US 3440111 A
Description (OCR text may contain errors)
K. H. DALE April 22, 1969 SOLVEN'I' DYEING OF ANODZED ALUMINUM- Filed June l5, 1966 KENNETH H. DALE United States Patent O 3 440 111 soLvENT DvErNG 6F NoDIzED ALUMINUM Kenneth Howard Dale, Henrico County, Va., assignoit` to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed .lune 15, 1966. Ser. No. 557,648 Int. Cl. C23f 5/04; B44d 1/34 U.S. Cl. 14S-6.1 15 Claims This invention relates to a novel method for dyeing anodized aluminous metals. More particularly, the invention concerns a system for the continuous dyeing of anodized aluminum, including a novel dye solvent removal and drying sequence.
It has long been known that anodized aluminum and aluminum base alloys can be dyed or colored by the application to the aluminum oxide coating of aqueous solutions of water soluble dyes, but colors produced in this way are deficient in light and heat f-astness and have a `tendency toward streaking. Hence it has been proposed in the prior art to employ for this purpose, spirit soluble dyes dissolved in alcohol or acetone or mixtures thereof. However, the water miscibility of these solvents results in the same shortcomings as in the case of water soluble dyes. Hence, it has been further proposed to utilize waterinsoluble dyes or colorants dissolved in water immisc-i'ble organic solvents, especially high boiling halogenated aromatic hydrocarbon solvents, for dyeing anodized aluminum, and `a system of this type is described in U.S. Patent No, 2,975,081.
Experience has shown, however, that in a system employing such water-immiscible organic solvents, the l'ow volatility of these solvents makes their removal from the dyed aluminum, and their recovery for reuse, expensive and difficult. Nevertheless, the complete removal of the dye solvent from the work after dyeing and before sealing of the dyed anodized article is essential to insure successtul dyeing.
In accordance with the present invention, there is pr-ovided a rapid, economical, and continuous meth-od for dyeing anodized aluminum, which employs a novel multiple solvent system for removal or stripping of the dye solvent from the dyed anodized aluminum, utilizing for this purpose a second, or stripping solvent, which is miscible with the dye solvent, but which will not dissolve or attack the dye itself, and will leave the dye in place and intact on the anodized article. Thus, the dyeing method of the invention necessitates the use of organic dyestuls which are soluble in the dye solvent, but which are insoluble in the stripping solvent. The dyes employed in the practice of the invention Will generally be oil soluble or spirit soluble dyes, but may even include Water soluble dyes if the latter are capable of meeting the conditions of solubility in the dye solvent, and of ins-olubility in the stripping solvent.
There are employed as dye solvents, in accordance with the invention, organic, `water-immi'scible solvents, which may be either acyclic or cyclic, or mixtures of such solvents. Thus, there may be employed halogenated hydrocarbons, such as carbon tetrachloride and methylene chloride, polyhydroxy compounds such as diethylene glycol alkyl ethers, alkyl derivatives of aliphatic acid amides, such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, and the like, and dimethylsulfoxide. Examples of cyclic and aromatic organic sol- 3,440,111 Patented Apr. 22, 1969 vents include quinoline, benzyl alcohol, nitrobenzene and halogenated benzenes, such as the chlorinated benzenes, including for example, chlorobenzene, orthodichlorobenzene, paradichlorobenzene, tetrachlorobenzene, and the like. Preferably there is used as a dye solvent a mixture of chlorinated benzenes known commercially as Polychlorobenzene, which includes penta, tetra-, triand monochlorobenzene, as well as some oand p-dichlorobenzene.
As a dye solvent removal or stripping agent, in accordance with the invention, there is advantageously employed a fluorinated aliphatic hydrocarbon containing at least three iluorine atoms. A preferred group of such stripping solvents is that of the chlorinated and fluorinated aliphatic hydrocar-bons which contain at least three norine atoms, and which are volatile, nontoxic, and noninflammable. Examples of such stripping solvents include:
Monochlorotriuoromethane (Freon 13), CCl`F3,
BJP. l'l4.\6 F. l,l,Z-trichloro-1,2,2-trifluoroethane (Freon ll3),
OCl2FC'ClF2, B.P. 117.6" F. sym-dichlorotetrafluoroethane, CClFZCClFg, B.P. 38.4 F. 1,2-dichloro-l,`l,2,2tetralluoroethane (Freon `114),
BEP. 4.l F.
