US2186001A - Flexible abrasive sheet material - Google Patents

Description

Patented Jan. 9, 1940 UNITED" STATES 2,186,001 FLEXIBLE massive suns-r MATERIAL Howard G. Battling, Chicago, 111., assignor, by mesne assignments, to Minnesota Mining &

Manufacturing Minnesota Company, a corporation of Application January 20, 1930, Serial No. 422,066 Renewed April 22, 1936 16 Claims.

In the accompanying drawing exemplify this invention there is illustrated a flexible abrasive material constructed in accordance with the principles of this invention, in which Figure 1 is a sectional view on a greatly enlarged scale of one form of the invention.

Figure 2 is a sectional view on a greatly enlarged scale of another form of the invention.

Figure 3 is a detail sectional view on a greatly enlarged scale, showing the backing partially stripped from the grit holding adhesive.

Figure 4 is a sectional view on a greatly enlarged scale of still another form of the invention.

larged scale, taken on line 55, Figure 1.

There are two types of abrasive paper, commonly termed "sandpaper. One is the ordinary sandpaper with a water soluble adhesive gritholding material and the other is of the waterproof variety which is generally used for what I is known as wet or water sanding operations. The waterproof variety is made with a paper backing and an adhesive (bond coat holding the abrasive grit) and chemically treated as to render the finished sheet of sandpaper insoluble in water.

When manufacturing such "a product of the waterproof variety in the past, the waterproof which anchors the grit to the paper backing, is of such a nature that it penetrates into the paper backing, directly contacting and waterproofing the fibres of the backing, to the extent of such 3 penetration. Some of the processes claim to regulate the extent of this penetrativeness, and this point has heretofore been particularly stressed as an important feature in the method used.

It has been found that an adhesive to'properly hold the grit grains firmly, should be tough and hard. While such toughness and hardness are essential qualifications for an emcient adhesive material of this nature, it has also been found where such an adhesive material is spread thinly on a flexible base material, such as paper or cloth, that there is a tendency for the adhesive 4 material, when dry, to become brittle, and if the paper or cloth is then bent or folded the adhesive material will crack or break. Therefore, to overcome this brittleness it is customary to add a plasticizing agent to the adhesive solution in volume suflicient to overcome the brittleness, yet not enough to impair the bonding qualities of the adhesive material, which would become more or less elastic if an excessive quantity of the plasticizer were used. Therefore, the quantity of the plasticizing agent must be carefully regulated to attain the required degree of plasticity.

If a waterproof adhesive bonding material without the plasticizing agent incorporated Figure 5 is a detail sectional view on an enadhesive, (sometimes termed the "bonding coat) etr'ates into the backing on which it iscdated andiwhich itimpregnates to a certain extent such penetration, there would be a tendency for those fibres or threads so contacted, to be coated with the adhesive bond material and to take on the physical properties of the adhesive bonding material, and become equally as stiff and hard as the adhesive bonding material itself, thereby destroying to a certain degree, the natural pliability of such fibres which existed before such penetration and impregnation took place. I I

It has been found that in adhesive bond coatings of which oils, gums and resins are constituent parts, that the vehicle penetrating into and impregnating the backing material on which the adhesive bond coat applied, carries fine, minute particles of the solids of such coatings, into the mass fibres or threads with such-impregnation which coats the fibres orthreads themselves, so contacted. Thus, it is evident as claimed, that the physical properties of the adhesive bond coat are imparted to the structure of the backing material so effected.

Ina finished product of abrasive paper, of the waterproof variety, flexibility and pliability are valuable features, therefore, any means or methods used to increase such pliability and-flexibility is of distinct importance and advantage and constitute an improvement in theart.

Heretofore, the means employed for producing pliability in a sheet of abrasive material, of the water resistant type, has been the use of an extra thin or lighter weight backing material for the forming base of the abrasive paper, or by the addition of oils and other materialsincorporated in the formulas and treatments of, and administered'to the abrasive paper.

The present invention, however, employs a separate and distinct layer, coating or application of flexible material to produce pliability in the finished sheet of abrasive paper. This is distinguishably and materially different from the usual method of including an ingredient in a formula, with other materials, in the adhesive bonding coat, or in the waterproofing processing of the product, to obtain pliability.

It has also been found that a superior type of water-resistant sandpaper can be made by a process eliminating the impregnation of the backing with the waterproof adhesive bond, which latter acts as a combination adhesive and waterproofing means.

It is one of the objects of the present invention to retain the maximum natural pliability possessed by the backing of paper, or cloth. To that end there is applied a coating, layer or applicacontacting the fibres or threads themselves, of the backing l2, and which former may ormay not be hygroscopic. Another purpose of this application i0, is to produce 'pliability' in the, finished product.

