Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/16—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies using synthetic lacquers or varnishes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2202/00—Metallic substrate
  • B05D2202/20—Metallic substrate based on light metals
  • B05D2202/25—Metallic substrate based on light metals based on Al
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
  • B05D3/068—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation using ionising radiations (gamma, X, electrons)

Definitions

• 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.
• 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.
• 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 225F 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 anddiscoloration effects unless suitably sealed. Therefore, it is common practice to seal this layer against unwanted staining or discoloration by certain so-called sealing treatments.
• 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.
• 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.
• 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.
• 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.
• crosslinking agents include 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 US. Pat. No. 3,330,659.
• the crosslinking agent is generally employed in the range of l 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.
• 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.
• 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.
• 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.
• 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.
• excess solution 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.
• 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.
• the solvent in this case is a vinyl monomer which enters into the polymerization reaction itself.
• 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.
• photopolymerization 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.
• 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.
• EXAMPLE 1 A composition was prepared from the following components:
• 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 US. 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.
• Solution A N,N'-methylenebisacry1amide Benzophenone Benzoyl peroxide Acrylonitrile Solution B
• Acrylamide N,N'-methylenebisacrylamide Benzophenone Benzoyl peroxide Acrylonitrile 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.
• EXAMPLE 8 A composition consisting of the following components was prepared:
• Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 g Hydrogen peroxide (3% aqueous solution) 2 cc Methyl alcohol 75 cc ⁇ Vater (distilled) cc Solution B Acrylamide 100 g Water (distilled) I00 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.
• RS 275 watt sunlamp placed at a distance of 12 inches.
• 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 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 l0 minutes exposure time was required to effect polymerization.
• 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.
• 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.
• 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.
• An oxalic acid anodized aluminum plate was coated with this formulation and immediately exposed to the sunlamp for 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.
• 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.
• Styrene 70 cc Acrylonitrile 30 cc N,N'-methylenebisacrylamide 2 g Benzophenone 0.5 g 30 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.
• 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 iodidemethanol test and the nonimage area of the anodized layer would not accept staining.
• a method of improving the properties of an anodized aluminum article which comprises:
• a photopolymerizable liquid composition comprising at least one polymerizable acrylic monomer, and at least one crosslinking agent
• the polymerizable composition also includes a sensitizer or initiator.
• the photopolymerizable composition comprises acrylamide, N,N'-methylenebisacrylamide and a solvent for said acrylamides.
• 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.
• 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.
• crosslinked copolymer is a copolymer of acrylamide and N,N'- methylenebisacrylamide.

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• 1971
  • 1971-02-01 US US00111648A patent/US3715211A/en not_active Expired - Lifetime
  • 1971-12-02 CA CA129,156A patent/CA953243A/en not_active Expired
• 1972
  • 1972-02-01 GB GB474872A patent/GB1325642A/en not_active Expired
  • 1972-02-01 DE DE19722204672 patent/DE2204672A1/de active Pending

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