US3698905A - Decorating anodized metal with dye imbibition transferred images - Google Patents

Abstract

DECORATING ANODIZED METALS, SUCH AS ALUMINUM, BY EXPOSING SAID ANODIZED METAL SUBSTRATE BEARING A LIGHTSENSITIVE LAYER TO ACTINIC RADIATION TO ESTABLISH A POTENTIAL RD OF 0.2 TO 2.2, APPLYING A DRY POWDER COMPRISING A WATER SOLUBLE DRY TO THE LIGHT-SENSITIVE LAYER, EMBEDDING THE DEVELOPING POWDER IN IMAGE-WISE CONFIGURATION INTO THE LIGHT-SENSITIVE LAYER, REMOVING THE DEVELOPING POWDER FROM THE NON-IMAGE AREAS AND MOLECULARLY IMBIBING AND TRANSPORTING SAID DYE FROM THE DRY POWDER INTO THE PORES OF THE ANODIZED METAL IN IMAGE-WISE CONFIGURATION BY CONTACTING SAID LIGHT-SENSITIVE LAYER WITH WATER VAPOR.

Description

United States Patent Office Patented Oct. 17, 1972 3,698,905 DECORATING ANODIZED METAL WITH DYE IMBIBITION TRANSFERRED IMAGES Warren Guy Van Dorn and James Maurice Hardenbrook,

Columbus, Ohio, assignors to A. E. Staley Manufacturing Company, Decatur, Ill. No Drawing. Filed Mar. 23, 1971, Ser. No. 127,354 Int. Cl. G03c 5/00, 7/00; G03f 3/04 US. Cl. 96-48 R 11 Claims ABSTRACT OF THE DISCLOSURE Decorating anodized metals, such as aluminum, by exposing said anodized metal substrate bearing a lightsensitive layer to actinic radiation to establish a potential R, of 0.2 to 2.2, applying a dry powder comprising a water soluble dye to the light-sensitive layer, embedding the developing powder in image-wise configuration into the light-sensitive layer, removing the developing powder from the non-image areas and molecularly imbibing and transporting said dye from the dry powder into the pores of the anodized metal in image-wise configuration by contacting said light-sensitive layer with water vapor.

DISCLOSURE OF THE INVENTION This invention relates to a method of decorating anodized metals.

The production of designs or decorations on anodized metals, usually aluminum, is of particular interest for the production of individual nameplates for attachment to machines. To a lesser extent these decorated metals are of interest for use as panels in the construction of buildings, for beverage cans, etc. Anodized metal surfaces have been decorated previously by applying a film of colorant from lacquers, varnishes and the like. Due to the extremely minute pores in anodized surfaces, most lacquers, varnishes or the like form a surface layer on top of the anodized metal. Such films are subject to deterioration since they can be removed by abrasion and are often opaque or even when transparent, the conventional coatings detract somewhat from the beauty of the anodized surface itself.

Anodized metals have also been decorated by dyeing, typically by dipping the anodized metal in a dye bath to provide a single overall color. One or more colors have also been applied to predetermined areas of anodized metals by applying photochemical resists to the anodized metal, exposing, to light to tan the resist in the exposed areas, washing out the unexposed areas and dipping the anodized metal in a dye bath. Such techniques have the disadvantage that they require complete removal of the unexposed areas before dipping in the dye bath and complete removal of the tanned resist after the application of the dye. These removal steps are complicated by the porous nature of the anodized metal and the crosslinked nature of the tanned resist. Further, since most light-sensitive layers capable of forming resists are inherently negative acting, it is usually necessary to employ a negative of the design or image to be reproduced on the predetermined layer.

US. Pat. 3,484,342 indicates that multi-color anodized aluminum objects can be prepared by printing a multicolor-mirror-dye-image on a paper surface and then transferring the dye image by sublimation from the printed sheet to the anodized aluminum surface. However, this technique has all the disadvantages inherent in conventional printing processes, plus the additional disadvantages inherent in the production of mirror images on the paper surface and, as explained in the patent, the rigid requirements on the dyes that may be utilized in the process. Further, this process is uneconomical for the production of relatively small quantities of high quality decorated nameplates.

The general object of this invention is to provide a direct method of producing decorated anodized materials. Another object of this invention is to provide a direct method of producing individual decorated anodized aluminum nameplates. Other objects will appear hereinafter.

We have now found that the objects of this invention can be attained by exposing an anodized metal bearing a light-sensitive layer protruding above the peaks of the anodized metal, capable of developing a R of 0.2 to 2.2 of the type described and claimed in commonly assigned application, Ser. No. 796,897, filed Feb. 5, 1969, to actinic radiation to establish a potential R, of 0.2 to 2.2, applying a dry powder comprising a water-soluble dye or dyes to the exposed light-sensitive layer, embedding the developing powder in image-wise configuration into the light-sensitive layer, treating the light-sensitive element with water vapor (moist warm air) to imbibe the dye or dyes from the dry powder into the pores of the anodized metal in image-wise configuration. The anodized aluminum layer acts as a receiving layer much like the water-swellable receiving layers described in aforementioned application Ser. No. 796,897.

In the preferred method of operation, it is desirable to apply a hydrophilic colloid to the anodized metal surface prior to the application of the light-sensitive composition. The hydrophilic layer tends to fill up the pores of the anodized metal and prevent the light-sensitive composition from working into the pores of the anodized metal with the result that a more uniform light-sensitive layer is produced for subsequent steps in the process. Failure to use a hydrophilic colloid to at least partially fill up the pores of the anodized aluminum object necessitates the application of a substantially thicker layer of light-sensitive material in order to fill up the pores of the anodized metal with sensitizer. It is essential in this invention that the hydrophilic colloid only fill up the pores of the anodized metal and not form a thick layer over the anodized surface. If the hydrophilic colloid forms a thick layer, the hydrophilic colloid acts as a receiving layer for the dye imbibition step and insufficient dye penetrates into the pores of the anodized metal. In such case, the image is above the surface of the anodized metal and the image intensity drops markedly when the hydrophilic colloid is removed. On the other hand, when the hydrophilic colloid fills up part or all of the pores of the anodized metal, there is substantially no loss in dye intensity when the anodized object is washed with water and substantially all of the hydrophilic colloid removed from the' surface of the anodized object. In this case, the dye is imbibed into the anodized metal.

