DK144481B - PROCEDURE AND COLOR ELECTROLYT FOR COLORING THE PRIOR BY ANODISATION PROTECTED PROTECTION OF ALUMINUM OR ALUMINUM ALLOYS - Google Patents

Description

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(19) DENMARK

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DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 1529/71 (51) int.CI, 3 C 25 0 1 1/22 (22) Filing Day 51 · Mar. 1971 (24) Race day 51 · tnai * · 1971 (41) Aim. available 5 Oct 1971 (44) Submitted 1 5 · MST · 1 982 (86) International application number - (86) International launch date "(85) Transfer day ** (62) Stock application no."

(30) Priority 2 Apr 1970, 4867/70, CH

(71) Applicant SWITZERLAND ALUMINUM AG, 3965 Chippis, CH.

(72) Inventor of Fritz Endtinger, CH: Walter Zweifel, CH: Fritz Schnee = Berger, CH.

(74) Associate Engineer Giersing & Stellinger.

(54) Method and color electrolyte for dyeing the front by annealing produced protective layers on aluminum or aluminum = alloys.

Several methods are known by which oxide layers produced by anodizing aluminum are stained by a further subsequent electrolytic treatment. Thereby, the essentially colorless anodizing layers are first used as electrodes and electrolyzed with alternating current in acidic solutions, which contain one or more of this treatment a dye-inducing qq of metal salts and possibly further additions. As model electrodes, as is well known in the art, such metals may also be used, inter alia, to form a coloring component of the color electrolyte.

Thus, e.g. salts of the elements Fe, Co, Ni, Mn, Cr, Bi, As,

Sb, Sn Ag, Cu, Au, Cd, Mo, Ti, Ca, Mg, V, Pb, Zn have been proposed as constituent parts of the color electrolytes and as anion-forming constituents in such electrolytes, the various substances and substance groups have been proposed. Thus, e.g. SO4, NO3, Cl, oxygenic acid of Se, Te, B, Cr, P as well as organic acids and acid anions such as acetates, tartrates, oxalates, citrates. Further cation-forming components of such electrolytes are known as NH4 +, amino and imino groups. As actual active color carriers, hitherto both metals and metal hydroxides, metal oxides and metal salts have been mentioned, all of which must be included in the oxide layers under these conditions. In these known methods, the bath composition is determined and produced, in particular by the choice of the dyeing metal salt, a type of color typical of the selected metal salt, and by the voltage-current conditions or the operating time of the current or both, the color depth is affected. Thus, one usually obtains only a moderately differentiable tint sequence with a once selected particular color electrolyte.

Thus, these known color methods have the disadvantage of each characteristic color tone selection requiring an independent color bath or in the color bath material changes or an exchange of the electrolyte.

A further disadvantage is the poor scattering ability of many electrolytes, which in practice works in such a way that dissimilar staining occurs without assistance. A poor dispersion of the electrolyte is manifested especially by indentations in the objects to be stained, in the form of light stains or on strips of large flat plates in the form of dark border zones. Usual countermeasures are e.g. cover means, auxiliary electrodes, suitable electrode arrangements, apertures, partly of metal and partly of plastic, as well as certain connection steps, e.g. shock at the beginning of dyeing. Such measures are known in the electroplating technique.

In the works which have led to the present invention, it was surprisingly found that it is possible from the large number of the metal salts known for the mentioned dyeing purposes as well as from the number of the electrolytic dyeing also available known anions to find and use at least two species of metal ions containing color electrolyte compositions with which one can safely and at a fairly wide range of the applicable concentrations be capable of pre-fabricated anodizing layers using only a single matter-defined color electrolyte to produce dyes in at least two tinted rows in one alloy. By two different tint rows, here is understood, in the context of the present invention, two such tint rows, both of which could not equally be produced color electrolytically in the pre-anodized layers using only one of the at least two staining metal salts to be used in all cases according to the present invention. invention.

Thus, the present invention consists in a method of dyeing the prior by anodizing, providing protective layers on aluminum and aluminum alloys in various tones by electrolytically treating the protective layer with alternating current using electrodes in acidic metal salt electrolytes containing at least two staining metal salts and the method of The invention is characterized by the use of a color electrolyte containing in solution salts of at least two metals which would separately produce tints which are different from the tints which would be produced by the other metal salts or salts, and can precipitates at least two different voltages and produces these different color tones as desired in one and the same color electrolyte by using variously high electrical voltages in the electrolytic treatment.

The color which, in the individual case of the process according to the invention, is to be produced in the anodizing layers and which is selectable from the two mutually different tint rows, is adjusted by adjusting the electric voltage electrolyte with one and the same two dyeing metal salts containing color electrolyte. flow conditions and the treatment duration appropriately.

However, not every combination of two dyeing metal salts in the color electrolyte has the property of being able to produce two different tint rows in pre-anodized layers.

