Corrosion inhibitors

Abstract

Corrosion protection agents, in particular for cavity preservation, containing: - at least one corrosion protection additive selected from alkali and alkaline earth sulfonates, salicylates, wool grease and combinations thereof, - at least one unsaturated compound (1) selected from unsaturated oils, unsaturated fats and / or unsaturated fatty acids, wherein a proportion of the unsaturated compound (1) is 1.5 to 2.1% by mass, based on the total weight of the corrosion inhibitor, and - urea (8) and / or at least one urea derivative, wherein a proportion of the urea (8) and / or the at least one urea derivative is less than 5% by mass, based on the total weight of unsaturated compound (1).

Description

[0001] The present invention relates to a corrosion inhibitor which is used in particular in cavity preservation, i.e. in cavities such as those found in vehicle bodies.

[0002] Cavity preservatives are particularly well-known in vehicle construction and, when applied to a metallic element, for example, they offer effective protection against corrosion when exposed to water or a moist environment. Common cavity preservatives contain waxes, greases, oils, or resins, as well as corrosion protection additives that are made applicable by dispersing them in solvents. The waxes, greases, or oils used are made adhesive, for example, through oxidative curing. This process produces aldehydes as decomposition products. Due to the harmful and odor-impairing effects of aldehydes, corrosion inhibitors that prevent or at least reduce the release of aldehydes would be advantageous.

[0003] DE 19 32 514 A describes a rust-protective polyolefin composition containing dicyclohexylammonium salts of aliphatic carboxylic acids.

[0004] CN 1 05 601 898 A relates to a water-based alkyd resin with excellent corrosion resistance and a process for its production, and belongs to the technical field of chemical engineering. The water-based alkyd resin is made from 10-20% by weight of long-chain diol, 1-10% by weight of polyhydric alcohol with at least three hydroxide residues, 10-35% by weight of long-chain diacid with at least six carbon atoms, 3-15% by weight of polybasic carboxylic acid with at least three carboxyl groups, 15-35% by weight of oleic acid, 1-10% by weight of urea, and substances containing imino groups.The preparation process includes the steps of adding urea to oleic acid and anhydride, introducing imino groups, adding a long-chain diacid, a polyhydric alcohol and a polybasic carboxylic acid, carrying out heating and dehydration for polymerization reaction until the acid value of the system is below 15 mg. KOH / g, carrying out a polymerization reaction of the mixture together with polybasic carboxylic acid until the acid value of the system reaches 30-60 mgKOH / g, and adding a neutralizer for neutralization and dilution to obtain the water-based alkyd resin.

[0005] WO 93 / 14166 A describes a corrosion protection paint of a type containing one or more polymeric binders dispersed in a liquid medium. The corrosion protection paint contains one or more neutral conjugated homopolymers or copolymers in an amount of 2 to 20 wt.% of the dried paint, the amount being within a range such that the electrical conductivity of the dried paint is less than 10 -9 S / cm, measured using the four-in-line probe method.

[0006] DE 10 2011 053 509 A1 discloses a method for the electroless coating of substrates comprising the steps: I. Providing a substrate, II. If appropriate, cleaning the substrate, III. Applying an activation layer of polyelectrolyte and / or salt with a first aqueous composition (= activating agent), IV. If appropriate, intermediate drying of the activation layer, V. Rinsing the activation layer, wherein the activation layer is not completely removed, VI. Contacting and coating the activated surfaces remaining after rinsing with an aqueous composition in the form of a solution, emulsion and / or suspension to form an organic subsequent layer (= precipitation layer), VII. If appropriate, rinsing the subsequent layer, VIII.Drying, wherein the activation layer is coated with an aqueous activating agent in the form of a solution, emulsion and / or suspension which contains at least one cationic polyelectrolyte and / or at least one cationically active salt dissolved in water, wherein the aqueous composition for forming the subsequent layer has precipitable, precipitable and / or saltable components which are anionically, zwitterionically, sterically and / or cationically stabilized, in which anionically and cationically stabilized components do not interfere with one another, and wherein the dry film formed from the activation layer and the subsequent layer has a thickness of at least 1 µm.

[0007] Based on this prior art, it is therefore the object of the present invention to provide a corrosion inhibitor which is characterized by a low release rate of aldehydes and is therefore safe to use, harmless to health and odor-optimized.

