US 3708321 A
Description (OCR text may contain errors)
Jan. 2, 1973 F. E. SPIELES 3,708,321
METHOD FOR APPLYING A METALLIC FLAKE FINISH Filed Sept. 18, 1970 APPLY LIQUID PRIMER COATING.
PREHEATTO DRY PRIMER COATING.
ELECTROSTATICALLY APPLY POWDER COATING OF A MIXTURE OF CLEAR THERMOPLASTIC MATERIAL AND METAL FLAKE s.
HEAT T0 FUSE THERMOPLASTIC POWDER.
ELE CTROSTATICALLY APPLY POWDER COATING OF CLEAR THERMOPLASTIC I MATERIAL HEAT T0 FUSE THERMOPLASTIC POWDER TO A SMOOTH COATING.
INVENTOR. FRANKLIN 5. 51 1212 5.
United States Patent 3,708,321 METHOD FOR APPLYING A METALLIC FLAKE FINISH Franklin E. Spieles, Delphos, Ohio, assignor to Hagan Manufacturing Company, Deiphos, Ohio Filed Sept. 18, 1970, Ser. No. 73,423 Int. Cl. Bb 5/02; B44d 1/092, 1/094 U.S. Cl. 11717 2 Claims ABSTRACT OF THE DISCLOSURE A method for applying a decorative, metallic flake finish to an article. The method comprises the steps of: (1) heating the article to above the melting temperature of a preselected transparent thermoplastic resin; (2) while the article is hot, coating the article with a mixture of aluminum foil flakes and the thermoplastic resin in powder form; (3) reheating the article until the powdered resin is fused; (4) while the article is hot, electrostatically coating the article with a second layer of a powdered, transparent thermoplastic resin; and (5) reheating the article to fuse the second powdered resin coating into a smooth layer. A primer coating may be applied to the article to increase adhesion between the article and the decorative finish. Cellulose acetate butyrate is a preferred thermoplastic resin. The prime-coating may be applied either in liquid form by spraying, or in powdered form by means of either a fluidized bed or an electrostatic sprayer. The powder coating may be applied by a fluidized bed.
BACKGROUND OF THE INVENTION This invention relates to coatings and, more particularly, to a method for applying a decorative, metallic flake finish to an article.
Finishes are commonly applied to articles of manufacture both for decorative purposes and for protection from corrosive and erosive environments. Decorative finishes comprising light reflecting metallic flakes randomly dispersed in a transparent layer of paint have been long desired, but have heretofore have diflicult and expensive to produce. By varying the flake size from large to small, the finish will vary from one of high light reflectance that sparkles in both natural and artificial light to one having a jewel-like appearance. In the past, finishes of this type have been used primarily for custom-made applications, since the time and the required labor in applying the numerous layers of the coating results in considerable expense. Metallic flake finishes have been seldom used for production lines because of the expense. In a typical application, several primer coats are first applied to the article to be coated, the last of which may include a color matching or contrasting the desired color of the completed article. Several coats of a transparent paint having colored flakes of metal dispersed therein are next applied until the entire surface area, or a high percentage of the surface area, is covered with the metallic flakes. Several coats of clear paint are then applied to completely encompass the metallic flakes, and additional coats of the clear paint are applied with sanding between coats, until a smooth finish having a desired thickness and luster is produced. To achieve a satisfactory finish by this process, as many as twenty-two or more individual coats may be applied. Considerable time is also required, since the paint must be allowed to dry between many of the applications. To date, the best finishes of this type have been made with a clear acrylic based paint. However, the acrylic paint has not always held up in extreme environments.
