JPH0261556B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to methods and coating compositions for inhibiting corrosion of metals. BACKGROUND OF THE INVENTION A variety of corrosion inhibitors are known, most of which are of the reservoir type and which are used in contact with metals.
Contained as an additive in solvent- or oil-based systems. Such inhibitors are thus contained, for example in boiling water, and are in continuous contact with the surface to be treated. Furthermore, corrosion inhibitors are known which are used on metal surfaces to form a protective film that does not require continuous replenishment; zinc phosphate or zinc chromate treatments are generally used for this purpose. However, such treatments provide only limited protection and have adverse environmental problems. Other chemicals, such as tannic acid, are used as so-called "rust converters" when applied to already rusted surfaces. However, such agents generally also have limited effectiveness in inhibiting rust. Problems to be Solved by the Invention The present invention provides a method for inhibiting the corrosion of metals by treating metals with optionally substituted 2-hydroxy-5-alkylbenzaldoximes (5-alkyl The substituent has 7 to 13 carbon atoms). The 5-alkyl substituent may be linear or branched, saturated or unsaturated. Particularly preferred are branched alkyl groups. Optional substituents on the benzene ring of the 2-hydroxy-5-alkylbenzaldoxime include:
Mention may be made, for example, of alkyl, aryl, alkoxy and aralkyl groups, especially halogen or nitro groups. The method of the invention is particularly suitable for inhibiting corrosion of zinc surfaces of iron, zinc, copper, tin and aluminum, especially mild steel and galvanized steel. Measures to solve the problem Although the metal may be treated directly with benzaldoxime, it is usually applied to the surface of the metal in the form of a solution of benzaldoxime in a suitable organic solvent or by applying benzaldoxime to water. Preference is given to using it as an emulsion or as an aqueous emulsion of a solution of benzaldoxime in an organic solvent. The benzaldoxime may itself be used before coating the surface to obtain a protective coating or as a pre-treatment of the metal, or it may be incorporated into the coating composition of the surface. Conventional organic solvents may be used for the benzaldoxime, including, for example, alcohols, ethers, ketones, and aliphatic and aromatic hydrocarbons. Particularly preferred solvents are those with sufficient wetting and drying properties, such as ethanol, isopropanol, toluene, xylene, chloroform and 1,
Includes 1,1-trichloroethane. Benzaldoxime water emulsions may be formed in a conventional manner using conventional dispersants and surfactants, including nonionic dispersants. Preferably, the metal 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 benzaldoxime. When benzaldoxime is used in this way, either directly or as a solution in an organic solvent, the surface of the metal is subsequently exposed to the liquid water and between the metal and benzaldoxime to be formed. Contact may be allowed for a sufficient period of time to form a complex, such as from 1 to 4 hours. Atmospheric water vapor may also be used, in which case the protective complex requires several days to fully form. The formation of the protective complex in the presence of water or steam is generally carried out prior to the rusting process, and there are no particular difficulties when the protective complex is carried out in this way over a period of time. Preferably, the metal is reacted with a water emulsion of benzaldoxime. This is because the treatment with benzaldoxime and the contact with water are carried out simultaneously, the protective film forms during the contact, and the time
This is because it may be as short as 5 minutes. Liquid benzaldoximes which can be formed directly into emulsions, such as liquid optionally substituted 5-alkyl-2-hydroxybenzaldoximes (in which case the 5-alkyl group has up to 14 carbon atoms) is particularly preferred. With the method of the present invention, corrosion control is obtained without the use of other surface coatings or without the use of other surface coating pre-treatments prior to use. In this way, the treatment may be used as temporary protection, for example, but
The metal is transferred from one location to the other. If necessary, the protective complex between metal and benzaldoxime may be removed with a suitable solvent, for example one of the solvents mentioned above. In this way, the method of the invention may be used for temporary protection of metal surfaces, and the protective coating is then dissolved before or during other treatments. Optionally, the benzaldoxime may be formulated with a surface coating composition, such as a paint (primer), lacquer, resin, or other protective coating. The surface coating may be a solvent-based composition, such as a cellulose/solvent-based primer paint, such as one used as a car "finish" paint.
