CS247176B2 - Metals coating agent - Google Patents

Abstract

The metal coating composition comprises as a corrosion inhibitor of 0.1 to 1.0 wt 10% optionally substituted 2-hydroxy- -5-alkylbenzaldoxime of 7 to 13 carbon atoms in the alkyl moiety and 90-99.9% solvents or carriers. It is suitable for corrosion inhibition metals, especially iron, zinc, copper, and aluminum and above all low-carbon zinc-coated steel.

Description

The present invention relates to a metal coating composition.

Various corrosion inhibitors are known, most of which are of the reservoir type and include as solvent additives or oil-based systems used in contact with metals.

Such inhibitors are contained, for example, in water which is in constant contact with the surface of the metal to be protected.

Inhibitors are also known which are applied to the metal surface and form a protective coating which does not necessarily have to be continuously replenished: for this purpose, a phosphate or zinc chromate treatment is commonly used. However, such treatment provides only limited protection and may have an adverse effect on the environment.

Other means, such as tannin, act as so-called rust transfer agents when applied to already rusted surfaces. However, such compositions have generally limited action with respect to inhibiting further rusting.

The metal coating composition according to the invention comprises as a corrosion inhibitor 0.1 to 10% by weight of optionally substituted 2-hydroxy-5-alkylbenzaldoxime having 7 to 13 carbon atoms in the alkyl moiety and 90 to 99.9% of a solvent, or carriers.

The composition according to the invention is particularly suitable for inhibiting the corrosion of iron, zinc, copper, tin and aluminum, in particular for inhibiting the corrosion of low-carbon steels and zinc-plated steel.

The alkyl moiety at the 5-position of the 2-hydroxy-5-alkylbenzaldoxime may be linear or branched, saturated or unsaturated. Branched alkyl groups are particularly preferred.

Possible substituents of the benzene core of the 2-hydroxy-5-alkylbenzaldoxime include, for example, an alkyl, aryl, alkoxy and aralkyl group, but the most preferred substituent is a halogen atom or a nitro group.

The metal may be treated directly with benzaldoxime, although it is generally preferred to apply benzaldoxime to the metal surface as a solution in a suitable organic solvent or as an aqueous benzaldoxime emulsion or as an aqueous emulsion of a benzaldoxime solution in an organic solvent. The benzaldoxime may be used to form a protective coating in the true sense of the term, or it may be used for pretreating the metal before the coating is applied, or it may be incorporated into the coating composition.

Conventional organic solvents may be used for benzaldoxime: examples include alcohols, ethers, ketones, and aliphatic and aromatic hydrocarbons. Particularly preferred are solvents which have good wetting and drying properties, such as, for example, ethanol, isopropanol, toluene, xylene, chloroform and 1,1,1-trichloroethane.

Aqueous benzaldoxime emulsions can be prepared in a manner known per se using conventional dispersing and surfactants, including nonionic dispersants.

Preferably, the metal surface is treated with benzaldoxime and the treated surface is simultaneously or subsequently contacted with water to promote the formation of a protective complex between the metal and the benzal doxime. Therefore, when benzaldoxime is used directly or as a solution in an organic solvent, the metal surface may subsequently be contacted with liquid water for a time sufficient to form a metal-benzaldoxime complex, for example, one to four hours. It is also possible to use water vapor in the atmosphere and in this case it takes a few days to develop the protective complex completely. Generally, the formation of the complex in the presence of water or water vapor occurs before the start of the rusting and is therefore not particularly disadvantageous if the complex is formed over a period of time.

It may be advantageous to treat the metal with an aqueous emulsion of benzaldoxime, as the benzaldoxime treatment and contact with water may then take place simultaneously and the protective coating may be formed over a contact time that may be less than 5 minutes. Liquid benzaldoximes which can be directly processed into an emulsion are particularly preferred: liquid, optionally substituted 5-alkyl-2-hydroxybenzaldoximes having an alkyl moiety in the 5-position containing less than 14 carbon atoms are examples.

Corrosion protection can be achieved by the composition according to the invention either without further surface treatment or as a pretreatment prior to application of another surface protecting coating composition. Therefore, treatments can be used such as temporary treatments to transfer metal from one location to another. Optionally, the metal-benzaldoxime protecting complex may be removed using a suitable solvent, for example one of the above solvents. The process of the invention can be used to temporarily treat a metal surface and the protective coating can then be redissolved prior to further processing.

