DE2230618A1 - TREATMENT METHODS FOR ALUMINUM SURFACES - Google Patents

Description

Herne, 8000 Munich 23,

Freiligrathstrasse 19 r »· ι ι η lj η l. Eisenacher Strasse 17

P.O. Box 140 Dipl.-Ing. RH Bahr _{Pa,. Anw Betzler}

Pat. Herrmann-Yrentepchl DidI. - PhVS. Eduard ΒβΐΖίβΓ Telephone: 39 8011

Telephone: 51013 r * 39 8012

⁵¹⁰¹⁴ Dipl.-Ing. W. Herrmann-Trentepohl aew "

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Bahrpatente Herne PATENTANWÄLTE Babetzpat Munich

Telex 08 229 853 _{Te | ex} S ₂₁₅₃₆₀

~ t bank accounts:

Bayrische Vereinsbank Munich 952 Dresdner Bank AG Herne 7-520 Postscheckkonto Dortmund 558 68

Ref .: MO ^ 357 HO / M, please indicate in the answer

Please send a letter to:

Munich

Michael N. Marosi

Treatment process for aluminum surfaces

Chemically pure aluminum has little commercial use because its tensile strength is only around 50 kg /

cm lies. With small additions of iron, for example or silicon, however, the tensile strength can be doubled. Certain aluminum alloys have tensile strengths of up to about 7,000 kg / cm. Compared to pure aluminum, these materials also have a higher hardness and a better deformability. They are also easier to machine.

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Aluminum possesses a natural resistance to corrosion due to the fact that it is on its surface forms a thin layer of aluminum oxide. A freshly machined surface of metallic aluminum instantly oxidizes and is covered with a thin, transparent layer of aluminum oxide that covers the Protects aluminum surface against further oxidation and against further reactions. However, this protection works not against substances that can dissolve the oxide layer or break it open mechanically. However, this is natural oxide coating is neither sufficiently strong nor sufficiently impermeable to prevent corrosion to prevent more difficult conditions, for example with long-term exposure to air humidity, with brief exposure to sea water or salt air, or with frequent mechanical contact.

At present, their methods of applying Protective layers on aluminum materials or objects known, for example anodizing, in which it is an electrolytic process, through which a protective layer instead of the natural oxide layer is deposited on the aluminum surface. A similar process is the so-called alum-mulling ("alumiliting"), which is a reverse electrolyzing process. The known Processes have disadvantages. They are relatively expensive and pose a risk to the operating personnel with it because of the high voltages that are used and the fact that the Surfaces are subjected to ion bombardment.

The above-mentioned coatings produced by anodizing and aluminizing reduce quite considerably

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the electrical conductivity of aluminum. So ^ the value of aluminum as a material for conductors, such as antennas for high frequency purposes, decreases Find use. After electrolytic treatments, the aluminum outer skin becomes harder, which leads to disadvantages in some uses of the aluminum materials or objects.

The above-mentioned known methods are unsatisfactory in terms of the protective effect they bring with them. The standard test for corrosion resistance consists in spraying salt water onto the aluminum surface with a salinity of $ 5> a temperature of 55 C and a relative humidity of $ 95 to $ 100. The resistance of the treated aluminum is measured as The amount of time that elapses before the surface of the sprayed salt becomes dull, blotchy and later is eaten away. The resistance of the treated aluminum surface is usually measured in years, with a year corresponds to a period of 24 hours, during which salt is sprayed on without any visible signs of corrosion. Under these Conditions are the resistance of the aluminum surface coatings, which have been formed by the above-mentioned known methods, in one wide range from 5 years or less to Io years. Most of the known processes result in coatings, whose resilience is much lower than the maximum of Io years.

Commercially used aluminum materials and many usable aluminum alloys also form natural

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borrowed aluminum oxide layers. However, they succumb faster corrosion, possibly due to galvanic effects within the alloy or due to the fact that corrosive agents penetrate through cracks in the layer. It therefore exists a need for a protective layer that is more effective than the naturally formed aluminum oxide layer and which beautifies the appearance of the aluminum.

