weight of a liquid urea-formaldehyde resin sold under the trade name "#840 Lauxite." with stirring until a smooth dispersion resulted.

A sheet of felted sisal weighing 12 oz. per sq. yard was coated on bothsides with the resin dispersion until the interstices between the fibres were well filled. After drying at 1''. until 75% of the volatiles were removed, the impregnated sheet was pressed at 250 lbs. per sq. in. at 250 F. for five minutes. At the end of this time the resin was transparent and showed good fusion. Residual moisture should be removed, either by further air drying or by oven heating at low temperatures, to form a tough, horny Product.

Example XII! ible waterproof bond and grit was then applied by a conventional sandpaper method to form the finishedabrasive article; Such a. backing when used wet became very fiexible due to the presence of the water plasticizable zein filler incorporated in the original sheet.

In preparing the solutions or mixes, the proor bond may be modified by the inclusion of suitable addition agents. For example, additional rigidity may be imparted by the inclusion of inert filling materials such as pulverized flint, while added flexibility may be imparted by adding suitable plasticizers such as high boiling'liquids which are compatible with the prolamine mixture.

In making coated abrasive products, it is desirable to bring about a certain amount of reaction between the constituents of the zein in order to impart increased strength and toughness. This may be accomplished by permitting the products to stand at ordinary temperatures for several days while there is still some water in the films. Underthese conditions, a reaction appears to take place which. strengthens and toughens the films. A similar result may also be accomplished by heating the products for a few hours at temperatures up to about to 200 F. Heating for a long period of time or at higher temperatures sometimes advances the products to the stage where they become brittle rather than strong, and consequently. it is desirable to avoid an over-cure. Similarly, in setting up the bonds in the molded articles, where mixtures of the phenolic resins with the zein are used as the bond, it is necessary to heat treat and cure the phenolic part of the binder, but it is also desirable to avoid a heat treatment which is either too we- D Der to make strong backings tracted or conducted at too high a temperature, in order to avoid the embrittling o! the zein constituent of the bond.

Instead of mixing the prolamine with the abrasive grains and effecting reaction in the abrasive mixture, I have found that the pro]- amines may be initially modified by reaction with furan derivatives such as furfural alcohol to provide resinous materials having new and unusual combinations of properties. An example of this feature of the invention follows:

Example XIV A resinous reaction product of zein and furfural alcohol was made as follows:

100 grams of Maizite were dissolved in a mixture of 75 parts ethyl alcohol and 25 parts water, 40 grams of furfural alcohol were then added andthe reaction started with the mixture at 75 F. by the addition drop by drop of a 35% HCl solution until drops had been added.

After standing for 12 hours, the reaction mixture was considerably darkened and films of this material formed by drying at 225 F; were tough and black in color. Upon standing an additional 12 hours the reaction mixture was solidicombination of physical properties of the bonding material and the adhesion of the bond to the abrasive grains, it is possible by the employment of my invention to provide abrasive articles having abrading characteristics not found with bonds heretofore used.

As stated, the compositions of the present in.- vention are relatively stable and are unusually satisfactory for thepreparation of coated abrasive products as a substitute for glue, particularly where the products are to be used in relatively humid climates, under which conditions glue has a, tendency to absorb moisture and soften.

I have described my invention in considerable detail and have included certain specific examples by way of illustration. It will be understood, however, that the invention has broader utility than the specific fields mentioned and that the compositions herein disclosed may be altered and modified to fit particular purposes. The invention, therefore, is not considered to be limited aaeaaea to the particular materials and compositions herein described, but rather to be defined by the scope or the appended claims.

I claim:

1. The method of making bonded abrasive articles which comprises wetting abrasive grains with a liquid comprising a liquid heat-hardenable phenolic resin in the proportion of approximately 50 parts by weight of the liquid to 900 parts of the abrasive, mixing the wetted grains with approximately parts of powdered zein,molding an article from the mixture, and heating the article at a temperature of about 250-2'l5 F. to cure the bond.

2. The method of making bonded abrasive articles which comprises wetting abrasive grains wit a l q c p in a liquid heat-hardenable phenolic resin and a furane derivative in the proportion of approximately 50 parts by weight of the liquid to 900 parts of the abrasive, mixing the wetted grains with approximately 100 parts of powdered zein, molding an article from the mixture, and heating the article at a temperature of about 250-2'75 F. to cure the bond.

3. A molded abrasive article such as an abrasive wheel or stone comprising abrasive grains joined together by a bond comprising the heat-hardened reaction product of a mixture comprising a liquid heat-hardenable phenolic resin and a powdered prolamine.

4. A molded abrasive article such as an abrasive wheel or stone comprising abrasive grains joined together by a bond comprising the heat-hardened reaction product of a mixture comprising a liquid heat-hardenable phenolic resin and powdered zein.

5. The method of making a molded abrasive article which comprises preparing a moldable mixture comprising abrasive grains, a liquid heathardenable phenolic resin and powdered zein, molding an article from the mixture. and heating the article to cure the bond.

6. A method of making bonded abrasive articles which comprises wetting abrasive grains with a liquid comprising a liquid heat-hardenable phenolic resin, mixing the wetted grains with a powdered material containing a substantial proportion of zein to form a moldable mixture, molding an article from the mixture, and heating the article to cure the bond.

7. A method of making bonded abrasive articles which comprises wetting abrasive grains with a liquid comprising a liquid heat-hardenabie phenolic resin and a furane derivative, mixing the wetted grains with a powdered material containing a substantial proportion of zein to form a moldable mixture, molding an article from the mixture, and heating the article to cure the bond.

- ROBERT L. SMITH.