US2217525A - Abrasive paper and process of making the same - Google Patents

Description

Patented Oct. 8, 1940 UNITED STATES PAT THE SAME

Nicholas E. Oglesby, Troy, N. Y.,' assignor to Belm- Manning Corporation, Troy, N. Y., a corporation of Massachusetts No Drawing. Application July 6, 1936,

- Serial No 89,268

16 Claims.

The invention relates to abrasive paper, commonly known as sandpaper, and the manufacture thereof, and with regard to its specific features toa waterproof abrasive paper.

One object of the invention is to provide a flexible abrasive paper. Another obfiect of the invention is to provide an abrasive paper which has high wet strength. Another object of the invention is to provide .waterproof abrasive paper which will not deteriorate rapidly with age. Another object of the invention isto provide waterproof abrasive paper resistant to cracking. Another object ofthe invention is to provide a process which produces a flexible abrasive paper. Another object of the invention is to produce various degrees of. flexibility in sandpaper. Other objects of the invention are to provide a simple, inexpensive and safe process for the production of sandpaper which can be readily controlled in 20 commercial use. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts, and in the several steps and relation andorder of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In carrying out the invention, I make use of any known machine for the production of paper from stock, as for example a Fourdrinier machine or a cylinder machine. I provide as a base paper stock any suitable furnish, for example rope, chemical wood pulp, purified wood pulp, lute, or

combinations thereof, and I may also use a certain amount of cotton or linen fiber. The stock may be disintegrated for the paper making machine in a beater with the beater roll lifted, in order to avoid hydration of the paper. then beat the stock to some extent, but preferably in order to introduce a maximum amount of materials hereinafter specified into the stock I avoid subsequent beating. The stock is then directed to the flow box of the Fourdrinier machine or the vats of a cylinder paper making machine and cient boric acid practically to neutralize the alkalinity of the viscose solution. The treatment of the paper with the solution of viscose may be 5 effected by means of a tub sizer or the like. To

machine, I treat it with a 1% solution of viscose as cellulose which has been pretreated with suifithe viscose solution I may add ammonium carbonate in suflicient quantities such that the liberation of carbondioxide during a subsequent drying operation may tend to complete the regeneration of the cellulose, such completion of regeneration being subject to control through the amount of ammonium carbonate added. In the type of product described, which is to be subsequently impregnated with an emulsion, it may sometimes be desired that this regeneration be incomplete in the base paper, since thereby a greater absorbency is accomplished. A subsequent heat treatment after the oil emulsion application completes the regeneration and develops a high degree of wet strength. If required. wetting agents 15 such as 'a neutralized sulphonated product of one or more of the oils, fats, higher alcohols and naphthalene derivatives may be added to the viscosesolution further to increase the absorbency of the finished paper.

In lieu of proceeding exactly as above specified, I may add the viscose in the beater, but I prefer to add it thereafter as better results are usually obtained by adding the viscose to the paper after the paper web is formed.

Subsequent to the treatment with the viscose, with or without the othr ingredients, and according to any of the methods of application as hereinbefore specified, the paper is dried. Thereafter I treat the paper with a flexible oil or resin. 3 I cause the paper to absorb an amount thereof which will leave in the dried paper, matter from about to 150% of the original paper weight. The flexible oil or resin may be applied by means of a tub sizer or thelike. The process, 5

so far as the application of the viscose and the flexible oil or resin are concerned, may I be continuous, if desired; that is to say, tub sizers for each may be provided at different positions along the drier. 0n the other hand, the 40 flexible oil or resin may be applied after the paper is removed from the drier.

' The fatty oils are particularly useful in this invention. By the fatty oils I mean to include 1 Pounds Heavy blown soya bean 011---; 100 Oleic acid 6.6 Triethanolamine 3.5 Water 100 55 the non-drying fatty oils such as castoruoil, the 5 or Whirlwind mixer.

Sodium hydroxide The triethanolamine should be added to the water and the oleic acid to the bean oil. The oil is then added slowly to the water while agitating with a high speed mixer, such as a Lightning The soya bean oil may be replaced with dejelled linseed oil or other suitable flexible oils. Likewise, flexible resins may be used.

The mixture prepared as specified is a water emulsion of the oil or resin. The product is made more flexible by the use of water to wet and to swell the fibers. Preferably the water has a pH of 7.2 or more. The fibers, being wet with water, are not readily wetted by the oil, varnish or resin.

