US2013925A - Sheet abrasive and method of making the same - Google Patents

Description

Sept. 10, i935 UNITE STATES SHEET ABRASIVE AND METHOD OF MAKING THE SAME No Drawing. Application February 6, 1929,

Serial No. 338,022

15 Claims. (Cl. 51280) My present invention relates in general to the treatment of material, preferably in sheet form, and more particularly the treatment of material for the purpose of forming or attaining composite structures, of which well known forms of abrasives such as what is commonly known as sand-paper is an example.

Although I hereinafter disclose the practice of my invention in connection with abrasives such as sandpaper, it will be understood that my invention, or certain features thereof, have a wider field of utility.

Composite structures of the abrasive type such as sandpaper or emergy cloth comprise generally (a) a base of sheet material, which may be felted as in the case of paper or woven as in the case of cloth, (b) a more or less finely comminuted resistant material having abrading properties, such as garnet or corundurn, and (c) a binder generally in the form of a glue which serves to bind the abrasive to the base.

The principal objects of my present invention reside in the provision of a binder which functions more efficiently than any known to me, that is, the abrasive article, including the binder disclosed herein and the backing or base of the abrasive article is tougher whether used dry or in a water abrading operation; the provision of an abrasive article having the characteristics hereinafter set forth which gives a better performance in use when employed in water abrading operations, is a more waterproof article and in which there is less slipperiness of the backing, thereby permitting the operator to maintain a better grip on the sheet when rubbing surfaces; the provision of an improved flexible waterproof abrasive article characterized by extensibility and compressibility to accommodate itself to bending when in use; the provision of such an article wherein the desired adhesive action between the binder and the backing is materially increased; the provision of an improved binder and abrasive article wherein a good balance ofdrying is attained without any tendency to crack when dry; the provision of an improved abrasive article wherein the backing or sheet is adequately permeated with the water-proofing medium which prevents the water or other liquid employed in wet sanding from entering the pores and eventually cause swelling of the backing,

thereby maintaining the original body much longer than many flexible abrasive article known to me; the provision of improved coatings which tend to increase the life of the paper in use without materially decreasing the flexibility of the 5 same when dry; the provision of an improved binding and sizing material which has moisture proofing characteristics and is flexible when dry.

This invention in one of its forms further includes the improvement which resides inincorporating soft oils in the backing or sheet in sufficient quantity to load the sheet but in a degree insufficient to result in rendering the sheet brittle when dry, in combination with a sealing coat on the surface to increase the waterproofness of the sheet and wherein the employment of a harder binding coat when dry is compensated for by the inclusion in the sheet of a waterproofed material which maintains the flexibility of the binder and the sheet but results in the provisibnof a backing having greater resistance to abrasion, that is, to breaking down of the binder when employed in a wet sanding or water abrading operation. V

In the employment of my present invention for the production of a flexible abrasive article, such for example, as sandpaper and the like, suitable for employment in a wet sanding operation (which I cite for purposes of example) I employ as the base, a sheet of material (which may be paper, cloth or the like) of such texture and thickness as will conveniently serve the employment contemplated, and as the abrasive such comminuted material (which may be crushed garnet) similarly adapted to serve the function in view, together with the binder hereinafter referred to in detail for attaching the grits to the paper; and suitable auxiliary coatings within and without the paper sheet which have characteristics which render the bond between the grit and the sheet highly tenacious and result in a relatively hard finish without materially detracting from the flexibility of the abrasive article when dry.

It is, of course, desirable that the binder utilized have the functions and characteristics not only of great mechanical strength and of great binding strength, but also that it be non-hygroscopic, permeative, moisture resistant, easily worked, readily obtainable, relatively inexpensive and capable of facile application to the sheet.

In the manufacture of water-proof abrasive sheets, I have treated the backing or sheet with a water-proofing solution and then applied coats of binder and grit, together with auxiliary coating or coatings on the back of the sheet or on both the back and front. The degree of resistance to permeation by water or other liquid employed in a wet sanding operation depends in part on the amount of water-proofed materials put into the sheet, and in part upon the degree of drying to which the materials employed are subjected, which in other flexible abrasive articles have made it necessary first to attain a fairly good drying of the auxiliary back-sizing in order to give high resistance to abrasion in the backing, that is, to prevent the paper wearing off the back when the operator is rubbing a surface in a wet sanding operation, and, though a highly eflicient result is obtained in such articles, these do not have the desired high resistance to abrasion of the backing characterizing the present invention.