Patented Jan. 2, 1973 Ice According to the present invention, an improved method is provided for applying to articles decorative and protective finishes having a metallic flake appearance. The process is simpler and less expensive to use than prior art methods and is particularly adaptable for use on continuous production lines. In a preferred embodiment, the finish comprises three fused coatings: a primer coating, an intermediate coating of mixed metallic or light reflective flakes and a transparent thermoplastic resin, and an outer coating of a transparent thermoplastic resin. The article being finished is preferably preheated prior to applying the intermediate coating, which is applied as a powder. The powdered thermoplastic resin is fused and the outer coating is applied, also as a powder and preferably while the article is hot. The finish is completed by fusing the outer coating. In a preferred embodiment, the intermediate and outer coatings are applied by electrostatic spraying. However, other techniques such as a fluidized bed may be used to apply the powdered coating. By using electrostatic techniques to apply the powder to a heated article, the second and third coatings can be made quite thick and the light reflecting flakes will be randomly oriented, rather than flat. In a preferred embodiment of the invention, the thermoplastic resin is cellulose acetate butyrate which is applied as a powder for the second and third coatings. However, in the broadest sense, any transparent thermoplastic resin having suitable properties for withstanding the environment in which the coated article is placed can be used for the coating material. The primer, when used, may be any commercially available type recommended as a base for the particular thermoplastic resin used in the decorative finish. The light reflective flakes are preferably of aluminum, but may be of any material which has a melting temperature appreciably above the melting temperature of the thermoplastic resin. When the resin is fused by heating the article, the applied heat must not melt the light reflecting flakes.
Accordingly, the primary object of the invention is to provide an improved method for applying to an article a decorative finish having a metallic flake appearance.
Other objects and advantages of the invention will become apparent from the following detailed description, reference being made to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING The single figure shows a simplified flow diagram of a process according to the preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the single figure, a simplified flow diagram is shown for a preferred embodiment of an improved method of applying to articles decorative finishes having a metallic flake appearance. The method has been found particularly adaptable for coating small to medium sized metal articles on a continuous, production line basis. The articles are first primed with a suitable prime material. The prime coating, which is optional, functions to increase adhesion of the decorative finish to the article. The prime material may be clear or, preferably, may have a pigment matching or contrasting the color of light reflective flakes which Will be dispersed in the finish. The prime coating may be applied either in liquid form by spraying or painting, or in powdered form by means of a fluidized bed or of an electrostatic sprayer.
After the prime coating is applied to the article, the article is preheated to evaporate any solvent in the primer and to facilitate applying the decorative finish. While the article is still hot, a mixture of a transparent, powdered thermoplastic resin and flakes of a light reflective material is applied to the article. Sufficient heat should remain in the article to at least partially fuse or sinter this coating. The article is then heated to completely fuse the thermoplastic powdered resin into a clear coating bonded to the randomly dispersed light reflecting flakes and to the prime coating on the article. While the article is still heated to a temperature above the melting temperature of the resin, a second coating of a transparent, powdered thermoplastic resin is applied. The article is again heated to fuse the second thermoplastic resin into a substantially smooth, continuous coating. The second coating of the powdered resinous material is preferably of a thickness to eliminate the roughness caused by the randomly oriented flakes in the prior coating.
The two coatings of powdered thermoplastic resin are applied by conventional techniques. Electrostatic spraying has been particularly convenient for applying uniform layers of the powdered coatings. Fluidized beds and charged fluidized beds have also produced satisfactory coatings. When the powder coating is charged, it can be applied to a cold article. However, preheating the article to above the melting temperature of the resinous coating material permits the application of a considerably thicker layer.
In a preferred embodiment, both the prime coating and the two powdered coatings of thermoplastic resinous material are cellulose acetate butyrate. Powdered resin of this type is available from Eastman Chemical Products, Inc. under the trademark Tenite. Cellulose acetate butyrate is particularly desirable because it forms a tough, dimensionally stable coating having long term resistance to weathering. However, it is within the scope of the invention to use other thermoplastic resins, for example, acrylics, other cellulosics, ionomers, polypropylenes, and polyvinyl chlorides. Given the desired properties of the finish as to strength, wear and scratch resistance, moisture and chemical resistance, high and low temperature resistance, and other environmental conditions to which the coated article will be subjected, the most suitable thermoplastic coating materials may be selected from, for example, the Modern Plastics Encyclopedia, McGraw- Hill, Inc., vol. 46, October 1969.