One such materialwhich has been found to be satisfactory for this purposeis gelatine, but it is to be understood that it is not desired to be limited to gelatine, as other coatings or applications of materials possessing the desired or neces# sary qualifications may be employed, such as suitable types of resins of the phenol formaldehyde condensation, or the glycerole phthalic anhydride products. l

If an application ID, of gelatine is employed, it will penetrate into and impregnate the backing material I! (Fig. 1), as at l3, to a certain degree,

-bonding material from directly contacting or but the gelatine, being highly flexible and hygroscopic will not interfere with the flexibility of the backing 12 even though the pe'nerated portion i3 01 the backing should take on or assume the physical characteristic of the gelatine coating Ill used, whichlatter should be'of an exceptionally pliable type. v

However, as illustrated in Figure 2, other coating materials may be employed which will not penetrate the backing but will become attached to the backing by surface adhesion only. Such a non-penetrating coating, or application i4, suitable for this purpose might be nitro-cellulose or cellulose acetate solutions of the proper types, or sheet material such as those mentioned, and also cellulose xanthate, but it is not desired to be limited to these materials for such a purpose as other. materials having the same qualities or characteristics, comparatively speaking, may be employed. These coatings or applications Ill-l4, will'hereafter be referred to as a -fiexible barrier application because it also serves as a barrier to prevent the grit-holding adhesive coatingthe fibres or threads themselves of the backing material, and produces pliability in the forming the flexible barrier application, which will penetrate a portion of the. backing, similar to the-gelatine coating, is a solution of polymer- The nitro-cellulose'compound application acts closely in the same capacity as the gelatine coating, previously referred to, m the fact that it will not permit the adhesive bonding coat to impreg ate the backing material, thereby preserving the natural pliability of the backing material and imparting the pliability of the nitro-cellulose.

compound application to the finished abrasive sheet.

That the nitro-cellu'lose compound acts as a barrier, and does not allow the adhesive bonding coat'to'direotly contact or coat the fibres or threads themselves, of the backing material, is

' proved "by the fact that the finished sheet. of

cause the nitro-cellulose compound to soften or dissolve. thereby permitting the backing material "bonding"material, aside from the removal of its 7 base, or backing material's support. 'Thia isrendered possible by reason of the fact thatthe tions are not miscible with theothers.

flexible. barrier coating forms a clearly defined zone-between the backing-material and the adhesive bond coating, thereby maintaining the lgzcking against penetration by the adhesive It has been shown that the method of making some of the sandpapers now on the market, consists in applying a plurality of waterproofcoatlugs to one side of a backing material, and applying to the side of the'backing material remaining uncoated, 'an application of some material as a means of waterproofing the back of the backing material, to prevent disintegration of the backing when it is used in water.

' It has been found that these plurality of coatings, regardless of the sequence of their applications, or the fact that each coating was permitted to dry before the application of a subsequent coat, were miscible when contacted one with the other. This actually resulted in these plurality of coating's practically commingllng into one continuous coating extending from the grit side of the sandpaper down to, and in some instances, through the backing material. The object being to prevent disintegration of the backing when it was used with water.

In the present invention the various applicamiscible barrier application prevents the coatings on one side of the barrier application from coming into commingling relation with the coating on the opposite side of the barrier application. Being immiscible with the other applications, it is possible to completely dissolve the barrier application by a suitable solvent, without dissolving the coatings between which the barrier application was interposed. Thus, the barrier application has established a clearly defined zone between the' coatings mentioned, and the object of its use is clearly shown.

Thus, it is evident, if the adhesive bonding material directly contacted the fibres or threads themselves of the backing material, it could not be stripped oil the latter because, the solvent used, while a solvent for the intro-cellulose compound, is not a solvent of the adhesive bonding material hereinafter referred to, to be employed as the grit-holding adhesive bonding material.-

It has been found when this same test. was administered to other abrasive papers, where the waterproof grit-bonding coat penetrated the backing, that no separation could be made between the backing and the grit-bonding coat because the latter had penetrated the backing and coated the threads or fibres themselves, contacted thereby. The only method by which a separation might be made was through the, use oi a solvent dissolving the material which had impregnated the backing, but, inasmuch as that portion which had impregnated the backing, and the waterproof grit-bonding coating were one and the same, naturally the solvent also dissolved the Theimwaterproof grit-bonding coating with the grit embedded therein. Furthermore, this proved that the plurality of waterproof coatings and the adhesive bonding coating were miscible. and, after drying had become practically one continuous penetrative material, whereas, in this invention the plurality of coats'are not miscible but separable. This is one of the main differences between the present invention, in which the adhesive bonding material does not-directly contact the fibres or threads themselves of the backing,

and an abrasive material which has its backing impre nated by the grit-bonding coating which does directly contact and coat the fibres and threads themselves, of the backing.