Alternatively, the benzaldoxime may be formulated into a surface coating composition, for example a (base reactive) coating composition, a lacquer, a resin or other protective coating composition. The surface coating composition may be a solvent-based coating composition, for example a cellulose-based reactive primer and a solvent based coating composition. Benzaldoxime is soluble in the solvents generally used for such primers (for example nitrocellulose) and can be directly incorporated therein. Benzaldoxime can also be used as an emulsion in aqueous Jimot emulsion coating systems, such as, for example, primer or polymer latex based protective coatings, such as acrylic latexes and styrene acrylic latexes, and vinyl acrylic copolymer latexes including acrylic-modified vinyl chloride-vinylidene chloride copolymer latex .

For example, benzaldoxime can also be incorporated into temporary alkali-removable protective coatings (whether solvent-based or emulsion-based) of the addition polymer, the polymer containing carboxyl groups.

Benzaldoxime or a solution or emulsion thereof may be applied to the metal in a manner known per se, for example by dipping, spraying or brushing. The deposition temperature can be 0 to 50 ° C, although the protective coating is formed more quickly at higher temperatures, for example, at 25 to 50 ° C. Generally, benzaldoxime solutions may contain from 0.1 to 10% by weight of benzaldoxime, the emulsions preferably containing from 0.1 to 5% by weight. In general, 0.1 to 2% by weight of benzaldoxime in the emulsion coating composition is sufficient to improve corrosion inhibition.

The treated metal can be polished and / or freshly cleaned, but it is an advantage of the process according to the invention that effective corrosion inhibition can be achieved even in the case of a slightly rusty surface. In fact, it has been found that generally better results are obtained when the surface is treated in the delivered condition than when the same surface is freshly polished or polished.

The composition of the invention may be combined with a conventional anti-corrosion treatment such as iron phosphatization and very effective corrosion protection is achieved when the method of the invention is used to treat the surface of phosphated iron.

The composition of the invention is not limited to any theory, but it appears that the process of the invention results in the formation of a chemically bonded complex between the benzaldoxime and the metal / metal oxide surface, thereby protecting against corrosion. In the treatment of iron, complex formation can be measured and controlled by developing a violet color on the surface. In the treatment of zinc and galvanized steel, the complex is colorless and is therefore not visually assessable.

As mentioned above, the process of the invention is equally effective on a slightly rusted iron surface and can be used as a rust transfer agent. It has been found that the process of the invention provides generally improved protection over known tannin-based rust transfer agents.

Improved corrosion protection is achieved when the complex between the metal surface and the benzaldoxime is stable and insoluble in water or dilute acid or in brine, i.e. under conditions to which the surface may be exposed to the atmosphere. It has been found that an optionally substituted 5-alkyl-2-hydroxybenzaldoxime whose alkyl moiety at the 5-position contains 7 or more carbon atoms is particularly suitable for the purposes of the invention. A particularly preferred alkyl moiety at the 5-position, which exhibits excellent protection against corrosion by water and dilute acid and in a solarium atmosphere is heptyl, octyl, nonyl, and dodecyl. The 5-nonyl group has a particularly good protective action against the acid and brine atmosphere.

The invention is illustrated by the following examples in which parts and percentages are by weight unless otherwise indicated.

Example 1

A sample of 25.4 x 25.4 mm polished low carbon steel is washed thoroughly with acetone and then ethanol and stored in kerosene for as long as necessary. Immediately before use, rinse with acetone.

The above treated sample is immersed in a 5% solution of 5-nonyl-2-hydroxybenzaldoxime in ethanol and then transferred to distilled water. The control sample is treated in the same way, but not treated with benzaldoxime and the like is immersed in distilled water. After 20 days, a violet-brown color develops on the test sample with only a slight loss of gloss. Weight loss is 0.001%. In contrast, the control sample is substantially rusted over the entire surface and the weight loss is 0.55%.

Example 2

The procedure described in Example 1 was repeated, but 5-dodecyl-2-hydroxybenzaldoxime was used as the corrosion inhibitor. The test sample and the control sample are immersed in distilled water for 8 days. The test sample shows no rust and no weight loss after this time. The control sample, on the other hand, is very rusty and exhibits a weight loss of 0.22%.

