DE102005023729A1 - Corrosion inhibitor and method for its current-free application - Google Patents

Abstract

The invention relates to an aqueous corrosion inhibitor for metallic substrates having a pH between 1 and 5, characterized in that it DOLLAR A a. at least one compound with a lanthanide metal as cation and / or a d-element metal with the exception of chromium as cation and / or a d-element metalate with the exception of chromium-containing metalates as anion and DOLLAR A b. contains at least one acid capable of oxidation with the exception of phosphorus-containing and / or chromium-containing acids. DOLLAR A Furthermore, the invention relates to a method for coating substrates with the aqueous corrosion inhibitor according to the invention.

Description

method and coating agent for electroless anti-corrosion coating Various metal substrates are known. They offer in comparison for anodic or cathodic corrosion protection coating in particular the advantage of the simpler and cheaper process as well as the shorter Process time.

at The electroless anti-corrosion coating has been used in the past in particular worked with chromium (VI) -containing coating compositions, since such coating agents offer a high degree of corrosion protection, easy to apply and cheap, if damaged by scratching yourself Heal and good adhesion of other layers of paint, which be applied to such a corrosion protection layer, ensure. In younger It has been found, however, that chromium (VI) -containing coating compositions size Problems with the environmental compatibility and classified as highly hazardous to health. Therefore One strives to fully chromium (VI) in anti-corrosion coatings replace.

The phosphating also used in the prior art is also ecological questionable, because next to the hypertrophierenden phosphate ions continue Nickel and cobalt ions are used. Continue to be at the phosphating big Converts amounts of the substrate metal into ions, which is undesirable in many cases. In addition, phosphating baths contain usually complex fluorides around precipitation-related sludge formation during the conversion process too avoid. Furthermore, there are a variety of chromium-free corrosion protection coating agents, which contain cobalt as a chromate and other metal fluorides. The fluorine-containing systems are particularly useful in the disposal of Metal substrates coated with such systems as critically classified as hydrogen fluoride released during recycling of the metal substrates can be.

In the consequence of the development of chromium-free coating agents further stated that in particular Coating compositions containing salts of lanthanide and d elements also a very good, the chromium-containing coating compositions to ensure comparable corrosion protection during current-free deposition.

In EP-A-1 217 094 discloses a conversion protective layer for aluminum described, which is deposited in a two-stage process. In the first Step become so-called anodic inhibitors, such as Permanganate, tungstates, vanadates or molybdate, from an aqueous solution with deposited at a pH of about 11 to 12 on the aluminum substrate. In the second step, so-called cathodic baths are made in another bath Inhibitors, such as lanthanide salts, such as cerium or Praseodymium salts, from an aqueous solution at deposited at a pH of about 3.5 on the first layer. This Two-stage process has the advantage that the deposition at room temperature whereas the process is due to its two-stage is consuming.

EP-A-0 534 120 also describes a two-step process for deposition a conversion protective layer for aluminum. In a first Step is the cleaned aluminum surface with deionized water at temperatures of 50 to 100 ° C thus treated that a porous one Aluminum oxyhydroxide layer forms. The thus coated aluminum surface is in a second step at 70 to 100 ° C with an aqueous solution of Combination of cerium salt and a metal nitrate to form the Conversion layer treated. Again, this is one elaborate two-stage process, which depending on the composition of the aqueous solution in the second step yet also the disadvantage of the deposition of other foreign metal ions from the metal nitrate has.

In US-A-5,221,371 are aqueous conversion inhibitors for aluminum surfaces described which Cerium chloride and potassium permanganate included. The deposition of described conversion inhibitor takes place at room temperature, wherein an acidic pH by the hydrolysis of the cerium chloride, which with the aluminum surface responds, is generated. To improve the corrosion protection is an aftertreatment of the conversion protective layer with a alkaline aqueous solution containing Molybdate, nitrite and metasilicates and / or with an organic solution recommended by silanes. Here, too, are therefore for a very good corrosion protection elaborate multi-stage coating processes, even with the help of of organic solvents necessary.

The aforementioned conversion inhibitors are usually on the redox potential of beschich coordinated substrate.

In WO-A-01/86016 describes a corrosion inhibitor which is a Vanadium component and another component that contains a metal selected from the group zirconium, titanium, molybdenum, tungsten, manganese and cerium contains. To have a good stability and to ensure corrosion protection of the conversion protection agent, has to be certain ratio of tri- and tetravalent vanadium to the total vanadium content can be adjusted and an organic compound can be added. To ensure a good adhesion of the corrosion protection layer, has to be Pickling agent, selected from the group of inorganic acids, organic acids and fluorine-containing compounds. The effect of in WO-A-01/86016 described corrosion protection is based in essential on a certain ratio of tri-and tetravalent Vanadium to the total vanadium content, which set comparatively expensive must become. This is exemplified by a mixture of vanadium compounds achieved with different oxidation states of vanadium.

