US2542058A - Polishing sheet - Google Patents

Description

`l Feb. 20, 1951 i R. G. RIEDEsEI. l 2,542,058

FOLISHING SHEET Filed Dec. 5. 1949 Po//Ish/ng /d/Ver j mdf/@M Patented Feb. 20, 1951 Richard G. Riedesel, St. Paul, Minn., assignor to vMinnesota Mining Manufacturing Company,

y St. Paul, Minn.,

a corporationy of Delaware Application December 5, 1949, Serial No. 131,072

l 7 Claims. This invention relates to coated sheet material having particular utility in thev wet polishing of glass, as well as in other polishing operations, and comprising a polishing-powder bonded to the exposed surfaces of resilient particles supported on a flexible backing.

The edges vof plate glass panels are commonly ground and polished against steel plates, cork wheels, or felt-covered discs, with loose abrasive or polishing grain being applied continuously as a slurry. in water. For the rough grinding, coated abrasive belts capable of operating under constarrt wetting with water have replaced the systems using loose abrasive grain. Prior to the present invention, however, most if not all of the polishing operations were carried out with iluid suspensions of jewelers rouge or similar polishing-powders applied to cork, felt, or other polishing-wheels or the like. f

My inventionprovides for more rapid polishing, in fewer passes, than is possible with methods employing loose powders. My invention also avoids the untidiness of these prior art polishing methods. Other advantages will lbe apparent from the ensuing description of the product.

Thel several figures of the drawing illustrate, in side elevation, various specific embodiments of my invention.

'I'he embodiment of Figure 1 includes a exible backing member l coated with a sizing lcoat Ily and carrying a layer of resilient particles I2 held in place by a rst adhesive binder I3. The upper coat 44 consisting oi a dispersion oi' polishing powder in an adhesive binder.

One specific example of a polishing-sheet made as indicated in Figure 1 and which has given excellent results in the wet polishing of'glass when used in the form of a continuous belt will now be described. While endless belts are preferred, it

will be apparent that my sheet material has utilf ity also in the form of discs, cones. at sheets or strips, etc.

. The llexible backing layer was prepared from stretched pre-shrunk drill cloth having a thread count of 76 vx 48 and weighing about 50 grainsper 24 sq. in. The cloth was first'impregnated with a 20% solution of 2o c. P. s. (4v-50% ethoxy) ethyl cellulose in a mixture of xylol and ethylene glycol monoethyl ether, and after drying was ffound to contain about -17 grains per 24 sq. in. 4 of the dry residue. During drying, the lwebwas held in a flat stretched condition. The ethyl cellulose stiiened the fabric, provided water-resistance, and improved the anchorage while reducing the penetration of the sizing coat.

The sizing coat consisted 'of 85 parts of polyand 11 parts of vinyl acetate (Vinylite AYAT) diatomaceous earth, in 148 parts of xylol and `148 parts of alcohol. Suiilcient of the solution lwas applied to provide 10'-12 grains/24 sq.vin. of the l solids after drying. This sizing coat further im.-

surface of the particles and the interposed binder is furtier coated with a polishing layer Il consisting of polishing-powder dispersed throughout an adhesive binder havingy somewhat greater ihmness and hardness than the first binder coat I3.

In the modiiication shown in Figure 2, a ilexible backing member is coated directly with an adhesive binder 23 into which are pressed. the resilient particles 22. `The particles 22 and adhesive layer 23` are then coated with a layer vof adhesive binder 25 and a nal covering of polish-- ing powder 2B.`

proved the water-resistance and non-stretching properties of the web, and also lprovided improved anchorage for the adhesive binder.

A drying-oil-modied'valkyd resin wavs'fusedas the binder for the resilient particIesf'SuitabIe binders are those previously employed in the coated abrasives industry for bonding' abrasive grit to fabric backings; cf. Guth Patent No.

2,202,765. One'specicalkydresin binder whichA has given `good results in the present invention is a linseed-oil-modifled vphthalic .glyceridey By its use, the vresilient'particles are rrnly and re- "siliently bonded to the sized backing. 'About Figure 3 showsfa modification in which each y resilient particle 321s rst separately encased in` a hardened coating 34 of a mixture of polishingpowder and adhesive, and is then bonded to the flexible backing 30 yby means of an adhesive binder layer 33. f

In Figure 4, the resilient particles 42 are bonded to the flexible backing 40. previously covered with a sizing coat Il, by means of an adhesive binder 25-30 grains/24 sq.'in. of thi'sbindevr, 0n the sol-r vent-free basis, is used. ,1 l I As the resilient particles, Iprefer to employ cork particles.l The comminutedcork is preferably screened to remove oli-size lumps and nes,

'the` portion v`cmjresponding 'approximately to `screen sizes of 24-36 vmesh beingretained in the present example, although other particle sizes may be used.` This material is spread lover .the

adhesive-coated, sheet and .pressed down with rollers, the excess then vbeing shaken oil', .Sub-

stanuany a sing1e-thicknessof'paruclesis ordinarily obtained where the binder weight and the 'less than 5 seconds.

ishing, using a slurry of powder and water,

particle size are as specifled. the weight of the layer of cork particles being approximately 9-10 grains/24 sq. in. The sheet is then placed in an oven for 24 hours, to remove the solvent and to cure the binder.

