DE1621080A1 - Process for the production of directly colored oxide coatings on aluminum and on aluminum alloys by means of anodic oxidation - Google Patents

Description

A process for Herstellunj # of stained directly Oxydüberzügen on aluminum and on aluminum alloys by anodic Oxydätion The invention relates to a process for Hers: tellung of di.rektgefärbten "Oxydüberzügen mannigfaltiger.FarbtUne -on aluminum and on aluminum alloys by anodic-Oxydation.- - The Decorative and corrosion-resistant surface treatment of semi-finished products or structural elements, based on aluminum, used for architectural and other outdoor purposes., is generally carried out by means of anodic oxidation, the aluminum or its alloys are anodically oxidized in a sulfuric acid bath by means of direct current or alternating current, then the colorless oxide coatings are subsequently by immersion or in some other way with inorganic pigments or organic dyes-treated. The organic dyes or inorganic.pigments, however, have only a low weather resistance and lightfastness, and the color that can be achieved depends to a considerable extent on the density and porosity of the oxide layer previously developed on the aluminum surface. Uniform, stain-free coloring can only be achieved in a technically complicated manner and at great expense.

Recently, the preparation of directly colored C> OxydUberzügen came to the fore, because the resistors> - "ndsfähigkei -. T of such coatings compared to the subsequently treated with dyes anodically oxidized Aluminiumüberzügen.besser The preparation of directly stained Oxydüberzügen is-among others by British Patent Nos. 962048 and 973_39.1, and by American Patent Nos. 30_31_387. The common feature of these processes is that the anodic treatment is carried out at a temperature between 20 and 55 ° C. in such an electrolyte bath which, in addition to a little sulfuric acid, contains a higher concentration of an aromatic sulfonic acid, for example sulfophthalic acid or sulfosalicylic acid. The baths used can also contain other additives, such as B. contain additives preventing the decomposition of aromatic sulfonic acids. Instead of sulfuric acid, metal sulphates which are completely or partially soluble in water are used in some cases. The a.nodic treatment is carried out - at least in the presence of sulfate by means of a direct current set between the voltage limits of 50 to 120 volts. Different color tones belong to the different voltage values.-No alternating current can be used instead of direct current. The duration of the anodic treatment varies between 20 and 65 minutes. The directly colored oxide coatings produced by the known processes have the disadvantage that coatings of gray-black or blackish-brown color are mainly obtained on the commercially available aluminum types Alloy metals of aluminum - manganese, zinc, magnesium, chromium or silicon are used. - Nickel Based on the known processes, it can be established that any warmer color tones are not produced on the surface of commercially available aluminum by anodic oxidation treatment using direct current or alternating current can...

The purpose of the invention is the production of permanent color and lightfast and.also sufficiently resistant to the effects of atmospheric corrosion Oxide coatings-harmonious color effect on-the surface of metallic-hand-normally Aluminum, through which the current architectural needs for structural materials can be satisfied.

The procedural invention ren for Prod-RECOVERY of directly stained AluminiumoxydüberzUg s can be characterized net gekennzeich that the surface of aluminum or its Legierungep #n absence of sulfuric acid or sulfate compounds in the presence of 1-8% formic acid und'1-8% Sulfosallcylsäure, further is anodically oxidized by 0.5-2.0 % hydroquinone. The production of warm-toned oxide coatings of any color in the above-mentioned color range by means of direct or alternating currents, between the voltage limits of 40 to 100 volts, at a constant cell voltage, depending on the voltage values used, can be ensured according to the invention.

By means of the method according to the invention, colorfast and lightfast coatings can be produced both by means of direct current and by means of alternating current within 1 30 minutes, 1-30 micrometers thick. The hardness of the layer is, depending on the quality of the base metal, HV 200-450 kp / m 2 , while its mechanical properties satisfy the practical requirements. The subsequent cold working (moderate deep drawing, bending) of the aluminum plates coated with thinner layers can be carried out without damaging the tension. The oxide coatings produced by means of direct current or alternating current have different porosities.

T he means of direct current coatings obtained are practically free from pores, while the means of alternating current produced coatings show a low porosity. To p - orenabdichtenden after-treatment of coatings-a impregnation with colorless Läcklösungen recommended.

The types of execution of the method according to the invention generally depend on the different values of the cell voltage used. The cell voltage was in a - 10 vol per -t corresponding #Abstufung set. Each voltage level corresponds to an easily reproducible oxide coating of different colors or different hues. In the case of the anodic treatment carried out with direct current, the current density in the first 2 minutes is a value of at most 10-15, A / dm then it decreases - in parallel - with the progress of the oxidation 2 - first to 4-5 a / dm, then later-stufenweise.zu a value below 1 a / dm 2. the Verminderung.der current density up to-a minimum value at the same time also shows the end of the #-anodic treatment, because in the riiedrigen values of the current density only a- practically insignificant further increase in thickness takes place. Experience has shown that a current control is not necessary during the anodic treatment.