In the drying process, while the fibers are still wet with water, the oil or resin is set to a flexible and a pliable but relatively immobile state, and the fibers being swollen and wet with water on their surfaces are not bound together to the extent that they would be if oils or resins, with or without organic solvents, were applied to dry paper. Subsequently, evaporation of the water and shrinkage of the fibers result in the production of a less dense saturated product than those produced heretofore. Small voids or pore spaces within the final product serve to relieve compressive and tensile stresses which inhibit flexibility.

Instead of the formula above given I may use the following:

I Pounds Heavy blown China wood oil 100 Oleic acid 3 Nopco B" (neutralized sulphonated corn oil) Water 100 In the case of either formula the oil in water emulsion is preferable to a water in oil emulsion, but a water in oil emulsion may in certain cases be used.

As an alternate method in which the paper flbers are swelled with water, I may first. saturate the paper with water containing oleic acid and triethanolamine in theproportion of 6.3 to 3.5, and in such concentration that thepaper will take up 6 to 20% of thecombin-ed solids in the form of solution, and then apply hot oil to the paper while it is still wet. The paper should contain at least 18% and preferably more moisture at the time the oil is applied. a

In either process, that is the emulsion process or the process in which the oil is applied to the wet sheet, the oil, varnish or resin used, as the case may be, should preferably be viscous and capable of being set to a relatively immobile state within a short time after heat is applied. A suitable viscosity for the heavy blown soya bean oil used by way of illustration is from about 18 poises to about 40 poises at 140 F. A suitable viscosity for the heavy blown China wood oil is from abbut 16 poises to about 4.? poises at 77 F..

I have discovered that the most flexible results will be obtained where a semi-drying oil, such as soya bean oil or dejelled linseed oil,is used. By dejelled linseed oil I mean an oil that has been produced by partially cracking a jelled linseed oil to destroy the firm linseed oil jelly and'produce instead thereof, a viscous definitely fluid product. Such dejelled linseed oil, soya bean oil, and similar semi-drying oils, when dried or set, tend to producea very flexible and firm jelly, but

under ordinary conditions of drying or curing do not set up to give a final product which is as hard or tough as China-wood oil similarly cured,

, comparatively flexible.

I may produce degrees of flexibility intermediate between that produced with soya bean oil 'on the one hand and China-wood oil on the other hand by using an emulsion of mixed soya bean and China-wood oils. A suitable emulsion for this purpose may be produced by replacing 25% of the soya bean oil shown in Example I by an "equivalent weight of China-wood oil. In this case the product will be less flexible than that produced with soya bean oil, but more flexible than that produced with China-wood oil, and the permeating 'medium will have a tensile strength intermediate between thetensile strengths produced by either oil.

In order to obtain specific properties for speciflc uses, I may use emulsions of various flexible varnishes and flexible resins, prepared with a variety of emulsifying agents, but I prefer to use in most cases for the emulsifying agent triethanolamine oleate since this material has to a high degree a softening or plasticizing effect on cellulose. As an alternative, however, I may use triethanolamine linoleate or triethanolamine palmitate, since these substances also are not only emulsifying agents but also have'a definite plasticizing or softening effect upon paper and similar cellulosic bodies.- As a plasticizing agent for the paper I may also add glycerine, diethylene glycol, triethylene glycol or sorbitol. Of these substances I prefer sorbitol as it is less subject to the influence of moisture, less volatile and more permanent.

With regard to the manner of application of the emulsions or any of them to the paper, I prefer a temperature of application of in the neighborhood of 90 F. This temperature will be varied somewhat with various emulsions and conditions of operation, and I note that the use of higher temperatures facilitates the ready saturation of the web with the emulsion but raising the temperature causes less stability of the emulsion.

The correct preparation of the base paper to be treated is important. The paper should have high wet strength in order that it may withstand the treatments hereinbefore specified and this is more especially so'in cases in which the oil or resin is applied after the paper is removed from the drier. In such a case the paper has to be put through a separate-paper handling equi ment and ought to be strong enough to withstand the treatment without breaking. The ad dition of the viscose solution is what gives this added wet strength according to the foregoing disclosure, but as an alternative I may use, instead of viscose, a solution of glue and glycerine to which I prefer to add paraformaldehyde to tan the glue. In this embodiment of the invention, I may use 8 to 18% of '70 millipoise glue and 12 to 24% glycerine, percentages being of the weight of the paper, in tub sizing equipment or after the paper is removed from the drier of the paper agent.

making machine. Still another manner of achieving wet strength is to apply, as specified for glue and glycerine, glue and sorbitol in the same proportions. Sorbitol is preferred to glycerine in that the product is thereby less subject to changes in its properties with changes in moisture. Furthermore, sorbitol is less volatile and. more permanent than glycerine. By way of comparing these alternatives for achieving wet strength, I note that viscose, in the proportion specified, results in more flexibility to the paper, while tanned glue glycerine and tanned glue sorbitol, used as specified, result in higher wet strength. A particular advantage of the use of viscose lies in the fact that but a small percentage of solids are thereby incorporated into the paper; there are no added problems of chemical incompatibility in subsequent treatments, because the viscose used is regenerated to form cellulose which is chemically the same as or similar to base paper stock.