Benzaldoximes are generally soluble in the solvents used in such primers (eg, nitrocellulose) and may be incorporated directly. Benzaldoxime can be used as a substrate for water emulsion surface coating systems, such as polymer latexes such as vinyl acrylic copolymer latexes, including acrylic and styrene/acrylic latexes and acrylate-modified vinyl chloride, vinylidene chloride copolymer latexes. It can also be used as an emulsion in a primer or protective coating. Benzaldoximes may be incorporated, for example, into temporary alkali-removable protective coatings (solvent-based or emulsion-based) of addition polymer systems in which the polymer has carboxyl groups. Benzaldoxime or its solutions or emulsions may be applied to the metal in the conventional manner, for example by dipping, spraying or brushing. Operating temperature is 0~
Rapid formation of the protective coating is carried out at a higher temperature range, for example 25-50°C, although it may be 50°C. Typically, solutions of benzaldoxime have from 0.1 to 10% by weight of benzaldoxime, whereas emulsions have from 0.1 to 5% by weight of benzaldoxime.
Generally, the presence of 0.1 to 2% by weight of benzaldoxime in the surface coating emulsion formulation is sufficient to obtain improved corrosion control. Although the metal to be treated may be brightly polished and/or freshly cleaned, it is an advantageous feature of the method of the invention that effective corrosion control is obtained even on slightly rusty surfaces. It has been found that actually better results are generally obtained when the surface is treated "as received" than when it is freshly cleaned or brightened. The method of the present invention may be combined with conventional corrosion control treatments, such as phosphate treatment of iron, and very effective corrosion control is obtained when the method of the present invention is used on phosphated iron surfaces. Although the scope of the invention does not apply as being limited to any particular theory, the method of the invention results in the formation of a chemically bonded complex between benzaldoxime and an iron/iron oxide surface; This provides corrosion control. When treating iron, complex formation may be monitored by the purple coloration of the surface. In the case of processing zinc and galvanized steel:
The complex is colorless and therefore the treatment is invisible. As mentioned above, the method of the invention is equally effective on slightly rusty surfaces and can also be used as a "rust converter" in this respect. In general, the method of the present invention provides improved protection as compared to conventional "rust converters" based on tannic acid. Improved corrosion protection occurs when the complex between the metal surface and the benzaldoxime is stable and insoluble in water or dilute acidic or salt compositions, as it does when exposed to the atmosphere. can get. Optionally substituted 5-alkyl-2-hydroxybenzaldoximes, in which the 5-alkyl group has 7 or more carbon atoms, are particularly suitable for this purpose. Particularly suitable 5-alkyl groups which exhibit excellent corrosion inhibition against water and dilute acidic and salt atmospheres are heptyl, octyl, nonyl and dodecyl. The 5-nonyl group exhibits particularly good protection against acidic and salt atmospheres. EXAMPLES The invention will now be explained with reference to examples. Parts and percentages in the examples are "parts by weight" and "% by weight." Example 1 1 in x 1 in glossy mild steel coupons were thoroughly cleaned with Ascent followed by ethanol and stored in kerosene until needed. Immediately before use, it was washed in Acentone. The test coupon made as described above was 5-
Nonyl-2-hydroxybenzaldoxime was soaked in a 5% solution of ethanol and then transferred into distilled water. Control coupons made in the same manner but not treated with benzaldoxime were
It was immersed in distilled water in the same way. After 20 days,
The test coupon had a purplish-brown color with only a slight trace of haze. A weight loss of 0.001% was recorded. By comparison, the control coupon was significantly rusted over its entire surface, with no weight loss.
It was recorded as 0.55%. Example 2 The method of Example 1 was repeated except that 5-dodecyl-2-hydroxybenzaldoxime was used as the corrosion inhibitor. The test and control coupons were soaked in distilled water for 8 days after which the test coupons showed no rust and no detectable weight loss. The control coupon rusted significantly and recorded a weight loss of 0.22%. Example 3 The method of Example 1 was repeated for 5-nonyl-3-bromo-
The procedure was repeated except that 2-hydroxybenzaldoxime was used as the corrosion inhibitor. The test and control coupons were soaked in distilled water for 8 days after which the test coupons showed no rust and no detectable weight loss. The control coupon rusted significantly and recorded a weight loss of 0.23%. Example 4 Shiny mild steel coupons were treated with a 5% ethanolic solution of 5-nonyl-2-hydroxybenzaldoxime as in Example 1 and exposed to air for 4 weeks. During this time, surfaces directly exposed to the atmosphere took on a purplish-brown color. At the end of four weeks, very slight rusting occurred. By comparison, the control coupons that were not treated with benzaldoxime were significantly rusted after only one week, while the control coupons that had been routinely treated with zinc chromate were significantly rusted after four weeks. Example 5 Shiny mild steel coupons were treated with a 5% ethanolic solution of 5-nonyl-2-hydroxybenzaldoxime as in Example 1 to give 18 W/V%
of hydrochloric acid at room temperature. After 5 hours of immersion, some corrosion was observed and the weight loss was 0.04%.
