Process And Product Of Cold Sealing An Anodized Aluminum Article By A Photo-polymerization Process

Abstract

A method of cold sealing an anodized aluminum article comprising photopolymerizing a cross-linked polymer in situ in the pores of the surface of the anodized layer on the article and the product produced thereby are described.

Description

The present invention pertains to a novel method of sealing anodized aluminum and to the product produced thereby. More particularly the invention is directed to a photosensitive process for producing a polymer within the porous anodized structure which results in an extremely abrasion and chemical resistant product, and which gives the appearance of a conventional hot water seal or nickel/cobalt acetate-hot water seal by virtue of said polymer filling the pores of an anodized aluminum layer.

As generally used herein, the word "aluminum" includes aluminum of various degrees of purity and various aluminum base alloys. The term "anodized aluminum" includes those oxide coatings produced artificially on aluminum as distinguished from the natural oxide films which are normally present on aluminum surfaces. The present invention is applicable to various types of anodized coatings and has particularly striking advantages when applied to anodic coatings produced in electrolytes containing oxalic acid and hereinafter referred to as "oxalic acid anodized aluminum." Therefore, the invention will be described in most detail in connection with coatings of the type mentioned above.

Anodic oxide coatings are commercially formed on aluminum by electrolytic action, e.g., as described in a book by S. Wernick and R. Pinner entitled Surface Treatment and Finishing of Aluminum and Its Alloys, published in 1964 by Robert Draper, Ltd., Teddington, England, and in numerous other texts in this field. Such coatings are superior mechanically and possess greater corrosion resistance than that of the base metal. The coatings are porous and absorbent and form a suitable base for adsorbing dyes and certain photosensitive substances, and find an important commercial justification in this respect. However, the pores are extremely fine, the porosity being on the order of 20-500 .times. 10.sup.9 pores per square inch according to information published in the Journal of the Electrochemical Society, Vol. 101, No. 2, pages 53-59 (1954) and are dependent on the anodizing conditions employed. Generally, the pores are of sufficient size to absorb water and certain other aqueous and liquid solutions of some substances but are not of sufficient size to admit many other materials of colloidal dispersions and of sufficiently high viscosities. Many clear liquids, such as varnishes, lacquers and liquid polymers, cannot be made to penetrate the anodized porous structure because of this fact and claims in the literature and prior patents to the effect that such materials penetrate the pores can be seen to be false upon close examination; where, in fact, it can be seen that only the spongy surface layer of the coating is penetrated by such materials if there is any appreciable penetration at all.

Vapors of synthetic resin-forming monomers such as styrene allegedly can be adsorbed by anodized coatings on aluminum and polymerized therein as described in U.S. Pat. No. 2,662,034, but the product is not a crosslinked polymer and such methods are both time consuming and expensive to operate.

Dissolved synthetic resin-forming materials can be adsorbed by the anodized coating but this procedure generally requires a long drying time to evaporate the excess solvent vehicle before polymerization can proceed unless a heating step is utilized, increasing the cost of the operation due to the power consumed and in some cases requiring venting of the heat chamber if flammable or poisonous solvents are expelled. If sufficient heat is needed, this may lead to crazing of the anodized layer which can occur at temperatures as low as 225.degree.F due to the differences in coefficients of thermal expansion of the anodized layer and the aluminum substrate.

The anodized coating on aluminum is subject to staining and discoloration effects unless suitably sealed. Therefore, it is common practice to seal this layer against unwanted staining or discoloration by certain so-called sealing treatments. Commonly practiced sealing techniques include immersion in boiling water or in solutions of dichromates or chromates, silicates, or metal salts such as nickel or cobalt acetates which hydrolyze in the coating to form hydroxides. Such treatments are objectionable because of the long sealing times involved, a tendency in some cases to soften the outer part of the anodized coating which produces a chalky surface layer and in the case of dichromates, an undesirable color may be imparted to the coating.