If the gelatine is employed for the flexible barrier application" as referred to, it may also be dissolved and the backing material stripped from the adhesive bonding material, which latter holds the grit. I

It is to be understood that the stripping of! of the backing material from the adhesive bonding material, described herein, does not occur during an ordinary sanding operation in which this invention is employed, but is disclosed herein merely for the purpose of having it clearly pointed out that there is no penetration of the adhesive bonding-materia] into the backing material under this invention. And, that this invention is therefore radically different from any abrasive material heretofore disclosed in the. art.

It has also been found, where the backing material used with this invention is of a woven fabric in which the weave or mesh between the network of threads, is open, or the fibres loose, the flexible barrier: application "I, as indicated in Figure 1, will contact and coat fibres or threads themselves of the fabric, permitting the spaces or mesh, in between the network of the threads, in some instances, to remain open or unfilled.

When the adhesive bonding coat ll,is then applied over the surface of the flexible barrier application III, the former will be prevented from directly contacting, or penetrating into, any of the fibres or threads themselves of the woven backing material i2. However, some of the adhesive bonding material may be forced into the spaces constituting the meshes, or between the network of the threads, orabout the fibres, caused by pressure when it is applied on the backing,

without however, penetrating into, or impregnating or directly contacting the fibres or threads themselves, of the backing material. It has also been found, wheresuch woven material is used for the backing, and after the flexible barrier'application, together with the backing material, have both been separated and stripped from oil the adhesive bonding material, (hereinbefore described as the test for ascertaining if there is any direct contact by the adhesive bonding material) that the surface of the adhesive bonding material opposite to that with the grit remaining imbedded therein, revealed under microscopic examination, small imprints, points or spikes on the surface of the adhesive bonding material which contacted, or adjoined the flexible barrier applica through the network of the threads, butthese imprints, points or spikes were found to be individual and separate, revealing they hadbeen so formed and imprinted by the cross threads in the network or weave of the threads in the material previously coated, by the flexible barrier application, which further substantiated the fact there had been no penetration of the adhesive bonding material into the backing materials fibres or threads, or direct contacttherewith.

Naturally, where a backing material of a closer weave, or texture, is employed there are no openings in the weave or network of threads sufilciently large for the adhesive'bonding material and flexible barrier application to so engage, and a microscopic examination, such as referred to,

- reveals only slight imprints'made by the outline flexible barrier application" ll-il, is applied the adhesive bonding material Ii in which the grit I5 is to be embedded, and which adhesive bonding material will not penetrate into, or dissolve the "flexible barrier application. The natural pliability of the backing material is thereby retained.

It is submitted, and it is desired to emphasize,

the fact, that a waterproofing solution, such as those disclosed in the formuiasused for manufacturing abrasive papers in the past, cannot because the waterproofing solution referred to, is

usually intended to be, or designated as being miscible with the adhesive bonding coat interposed between the backing material (previously waterproofed) and the abrasive grit.

While the'fiexible barrier application of this invention may impregnate or penetrate into the backing material and contact and coat the fibres or threads themselves, none of the solvents of the adhesive bond coating, applied over the top of the flexible barrier application, effect the latter. Furthermore, to prevent the possibility of any direct contact by the adhesive bonding coat with the threads or fibres themselves, of the backing material, the flexible barrier application is unbroken or continuous over the surface of the backing and the adhesive bond coat and such barrier coating are not miscible.

Where the waterproof agent and the adhesive bond coat, under the conditions of application as used in the waterproof abrasive paper now sold, are intendedv to respectively cause waterproofing and bonding action, it is clear that either may be applied before the other, and there is no necessity for-sequence in the order of their application, because their miscibility will be unthrough itself and its protective or barrier feaindependent application for procuring pliability tures, it-must necessarily be applied first to the backing material, or before the adhesive bond coat is applied, and the latter must be applied on top of, or over the flexible barrier application. It is thus easily observed that ii the adhesive bond coat were applied first it would directly contact and coat some of the fibres or threads of the backing material. However, the flexible barrier application of this invention is a separate, distinct and individual application from the adhesive bond coat, and one of its objects is to act as an effective barrier to the latter if the, former is applied first. And another object of the flexible barrier coating is to procure and impart pliability to the finished product, and not as a waterproofing agent.