According to the invention, the natural oxide layer is used by a new treatment with others Materials to form a protective layer that is stronger and more resistant for long periods of time against the occurrence of further oxidation or against the destructive effect of corrosive agents. The coating according to the invention is also pleasant in appearance and gives the aluminum a white color that previously could only be achieved by painting the surface.

In the method according to the invention, the natural oxide that is on the surfaces of aluminum materials or objects is located, at least partially left on the surface and4 at least partially converted into an aluminum compound, which acts as an extremely thin film on both the underneath Aluminum, as well as the possibly existing layer of unconverted, natural Oxide covers and protects. The aluminum compound produced in this way according to the invention forms a non-porous, flat film that is not only resistant to the effects of corrosive agents, but also

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protects against mechanical abrasion to the right extent. aside from that this film gives the aluminum its aesthetically pleasing, white color.

The method according to the invention represents a chemical treatment method with several stages, of which some are relatively unimportant and are only listed for the sake of the invention and the overall aluminum treatment become easier to understand.

In the first stage of the process, the arbitrarily formed aluminum raw material, for example in the form of flattening or extruded, or the object made from the aluminum that is to be treated is immersed in a cleaning liquid or brought into contact with the cleaning liquid in some other way. This is to remove surface buildup of dirt, oil and grease. The cleaning liquid is preferably a weak solution of a non-ionic detergent, for example from 1/2 $ to 2o #, which carefully cleans the metal surface and carries away the foreign bodies due to its wetting effect and emulsion-forming effect foreign bodies deposited on the in the bath metal again .. the metal surface is then ready for the action of the chemicals by the inventive process on the adhering to the surface oxide film. the cleaning bath is preferably maintained at room temperature. However, it is also possible with up to 65 ⁰ C work to meet the needs of certain manufactured items.

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In the next stage of the process, the aluminum is immersed in a bath which is a solution of preferably 2 to 2o wt.% Sodium hydroxide, wherein the treatment duration is for example 1 to ό minutes. The temperature of the bath is between the ambient temperature and a temperature of up to 55 to Öo ° C. In this process step, the natural and cleaned surface layer of aluminum oxide is at least partially converted into sodium aluminate, which is freed from the surface of the aluminum in the process. If there are impurities in the oxide surface, as is usually the case, the aluminum surface is discolored in this process step, the metal surface usually being slightly etched.

In the next process step, the aluminum object is rinsed with cold water, inside a tank with a constant flow of clean water at ambient temperature is working. The rinse removes the sodium hydroxide and stops its action on the aluminum surface.

The aluminum object is then immersed in an acid-proof tank that has a 2 to 2o # Contains aqueous solution of a material, which is called Recobright-D for the purpose of a shorter term can be. The treatment lasts 2 to 10 minutes at room temperature. Recobright-D is made by that one in water 1 to 5.5 parts by weight Sodium dichromate, 2 to 6 parts by weight sodium fluoro acid and dissolves 10 to 20 parts by weight of sulfuric acid. This bath has a chemical effect on the oxidation products which were vacated in the bath of the second process stage. The product of the present chemical

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Reaction is removed from the aluminum objects and dissolved in the acid bath.

The aluminum item will then, as well as in the third stage, rinsed with cold water.

In the following and most important stage of the driving, the aluminum object is immersed in a bath, which is an aqueous solution of four soluble, normally represents solid chemical compounds. Each of the compounds is granulated or powdered Shape before. For more convenient handling and easier preparation of the bath, the connections combined into a set, dry physical mixture. The solution of this mixture should have a strength of about 3 to 25 wt. $, where a slight dependence on small changes in the setting of the dry mix that dissolved is present.

A strength of $ 3 to $ 25 is effective, however a strength of lo # preferred. The temperature of the The bath is preferably at room temperature. Since the solution of this bath has a slightly acidic character, the pH value being preferably 5.0 to 6.8, the tank for this bath is provided with an acid-resistant one Lining provided.