If, under the other methods known to me, a harder auxiliary coating material is employed, this results in stiffening the sheet beyond the degree desired. In my present invention, I provide binding and auxiliary or sizing coats which permit of the provision of a much harder outer surface and thereby an increase in durability of the sheet, at the same time, providing for suflicient flexibility of the sheet when the grit is applied so that the cooperation of the preliminary paper treatment and sizing coats with the sheet and the bonding coat result in a balance of flexibility, together with an increase in external hardness of the sheet.

In making the new abrasive article of this invention, I prefer to apply a relatively thin top or front coat as a presizing designed not to penneate the sheet materially but serving as a penetration controlling coat when the binder coat is applied. I then apply the binder coat; then the grit. I then apply in succession two relatively soft coats to the back of the sheet, that is, to the side opposite to the grit. I prefer that the second auxiliary back sizing coat be of a softer material when set than that of the first back sizing coat so as to not materially detract from the flexibility of the finished product, sandpaper.

To sum up, after the sheet has been treated, and, therefore, includes a backing, presized on the front, that is, having at least one front presizing coat, the primary binding coat is applied to the front of the sheet, and before this coat becomes set or dry a layer of the grits is deposited thereon, preferably without the application of external pressure. Then I apply the backsizing coats and a sand sizing coat, that is, a coat is applied over the grits and primary binding coat for compensating for any absorption of the primary binder by the base or backing. The: sheet is then, when dry, ready for use. The sheet may, for some purposes, at the outset, though not necessarily, contain soft oils tending to render the sheet itself waterproof.

From the foregoing, it will be seen that the abrasive sheet, with all of the advantages of this invention, includes the following principal elements a treated sheet which may contain soft oils in such amount as to render the sheet substantially water-proof; a presizing front coat; a binding grit carrying coat; one or more backsizing coats which prevent the entrance of water into the back of the sheet where the operators hand comes in contact; and a sand sizing coat It is preferable that the sand sizing coat and grit binding coat be relatively hard when dry; and that the backsizing coats be soft. It will thus be seen that a relatively hard outer surface is attained which will protect the binder coat and yet not materially detract from its flexibility and that the soft oils in the sheet when employed will permit of a flexing of the sheet without a tendency to crack. I thus attain a selection of relatively hard materials to hold the grits on the sheet and relatively soft materials to give flexibility where it is most needed and to compensate for any tendency in the relatively hard binding coats to render the sheet brittle.

As an example of the relative characteristics as to hardness of the various coatings employed, the sandsize coat and binder coat preferably include, as one of their ingredients, one of the hardest oils when dry that is available for my purposes, and which does not crack when dry; a presizing designed to control penetration of these hard oils into the backing, the primary backsizing coat is of a soft material and the second coat of backsizing is of such a soft material that when placed on a glass it may be scraped off with the finger-nail several days after application. Thus a controlled penetration of the liquid employed in an abrading operation into the pores of the flexible backing may be attained for increasing the flexibility of the abrading article in use without destroying. the bond between the grit, adhesive, and sheet.

In this way, I am enabled to provide for elongation of the backing which will prevent the finished article from becoming brittle, or cracking when bent.

In carrying out the the improved abrasive article of this invention, which processI believe to be new, and in order to obtain the proper drying cycle and to reduce the time required, I prefer to apply both coats of the backsizing in the second operation, that is, for example, the coated sheet is passed through a set of squeeze rolls which apply oil on the backside and then the sealing coat is applied thereto. Instead of sending it two trips through the steps of receiving two backsizing coats, I apply both coats of backsizing in the second operation. The second coat of the backsizing thus seals the surface so that oxidation is retarded in the center of the fibre cellulose sheet.

In the present invention, I find that it is possible to employ a clear binder for retaining the grits, that is, the employment of a pigment in the binder to control penetration into the paper stock is not necessary, and I find that in the employment of a clear binder, when properly controlled substantially all the strength of the adhesive therein may be used in retaining the grits.