Unsealed oxalic acid anodized aluminum is characterized by a color ranging from silver to bronze, depending on the base metal employed or it may possess a yellow color which in some cases is undesirable and usually is rectified by conventional sealing techniques to produce a bright to semiopaque metallic luster. Conventional sealing by waxes, lacquers, varnishes, oils or resins act by imparting a superficial impervious layer on top of the anodized coating and fail to penetrate the porous structure and fail to mask out the objectionable yellow color, and fail to provide an adequate seal against corrosive elements of the order obtained by conventional hot water or hot water-sealing salt bath techniques.

The principal object of this invention is to improve the various properties of sealed anodized coatings on aluminum.

It is a further object of this invention to provide a method of impregnating the pores of anodized aluminum with a photopolymerizable monomer material which can be polymerized without expensive special equipment.

It is a further object of this invention to provide a highly abrasion and chemical resistant seal which completely fills the pores of anodized aluminum, without softening the surface or making it chalky, eliminating the need for heat requirements, eliminating the effects of elevated temperature crazing on such coatings, and specifically eliminating the objectional yellow color characteristic of unsealed oxalic acid anodized aluminum.

It is another object of this invention to provide a method whereby there is no unreacted by-product or vapor produced either as a result of the reaction or the sealing method employed.

It is another object of this invention to provide a method of sealing an anodized layer at room temperature using an ordinary sunlamp exposure and eliminating the need for a drying period or a heating step.

It is another object of this invention to provide a method of sealing an anodized layer by a photopolymerization process wherein the anodized pore is completely filled by the polymer material without the presence of an excess of plastic material on the surface of the anodized layer which would in some cases detract from the overall appearance of the finished product.

The invention has as a particular object the production of anodized aluminum articles which are impregnated with liquid monomers or dissolved solid monomers, together with a suitable crosslinking agent and the appropriate sensitizers and initiators, exposing said impregnated layers to a suitable light source in order to effect photopolymerization of the monomeric mixture substantially throughout the porous structure, in contrast to having a mere overlying surface coating of resins or requiring specialized equipment or power consumption, as is the case with prior methods.

It is a further object of one aspect of this invention to provide a method whereby the photopolymerized mixture is crosslinked only throughout the porous structure and possibly to some extent on the surface of the anodized layer, where the excess surface polymer, not being crosslinked can be easily removed.

It is a further object of this invention to provide a method whereby the porous anodized structure is completely filled by the photopolymerized-crosslinked material in contrast to those methods whereby a low molecular weight material dissolved in a relatively large amount of solvent is impregnated into the anodized porous layer, resulting in a pore which is relatively unfilled.

It is a further object of this invention to provide a method where, as a result of the photoinitiated polymerization reaction within the filled anodized porous structure, an improvement in overall appearance in regards to brilliance of the finished article, particularly in regards to oxalic acid anodized aluminum is obtained as distinguished from anodized coatings provided with overlying coatings or films of resinous and like substances, such as are obtained with varnishes and lacquers, and as distinguished from high solvent type vehicles containing dissolved resinous substances and the like where an impregnated situation may exist but the anodized porous structure remains relatively unfilled.

It is another object of this invention to provide a method whereby no unreactive components are utilized in the photopolymerization sealing operation, thereby eliminating the problems associated with heating, solvent removal, and venting considerations.

It is a still further object of this invention to provide a method whereby unwanted vapors which are generated, for example, in sealing operations involving boiling water are eliminated. This aspect will be especially appreciated by those persons involved in the darkroom processing of photographic images embedded in the anodized layer.

Other objects, advantages, and features will become more clearly apparent from the following description of the invention.

Generally, the invention relates to a novel process for improving the properties of anodized aluminum by impregnating the pores with a photopolymerizable monomer or combinations thereof, by a solution of solid monomer dissolved in a liquid monomer, or a liquid monomer which is miscible with a second liquid monomer, or with an aqueous solution or other low boiling point liquid solution which is either a solvent for, or miscible with, a solid monomer or liquid monomer or combinations thereof, together with a monomer crosslinking agent in the presence of a suitable catalyst and sensitizer, exposing said impregnated layer while still wet regardless of the nature of the solvent system employed, to an ordinary sunlamp, for example, for a relatively short period of time, which causes a photopolymerization and crosslinking reaction to occur in the pores of said anodized layer and removing any excess material from the surface by means of appropriate solvent or mechanical action.