Thus, e.g. In the prior art known Sn-containing color electrolytes which contain partly Ni or Co salts and partly also Sn salts, two different tint rows are not produced, but only one tint series. As a rule, however, a good result useful in the color electrolytic method of the present invention is a combination of two dyeing metal salts containing electrolyte if two dyeing metal salts are selected, each of which alone produces one different from the other metal salt. In addition, in most cases they employ a routine effort by one of ordinary skill in the art (theoretical considerations, test experiments) without particular difficulties to determine two parameters, anion species and pH, by which each of the two metal electrolytes of the color electrolyte can produce its color effect in the anodizing layers. The latter condition is usually easily met if each of the two metal salts is already alone color-electrolytically active in the same or at similar pH ranges. However, in many cases such suitable parameters can be determined and used also in the selection and addition of suitable anionic agents or of colored, complexing compounds or of special substances, including buffers which effect a favorable change in the formation of two colorfully different pigments. bath composition. In connection with the works which have led to the present invention, the following have been found hitherto, according to the nature of the different single staining of the metal salt in question, arranged exemplary metal salt color groups:

Tint Group Brownish Reddish Yellow Bluish

Ni salts Cu salts Ag salts Mo salts

Sn salts Cd salts

Co-salts

From this it can be seen that e.g. from Sn-salt and Cu-salt or from Ag-salt and Cu-salt or from Cd-salt and Sn-salt, as a rule, by the selection and use of anions suitable for the color electrolysis known in the art. buffers for pH and / or per se known additives favorable to the color electrolysis, e.g. NH4 salts can be assembled into a two different color tone series, for use in accordance with the present invention, suitable double metal salt electrolyte.

Furthermore, it is evident that double metal salt electrolytes, which as dyeing metal salts, contain only metal salts of one color tone series, ie e.g. only Sn and Co salts, or e.g. only Cd and Ag salts will be unsuitable color electrolytes for use in the process of the present invention.

The one metal ion species and its valence stage are essentially the cause of one, the other metal ion species of the other obtainable color tone series according to the invention. It is understood that it is therefore up to the person skilled in the art, in accordance with the prerequisites for the individual case, to select the concentration ratios of the two metal ion species, respectively, to ascertain these in test experiments, because if too much reduction of the concentration or activity of a metal ion species does not occur. two different tint rows are generated by one and the same color electrolyte.

The time program of switching on the voltage steps selected at any given time, the duration as such and the height of the final voltage affect the color tone of the two different color tones produced according to the invention and can easily be ascertained by the person skilled in the art by means of samples. The processing time also affects the depth of color in the method according to the invention, though substantially less the nature of the tint series produced, as this is also known for the known methods based on only a single tint series.

144481 5

Also the concentration of the additional additives, e.g. acids, determines the appearance of the two color ranges. However, according to the invention, it is essential in each case that with one and the same, at least two different dyeing metal salts containing electrolyte, when selecting the electrical conditions in one and the same alloy, at least two mutually different continuous tint rows may be produced.

It is understood, according to the foregoing considerations, that it is possible and in many cases convenient for the baths to be used in accordance with the invention and to provide at least two tinted rows, to use additional additives and methods known per se, e.g. for the purpose of stabilizing the valence or electrolyte pH of the metal ions.

It is up to the person skilled in the art to practice the staining method of the present invention in a manner known per se to select the most favorable model electrode material at all times, e.g. graphite, aluminum, metal carbides or e.g. a metal electrode of a metal which, as a compound, forms a component of the color electrolyte. It will also be possible for the person skilled in the art to select, depending on the nature of the metal salt combination, selectable and selected in the individual case according to the invention, the adjustment of the pH value and the temperature of the color electrolyte suitable for the particular color purpose and for the metal salt combination concerned. The person skilled in the art knows methods by means of the optima definitive test experiments in question or by theoretical considerations. In this case, especially in the case of the choice of combined metal salt electrolytes other than those mentioned below, for example, substantially other pH values than those mentioned below may also be considered.

Furthermore, it is the skill of the person skilled in the art to compensate for changes in composition or pH caused by appropriate substance additives and purification measures caused by consumption or time-dependent decomposition of an electrolyte of the kind to be used in accordance with the invention.

In principle, any anodizing layers produced beforehand can be stained by the method of the invention. However, it is preferred to apply the method to anodizing layers previously produced in baths which contain, as a major component, at least one acid of the sulfuric acid, chromic acid or sulfamic acid group.

The invention further relates to a color electrolyte suitable for use in the process of the invention, which contains at least two coloring metal salts and which satisfies the general requirements stated above. The color electrode of the invention is characterized in that it contains at least two species of differently colored metal ions from each of the groups consisting of 1) Ni, Sn, Co, Mn, 2) Cu, 3) Ag, Cd and 4) Mo and as anionic acid at least one acid or one salt, preferably at least two acids or two salts of the group consisting of citric, tartaric, maleic, succinic, fumaric, adipic, acetic, lactic, malonic, phthalic, sulfuric, selenic, phosphoric and boric acids , formic acid, sulfamic acid, sulfosalicylic acid, sulphanilic acid and phenolic sulfonic acid.

An example is given below of a copper and silver ion-containing electrolyte composition and of the two tinted rows obtainable according to the invention.

Example 1

Material to be stained: AlMg 1.5 plate, anodized in a sulfuric acid electrolyte.