The sheet is now ready for application of the polishing layer, which in this case is a mixture of air-float tripoli (siliceous polishing-powder) and phenolic resin varnish, '75 parts by weight of the tripoli being mixed into enough liquid varnish to provide 29 parts by weight of non-volatile components. The coating weight of this mixture, on the dry basis, is '104 grains per 24 sq. in. Further heating of the coated sheet cures the varnish binder to a hard and tough state.

Endless belts may be made from the coated and cured sheet material by slitting to proper y width, and skiving and splicing together the ends of a section of desired length, in accordance with well-known practice. The resulting belt retains its shape and strength when operated under a constant stream of water. It reduces roughground glass edges to a smooth polished condition rapidly and eiliciently. For example, plate glass rough-edged with grit 320 abrasive belt was nished to the desired high polish by the action of the polishing-belt as above described, operating under a constant stream of water, in

Prior art methods of finwould have required at least several minutes to produce an equally acceptable edge.

Thus my novel sheet material provides for increased speed and eiliciency of polishing. An

additional and unexpected advantage is the long service life of these polishing-belts. Cork is quite friable, and under the severe pounding experienced in wet grinding would be expected to shear or break oif, or to pull away from the binder, after only a few passes across the workpiece. On the contrary, however, I have discovered that the presence of the cork particles improves both the service life and the polishing speed and eiiiciency of such belts, as well as the quality of the nish produced. For example, a belt made with the same mixture of tripoli and varnish, coated directly on the treated and sized cloth backing but in the absence of the cork particles, produced scratches in the glass edge and was no longer effective after only minutes of service. In contrast, the belt having a layer of cork particles and made in accordance with the foregoing example produced a scratch-free finish and was still useful after one hour of 0peration. Furthermore my cork-containing belt was easier to handle. the layer of cork and binder making the strip less limp and more water-resistant.

In probable partial explanation of the superior results obtained with my novel sheet material, the following suggestions are offered. The presence of the resilient mass beneath the polishing powder maintains a more nearly constant pressure of all operative powder particles against the surface to be polished, hence a maximum polishing effect is obtained, and somewhat coarser powders may be employed than would otherwise y particles emphasizes the yielding qualities of the base while still permitting the use of a hard, rm binder for getting the maximum cutting eiliciency from the powder. The cork particles themselves aid in burnishing and improving the polish of the work-piece.

Regardless of the particular reasons and mechanisms involved, the fact remains that actual tests have shown my novel polishing-sheet, particularly in the form\of endless belts on a wet-sanding machine, to\provide faster, more eicient, more economical, and generally superior industrial polishing of the edges of glass panels and other surfaces than has been possible by means of previously employed systems.

It will be apparent from Figures 2-4 that a number of alternative structures may be employed. Figure 2, for example, illustrates a sheet in which the sizing coate of Figure 1 is eliminated, and the polishing-powder is applied as a separate dry coating to the outer binder layer prior to drying and curing the same. In this construction, the backing is preferably more completely filled with the ethyl cellulose or equivalent impregnating material, and in most instances a somewhat larger amount of adhesive binder for the resilient particles is applied in order still further to impregnate the adjacent surface of the backing. The outer binder layer may be somewhat lighter than that of the construction shown in Figure 1, and the total amount of .polishing-powder will then be reduced also. However, all of the powder will be at, or very close to, the surface of the sheet and hence at a posiiton of maximum effectiveness.

In Figure 3 the cork 'particles are individually completely surrounded by, or encased in, a shell of the mixture of polishing-powder and binder, and the encased particles are bonded directly to the impregnated backing by means of an additional amount of a somewhat softer type of adhesive binder. Only one binder coat on the sheet material, and only one oven treatment, is required for this structure.

Figure 4 illustrates another' modification in which a single binder coat is sufcient. In this case, the single binder composition carries both the resilient particles and the polishing-powder.

It will be apparent, in view of the description,

that many other combinations, to provide analogous advantages, are possible, and such combinations and variations are contemplated as coming within the scope of the appended claims.

Additionally, many other equivalent materials and components will be apparent to Vthose familiar with the art, in view of the teachings here provided, and such elements are also contemplated.

