DE718317C - Process for the production of corrosion-resistant coatings on metals - Google Patents

Description

GERMAN EMPIRE

ISSUED AH

MARCH 9, 1942

REICH PATENT OFFICE

PATENT LETTERING

CLASS 48d GROUP 4 oi

M 146502 VIJ48d

have been named as inventors.

Patented in the German Reich by ig. November 1939, when the patent was granted on February 19, 1942

is used.

The usual coating processes using phosphoric acid and chromic acid or their salts initially form a phosphate layer in a phosphate solution, which is then treated in a chromate solution.

There is also known a method which is one of phosphoric acid and chromate Allow the solution to dry on the surface to be protected. These solutions are supposed to be constructed so that no etching of the surface to be treated can occur, rather only a crust of the salts in the solution dries up on the surface (American patent 2030601). There The various solutions mentioned are fairly concentrated, preparing to dry up same difficulties. In many cases it is only possible at high temperatures, while drying at Room temperature due to the hygroscopicity of the salts used, drying is incomplete takes place and the remaining moisture residues then form foci from which rust can occur.

It has now been found that these disadvantages can be avoided and layers are obtained that form an excellent adhesive base for paints if you have solutions on the Metal surface, especially on iron and steel, lets dry the phosphoric acid and chromic acid in such proportions that these solutions are corrosive.

In the case of such solutions, because of their aggressiveness, working with less Concentration possible. By the same token, the layer is well trained

much less dependent on the pre-cleaning, since the etching means the pre-treatment, corrected if necessary. The specified treatment solution also allows greater freedom in the application of the Pre-cleaning conditions too, without thereby causing the formation of disruptive large Phosphate crystals in the coating must be expected. The lower concentrations the solutions also allow drying at room temperature, so that this process can also be used for large, stationary structures, for example bridges, can be used.

In the case of the solutions used in the present process, this is used for rust protection required phosphate in the form of a phosphoric acid and the chromic acid either as such or as an alkali chromate or Dichromate applied, because the addition of one of these gives in the presence of Phosphoric acid chromic acid.

Whether or not the solution etches the metal surface depends on both the concentration of phosphoric acid and hexavalent chromium as well as the quantitative ratio of these two from each other.

It is known that chromic acid is, within certain limits, a marked obstacle Has an effect on the attack of phosphoric acid on iron surfaces. Since etching is to occur, certain must Conditions of the solution can be selected. For example, if a concentration of orthophosphoric acid of 0.5% is applied, a ratio of chromic acid to phosphoric acid such as 0.35: ι no etching of the metal cause. Therefore, the invention cannot be achieved. However when you get the ratio lowered to 0.25: 1, a noticeable reaction with the metal occurs, the a protective layer of iron phosphate, trivalent chromium and possibly about hexavalent chromium Chromium that has not been reduced forms. Any ratio of 0.25: 1 or therefore, less will cause etching and the formation of the desired reaction products.

The following may be mentioned as a further example: At a concentration of orthophosphoric acid of 4% prevents a ratio of chromic acid to phosphoric acid such as 0.25: 1 the etching, while a ratio of 0.15: ι occur the desired process leaves.

Here, etching is understood to mean visible etching. The ratio of phosphoric acid to chromic acid should be adjusted so that a visible etching on the surface is achieved.

When carrying out the process, the metal to be treated is first through a suitable agent cleaned. Procedures such as wiping with a solvent or Vapor degreasing is usually used on small objects or wherever only a limited amount is enforced. Alkali cleaning is mostly applied in Process steps involving automobile parts or sheet metal or similar large objects are to be treated. In these cases "cleaning" is followed by a water rinse to remove the alkali.

In the case of large objects, such as structural parts of buildings, fat is usually required in addition to a significant amount of loose filament and rust will be removed. After cleaning, the metal is for that of the invention Procedure ready.

If there is residual grease or oil on the surfaces, it can be difficult be to get even wetting and therefore it is going to get bad results too avoid, usually advisable, adding a wetting agent to the treatment solution. There is a wide variety of such materials that are suitable for this purpose. Sodium Lauryl Sulphate, known commercially as Gardinol or Duponol (trademarks) is, is very effective, as is the sodium salts of laurylarylsulfonic acids, for example Sodium lauryl benzene sulfonate and some of the free sulfonic acids, one of which is Nuvonacco NN (trademark) is known.