Task and solution

 in the Light of the aforementioned prior art, it was the task the invention, an ecologically largely safe corrosion inhibitor to find, which means a technically easy to carry out Process to be protected Substrate can be applied. In particular, the corrosion inhibitor should in a one-step process preferably low temperatures can be applied in a relatively short time be. The influence of Foreign metal ions and corrosive removal of substrate metal preferably be kept low. Furthermore, the corrosion inhibitor should for as possible many different metal substrates develop effective protection and largely independent from the redox potential of the substrate to be coated.

• (A) mindestens eine Verbindung mit einem Lanthanid-Metall als Kation und/oder einem d-Element-Metall mit Ausnahme von Chrom als Kation und/oder einem d-Element-Metallat mit Ausnahme von chromhaltigen Metallaten als Anion sowie
• (B) mindestens eine zur Oxidation befähigte Säure mit Ausnahme von phosphorhaltigen und/oder chromhaltigen Säuren

enthält.In the light of the aforementioned objects, an aqueous corrosion inhibitor for metallic substrates having a pH of between 1 and 5 was surprisingly found

• (A) at least one compound with a lanthanide metal as cation and / or a d-element metal with the exception of chromium as cation and / or a d-element metalate with the exception of chromium-containing metalates as anion, and
• (B) at least one acid capable of oxidation with the exception of phosphorus-containing and / or chromium-containing acids

contains.

Farther became a one-step process for corrosion protection equipment metallic Substrates found, characterized in that the substrate in a bath of immersed in the aforementioned corrosion inhibitor, wherein the Corrosion inhibitor is deposited electrolessly.

Description of the invention

Component A of the coating composition according to the invention

The the component A forming salt has as a cationic component Lanthanidemetallkationen and / or d-metal cations.

preferred Lanthanide metal cations are lanthanum, cerium, praseodymium, neodymium, Promethium, samarium, europium and / or dysprosium cations. All Particularly preferred are lanthanum, cerium and Prasedymkationen. The Lanthanide metal cations can in one-, two-, three- and / or tetravalent oxidation state, wherein the trivalent and / or tetravalent oxidation state is preferred.

preferred d-metal cations are titanium, vanadium, manganese, yttrium, zirconium, Niobium, molybdenum, tungsten, Cobalt, ruthenium, rhodium, palladium, osmium and / or iridium cations. Excluded as d-element cation is the chromium cation in all oxidation states. Very particular preference is given to vanadium, manganese, tungsten, molybdenum and / or yttrium cations. The d-element cations can in mono- to hexavalent oxidation state, with a three to six valent oxidation state is preferred.

The salts of the abovementioned cations of component (A) are preferably very readily soluble in water Lich. Particular preference is given to salts [cation] n [anion] m (with n, m> = 1) having a solubility product LP = [cation] ⁿ · [anion] ^m > 10 ^-8 · mol ^{(n + m)} / I ^{(n + m)} , most preferably salts with a solubility product LP> 10 ^-6 · mol ^{(n + m)} / I ^{(n + m)} . In a very particularly preferred embodiment of the invention, the concentration of the salt or salts (A) in the corrosion inhibitor is from 10 ^-1 to 10 ^-4 mol / l, in particular from 5 · 10 ^-1 to 10 ^-3 mol / l.

The become the anions forming the salts (A) with the d-element cations preferably in such a way selected, that the above conditions for the solubility product P are given. Anions of oxidizing acids are preferred Elements of VI., VII. And VIII. Subgroup of the Periodic Table the elements and anions of oxidizing acids of the elements of V. and VI. Main group of the periodic system of the elements with the exception of Anions of oxidizing acid used by phosphorus and chromium, in particular nitrates, nitrites, Sulfites and / or sulfates. Further preferred as anions are halides except fluorides, in particular chlorides and bromides.

In a further preferred embodiment of the invention the d-element cations are also potentially complexes with mono- and / or multidentate ones anionic ligands present. Preferred ligands are optionally functionalized terpyridines, optionally functionalized Ureas and / or thioureas, optionally functionalized Amines and / or polyamines, in particular EDTA, imines, in particular imino-functionalized pyridines, organosulfur compounds, such as in particular optionally functionalized thiols, thiocarboxylic acids, thioaldehydes, Thioketones, dithiocarbamates, sulfonamides, thioamides and especially preferably sulfonates, optionally functionalized organoboron compounds, in particular boric acid ester, optionally functionalized polyalcohols, in particular Carbohydrates and their derivatives as well as chitosans, if necessary functionalized acids, in particular di- and / or oligofunctional acids, if appropriate functionalized carbenes, acetylacetonates, optionally functionalized Acetylenes, optionally functionalized carboxylic acids, such as especially carboxylic acids, which are bound ionically and / or co-ordinatively to metal centers can, as well as phytic acid and their derivatives.

All particularly preferred ligands are phytic acid, its derivatives and sulfonates, which are optionally functionalized.