Any normally liquid to solid photopolymerizable unsaturated organic compound is useful in the practice of this invention. Preferably, such compounds should be ethylenically unsaturated, i.e. contain at least one non-aromatic double bond between adjacent carbon atoms. Compounds particularly advantageous are the photopolymerizable vinyl or vinylidene compounds containing a

group activated by direct attachment to a negative group such as halogen,

--C .tbd. N, --C .tbd. C, --O--, or aryl. Examples of such photopolymerizable unsaturated organic monomers include acrylamide, acrylic acid, acrylonitrile with acrylamide, acrylonitrile with acrylic acid and acrylamide, acrylamide with acrylic acid, N-ethanol acrylamide, diethylacrylamide, methacrylic acid, calcium acrylate, methacrylamide, vinyl acetate, methylmethacrylate, methylacrylate, ethylacrylate, vinyl benzoate, vinyl pyrrolidone, vinyl methyl ether, vinyl butyl ether, vinylisopropyl ether, vinylbutyrate, butadiene, or mixtures of ethylacrylate with vinyl acetate, acrylonitrile with styrene, butadiene with acrylonitrile and the like.

Difunctional monomers contain two reactive double bonds per molecule, and their use in conjunction with the vinyl monomers serve to radically increase the molecular weight of the polymer and radically alter other physical properties of the polymer as well. These compounds serve to crosslink the polymeric chains and are generally referred to as crosslinking agents. Among such agents are included compounds such as N,N'-methylenebisacrylamide, triallyl cyanurate, divinyl benzene, divinyl ketones, diglycol diacrylate, diethyl maleate, allyl anthranilate, N,N'-hexamethylenebisacrylamide, and ethylene dimethacrylate. Other crosslinking agents suitable for the present invention are described in U.S. Pat. No. 3,330,659. The crosslinking agent is generally employed in the range of 1 to 50 parts of the monomer concentration with 10 parts being generally sufficient to significantly increase the molecular weight of the polymer and decrease the solubility to various solvents.

A monofunctional monomer contains a single reactive double bond per molecule and yields a linear polymer which, in the case of acrylamide, is water soluble. Utilizing a relatively small amount of a difunctional monomer with two reactive double bonds per molecule such as N,N'-methylenebisacrylamide results in the chains being crosslinked by the difunctional units to form a vast network which radically alters the physical properties of the polymer, rendering it insoluble in water and virtually all common organic solvents. Since liquid acrylonitrile is also a polymerizable vinyl monomer, capable of crosslinking with N,N'-methylenebisacrylamide, a solvent is provided, for the crosslinking agent and acrylamide monomer which in itself becomes a part of the finished product and eliminates the problems associated with drying times and solvent evaporation and removal. In addition, such a system goes into the pores of anodized aluminum quite easily and with the needed sensitizers to ultraviolet light can be polymerized in situ, assuring an effective seal and eliminating the objectionable color characteristic of oxalic acid anodized aluminum by virtue of the pores being filled.

This method has the decided advantage over other cold sealing techniques in that a solvent is generally used with the dissolved polymer which as a rule requires heat to drive off excess solvent or to effect crosslinking or film formation or both. Inasmuch as a relatively large amount of solvent is required in order to obtain sufficiently fluid viscosity in order to penetrate the pores, this situation may seal the anodized layer but will not mask out the objectionable color or give the appearance of a normal hot water seal. Unless thicker layers are applied, the pore will not be filled and complete sealing may not occur. On the other hand, if excess solution is applied, a film may be left on the surface of the anodized layer and although sealed, an obvious plastic layer detracts in some cases from the finished appearance of the metal. To avoid this situation, the conventional cold sealing material would have to be carefully metered on, being subject to the variety of different anodized thicknesses as well as the porosity of the anodized layer, or the excess removed after curing.

In the photopolymerization cold sealing technique, all problems associated with excess solvent are eliminated since the solvent in this case is a vinyl monomer which enters into the polymerization reaction itself. Secondly, the technique can be tailored to the extent that crosslinking takes place only in the pore of the anodized layer and possibly to some extent on the surface as well. The excess surface material which has not been crosslinked can be removed in an appropriate solvent or by a mechanical action, leaving the crosslinked portion of the sealer unaffected within the anodized porous layer.