From an application point of view, an important advantage of the process according to the invention is that alternating current can also be used in the odic treatment. In-the case of the alternating current, the oxidation is conducted at a the DC similar abgestuften- cell voltage, performed until the - current density -.- / dm decreases after reaching a maximum Anfangswertes-- up to the limits 2 A 5-7. The oxide layer obtained from an oxidation carried out with alternating current generally has a warmer hue (golden-yellow-golden-brown, bronze-colored-red-t-brown # thin-k-el-brown-brownish - so, black). According to the method according to the invention, by varying the quality of the base metal, the type 5 of the oxidizing current, the temperature of the electrolysis bath and the cell voltage, and also the duration of the oxidation, a much wider selection of parbenes can be achieved than with any other known method, The variety of the color scale is also increased by the fact that under given reaction conditions in a lower concentration electrolyte bath, coatings of a gray hue are formed, while in more concentrated solutions mostly coatings of a reddish-brown hue are formed.

The advantages of the process according to the invention are summarized below: 1. In the usual anodic oxidation devices, directly colored oxide coatings in various shades of parquet can be produced extremely economically by means of reagents, the necessary reagent costs and the power requirement do not exceed the usual expenditure.

2. The technological time required to develop the coating can be reduced to about half or even lower. This is the The capacity of the anodizing equipment can be increased considerably.

Productivity and economy are also increased by the fact that - as a result of the abolition of conventional subsequent coloring " three partial treatments of the technological'Dehandlungsgäh ge are superfluous.

4. For anodic oxidation, alternating current can be used in the same device as well as direct current are used.

5. In the case of: kbige color shades of the structural material aluminum can be produced on commercially available aluminum, i. H. the anodic treatment does not require specially heat treated or alloyed aluminum structural materials. 6. "The stability of the bath according to the invention in relation to that of the dye baths known for similar purposes - is significantly increased by the addition of stabilizer, the solution shows no reddish discoloration or decomposition". 7. Any desired color effects can be achieved by changing the voltage scale .

The invention is illustrated in more detail by means of the following examples.

Example * 1 The work piece to be subjected to anodic oxidation is degreased in a known manner at a temperature of 80-90 ° C. in a 10-15 % sodium hydroxide solution or in a solution which contains a surface-active agent, and the oxide layer is removed , rinsed off with water, then any caustic residues are neutralized with a 1: 1 diluted sal, detergent acid solution. After repeated rinsing with water, the direct coloring anodic oxidation is carried out at room temperature.

Upon completion of the on - odic oxidation that is, rbeitsstUck with water abundantly washed-dannmöglichst with a warm air flow -. Dried. The covering or pore-sealing post-treatment of objects that are to be exposed to the weather in the outside area is carried out by means of saturation with a colorless synthetic resin lacquer solution and subsequent drying. This lacquer coating can be dispensed with for objects to be used indoors.

--Aluminium before! A purity of 99.5 % 99.5% is anodically oxidized with a direct current in an electrolyte bath containing 3 % formic acid, 5% sulfosalicylic acid and 0.5% hydroquinone. The cell voltage is set to a "value between 50 and 80 volts. When developing thinner layers (from 10 to 15 micrometers), the duration of the oxidizing treatment is 10-15 minutes, while for thicker layers (from 15 to 30 micrometers) 15 30 minutes are necessary. Depending on the cell tension used, the oxide coating formed has the following colors: 50 V 6o v 70 V 8o v golden yellow brass colored grayish bronze colored oil brown CD If the anodic treatment is carried out under the same conditions, but only for a shorter period (1 - 2 minutes), the developed 01-lyd coatings will - depending on the cell voltage - have the following colors: 50 - 6o v 70 - 8o v iridescent pale gold color pale gold color The previous experiment is repeated with the change that the electrolyte bath contains only 3 - 5% formic acid. After switching on the current, a colorless thin oxide layer develops on the surface of the base metal when the current density changes. Further anodic treatment reveals local corrosion spots and brown discoloration in places on the base metal. Apart from these brown oxide spots on the base metal, no direct colored oxide coating forms after a long period of treatment. During this experiment, the voltage of the direct current was varied between 10 and 90 volts. No significant differences were observed in the various - cell voltages, - electrical breakdowns were observed at the edges of the work piece at the peaks - oTers of the cell voltage - see.

The experiment naäh Example 1 was repeated with- that change daij one, 3 - 5 Sulfosalicy1säure containing electrolyte without the addition of formic acid and hydroquinone was formed .-- In application of a direct current of 90 V 10-- voltage at room temperature to The aluminum surface shortly after switching on the current a thin, compact, colorless oxide layer, the so-called barrier layer. As a result of the barrier effect of this layer, the current density quickly reached a minimum value (0, 1 - 0.2 A / dm 2, with the formation of oxides practically not taking place.