In a color electrolyte containing 5 g / l CuSO4.5H2O 0.5 g / l AgN03 10 g / l concentrated H2SO4 and having a pH of 1.2, the two tinted rows of yellow (derived from silver ions) and copper red (derived from from Cu ions) under the following voltage and time conditions:

Color Tone In AC Voltage Color Time

Volt min.

yellow light yellow 8 1 medium yellow 8 5 dark yellow 8 10

Tint series II copper red light brown 14 1 medium brown 14 2.5 dark brown 14 10

With this Cu-Ag electrolyte, the sulfuric acid can be completely or partially replaced by a number of other acids, e.g. tartaric, oxalic, succinic, phthalic, sulfamic, sulfosalicylic and citric.

A color tint other than that set forth in Example 1, as explained in the following Example 2, may be obtained by a color electrolyte which, in addition to at least Cu ions, also contains Sn ions and at least one acid or an acid. acid salt from the group consisting of citric acid, tartaric acid, malonic acid, phthalic acid, and at least one additional acid or an acid salt from the group consisting of sulfuric acid, selenic acid, phosphoric acid, boron fluorohydric acid, formic acid, sulfamic acid, sulfosalicylic acid, sulfanilic acid and phenolic sulfonic acid.

Such a color electrolyte can e.g. contain 0.5 - 100 g / l Sn-II sulphate 0.5 - 70 g / l CuSO 4 .5H 2 O 0.5 - 100 g / l citric acid 0.5 - 100 g / l concentrated sulfuric acid.

A color electrolyte of this type, which is particularly well-chosen for producing the tinted rows of Example 2, contains Sn-II sulfate 5-20 g / l, preferably 13-17 g / l.

Cu-II sulphate (CuSO4.5H2O) 5-10 g / l citric acid 5-20 g / l, preferably 8-12 g / l concentrated sulfuric acid 5-20 g / l, preferably 8-12 g / l.

It has been found that in this example of bath composition instead of citric acid or the other organic acids mentioned above, any other organic acids with good results in connection with the invention cannot be used. Thus, e.g. in the example just described of an electrolyte composition of the following organic polybasic acids as a substitute for citric acid by otherwise the same measures according to the invention no staining or only a single tint sequence: malic acid, formic acid. The formic acid cannot always consistently represent an acid of the first group of acids.

Also not substituted for the acids listed above as a constituent of an Sn-containing electrolyte type of the acid group sulfuric acid, selenic acid, phosphoric acid, etc. any inorganic acids can be used with good results. Thus, e.g. the following inorganic acids at otherwise the same bath composition of this type and under the same conditions of the invention either no staining or only a single tint sequence: hydrofluoric acid, nitric acid, chromic acid.

Example 2

Pre-anodizing to produce the layer, which was stained here:

Al plate 300 x 600 x 1 mm of the alloy AlMg 1.5 sulfuric acid 165 g / 1, temperature 18 ± 1 ° C current density 1.5 Amp / dm2, voltage 16-18 V direct rinse in water before dyeing, model electrode: lead .

8 U4481

Coloring in the following two different color tones: In bronze-beige tones over black-brown to black, II reddish-beige tones over wine-red-brown to black, whereby the red character when viewed at a gloss angle appears stronger. The color electrolyte contains: 15 g / l Sn-II sulphate 7.5 g / l CuSO4.5H 2 O 10 g / l citric acid 10 g / l concentrated sulfuric acid.

ρΗ value approx. 1.3 bath temperature 20 ° C

Model electrodes: 5 mm diameter graphite rods.

As shown in the following table, with this color electrolyte, at the lower voltages, a reddish tint sequence is produced, but at higher voltages a beige tint sequence.

Color AC voltage Processing time Current density

Amp / dm 2

Volt min. beginning. slutn.

Color tones I

bronze beige 14 1 1.5 0.25 black brown 16 1.5 1.5 0.3 black 6 1 + 8 temporarily 0.5 in total + 10 after the other 0.5 10.5 1.5 0.3 + 12 another 0.5 min.

+ uj 8

Color Tone Series II

reddish-beige 8 5 1.5 0.3 burgundy-brown 10 8 1.5 0.3 black 12 15 1.5 0.3

The good dispersibility of this color electrolysis is shown in the following example. Example 3

A U-profile of the AlMgSi 0.5 alloy, 80 mm deep, 20 mm wide on the inside, was pretreated in the manner described in Example 2 above. The U-profile was then colored in the same electrolyte as in Example 2, with a 14 Volt AC voltage applied for 5 minutes. The profile was thus colored uniformly dark brown, also in the recess. This shows the good spreading ability.

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The facts and general guidelines given by the present invention that it is possible to produce not only one color tone series, but two mutually different color tone rows in the anodizing layers, in one and the same two different dyeing metal salts containing color electrolyte. importance for the practical industrial dye electrolysis, since using a single dye electrolyte, optional dyes can be produced in at least two different tints, which has so far required more dye electrolytes or at least the replacement of the dye electrolyte. The dyeing method according to the invention colors advantageously with good spreading ability, i.e. that the stains produced according to the invention are uniform, well reproducible and to a large extent independent of the shape of the subject to be stained and its arrangement with respect to the model electrodes.