Pliability and flexibility in a sheet of sandpaper is of far greater import than the life or endurance of the backing itself, when the latter does not completely disintegrate for a period constituting the usefulness of the sheet of sandpaper. For instancethe average life of a sheet of sandpaper,

standard size, 9 x ll'inches, (waterproof) when used for a regular water sanding operation on an 7 treated, aside from a thin back surface-coatingof a water resistant solution, can be used which will retard the penetration of the :waterfor this period of time, or, at least until thesheet of sandpaper has servedits usefulness.

Another of the objects of the present inven-' tion is to supply an abrasive sheet material, with .its intermediate flexible barrier application,

which will offer a very pliable sheet of sandpaper and one which will bend and conform to many irregular surfaces such as moldings, corners of windows, and the hinges on automobile bodies.

' Sanding over and around these places usually causes sandpaper to crack or breakif it is not sufficiently pliable.

To increase the life or endurance of the paper, or the backing on sandpaper, to a point be-' 'yond its usefulness is neither logical nor advantageous to users and it is therefore not the object of invention to provide a sheet of abrasive material processed and protected so as to render the finished materialabsolutely insoluble in water, or to make it waterproof in 'the full meaning of that term. It is another object of this invention to produce, by aprocess differing from those formerly 'used, a superior sheet of flexible abrasive material which is water, oil and gasoline resistant and possessing natural pliability of its backing materially aided by-its interposed flexible barrier application.

me, having its adhesive bonding or grit-holding 'coat, fastened to the fabric backing material by protruding or extending in and about some of the fibres or threads of the fabric'backing ma terial, without the grit-holding adhesive bond material directly contacting or coating the fibres or threads themselves, of said fabric backing material. v I

The flexible abrasive sheet material constituting the subject. matter of this invention differs in other ways from the waterproofmaterial heretofore referred to. In the present invention one (or more) applications of a semi-plastic adhesive bonding material is applied to a forming base, or backing material, previously treated with a flexible barrier applicatiomhereinbefore described. The semi-plastic adhesive material recommended for theinvention described herein, although it is notdesired to limit the invention to the use thereof, because of other materials which may be used, is however, diflerent from the materials used for grit adhesive bonding purposes which have been employed in many ofthe prior or disclosed formulas for use in the manufacture of other sandpapers, in the-fact principally, that this one in questionis a derivative, or an isomer of rubber material. It'

hasbeen particularly described in applicant's application bearing Serial Number 413,679, filed December 12, 1929. It may be further described as (a) a' homogeneous thermoplastic artificial isomer of undissolved rubber having a less chem ical unsaturation than rubber, or (b) a new composition of matter, the product of reaction, under the influence of heat, of p-phenol sulfonic acid dispersed through a mass of undissolved rubber. This adhesive material must not be classed with vulcanized rubber as it is an"entirely"dif ierent material.

While the said semi-plastic adhesive bonding material is yet in a tacky state, and before it dries, the abrading grit is applied in the usual manner known to the art. The material is then dried by evaporation of its solvents. This may be done without the use of heat. However, for hastening the manufacturing processes, evaporation of the solvents may be accelerated by the application of heat to the required temperature,

preferably not in excess of 125 degrees Fahrenheit. The usual method is to pass the abrasive material, treated as thus described, through a room, compartment or chamber with the temperature at approximately the degree specified.

After drying, there is applied a solution Ii,

(preferably of a different material than that of the adhesive bonding material) to the face of the abrasive grit so as to render the grit-holding surface resistant to oil and gasoline and .in the specification and claims where the term -liquld resisting is employed in describing such coating, thesame shall be-construed to mean gasoline or oil resisting. This material will not penetrate the adhesive bonding material holding the grit, nor into the flexible cation material.

The adhesive described, made from the isomer of rubber, is inherently water resistant, but it is not impervious to the action of oil and gasoline, which are some of the lubricants used in the various sanding operations instead of water.

as the lubricating agent. Therefore, when the isomer of rubber is the adhesive .bond used for holding the abrasive grit, the last mentioned coating over the surface of the grit, is applied as a gasoline andoil resistant protective coating. The use of this coating as a waterproofiing means is unnecessary because in this invention the isomer of rubber material as stated, is inherently water resistant, and if additional waterproofing were the objective of this coating it would be recommended that this additional waterprooflng solution be composed of the isomer of rubber but carrying less solid content than the first, or adhesive grit bond coating. But, for the gasoline and oil resistant coating it is recommended that the principal basic constituent elements be of a phenol formaldehyde condensation product, (b) in cmnbination with polymerizedvinyl compound or (0) one made from polymerized vinyl compound without the former. Either of the three mentioned is to be dissolved in any solvent best suited for the type used, with tween the backing and the grit. If there were danger of starving the bond between the backing material and the grit, an auxiliary bonding coat applied in the same manner might be necessary but it must beTe'menibered particularly, that there can be no so-called starving of the adhesive bond employed in this invention, be-

barrier applicause there can be no absorption of the adhesive or bond coat, by the backing material, as the possess the advantages of also being oil and gasoline resistant.

