US2276685A - Process of coating porous articles - Google Patents

Description

March 17, 1942. A|... M. BRlGl-IT PRocEss oF comme PoRoUs ARTICLES Filed Nov'. 1-, 1958 I Patented Mar. 17, 1.942

2,276,685 PROCESS or CoA'rING PoRoUs ARTICLES Elvin M. Bright, M. Wallace,

Dayton, Ohio, assignor to John Cincinnati, Ohio, as trustee Application November 1, 1938, Serial No. 238,215

1 Claim.

This invention relates to coating of articles and more particularly to the coating of articles having a porous surface, such as articles made from wood or the like, or molded articles made rom a porous material such as sawdust and other porous moldingmaterials.

An object of this invention is to provide a mask for a portion of the article to be coated.

Another object of this invention is to provide a priming coat forming a bond between the surface of the article to be coated and the outer coating.

Another object of this invention is to provide a ller to be applied over the priming coat, so as to smooth irregularities in the wood or the article, so as to present a uniform, flat or even surface. e

Another object of this invention is to provide a priming coat which Another object of this invention is to impreg- .nate wood with 'nitrocellulose material.

Y Another object of this invention is to providev a coating for an article havng a porous, irregular surface, which coating is cheap, efiicient and at the same time presents a uniform, glossy surface.

Other objects and advantages reside in the construction of parts, the combination thereof and the mode of operation, as will become more apparent from the following description.

Referring to the drawing, i

Figure 1 is a perspective view of a shoe heel made from wood that is to be coated with nitrocellulose material.

Figure 2 is a cross sectional view taken substantially on the line 2-2 of Figure 1, to showi the several coatings.

Figure 3 is a schematic diagram showing the process of applying a nitrocellulose coating or other coating to the article to be coated.

Numerous attempts have been made to provide a cheap priming coating for wooden or other porous articles to be coated, which priming coating is to function as a bond between the article to be coated and the outside finishing coating. None have been satisfactory when usinga nitrocellulose coating or a nitrocellulose finish, which coating has not been bonded to the article but will form a bond between the nitrocellulose co ting and the` article to be coated.

the past, the air or solution will penetrate the pores of the wood, ex-

has formed a tight encasement without a bond.

between the article to be coated andthe outer nitrocellulose coating, whether this outer coating be applied in the form of sheets or by spraying or by dipping. Furthermore, when dipping the article into nitrocellulose solutions as used in of minute bubbles.

.found that by dipping the wooden article into gasses retained by the pores of the wood are liberated and will cause blisters underneath the coating, resulting in a defective coating.y The elimination of this air has been an unsolved problem. Before discussing the solution to this problem, a brief explanation will be made of a preliminary masking step in the process.

Masking If the entirearticley is not to be coated, any portion may be exposed by masking such portion. Any suitable masking material that does not form a bond with the coating material and that has no objectionable features as far as the article is concerned may be used. `If a wooden article is to be masked, it may be coated with either potassium or sodium silicate, more commonly known as waterglass The nitrocellulose material does not adhere to masking material. Furthermore, the waterglass does not in any manner injure the wood later to be exposed. Although waterglasshas been disclosed for the purposes of illustration, any other suitable masking material may be used. l

Priming and bonding film or coating By dipping the article tobe coated in a very thin solution of nitrocellulose material, wherein the greater portion of the solution consists of the solvent for the nitrocellulose material, this thin pelling the air and the gases therein in the form For example, it has been one-fourth pound of nitrocellulose material dis.- solved in one gallon of Isotone, which is a trade name for a solution consisting of sixty percent acetone, twenty-five percent isopropyl acetate and fifteen percent anhydrous isopropanol, that bubbles will form upon the outer surface of the article to be coated and eventually be liberated therefrom if the solution is not agitated over a period of twenty-five to forty minutes depending upon the condition of the wood, the shape of the body to be coated, the extent of the masked area, the quality of the material, the porosity of the article, etcetera. y

By agitating the solution in which the article is dipped, during the time merged, the liberation of the gases is greatly accelerated. vThe-time is reduced to five to eight minutes, which is sufiicient time to permit all of the air that will cause any deleterious effects to This making step will now be described.

the waterglass that the mme is subbe expelled from the surface of the article to be coated.