In somewhat greater detail, the anodized metal, preferably anodized aluminum containing a hydrophilic colloid filling up at least part of the pores of the anodized metal, is decorated by coating the anodized metal with a lightsensitive layer capable of developing R of 0.2 to 2.2, preferably 0.4 to 2.0, exposing the element to actinic ra diation to establish a potential R of 0.9 to 2.2, applying a dry powder comprising a water-soluble dye or dyes to the exposed light-sensitive layer, embedding the developing powder in image-wise configuration into the light-sensitive layer, treating the light-sensitive layer with Water vapor (moist warm air) to imbibe the dye or dyes from the dry powder into the pores of the anodized metal in imagewise configuration. The sensitizer and developing powder remaining on the surface of the hydrophilic layer are removed with a solvent.

When this invention is employed to produce objects having three or more colors (the first color being anodized metal surface and the second color being the first imbibed dye image), it is desirable to employ a water-insoluble sensitizer and remove sensitizer layer and embedded carrier powder particles from the surface of the anodized metal by washing with a suitable solvent for the sensitizer. In general, it is also preferred that the solvent be capable of dissolving the carrier for the developing powder. However, solvent insoluble carriers will be removed at the same time as the light-sensitive layer in any case. The anodized metal layer, preferably bearing the hydrophilic colloidal layer is then resensitized, exposed to light to a second pattern, developed with a second developing powder comprising a second dye or dyes and the second dye or dyes imbibed into the anodized surface. This technique may be repeated as many times as desired. If the pores of the anodized metal are filled with a hydrophilic colloid prior to dye imbibition, it is preferred that the hydrophilic colloid be removed by a simple water washing step after the last dye image is imbibed into the anodized metal. At this point the anodized metal may be sealed, if desired, or left unsealed.

The pores of the anodized metal are at least partially filled by applying an aqueous solution or dispersion of a suitable hydrophilic colloid by any means dictated by the nature of the colloidal composition, such as by spray, roller coating or air knife, flow, dip or whirler coating, curtain coating, etc. For example, a 0.1 to 30% by weight aqueous solution or dispersion of hydrophilic colloid can be flow coated over the surface of the anodized metal using a rod, wire wrapped rod, doctor blade, etc. to assure that the hydrophilic colloid does not protrude above the surface of the anodized metal but only fills the pores thereof.

Suitable hydrophilic colloids include polyvinyl alcohol, starch, hydroxyethyl starch, carboxyrnethyl starch, cyanoethyl starch, hydroxyethyl cellulose, carboxymethyl cellulose, gelatin, gum tragacanth, gum arabic, dextrin, dextran, Carbopol (carboxy polymethylene), etc. Of these, the cold Water soluble hydroxy containing polymers free of carboxyl groups such as polyvinyl alcohol are preferred since these materials can be readily removed from the pores of the anodized metal after the dye imbibition of colorant or colorants. The' carboxyl containing materials have the disadvantage that they chemically bond to the anodized metal and are not readily removed with cold water.

The light-sensitive layers are formed by applying a thin layer of solid, light-sensitive, film-forming organic material having a potential R of 0.2 to 2.2 to the anodized layer, preferably anodized metal having a hydrophilic col loid filling up at least part of the pores of the anodized metal, by any suitable means dictated by the nature of the film-forming material (hot-metal, draw down, spray, roller coating or air knife, flow, dip or whirler coating, curtain coating, etc.) so as to produce a reasonably smooth homogeneous layer projecting from 0.1 to 40 microns above the peaks of the anodized metal employing suitable solvents as necessary.

As indicated above, the light-sensitive elements employed in this invention have a R of 0.2 to 2.2. If the R is below 0.2 the light-sensitive layer is too hard to accept a suitable concentration of powder particles. On the other hand, if the R is above 2.2, the developing powder will not embed as a monolayer and the light-sensitive layer may stick to the transparency in vacuum frame exposure equipment. The R of positive-acting, light-sensitive layers, which is called R is a photometric measurement of the reflection density of a black powder developed light-sensitive layer after a positive-acting, light-sensitive layer has been exposed to suflicient actinic radiation to convert the exposed areas into substantially powder-non-receptive state (clear the background). The R of a negative-acting, light-sensitive layer, which is called R is a photometric measurement of the reflection density of a black powder developed area, after a negative-acting, light-sensitive layer has been exposed to suflicient actinic radiation to convert the exposed areas into a powder-receptive state.

The reflection density of a solid, positive-acting, lightsensitive layer (R is determined by coating the lightsensitive layer on a white substrate, exposing the lightsensitive layer to suflicient actinic radiation image-wise to clear the background of the solid, positive-acting, lightsensitive layer, applying a black powder (prepared from 77% Pliolite VTL and 23% Neo Spectra carbon black in the manner described below) to the exposed layer, physically embedding said black powder under the conditions of development as a monolayer in a stratum at the surface of said light-sensitive layer and removing the nonembedded particles from said light-sensitive layer. The developed organic layer containing black powder embedded image areas and substantially powder free non-image areas is placed in a standard photometer having a scale reading from 0 to reflection of incident light or an equivalent density scale, such as on Model 500 A photometer of the Photovolt Corporation. The instrument is zeroed (0 density; 100% reflectance) on a powder free nonimage area of the light-sensitive organic layer and an average R reading is determined from the powder developed area. The reflection density is a measure of the degree of blackness of the developed surface which is relatable to the concentration of particles per unit area. The reflection density of a solid, negative-acting, light-sensitive layer (R is determined in the same manner except that the negative-acting, light-sensitive layer is exposed to sufficient actinic radiation to convert the exposed area into a powder-receptive area. If the R under the conditions of development is between 0.2 to 2.2, the solid, light-sensitive organic material deposited in a layer is suitable for use in this invention.

