DE1287891B - Process for applying a phosphate coating to surfaces made of iron or zinc - Google Patents

Description

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It has long been known to apply a zinc phosphate solution with a phosphate coating

mainly consisting of iron or zinc, the upper manganese content described (German patent

to apply surfaces by touching them with an acid font 741 937).

aqueous solution of metal phosphates, the metal of which the invention relates to a process for

enters the coating, treated. Originally 5 application of a phosphate coating to surfaces

For this purpose, iron phosphate and manganese were made from iron or zinc with the help of aqueous acids

phosphate used. For a number of years solutions containing zinc phosphate, oxidation accelerator

However, it is mainly used for zinc phosphate and contains manganese at one temperature

manure. When the solutions on the surfaces to a maximum of 38 ° C, characterized in that

are sprayed, almost exclusively zinc-io the surfaces are sprayed with a solution,

phosphate solutions used. in which the manganese content is between 5 and 50 weight

The rate of coating formation is of the percent, preferably between 5 and 20 weight of great practical importance, and one reason the percent of zinc content is
It was not to be expected that if the manganese content specified in a zinc phosphate solution was maintained, a spray treatment would be more effective than an iron or manganese solution at a temperature of at most 38 ° C for the phosphate solution. The speed of the formation of a satisfactory, crystalline and formation-resistant coating is achieved by adding an accelerator. This is substantially increased. As such, nitrates, particularly nitrites, surprisingly low in terms of low or chlorates are common. The layer formation rate of manganese phosphate also increases with increasing temperature solutions themselves.

However, for other practical reasons, it is well known that a phosphating solution works

It is desirable to keep this as low as possible. Metal partly because it goes into the layer,

The coating process can generally be lost in distribution and partly in discharge. It was found,

drive that in the heat, at lower temperatures 25 that it is possible to reduce the weight ratio of

or be carried out in the cold. To adjust manganese to zinc in the solution so that

While for many years only the hot processes it is the same as the ratio of the proportions in

were applied today are also at lower levels where the metals disappear from the solution.

Temperatures and procedures to be carried out. This has the result that the solution has set

borrowed, at which temperatures from 38 to 49 ° C can be used 30 and supplemented using the

will. In the following, the cold process shall mean the same chemical mixture. This relationship

such procedures are understood, which in the case of room changes naturally with the working conditions,

temperature, i.e. at temperatures from 4 to 38 ° C, but it is generally from 0.10: 1 to 0.13: 1

but usually not above 21 ° C, manganese carried to zinc.

will. It is known that, for a satisfied, one can get into the solution in any way

Achieving performance of a cold process that is introduced as phosphate, for example as phosphate or

animal solution must accelerate very strongly and that than other salt. Preferably manganese is used as

they have to be more concentrated and have a higher pH added to manganese sulfate.

must have as solutions that must be used when using To produce very good coatings higher temperatures to corresponding results 40 solution have a pH value greater than 3

to lead. and a total acidity of over 20. Under total

It is also known that phosphating solutions have acidity of the solution, the number of milliliters is 0, ln-

normally understood either in diving or by NaOH, which is necessary to 10 ml of the

Syringes are used and that a coating solution to the phenolphthalein endpoint at neutrageschurz, which are portable during a dipping process. The ratio of total acidity to free

can be too slow for a spray process. The acidity of the solution is preferably between 50: 1

Spray techniques are commonly used, um and 100: 1. Under free acidity, the number becomes

large workpieces, understood by means of transport devices milliliters 0, In-NaOH, which is necessary

are transported to be provided with a coating. by 10 ml of the solution to the bromophenol blue die Workpieces must be neutralized in as short as possible an end point of 50.

Time during its passage through a spray. The solution preferably contains nitrate as a loading

system can be provided with a coating. The cold accelerators.