In addition to the expulsion' of the air from the outer` surface of the article to be coated, the dipping ofv the article in this thin solution of nitrocellulose material results in some of the nitrocellulose Ymaterial actually soaking into the pores of the wood, which has in the past been considered absolutely impossible. If the dipping solution contained much more nitrocellulose material, the solution would be much thicker, so as to form an exterior coating which would encase the article without expelling the air and without penetrating the pores of the wood. After the article is coated with this thick coating, some of the solvent would undoubtedly liberate some of the entrappved air, driving this air to the surface beneath the coating, where it forms a bubble that is not released but may show up as a bulge in the finished article. The thin lm covering the surface of the article .coated with the extremely thin coating is impregnated or soaked into the surface of the wood, so as to form a. rigid bond with the article. This priming coat is permitted to 'dry partially in the open air, without any particularly deleterious effect, as the coating is so thin that there is not sufflcient thickness to house or enclose deleterious gas bubbles usually formed in nitrocellulose coating from rapid evaporation of the solvent when cured in the air.

Finishing coat or coating The finishing coating may include (a) a dipped cellulose coating either with or without the use of a filler coating; (b) a spray coating either with or without a filler coating, or (c) a coating formed by applying sheets from preformed sheets of cellulose material.

In view of the ller coating when used being applied first, the application of the filler coating will now be described.

Filler coating Heels formed from Wood or other porous material usually have some of the grains exposed, leaving rough surfaces. Even though the wood may appear to have a highly polished surface before the application of the priming coating, the l surface after being primed usually gets rough,

' due to the inherent structure of the material of the article. Therefore, it is necessary either to refinish the surface or to use a ller coating to eliminate the irregularities. The former is not satisfactory for the reason that it is impractical to polish a moist surface and the cost is prohibitive. In the next place, if the priming coating were permitted to harden to permit finishing, the purpose of the priming coating would be partially defeated, as it does not form a good bond where the outer film has been removed.

A ller coating may be applied by dipping the article into a liquid including a suitable comminuted inert filler material suspended in nitro- .cellulose material dissolved in a suitable solvent. Comminuted diatomaceous earth has^been found to give excellent results as an inert filler material.

Due to the surface tension of the nitrocellulose material when it is cured, the filler coating has a tendency to fill the pores and the grain ofthe Wood, so as to completely conceal the underlying material. This coating may be cured by the process disclosed in my Patent No. 2,130,225 granted A Sept. 13, 1938, which process includes the steps of cyclically dipping or submerging the freshly coated article into a solution having an attraction for the solvent used in dissolving the nitrocellulose material, in which solution the nitrocellulose is substantially insoluble, then subjecting the article to a gaseous medium saturated with fumes from the solvent used in dissolving the nitrocellulose material.

If nitrocellulose material were used without having added thereto a i-lller material, the shrinkage would force the nitrocellulose material into the dips or detailed'low and high areas of the article. By adding the ller material, it functions to' offset 'the deleterious shrinkage of the nitrocellulose material. This filler material prevents the free fiow of the nitrocellulose material. It actsas a buffer or impedance to the fiow of the nitrocellulose material. Therefore, the outer surface of the cured filler material has substantially the same contour as it had immediately after the article was removed from the dipping solution when the outer surface was smooth due to surface tension of the liquid coating material. However,- the cured surface of the filler coating does' not have .the desired gloss and texture. That` being the case, it is necessary to add a finishing coating that acts as a veneer plastic ply coating.

After the filler coating, which may include the desired pigment'or dye, has been applied and cured sufficiently, the final flnishing coating may be applied.

For the purposes of illustration, it has been found that as a filler coating, two and one-half pounds of nitrocellulose material dissolved in one gallon of Isotone having added thereto threefourths pound diatomaceous earth and a suitable pigment or the like, produces excellent results. Any other suitable filler material may be used.

Finishing coating Removal of coating overlying mask When coating such articles as wooden shoe heels, it is necessary to remove the coating from the top of the heel and also from the bottom. It has been found that by masking the top and the bottom of the heel, as described above, by a suitable material such as waterglass, the priming coating and the subsequent coatings will not penetrate the wood covered by this masking material. Thus, after the article has been coated, thenitrocellulose material extending across the top of the heel and across the bottom of the heel may be cut away and removed bodily, so as to leave the wood exposed. This process-will now be described as ppllied to the coating of a ladies wooden shoe In the drawing, the reference character I0 indicates a heel of a ladies shoe, which has been turned from Wood or formed lfrom a plastic including sawdust, which heel is rough, due to the grain in the Wood, and therefore must be coated, so as to fill the grain of the Wood. The top sur- -face l2 of the heel and the bottom, which has not been shown, must have the Wood exposed i be satisfactory.

after the heel has been coated. I'hat being th case, the top surface of the heel andthe bottom thereof are rst coated with potassium or sodium silicate, more commonly known as waterglass. This has been shown schematically by the first square shownjin Figure 3. After the masking coating has been applied over the surfaces to be exposed, theheel is dipped into a thin nitrocellulose coating ld, as described above, and preferably while the solution is agitated. The solution is agitated from below the liquidlevel Aand preferably below the lower. level of the heel by a controlled movement. This movement -should cause the liquid in the vicinity of the submerged article to have an upward movement so as to sweep upwardly the bubbles forming on the surface of the article. This sweeping action of the bubbles causesI these bubbles to rise to the surface of the solution. Any suitable agitator causing the solution to-have the desired eddy currents may be used.