In cases in which the content of chromic acid is not so high that it causes disruptive reactions the use of alcohol is permitted. Tertiary butyl alcohol is one of the least reactive and therefore towards the lower alcohols preferable.

Although there are some differences in the effectiveness of the various wetting agents, 0.5 to ι % is usually sufficient. If alcohol is used, amounts up to 5% or more may be necessary.

Numerous methods can be used for the application of the treatment solution will. In all cases it is important that the surface with the solution is no even is wetted so that the etching takes place evenly over the entire surface. The solution can be applied with a brush or with a spray gun, or the object can be briefly immersed in a solution bath will.

After wetting, the solution is allowed to dry on the surface. The so The resulting coating then contains iron phosphate, trivalent chromium and possibly some low-grade chrome.

In the case of the weaker solutions, air drying is usually sufficient, but in the case of higher concentrations it may be advisable to use more drying. After drying, the treated item is ready without any special further treatment, finished with paint, enamel, varnish, etc. to become.

The following are examples of solutions used in practicing the invention can be:

phosphorus
acid chrome
acid Duponol-WA- No. 4.0 0.6ο paste
Wetting
middle I. 4.0 0.20 0.5 2 7.0 ΐ, 05 0.5 3 7.0 0.35 o, 5 4th 10.0 ΐ, 50 0.5 5 10.0 ο, 5θ o, 5 6th o, 5

A particular example showing the application of the method is given below given:

An object made of cold-rolled steel is freed from oil and grease by rubbing it with gasoline and then drying the surface with clean cloths. A solution containing 10% phosphoric acid, 1.5% chromic acid and 0.5% Duponol WA paste as a wetting agent is then applied to the surface by means of a brush. When the surface is evenly wetted, the object is placed in an oven and ^{dried at 150 °} C. for 3 minutes.

+0 It is then taken out and allowed to cool serene and ready for any application you want with no further treatment Color coating.

One can, if so desired, that

^ s metal or the solution or both before application of the anti-rust process to facilitate the chemical reaction and accelerate drying.

Also can be many concentrations and

so many different ■ relationships between Phosphoric acid and hexavalent chromium are used. In all cases it is necessary that the prevailing conditions are an etching of the iron surface by the ones present Allow phosphoric acid.

Any of the various phosphoric acids can take the place of orthophosphoric acid, such as phosphorous acid, meta- and pyrophosphoric acid and hypophosphorous acid Acid. The anhydrides, such as phosphorus pentoxide, can also be used as these compounds are added Acid properties are obtained from aqueous solutions. To make the transport cheaper the funds can be prepared in concentrated form and only applied to the before use suitable strength to be diluted. In cases where the use of a wetting agent or alcohol is desired, it is preferable to add them after dilution because they react with the chromic acid as long as this is available in concentrated form.

The rust protection method according to the invention makes it possible to treat iron surfaces. yours, for which it was impossible after the usual coating process. The solutions can be used for stationary objects such as bridges, structural parts of buildings, large oil tanks, cars, etc. can be used without the need for large-scale tanks or spray chambers would be. The application of heat can be dispensed with for the entire process, which is impossible with the known phosphate process. The resulting coating is In comparison to the known phosphate coatings as a color base, it can be judged as favorable.

It has been found that sometimes the addition of a wetting agent to a solution which contains chromic acid and phosphoric acid, the solution causes the metal surface etches, while no etching occurs without a wetting agent. The real reason for this is not entirely certain, but solutions and conditions and coatings that work this way are included in the invention.

Claims (2)

Patent claims: 1. Process for producing corrosion-resistant coatings from metals, in particular Iron and steel with a film of water on the metal surface Solution "is brought to action and allowed to dry up, characterized in that for this purpose an aqueous Solution used is the phosphoric acid and chromic acid in such concentrations contains that it can visibly etch the metal surface, in a ratio of not more than 0.25, preferably no more than 0.15 part chromic acid per 1 part phosphoric acid. 2. The method according to claim 1, characterized in that the solution has wetting agents can be added.