US 2838890 A
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Description (OCR text may contain errors)
' abrasive particles during use.
CELLULOSIC PRODUCT James W. McIntyre, Appleton, Wis., assignor, by mesne assignments, to Kimberly-,Clark Corporation, a corporation of Delaware Y Application April 18, 1955, Serial No. 502,039
3 Claims. (Cl. 51-185) This invention relates generally to abrasive coated;
sheet material, and is more particularly directed to an improved form of base sheet for abrasive material and the method ofmaking same.
In abrasive coated products wherein the abrasive grain coverage is substantially uniform and rather closely packed, there is a normal tendency of the grain coating to lill or load with abraded material andthe loosened This loading results in a loss of abrading eiiiciency and, also, provides an uneven surface on the abrasive sheet which is likelyto produce an uneven surface on thevarticle being abraded. Several means have been employed in' an attempt to avoid this loading of the abrasive coated sheet With loose particles, including the application of the abrasive grain to a sheet in an open pattern so as to provide non- Ycoatedareas for accepting the abraded material. However, such previously devised means have not been entirely satisfactory for various reasons, and the present invention is Vthe result of further efforts to provide a more satisfactory solution of the foregoingV and other problems V:relatingto abrasive coated sheets.
The primary object of this invention is to provide an improved type of base sheet for abrasivefcoated sheet material. Another object is to provide an improved abrasive sheet which is Waterproof, properly flexible, and
which includes means for preventing the loading of the sheet with abraded material during use. A further and important object of the invention is to provide an improved method for making a base sheet for `an abrasive coating, as well as for making a sheet of abrasive coated material.
Other objects and advantages will become apparent from the following description of the improved sheet material referred to above and the method for making same, with reference to the accompanying drawings.
Fig. l is a fragmentary plan view of an abrasive sheet vembodying the principles of this invention.
Fig. 2 is an enlarged sectional viewof the base sheet, priorto applying the abrasive.
Fig. 3 is an enlarged sectional Viewfofthe completed abrasive sheet material.
Fig. 4` is a View, similar to Fig. 3, of a modiiied form of abrasive sheet material.
Fig. 5 is a diagrammatic showing of a method embodying the present invention.
In the formation of an abrasive coated product there is, of course, necessarily a base sheet to which the abrasive material is adhesively applied. In many instances this base sheet is of liexible'material, so as to be con- 'formable with the surface deviations of the articles which k'are to be abraded.l A woven fabric sheet may be'used but such a sheet is too costly for many uses and,` also7 the crossed fibers present raised portion which provide an uneven surface in the finished abrasive cloth. Conse- V quently, paper is frequently used as a base sheet for abrasives, and the present invention is particularly directed ICC to an improved form of paper base sheet, although it will be apparent from the following description that the invention isV clearly applicable to any non-Woven ibrous sheet material.
As indicated above, one of the more important features of this invention is the provision of a base sheet which includes a means for preventing the loading of the abrasive coated sheet with abraded material. To overcome this ditlculty the base sheet is provided with many small openings through which the abraded material can escape. The size and shape of such openings is determined n part by the size of the abrasive particles and in part by the characteristics of the material to be abraded. Then, too, the desired strength and exibility for the base sheet, as Well as the degree of self-cleaning required, will be important factors in selecting the size and spacing of the openings in the sheet. Generally, in the manufacture of a base sheet having a basis weight of from about 30 to 150 pounds per ream of 480 sheets 24 by 36 inches for use with abrasives from 60 to 320 standard size, it has been found desirable to utilize openings having an area of from about .003.to .030 square inch. Although described herein With respect to circular openings, it will be apparent that other shapes of openings may be used. Further, with the aforementioned materials it is preferable that the openings in the base sheet comprise from about 20 to 55 percentof the total area of the sheet.
The openings or perforations in the base sheet may be formed in any of several different ways. For example, the perforations might be made as the web is being formed in the paper-making machine, as by plugging selected areas of the forming Wire or by perforating the web during the pressing or drying steps. Then too, the paper might be perforated by suitable mechanical means after it has left the paper-making machine. The determination as to how the paper sheet is to be perforated is primarily a matter of cost, but, as will be seen later, the-stage in the production of the abrasive sheet at which such perforation is to be completed is an important factor in the present invention.