Although the R of light-sensitive layers is determined by using the aforesaid black developing powder and a white substrate, the R is only a measure of the suitability of a light-sensitive layer for use in the present invention.

Since the R of any light-sensitive layer is dependent on numerous factors other than the chemical constitution of the light-sensitive layer, the light-sensitive layer is best defined in terms of its R under the development conditions of intended use. The positive-acting, solid, lightsensitive organic layers useful in this invention must be powder receptive in the sense that the aforesaid black developing powder can be embedded as a monoparticle layer into a stratum at the surface of the unexposed layer to yield a R of 0.2 to 2.2 (0.4 to 2.0 preferably) under the predetermined conditions of development and lightsensitive in the sense that upon exposure to actinic radiation the most exposed areas can be converted into the nonparticle receptive state (background cleared) under the predetermined conditions of development. In other words, the positive-acting, light-sensitive layer must contain a certain inherent powder receptivity and light-sensitivity. The positive-acting, light-sensitive layers are apparently converted into the powder-non-receptive state by a light-catalyzed hardening action, such as photopolymerization, photocrosslinking, photooxidation, etc. Some of these photohardening reactions are dependent on the presence of oxygen, such as the photooxidation of internally ethylenically unsaturated acids and esters, while others are inhibited by the presence of oxygen, such as those based on the photopolymerization of vinylidene or polyvinylidene monomers alone or together with polymeric materials. The latter requires special precautions, such as storage in oxygen-free atmosphere or oxygen-impermeable cover sheets. For this reason, it is preferable to use solid, positive-acting, film-forming organic materials containing no terminal ethylenic unsaturation.

The negative-acting, solid, light-sensitive organic layers useful in this invention must be light-sensitive in the sense that, upon exposure to actinic radiation, the most exposed areas of the light-sensitive layer are converted from a nonpowder-receptive state under the predetermined conditions of development. to a powder-receptive state under the predetermined conditions of development. In other words, the negative-acting, light-sensitive layer must have a certain minimum light-sensitivity and potential powder receptivity. The negative-acting, light-sensitive layers are apparently converted into the powder receptive state by a light-catalyzed softening action, such as photodepolymerization, photoisomerization, etc.

In general, the positive-acting, solid, light-sensitivelayers useful in this invention comprise a film-forming organic material in its naturally occurring or manufactured form or a mixture of said organic material with plasticizers and/or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable positive-acting, film-forming organic materials which are not inhibited by oxygen, include internally ethylenically unsaturated acids, such as abietic acid, rosin acids, partially hydrogenated rosin acids, such as those sold under the name Staybelite resin, wood rosin, etc., esters of internally ethylenically unsaturated acids, methylol amides of maleated oils such as described in US. Pat. 3,471,466, phosphatides of the class described in application Ser. No. 796,841, filed on Feb. 5, 1969, now US. Pat. 3,585,- 031, in the name of Hayes, such as soybean lecithin, partially hydrogenated lecithin, dilinolenyl-alpha-lecithin, etc., partially hydrogenated rosin acid esters, such as those sold under the name Staybelite esters, rosin modified alkyds, etc.; polymers of ethylenically unsaturated monomers, such as vinyltoluene-alpha methyl styrene copolymers, polyvinyl cinnamate, polyethyl methacrylate, vinyl acetatevinyl stearate copolymers, polyvinyl pyrrolidone, etc.; coal tar resins such as coumarone-indene resins, etc.; halogenated hydrocarbons, such as chlorinated waxes, chlorinated polyethylene, etc. Positive-acting, light-sensitive materials, which are inhibited by oxygen include mixtures of polymers, such as polyethylene terephthalate/sebacate, or cellulose acetate or acetate/butyrate, with polyunsaturated vinylidene monomers, such as ethylene glycol diacrylate or dimethacrylate, tetraethylene glycol diacrylate or dimethacrylate, etc.

Although numerous positive-acting, film-forming organic materials have the requisite light-sensitivity and powder-receptivity at predetermined development temperatures, it is generally preferable to compound the filmforming organic material with photoactivator(s) and/ or plasticizer(s) to impart optimum powder receptivity and light-sensitivity to the light-sensitive layer. In most cases, the light-sensitivity of an element can be increased many fold by incorporation of a suitable photoactivator capable of producing free-radicals, which catalyze the lightsensitive reaction and reduce the amount of photons necessary to yield the desired physical change.

Suitable photoactivators capable of producing free-radicals include benzil, benzoin, Michlers ketone, diacetyl, phenanthraquinone, p-dimethylaminobenzoin, 7,8-benzoflavone, trinitrofluorenone, desoxybenzoin, 2,3-pentanedione, dibenzylketone, nitroisatin, di(6-dimethylamino-3- pyradil) methane, metal naphthanates, N-methyl-N-phenylbenzylamine, pyridil, 5,7-dichloroisatin, azodiisobutyronitrile, trinitroanisole, chlorophyll, isatin, bromoisatin, etc. These compounds can be used in a concentration of .001 to 2 times the weight of the film-forming organic material (.1%200% the weight of film former). As in most catalytic systems, the best photoactivator and optimum concentration thereof is dependent upon the film-forming organic material. Some photoactivators respond better with one type of film former and may be useful with substantially all film-formers in wide concentration ranges.