It was hot. However, the control coupons that were not treated with benzaldoxime had a weight loss of 2.0%.
It was found to suffer from significant surface corrosion with %. Example 6 Shiny mild steel coupons were treated with a 5% ethanolic solution of 5-nonyl-2-hydroxybenzaldoxime as in Example 1 and thoroughly immersed in a 3% aqueous salt solution. After 7 days, the coupon took on a purplish-brown color, which, after washing with water and then with Ascent, showed the same bright shiny surface that appeared on the original coupon. Almost no corrosion was observed, and the weight loss was only 0.05%. In contrast, untreated coupons did not lose their luster quickly, with an average weight loss of 0.26%. Example 7 Galvanized steel coupons were treated with a 2% ethanolic solution of 5-nonyl-2-hydroxybenzaldoxime using the method of Example 1 and soaked thoroughly in distilled water. After 7 days at room temperature, the coupons showed only some white rust and a weight loss of 0.02%. In contrast, the coupons that were not treated with benzaldoxime showed significant build-up of white rust and were severely etched.
The weight loss of untreated coupons was 0.3%. Example 8 A rusty steel guard was lightly brushed to remove rough rust and one cross section was coated with 1,000 g of 5-nonyl-2-hydroxybenzaldoxime.
Treatment was carried out using a brush with a 10% strength by weight solution in 1,1-trichloroethane. Another section of the guard was treated in the same manner with a 10% by weight solution of tannic acid in water. The guard was exposed to the elements on the roof. The sections treated with benzaldoxime developed a dark surface coating in about two days and showed no corrosion over the two month test period. A black coating was formed on the cross section of the guard treated with tannic acid within a few minutes, but the rusting disappeared within a week. Guards treated with benzaldoxime showed no corrosion when exposed to the elements for an additional three months. Example 9 5-nonyl-2-hydroxybenzaldoxime was added at a concentration of 1% by weight to many commercially available cellulose-based primer paints sold as automotive "finish" paints. After thorough mixing, the paint containing benzaldoxime was applied by brushing onto the surface of a mild steel coupon and allowed to dry overnight. A control sample was made in the same manner using non-denaturing paint. Both the test and control samples were pierced through the paint film with a large cross-shaped spot. It was fully immersed in a 3% salt aqueous solution for 3 days. When the coupons were removed and inspected, it was found that the coupons treated in each case with the benzaldoxime-containing paint exhibited rust only within the area of the scratched cross. In contrast,
Coupons treated with non-denaturing paint showed extensive rusting not only within the scratched cross but also in the surrounding painted area. In some cases of commercially available cellulose-based primer paints tested, the adhesion of the paint film to the coupon was broken over a wide area adjacent to the applied cross. Example 10 A commercially available steel "chain wire" of 19 mm diameter was obtained with three treatments: (A) annealed and soaked in acid water; (B) annealed and soaked in acid water and phosphoric acid. treated with zinc; (C) annealed and soaked in acid water followed by oil coating (film thickness 3.7 microns, oil density at 20°C);
0.889g/and coated surface 269m ² /). Samples (A) and (B) were treated with a solution of 5-nonyl-2-hydroxybenzaldoxime in 1,1,1-trichloroethane at various concentrations, and the untreated control sample and sample (C ) was compared. All samples were exposed directly to outdoor roof weather during adverse winter weather. The results obtained are listed in the following table;

[Table] No rust was observed at the end.