Since both the trackene mixture that is dissolved, as well as the aqueous solution of this mixture prior to reaction with the surface layer of the aluminum article consists of more than one chemical compound,

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and. Since you cannot assign a single chemical name to it, this dry mixture is named in the following after its sales name, namely Recobright-2o. Recobright-2o is a newly set composition of four separate chemical compounds. Es.sind this: amidosulfonic acid with Io to Oo wt ^ a 'j'% or more carboxylic groups per molecule containing carboxylic acid having from Io to 60 wt ^, a potassium salt of a halo acid having 2 to j5o weight and an anionic detergent. 0.. , 5 to 15 wt. The detergent is preferably diluted with 60% of a suitable inert material. The Recobright-2o solution is a fast-acting, highly ionized bath. The wetting agent in the bath of this process step increases the wetting effect of the water on the metal surface, so that the three other chemicals act more quickly on the aluminum and its surface oxide or another coating can. The detergent is highly ionized and helps to keep the bath at the desired pH.

After staying in the bath for 5 to 50 minutes, off Recobright-2o at room temperature is an extremely thin, almost monomolecular film of a complex salt on the surface of the aluminum. The layer that is formed during the reaction as part of this process step consists of a material which was sprayed for 250 hours with Able to withstand salt. This means that the useful life is more than 10 years. Even the material has very good reflective properties which are of great use when the aluminum is used in heating devices or lighting devices will. Furthermore, the material gives the surface

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of the aluminum object on which it has been formed is a beautiful white color that adds to the charm of the Metal increased. The coating also has a high level of durability.

The surface coating that is produced in the reaction during this process step represents a chemical compound of a complex nature, which so far has neither occurred in nature nor produced in the laboratory could be. This compound has never been used as a coating for aluminum, either alone, still together with aluminum oxide.

After being removed from the tank containing the Recobright-2o solution, the aluminum becomes a cold water rinse as described in connection with the third process step.

Then the aluminum object with the treated surface is immersed in a resin solution, for example consists of the well-known melamine-formaldehyde resin. The resin is a copolymerized acrylic resin, which contains mono-, homo- and terpolymers as well as some additives, such as methacrylates, fillers and anti-sticking agents such as high molecular weight alcohols and ethers. Such a resin will from the company Röhm & Haas under the name QR 48 ^ manufactured. The resin solution has a pH of about 9, and the immersion time of the aluminum object takes about 2 to J5 minutes.

The aluminum article is then placed in an oven

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Subjected to heat treatment at a temperature of about 12o C to 150 C for a period of time of about Io minutes. For best results, it is preferable to choose a temperature of about 155 ° C. The heat treatment leads to rapid drying of the coated metal object.

The four chemical compound Recobright-20 mixture mentioned above can be used in can be generated satisfactorily in the following setting, but without this information being a Should represent limitation:

percent

Amidosulfonic acid 4o strength of the

Citric acid 44 solution

Potassium bifluoride 14

Sodium alkyl aryl

Sulphonate 4o $ active 2

If a lower percentage is chosen for one or more of these ingredients in the mixture, the mix must be stronger to compensate for this. Will be the percentage of any of these ingredients is increased considerably, the mixture is still effective, but the excess is that particular Component is not required for the reaction and therefore remains behind. This only has the effect that the cost of treatment per aluminum batch increases.

If in the Recobright-2o mix or in the Recobright-D mix one of the materials with a considerable

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borrowed a greater percentage than the invention claims is represented, the inventive method still carry out, provided that the excess amount behaves as inert to the reactions taking place.

The expression used here ;. "Aluminum object" includes all metal raw parts or processed metal parts in which the alloy component aluminum predominates. This term also includes pure aluminum, commercial aluminum, aluminum objects, which are coated with aluminum oxide or other oxidation products, and finally aluminum alloys, which are subject to corrosion.