Prior to applying an adhesive substance and the abrasive particles to the base sheet, there is generally applied a `saturant as Well as a barrier coating, although the former might be eliminated Without detracting from the present invention. The saturant is usually water dispersed material and is primarily utilized to lend added weight, strength and flexibility to the completed abrasive sheet. The barrier coating is in the nature of an impervious nlm-forming material and may be a resin, such as a plasticized vinyl chloride, which is effective to prevent the subsequently applied adhesive from striking through and stitfening the sheet. A base sheet which is stiffened by striking through of the adhesive will crack when used and will not be suthciently conformabie. in the latter respect it is important that the base sheet be kept soft internally and this is provided for by the barrier coat. I
It is important to the present invention that the barrier coating be applied after the base sheet has been perforated, so that such coating will also cover the dening edges of all of the openings or .perforations in the sheet, as shown in Figs. 2-4. In this Way, the base sheet is not only sealed on the surface thereof but, also, inwardly of the sheet along the edges of the many small opel.- ings. If the barrier coating is applied before perforating the sheet, the perforation will expose the fibers surrounding each of the perforated openings and permit the adhesive to be absorbed by these fibers and strike into the sheet. This will result in a stiff and brittle sheet, which wil-l cra-ck readily during use. Then, too, ifthe sheet is perforated Yafter the barrier coating isapplied -to'the base sheet, there is a `substantial lossin coating material, as well as saturant if the latter has been used. Usually, a double faced abrasive sheet will be made, wherein the abrasive material is applied to both sides of the base sheet, as shown in Fig. 3. However, the .sheet may be made so that only one side will contain abrasive material, as seen in Fig. 4. In the latter instance it is desirable to provide a suitable backing, since the barrier coating presents a generally smooth surface and will otherwise make the sheet slippery and difficult to hold.
Further, it is advantageous, although not necessary, to apply the saturant after the sheet has been perforated, if a saturant is being used. The saturant will strike in more rapidly and more completely with the sheet perforated. Perhaps the greatest advantage, however, is the saving in the amount of saturant used in the sheet. lf the saturant is applied before ,perforating the sheet, a very considerable portion of it will be lost together with the punched-out .portions of the sheet which become waste material.
With respect to the amount of saturant to be used, it is believed to be most practical to use an amount within the range of from percent to about l0() percent, by weight, of the weight of the base sheet, i. e. with a base sheet having a basis weight of say 8O pounds per ream of 480 sheets 24 x 36 inches, from 0 to 80 pounds of saturant may be used to afford practical results. The amount of saturant selected within this range will be de termined primarily by the amount of added weight and strength and the degree of flexibility which is desired for the finished sheet.
The amount of barrier coating required for the sheet will, of course, depend largely upon the thickness of the sheet and the number and size ofl openings therein. Generally, however, it is believed that with base sheets of the type indicated above, i. e. having a basisweight of 30 to 150 pounds per ream of 480 sheets 24 xV 36 inches and having openingsV comprising from 20 to 55 percent of the sheet area, a practical range for the amount of barrier coating to be'used for the treatment of the sheet in the described manner is from about 2 to about 40 pounds per standard ream of paper. As described, the barrier coating will cover both surfaces of the base sheet and the edges of the openings formed in the sheet.
In the final formation ofthe abrasive sheet, after the saturant and barrier coating have been applied, a suio able adhesive is applied to the surface of the sheet, and the abrasive material is dispersed uniformly over the face of the sheet and bonded thereto by the adhesive material.
With reference now to the drawings which illustrate particular embodiments of the present invention, it is seen in Fig. l that the fibrous sheet 10 contains many small openings 12., which are rather closely spaced and preferably arranged in a uniform .pattern so as to provide for a maximum escapement of the abraded material. ln one instance, for example, satisfactory results'were obtained by using a 6 mil kraft sheet and perforating it with 1/12 inc'h diameter circular holes which were staggered Ms inch between the center of the holes. In this respect, it is believed that perforation of the sheet after it is formed, as by the perforating roll 14 shown in Fig. 5, is best because the edge of the perforated openings are then sharp and provide free passage of abraded particles therethrough. Openings formed in the web on the paper machine by blocking some of the openings in the web forming wire tend to be somewhat irregular and, consequently, hamper the passage of the abraded particles through the sheet.
In order to .provide additional strength and flexibility to the base sheet, the sheet was then saturated with a butadiene acrylonitrile elastomer. Approximately 50 parts dry weight of the elastomer `were used per 100 parts of base paper ber. The saturant may be applied to the sheet in any suitable manner, such as the coating rolls 4 16 and 18 (Fig. 5), operating in connection with a tank 20 containing the saturant.
After suitably drying the saturated base sheet, as by the heating lamps 22, there was then applied a resinous barrier coating 24 by the use of roll coating apparatus including a pair of squeeze rolls Z6 and 28, with the latter partially immersed in the coating material contained in an open tank 30. Essentially, this coating was a polyvinyl chloride resin plasticized with a butadiene acrylonitrile elastomer. The barrier coating was applied to the sheet in the amount of 14.4 pounds per 24 x 36 inch-480 sheet ream of base sheet. The basis weight of the paper before perforation and saturation was 35.5 pounds, and the weight of the ream after perforating and saturating was 35.7 pounds per ream of 480-24 by 36 inch sheets. The sheet was then run through a drier, such as the battery of heating lamps 32, in order to set the barrier coat and condition the sheet for the addition of an adhesive or make coat 34, the abrasive material 36, and a grain sizing 35, to complete the abrading sheet which is shown in Fig. 3.
