US2375814A - Coated abrasive - Google Patents

Description

y 1945. N. E. OGLESBY A T 2,375,814

COATED ABRASIVE Filed Oct. 6, 1942 ATTORNEYS.

Patented May 35, E45

QUATED ABRASIV E Application @ctober 6, 1942, Serial No. 460,996

(ill. 51--301) 8 killaims.

This invention relates to the manufacture of coated abrasives and/or the treatment of coated abrasives after manufacture.

In the use of coated abrasives on many classes of work, it has always been a problem to prevent what is known as loading of the coated abrasive which is caused by the debris, removed in an abrading operation, becoming embedded between the grains. Such loading leads to rapid loss of out or the coated abrasive, with the result that becomes ineffective as an abrading device long before the abrasive grains have become dull or are torn from the sheet. Various methods of overcoming this dimculty have been resorted to but none of them points to the complete solution of the problem. In order to decrease loading, special coated abrasives, known as open coated productswith wide spacings between the grains, are employed. Likewise, many lubricants have been used to reduce loading as well as to give a superior finish. Such lubricants include water, to which is often added a surface wnsion-lowering or wetting agent such as Turkey red 011. Water and such a wetting agent are normally used with what is known in the trade as waterproof sandpaper. Likewise, various petroleum fractions, either with or without light lubricating oil added thereto, have been used as lubricants for both waterproof and glue bond sandpaper. It has also been proposed to apply wetting agents, i. e., surface tension depressants, to the surface of waterproof coated abrasive sheets so that when water is used as a lubricant in the sanding operation, its surface tension will be lowered thereby to render it a more efficient lubricant. In most sanding operations the lubricating water is add ed more or less continuously with the result that the surface tension depressants are readily washed away from the sheet to which they are applied and are relatively inefiective.

It is an object of the present invention to decrease the loading of coated abrasives and it is a further object of the present invention toprovide a layer of material between the adhesive of the coated abrasive and the work that is being t is a further object of gressively finer grain finish, the coated abrasive finally being discarded when the rate of out has become too slow. By my invention I not only reduce the loading of the coated abrasive and illcrease its useful life, but I also provide a coated abrasive or a treatment for coated abrasives which results in a more uniform cutting rate and a more uniform finish throughout the useful life of the coated abrasive.

In carrying out my invention I treat the coated abrasive, either waterproof or glue bond, made according to the prior art or any reasonable modiflcation thereof, with a layer of matter which has some or all of the following'properties:

(1) A relatively low frictional resistance to movement over the material'to be abraded when a; specific sanding lubricant is used.

(2) If foruse with-a water lubricant, some constituent of the layer of matter preferably lowers the surface tension of the water, e. g., a water dispersible constituent which may be dissolved and leached out of the layer.

' (3) When wetted and saturated with the sand ing lubricant, the cohesive strength of the layer is relatively low so that fragments may break away from. time to time and carry with them sanded debris that would otherwise load the paper.

(4) Swells to a marked degree without readily v dissolving when penetrated by the sanding lubricant so that there is a progressive swelling and weakening of the layer during the abrading operation, whereby new parts of the layer move toward the level of the grain, from which new parts of the layer, fragments can break or wear away from time to time and carry with them the abraded debris that would otherwise load the coated abrasive.

In cases where waterproof sandpaper is to be I used witha water lubricant, I find hide glue and/or casein useful materials as a base for the preparation of my special treatments. I also find neutralized sulphonated castor oil, triethanolamine oleate and gum karaya. useful mod- -ifying agents for such base materials; .Where casein is used as the base material as hereinafter described, it is usually not preferred to tan the 55 base material, as. for instance, by the use of formaldehyde, but wherehardening of the casein base i desired it may be accomplished by tanning. Where glue is used as a base material, tanning is usually preferred though not always essential, and such tanning ma be accomplished,

as stated before, by treating the layer of material applied to the coated abrasive, as hereinafter described, with formaldehyde as, for instance, a to solution in water, after the layer of material has become gelled or partially or completely dried. Tanning of the glue or similar protein material may, however, be accomplished by including in the compositions, such agents as potassium dichromate or hexamethylene tetramine, the tanning occurring upon heating of the dried layer of treatment.