[0008] This object is achieved by a corrosion inhibitor containing at least the following components: a) at least one corrosion inhibitor additive, b) at least one unsaturated compound selected from unsaturated oils, unsaturated fats, and / or unsaturated fatty acids, and c) urea and / or at least one urea derivative. The corrosion inhibitor is particularly designed for cavity preservation, for example, for use in vehicle construction, and is suitable for application using conventional methods.

[0009] As the first essential component, the corrosion inhibitor according to the invention contains at least one corrosion inhibitor additive. A corrosion inhibitor additive can be used alone or in combination with corrosion inhibitors. The corrosion inhibitor(s) to be used are selected from alkali and alkaline earth sulfonates, salicylates, wool fat, and combinations thereof. Calcium sulfonate is particularly preferred because it is available at moderate prices and, in addition to being easy to process, offers very good corrosion protection.

[0010] Another essential requirement is at least one unsaturated compound selected from unsaturated oils, unsaturated fats, and / or unsaturated fatty acids. An unsaturated compound can be used alone, or a combination of two or more unsaturated compounds from unsaturated oils, unsaturated fats, and / or unsaturated fatty acids can be used. The unsaturated compound imparts a water-repellent effect to the corrosion inhibitor. It can be made adhesive through oxidative curing and thus bonded to the surface to be protected. However, the unsaturated compounds are also responsible for aldehyde formation. A reaction mechanism is postulated in which a hydrogen atom is first abstracted from the unsaturated compound. This creates a radical that, upon addition of oxygen, forms a hydroperoxide, which is subsequently cleaved into aldehydes.

[0011] To curb the formation of free aldehydes, the invention specifically utilizes urea and / or at least one urea derivative, which reacts with the resulting aldehyde in a (poly)condensation reaction and binds it. Thus, the formation of free aldehydes is prevented or at least significantly reduced, so that the corrosion inhibitor can be classified as user-friendly and harmless from a health perspective. By preventing the release of aldehydes, odor impairment is also effectively prevented. The application and processing of the corrosion inhibitor according to the invention thus offers significant advantages.

[0012] Examples of urea derivatives include melamine, dimethyl urea, ethylene urea, dicyandiamide, thiourea, and diaminohexane. Urea is particularly preferred because it is water-soluble, thus offering good processability, and is also safe from a toxicological and health perspective. Urea is also preferred for cost reasons.

[0013] Other common additives, such as solvents, color additives, fillers, rheology additives, anti-skinning agents and the like, can complete the corrosion inhibitor according to the invention.

[0014] The subclaims contain advantageous developments and refinements of the invention.

[0015] To particularly effectively prevent the formation of free aldehydes, the invention provides that the proportion of urea and / or the at least one urea derivative is less than 5% by mass and advantageously 0.1% to 1.2% by mass, in each case based on the total weight of unsaturated compound. These small amounts are already sufficient to bind resulting aldehydes by polycondensation and convert them into a harmless and odor-reduced polymer. If several urea derivatives or urea with one or more urea derivatives are used in combination, the total content of urea and urea derivatives is less than 5% by mass and in particular 0.1% to 1.2% by mass, based on the total weight of unsaturated compound.

[0016] In order to achieve a very good water-repellent effect and reduce sensitivity to moisture, the invention further provides that the proportion of the unsaturated compound is 1.5 to 2.1 mass%, in particular 1.8 to 1.9 mass%, based on the total weight of the corrosion inhibitor. If several unsaturated compounds are used in combination, the total content of unsaturated compounds is 1.5 to 2.1 mass%, and in particular 1.8 to 1.9 mass%, based on the total weight of the corrosion inhibitor.

[0017] Due to its good reactivity and its environmentally and health-safe application, the unsaturated compound is preferably selected from natural oils. For cost reasons, as well as its high reactivity to oxidative curing, the unsaturated compound is preferably selected from linseed oil, peanut oil, olive oil, safflower oil, walnut oil, sunflower oil, rapeseed oil, almond oil, grapeseed oil, and pumpkin seed oil. Particularly suitable fatty acids include linoleic acid, oleic acid, linolenic acid, and naphthenic acid.

[0018] The corrosion inhibitor further advantageously contains at least one redox-active metal salt and / or metal oxide. The redox-active metal salt or metal oxide is not specifically restricted, as long as the metal atom contained can exist in multiple oxidation states, which is a prerequisite for redox activity. It accelerates the oxidative curing of the unsaturated compound. Preferred metal oxides are those of iron and manganese, with manganese oxides being able to exist in all oxidation states, such as Mn(II / III / IV / V / VI) oxide. Co(III) oxide and Co(II) oxide are also suitable.