In photopolymerization, photochemical reactions initiate a series of reactions in which many small monomer molecules combine to form long polymer chains. Most practical monomers have the general molecular structure

where either one or both of X and X' are electron withdrawing substituents that activate the adjacent double bond. Photopolymerization of such monomers can proceed only when an initiator is present in the system. An initiator can be either a monomer molecule that has received enough energy to combine with another monomer molecule or, more commonly, an initiator can be a different material which is more easily activated than the monomer. The activation takes place through the absorption of energy; in this case light quanta which is then dissipated throughout the substance to produce a short lived intermediate known as a free radical. An impressive number of compounds useful as photoinitiators and/or sensitizers have been reported in the literature and their choice depends on the particular monomer employed as well as the nature of the light source used to initiate photopolymerization. Among these are the broad class of carbonyls such as diacetal, benzil, or benzoin and its congeners, the acyloins such as .alpha.-alkylbenzoin; benzophenone or substituted benzophenones such as 4,4'-bis-dimethylaminobenzophenone, known as "Michler's ketone"; organic sulfur-containing compounds such as diphenyl disulfide; peroxide compounds such as ditertbutyl peroxide or benzoyl peroxide; redox systems, for example organic peroxides in the presence of certain reducing agents such as ferric compounds such as ferric ammonium oxalate; azo and diazo compounds such as azomethane or the diazonium chloride of p-aminodiphenylamine; organic halogen compounds such as .alpha.-chloromethylnaphthalene; organic halogen sulfur-containing compounds such as benzene sulfonyl chloride; certain photoreducible dyes such as rose bengal or acriflavine and in conjunction with reducing agents such as stannous chloride, or ascorbic acid; etc. A more complete listing of the various combinations of sensitizers and catalysts which can be used in the spirit of this invention is described by Jaromir Kosar, *(*"Light Sensitive Systems" 5, John Wiley and Sons (1965).) and are known in the art.

The nature of the light source used to effect photopolymerization will depend on the sensitizer or sensitizer-catalyst combination employed. While ultraviolet light sources are generally the most efficient for initiating a photopolymerization reaction by using certain photoreducible dyes and reducing agents and combinations thereof, the light source can be extended through the entire visible portion of the spectrum. X-rays or gamma rays could also be used.

The advantages of this invention will be made further apparent by the following examples; although, it is to be understood that the invention is not restricted thereto.

EXAMPLE 1

A composition was prepared from the following components:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Acrylonitrile 100 cc

The resulting solution was coated on an oxalic acid anodized aluminum plate and immediately exposed to a General Electric RS 275 watt sunlamp placed at a distance of 12 inches. Within 5 to 10 minutes exposure a solid polymeric surface film had formed which, when removed, left an anodized layer of high gloss and brilliance which was sealed against staining. An identical untreated oxalic acid anodized aluminum plate was characterized by a yellow coloration and would very strongly accept staining by dyes, indicating pore penetration had occurred on the above treated plate. Additional plates prepared by the same method have been immersed in water, methyl ethyl ketone, acrylonitrile, trichloroethylene and isopropyl alcohol for periods of up to 6 weeks. The anodized layer was unchanged in appearance and still was sealed against staining.

The above solution was coated onto an oxalic acid anodized aluminum article, whose anodized layer contained a fully developed and fixed silver image produced as described in U.S. Pat. No. 2,766,119, for example. The article was exposed and treated in the same manner as before. The resulting article is characterized by an improved gloss and brilliance in the nonimage area and an improved density and blackness in the image area as compared to a conventional hot water seal or combined hot water-sealing salt additive bath. The integrity of the seal was verified by placing a drop of iodine-potassium iodide mixture dissolved in methanol on an image area of the anodized layer. No fading was apparent after the so-treated area was allowed to set for several minutes. An unsealed imaged plate so treated with iodine will fade in several seconds under the same conditions.

EXAMPLE 2

A composition having the following components was prepared:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Acrylic acid 7 cc Acrylonitrile 100 cc

The resulting solution was coated onto an oxalic acid anodized aluminum article and exposed to a General Electric RS 275 watt sunlamp placed at a distance of 12 inches from the article for a period of 20 minutes. The resulting excess resinous surface film was removed, leaving a highly brilliant glossy surface as obtained in Example 1.