Instead of using paraformaldehyde to tan the glue, I may use any other suitable agent, such as formaldehyde, which is preferably added to the treated sheet as a 10 to 15% solution thereof in water, or on the other hand hexamethylene tetramine may be added to-the glue solution or as a separate solution like the formaldehyde.

By my process as described in the various embodiments thereof, it is possible to produce a saturated paper which is more pliable or flexible than the original base paper stock. I believe one important distinction to be this: I avoid the encasing-of fibers of the paper with a layer of cured oil or resin. In processes which have been used to impregnate paper previously I believe that there has resulted an encasing of the fibers with cured oil or resin, usually while hot and dry and in a shrunken condition, with the result that subsequent absorption of moisture has caused a swelling of the fibers which then exerted a force against the encasing layer. In such a condition the fibers have been less pliable than the original paper since they were too tightly bound together.

Furthermore, I believe that in the past the individual fibers have been bound together by the impregnating material, thereby definitely stiffening the product even though the bonding medium is itself flexible. I further believe that by wetting and swelling the fibers with water either simultaneously with or prior to the impregnation, I avoid both the rigid encasing and the excessive bonding together of the fibers. As confirmation of my theory I point to the fact that the present product is less dense than a product treated with oils without a swelling Not only is water which I use a swelling agent but glycerine and sorbitol are such also. Additional reasons why I am enabled to achieve the results as to flexibility specified reside in the fact that soya bean oil or dejelled linseed oil are more flexible than the paper fibers and also in the fact that triethanolamine oleate has a softening action upon the paper fibers. The latter is true also of sorbitol, glycerine and triethanolamine glycol. These same materials also soften glue.

Where the paper saturated in accordance with the present invention is to be used immediately for coating, usually the curing of the oils or resins attained on the drying drum subsequent o tub sizing will suffice and avoid spontaneous combustion, and the final curing of the impreghating material may be carried out simultaneously with the final curing of the coating material hereinafter described. Otherwise, and especially where China Wood oil or linseed oils are. employed, I further cure the impregnated paper with heat, for example in a drying room equipped for festooning the web, for example using aheat of from 130 F. to 175 F. for a period of approximately 8 to 24 hours.

The paper stock for carrying out the invention and the adjustment and type of paper making machine may be such as to produce a paper weighing lbs. to the paper ream, in order satisfactorily to carry out the invention in any of the embodiments. However, higher or lower weights may be used according to the product desired.

Having thus made the paper base, I use it for backing in the production of sandpaper, which is waterproof to a greater or lesser degree, by applying upon said paper base the following:

(1) A coat of varnish or flexible resin,

(2) A coat of abrasive grains or grits such as emery, fused alumina, silicon carbide, garnet or other abrasive material, and

(3) A sizing coat of varnish or flexible resinous material applied over the abrasive grains or grits.

I may furthermore apply a sizing coat of drying oil, such as China wood oil or varnish, to the paper backing before the first of the abovementioned applications. As a binder for hold ing the grit and as a sizing coat which is applied over the grit, the compositions disclosed in U. S. Letters Patent No. 1,565,028 to Francis G. Okie may be used; also those in Reissue Letters Patent No. 17,584 to Francis G. Okie, or I may employ as binders or sizing coats the oil' modified glyptals or varnishes preparedby the dissolving of soluble phenolic resins in China wood oil during the varnish making process.

The foregoing process permits a definite control over the flexibility of the product during its fabrication. According to the particular saturating composition used, various degrees of flexibility may be obtained. Where one of the more flexible papers produced in accordance with this invention is embodied in a waterproof sandpaper, such is very definitely flexible and to a higher degree than products heretofore known. By reason of the fact that the backing is extremely flexib1e,, it is possible to use harder and less flexible binders and sizing coats for the grit, Without producing sandpaper which is too stiff for practical use and which is subject .to peeling or flaking of the coat.