The acyloin and vicinal diketone photoactivators, particularly benzil and "benzoin are preferred. Benzoin and benzil are effective over wide concentration ranges with substantially all film-forming, light-sensitive organic materials. Benzoin and benzil have the additional advantage that they have a plasticizing or softening effect on filmforming, light-sensitive layers, thereby increasing the powder receptivity of the light-sensitive layers. When employed as a photoactivator, benzil should preferably comprise at least 1% by weight of the film-forming organic material (.01 times the film former weight).

Dyes, optical brighteners and light absorbers can be used alone or preferably in conjunction with the aforesaid free-radical producing photoactivators (primary photoactivators) to increase the light-sensitivity of the light-sensitive layers of this invention by converting light rays into light rays of longer lengths. For convenience, these secondary photoactivators (dyes, optical brighteners and light absorbers) are called superphotoactivators. Suitable dyes, optical brighteners and light absorbers include 4-methyl-7-dimethylaminocoumarin, Calcofiuor yellow HEB (preparation described in US. Pat. 2,415,373), Calcofluor white SB super 30080, Calcofluor, Uvitex W. conc., Uvitex TXS conc., Uvitex RS (described in Textil- Rundschau 8 [1953], 339), Uvitex WGS conc., Uvitex K, Uvitex CF conc., Uvitex W (described in Textil-Rundschau 8 [1953], 340 Aclarat 8678, Blancophor OS, Tenopol UNPL, MDAC 8-8844, Uvinul 400 Thilflavin TGN conc., Aniline yellow-S (low conc.), Seto Flavine T 5506-140, Auramine O, Calcozine yellow 0X, Calcofluor RW, Calcofluor GAC, Acetosol yellow 2 -RLS-PHF, Eosine bluish, Chinoline yellow-P conc., Ceniline yellow S (high conc.), Anthracene blue Violet fluorescence, Calcofiuor white MR, Tenopol PCR, Uvitex GS, Acid-yellow-T- supra, Acetosol yellow 5 GLS, Calcocid OR. Y. Ex. conc., diphenyl brilliant fiavine 7 GFF, Resofiorm fluorescent yellow 3 GPI, Eosin yellowish, Thiazole fluorescor G, Pyrazalone organe YB-3, and National FD & C yellow. Individual superphoto activators may respond better with one type of light-sensitive organic film former and photoactivator than with others. Further, some photoactivators function better with certain classes of brighteners, dyes and light absorbers; For the most part, the most advantageous combinations of these materials and proportions can be determined by simple experimentation.

As indicated above, plasticizers can be used to impart optimum powder receptivity to the light-sensitive layer. With the exception of lecithin, most of the film-forming, llght-sensitive organic materials useful in this invention are not powder-receptive at room temperature but are powder-receptive above room temperature. Accordingly, It is desirable to add sufiicient plasticizer to impart room temperature (15 to 30 C.) or ambient temperature powder-receptivity to the light-sensitive layers and/or increase the R range of the light-sensitive layers.

While various softening agents, such as dimethyl phthalate, glycerol, vegetable oils, etc. can be used as plasticizers, benzil and benzoin are preferred since, as pointed out above, these materials have the additional advantage that they increase the light-sensitivity of the film-forming organic material. As plasticizer-photoactivators, benzoin and benzil are preferably used in a concentration of 1% to by weight of the film-forming solid organic maer1a The preferred positive-acting, light-sensitive film formers containing no conjugated terminal ethylenic unsaturation include the esters and acids of internally ethylenically unsaturated acids, particularly the phosphatides, rosin acids, partially hydrogenated rosin acids and the partially hydrogenated rosin esters. These materials, when compounded with suitable photoactivators, preferably acyloins or vicinal diketones together with superphotoactivators, require less than 2 minutes exposure to clear the background of light-sensitive layers.

In general, the negative-acting, light-sensitive layers useful in this invention comprise a film-forming organic material in its naturally occurring or manufactured form, or a mixture of said organic material with plasticizers and/ or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable negative-acting,

film-forming organic materials include n-benzyl linoleamide, dilinoleyl-alpha-lecithin, castor wax (glycerol 12- hydroxy-stearate), ethylene glycol monohydroxy stearate, polyisobutylene, polyvinyl stearate, etc. Of these, castor wax and other hydrogenated ricinoleic acid esters (hydroxystearate) are preferred. These materials can be compounded with plasticizers and/or photoactivators in the same manner as the positive-acting, light-sensitive, filmforming organic materials.

Some solid, light-sensitive organic film formers can be used to prepare either positive or negative-acting, lightsensitive layers. For example, a poly(n-butyl methacrylate) layer containing 20 percent benzoin (20 parts by Weight benzoin per 100 parts by weight polymer) yields good positive-acting images. Increasing the benzoin level to 100 percent converts the poly(n-butyl methacrylate) layer into a good negative-acting system.

The light-sensitive layer must protrude at least 0.1 micron above the peaks of the anodized metal and preferably at least 0.4 micron in order to hold suitable powders during the development. If the light-sensitive layer protrudes less than 0.1 micron, or the developing powder diameter is more than 25 times layer thickness, the lightsensitive layer does not hold the developing powder with the necessary tenacity. In general, as layer thickness increases, the light-sensitive layer is capable of holding larger particles. However, as the light-sensitive layer thickness increases, it becomes increasingly difiicult to maintain film integrity during film development. Accordingly, the light-sensitive layer must protrude from 0.1 to 40 microns above the peaks of the anodized metal, preferably from 0.4 to 2.5 microns.