These fluorinated compounds are miscible with the types of dye solvents mentioned above.
It has been found that for successful dye solvent stripping, the fluorinated compound must contain at least three luorine atoms. lFewer than three fluorine atoms produce streaking elfects by attack of the stripping solvent on the dyes themselves, possibly owing to the presence of chlorine atoms in the molecule. Such streaking is produced, for example, by compounds such as trichlorom-onouoroethane and tetrachlorodilluoroethane, which contain only one or two uorine atoms. The presence of three or more fluorine atoms in the molecule is believed to suppress the solubilizing action of the chlorine atoms on the dyestuif molecule.
The oil soluble and spirit dyes which have the additional characteristic of being insoluble in the stripping agents, as explained previously, include both dyestuffs and dye intermediates which are members of the azo, anthraquinone, indigo, thioindigo, phthalocyanine classes of dyes. Speciic examples of such dyes include:
Red Violet PH Pigment Violet 19 (CJ. 46500) Prior to the application of the dye and dye solvent, the anodized article must be thoroughly washed to remove all traces of the anodizing electrolyte, and must be fully dried. This may be conveniently accomplished by Water rinsing, followed by removal of the Water by treatment of the wet anodized article with an organic solvent, such as a chlorinated aliphatic hydrocarbon solvent, which is capable of forming a constant boiling mixture or azeotrope with the water. Examples of such solvents include trichloroethylene, ethylene dichloride, propylene dichloride, and the like, trichloroethylene being preferred for this purpose. The trichloroethylene preferably contains a wetting agent or surfactant, and is applied to the anodized article at an elevated temperature, for example, at a temperature of about 180 to 250 F., for a period of about 30 to 50' seconds. The hot solvent extracts the water to form a constant boiling mixture having a boiling point (163 o 1&37" F.) lower than that of water or of trichloroethylene (187 F.), and is vaporized. The trichloroetylene-water vapor mixture is condensed, and the trichloroethylene is recovered and recycled to the drying operation.
The novel method of the invention for dyeing anodized aluminum therefore comprises the steps of (a) removing water from a wet anodized aluminum article by applying to the article an organic solvent capable of forming a constant boiling mixture with the water present, at an elevated temperature; (b) applying to the dry anodized aluminum surface a solution of a dyestuff in a water immiscible organic dye solvent to produce a color thereon; and (c) removing and recovering said dye solvent from the dyed but solvent wet article and drying said article by treating the article with an organic stripping solvent which is miscible with the dye solvent but which is not a solvent for the dye. The foregoing method may be operated continuously, with all solvents being continuously recovered and reused.
After removal of solvents and drying of the dyed articles, the colored anodized coating may be sealed by conventional sealing methods, including hot water, cobaltnickel acetate solution, chlorinated paraffin, alkali metal dichromates, and the like.
The practice of the invention will be more fully understood by reference to the accompanying drawing which illustrates a form of apparatus suitable for performing the method, but which is not to be regarded as limiting.
In the drawing, there is shown schematically an arrangement of three components, of which 1 designates a unit for the drying of wet anodized aluminum articles with an organic solvent, with provision for recovery of the solvent. The unit comprises a divided tank 2 separated into two portions by partition 3, and provided at its upper end with condensers 4 and 5, and at its lower portion with heating coils 6 and 7. The water wet anodized aluminum part is placed in first section the water removal unit where it is contacted with hot (180- 190 F.) trichloroethylene containing a surfactant, either by immersion or curtain flowing for 30-50 seconds. The solution is vaporized and the vapor collects as liquid on the condensing coils and is caught in troughs 8 below the coils and Hows to water separator 9 where water is extracted and the trichloroethylene is returned to the drying solution. The water-free anodized article is then transferred to the second section 11 of the tank for about 30 seconds. This section contains hot liquid-vapor trichloroethylene, wherein the article is further cleaned and dried by the hot vapor, and any residual surfactant is removed.
The water-free, dry anodized article is then transferred to the dye application unit 12 where the article is contacted by a hot solution of dyestuff by owing, curtain coating or spraying. The dye application unit, in the form shown, is provided with a pump 13, heating means |14, and spray circulation system 15. The bulk of solvent may be recovered by a suitable system, such as an alumina absorption column, not shown.