It is customary to soak waterproof sandpaper in water, often warm water, before using in order to increase the flexibility of the product, flexibility being conducive to conformity of the sheet to the contour of the work and to the production of a better finish than a stiffer product where the same grit size is used. When heretofore existing waterproof sandpaper was soaked to increase its flexibility, there wasa material decrease in the strength of the backing. The Wet strength treatment embodied in the present process is effective in producing a product having high strength following the customary soaking and in use. Therefore, the product is more resistant to mechanical disintegration when used in the subsequent hand or machine sanding operation. Furthermore, triethanolamine oleate serves as a plasticizer for the cellulose and less soaking is required to produce the desired degree of flexibility. The low density or porosity,

of the backing and the presence of the plasticizer, such as triethanolamine oleate, increases the rate of softening when the product is soaked.

It will thus be seen that there has been provided by this invention a method and an article in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. The product made in accordance with claim 5 comprising porous base paper, said porous paper having its pores incompletely filled with a water-resistantmedium dried to a flexible condition, said water resistant medium being selected from the group consisting of semi-drying oils, drying oils and flexible resins, said waterresistant medium being present to the extent of from to 150% of the weight of the paper fibres and a coat of abrasive grits held to said treated paper by a binder comprising a member selected from the group consisting of varnishes and resins, said composite product being water-resistant and not subject to cracking when bent, and the bond between the abrasive grains and the base being of a nature that will prevent splitting or peeling when the composite article is subjected to flexing and bending in normal handling and use.

'2. The product made in accordance with claim 5 comprising porous base paper, said porous paper having its pores incompletely fllled with a water-resistant medium dried to a flexible condition, said water-resistant medium being selected from the group consisting of semi-drying oils, drying oils and flexible resins, said waterresistant medium being present to the extent of from 50 to 150% of the weight of the paper 5 fibres, said porous paper also containing a softening agent, and a coat of abrasive grits held to said treated paper by a binder comprising a member selected from the group consisting of varnishes and resins, said composite product being water-resistant and not subject to cracking when bent, and the bond between the abrasive grains and the base being of a nature that will prevent splitting or peeling when the composite article is subjected to flexing and bending in normal handling and use.

3. The product mad-e in accordance with claim 5 comprising porous base paper, said porous paper having its pores incompletely filled with a water-resistant medium dried to a flexible condition, said wa ter-resistant medium being selected from the group consisting of semi-drying oils, drying oils and flexible resins, said waterresistant medium being present to the extent of from 50 to 150% of the weight of the paper flbres, said porous paper containing an agent adapted to impart wet strength to the paper, and a coat of abrasive grits held to said treated paper by a binder comprising a member selected from the group consisting of varnishes and resins, said composite product being water-resistant and not subject to cracking when bent, and the bond between the abrasive grains and the base being of a nature that will prevent splitting or peeling when the composite article is subjected to flexing and. bending in normal handling and use.

4. The product made in accordance with claim 5 comprising porous base paper, said porous paper having its pores incompletely filled with a water-resistant medium dried to a flexible condition, said water-resistant medium being selected from the group consisting of semi-drying oils, drying oils and flexible resins, said waterresistant medium being present to the extent of from 50 to 150% of the weight of the paper fibres, said porous paper containing a softening agent and an agent adapted to add wet strength to the paper, and a coat of abrasive grits held to said treated paper by a binder comprising a member selected from the group consisting of varnishes and resins, said composite product being water-resistant and not subject to cracking when bent, and the bond between the abrasive grains and the base being of a nature that will prevent splitting or peeling when the composite article is subjected to flexing and bending in normal handling and use.

5. A process of producing coated abrasives comprising using paper of suitable porosity, treating the paper with a water-resistant saturating medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate in the paper the saturating medium to the extent of from 50 to 150% of the base paper weight, said incorporation of said medium in the paper taking place in the presence in the paper of above substantially 18% of water, the percentage of water being figured on the base paper weight, drying thesaturated paper and applying to said saturated paper a flexible waterresistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which it not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

6. A process of producing coated abrasives comprising using paper of suitable porosity, such that from 50 to of a saturating medium may be absorbed, saturating the paper with an aqueous emulsion of a water-resistant medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base paper weight, drying-the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group consisting, of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable,

composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

'7. A process of producing coated abrasives comprising using paper of suitable "porosity, such that from 50m 150% of a saturating medium may be absorbed, including in the paper an agent adapted to soften the paper, saturating paper with an aqueous emulsion of a water-resistant medium which is flexible when set and selected from the group consisting of semi-drying oils. drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base paper weight, drying the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

8. A process of producing coated abrasive comprising using paper of suitable porosity such that from 50 to 150% of a' saturating medium may be absorbed, including an agent adapted to add wet strength to the paper, saturating the paper with an aqueous emulsion of a water-resistant medium which is flexible when set, and selected from the group consisting of semi-drying oils, drying oils and flexible resins to "incorporate therein themedium to the extent of from 50 to 150% of the base paper weight, drying the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