The employment of a presizing coat on the sheet beneath the binder coat prevents an undue penetration of the sheet by the clear binder. I have found that I can obtain control of the application of the clear binder so as to prevent its undue penetration into the sheet by applying the binder to raw paper stock, which has been presized on the face but not previously backsized. I have found that in doing this, less penetration of the sheet by the grit binding coat takes place, probably due to the fact that in the prior operations known to me, the backsizing thinners,

44 process of manufacturing in evaporating, apparently exert a suction or capillary action on the binder applied to the opposite side of the sheet to hold grits and thus tend to pull the binder into the sheet.

In applying the various coatings by my preferred process which prevents the undue penetration of the sheet by the clear binder, I preferably first presize the paper and then apply the clear binder and a grit. The sheet thus treated and which may contain the waterproofing. oils referred to, is then passed one trip through an oven maintained at a temperature of between F. to 180 F. for 36 to 48 hours, the oven being zoned so that the sheet first gets the high heat, and the solvents employed are quickly driven off before they permeate the whole drying room. The major portion of the oven has a temperature of about 125 to F. After this trip through the oven, the two backsizing coats and the sandsizing coat are applied, and the paper again passed one trip through an oven, maintaining substantially the same temperature cycle as in its first trip.

In order to give the hard finish to the paper, the sand-sizing coat is applied before the second oven. In the article that passes two trips through an oven, the presizing coat, clear binder and sand are on the paper on the first trip, and the two backsizing coats and the sand-sizing coat are applied to the paper for its second trip through the oven.

I have discovered that gums and resins, natural or synthetic, having the desired characteristics such, for example, as rosin and other gums and resins, perform the functions desired, that is, of giving the necessary mechanical and binding strength and waterproofness which produces a binder suitable for my purposes, when employed with a suitable vehicle.

In preparing the binder for use, the gum or resin is employed in connection with a suitable vehicle which I prefer is of the type such, for example, as China-wood oil, linseed oil, or both. Certain other oils, such as semi-drying oil (soyabean oil) are suitable for that purpose.

In employing the gum or resin prepared with a vehicle such, for example, as China-wood oil, to one surface of the base or backing, I have found that the action of a vehicle involves a penetration of the base and, in some instances, this results in a weakening of the binding action and, while not suflicient to destroy the usefulness of the binder for some purposes, it is undesirable. My experience with this binder has shown that the application of a sizing coat to the back of the sheet tends to create a suction or capillary action and in order to prevent an undue penetration, in other inventions I have employed a filler for preventing a too great a penetration into the backing. However, by omitting the backsizing coats until after the binder is applied and fairly dry, I am enabled to employ a clear binder without the necessity of incorporating ingredients for preventing undue penetration. This function is further attained by the employment of a presize, that is, a sizing coat which is applied to one side of the sheet which is to receive the binder.

In my preferred practice in the production of this invention I employ presizes depending on the absorbency characteristics of the paper and the fluidity of the binder.

For dense papers, which do not absorb readily, the following examples of solutions used are representative.

Preferred Example No. 1 Parts China-wood oil 20.5 5 Rosin 3.5 Ester gum 2.0 Lime- 0.13 Manganese oxide 0.015 Litharge 0.035 10 Lead acetate 0.50 Cobalt 0.015 Oleum 70.805 Turpentine 1.50 Aluminum stearate 1.000 15 Preferred Example No. 2 Parts Oleum spirits 96.0 Metal soaps, such as aluminum stearate, 20

aluminum, palmitate, magnesium oleate, etc 4.0

For papers which are quite absorbent, or to control more fluid binders, a pigment may be added to such solutions as represented in Examples No. 1 and No.2.

A representative formula for a presizing solution containing a pigment is as follows:

Parts Formula No. 1 45 30 Formula No. 2 45 Blanc fixe (magnesium silicate or the like) 10 For papers which are very absorbent I use a It is not intended that I should limit myself to the use of the above to obtain a great degree of finesse in the presizing principle. 45

I have further found that solutions such as cellulose acetate or cellulose acetate combined with other oils; other metal soap, such as calcium oleate, and the like; and combinations of these solutions, with pigment such as magnesium 50 carbonate, blanc fixe, magnesium silicate, and the like; and synthetic resin solutions, such as phenol formaldehyde resins, may be used, depending on degree of control of binder penetration desired, and varying absorbency qualities 55 of paper stock used.