[0019] For environmental protection reasons, occupational safety aspects and from a toxicological point of view, the redox-active metal salt or metal oxide is preferably at least one iron oxide and in particular FeO, Fe2O3 and / or Fe3O4.

[0020] A further advantageous development provides for the redox-active metal salt or metal oxide to be transparent. This transparency not only has optical advantages (no color impairment due to the corrosion inhibitor according to the invention), but is also advantageous with regard to the catalytic rate. It is assumed that transparent metal salts and metal oxides are so small particles and yet have such a large surface area that they are particularly easily oxidized or reduced.

[0021] To increase the reaction rate of the crosslinking or curing reaction of the corrosion inhibitor, the proportion of the redox-active metal salt and / or metal oxide is advantageously selected to be between 0.0015 and 0.004 mass%, and in particular between 0.002 and 0.003 mass%, based on the total weight of the corrosion inhibitor. If multiple metal salts and / or metal oxides are present, the quantities refer to the sum of all metal salts and metal oxides.

[0022] According to a further advantageous development, the corrosion protection agent contains, in particular, at least one curable resin, preferably a compound that crosslinks through radical polymerization. This can permanently increase the corrosion protection effect.

[0023] The compound crosslinked by radical polymerization is not specifically limited. According to the invention, it is an unsaturated resin, i.e., a polymeric compound that is unsaturated and thus contains one or more double bonds. The compound crosslinked by radical polymerization contributes to the formation of the preservative anti-corrosive film. The crosslinking reaction of the crosslinking compound hardens the protective film, forming a two- or even three-dimensional structure that is resistant to the effects of moisture and is not attacked by water. This reaction can be accelerated by the addition of a redox-active metal salt and / or metal oxide.

[0024] Further advantageous in light of a good water-repellent effect and high mechanical stability, the compound crosslinked by radical polymerization is preferably selected from unsaturated alkyd resins, unsaturated acrylic resins and unsaturated polyesters.

[0025] According to a further advantageous development of the corrosion inhibitor according to the invention, it further contains at least one metal soap. Suitable metal soaps include zinc(II) soaps and calcium(II) soaps. Calcium stearate and / or zinc stearate are particularly suitable. The use of metal soaps initiates a further drying mechanism: The metal ion of the metal soap has a coordinating effect on polar groups, particularly on carboxyl groups and hydroxyl groups. This means that the metal ion intercalates between the polar groups, such as those that may be present, for example, in the unsaturated compound or the compound crosslinked by radical polymerization, thereby enabling a type of physical crosslinking. This contributes to the overall crosslinking rate and thus to the drying speed.

[0026] Furthermore, the proportion of the metal soap(s) is advantageously 0.01 to 0.10 mass%, and in particular 0.02 to 0.07 mass%, based on the total weight of the corrosion inhibitor. This allows the curing compounds to dry thoroughly, thus forming a particularly durable corrosion protection film.

[0027] Further details, features, and advantages of the invention will become apparent from the following description and the figures. They show: Fig. 1 a reaction scheme for the formation of aldehydes from unsaturated compounds and Fig. 2 a reaction scheme for preventing the formation of free aldehydes in an advantageous further development of the corrosion inhibitor.

[0028] The present invention is explained in detail using an exemplary embodiment. The figures depict only the aspects of interest with regard to the corrosion inhibitor according to the invention; all other aspects have been omitted for the sake of clarity.

[0029] In detail, Fig. Figure 1 shows a possible reaction scheme for the formation of free aldehydes 5, 6 from unsaturated compounds as used in the present invention. Reference numeral 1 thus represents an unsaturated compound selected from unsaturated oils, unsaturated fats, and / or unsaturated fatty acids. The radicals R and R' are any radicals, for example, hydrocarbon radicals.

[0030] The unsaturated compound 1 reacts with a radical R''· (where the radical R'' is any radical and, for example, a hydrocarbon radical) with elimination of R''H and formation of a radical of the unsaturated compound 2, which can exist in several mesomeric forms, as indicated by the double arrows and the square brackets.

[0031] Subsequently, the diradical oxygen attaches to form a hydroperoxide radical 3, which in turn can exist in several mesomeric forms.

