DE1014816B - Process for preparing metal surfaces for the application of enamels - Google Patents

Description

The invention relates to the production of enamels, in particular an improvement of the method for Application of enamels to metallic surfaces.

Patent application M 22587 VIa / 48 c describes a method for preparing metal surfaces for the application of enamels, in which a phosphate-oxide coating is applied, the PO ₄ content of which has a weight of 0.1 to 6.5 mg / dm ² and its total weight is 40 to 1300 mg / dm ² . This process can be carried out in such a way that first a metal phosphate coating is applied to the metal surface, the layer ^{weight of which is 0.1 to 6.5 mg PO ^ / dm 2} , and this phosphate coating is applied in an oxidizing atmosphere to form a phosphate-oxide coating the metal surface is heated. In this process, the phosphate coating applied to the metal surface is preferably rinsed before this base is annealed in an oxidizing atmosphere.

It has now been found that this rinsing of the phosphate coating is of particular importance and that this rinsing must be carried out under carefully monitored conditions when the phosphate-oxide coating should be smooth and bubble-free after annealing, which is important for the quality of the enamel is. In cases where the usual tap water is used, the results will be very different and often get stained material. In some cases phosphate-oxide coatings were formed, which were completely satisfactory for the subsequent application of an enamel coating, in in other cases a markedly blistered surface was obtained. It was found that this Bubble formation is due to the presence of certain amounts of unwanted ions that are present in the rinse water are due.

It was found that the phosphate oxide layer formed according to the method of the patent application M 22587 VIa / 48 c is then free from blistering if the rinse water is less than contains about 0.007 g / l halogen ion, namely chloride ions, bromide ions, fluoride ions and iodide ions. The rinse water should also contain less than 0.06 g / l sulfate ions and less than 0.04 g / l hydroxyl ions to be available. If the concentration of these ions in the rinse water is kept below the stated limits then there will be no blistering of the phosphate-oxide coating and the subsequently applied The enamel coating is smooth and free from superficial undulations or defects.

Rinsing should preferably be carried out in such a way that all substances are thoroughly removed. which are not firmly connected to the phosphate coating on the base surface. This can be done by

of metal surfaces
for applying emails

Addition to patent type notification M 22587 IVc / 48 c
(Interpretation document 1 011 244)

Applicant:

Metallgesellschaft Aktiengesellschaft,
Frankfurt / M., Bockenheimer Anlage 45

Claimed priority:
V. St. v. America May 12, 1955

Marco James Cramer, Royal Oak, Mich. (V. St. A.),
has been named as the inventor

can be achieved that the object covered with the coating is sprayed with the rinse water or immersing it in the rinse water, but in both cases the rinse water should be relatively high Speed compared to that to be flushed. Surface can be moved. Good results have been achieved in achieved in all cases where foreign ions are removed or distilled water was used in the rinsing. It is sufficient to use one that is free from foreign ions Water after pre-rinsing with tap water.

It is known to those skilled in the art that in cases where the rinse water is kept in containers and the object is immersed therein and agitated violently to effect rinsing, the Contaminants from. removed from the surface covered with the phosphate coating, im Rinse water accumulate to the extent that workpieces pass through the rinse water tank will. In this type of treatment it is therefore necessary that careful attention be paid to the fact that the amount of halogen, sulfate and hydroxyl ions does not increase beyond the limit given above. the end for this reason it is desirable to discard the rinse water and do the rinse with a quick agitation Carry out spray jet.

7 »65 * 236

The disruptive effect of unwanted ions present in the rinse water can be seen from the following examples emerge:

example 1

An aqueous acidic phosphate solution was prepared containing 12.5 g / l of monosodium phosphate, and a _pH value of 5.2 had. A number of clean steel sheets were immersed in various proportions of the solution for 1 minute at temperatures between 66 and 74 ° and removed again. The sheets were covered with the known metal phosphate coating, which had a layer weight between 3.2 and 3.9 mg / dm ² . After being removed from the phosphate solution, the sheets were sprayed with Detroit tap water for 30 seconds, allowed to drain and left in a muffle furnace with the doors partially open at a temperature of 790 ° for 5 minutes. After removal from the oven, it was found that some of the trays had small bumps or blisters of a cloudy blue color near the lower edge from which the rinse water dripped during the spraying. These blistered ones. Parts clearly showed a haze, while the remaining oxide-phosphate coatings had a bright blue-black color.

Another number of panels were treated in the same alkali phosphate solutions and for 30 seconds splashed with distilled water before they were placed in the same muffle furnace. These Panels showed no blistering.

Example 2

A portion of the aqueous phosphate solution described in Example 1 was used to make a other number of steel sheets to be treated under the conditions as described in Example 1. After the phosphate coating had formed, the metal sheets were immersed in a rinsing container, the tap water from Detroit, and vigorously agitated it before it was placed in the muffle furnace under the conditions described in Example 1 conditions described were introduced. A number of satisfactory sheets were first made the muffle furnace before blistering occurred. When bubbling occurred, the rinse water became analyzed and found that it contained 0.007 g / l chloride ion. With rinse water, that less when 0.007 g / L contained chloride ion, no bubbling was observed.

Various rinsing waters were then produced that contained the other halogen ions, bromide, Fluoride and iodide, and these, too, were blistered as soon as the rinse water contained more than 0.007 g / l halogen ions.

Much smaller amounts of sodium hydroxide were added to a container of distilled water Water used to rinse metal sheets treated in the above-mentioned phosphating solution and no bubbling was observed until the rinse water was 0.04 g / l Contained hydroxyl ions. When the rinse water contained more than 0.04 g / L of hydroxyl ions, bubbling occurred observed.

A container with distilled water, which was used to rinse steel sheets that had been treated in the above-mentioned phosphate solution sodium sulfate was added so that it contained small amounts of sulfate ions. It wasn't Bubbling observed until the sulfate ion content of the rinse water reached 0.06 g / L. Blistering was observed when the rinse water contained more than 0.06 g / l sulfate ions.

Claims (3)

Patent claims: 1. Process for preparing metal surfaces for the application of enamels according to patent application M 22587 VI a / 48 c, characterized in that the phosphate coating before oxidizing glow is rinsed with a water that contains less than 0.007 g / l halogen ions, Contains less than 0.06 g / l sulfate ions and less than 0.04 g / l hydroxyl ions. 2. The method according to claim 1, characterized in that a deionized for rinsing Water is used. 3. The method according to claim 1 and 2, characterized in that distilled for rinsing Water is used. © 709 654/236 8.57