One of the virtues of the presize is that it prepares the surface of the sheet to receive the clear binder and which tends to prevent undue penetration and, as well, serves to seal the front 60 side of the sheet in a manner similarly to the backsize, which is applied later, to seal the opposite side.

In my preferred employment of a clear binder the same may include the following ingredients 65 in proportions by parts:

Oleum 12.5 75

Preferred Parts China-wood oil 27.0 Linseed nil 31.4 Manganese oxide 0.38 Litharge 0.26 Rosin- 7.5 Kauri 13.3 Ester gum 7.2 Ole 12.5

The sand sizing coat is applied over the grits and binder and for my purposes may include the ingredients in parts as follows:

The backsizing coat which is softer than either the clear binder or the hard external sand sizing coat may include the following ingredients by parts:

General Parts Vegetable drying oils 30.00 Resin 7.00 Cobalt acetate 0.25 Gilsonite 1.82 Soap chips 1.49 Isinglass 1.49 Alu 1.07 Water 20.00 Oleum 36.88

Preferred Parts China-wood oil 21.00 Linseed oil 9.00 East India nubs 7.00 Cobalt acetate 0.25 Gilsonite 1.82 Soap chips 1.49 Isinglass 1.49 Alum 1.07 Water 15.00 Oleum 36.88 Ethyl alcohol 5.00

The auxiliary backsizing coat, that is, the secand coat applied to the back of the sheet, may include the following ingredients by parts:

Second backsizing solutions may include the parts as in the formula hereinafter.

Parts Nitrocellulose 9.4 30 Raw or heat treated China-wood oil 10.5 Raw or blown castor oil 2.7 Ester gum 3.8 Silica 19.5 Water 1.5 35 Butylcellosolve 24.0 Mineral spirits 28.6

From the foregoing, it will be understood that the presize may include fillers for preventing penetration where it is desired to first backsize the 40 paper, that is, apply the backsizing coats in the Formulae D and E, before applying the binder.

After the presize, clear binder adhesive and sand have been applied to the paper, the article is suitably forced dried, that is, partially baked", as it is said, to the desired extent by subjecting it in the usual manner to a temperature which I prefer to control at approximately about 125 to 180 F., depending upon the degree of hardness desired, and for a required period of time, preferably 36 to 48 hours. It will be obvious that the hardness of finish of the article may be varied as desired by obtaining variations in the temperature employed and the time which the article is subjected to heat.

The backsizing coats of the formula: D and E and the hard sand size coat of Formula C are then applied, and the article again subjected to the desired hardening temperature which may be the same as that previously pointed out.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. Flexible sheet abrasive article including a backing having an adhesive and grit on one surface thereof and impregnated with a water-proofing composition, and a non-impregnating sealing coating applied to the surface of the sheet opposite to said grit and adhesive, said sealing coating being softer when dry than said adhesive.

2. The process of making a stable waterproof abrasive article in the nature of sandpaper or the like, which includes employing a flexible sheet of fabric which has been treated to prevent disintegration when used in a water abrading operation, applying thereto a grit or layer of abrasive particles, and a waterproof stable adhesive bond, and applying anon-penetrating sealing coat to the opposite surface of said abrasive article, and applying heat to the article in each instance after application of said bond and said sealing coat.

3. Flexible sheet abrasive material including a backing and a plurality of coatings one of which serves to secure the grit to the sheet and said coatings being composed of materials which when set are progressively harder within suitable degrees of hardness from the non-abrasive side toward the abrasive coated side of the article.

4. Flexible sheet abrasive material including a backing and a plurality of heat solidified coatings one of which serves to secure the grit to the sheet and said coatings being composed of materials which when set are progressively harder within suitable degrees of hardness from' the non-abrasive side toward the abrasive coated side of the article. i

5. The new article of manufacture in the nature of sandpaper which includes a backing, a presizing coating applied to one surface of said backing, a binder coating of relatively hard but flexible material when set applied to said presizing coating which thereby serves to control penetration by said binder coating, the latter containing a grit or abrasive, a grit sizing coating applied to said binder coating, and an auxiliary sizing coating relatively softer than the binder coating when set applied to the opposite side of said backing and penetrating the backing to a predetermined degree for compensating for any tendency of said binder coating to render the article materially inflexible when set.