Normally made waterproof or glue bond coated abrasives may be used in carrying out my'in- Since, however, for different purposes treated in accordance with the art of making waterproof sandpaper, in case my invention is being carried out in connection with the manufacture of waterproof sandpaper. In case the invention is being carried out in connection with the manufacture of glue bond sandpaper, such waterproofing treatment is not necessary or normally employed. 6 is a making coat of adhesive which may be, for example, an oil-modified alkyd resin modified with an oil-soluble phenolic resin according to the present art if flexible waterproof sandpaper is being made, a phenol-formaldehyde resin according .to the present art if relatively inflexible waterproof sandpaper is being v manufactured, or a coating of hide glue if glue bond sandpaper is being manufactured. I is a suitable coating of abrasive grits in accordance with the known art. 8 is a sizing coat of adhesive applied according to the known art and may consist of any one of the three materials described in connection with the making coat 6 according to the type of sandpaper that is being manufactured. 9 is a special layer of my treatment appliedover the sand sizing coat 8 and maybe selected from the various examples of treatments hereinafter described according to the intended use of the product being made, that is, according to whether the product is to be used with a water type lubricant or a lubricant of organic solvents such as the petroleum or cyclic hydrocarbons.

The following composition has been found ve y satisfactory for many machine sanding operationsand many hand sanding operations where a water type lubricant is in use:

Conventional #280-A Waterproof Sandpaper was coated with the composition of Example 1, using conventional sandpaper coating rolls. The

- amount of coat applied was 1.12 lbs. of non-volatile matter per sandpaper ream. After the wa ter was evaporated in the drying operation the treated side of the web was coated with a 15% solution of formaldehyde and again allowed to dry. The product produced was found much more efficient in sanding operations, both machine operations and hand operations, than a control untreated product. In addition to being a more efficient abrasive, an unexpected advantage was noted. The coarse, scratchy finish usually produced with a new piece of the control coated abrasive was not obtained, the initial finish being equal to the superior finish normally obtained with the control piece of sandpaper after it had lost its initial sharpness. The rate of cut of the treated coated abrasive was much more constant throughout its life than the rate of cut of the untreated coated abrasive; There was a marked decrease in the loading of the treated coated abrasive as compared with the control.

vOther suitable compositions for use on popular grades of waterproof sandpaper and with a water type lubricant such as grades 320 and 280, are as follows:

The composition of Example 3 is preferably tanned with formaldehyde after the composition is either gelled or partially or completely dried.

Example 4 Percent Casein 9.60 Gum karaya 0.95 Neutralized sulphonated castor oil 14.20 NH; (ammonia) 0.26 Water' 74.99

It is normally preferred to omit the step of tanning where this composition is used.

Example 5 Percent 86 M. P. hide glue 9.33 Triethanolamine oleate 9.33 Water 81.34

. in connection with Example 1.

While not always necessary, it i usually preferred to tan the composition of Example 5 after it is gelled or partially or completely dried.

All of the coatings of Examples 1, 2, 3, 4 and 5 may be applied by calender rolls as described The compositions given are as used for the grits previously specified, namely, 320 and 280. Where coarser grits are being treated and heavier coatings are required, it is usually advisable to raise the viscosity and solids contents as required by decreasing the water contents of the various examples, 1 to 5 inclusive.

In making up the various solutions, it is ad- I visable to dissolve the glue in a part of the water and the neutralized sulphonated castor oil, gum karaya or triethanolamine oleate respectively in separate portions or the water and then mix the solutions. Where casein is used in any of the compositions it is preferably dissolved in part of the water containing the ammonia, which may be conveniently added to the water in the form of a concentrated solution of ammonium hydroxide. The casein so dissolved is added to the other constituent dissolved as described.

Examples 6 and 7 shown below have been found particularly useful in connection with the treatment of max Waterproof Cloth intended for use in the sending of plastics as, for example, cellulose acetate butyrate plastics, with a water lubricant. The backing of the 2'20-X Waterproof Cloth was a drills cloth treated according to the known art and having making and sizing coats of adhesive consisting of phenol-formaldehyde resin. The sanding operation was carried out on a conventional beit sander.

Example 6 Per cent Gossip 8.75 Nl-is (ammonia) .21 145 M. P. hide giue 4.37 Neutralized sulphonated castor oil 14.43 Water 72.24

The composition was tanned by treatment with formaldehyde solution, as previously described, in connection with Example 1.