Example 3

The procedure described in Example 1 was repeated except that 5-nonyl-3-bromo-2-hydroxybenzaldoxime was used as the corrosion inhibitor. The test sample and the control sample are then immersed in distilled water for 8 days. The test sample shows no rust and no weight loss after this time. The control sample, on the other hand, is very rusty and exhibits a weight loss of 0.23%.

Example 4

A sample of polished low carbon steel is treated with a 5% ethanol solution of 5-nonyl-2-hydroxybenzaldoxime as described in Example 1 and then exposed to the atmosphere for four weeks. During this time, a violet-brown color develops on the surface exposed to direct environmental exposure. At the end of four weeks, very little rusting is observed. On the other hand, a control sample not treated with benzaldoxime shows a strong rust after only a week, while a control sample subjected to conventional zinc chromate treatment also shows a strong rust after four weeks.

Example 5

A sample of polished low carbon steel is treated with 5% ethanol solution of 5-nonyl-2-hydroxybenzaldoxime as described in Example 1 and fully immersed in 18% (w / v) chloro-hydrogen acid at room temperature. After a five-hour immersion, certain signs of attack are evident and the weight loss is 0.04%. However, a control sample that is not treated with benzaldoxime shows a very strong rust surface attack and a 2.0% weight loss.

Example

A polished low carbon steel sample is treated with 5% ethanol solution of 5-nonyl-2-hydroxybenzaldoxime as described in Example 1 and fully immersed in a 3% aqueous salt solution.

After seven days, a violet-brown color develops on the sample which, after washing with water and then acetone, leaves a glossy surface similar to that of the initial sample. Slight corrosion and a weight loss of only 0.05% are observed. In contrast, the untreated sample rapidly loses shine and exhibits a weight loss of 0.26%.

Example 7

A sample of galvanized steel is treated with a 2% ethanol solution of 5-nonyl-2-hydroxybenzaldoxime as described in Example 1 and then fully immersed in distilled water. After seven days at room temperature, the sample showed only slight signs of white rust and a weight loss of only 0.02%. In contrast, samples not treated with benzaldoxime show significant deposits of white rust and are strongly etched. The weight loss of the untreated samples is generally 0.3%.

Example 8

The rusted steel beam is slightly brushed to remove free rust and one portion is treated by applying a 10% solution of 5-nonyl-2-hydroxybenzaldoxime in 1,1,1-trichloroethane with a brush. Another portion of the beam is treated in a similar manner using a 10% by weight solution of tannic acid in water. The beam is exposed to the surroundings on the roof, the benzaldoxime treated parts will form a dark surface coating in about two days, and there will be no further signs of corrosion for a test period of two months.

On the tannic-treated part a black coating develops within minutes, but further rusting is evident during the week. The benzaldoxime treated portion still shows no further signs of rust when exposed to the environment for another three months.

Example 9

5-nonyl-2-hydroxybenzaldoxime is added at a concentration of 1% by weight to a number of commercially available cellulose-based base coatings sold as car paints. After thorough mixing, the benzaldoxime-containing paint is applied by a child to the surface of the low carbon steel sample and allowed to dry overnight. In the same way, a control sample is prepared using an unmodified paint. Both the test sample and the control sample are scratched in large squares to penetrate the coating film and fully immersed in 3% aqueous salt solution for three days.

When removing and examining the specimens, it is apparent that in each case the specimen has been treated with a benzaldoxime-containing paint, only signs of rust appear only in scratches. In contrast, samples treated with unmodified paint exhibit extensive rusting not only in scratches but also (and the like) in areas coated around the lines. In the case of some commercially available cellulose-based base coatings subjected to the test, the adhesion of the coating film to the sample is impaired in large areas around the grooves.

Example 10

In the case of steel wire for chains with a diameter of 19 mm, the following modifications shall apply:

A / annealing and pickling at the manufacturer,

B / annealing, pickling and treatment with zinc phosphate at the manufacturer,

C) annealing and pickling and subsequent application of an oil coating of the type used by the manufacturer / coating thickness of 3.7 microns: oil density 0.889 g / l at 20 ° C and an opacity of 269 m ² / l).