The preferred method of applying light-sensitive layers of predetermined thicknesses to the anodized metal (including anodized metal filled with hydrophilic colloid) comprises flow coating a solution in an organic solvent vehicle (hydrocarbons, such as hexane, heptane, benzene, etc.; halogenated hydrocarbons, such as chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, etc.; alcohols, such as ethanol, methanol, isopropanol, etc.; ketones, such as acetone, methyl ethyl ketone, etc.) of the light-sensitive organic film-former alone or together with dissolved or suspended photoactivators or plasticizers onto the base. The hydrocarbons and halohydrocarbons, which are excellent solvents. for the preferred positiveacting, light-sensitive film formers, containing no terminal conjugated ethylenic unsaturation, are the preferred vehicles because of their high volatility and low cost. Typically, solutions prepared with these vehicles can be applied to the base and air dried to a continuous clear film in less than one minute. In general, the halohydrocarbons have the advantage that they are non-flammable and can be used without danger of flash fires. However, many of these, such as chloroform and carbon tetrachloride must be handled with care due to the toxicity of their vapors. Of all these solvents, 1,1,1-trichloroethane is preferred since it has low toxicity, is non-flammable, low cost and has high volatility. In general, the thickness of the light-sensitive layer can be varied as a function of the concentration of the solids dissolved in the solvent vehicle.

After the anodized metal is coated with a suitable solid, light-sensitive organic layer, a latent image is formed by exposing the element to actinic radiation in image-receiving manner for a time suflicient to provide a potential R of 0.2 to 2.2 (clear the background of the positive-acting, light-sensitive layers or establish a potential R of 0.2 to 2.2 with negative-acting, light-sensitive layers). The lightsensitive elements can be exposed to actinic radiation through a photographic positive or negative, which may be line, half-tone or continuous tone.

As indicated above, the latent images are preferably produced from positive-acting, light-sensitive layers by exposing the element in image-receivin g manner for a time sufficient to clear the background, i.e. render the exposed areas non-powder-receptive. As explained in common-1y assigned application Ser. No. 796,847, now U.S. Pat. 3,637,385, the amount of actinic radiation necessary to clear the background varies to some extent with developer powder size and development conditions. Due to these variations it is often desirable to slightly overexpose line and half-tone images in order to assure complete clearing of the background. Slightly more care is necessary in producing continuous-tone powder images since overexposure tends to decrease the tonal range of the developed image. In general, overexposure is preferred with negative-acting, light-sensitive elements in order to provide maximum contrast.

After the light-sensitive element is exposed to actinic radiation for a time sufficient to clear the background of a positive-acting, light-sensitive layer or establish a potential R of 0.2 to 2.2, a developing powder having a diameter or dimension along one axis of at least 0.3 micron comprising a dye is applied physically with a suitable force, preferably mechanically, to embed the powder in the light-sensitive layer. The developing powder can be virtually any shape, such as spherical, acicular, platelets, etc.

The developing powders suitable for use in dye imbibition imaging processes comprises one or more water-soluble dyes. Generally the dye or dyes are on a solid carrier in order to control the particle size of the developing powder and to control the intensity of the final dye image. The dye or dyes can be ball-milled with the solid carrier in order to coat the carrier with dye. If desired, dyes can be blended above the melting point with various solid carriers, ground to suitable size and classified. In some cases it is advantageous to dissolve dye and carrier in a mutual solvent, dry and grind to suitable size. Preferably, the carrier is coated with dye, since the dye is more readily and more efiiciently embedded into the substrate. If the dye is in the carrier matrix, more dye must be employed to obtain comparable brilliance and image density. However, the latter route tends to preclude individual dye particles from embedding in nonimage areas.

Suitable solid carriers include polymeric or resinous materials, such as Pliolite VTL (vinyltoluene-butadiene copolymer), polymethyl methacrylate, polystyrene, rice starch, corn starch, phenol-formaldehyde resins, etc.; organic monomeric compounds such as hydroquinone, sorbitol, manitol, dextrose, tartaric acid, urea, animal glue, gelatin, g-um arabic, Carbowaxes, polyvinyl pyrrolidone, etc. Suitable metal powders include aluminum flakes, nickel flakes, rhodium powders, etc.

For use in this invention, it is generally preferred that the solid carrier is water insoluble and organic solvent soluble. In this way, none of the solid carrier migrates into the pores of the anodized metal during the dye imbibition step and the solid carrier can subsequently be removed readily with solvent solution to restore the original characteristics of the anodized metal for the next image.

Suitable water soluble dyes include Alphazurine 2G, Calcocid Phloxine 2G, Tartrazine, Acid Chrome blue 3BA Conc., Acid Magenta 0., Ex. Conc., Neptune Blue BRA Conc., Nigrosine, Jet Conc., Patent Blue AF, Ex. Conc., Pontacyl Light Red 4 'BL Cone. etc.

The black developing powder for determining the R of a light-sensitive layer is formed by heating about 77% Pliolite VTL (vinyl-toluene-butadiene copolymer) and 23% Neo Spectra carbon black at a temperature above the melting point of the resinous carrier, blending on a rubber mill for fifteen minutes and then grinding in a Mikro-atomizer.

The developing powders useful in this invention contain particles having a diameter or dimension along at least one axis from 0.1 to 40 microns, preferably from 0.5 to 15 microns with powders of the order of 1 to 15 microns being best for light-sensitive layers of 0.4 to 10 microns. Maximum particle size is dependent on the thickness of light-sensitive layer while minimum particle size is independent of layer thickness. Electron microscope studies have shown that developing powders having a diameter 25 times the thickness of the light-sensitive layer cannot be permanently embedded into light-sensitive layers, and generally speaking, best results are obtained where the diameter of the powder particle is less than about times the thickness of the light-sensitive layer. For the most part, particles over 40 microns are not detrimental to image development provided the developing powder contains a reasonable concentration of powder particles under 40 microns, which are less than 25 times, and preferably less than 10 times, the light-sensitive layer thickness. However, other things being equal, the larger the developer powder particles (above 10 microns), the lower the R of the developed image.

