US2219263A - Sheet abrasive and method of making the same - Google Patents

Description

Patented Oct. 22, 1940 PATENT OFFICE SHEET ABRASIVE AND METHOD OF MAKING THE SAME Francis Gurney Okie, St. Paul, Minn.,'assignor to Minnesota Mining 8; Manufacturing Company, St. Paul, Minn., a corporation of Delaware No Drawing. Original application February 6,

1929, Serial No. 338,022. plication April 28, 1933, Serial No. 668,384.

newed October 25, 1939 6 Claims.

My present invention relates in general to the treatment of material, preferably in sheet form, andmore 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 sandpaper 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 emery 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, (1)) a more or less finely comminuted resistant material having abrading properties, such as garnet or corundum, 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 efliciently 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 of drying 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 waterproofing 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 in any flexible abrasive article known to me; the provision of improved coatings which tend to inscopic, permeative,

Divided and this apcrease the life of the paper in use without materially decreasing the flexibility of the 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 in incorporating soft oils in the backing or sheet in sufficient quantity to load the sheet but in a degree insuflicient 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 provision of 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.

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-hygromoisture resistant, easily worked, readily obtainable, relatively inexpensive and capable of facile application to the sheet.

In the manufacture of waterproof abrasive sheets, I have treated the backing or sheet with a waterproofing 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 emtemal pressure.

ployed in a wet sandins operation depends in part on the amount of waterproofed 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 of! the back when the operator is rubbing a surface in a wet sanding operation, and, though a highly efllclent ,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 stiflening the sheet beyond the ficient 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 permeate 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 ex- 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 waterproof; 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 applied to said binding coat and grit where desirable or necessary.

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 afiexing of the sheet without a tendency to 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.

In this way, I am enabled to provide for elon- Y gation of the backing which will prevent the finishing article from becoming brittle, or cracking when bent.

In carrying out the process of manufacturing the improved abrasive article of this invention, which process I 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, 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 animus 3 meate the whole drying room. The major portion of the oven has a' temperature of about 125 F. to

130 1". After this trip through the oven, the two backsizing coats and the sandsizing coat are aps plied, 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 sandsizing 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 sandsizing coat are applied to the paper for 'its second trip 16 through the oven.

I have discovered that natural or synthetic, having the desired characteristics such, for example, as rosin and other gums and resins, perform the functions desired,

20 that is, of giving the necessary mechanical strength for abrasion operations and binding strength by compatibility to the abrasive and waterproofness which produces a binder suitable for my purposes, when employed with a 20 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 sufiicient to destroy the usefulness of the binder for some purposes, it is un- 0 desirable. 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 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.

5 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,

m the following examples of solutions used are representative.

gums and resins,

Preferred Example No. 2

Parts Oleum spirits 96.0 Metal soaps, such as aluminum stearate,

aluminum, palmitate. magnesium ole- 5 ate, etc 4.0

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

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

Parts Formula No. 1 45 Formula N0. 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 30 of finesse in the presizing principle.

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 35 these solutions, with pigment such as magnesium 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 penetra- 0 tion desired, and varying absorbency qualities 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 4,5 penetration and, as well, serves to seal the front 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 50 the same may include the following ingredients in proportions by parts:

The sandsizing coat is applied over the grits 76 and binder and for my purposes may include the ingredients'in parts as follows:

General Parts Vegetable drying oils 34 Resin 13 Lime 0.2 Manganese oxide 0.04 Litharge 0.09 Lead acetate 0.04 Cobalt acetate 0.001 Oleum 45.629 Turpentine 7.0

Preferred Parts China-wood oil 34 Rosin 5.0 Ester gum 8.0 Lime 0.2 Manganese oxide 0.04 Litharge 0.09 Lead acetate 0.04 Cobalt acetate 0.001 Oleum 45.629 Turpentine 7.0

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

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

General Parts Nitrocellulose sec.) 8.8 Vegetable drying oil 13.2 Oleum 29.0 Nitrocellulose solvent 25.5

Ground silica 17.0 Resin 4.5

Water 2.0 Plasticizer or softener.

Second back sizing solutions may include the parts as in the formula hereinafter.

Parts Nitrocellulose 9.4 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 Butyl cellosolve 24.0 Mineral spirits 28.6

From the foregoing, it will be understood that the pre-size may include fillers for preventing penetration where it is desired to first back size the paper, that is, apply the back sizing coats in the formulae D and E, before applying the binder.

After the pre-size, clear binder adhesive and sand have been applied to the paper, the articleis 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 to 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 tempera ture employed and the time which the article is subjected to heat.

The back sizing coats of the formulae D and E and the hard and 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.

This application is a division of my application Serial No. 338,022, filed February 6, 1929, noW Patent No. 2,013,925 issued September 10, 1935. Reference is also made to my application Serial No. 755,445 filed November 30, 1934, now Patent No. 2,169,277 issued August 15, 1939 and to my application Serial No. 213,519 filed June 13, 1938 as a division of the present case, in which other phases of my invention are claimed.

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

1. A composition for forming a sizing coat comprising a cellulose ester about 7.2 to about 9.4 parts, a drying oil about 8.0 to about 13.2 parts, resins about 2.5 to about 4.5 parts, with mixed solvents for the water-proofing materials.

2. A composition in accordance with claim 1 containing about 2.5 to about 2.7 parts of a plasticizer taken from the group consisting of castor oil, raw castor oil, blown castor oil.

3. A composition in accordance with claim 1 containing about 17 to about 19.5 parts of a mild friction increasing material comprising silica.

4. The composition for forming a sizing coating comprising cellulose ester about 8.8 parts, drying oil about 13.2 parts, resins about 4.5 parts, mild friction increasing material comprising silica about 17 parts and mixed solvents for the waterproofing materials.

iii)

5. The composition for forming a sizing coating comprising nitrocellulose about 9.4 parts, China-wood oil about 10.5 parts, blown castor oil about 2.7 parts, ester gum about 3.8 parts, mild friction increasing material comprising silica about 19.5 parts and a mixed solvent for the waterproofing materials.

6. The composition for forming a sizing coating, comprising nitro-cellulose about 7.2 parts, a. drying oil about 8 parts, blown oil about 2.5 parts, ester gum about 2.5 parts, the composition including mixed solvents for the ingredients afore- 6 mentioned.

FRANCIS GURNEY OKIE.