.This priming coating is permitted to dry in the air for a short period of time. However, this coating should not be permitted to set or harden, as it is very desirable that the subsequent coating IS, which may consist of a ller material and Y nitrocellulose material dissolved in a suitable solvent as' for example Isotone, be applied before the priming coating 'has hardened, that is, while it is moist, as the bond between the priming coating and the iiller material would then dipping the article into a solution consisting of nitrocellulose material dissolved in Isotone having added thereto diatomaceous earth and preferably a suitable pigment.

coating solution.

This nal coating solution may contain a pigment, or it may be clear. coating the nished article has greater depth to it. Whether or not a pigment is added to this coating depends entirely upon the condition of the ller coating and the'requirements of the finished article. This coating I8 preferably con- By providing a clearaevaese c.

Y This s olvent softens be more effective. The ller material may be applied by sists of nitrocellulose material dissolved in Isotone, havingthe desired thus coated is again subjected to the curing, the same as already described and as fully shown in my aforementioned patent.

After the nal coating has been cured, the ends subjected to a clicking maof the heel maybe chine, so as to remove the coating material overlying the masking material, which coating material isjeasily removed, as it does not adhere to the waterglass. The article is now nisned and ready for use.

AlthoughaI heel hasbeen of illustration, dippedcan be subjected to the process described above.

used for the purpose Spray coating For some types of usage, a cheaper coating may Instead' of applying the 311er coating and a nishing coating, a coating may be sprayed directly upon the priming coating,

viscosity. The article any type of article adapted to be mterial in which spray coating adheres to the priming coatt5 'with the moist coating forms a ller coating Application of nitrocellulose sheets For some types of work it maybe desirable to apply sheets of nitrocellulose material directly to the article after it has been primed. Isotone or any other suitable solvent is preferably applied to the inside of the sheet to be applied to the article. the side of the sheet coming in contact with the moist priming nitrocellulose material that is saturated into the outer surface of the article to' be coated. The moist inner side of the sheet coming in contact a homogeneous union, so that the impregnated priming coating and the outer applied sheeting form a unitary structure. Thus, a coating may be formed from vapplied sheets that has the chaiacteristicsfof a unitary impregnated coating. The priming coating constitutes a bond between the article and the covering sheet. Where the surface of the coated article is irregular, as for example a shoe heel, the sheet is preferably first preformed into I the approximate shape of the nished article,

by any method well known to thosev skilled in the art.

Although a shoe heel has been used as the article to be coated, the processes .of applying the 'coating are applicable to any other. suitable article. Instead of nitrocellulose material, any other suitable coating material having characteristics similar to nitrocellulose material may be used, as for example de-nitrated nitrocellulose material and other cellulose materials such -as i scribed, it wm be understood that within the purview of this invention, equivalents not excluded by the prior art are included which are capable of carrying' out the objects as disclosed and '.dened in the appended claim.

Having thus described my invention, I claim:

The method of 'bonding a nitrocellulose coating to a. wooden article including the steps of masking the mrtions of the article later to be exposed Without a coating, dipping the masked article into a thin solution consisting of nitrocellulose material dissolvedin a suitable solvent so as to expel the air from the pores of the wood and so as to impregnate the outer surface of the Wood with the nitrocellulose material priming lm, partially drying the priming nlm, applying by dipping the impregnated article While the priming lm is moist into a solution including nitrocellulose material dissolved in a suitable solventhaving added thereto a lier material, c the coating. dipping the article into a nishing coating including nitrocellulose'material dissolved in a suitable solvent and curing the nishing coating by cyclically dipping the article into a solution -havingan attraction for the solvent used in dissolving the nitrocellulose which solution the nitrocellulose material is substantially insoluble, and removing the a zone saturated with the fumes from the solvent used in dissolving the nitrocellulose material, so as ,to cure the coating, and bodily removing 'the nitrocellulose material overlying the masking material.

ENDE M. BRIGHT.

coating of

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