6. The new article of manufacture in the nature of sandpaper which includes a backing, a sizing coating on said backing, an adhesive binding coating and a layer of grit held by said adhesive coating upon said sizing coating, an outer auxiliary coat of a softer material than said binding coating applied thereto, said binding and auxiliary coatings tending to harden the outer surface without materially detracting from the flexibility of the article when dry, and a sizing coating applied to the back of the article and adapted to penetrate the sheet for modifying the flexibility thereof and said article when dry.

'7. As an article of manufacture, a flexible abrasive sheet consisting of two layers of separate material secured together, grit embedded in one of said layers only, and a flexible backing material secured to the other layer, the last recited layer constituting a flexible barrier between the backing material and thegrit holding layer.

8. As an article of manufacture, a flexible abrasive-sheet, consisting of two layers of separate materials secured together, grit embedded in one of said layers only, a flexible backing material secured to the other layer, the last recited layer constituting a flexible barrier between the backing material and the grit holding layer, and a liquid resisting coating over the grit holding surface.

9. As an article of manufacture an abrasive element consisting of a sheet of flexible backing material, a flexible barrier coating on said backing, a layer of grit, or abrasive particles, and an adhesive bond between said flexible barrier coat ing and said grit, said barrier coating forming a clearly defined zone between the backing and the adhesive bond, whereby said adhesive bond and grit may be separated with respect to the backing while the adhesive bond 5 and grit aflixed thereto, remains substantially intact and undissolved.

10. As an article of manufacture an abrasive sheet consisting of a sheet of non-metallic flexible backing material, fgrit or abrasive particles, 10 a plurality of superposed layers of separate materials between said grit and backing, one of said layers constituting an adhesive bond for the grit, the other layer serving to prevent impregnation of the grit holding layer into the said backing. 15

11. A new article of manufacture in the nature of sandpaper comprising a backing material and a plurality of separate layers attached thereto, one layer including a resinous material serving as a binder for a grit or layer of abrasive par- 20 ticles, and another of said layers including a cellulosic compound interposed between said binder layer and the backing.

12. The process of making a stable waterproof abrasive article which includes as steps thereof 25 applying to a flexible sheet of fabric a layer of grit or abrasive particles, and a plurality of coats of waterproof material by interposing as one of said coats a relatively hard, stable penetrative adhesive bond for retaining the grit, and inter- 30 posing another of said coats for controlling penetration of said adhesive bond into the sheet, and applying a relatively soft flexing coat to the opposite surface of the sheet.

13. The process of making a stable waterproof 35 abrasive article which includes as steps thereof applying to a flexible sheet of fabric a layer of grit or abrasive particles, and a plurality of coats of waterproof material by interposing as one of said coats a relatively hard, stable, penetrative, 40 adhesive bond for retaining the grit, and interposing another of said coats to act in the nature of a barrier coat for controlling penetration of said adhesive bond into the sheet, and applying a relatively soft flexing coat to the opposite sur- 45 face of the sheet.

14. As an article of manufacture,an abrasive sheet consisting of a sheet of flexible backing material, grit or layer of abrasive material, a plurality of superimposed layers of separate materials between said grit and backing, one of said layers constituting an adhesive binder for the grit, the other layer serving to control penetration of the grit layerinto the said backing,

15. The new article of manufacture in the na- 55 ture of sandpaper which includes a backing, a pre-sizing coating applied to one surface of said backing, a binder coating of relatively hard but flexible material when set applied to said presizing coating which thereby serves to control 60 penetration by said binder coating, the latter containing a grit or abrasive, and an auxiliary sizing coating relatively softer than the binder coating when set applied to the opposite side of said backing and penetrating the backing to a predetero5 mined degree for compensating for any tendency of said binder coating to render the article materially inflexible when set.

FRANCIS G. OKIE.