EXAMPLE 3

A composition of the following components was prepared:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Methylmethacrylate 7 cc Acrylonitrile 100 cc

This composition was applied the same as in Example 1 and essentially the same results were obtained.

EXAMPLE 4

The following composition was prepared:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Acrylic acid 100 cc Methylmethacrylate 10 cc Acrylonitrile 100 cc

The resulting solution was applied to an oxalic acid anodized aluminum plate and treated as before. Again a 20 minute exposure was required.

EXAMPLE 5

The following two compositions were prepared from the indicated components:

Solution A N,N'-methylenebisacrylamide 2 g Benzophenone 1 g Benzoyl peroxide 0.5 g Acrylonitrile 100 cc Solution B Acrylamide 30 g N,N'-methylenebisacrylamide 0.5 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Acrylonitrile 100 cc

Solution A was coated onto an oxalic acid anodized aluminum article within which anodized layer a fully developed and fixed silver image was present. The excess solution was then poured off and Solution B applied in excess and exposed as before. Polymerization was essentially complete in 5 minutes after which the excess surface film was easily removed by a light scrubbing action under running tap water since the excess surface polymer is essentially not crosslinked to yield an exceptionally bright, glossy surface appearance which again passed the iodine-potassium iodide-methanol sealing test in addition to satisfying an abrasion test conducted with a Tabor abrader, which satisfies the requirements outlined under Mil. Spec. GG-P-455-b.

EXAMPLE 6

A composition having the following components was prepared:

Acrylamide 37 g N,N'-methylenebisacrylamide 2 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Ethyl alcohol 100 cc

The resulting solution was coated onto an oxalic acid anodized aluminum plate and immediately exposed to a 275 watt General Electric RS sunlamp placed at a distance of 12 inches for a period of 7 minutes. Essentially the same result was obtained as in Example 1.

EXAMPLE 7

A composition of the following components was prepared as follows:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 g Benzoyl peroxide 0.15 g Acetonitrile 100 cc

The solution was coated onto an oxalic acid anodized aluminum plate and immediately placed under a General Electric RS 275 watt sunlamp placed at a distance of 12 inches for a period of 10 minutes after which the coating had polymerized. The excess surface polymer was removed, resulting in a sealed anodized surface comparable to that obtained in Example 1.

EXAMPLE 8

A composition consisting of the following components was prepared:

Acrylamide 100 g N,N'-methylenebisacrylamide 5 g Benzophenone 1 g Benzoyl peroxide (dissolved in ethanol) 0.5 g Water (distilled) 100 cc

It was necessary to dissolve the peroxide in ethanol in order to incorporate it into the above solution. The above composition when coated onto an oxalic acid anodized layer required 20 minutes of exposure to the previous mentioned light source. The resulting impregnated polymerized layer was sealed as before with regards to abrasion and staining tests.

EXAMPLE 9

A composition of the following components was prepared:

Acrylamide 100 g N,N'-methylenebisacrylamide 5 g Ferric ammonium oxalate 1 g Hydrogen peroxide (3% aqueous solution) 5 cc Water 100 cc

The resulting solution was coated onto an oxalic acid anodized plate and immediately exposed to the 275 watt sunlamp at a distance of 12 inches. Within 1 to 2 minutes, a solid polymeric surface film was obtained which, when removed, resulted in an anodized layer of high gloss and brilliance which was sealed against staining.

EXAMPLE 10

The following two compositions were prepared from the indicated components:

Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 g Hydrogen peroxide (3% aqueous solu- tion) 2 cc Methyl alcohol 75 cc Water (distilled) 25 cc Solution B Acrylamide 100 g Water (distilled) 100 cc

Solution A was coated onto an oxalic acid anodized aluminum layer and allowed to set for 1 minute and the excess poured off. Solution B was then applied and the impregnated anodized layer immediately exposed to the General Electric RS 275 watt sunlamp placed at a distance of 12 inches. A clear, amorphous, solid surface film had formed in 1 minute which, when removed, resulted again in an anodized layer of high gloss and brilliance, with no evidence of the yellow color characteristic of the unsealed layer and which would not accept a dye. Essentially the same result was obtained by adding 5% N,N'-methylenebisacrylamide to Solution B. The same result was also obtained by combining Solution A and B in equal amounts and applying this combined mixture to an oxalic acid anodized layer.