Example 7 Per cent Casein 12.12 NHs (ammonia) .29 Neutralized sulphonated castor oil- 13.28

Paraformaldehyde 1.10 Water 73.21

Normal machine abrading operations are more severe than hand operations. For this reason. the special layer of this invention, where the cyclic hydrocarbons.

product is intended for severe machine opera" tions, may be tougher and have more cohesive strength when wet than those found most efi'lcient for hand sanding operations and light machine operations. Such increased toughness and increased cohesive strength when wet may b with ammonia both being good emulsifyin agents.

The composition of Example 8 was used to coat a #50 coated abrasive having glue making and sand sizing coats, a coating of #50 silicon carbide grains and a backing consisting of print cloth combined to 110 1b. kraft paper with hide glue. The product so produced was found to be an efilcient abrasive when used with a lubricant known as "Varnolene which is a petroleum fraction sold by the Standard Oil Company of New Jersey. 1

Where finer grits-are to be coated with the composition of Example 8 the solids and viscosity of Example 8 may be lowered by increasing the water content. Where still coarser grits are to be coated, the viscosity and solids content may be increased by decreasing the water content of Example 8.

The raw rubber of Example 8 is readily swelled by such solvents as the petroleum fractions and The cohesive strength and tackiness of the rubber is decreased as required by the added wax to produce a composition of relatively low cohesive strength and with a low frictional resistance against movement over many pieces of work where the, hydrocarbons or other suitable organicliquids are used as sanding lubribeing resistant to and substantially insoluble in a sanding lubricant, and another coating'applied over said abrasive grains and said abrasive-hold ing adhesive coatings, said last coating being readily swelled, and weakened, but not readily ,dissolved by said sanding lubricant, said last accomplished by increasing the glue and/or casein in a given composition or by decreasing the amount of modifying agents of the type of neutralized sulphonated castor oil or triethanolamine oleate.

A composition of the type of Example 8 is useful in connection with the treatment of glue bond coated abrasives and waterproof coated abrasives where the sanding lubricant is an organic solvent such as a petroleum hydrocarbon or a cyclic hydrocarbon.

Example 8 Per cent Rubber 25.00 Paramn wax 25.00 Stearic acid Casein NH: (ammonia) .56 Water 46.94

Rubber in a form which is readily swelled but only slowly dissolved in the liquid hydrocarbon, e. g., a concentrated latex or redispersed rubber may be used to prepare the above composition. The stearic acid and casein are rendered water soluble by the addition of ammonia in accordance with the knownart and the paramn wax is added in the form of an emulsion, the ammonium stearate and the ammonium caseinate formed coating being adapted to disintegrate slowly and to decrease the loading and to improve the uniformity of the abrading by said coated abrasive when used in a sanding operation with said sanding lubricant and said abrasive-holding adhesive coatings being adapted to and suflicient to hold the vast majority of said abrasive grains to said backing while said top or outermost coating is disintegrating in an abrading operation with said sanding lubricant.

7 2. A coated abrasive comprising a reinforcing backing, a layer of abrasive grains anchored thereto by at least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasiveholding adhesive applied over the grains as a sizing adhesive, at least the said sizing adhesive being resistant to and substantially insoluble in a sanding lubricant comprising water and anholding adhesive coatings being adapted to and suflicient to hold the vast majority of said abrasive grains to said backingwhile said top or ingoperation withsaid sanding lubricant comprising water.

3. A coated abrasive comprising a reinforcing backing, a layer of abrasive grains anchored thereto by at least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasiveholding adhesive applied over the grains as a sizing adhesive, at least the said sizing adnesive being resistant to and substantially insoluble in a sanding lubricant comprising hydrocarbon which is liquid at the sanding temperatures, and another coating applied over said abrasive grains and said abrasive-holding adhesive coatings, said last coating being readily swelled and weakened but not readily dissolved by said sanding lubricant comprising said hydrocarbon, said last coating being adapted to disintegrate slowly and to decrease the loading and to improve the uniformity of the abrading by said coated abrasive when used in a, sanding operation with said sanding lubricant comprising said hydrocarbon and said abrasive-holding adhesive coatings being adapted to and sufficient to hold the vast majority of said abrasive grains to said backing while said top or outermost coating is disintegrating in an abrading operation with said sanding lubricant comprising hydrocarbon.

