US 2937934 A
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Description (OCR text may contain errors)
May 24, 1960 K. F. NEFF-LEN 2,937,934
PLASTIC FILM ABRASIVE SHEET Filed June 29, 1951 5 Fig. 2
Kar! I''Neffien United States PLASTIC FlIM ABRASIVE SHEET Karl F. Nelen, Bethesda, Md., assignor to the United States of America as represented by the Secretary of Commerce Filed June 29, 1951, Ser. No. 234,167
6 Claims. (Cl. 51-293) (Granted under Title 35, U.S. Code (1952), sec. 265) ilm abrasive sheet for use in polishing surfaces to micron finishes.
Abrasive papers are made at present by securing the abrasive on the surfaces by plating, spraying, gluing, or by forcing the abrasive into the backing material. These methods, however, will allow the abrasive material to loosen, especially when water or other coolants are used. As a result some -of the abrasive material is detached from the backing and may become embedded in a metallic or crystalline surface being polished. This surface may then abrade other surfaces with which it comes into contact. Another disadvantage is that the life of the abrasive paper is greatly reduced by this loss of abrasive material. When the abrasive paper is 4expensive because of the use of a scarce material, such as diamond dust, this latter consideration becomes very important.
Another disadvantage of the above methods is that the abrasive material is held rather rigidly in the backing, and since many abrasive materials are brittle (particularly abrasives made of the dust of precious stones) there is a tendency for the abrasive to break off thereby reducing the effectiveness of the abrasive paper.
It is therefore the primary object ofthe invention to provide an abrasive paper from which the abrasive is not easily detached.
Another object is to provide an abrasive paper which is not affected by water or other coolants.
It is another object of the invention to provide for an abrasive paper in which the material is held in such a manner that the binder acts as a cushion for the abrasive material thereby reducing the tendency of the abrasive particles to break or shatter.
Still another object is to provide an abrasive paper which is simple and inexpensive to make.
Other objects and advantages of the invention will become apparent by reference to the detailed description below and to the accompanying drawings, in which:
Figure 1 is a representation of a vertical cross section of a sheet of the abrasive material of my invention.
Figure 2 is a representation of one stage in the manufacture of the plastic film abrasive paper.
Figure 3 is a representation of another stage in the manufacture of the abrasive.
In Figure l there is shown an abrasive 1 embedded in a plastic material 2, this being held to a suitable backing 3 by an adhesive 4.
The plastic used may be any vinyl plastic or any plastic that will hold the abrasive firmly, be resistant to coolants and have elastic qualities similar to those of the vinyl plastics.
The backing 3 in Figure 1 may be paper, cloth, metal,
or some plastic. The choice of backing will depend a1- most entirely upon the -use to which the'abrasive is to be put.
The binder used will depend` upon the type of backing but in most cases a vinyl plastic can be used as the binder.
Figure 1 shows the plastic layer bonded to a backing. However, for many purposes the backing is not necessary and therefore can be eliminated.
Figure 2 shows one stage in the manufacture of the plastic film abrasive. Vinyl chloride acetate, the plastic used in this particular instance, is dissolved in a suitable solvent, such as cyclohexanone. To this solution is `added the abrasive-in this case diamond dust. The size and quantity of the dust particles added will depend upon the degree of abrasiveness and the concentration desired. This mixture is poured onto a smooth plate 5, which together with the sides 6 serves to form a mold for the plastic. When the plastic is initially poured into/the mold, the diamond dust 1 is more or vless uniformly distributed throughout the plastic 2. This is shown in Figure 2. As indicated in Figure 1, it is desired to have all of the abrasive lie in a single plane and therefore enough solvent must be used so that the viscosity of the solution will be such that all of the abrasive will settle to the bottom ofthe plasticlm before the plastic dries. Therefore the amount of solvent used must be determined for each grade of iineness of each abrasive of a particular density. The least possible amount of solvent is used in each case so that the drying time can be kept to a minimum.
yFigure 3 shows the final appearance of the mixture in the mold. All of the diamond dust has settled to the bottom of the mixture and is lined up along the smooth face of the plate 5. When all of the solvent has evaporated and the diamond dust is held firmly in the plastic, the plastic iilm can be stripped from the smooth plate.