The make coat 34 and the grain sizing 3S may be any suitable adhesive material, including those varnishes now generally used in making abrasive coated sheets, and are for bonding the abrasive material or grit to the sheet and for holding the grit particles in a fixed, upright position. In the described example, the make coat was 21.7 pounds per ream, the grain sizing was in the amount of 29.5 pounds per ream, and a #280 grit was applied to the sheet. In the illustrated embodiment (Fig. 5) the adhesive or make coat was roll coated on the sheet by a pair of rolls 38 and 40 operating in a tank 42 of adhesive material. The abrasive material 36 and the grain sizing 35 was then applied in a manner generally known in the art and, therefore, not shown in Fig. 5.
In the modification illustrated in Fig. 4, the product was similarly formed except that the abrasive material 36 was applied to only one side of the sheet 10. It will be noted, however, that the barrier coating 24 is desirably extended to both sides of the sheet, since the adhesive, make coating and abrasiveA material will invariably extend into the openings 12. Consequently, the saturant is contained within the sheet and the materials applied subsequent to the barrier coat are prevented from striking through.
Although described with respect to particular materials, it will be apparent to those skilled in the art that other materials may be employed without departing from the principles of this invention. For example, other highly plasticized resins might be used as a saturant in place of the elastomer mentioned above. It is desirable, however, that a flexible saturant be used, because the saturant cannot be plasticized after the barrier coating is applied. Further, other materials such as a copolymer of butadiene acrylonitrile may also be used as a barrier coating. It is important, however, that the barrier coating electively seal the base sheet, so that the subsequently applied adhesive does not strike through and stiffen the sheet.
And, although described with respect to paper sheets, it should be understood that the present invention is also applicable to other non-woven sheet material, such as might be formed from glass fibers, synthetic fibers, blends of textile fibers, and the like. l Back to regular machine It should also be understood that the apparatus described with respect to Fig. 5 is not essential to the present invention, and the illustrated equipment is intended only as an example of the type of means which may be employed in practicing the disclosed method. Obviously, the process may be continuous or interrupted as desired.
l. A flexible base for an abrasive coated sheet comprising a paper sheet having a large number of relatively small openings throughout the sheet, said sheet having a basis weight of between about 30 to 150 pounds per ream of 480 sheets, 24 by 36 inches, each of the openings in I said sheet having an area within the range of from about .003 to .030 square inch and the total area of the openings comprisingfrom about 20 to 55 percent of the total area of said sheet, said perforated sheet being impregnated with a butadiene acrylonitrile elastomer in an amount not greater than about 100 percent, by weight, of the basis weight of the paper sheet, and a barrier coating of a plasticized vinyl chloride covering said perforated sheet and extending through the openings therein to protectively cover the surfaces of said sheet and the opening-dening edges therein, said barrier coating being present in an amount of from about 2 to 40 pounds per ream of the perforated paper sheet.
2. An abrasive coated sheet comprising a paper base sheet which is perforated to provide a large number of relatively small openings throughout the sheets, said base sheet having a basis weight, before it is perforated, of between about 30 and 150 pounds per ream of 480 sheets, 24 by 36 inches, each of the openings in said sheet having an arca within the range of from about .003 to .030 square inch and the total area of the openings comprising from about 20 to 55 percent of the total area of the sheet, said perforated sheet being impregnated with a butadiene acrylonitrile elastomer in an amount not greater than about 100 percent, by weight, of said basis weight of the base sheet, a barrier coating of a plasticized vinyl chloride covering said perforated sheet and extending through the openings therein to protectively cover the exposed surfaces of said sheet including the edges of the openings therein, said barrier coating being present in an amount of from about 2 to 40 pounds per ream of the perforated paper sheet, an adhesive material covering said barrier coating on at least one side of said sheet, and abrasive material within the range of from 60 to 320, standard particle size, uniformly dis- 6 tributed over said sheet and held thereto by said adhesive material.
3. A method for forming an abrasive coated product comprising the formation of a tiexible, non-woven brous web having a basis weight between about 30 and 150 pounds per ream of 480 sheets, 24 by 36 inches, and having a large number of relatively small openings throughout the web, each of said openings having an area within the range of from about .003 to .03() square inch and the total area of the openings comprising from about 20 to 55 percent of the total area of the web, impregnating the web with a butadiene acrylonitrile elastomer in an amount not greater than about percent, by weight, of the web, applying a barrier coating of a plasticized vinyl chloride to the web to cover the exposed surfaces thereof including the edges of the openings therein, said barrier coating being applied in an amount of from about 2 to 40 pounds per ream of said web, applying an adhesive material to at least one side of the web, and depositing abrasive particles within the range of from 6.0 to 320, standard particle size, uniformly over the web so as to affix said particles to the web by said adhesive material.
References Cited in the le of this patent UNITED STATES PATENTS 1,565,027 Okie Dec. 8, 1925 1,615,231 Power Jan. 25, 1927 1,687,453 Klein et al. Oct. 9, 1928 2,013,925 Okie Sept. 10, 1935 2,138,882 Robie Dec. 6, 1938 2,178,381 Trinkle Oct. 31, 1939 2,236,597 Hatch Apr. l, 1941 2,347,662 Carlton et al. May 2, 1944 2,665,528 Sternfeld et al. Jan. l2, 1954 FOREIGN PATENTS 613 Great Britain Mar. 9, 1859