EXAMPLE 11

A composition was prepared where the coating solution consisted of the following components:

Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 g Hydrogen peroxide (3% aqueous solution) 2 cc Methyl alcohol 75 cc Water (distilled) 25 cc Solution B Acrylamide 100 g Methyl alcohol 150 cc

The results were the same as obtained in Example 1 except the time of exposure required to effect polymerization was increased to 5 minutes.

EXAMPLE 12

The following two compositions were prepared accordingly:

Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 g Hydrogen peroxide (3% aqueous) 2 cc Methyl alcohol 75 cc Water (distilled) 25 cc Solution B Acryalmide 25 g Acrylonitrile 100 cc

Solution A was coated onto an oxalic acid anodized aluminum plate and allowed to set for 1 minute and the excess poured off. Solution B was then applied and the impregnated layer immediately exposed to the General Electric RS 275 watt sunlamp placed at a distance of 12 inches from the plate. The results were the same as obtained in Example 10, except 10 minutes exposure time was required to effect polymerization.

A 5% N,N'-methylenebisacrylamide addition to Solution B or combining Solution A and B in a 1:1 volume ratio gave essentially the same result.

EXAMPLE 13

A composition of the following indicated components was prepared:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Ferric ammonium oxalate (0.01M) 5 cc Hydrogen peroxide (3% aqueous) 0.5 cc Methanol 35 cc Water (distilled) 25 cc

The resulting solution was coated onto an oxalic acid anodized aluminum article and exposed for 3 minutes with a General Electric RS 275 watt sunlamp placed at a distance of 12 inches from the article to effect polymerization. The clear, amorphous, excess surface film was removed leaving a bright, glossy anodized surface appearance with no evidence of the characteristic unsealed yellow coloration and resisted staining or coloring.

EXAMPLE 14

A composition was prepared from the following indicated components:

Acrylamide 7 g N,N'-methylenebisacrylamide 0.7 g Ferric ammonium oxalate (0.01M) 1.0 cc Hydrogen peroxide (3% aqueous) 0.1 cc Methanol 6 cc Water 4 cc Acrylonitrile 10 cc

This composition when coated onto an oxalic acid anodized aluminum article and exposed for 3 minutes resulted in an especially brilliant, glossy appearance when the excess surface polymer was removed.

EXAMPLE 15

A composition was prepared from the indicated components:

Acrylamide 100 g N,N'-methylenebisacrylamide 5 g Ferric ammonium oxalate (0.01M) 5 cc Hydrogen peroxide (3% aqueous) 3 cc Sodium tetradecyl sulfate 0.2 cc Water 100 cc

The resulting solution was coated onto an oxalic acid anodized aluminum article and allowed to set for 5 minutes prior to exposure. The degree of gloss and brilliance obtained is somewhat improved over that obtained in Example 9.

EXAMPLE 16

The following composition was prepared:

Acrylamide 20 g N,N'-methylenebisacrylamide 4.5 g Acrylonitrile 50 cc Acrylic acid 5 cc Hydrogen peroxide (3% aqueous) 10 cc Ferric ammonium oxalate (0.01M) 10 cc Methanol 10 cc

This composition, when coated onto an oxalic acid anodized aluminum article, polymerizes to a film in 5 minutes when placed at a distance of 12 inches from a 275 watt sunlamp. The degree of gloss is approximately the same as obtained in Example 15 when the excess surface polymer is removed.

EXAMPLE 17

A composition of the following indicated components was prepared:

Acrylamide 20 g N,N'-methylenebisacrylamide 4.5 g Acrylonitrile 50 cc Acrylic acid 5 cc Hydrogen peroxide (3% aqueous) 10 cc Ferric ammonium oxalate (0.1M) 10 cc Methanol 10 cc Water (distilled) 20 cc

This composition gave essentially the same result as obtained in Example 16, except the coating polymerized in 1 to 2 minutes under the same exposure conditions.