Phosphating is still more desirable in spraying processes than in dipping processes, because the chemical mixture used should contain nitrate and loss, and thus the consumption of fuel, especially phosphate, preferably in a weight ratio, especially in spraying systems , especially from 0.2: 1 to 0.4: 1 NO ₃ : PO ₄ . To be up ahead. the solution may also contain another one

Although it is known which modifications of the oxidation accelerator, for example sodium solution, are necessary in order to form a nitrite coating. A cold dip chlorate can also be used as a further accelerator to enable cold dipping; however, chlorate causes only very little in processes and spray cold processes do not increase the free acidity at all. The coatings produced in the cold during the solution, so that it is necessary to counteract this increase available in a spraying process by adding, for example, sodium time, coatings are not satisfactory, since carbonate. Nitrites, which themselves are not resistant enough to act as a neutralizing agent, are by far preferred. Rinsing and drying without rusting against the concentration of nitrite will preferably be in between. 0.015 and 0.075 percent by weight, calculated as NaNO ₂ ,

For cold phosphating in the immersion process, and in particular at about 0.040 percent by weight

keep. It is known that nitrite must be added to a coating-forming solution either continuously or in be added at regular intervals.

In contrast, chlorate can be used in the mixture to make up and supplement the solution chemicals used are added.

It has also been found that better results are obtained when the solution is added contains an aliphatic hydroxy acid, for example tartaric acid or a water-soluble salt thereof. The amount of such an acid or such a salt is expediently 0.02 to 4.0 g / l, calculated than tartaric acid. The quality of the coatings can also be achieved by adding a small amount of bromide ions, for example about 0.5 g / l, calculated as NaBr, can be improved.

When applying coatings to iron surfaces for which the method according to the invention is particularly applicable, iron enters the solution as ferrous iron, which is added in the presence of nitrite Ferric iron is oxidized. This gradually saturates the solution with ferric ions. It was found, that over large operations the most even results are obtained when the concentration at ferric ions is constant. It is therefore preferable to start from a solution containing ferric ions is saturated by adding these ions, e.g. in the form of ferric sulfate, to the solution from the start will. Normally an addition of about 0.02 g / l ferric iron is appropriate for this purpose. the However, concentration can vary from 0.006 to 0.06 g / l. The required ferric ions can be in can easily be added to the above chemical mixture.

In order to obtain good quality phosphate coatings, iron surfaces must first be cleaned to remove dirt and the protective film generally present from mineral oil. It is important that this cleaning does not render the surface passive to the coating forming agent Solution. To meet this condition, there are various ways of cleaning it It is of course preferable to use a cleaner that is also effective in the cold. the Surfaces can therefore be cleaned with an organic solvent such as kerosene. However, they are preferably cleaned in the usual way with an alkaline cold cleaner then phosphated directly or with the interposition of one or more water rinses. Preferably a cold cleaner is used that is free or essentially free of condensed phosphates has a pH of less than 12 and contains an emulsified organic solvent.

Iron surfaces are also occasionally coated with a mixture of a mineral oil and a drying agent or semi-drying oil protected against corrosion. It has been found to be satisfactory For cleaning such surfaces, the pH value of the alkaline cleaner used does not fall below 11, i.e. should be between 11 and 12.

The metal surfaces can also be made using a method not previously published where the cleaning solution is a phosphating solution based on zinc phosphate, which in addition either a suitable surfactant or an emulsified organic solvent, such as kerosene, is used.

example

Steel sheets were treated in seven stages as follows: In the first stage, the sheets were cleaned. A solution was used comprising 5 g / l of a pulverulent mixture below a specified composition and 10 g / l of an emulsion of 30 weight percent gasoline (flash point 46 ⁰ C), 30 weight percent petroleum, ίο residual water and containing emulsifiers. The powdery mixture had the following composition:

Parts by weight

Sodium metasilicate (Na ₂ SiO ₃ · 5 H ₂ O) .. 616

Sodium metaborate (Na ₂ B ₂ O ₄ · 8 H ₂ O) .. 300
Layer refining agent 50 containing 1.5% titanium

Fatty alcohol - ethylene oxide condensation product 10

Nonylphenol ethylene oxide condensation

product 15

with 8 to 10 moles of ethylene oxide 15

Nonylphenol-ethylene oxide condensation product with 1 to 2 moles of ethylene oxide 9

The solution was sprayed onto the metal sheets at 21 ° C. for 1 minute.

In the second stage, the metal sheets were rinsed by spraying with water at 21 ^° C. for 30 seconds.