In summary, the invention thus relates to a method for producing a white coating on the Surface of aluminum objects as protection against corrosive effects and as a decorative coating. The method comprises treating the aluminum objects with a mixture of amidosulfonic acid, a carboxylic acid having J5 or more carbon groups per molecule, a potassium salt of a halogen acid and an anionic detergent.

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Claims (1)

Claims 1. Process for coating aluminum objects with a coating of adhesive material, characterized in that aluminum oxide is the chemical Exposure to an adjusted aqueous solution of sulfamic acid, a carboxylic acid with three or more Carbon groups per molecule, a potassium salt of a halogen acid and an anionic detergent. 2. The method according to claim 1, characterized in that the constituents are present in the following weight ratios: amidosulfonic acid Io up to 60 %; Carboxylic acid 10 to 60 %, potassium salt of a halogen acid 2 to 50%, anionic detergent 0.5 j5. Method according to Claim 2, characterized in that the aluminum object is initially cleaned of foreign substances adhering to it, that the aluminum oxide is then released and detached from the aluminum object by treatment, and that the released oxides are then treated with an adjusted solution , from water, from amidosulfonic acid with Io to 6o wt. %, from a carboxylic acid containing 3 or more carbon groups per molecule, with Io to 6o wt. ^, from a potassium salt of a halogen acid with 2 to Jo wt. % and from an anionic detergent with 0.5 to 15 wt. # consists, this solution - 12 209884/1202 reacts with the released oxides to form a thin coating on the surface of the aluminum object to deposit from a material resulting from the reaction. 4. The method according to claim j5, characterized geke η η - ζ eich η et that sodium hydroxide is used to release the oxides. 5. The method according to claim 5 * characterized in that the treatment material is a dry mixture dissolved in water, which consists of the following ingredients in approximately the following composition: amidosulfonic acid 4o #, citric acid 44 $, potassium bifluoride 14 $ and sodium Alkyl aryl sulfonate 2.%. 6. The method according to claim 4, characterized in that the solution of the mixture approximately Is $ 3. 7. The method according to claim 6, characterized in that the object is immersed in a resin and a \
is subjected. immersed and a heat treatment at at least 12o C 8. A method for coating with an aluminum oxide position, _r provided aluminum objects with a corrosion-resistant film, characterized in that the aluminum object is cleaned with an anionic wetting agent; that it is immersed in a sodium hydroxide; that it is rinsed off with water; that it is immersed in an aqueous solution of sodium dichromate, - 15 2098Ö4 / 1202 Sodium hydrofluoric acid and sulfuric acid are immersed in an effective ratio of approximately 1.7: 2: 1ο; that it is rinsed with cold water; that it contains in an aqueous solution of sulfamic acid of Io to 6o wt. ^, of a carboxylic acid) or more Caroongruppen per molecule, from Io to όο wt.%, of a potassium salt of a halogen acid of 2 to ^ o wt.% and immersing of an anionic detergent of 0.5 to 15 wt.%; that it is immersed in a resin; and that it is heat-treated at a temperature of at least 120 ⁰ C. 9. Discontinued material for the treatment of aluminum objects which have a thin coating of aluminum oxidation products, characterized in that the material consists of a dry mixture of the following chemical compounds: amidosulfonic acid Io to όο wt. ^; a carboxylic acid containing three or more carbon groups per molecule, Io to 6o wt. ^; a potassium salt of a halogen acid 2 to 5 % by weight , and an anionic detergent 0.5 to 15% by weight . 10. Aluminum article, in which the main component of the body is aluminum and in which the body is coated on its outer surfaces with an extremely thin film, characterized in that the main component of this film consists of a material which results from the chemical reaction between Aluminum oxide and an adjusted aqueous solution has formed, this aqueous solution consisting of: amidosulfonic acid with Io to Go wt. #; a carboxylic acid containing three or more carbon groups per molecule with Io to Oo wt %; a potassium salt of a halogen acid with 2 to ~ j> o wt. ^; and an anionic detergent with 0.5 to 15 wt. ^. 2098ÖA / 1202