EXAMPLE 18

The following composition was prepared:

Acrylic acid 50 cc N,N'-methylenebisacrylamide 10 g Hydrogen peroxide (3% aqueous) 5 cc Ferric ammonium oxalate (0.01M) 5 cc

This composition, when coated onto an oxalic acid anodized aluminum plate and immediately exposed to the aforementioned light source, polymerized in 2 minutes to a particularly hard, resistant coating which, when removed, resulted in a clear, non-yellow, stain resistant anodized layer.

EXAMPLE 19

The following composition was prepared from the indicated components:

Acrylic acid 50 cc Methylmethacrylate 20 cc N,N'-methylenebisacrylamide 2 g Hydrogen peroxide 5 cc Ferric ammonium oxalate 5 cc

This coating yields essentially the same results obtained in Example 18, except that a 5 minute exposure was used.

EXAMPLE 20

A composition having the following components was prepared:

Acrylamide 90 g N,N'-methylenebisacrylamide 3.5 g Acrylic acid 40 cc Acrylonitrile 100 cc Hydrogen peroxide (3% aqueous) 10 cc Ferric ammonium oxalate (0.01M) 10 cc Sodium tetradecyl sulfate 0.2 cc Water 60 cc

This composition, when coated onto an oxalic acid anodized article, resulted in a plate with about the same final appearance as obtained in Example 5. The polymerization exposure time was reduced to 1 minute however. The above composition was also coated onto an oxalic acid anodized aluminum article within which a fully developed and fixed silver image was present. The resulting article is characterized by an improved gloss and brilliance in both the image and nonimage area as well as a more neutral black coloration in the image area as compared to an equivalent article which was sealed in a boiling water-nickel-cobalt acetate sealing bath. The integrity of the above sealed material was confirmed by the methanol-potassium iodide-iodine bleaching test in the silver image area and the nonimage area would not accept a dye.

EXAMPLE 21

A composition of the following components was prepared:

Acrylamide 25 g N-vinylpyrolidone 2.5 g N,N'-methylenebisacrylamide 2.5 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g Acrylonitrile 100 cc

An excess solution was coated onto an oxalic acid anodized aluminum article and exposed immediately to a General Electric RS 275 watt sunlamp placed at a distance of 12 inches for a period of 2 minutes. When the excess surface coating was removed, a glossy, highly reflectant surface was noted similar to that obtained in Example 1.

EXAMPLE 22

A composition consisting of the following indicated components was prepared:

Acrylamide 25 g Diethyl maleate 2.5 g Acrylonitrile 100 cc Benzophenone 0.5 g Benzoyl peroxide 0.25 g

An oxalic acid anodized aluminum plate was coated with this formulation and immediately exposed to the sunlamp for 5 minutes after which the excess coating was removed, providing a highly brilliant surface appearance with no characteristic yellow color which is evident on an unsealed oxalic acid anodized aluminum surface.

EXAMPLE 23

A composition consisting of the following components was prepared:

Acrylamide 25 g Allylanthranilate 2.5 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g Acrylonitrile 100 cc

Essentially the same result was obtained as in Example 1, except a 2 minute exposure time was utilized.

EXAMPLE 24

A solution consisting of the following indicated components was prepared:

Acrylamide 25 g Ethylene dimethacrylate 2.5 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g Acrylonitrile 100 cc

The resulting solution was coated onto an oxalic acid anodized aluminum article which was characterized by a very strongly objectionable yellow color appearance and exposed to the 275 watt sunlamp for 3 minutes. After the excess surface polymer was removed a brilliant, highly reflectant, glossy surface was obtained, similar to that obtained in Example 1.

EXAMPLE 25

A composition of the following indicated components was prepared:

Acrylamide 25 g N,N'-hexamethylenebisacrylamide 2.5 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g Acrylonitrile 100 cc

The resulting solution was coated onto an oxalic acid anodized aluminum article and exposed for a period of 4 minutes with a General Electric RS 275 watt sunlamp placed at a distance of 12 inches from the article in order to effect polymerization. The surface polymeric film was removed, leaving a bright, glossy anodized surface appearance with no evidence of the characteristic unsealed yellow coloration and which would not accept a dye or stain.