EXAMPLE A sample of copper foil (0.1 mm thick) was cleaned with a solvent wash or a short nitric acid wash, and 5-nonyl-
Treated with a 2% ethanolic solution of 2-hydroxybenzaldoxime. All samples were exposed to the elements on a roof for 7 days. During this time, the surface took on a slightly yellowish color, but did not lose its luster. The samples were then washed with acetone to remove the surface treatment, and the surface of the copper foil was once again shiny, with no differences found between the sample and the sample prepared by the nitric acid wash. In comparison, untreated copper foils significantly lost their luster in about one hour, while copper foils treated with a known corrosion inhibitor, benztriazole, lost significantly their luster after 8 days of exposure. Example 12 Typical aluminum alloy BS L70 (Cu4.4%,
5.08cm (2in) of Mg0.5%, Si0.7% and Mn0.8%)
×5.08cm (2in) coupon, 5-nonyl-2
- treated with a 2.5% ethanolic solution of hydroxybenzaldoxime and then immersed in a 1% saline solution for 4 weeks. During this time, the treated surface took on a slightly green color. The surface treatment was then removed by washing with acetone, revealing the original shiny surface.
No corrosion/pitting was observed. In contrast, control coupons that were not treated with aldoxime became cloudy, did not lose their white color, and were
It showed significant pitting after being immersed for a week. Example 13 Tin-coated steel coupons (tin 0.5 g/m ² ) were
- Treated with a 2% ethanolic solution of nonyl-2-hydroxybenzaldoxime. A commercially available epoxy lacquer was then used and cured in an oven at approximately 200° C. for 10 minutes. The large cross was scratched onto a cured Lutzker film and the coupon was then placed in a salt spray chamber for 24 hours.
The band around the cross-shaped area took on a purple color, but corrosion of the film was not a problem. In contrast, the same tin-coated steel coupons that had been subjected to conventional chromate treatment prior to use with Lutzker showed significant corrosion of the film near the cross-shaped points after 24 hours in a salt spray chamber. . Example 14 5-nonyl-2-hydroxybenzaldoxime was added at a concentration of 5% by weight to a solution of an acrylic polymer in technical grade methyl alcohol at 16% solids. After thorough mixing, the benzaldoxime-containing polymer mixture is applied by brushing onto the surface of a mild steel coupon, dried and
Allowed to cure for several hours. A control sample using an acrylic polymer solution but containing no benzaldoxime was prepared in the same manner. Both test and control samples were soaked in distilled water for several days. When the coupons were removed and tested, the coupons treated with the benzaldoxime-containing polymer showed only slight rust within the range of application. In contrast, control coupons treated with unmodified polymers exhibited significant under-film rusting resulting from scratching as well as extensive film failure. Example 15 Mild steel coupons were treated with an acrylic polymer solution containing 2-hydroxy-5-nonylbenzaldoxime as in Example 14 and exposed together with a control coupon having an acrylic coating containing no benzaldoxime. exposed to the elements on the roof. 4
When tested after a week's exposure, the test samples treated with the polymer solution containing benzaldoxime showed little rusting except for a few spots within the exposed zones. In contrast, the control coupons rusted significantly within the struck zone and exhibited under-film corrosion in adjacent zones. Further wide spots appeared on the surface, indicating that the polymer film was broken.

Claims (1)

[Scope of Claims] 1. The metal is optionally substituted 2-hydroxy-5-alkylbenzaldoxime (5-
A method for inhibiting corrosion of metals, characterized in that the alkyl substituents have 7 to 13 carbon atoms. 2. The method according to claim 1, wherein the metal is iron, zinc, copper, tin or aluminum. 3. The method according to claim 2, wherein the metal is a zinc surface of mild steel or galvanized steel. 4 5-alkyl substituents are heptyl, octyl,
A method according to any one of the preceding claims, wherein the nonyl or dodecyl. 5. Process according to any one of the preceding claims, in which benzaldoxime is used on the surface of the metal in the form of a solution in an organic solvent. 6. The method of claim 5, wherein the solution contains 0.1 to 10% by weight of benzaldoxime. 7. Benzaldoxime is used on the surface of the metal in the form of a water emulsion of benzaldoxime or as a water emulsion of a solution of benzaldoxime in an organic solvent.
~The method according to any one of paragraphs 5 to 5. 8 Water emulsion is benzaldoxime 0.1~
8. A method according to claim 7, containing 5% by weight. 9. A method according to any one of the preceding claims, wherein the benzaldoxime is formulated as a surface coating composition. 10 optionally substituted 2-hydroxy-5-alkylbenzaldoximes (5-alkyl substituents have 7 to 13 carbon atoms) 0.1 to 10
A solvent-based metal coating composition containing % by weight. 11 optionally substituted 2-hydroxy-5-alkylbenzaldoximes (5-alkyl substituents have 7 to 13 carbon atoms) 0.1 to 5
A water emulsion matrix metal coating composition containing % by weight.