Although particles over 40 microns are not detrimental to image development, the presence of particles under 0.1 micron diameter along all axes can be detrimental to proper image formation. In general, it is preferable to employ developing powders having substantially all powders having a diameter along at least one axis not less than 0.3 micron, preferably more than 0.5 micron, since particles less than 0.3 micron tend to embed in nonimage areas. As the particle size of the smallest powder in the developer increases, less exposure to actinic radiation is required to clear the background.

In general, somewhat more deposition of powder particles into non-image areas can be tolerated when using a black developing powder than a colored powder, since the human eye is less offended by gray background on non-image areas than by the deposition of colored particles in non-image areas. Therefore, the concentration of particles under 0.1 micron and the size of the developing powder is more critical when using a cyan, magenta or yellow developing powder. For best results, the developing powder should have substantially all particles (at least 95% by weight) over 1 micron in diameter along one axis and preferably from 1 to microns for use with light-sensitive layers of from 0.4 to 10 microns. In this way, powder embedment in image areas is maximum and relatively little powder is embedded into non-image areas.

In somewhat greater detail, the developing powder is applied directly to the light-sensitive layer, while the powder receptive areas of said layer are in at most only a slightly soft deformable condition and said layer is at a temperature below the melting point of the layer and powder. The powder is distributed over the area to be developed and physically embedded into the stratum at the surface of the light-sensitive layer, preferably mechanically by force having a lateral component, such as to-and-fro and/or circular rubbing or scrubbing action using a soft pad or fine brush. If desired, the powder may be applied separately or contained in the pad or brush. The quantity of powder is not critical provided there is an excess available beyond that required for full development of the area, as the development seems to depend primarily on particle-to-particle interaction rather than brush-to-surface or pad-to-surface forces to embed a layer of powder particles substantially one particle thick (monoparticle layer) into a stratum at the surface of the light-sensitive layer. When viewed under an inverse microscope, spherical powder particles under about 10 microns in diameter enter the powder-receptive areas first and stop dead, embedded substantially as a monolayer. The larger particles seem to travel over the embedded smaller particles which do not rotate or move as a pad or brush is moved back and forth over the developed area. Non-spherical particles, such as platelets, develop like the spherical powders except that the fiat side tends to embed. Only a single stratum of powder particles penetrates into the powder-receptive areas of the light-sensitive layer even if the light-sensitive layer is several times thicker than the developer particle diameter.

After the powder application, excess powder remains on the surface which has not been sufiiciently embedded into, or attached to, the film. This may be removed in any convenient way, as by wiping with a clean pad or brush usually using somewhat more force than employed in mechanical development, by vacuum, by vibrating, or by air doctoring. For simplicity and uniformity of results, the excess powder is usually blown off using an air gun having an air-line pressure of about 20 to 40 p.s.i.

At this point the powder particles comprising a water soluble dye, held in image-wise configuration in particulate form in the light-sensitive layer, are separated from the anodized metal by the light-sensitive layer. An aesthetically more pleasing image is then produced by treating the developed image with water vapor, molecularly imbibing said dye into the anodized metal. Other things being equal, the particulate dye image changes from a pale or pastel color to a brilliant, saturated, more pleasing hue. The light-sensitive layer, which preferably contains no conjugated terminal ethylenic unsaturation, is then removed from the surface of the anodized metal with a solvent for the light-sensitive layer which is a poor solvent for the surface of the substrate. 1,1,1-trichloroethane is particularly well suited for use in this step. Removal of the light-sensitive layer and the carrier for the developing powder renews the surface of the anodized metal so that it can be resensitized with a substantially even layer of sensitizer.

As indicated above, the water soluble dye is separated from the anodized metal by the light-sensitive layer. Although the transportation of the dye through the solid, organic layer is not completely understood, it is believed that in most cases dye imbibition is due to weakening of the light-sensitive layer by the powder particles employed during deformation imaging creating potential points of stress in the film surface. Subsequently, when the water vapor contacts the light-sensitive layer, a second stress is imposed upon the light-sensitive layer resulting in fracturing of the light-sensitive layer and transportation of the dye through the light-sensitive layer and imbibition of said dye into the anodized metal pores. In other cases dye imbibition may be due to water vapors diffusing the dissolved dye into the light-sensitive layer. In any event, the water vapor must be capable of transporting the dye through the organic light-sensitive layer.

Experiments have shown that the development of various light-sensitive elements, such as Staybelite Ester #10 and Staybelite resin, with developing powder weakens the film layer. For example, when these light-sensitive elements are developed with undyed developing powder, it is possible to imbibe water soluble dye into the receiving layer in image-wise configuration by merely dipping the developed light-sensitive element into an aqueous dye bath. In such case the water soluble dye enters the hydrophilic receiving layer in the areas defined by the undyed powder particles. Accordingly, in such case, it is clear that transportation of the dye through the light-sensitive layer is at least partially due to weakening of the light-sensitive layer by developer particle.

It has also been found that the above light-sensitive materials have a tendency to puddle up in the exposed areas in image-wise configuration when merely exposed to light and treated with water vapors. Accordingly, dye imbibition of water-soluble dyes through these materials is also partially due to the ability of moist warm air to disrupt the unexposed areas of the light-sensitive layer. In other cases, such as in the case of phosphatide lightsensitive elements, the exposed areas of the light-sensitive layer are converted into a more water-soluble condition than the unexposed areas as explained in aforementioned copending application, Ser. No. 796,841 of Hayes, filed Feb. 5, 1969, now U.S. Pat. 3,585,031. In such case, water vapor tends to transport the dye image through the exposed areas of the light-sensitive element with the result that the original positive powder image changes into a negative dye imbibition image. In still other cases, it has been possible to prevent passage of water-soluble dye into the dye imbibition receiving layer by adding various hydrophobic agents, such as silicone oils in a concentration of 200 parts per million to various light-sensitive layers, such as those based on Staybelite resins and esters. The silicone tends to act as a waterproofing agent in this environment and no dye imbibition with water vapor is possible since water vapor is incapable of transporting the dye through the lightsensitive layer. Dye imbibition of water-soluble dye through light-sensitive layers based on poly(n-butyl methacrylate) and other high molecular weight hydrophobic polymers, is relatively diflicult due to the extreme hydrophobic nature of these film formers. Accordingly, routine experimentation may be carried out to determine which aqueous solvents are best for transporting specific dyes through particular light-sensitive elements.