Samples (A) and (B) were treated with solutions of 5-nonyl-2-hydroxybenzaldoxime in 1,1,1-trichloroethane of varying concentrations and compared to untreated controls and (C). All samples are exposed to the open roof during adverse weather and winter months. The results are shown in the following table:

The + sign in the table indicates that no rust was observed at the end of the test after exposure to the environment for 40 days and 40 nights.

Table 1

Sample Aldoxime Concentration The number of days that the first one occurs

% in solvent wt. signs of rusting AND - less than 1 AND 2.5 21 AND 5.0 30 (B) - less than 3 (B) 2.5 30 (B) 5.0 greater than 40 C - 7

Example 11

A copper foil sample (0.1 mm thick) was cleaned with solvent or briefly washed with nitric acid and treated with a 2% ethanol solution of 5-onyl-2-hydroxybenzaldoxime. All samples are exposed to the weather for 7 weeks. During this time, a faint yellow color develops, but there is no loss of gloss. The samples are then washed with acetone to remove the surface coating and the copper foil surface is returned to its original gloss. No difference was found between the samples prepared by the solvent wash and the samples prepared by the nitric acid wash.

The control untreated copper foil, on the other hand, exhibits a strong gloss loss within one hour, while the copper foil treated with known anti-corrosion agents, e.g. benztriazole, suddenly exhibits a strong gloss loss after 8 days of weathering.

Example 12

50.8 x 50.8 mm sample of typical aluminum alloy / 4.4 wt% copper,

0.5% magnesium, 0.7% silicon and 0.8% manganese are treated with a 2.5% ethanol solution of 5-nonyl-2-hydroxybenzaldoxime and then completely immersed in a 1% aqueous salt solution for four weeks.

During this time, a slightly green color develops on the treated surface. The surface treatment is then removed by washing with acetone and the original glossy surface is restored. No signs of pitting are visible.

Severografla, n. P., MOST

Price 2,40 Kčs

Upstream, the control sample not treated with aldoxira becomes dull and whitish after immersion in salt solution for four weeks and shows severe pitting corrosion.

Example 13

The tinned steel sample (0.5 g / m tin) is treated with a 2% ethanol solution of 5-nonyl-2-hydroxybenzaldoxime. Then a commercially available epoxy varnish is applied and allowed to cure in an oven at 200 ° C for 10 minutes. Large squares are engraved with the cured lacquer film and the samples are placed in the brine spray chamber for 24 hours. Areas in the vicinity of the scratches develop a purple color, but corrosion is negligible.

In contrast, samples of the same tin-plated steel, which are normally treated with chromate prior to application of the epoxy varnish, show very intense corrosion around the scratches after exposure to the salt chamber for 24 hours.

Example 14

At a concentration of 5% by weight, 5-nonyl-2-hydroxybenzaldoxime is added to a solution of the acrylic polymer in industrial methylated alcohol having a dry matter content of 16%. After thorough mixing, the polymer blend containing benzaldoxime is brushed onto the surface of the low carbon steel sample and allowed to dry and cure for several hours. A benzaldoxime-free acrylic polymer solution is used for the control sample, and the coating is formed in a similar manner. Both the test and control samples are scratched to form large squares down to the metal and immersed perfectly in distilled water for seven days.

After removal of the sample, samples treated with a benzaldoxime-containing polymer are found to show slight signs of rusting only at the scratch points. In contrast, the control sample treated with the unmodified polymer exhibits a strong rust due to attacking the area under the coating around the scratches and peeling of the film.

Example 15

The low carbon steel sample was treated with an acrylic polymer in the form of a solution containing 2-hydroxy-5-nonylbenzaldoxime, as described in Example 14, and then exposed to the roof environment with a benzaldoxime-free acrylic coated control sample. After four weeks of exposure, the test sample with a polymer solution containing benzaldoxime showed no signs of rusting except for small signs of rusting at the scratches. In contrast, the control sample exhibits severe rusting at the scratch points and surrounding areas indicative of metal attack under the coating. In addition, there is considerable point corrosion on the surface, indicating that the polymer film has peeled off.

Claims (1)

A metal coating composition comprising, as a corrosion inhibitor, 0.1 to 10% by weight of an optionally substituted 2-hydroxy-5-alkylbenzaldoxime having 7 to 13 carbon atoms in the alkyl moiety and 90 to 99.9% of a solvent or carrier.