EXAMPLE 26

A composition having the following indicated components was prepared:

Acrylamide 90 g N,N'-hexamethylenebisacrylamide 3.5 g Acrylic acid 40 cc Acrylonitrile 100 cc Hydrogen peroxide (3% aqueous) 10 cc Ferric ammonium oxalate (0.01M) 10 cc Water (distilled) 60 cc

This composition, when coated onto an oxalic acid anodized article, polymerizes to a film in 1 to 2 minutes when placed at a distance of 12 inches from a 275 watt sunlamp. The resulting surface film was removed, leaving a surface appearance similar to that obtained in Example 25 and which resisted staining.

EXAMPLE 27

A monomer solution was prepared from the following indicated components:

Styrene 70 cc Acrylonitrile 30 cc N,N'-methylenebisacrylamide 2 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g

This composition, when coated onto an unsealed oxalic acid anodized aluminum article and exposed for 2 to 3 minutes, resulted in a brilliant, glossy surface appearance when the excess surface polymer was removed.

EXAMPLE 28

The following composition was prepared:

The following composition was prepared:

Styrene 100 cc Maleic anhydride 25 g N,N'-methylenebisacrylamide 5 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g

The resulting solution was coated onto an oxalic acid anodized plate and immediately exposed to the General Electric RS 275 watt sunlamp at a distance of 12 inches. Within 2 to 3 minutes, a solid polymeric surface film was obtained which, when removed, resulted in an anodized layer of high gloss and brilliance, exhibiting no evidence of the characteristic yellow coloration and which was sealed against staining.

EXAMPLE 29

A composition having the following components was prepared:

Styrene 60 cc Maleic anhydride 25 g Acrylonitrile 40 cc N,N'-methylenebisacrylamide 5 g Benzophenone 0.5 g Benzoyl peroxide 0.25 g

The above composition was coated onto an oxalic acid anodized aluminum article within which a fully developed silver image was embedded. An exposure time of 2 minutes was deemed sufficient to photopolymerize and crosslink the excess surface film at a distance of 12 inches from the General Electric RS 275 watt sunlamp. The resulting excess surface film was removed leaving an improved gloss and brilliance in the nonimage area as well as an improved apparent density and blackness in the image area, as compared to that obtained by a conventional hot water-sealing salt bath technique. The developed silver image area would not fade given the iodine-potassium iodide-methanol test and the nonimage area of the anodized layer would not accept staining.

Claims

I claim:

1. A method of improving the properties of an anodized aluminum article which comprises:

applying to the porous surface of an unsealed anodized aluminum layer a photopolymerizable liquid composition comprising at least one polymerizable acrylic monomer, and at least one crosslinking agent; and

cold sealing the porous surface of said article by exposing said composition to a suitable dose of radiation thereby photopolymerizing the composition in the pores of the surface of said article.

2. The method of claim 1 wherein the anodized article contains a developed and fixed silver image in the pores of said article prior to application of said polymerizable composition.

3. The method of claim 1 wherein the crosslinking agent is a difunctional monomer.

4. The method of claim 1 wherein the polymerizable composition also includes a sensitizer or initiator.

5. The method of claim 1 wherein photopolymerization is the result of exposure to ultra violet radiation.

6. The method of claim 1 wherein the photopolymerizable composition comprises acrylamide, N,N'-methylenebisacrylamide and a solvent for said acrylamides.

7. A cold sealed anodized article in which the pores of the porous anodized surface layer are filled with a cross-linked copolymer of at least one photopolymerizable acrylic monomer and at least one cross-linking agent.

8. A cold sealed anodized article according to claim 7 in which the photopolymerizable monomer impregnated in the pores is a mixture of acrylamides and acrylonitrile.

9. A cold sealed anodized article according to claim 7 in which a developed and fixed silver image is in the pores along with the crosslinked copolymer.

10. A cold sealed anodized article according to claim 7 in which the crosslinked polymer is a copolymer of at least one acrylic monomer and a difunctional crosslinking agent.

11. The article of claim 7 wherein the crosslinked copolymer is a copolymer of acrylamide and N,N'-methylenebisacrylamide.