[0032] The hydroperoxide radical 3 then attaches to a double bond to form a four-membered ring transition state. The unstable intermediate 4 is obtained.

[0033] The unstable intermediate 4 finally reacts with R''H to release R''· and form two aldehydes 5, 6.

[0034] Fig.Figure 2 illustrates a possible reaction scheme for preventing the formation of free aldehydes or for binding aldehydes by a polycondensation reaction as triggered by the corrosion inhibitor according to the invention.

[0035] Thus, aldehyde 7 (where R is any residue, for example a hydrocarbon residue) reacts with urea 8 to release n moles of water and form a polycondensation product 9.

[0036] The reaction is pH-dependent, meaning that depending on the pH, polymer chains of varying lengths form in the polycondensation product 9, with the elimination of water. An optimal reaction condition for long-chain polymerization is an acidic pH. However, polycondensation also occurs at neutral or basic pH values. However, low-molecular-weight compounds are preferentially formed, which is irrelevant for the binding of the aldehydes and thus for minimizing odor and ensuring the corrosion inhibitor's safety.

[0037] It was found that an addition of just 1 mass% urea, based on the total weight of unsaturated compound, achieved a reduction in aldehyde emission of 50 to 75%.

[0038] The foregoing description of the present invention is for illustrative purposes only and not for the purpose of limiting the invention. Various changes and modifications are possible within the scope of the invention and its equivalents. List of reference symbols: 1 unsaturated compound 2 Radical of the unsaturated compound 3 Hydroperoxide radical 4 unstable intermediate 5 Aldehyde 6 Aldehyde 7 Aldehyde 8 Urea 9 Polycondensation product

Claims

[1] Corrosion protection agents, in particular for cavity preservation, containing: - at least one corrosion protection additive selected from alkali and alkaline earth sulfonates, salicylates, wool grease and combinations thereof, - at least one unsaturated compound (1) selected from unsaturated oils, unsaturated fats and / or unsaturated fatty acids, wherein a proportion of the unsaturated compound (1) is 1.5 to 2.1% by mass, based on the total weight of the corrosion inhibitor, and - urea (8) and / or at least one urea derivative, wherein a proportion of the urea (8) and / or the at least one urea derivative is less than 5% by mass, based on the total weight of unsaturated compound (1). [2] Corrosion protection agent according to claim 1, characterized bythat a proportion of the urea (8) and / or of the at least one urea derivative is 0.1 mass% to 1.2 mass%, based on the total weight of unsaturated compound (1). [3] Corrosion protection agent according to claim 1 or 2, characterized by that a proportion of the unsaturated compound (1) is 1.8 to 1.9 mass%, based on the total weight of the corrosion inhibitor. [4] Corrosion protection agent according to one of the preceding claims, characterized by that the unsaturated compound (1) is selected from natural oils, in particular from linseed oil, peanut oil, olive oil, safflower oil, walnut oil, sunflower oil, rapeseed oil, almond oil, grape seed oil and pumpkin seed oil or from linoleic acid, oleic acid, linolenic acid and naphthenic acid. [5] Corrosion protection agent according to one of the preceding claims, further comprising at least one redox-active metal salt and / or metal oxide. [6] Corrosion protection agent according to claim 5, characterized bythat the redox-active metal salt or metal oxide is a cobalt oxide, manganese oxide or iron oxide and in particular FeO, Fe2O3 or Fe3O4. [7] Corrosion protection agent according to claim 5 or 6, characterized by that the redox-active metal salt or metal oxide is transparent. [8] Corrosion protection agent according to one of claims 5 to 7, characterized by that a proportion of the redox-active metal salt and / or metal oxide is 0.0015 to 0.004 mass%, in particular 0.002 to 0.003 mass%, based on the total weight of the corrosion inhibitor. [9] Corrosion protection agent according to one of the preceding claims, further comprising at least one curable resin, in particular a compound crosslinked by radical polymerization. [10] Corrosion protection agent according to claim 9, characterized by that the curable resin is selected from unsaturated alkyd resins, unsaturated acrylic resins and unsaturated polyesters. [11] Corrosion protection agent according to one of the preceding claims, further comprising at least one metal soap, in particular calcium stearate and / or zinc stearate. [12] Corrosion protection agent according to claim 11, characterized by that the proportion of the metal soap is 0.01 to 0.10 mass%, in particular 0.02 to 0.07 mass%, based on the total weight of the corrosion inhibitor.

Images