., _'- the 3-iente.dabei an aqueous solution - - containing hydroquinone-5 af2 Sulfosalicy1säurä und.0 ..- 5% Der7Versu.äh of Example 1 was repeated, al s electrolyte d. When using a "direct current of 10 90 V voltage at room temperature" - shortly after switching on - the current developed similarly to the previous experiment, a barrier layer of the oxide "and the current level quickly settled down to a minimum value. After the development of the colorless barrier layer, no further oxide formation took place. - In the previous experiment, the hydroquinone does not take part in the conduction of the current, it serves as a stabilizer of the bath, bath solutions without hydroquinone turn brownish-red after a short use In the presence of hydroquinone, the oxidizing electrolyte retains its original pale yellow color even after a long period of operation, and no decomposition products which interfere with anodic oxidation are formed in the solution.

Example 2 The procedure is as in Example 1, but with the difference that the anodic treatment is carried out with alternating current at a cell voltage between −50 and 80 V. The duration of the anodic treatment is thinner in the development layers 10 - 15 minutes, with thicker layers 15 - _30 minutes.

The color of the formed oxide coating is, depending on the cell voltage, as follows: 50 V 6o v 70 V 8o v golden yellow golden brown bronze red brownish black The previous experiment is repeated with the difference that the duration of the anodic treatment is limited to 1-2 minutes. The oxide coating formed has the following colors: 50 - 6o v 70 8o v pale gold with a red tinge pale antique gold The request according to Example 2 is repeated, but an aqueous solution containing 3 - 55 % formic acid is used as the electrolyte bath. When using alternating current between the cell voltage values of 10 to 120 V, an is formed at room temperature in an extremely short time after switching on the current colorless oxide barrier layer on the aluminum surface. As a result of the blocking effect, the current density decreases rapidly and the further development of the oxide layer does not occur. Similar experiences resulted - also when the previous experiment with alternating current - was repeated in the absence of formic acid in an electrolyte bath, the -3-5 %. Sulphosalicylic acid or - _ 3 - 5 % -sulphosalicylic acid and 0.5 % hydroquinone contained.-Example _3 An aluminum alloy AlMg, 4- or A1M9 5 was in a solution containing formic acid " 5% sulfos.alicylic acid and 0, hydroquinone mixture contained 5%, subjected to anodic treatment. the cell voltage was varied between the limits from- 40 to 80 V according to the desired shade. for DC # is a treatment period of 10 15 minutes, however, with alternating current, a duration of 10 - Applied for 30 minutes.

The oxide coating formed showed the following colors, depending on the cell voltage or the use of direct current or alternating current: # G 1 calibrated ro m 4o v 50 V # 6o V 70 V 8o v light medium #dark coffee brown # -Mat4 dark brown .W echs e.1 electricity 50 V - 6o v 70. V 8o v antique gold light bronze red brown chocolate brown Example 4_ An aluminum alloy of quality * AlNgSi 0.5 AlMgSi 1 or AlMgSi 2 is subjected to an anodic treatment in an electrolyte bath identical to that of Example 1 by means of direct current or alternating current according to the color to be achieved between the cell voltage limits of 50 to -80 V. The duration of treatment is in development of thinner layers 10 to 15 minutes while with thicker layers 15 - 30 minutes is necessary. The color of the formed oxide coating was, depending on the applied cell voltage or

from the use of a direct current or alternating current, as follows: G 1 calibrate current 50 V 6o v 70 V 80 V .light dark dark gray dark olive green "Khaki f ArbIG Alternating current 50 V 6o v 70 V 80 V golden brown bronze colored tobacco brown chocolate brown EXAMPLE 5 An aluminum alloy of AlCuM9 quality was produced in an electrolyte bath of the same composition as in Example 1 by means of a direct current or alternating current which, according to the desired color tones, results in cell voltages between 60 and 50% "-this anodic treatment was subjected -eingestell t. The Behändlunäsdauer was 10-- 15 minutes.

Depending on the use of a direct current or alternating current or of the cell voltage used, the oxide coating formed had the following color tones: e- first r- om 6o v 70 V 80 V golden yellow grayish brown dark * leaf # girau # W ech s e 1 stream 60 V 70 V dark dark milk-coffee-brown- '

Claims (2)

P at entans p r U che 1. Ve'rfahren for the preparation of directly stained oxydüber # coatings on aluminum and on aluminum alloys by anodic oxidation. characterized g e k ennzeichnet that the anodic oxidation in 1 - 8% formic acid and 1 8% sulfosalicylic acid, furthermore 0,5 - 2,0% of hydroquinone is conducted containing bath. 2. The method, k according to claim 1, characterized e g s nz eichnet that the anodic oxidation is carried out within the .Spannungsgrenzen-40 and 100 volts. -3. Verfahren.nach claims 1 and 2, characterized ek ennzeich g, net direct current that is applied to the anodic oxidation. 4. The method according to claims 1 and 2, characterized g e k ennzeichnet that in the anodic 0 "lydation, AC is applied. 5. The method according to claim 1, characterized ennzeichnet g e k that the duration of the anodic oxidation to a period of 1 - 30 mins 6. A method according to claim 1, characterized k g e is -eingestellt et ennzeichn that the anodic oxidation is carried out at room temperature..