9. A process of producing coated abrasives comprising using paper of suitable porosity such that from 50 to 150% of a saturating medium may be absorbed, including an agent adapted to soften the paper and an agent adapted to impart wet strength to the paper, saturating the paper with an aqueous emulsion of a water-resistant medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base paper weight, drying the saturated paper and applying to said saturated paper a flexible waterresistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which tlg bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

10. A process of producing coated abrasives comprising using paper of suitable porosity, such that from 50 to 150% of a saturating medium may be absorbed, including in the paper as an agent adapted to soften the paper, a member selected from the group consisting of glycerine and sorbitol, saturating the paper with an aqueous emulsion of a water-resistant medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base paper weight, drying the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable,

- composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

11. A process of producing coated abrasives comprising using paper of suitable porosity such that from 50 to 150% of a saturating medium may be absorbed, including regenerated cellulose in the paper as an agent to add wet strength to the paper, saturating the paper with an aqueous emulsion of a water-resistant'medium which is flexible when set, and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base paper weight, drying the saturated paper and applying to said saturated paper a flexible waterresistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

12. A process of producing coated abrasives comprising using paper of suitable porosity such that from 50 to 150% of a saturating medium may be absorbed, including in the paper tanned glue-glycerine as an agent adapted to add wet strength to the paper, saturating the paper with an aqueous emulsion of a water-resistant medium which is flexible when set, and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base paper weight, drying the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group con-- sisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a-durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

13. A process of producing coated abrasives comprising using paper of suitable porosity such that from 50 to 150% of a saturating medium may be absorbed, including in the paper tanned glue-sorbitol as an agent adapted to add wet strength to the paper, saturating the paper with an aqueous emulsion of a water-resistant medium which is flexible when set, and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate therein the medium to the extent of from 50 to 150% of the base pap-er weight, drying the saturated paper and 'applying to said saturated paper a flexible water-resistant binder coating com prising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which isnot subject to cracking when bent and in which the bond between the binder coat and the base is maintained when thearticle is subjected to flexing and bending in normal handling and use.

14. A process of producing coated abrasives comprising using paper 01' suitable porosity, including in the paper an agent adapted to add wet strength to the paper, treating the paper with a water-resistant saturating medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate in the paper the saturating medium to the extent of from to of the base paper weight, said incorporation of said medium in the paper taking place in the presence in the paper of above substantially 18% of water, the percentage of water being figured on the base paper weight, drying the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive g'rits, and setting the binder, whereby a durable composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

15. A process of producing coated abrasives comprising using paper oisuitable porosity, including in the paper an agent adapted to soften the paper, treating the paper with a water-resistant saturating medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate in the paper the saturating medium to the extent of from 50 to 150% of the base paper weight, said incorporation of said medium n the paper taking place in the presence in the paper of above substantially 18% of water, the percentage of water being figured on the base paper weight, drying the saturated paper and applying to said saturated paper a flexible waterresistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating ofabrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

16. A process of producing coated abrasives comprising using paper of suitable porosity, including in the paper an agent adapted to soften the paper and an agent adapted to impart wet strength to the paper, treating the paper with a water-resistant saturating medium which is flexible when set and selected from the group consisting of semi-drying oils, drying oils and flexible resins to incorporate in the paper the saturating medium to the extent of from 50 to 150% ,of the base paper weight, said incorporation of said medium in the paper taking place in the presence in the paper of above substantially 18% of water, the percentage of water being figured on the base paper weight, drying the saturated paper and applying to said saturated paper a flexible water-resistant binder coating comprising a member selected from the group consisting of varnishes and resins, and a coating of abrasive grits, and setting the binder, whereby a durable, composite waterproof abrasive article is formed which is not subject to cracking when bent and in which the bond between the binder coat and the base is maintained when the article is subjected to flexing and bending in normal handling and use.

NICHOLAS E. OGLESBY.

CERTIFICATE OF CORRECTION. Patent No. 2,217, 2 October 8, 191m.

NICHOLAS E. OGLESBY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page L second column, line L O, claim 5, for the word "it" read --is-; line 71, claim 7, after "saturating" insert -the--; page 5, first column, line 114., claim 8, for "abrasive" read abrasivesand that the sa'idlletters Patent should be read with this correction therein that the same may conform to the record of the case in the 'Patentoffice.

, Signed and sealed this 17th day of December, A. D. 19).;0.

Henry Van Arsdale, (Seal) Acting Commiseioner of Patents.