The preferred method of forming multi-colored reproductions comprises coating anodized aluminum containing a hydrophilic colloid filling up the pores of the anodized metal with a halohydrocarbon solution of a light-sensitive organic film former containing no conjugated terminal ethylenic unsaturation to form a light-sensitive layer protruding from about 0.5 to 2.5 microns above the peaks of the anodized metal, capable of developing a R of 0.4 to 2.0; exposing said light-sensitive organic layer to actinic radiation in image-receiving manner to establish a potential R, of 0.4 to 2.0; applying to said layer of organic material, free-flowing powder particles comprising a water-soluble dye and a 1,1,1 trichloroethane soluble carrier, said powder particles having a diameter along at least one axis of at least one micron; while the element is at a temperature below the melting points of the powder and the organic layer, physically embedding said powder particles as a monolayer in a stratum at the surface of said light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; removing non-embedded particles from said organic layer to develop an image; molecularly imbibing water-soluble dye into the pores of the anodized metal by contacting the particles embedded in said organic layer with vapors of Water or steam; removing said light-sensitive organic film former containing no conjugated terminal ethylenic unsaturation and the carrier for said dye with 1,1,1 trichloroethane clearing agent; coating the substrate bearing the first color in image-wise configuration in the surface of said substrate with a solid, light-sensitive organic film former containing no conjugated terminal ethylenic unsaturation from a 1,1,1-trichloroethane vehicle to form a second light-sensitive organic layer protruding from about 0.5 to 2.5 microns above the peaks of the anodized metal, capable of developing a R of 0.4 to 2.0; exposing said light-sensitive layer to actinic radiation in image-receiving manner to establish a potential R of 0.4 to 2.0; applying to said layer of organic material free-flowing powder particles comprising a second Water soluble dye and carrier, said powder particles having a diameter along one axis of at least one micron; while the layer is at a temperature below the melting points of the powder and of the organic layer, physically embedding said powder particles as a monolayer in a stratum at the surface of said second light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; removing the non-embedded particles from said organic layer to develop a three color reproduction (two dye images on an aluminum background); molecularly imbibing water soluble dye into the anodized layer by contacting the particles embedded in said organic layer with vapors of Water or steam; removing said second lightsensitive layer and second developer powder layer with 1,1,l-trichloroethane clearing solution and repeating the process to put down a third, fourth, fifth dye image. After the last image is put down, the hydrophilic colloid is pref- 12 erably removed by flowing water over the surface of the imaged anodized metal or by placing the anodized metal in a suitable water bath. Alternatively, the hydrophilic colloid may be left in the pores of the anodized metal.

If desired, after the first dye image is imbibed into the pores of the anodized aluminum and sensitizer and carrier particles are removed with organic solvent, the imaged anodized metal may be dipped into a suitable dye bath to form a complementary image, i.e. dye penetrates into the pores of the anodized aluminum containing no previous dye image and dye penetrates into the pores of the anodized metal bearing the first dye image forming a complementary color. Typical of this would be the formation of a first cyan image, followed by dipping the anodized metal into a yellow dye bath resulting in the formation of a green image on a yellow background. In this technique, the cyan portion of the image would be converted to green and the background area would be yellow.

The following examples are merely illustrative and should not be construed as limiting the scope of our invention:

EXAMPLE I A 15% by weight aqueous solution of polyvinyl alcohol (Elvanol 71-30) was drawn down with a glass rod over the pores of an anodized aluminum plate barely filling the pores of the anodized metal. Sixty-four one hundredths of a gram of Staybelite Ester #10 (partially hydrogenated rosin ester of glycerol), .19 gram benzil and .14 grame 4 methyl 7 dimethylaminocoumarin dissolved in 100 mls. Chlorothene (1,1,1-trichloroethane) was applied to the polyvinyl alcohol filled anodized aluminum by flow coating the solution over the substrate supported at about a 60 angle with the horizonal. After air drying for one minute, the light-sensitive element was placed in contact with a yollow half-tone separation positive in a vacuum frame and exposed to a carbon are for about one minute. The light-sensitive element was removed from the vacuum frame and developed by rubbing a cotton pad containing a tartrazine (yellow)-Pliolite VTL (vinyltoluene-butadiene copolymer) of from about 1 to 15 microns diameter along the largest axis, across. the exposed element, thereby embedding the yellow developing powder into the unexposed areas of the light-sensitive layer. The excess powder was removed from the lightsensitive layer by impinging air at an angle of about 30 to the surface until the surface was substantially free of powder. The reproduction was then wiped with a fresh cotton pad resulting in an excellent half-tone reproduction of the original yellow separation transparency. The developed image was placed over a beaker of boiling water for about 15 seconds during which time the yellow dye image was imbibed and molecularly dispersed in halftone, image-wise configuration into the pores of the anodized aluminum. The molecularly dispersed image changed from a pale yellow to a more brilliant, saturated aesthetically pleasing yellow hue. The light-sensitive layer and Pliolite VTL developing powder on the surface of the anodized aluminum plate were removed by flow coating Chlorothene clearing solution over the layer leaving the yellow image in the pores of the anodized aluminum.

A second color was imbibed into the pores of the anodized aluminum by resensitizing the anodized aluminum with the same light-sensitive solution used to develop the first yellow image, exposing the light-sensitive element through the cyan separation positive, developed in the manner described above using a cyan developing powder composed of 20% by weight Alphazurine 2G and by weight Pliolite VTL, the excess developing powder was removed and the cyan image was molecularly imbibed into the pores of the anodized aluminum by holding the element over a beaker of boiling water for about 15 seconds. The light-sensitive layer and Pliolite VTL developing powder were then removed by flowing Chloro- 13 thene clearing agent over the surface of the developed image.