The light reflecting flakes which give the finish a distinctive appearance are preferably formed from aluminum foil. Such flakes are commercially available in a wide range of colors and sizes. However, flakes of other metals such as steel foil may be used or flakes of silvered or colored resinous films may be used. Where the flakes are formed from resinous tfilms, they must have a melting point appreciably above the melting point of the thermoplastic material of which the object is coated. Light reflective flakes of coated Mylar film having a melting temperature of approximately 480 F. may, for example, be dispersed in a cellulose acetate butyrate coating wherein the coating is fused by heating to a temperature in the range of 300 F. to 375 F.
To illustrate further the process of the invention, the following example particularly illustrates the process in finishing a specific article:
EXAMPLE A decorative, weather resistant finish was applied to metal flower vases of a type used in cemeteries and having a height of approximately nine inches. The vase was cast from a base metal. The vase was initially sprayed with a bronze pigmented liquid primer. The vase was then heated to 375 F. for approximately fifteen minutes to volatilize the solvent from the liquid primer and to facilitate in applying the next coating. While the vase was still hot, the vase was electrostatically sprayed with a mixture having a ratio of four pounds of clear cellulose acetate butyrate to one pound of bronze colored aluminum flakes until the exposed surface areas of the vase were substantially percent covered with randomly oriented aluminum flakes. The vase was then placed in an oven and heated to 375 F. for approximately five minutes to melt the powdered cellulose acetate butyrate. While the vase was still hot, the vase was electrostatically sprayed with a coating of transparent cellulose acetate butyrate powder. The vase was again heated at 375 F. for approximately five minutes to fuse the latter powdered coating into a smooth coating extending continuously over the outer surfaces of the vase. Upon cooling, the vase had a bronze finish with a jewel-like sparkle and with excellent weather resistant properties. The randomly oriented aluminum flakes gave the finish a threedimensional appearance.
Although the powdered thermoplastic resin is preferably fused by heating, other techniques may be used. The powdered resin may, for example, be melted by exposure to hot vapors of a suitable solvent. After the resin flows into a continuous, uniform coating, any absorbed solvent is volatilized. It will be apparent to those skilled in the art that many other variations may be made in the materials and application of the above-described coating method without departing from the spirit and the scope of the claimed invention.
What I claim is:
1. A method for applying a decorative finish to an article comprising the steps of applying a solvent-containing primer coating to the article, evaporating the solvent from the primer coating by heating the article to an elevated temperature between 300 F. and 600 F., electrostatically applying, while the article is still hot, 'an intermediate coating consisting of a mixture of one part by weight of decorative light-reflective aluminum foil flakes and substantially four parts by weight of powdered transparent cellulose acetate butyrate resin on the article, melting the transparent resin by heating the article to an elevated temperature between 300 F. and 480 F., electrostatically applying, while the article is still hot, an outer coating of powdered transparent cellulose acetate butyrate resin on the article and heating the article to melt the outer coating to form a smooth transparent finish over the intermediate coating.
2. A method according to claim 1, wherein the primer coating has a color matching the color of the aluminum foil flakes.
References Cited UNITED STATES PATENTS 2,004,567 6/1935 Brumbaugh 4136 2,748,019 5/1956 Schramm 117-31 2,931,736 4/ 1960 Park 1179 2,974,060 3/ 1961 Dettling 117-21 3,010,845 11/1961 Schornstheimer 117-7 1 3,085,025 4/1963 Eaton 1179 3,117,886 1/1964 Glynn 11745 3,264,132 8/ 1966 Merrill et al. 11731 3,399,070 8/1968 Scharf 1174 3,490,934 1/1970 Oakley et a1. 117-18 3,194,675 7/1965 Carter et a1. 11729 3,377,183 4/ 1968 Hurt et a1. 11717 3,336,903 8/ 1967 Point 11717 X 3,140,195 7/1964 Nagel 11721 3,513,012 5/1970 Point 11717 3,351,504 11/1967 De Hart 11721 X 3,028,251 4/1962 Nagel 11721 3,546,017 12/ 1970 Pendleton et a1. 117-21 X WILLIAM D. MARTIN, Primary Examiner M. SOFOCLEOUS, Assistant Examiner US. Cl. X.R.
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