CS196175B1 - Agent for making coats from amorphous phosphate - Google Patents

Description

The invention relates to amorphous phosphate coating compositions which are particularly suitable as interlayers under organic coatings.

The prior art coating compositions of this type give coatings with satisfactory mechanical properties throughout the protective system, i. with sufficient adhesion to both the base metal and the organic coating, but the phosphate coatings themselves have little corrosion resistance.

For example, amorphous phosphate coatings have been prepared in a bath containing ^? 5 g / l of phosphoric acid and 3.1 g / l of sodium chlorate or containing 15% by weight of phosphate; anhydrous phosphoric acid, 0.25% molybdic acid, 3% complexone and 81.75% water. The corrosion resistance of these coatings was monitored as follows: the test sample was immersed in a 1% sodium chloride solution at 20 ° C for 5 minutes. Then the sample was removed, rinsed with water and suspended freely in air. After 1 hour the sample was visually evaluated. When there were no signs of rust, the test was repeated by repeating the previous cycle. The number of test cycles until the formation of rust marks on the sample was determined.

The coating samples prepared by known means showed a corrosion resistance of at most 1 cycle.

These drawbacks are largely eliminated by the amorphous phosphate coating composition of the present invention, which consists of 20 to 95 weight percent alkali metal or araonium phosphate, 0.05 to 5 weight percent.

% of a water-soluble metal compound of the fifth or sixth group of the periodic table, for example tungstic acid, up to 30% by weight of an alkali metal fluoride, for example sodium fluoride, 1 to 30% by weight of a water-soluble aromatic acid salt nitrobenzoic acid and from 0.1 to 30% by weight of a surfactant, for example, a condensation product of ethylene oxide with lauryl alcohol. It is also an object of the present invention to find an optimum concentration range of the composition in the solvent, after which the phosphatizing bath itself is formed. The principle of this solution is that for 1 part of said active ingredients, the preparation according to the invention contains 10 to 200 parts of solvent, for example water.

The formation of amorphous phosphate coatings using the composition according to the invention significantly increases the corrosion resistance of these coatings while maintaining a satisfactory adhesion of the entire protective system even in the event of mechanical damage by scratches, abrasion, etc. in some places. the cost of anti-corrosion protection for the lifetime of the product.

The steel parts treated with the composition according to the invention have a surface coating of amorphous ferrous phosphate with a high corrosion resistance which allows a firm anchoring of the subsequent coating. This type of conversion coating is particularly suitable as an intermediate layer under powdered plastics.

The invention is further elucidated by describing examples of its composition.

Example 1

The following substances were mixed and thoroughly mixed in the following order: dihydrogen phosphate

ammonium 80 X wt. tungstic acid 0.4 % hmo t hydrogenodi fluoride ammonium 8 X hmo t. b e n z o and n sodium 8 X wt. Condensation product 1 aurylalcohol with ethylene oxide 3.6 7- wt 40 g of the resulting solid preparation was roz- released with stirring in 1 liter water.

Gray-blue coatings of amorphous phosphate, which exhibited corrosion resistance three to four times higher than those prepared using known agents, were excluded from the movement bath thus prepared.

Example 2

The following substances were mixed and thoroughly mixed in the following order:

dihydrogenophosphate

sodium 77 X wt. ammonium molybdate 0.4 X wt sodium fluoride 7.7 X wt m-nitro- benzoová 7.7 X wt condensation product ethylene oxide with propylene oxide 7.2 X wt

g of the resulting solid preparation was dissolved in 1 l of water with stirring.

From the phosphate bath thus formed, blue amorphous phosphate coatings which exhibited four times the corrosion resistance to coatings prepared using known compositions were excluded in the corrosion tests.

The amorphous phosphate coating prepared using the composition of the invention may be used as a passive anti-corrosion layer for in-process or other short-term storage of components and articles, or as an intermediate layer prior to the application of organic coatings. In this case, the amorphous phosphate coating composition of the invention simplifies the surface preparation process prior to the organic coatings since it also has degreasing effects. This makes it possible to treat even a slightly greased or not completely degreased surface of parts and products.

Claims (2)

SUBJECT V 1. Amorphous phosphate coating composition comprising from 20 to 95% by weight of an alkali metal or araonium phosphate, 0.05 to 5% by weight of a water-soluble metal compound of the fifth or sixth group of the periodic element, for example tungstic acid, 1 to 30% by weight of alkali metal fluoride or ammonium, for example ammonium hydrogen difluoride, 1 to 30% by weight in water Solvents of a single aromatic acid aromatic acid salt such as m-nitrobenzoic acid and 0.1 to 30% of a nonionic surfactant such as ethylene oxide condensation product with lauryl alcohol. 2. Composition according to claim 1, characterized in that it contains from 10 to 200 parts of solvent, for example water, per part of active ingredients.