As pointed out above, the diamond dust settles to the bottom of the plastic solution, vand therefore this method will require less abrasive material than abrasive papers in which the abrasive is uniformly distributed throughout the film. Another result of this sedimentation method of preparation is that all of the cutting edges of the abrasive material lie in the same plane. Obviously this result is highly desirable when polishing surfaces to micronishes.
As indicated by the drawings, the plastic tends to completely surround the diamond particles thereby providing a very strong bond between the abrasive and the plastic. Only the very outermost edges of the particles are exposed to the surface to be polished. If any of the plastic does cover the abrasive surface it will be wiped away during the first polishing motion, since the plastic is cornparatively soft. Another result of this characteristic of the plastic is that as the particles tend to wear down, any of the plastic that tends to protrude beyond the abrasive surface will be wiped away thereby always leaving the abrasive surface in contact with the metallic surface to be polished.
In abrasives made according to the prior art some diamond particles tend to wear down more slowly than others, and as a result the surface being polished may become scored. However, the abrasive sheet -made according to the present invention eliminates this difficulty. If some of the particles do wear down more slowly than others, the pressure on these harder particles will increase and, since the plastic is comparatively soft, these particles will be forced back into the plastic until the entire abrasive surface again lies in the same plane. To get this result, however, the layer of diamond dust must be comparatively thin compared to the thickness of the plastic layer. This result is easily obtained owing to the method of manufacture. By choosing the proper amount of diamond dust to be added to the plastic solution and thoroughly mixing to insure uniformity, the thickness of the layer of abrasive material lis readily controlled. n
As previously mentioned, diamond particles are rather brittle and tend to break oi if too much pressure is applied to them. However, it has been found that the vinyl plastics provide a medium for holding the diamond dust that is highly elastic, and as a result the plastic provides a cushioning effect that almost completely eliminates this difficulty.
It will be apparent to those skilled in the art that this invention is not restricted to' only abrasive sheets. The invention might take the form of an abrasive stick or an abrasive block` This invention may be manufactured in any desired size or shape.
It will be apparent that the embodiments shown are only exemplary and that various modifications can be made within the scope of my invention as defined in the appended claims.
1. The method of making a plastic film abrasive sheet which comprises dissolving a plastic material in a suficient amount of solvent to permit complete gravity settling of abrasive material, adding an abrasive material to said plastic material and said solvent, thoroughly blending the mixture, and pouring said mixture into a mold.
2. The method of making a plastic film abrasive sheet which comprises dissolving a vinyl plastic in a sufficient amount of solvent to permit complete gravity settling of abrasive material, adding an abrasive material to the solution, thoroughly blending the mixture, pouring said mixture into a mold, and allowing said abrasive material to settle to the bottom of said mixture,
3. The method of making a plastic film abrasive sheet which comprises dissolving vinyl chloride acetate in a suflicient amount of cyclohexanone to permit complete gravity settling of abrasive material, adding an abrasive material to the solution, thoroughly blending the mixture, pouring said mixture into a mold, allowing said abrasive material to settle to the bottom of said mixture, and drying said mixture.
4. The method of making a plastic film abrasive sheet which comprises dissolving a plastic in suthcient amount of solvent to permit complete gravity settling of abrasive material, the amount of said solvent added being determined by the neness and the density of said abrasive material, adding said abrasive material to said plastic material and said solvent, thoroughly mixing the mixture of said plastic, solvent, and abrasive material, pouring said mixture onto a smooth surface, 'allowing substantially all of said abrasive material to settle to the portion of said mixture adjacent to said smooth surface, drying said mixture, and'then stripping said plastic tilrn abrasive sheet from said smooth surface.
5. The invention as recited in claim 4 in Which` the plastic is vinyl plastic and the said abrasive material is diamond dust.
6. The invention as recited in claim 5 in which the vinyl plastic is vinyl chloride acetate and the solvent is cyclohexanone.
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