Cloth backings have also been successfully impregnated with polystyrene resin or polyvinyl butyral resin in place of ethyl cellulose. Suitable papers or other brous webs having the required strength and dimensional stability may replace the fabric. Vulcanized fiber, and various resinous or polymeric films, may replace the impregnated brous web here specified as the backing member.

In place of vinyl acetate polymer, plasticized phenolic resins have been employed as the sizing coat Il of Figure 1; and polyvinyl butyral -resin was then used to replace the alkyd resin binder I3 and the binder of the polishing layer I 4. In another example, a'drying oil modified phenolaldehyde resin as the binder for the polishingpowder provided excellent results. One specific formula of this type employs a varnish comprising one part of para-phenyl-phenol: formaldehyde resin (Bakelite BR254) and three parts of dicyclopentadicne-modiiledlinseed oil C115-5 oil), applied from solution in xylol and naphtha. Polyvinyl butyral modified withv minor 'proportions of phenolic resin has also been used. 'I'hese and other similar film-forming adhesive materials are all found to have desirable qualities. Much softer materials are to be avoided, however, because of their lack of required strength; and much harder materials, e. g. combinations of polyvinyl butyral with an excessively high proportion of phenol-aldehyde resin, are undesirable since they may cause scratching of the worksurface in some cases.

The various combinations of imoregnants, sizes, and binders hereinabove noted have been found to provide particularly desirable results in combination with cork particles and tripoli polishing-powder for polishing glass edges. The relatively hard outer binder adheres firmly to the i cork particles and the surrounding somewhat softer inner binder, which in turn adheres well to the cork and to the sizing layer where such is used, or directly to the impregnated brous backing as indicated in Figure 2, to provide a'wellunified compositev sheet. For polishing other classes of materials, still other combinations are found suitable. Thus, a sheet such as indicated in Figure 4 was found to be excellent for polishing resinous'panels such as methyl methacrylate polymer (Lucite) when made with a cloth backing impregnated with polyvinyl butyral resin and primed with a heat-setting phenol-aldehyde resin applied from solution in water, alcohol and ethylene glycol monoethyl ether, and with a polyvinyl butyral resin binder for the cork particles an` iron oxide polishin -powder was used.

Air-float tripoli, a fl ely divided silica polishing-powder, combines rapid cutting action with \and the mineral polishlg-powder. In this case,

' excellent polishing action when used in these novel polishing-sheet structures for such applications as the polishing of glass, even though under ordinary lapping usage, such powder is considered to be too coarse for final polishing. L Pumice powder of 3F or 4F grade is also satisfactory. Materials such as polishing grades of tin oxide, cerium oxide, or iron oxide are much slower and, for my purposes where the polishing of glass is concerned, are needlessly fine. These are thel classes of polishing-powders ordinarily required to be used in commercial polishing operations on glass, in order to avoid scratching of the glass surface.

As the resilient particles, I greatly prefer to employ cork particles, since, as previously mentioned, these provide an additional burnishing action in addition to a particularly advantageous glass edges, comprising a flexible, water-resistant,

dimensionally stable backing, a layer of cork particles adherently bonded to one surface thereof, and a mineral polishing-powder uniformly adherently bonded to the outer surfaces of said particles. 1

3. A polishing-sheet suitable, in'the form o an endless belt, for wet-polishing of glass edges, comprising a exlble, water-resistant, dimensionally stable backing, a layer v'of cork particles adherently bond d to one surface thereof, and a' mineral polishing-powder surrounding each cork particle and adherently bonded thereto.

4. A polishing-sheet suitable, in the form of an endless belt. for wet-polishing of glass edges, comprising a flexible, water-resistant, dimensionally stabl.x backing, a layer of cork particles adjacent one surface thereof, and an adhesive containing uniformly admixed polishing-powder, said binder surrounding tach cork particle and adherently bonding said particles to said back- V ible, water-resistant. dimensionally stable backing comprising a porous fabric base impregnated with a flexible water-resistant film-forming polymer and surface-sized with a flexible waterresistant film-forming polymer, an inner resinous adhesive binder layer, a layer of resilient particles, and an outer resinous binder and polishing layer comprising a mineral polishingpowd r uniformly distributed throughout a varnish binder, each successive layer being firmly bonded to the previously-named layer.

7. A polishing-sheet comprising in order a ilexible, water-resistantsdimensionally stable backing comprising a porous cloth impregnated with a water-resistant,l film-forming cellulose polymer composition, a surface sizing of a film-forming vinyl polymer composition, an inner alkydresin adhesive binder layer, a layer of resilient cork particles of about 24--36 meshsize, and an outer binder and polishing layer composed lof mineral polishing-powder uniformly distributed throughout a phenolicresin-drying oil varnish, each successive layer being firmly bonded to the previously named layer.

- a RICHARD G. RIEDESEL.

No references cited.

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