In the third stage, it was rinsed again with fresh water, again for 30 seconds at 21 ° C. The metal sheets were then sprayed with a phosphating solution ^{at 21 ° C. for 1 minute.} This solution was made by diluting a concentrated mixture of chemicals and then adding some zinc carbonate to lower the free acidity. The diluted solution had the following composition:

, ₀ Mn 0.9 g / l

Zn 7.6 g / l

Ni 0.05 g / l

Fe +++ 0.02 g / l

SO ₄ 1.3 g / l

PO ₄ 19.6 g / l

NO ₃ 4.6 g / l

Tartaric acid 1.0 g / l

Sodium nitrite was added to the solution in an amount of 0.5 g / l. The total acidity of the solution was 30 points and the free acidity was 0.5 point.

After the coating had formed, the panels were first rinsed with water by spraying at 21 ° C. for 30 seconds. A solution was then sprayed for 30 seconds at 21 ^° C. which contained 0.03 g / l H ₃ PO ₄ and 0.03 g / l CrO ₃ . Finally, the plates in the oven at 12O ⁰ C were dried.

Over the course of a long period of throughput, the strength of the solution was repeatedly replenished by the addition of the concentrated chemical mixture, and sodium nitrite was continuously added throughout. Excellent coatings were obtained with a layer weight of 1.36 g / m ² .

For comparison, a standard zinc phosphate solution accelerated with nitrate and nitrite was used in the same

Chen system used to apply a coating to steel sheets at a temperature of 43 ° C. Excellent coatings weighing 1.54 g / m ² were obtained.

Panels which had each been treated according to the two processes described were provided with a layer of a black, oil-modified alkyd stoving lacquer and tested for their behavior. These investigations showed that the adhesive strength of the paint on the ^{sheets treated at 21 °} C. was significantly better than on the sheets treated ^{at 43 ° C.} In the salt spray test, the formation of rust from the scratch was somewhat less in the sheets treated at 21 ° C. When the usual zinc phosphate solution used for comparison was applied at 21 ^° C. instead of at 43 ^° C., the metal sheets provided with a coating were all rusted to such an extent that it was not considered necessary to paint some of them and check the behavior.

Claims (9)

Patent claims: 1. A method for applying a phosphate coating to surfaces made of iron or zinc with the help of aqueous acidic solutions containing zinc phosphate, oxidation accelerators and manganese, at a temperature of at most 38 ⁰ C, characterized in that the surfaces are sprayed with a solution in that the manganese content is between 5 and 50 percent by weight, preferably between 5 and 20 percent by weight, of the zinc content. 2. The method according to claim 1, characterized in that the surfaces with a solution where the weight ratio of manganese to zinc is between 0.10: 1 and 0.13: 1 lies, and that the solution is supplemented with an agent when used, the manganese and Contains zinc in the same proportion as the solution. 3. The method according to claims 1 and 2, characterized in that the surfaces with a solution into which manganese in the form of manganese sulfate has been injected. 4. The method according to claims 1 to 3, characterized in that the surfaces with a solution with a total acidity greater than 20 and in which the ratio from total acidity to free acidity is from 50: 1 to 100: 1. 5. The method according to claims 1 to 4, characterized in that the surfaces are sprayed with a solution which is prepared and supplemented with an agent containing nitrate as an accelerator and in which the weight ratio of NO ₃ : PO ₄ 0.2 : 1 to 0.4: 1. 6. The method according to claim 5, characterized in that the surfaces are sprayed with a solution which additionally contains nitrite, preferably in an amount of 0.015 to 0.075 percent by weight, calculated as NaNO ₂ . 7. The method according to claims 1 to 6, characterized in that the surfaces with a solution containing an aliphatic α-hydroxy acid, preferably tartaric acid or one of its water-soluble salts in an amount of 0.02 to 4.0 g / l, calculated as tartaric acid, contains. 8. The method according to claims 1 to 7, characterized in that iron surfaces be sprayed with a solution which is saturated with ferric ions during preparation. 9. The method according to claims 1 to 8, characterized in that the surfaces before the phosphating can be cleaned by spraying with an alkali cleaner that is free or im is essentially free of condensed phosphates, an emulsified organic solvent and has a pH of below 12, preferably between 11 and 12.