The solvent-wet, dyed anodized article is then transferred to a solvent drying-recovery unit 16 where stripping of the dye solvent takes place. This is done by contacting the article for 30-40 seconds by a hot (110- 115 F.) solvent which has selective solubility or miscibility for the dye solvent and in which the dye is substantially insoluble. This unit is also provided with partition 17, and with heating coils 17 and A18, and condensers 19 and 20. The warm stripping solvent vapors remove the dye solvent and dry the article, while the two solvents are collected in the sump of the unit. The stripping solvent is distilled over at about -140 F. when it becomes enriched with dye solvent, and after distillation, the recovered dye solvent can be returned to the dye application unit. The solvent-free, dry, dyed anodized article is then ready for sealing by any conventional method.
The following example illustrates the performance of the method, but is not to be regarded as limiting:
Example A panel of aluminum alloy 1030 was cleaned, etched, and anodized for 60 minutes in 15% sulfuric acid at 70 F. at a current density of 12 amperes per sq. ft., and rinsed with water. The panel was dried with trichloroethylene containing a surfactant at F. for 40 seconds. The dry panel was dyed for 20 minutes in a solution of Golden Yellow LG dyestuff in orthodichlorobenzene at 70 C. in a concentration of 4 g. per liter. The panel was dried by treatment with trichloro triuoroethane at 100-115 F. for 30-40 seconds, to effect removal of residual orthodichlorobenzene. The article was then sealed in boiling water for 20 minutes. The sample was heated to 300 C. in an oven for 1 hour, cooled to room temperature, heated to 400 C. for 30 minutes, and cooled. It retained its original dyed shade and showed no heat fading.
What is claimed is:
1. Method for dyeing anodized aluminum comprising the steps of: (a) removing water from a wet anodized aluminum article by applying to the article an organic dehyrating solvent capable of forming a constant boiling mixture with the water present, at an elevated temperature; (b) applying to the dry anodized aluminum surface a solution of a dyestutf in a water-immiscible organic dye solvent to produce a color thereon; and (c) removing and recovering said dye solvent from the dyed but solvent-wet article and drying said article by treating the article with an organic stripping solvent which is miscible with the dye solvent but which is not a solvent for the dye.
2. The method of claim 1 which includes the further step of sealing the dyed anodized coating.
3. The method of claim -1 in which the dehydrating solvent is trichloroethylene.
4. The method of claim 1 in which the stripping solvent is a fluorinated aliphatic hydrocarbon containing at least three iluorine atoms.
5. The method of claim 1 in which thc dye solvent is a chlorinated benzene.
6. Method for dyeing anodized aluminum comprising the steps of (a) applying to a dry anodized aluminum surface a solution of a dyestutf in a water-immiscible organic dye solvent to produce a color thereon; and (b) removing and recovering said dye solvent from the dyed but solventwet aluminum and drying said aluminum by treating it with an organic stripping solvent which is miscible with the dye solvent but which is not a solvent for the dye.
7. In the method for dyeing anodized aluminum including applying to the dry anodized aluminum surface a solution of a dyestuff in a water-immiscible organic dye solvent to produce a color thereon, the improvement which comprises removing and recovering said dye solvent from the dyed but solvent-wet aluminum and drying said aluminum by treating it with an organic stripping solvent which is miscible with the dye solvent but which is not a solvent for the dye.
8. The method of claim 7 in which stripping solvent is a fluorinated aliphatic hydrocarbon containing at least three uorine atoms.
9. The method of claim t8 in which the stripping solvent is a fluorinated and chlorinated aliphatic hydrocarbon containing at least 3 fluorine atoms.
10. The method of claim 6 in which the dye is an oil soluble dye.
y11. The method of claim `6 in which the dye solvent is a chlorinated benzene.
6 12. The method of claim 6 in which the stripping sol- References Cited vent is a `iluorinated aliphatic hydrocarbon containing at UNITED STATES PATENTS least three fluorine atoms.
13. The method of claim 6 in which the stripping sol- 2975081 3/1961 Klrby et al 148-61 vent is a fluorinated and chlorinated aliphatic hydrOcar- 5 Dssaner 148-6'1 bon containing at least three :fluorine atoms. 5 Klrby et al 148-6'1 `14. The method of claim 6 in which the dye is sub- RALPH S. KENDALL Primary Examiner stantially insoluble in the stripping solvent.
1s. The method of claim ,a in which is included the US C1- X-R- further step of sealing the dyed anodized coating. 10 117-49, 62, 127; 204-35