As shown in Figure 4 a plurality of layers or applications of backing materials I! and flexible barrier applications l8 may be superposedwhen extra coarse grit grains are employed, to give greater strength to the backing, and yet retain pliability and flexibility, and the backings and flexible barrier applications" are alternately arranged.

What is claimed as new is:

1. As an article of manufacture, an abrasive backing and said bonding material, said layer being hygroscopic and immiscible with the adhesive bonding material.

2.As an article of manufacture, a flexible abrasive sheet consisting of a flexible backing,

an adhesive stratum serving as a bonding component, abrasive grains embedded in said adhesive bonding component and a layer of material between said backing and bonding component, said layer being immiscible with the ad: hesive bonding component, said bonding component comprising a synthetic plastic compound having water insoluble properties comprising a rubber isomer, said layer serving as a barrier between the bonding component and the backing, preventing starving of the material of said component into the backing.

3. As an article of manufacture, an abrasive a sheet in accordance with claim 2 in which a sizing of a phenol aldehyde condensation resin imparts liquid resisting" properties to the abrasive face of the article.

4. As an article of manufacture, an abrasive sheet in accordance wih claim 2 in which a sizing of a polymerized vinyl compound, imparts liquid resisting properties to the abrasive face of the article.

5. As a new article of manufacture, a flexible abrasive sheet consisting of a flexible backing,

an adhesive stratum serving as a bonding component, abrasive grains embedded in said adhesive bonding component, and a layer of material between said backing and bonding component, said layer being hygroscopicand immiscible with the adhesive bonding component,

said bonding component comprising a synthetic plastic compound havingwater insoluble properties comprising a rubber isomer, said layer serving as a barrier between the bonding coming 01 a polymerized vinyl compound,

.terial between said backing in bonding component, said layer being a glue base material immiscible with the adhesive bonding component, said bonding component comprising a syntnetic plastic compound having water insoluble properties comprising a rubber isomer, said lay-,- er serving as a barrier between the bonding component and the backing, preventing starving of bonding material of said component into the backing. i

9. As an article of manufacture, an abrasive sheet in accordance with claim 8 in which a sizing of a phenol aldehyde condensation resin imparts liquid resisting properties to the abrasive face of the article.

10. As an article of manufacture, an abrasive sheet in accordance with claim 8 in which a siz ing of a polymerized vinyl compound imparts liquid resisting" properties to the abrasive face of the'article.

11. As an article of 'manufacture, a flexible abrasive sheet consisting of a. flexible backing, an adhesive stratum serving as a bonding component, abrasive grains embedded in said adhesive bonding component, and a layer of material between said backing and bonding component, said layer being fibreless cellulosic material immiscible with the adhesive bonding component, said bonding material comprising a synthetic plastic compound having water insoluble properties comprising a rubber isomer, said layer serving as a barrier between the bonding component and the backing, preventing starving of the bonding material of said component into the backing.

12. As an article of manufacture, an abrasive sheet in accordance with claim 11 in which a sizing of a phenol aldehyde condensation resin imparts liquid resisting properties to the abrasive face of the article.

13. As an article of manufacture, an abrasive sheet in accordance with claim 11 in which a sizing of a polymerized vinyl compound, imparts liquid resisting properties to the abrasive face of the article.

14. As an article of manufacture, a flexible abrasive sheet consisting of a flexible backing, an adhesive stratum serving as a bonding component, abrasive grains embedded in said adhesive bonding component and a layer of material between said backing and said bondingv component, said layer being a glycerol polybasic acid resinous compound immiscible with the adhesive bonding component, said bonding component comprising a synthetic plastic compound having water insoluble properties comprising a rubber isomer.

l5. Asanarticle of manufacture, an abrasive sheet in accordance with claim 14 in whicha sizf ing of a phenol aldehyde condensation resin imparts"liquid resisting properties to the abrasive face of the article.

.16. As an article of manufacture, an abrasive sheet in accordance with claim 14 in which a siz- .,ing of a polymerized vinyl compound imparts liquid resisting" properties to the abrasive face of the article.

' 'HOWARD'G. BARTHNG.

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