4. A coated abrasive comprising a reinforcing backing, a layer of abrasive grains anchored thereto by at least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasiveholding adhesive applied over the grains as a sizing adhesive, at least the said sizing adhesive being resistant to and substantially insoluble in a sanding lubricant comprising water and another coating applied over said abrasive grains and said abrasive-holding adhesive coatings, said last coating comprising a solid protein which is readily swelled and weakened bycold water but which is not readily dissolved thereby and said last coating being adapted to disintegrate slowly and to decrease the loading and to improve the uniformity of the abrading by said coated abrasive when 'used in a sanding operation with said sanding lubricant comprising water and said abrasiveholding adhesive coatings being adapted to and suflicient to hold the vast majority of said abrasive grains to said backing while said top or outermost coating is disintegrating in an abrading operation with said sanding lubricant comprising water.

5. A coated abrasive comprising a. reinforcing backing, a layer of abrasive grains anchored thereto by at least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasive-holding adhesive applied over the grains as a sizing adhesive, at least the said sizing adhesive being resistant to and substantially insoluble in asanding lubricant comprising water and another coat-, ing applied over saidab'rasive grains and said abrasive holding adhesive coatings, said last coating comprising a tanned solid protein which is readily swelled and readily weakened but not readily dissolved by said sanding lubricant comprising water, said last coating being adapted to the vast majority of said abrasive grains to said backing while said top or outermost coating is disintegrating in an abrading operation with said sanding lubricant comprising water.

6. A coated abrasive comprising a reinforcing backing, a layer of abrasive grains anchored thereto by at least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasive-holding adhesive applied over the grains as a sizing adhesive, at least the said sizing adhesive being resistant to and substantially insoluble in a sanding lubricant comprising water and another coating applied over said abrasive grains and said abrasive-holding adhesive coatings, said last coating comprising a solid protein which is readily swelled by cold water but not readily dissolved thereby, and a water dispersible constituent which may be dissolved and leached out of the layer of said special coating and which is effective to lower the surface tension of water, said last coating being adapted to disintegrate slowly and to decrease the loading and to improve the uniformity ofthe abrading by said coated abrasive when used in a sanding operation with said sanding lubricant comprising water and said abrasive-holding adhesive coatings being adapted to and suflicient to hold the vast majority of said abrasive grains to said backing while said top or outermost coating is disintegrating in an abrading operation with said sanding lubricant comprising water.

7. A coated abrasive comprising a reinforcing backing, a layer of abrasive grains anchored thereto by at, least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasive-holding adhesive applied over the grains as a sizing adhesive, at least the said sizing adhesive being resistant to and substantially insoluble in a sanding lubricant comprising liquid hydrocarbon solvents, and another coating applied over said abrasive grains and said abrasive-holding adhesive coatings, said last coating comprising rubber in a form which is readily swelled but not readily dissolved by said liquid hydrocarbon solvents and an agent effective to weaken the rubber coating and render the same relatively non-tacky, said last coating being adapted to disintegrate slowly and to decrease the loading and to improve the uniformity of the abrading by said coated abrasive when used in a sanding operation with said sanding lubricant comprising said liquid hydrocarbon solvents and said abrasive-holding adhesive coatings being adapted to and suificient to hold the vast majority of said abrasive grains to said backing while said top or outermost coat ing is disintegrating in an abrading operation with said sanding lubricant comprising liquid hybacking, a layer of abrasive grains anchored by said coated abrasive when used in a sanding operation with said sanding lubricant comprising water and said abrasive-holding adhesive; coatings being adapted to and sufflcient to hold thereto byat least one coat of abrasive-holding adhesive interposed between the grains and the backing and by at least one coat of abrasiveholding adhesive applied over the grains as a sizing adhesive, at least the said sizing adhesive being resistant to and substantially insoluble in a sanding lubricant comprising liquid hydrocarbon solvents, and another coating applied over said abrasive grains and said abrasive-holding adhesive coatingsjsaid last coating comprising rubber in a. form which is readily swelled but not readily dissolved by said liquid hydrocarbon solvents and a constituent which may be dissolved and leached out of the layer of said special coating by said hydrocarbomsolventl. said last coat-' ings being adapted to and sufliclent to hold the vast majority of said abrasive grains to said backin; while said' top or outermost coating is disintegrating in an'abrading operation with said sanding lubricant comprising liquid hydrocarbon solvents.

- NICHOLAS E. OGLESBY.

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