US2266353A

US2266353A - Coating for metallic articles

Info

Publication number: US2266353A
Authority: US
Inventors: Clifford R Carney
Original assignee: Individual
Current assignee: Individual
Priority date: 1939-04-18
Filing date: 1939-04-18
Publication date: 1941-12-16
Anticipated expiration: 1958-12-16

Description

' objects of aluminum.

Patented Dec. 16, 1941 rd a. Carney, Miami, Fla.

'No Drawing. Application April 18, 1939, Serial No. 268,644

'2 Claims. (01. 621(l8.5)

This invention relates to methods of treating aluminum and like surfaces, and more particularlyto improved methods of providing a finish-- ing andprotective coating upon the external surfaces of aluminum ice trays 'and grids or other In order to obtain protective coatings on aluminum surfaces it has been customary in the past to make the aluminum object to be coated the anode in an electrolytic cell having a solution of sulphuric acid as the electrolyte. The resultant coating is a surface layer which is very porous, of varying" thickness and varying hardness characteristics. When used for the manufacturing of grids or trays or similar objects the coating is washed and then the pores are sealed by the use of oils, waxes, lacquers or the like. This electrolytic treatment, the separate washing and sealing operations involve a relatively high cost of processing.

It is accordinglyan important object of the present invention to provide a protective coating for aluminum surfaces which is highly resistant to corrosion and which is readily applied by a simple and relati ely inexpensive coating operation.

A further object of the invention is to provide a finishing coating for aluminum surfaces which has a satiny finish very similar to that of an anodic coating.

A further. object of the invention is to provide a protective coating for the above stated purpose whichconsists of a hard tough film of high gloss and which will readily fill the hills and valleys and pores ofthe metal surfaces treated and produce a thoroughly smooth surfaced product.

Other objects and advantages of this invention will appear in the following description and appended claims. Before explaining in detail the present invention it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and it is, not intended to limit the invention beyond therequirements of the prior art.

In accordance with the present invention coatingsof the type described above are prepared by first subjecting the object to be coated, for ex-v ample an aluminum ice tray or grid, to an etching treatment employing any suitable etching medium such as an acid or 'basic. etching agent as, for example, sulphuric or hydrochloric acid or caustic soda. The etched object is'then finished by spraying the object with a urea resin baking enamel, and then subjecting the object thus coated to temperatures in the neighborhood of 300 F. in a baking oven to fuse and finally harden the coating. .4

In a preferred embodiment of the invention the urea resin baking enamel may contain the following ingredients in the following approximate proportions:

Parts by weight Urea 60 Formaldehyde (37% strength) 321 Glycerol phtb ai'e 60, Butyl alcohol 222 Such a coating is converted from its fluid form to a solid form by a polymerization of the resin under the influence of heat. The finish is a hard, clear finish which has suflicient strength and flexibility to withstand the strains to which it is subjected in use and is highly resistant to corrosion.

The finish effectively ,seals the pores in the metal surfaces which have been opened by the g. action of the etching medium and thus, when the finish is used on the surfaces of objects" such as ice trays and grids, the coating prevents the penetration of water in the exposed pores and urea resin enamel as used herein.

face which is exceedingly smooth and glossy and otherwise attractive. Although the method used to prepare the coatings involves a baking as well as a coating step, it is readily seen that the meth- .od is very simple and decidedly less expensive than the methods employed in anodizing metal Moreover, the baking assists in providobjects.

- ing a coating which is'toug'her'and more resistant to abrasion.

It. is to be understood that other coating methods may be employed to apply the enamel, such as dipping or the like, although the use of spraying methods is preferred. Also any suitable device or method of baking may be utilized, provided the temperature can be readily maintained at about 300 F. p

The methods of the present invention may also be applied to unetched surfaces, yet it has been found that a more satisfactory appearance is obtained when the objects being treated are first cleaned and prepared for the coating step by means of an etching operation. In .some instance it is advantageous to anodize as well as etch, the metal prior to applying the enamel, although such combined treatments are usually to be avoided due to the increased cost. 7

Where the object being coated is an ice tray or other article which is exposed to cold or freezing temperatures, it is frequently desirable to supplement the enamel coating with a thin coating of wax which not only adds to the appearance of the tray but permits easier removal of its ice contents by mechanical appliances. An .improved method of applying such coating, using wax in the form of a powder, is described in my copending application filed simultaneously with the present application.

Although the invention has been described as applying primarily to the treatment of ice trays and grids and similar equipment, it may be employed with equal success in connection with other aluminum objects such as the interior shells I of refrigerators and various parts employed in the automobile and aeronautical industries.

I claim: Y

1. An aluminum tray and grid for receiving water to be frozen, said tray and grid possessing on their respectiv water contacting surfaces a water-repellant adherent relatively flexible protective coating, said coating comprising a baked enamel-like layer containing glycerol phthalate and the condensation product of approximately 60 parts by weight of urea and 320 parts by weight of formaldehyde.

2. An aluminum tray. and grid for receiving water to be frozen, said tray and grid possessing on their respective water contacting surfaces a water-repellant adherent relatively flexible protective coating, said coating consisting of the baked enamel-like reaction product of approximately 60 parts by weight of urea, approximately 320 parts by weight of 37% formaldehyde, ap-

proximately parts by weight -of glycerol phthalate, and approximately 220 parts by weight of butyl alcohol. Y

CLIFFORD R. CARNEY.