A magenta image was then deposited using the same light-sensitive solution and the same technique except that a developing powder composed of 20% Carmoisine and 80% by weight Pliolite VTL was used. After the magenta dye was molecularly imbibed into the pores of the anodized aluminum, the light-sensitive layer and Pliolite VTL developing powder was removed by flowing Chlorothene over the anodized aluminum plate. The polyvinyl alcohol in the pores of the anodized aluminum was removed by washing with cold tap water leaving the image in the pores of the anodized aluminum.

The developing powders employed in this example were prepared by ball-milling for twenty-four hours 20 parts by weight of the appropriate dye and 80 parts by weight of Pliolite VTL.

EXAMPLE II This example illustrates the preparation of a decorated anodized aluminum plate wherein no polyvinyl alcohol subbing layer was employed. One and ninety-two onehundredths of a gram Staybelite Ester #10, 0.77 gram benzil and 0.575 gram 4-methyl-7-dimethylaminocoumarin dissolved in 100 mls. Chlorothene were flow coated over the bare anodized aluminum plate, exposed to actinic radiation through a cyan printer for approximately one minute, developed with a 100% cyan dye in the manner described in Example I, molecularly imbibed into the pores of the anodized aluminum in image-wise configuration by holding the element over boiling water and the light-sensitive layer removed by flowing Chlorothene over the anodized aluminum plate.

EXAMPLE III Example I was repeated except that the polyvinyl alcohol subbing layer was applied by flow coating a .1% by weight polyvinyl alcohol solution. The resultant images were somewhat splotchy indicating that either the thickness of the polyvinyl subbing layer had to be increased in order to get a good image or the total solids in the light-sensitive solution had to be increased in order for the light-sensitive layer to protrude above the pores of the anodized aluminum.

EXAMPLE IV Example II was repeated with essentially the same results except that the light-sensitive solution was composed of 2.88 grams Piccolastic E-75 (modified polystyrene), 1.15 grams benzil and .432 gram 4-methyl-7-dimethylaminocoumarin in 100 mls. Chlorothene and a 100% Carmoisine magenta dye was employed as the developing powder.

When this example was repeated using two-thirds the solids of the light-sensitive solution described above, only an extremely weak image was formed indicating that it is necessary to employ a higher solid, light-sensitive solution or else partially fill the pores of the anodized aluminum in order to get a relatively strong saturated image in the pores of the anodized aluminum.

Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing is interpreted as illustrative only and the invention is defined by the claims appended hereafter.

What is claimed is:

1. The process of decorating anodized metals which comprises the steps of exposing an anodized metal substrate bearing a light-sensitive layer capable of developing a R of 0.2 to 2.2 to actinic radiation in image-wise configuration to establish a potential R of 0.2 to 2.2, applying a dry powder comprising a water-soluble dye to the exposed light-sensitive layer, embedding the developing powder in image-wise configuration into the light-sensitive layer, removing the developing powder from the nonimage areas and molecularly imbibing and transporting said dye from the dry powder into the pores of the anodized metal in image-wise configuration by contacting said light-sensitive element with water vapor.

2. The process of claim 1, wherein the pores of the anodized metal are at least partially filled with a hydrophilic colloid.

3. The process of claim 1, wherein said light-sensitive layer is removed from the surface of the anodized metal with a solvent for the light-sensitive layer after imbibing said dye into the pores of said anodized metal.

4. The process of claim 1, wherein said light-sensitive layer is a positive-acting light-sensitive layer capable of developing a R of 0.4 to 2.0.

5. The process of claim 4, wherein said dry powder comprises a carrier for said water-soluble dye.

6. The process of decorating an anodized aluminum object which comprises the steps of exposing an anodized aluminum object bearing a light-sensitive layer, capable of developing an R of 0.2 to 2.2 to actinic radiation in image-wise configuration to establish a potential R of 0.2 to 2.2, applying a dry powder comprising a watersoluble dye to the exposed light-sensitive layer, embedding the developing powder in image-wise configuration into the light-sensitive layer, removing the developing powder from the non-image areas and molecularly imbibing and transporting said dye from the dry powder into the pores of the anodized metal in image-wise configuration by contacting said light-sensitive element with water vapor and removing said light-sensitive layer with a solvent for said light-sensitive layer.

7. The process of claim 6, wherein after the light-sensitive element is removed with a solvent for said light-sensitive layer, the anodized metal is sensitized with a second light-sensitive layer capable of developing a R of 0.2 to 2 .2, said second light-sensitive layer is exposed to actinic radiation in image-wise configuration to establish .a potential R of 0.2 to 2.2, developed with a second dry powder comprising a second water soluble dye, said second powder is embedded into the second light-sensitive layer in image-wise configuration, developing powder is removed from the non-image areas, and said second dye from said second dry powder is molecularly imbibed and transported into the pores of the anodized metal in image-wise configuration by contacting said light-sensitive layer with water vapor.

8. The process of claim 7, wherein the pores of said anodized metal are at least partially filled with a hydrophilic colloid.

9. The process of claim '8, wherein said hydrophilic colloid is removed from the pores of said anodized aluminum after the last dye image is imbibed into the pores of said anodized metal.

10. The process of claim 7, wherein all of said lightsensitive layers are positive-acting, light-sensitive layers capable of developing a R of 0.4 to 2.0.

11. The process of claim 10, wherein said powders comprise a carrier for said water-soluble dyes.

References Cited UNITED STATES PATENTS 2,384,857 9/1945 Terry 96-33 NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner U.S. Cl. X.R. 9617, 38.1, 35