In a further embodiment of the invention contain the salts (A) d-element-metalates as anions, that together with the d-element cations or for alone the salt (A) can form. Preferred d elements for the Metallates are vanadium, manganese, zirconium, niobium, molybdenum and / or Tungsten. Very particularly preferred are vanadium, manganese, tungsten and / or molybdenum. As a d-element metalate except chromates in all oxidation states. Especially preferred d-element metallates are oxoanions, in particular tungstates, Permanganate, vanadate and / or molybda-form the d-element-metalates alone, this means without Lanthanidmetallkationen and / or d-metal cations the salt (A), so applies to the preferred solubility product LP of such salts the predicted. Preferred cations of such salts are optionally substituted with organic radicals ammonium ions, Phosphonium ions and / or sulfonium ions, alkali metal cations, in particular lithium, sodium and / or potassium, alkaline earth metal cations, in particular beryllium, magnesium and / or calcium. Especially preferred are those optionally substituted with organic radicals Ammonium ions and the alkali metal cations, which are a particularly high solubility product Ensure LP of salt (A).

When Component (B) of the corrosion inhibitor according to the invention if at least one acid capable of oxidation is used in such a way, that the pH of the anticorrosive agent between 1 and 5, preferably between 2 and 4 lies. Preferred acids (B) are selected from the group of oxidising mineral acids, in particular nitric acid, nitrous Acid, sulfuric acid and / or sulphurous acid.

to Adjustment of the pH can, if necessary, a buffer medium used such as salts of strong bases and weak acids, such as in particular ammonium acetate.

When continuous phase is for the coating composition according to the invention Water is used, preferably deionized and / or distilled Water.

Prior to the application of the coating composition according to the invention, the substrate is purified in a preferred embodiment of the invention, in particular of oily and greasy residues, preference being given to using detergents and / or alkaline cleaning agents. In a further preferred embodiment of the invention, the cleaning with detergents and / or alkaline cleaning agents is rinsed again with water before the application of the coating composition according to the invention. For the removal of deposits and / or chemically modified, in particular oxidized, layers On the surface of the substrate, in a further preferred embodiment of the invention, before the rinsing step, a mechanical cleaning of the surface, for example with grinding media, and / or a chemical removal of the surface layers, for example with deoxidizing cleaning agents, take place.

The thus pretreated substrate is treated with the corrosion inhibitor according to the invention in Brought in contact. This is preferably done by immersion or Passing the substrate through or through a bath containing the corrosion inhibitor of the invention. The residence times of the substrate in the corrosion inhibitor according to the invention are preferably 1 second to 10 minutes, preferably 10 seconds to 8 minutes and more preferably 30 seconds to 6 minutes. The temperature of the bath containing the corrosion inhibitor of the invention is preferably between 25 and 90 ° C, preferably between 30 and 80 ° C, especially preferably between 35 and 70 ° C.

To the treatment of the substrate with the corrosion inhibitor according to the invention is preferably a drying of the composite of substrate and corrosion inhibitor by dry blowing or by drying at temperatures between about 30 and 200 ° C carried out, wherein the drying temperature and the type of drying or apparatus for the advantageous effect of the corrosion protection agent according to the invention can be considered largely uncritical.

The Corrosion inhibitors according to the invention can be surprising on a big one Spectrum of substrates are used and is broad independent of the redox potential of the substrate. Preferred substrate materials are zinc, iron and aluminum, and their alloys, the The aforementioned metals preferably at least 20 wt .-% in the alloys available. Preferably, the substrates are formed as sheets, such as in the automotive industry, the construction industry and the mechanical engineering industry. The with the coated corrosion inhibitor according to the invention Sheets are used especially for shaped sheets and for coil coating (Coil coating) of sheet metal for use.

In a most preferred embodiment of the invention the corrosion inhibitors of the invention for sealing cut edges of the sheets described above used. In particular, there is the sealing of the cut edges of already coated sheets.

In a further embodiment The invention relates to the invention with the corrosion inhibitor coated substrates with further also electrolessly depositable Coating coated. Preference is given to coating compositions with organic ingredients that have both good adhesion to the Layer of the corrosion protection agent according to the invention as well as the uncoated substrate. Such organic Coating agents are described, for example, in DE-A-37 27 382, WO-A-99/29927, WO-A-01/86016 and WO-A-96/10461.

The in the following Examples are intended to further illustrate the invention.

Example 1a: Production the corrosion protection agent according to the invention 1a

In One liter of distilled water is added to 1.77 g (0.01 mol) of ammonium molybdate tetrahydrate and 3.83 g (0.01 mol) of yttrium nitrate hexahydrate.

The solution is made by nitric acid adjusted to a pH = 2.5. If necessary, the setting of the The above-mentioned pH counter-buffered with aqueous ammonia solution.

Example 1b: Preparation the corrosion protection agent according to the invention 1b

In one liter of distilled water is added to 1.77 g (0.01 mol) of ammonium molybdate tetrahydrate, 3.83 g (0.01 mol) of cerium nitrate hexahydrate and 16.5 g of phytic acid (0.025 mol) dissolved.

The solution is made by nitric acid adjusted to a pH = 2.5. If necessary, the setting of the The above-mentioned pH counter-buffered with aqueous ammonia solution.

Example 2: Coating the substrate with the corrosion inhibitor according to the invention

The Substrate (Example 2a: Sheet steel, Example 2b: sheet of galvanized Steel) is 5 minutes at 55 ° C in a cleaning solution (Ridoline C72 Henkel) and then with distilled water rinsed.

Subsequently, will The rinsed with distilled water plate is immediately at 45 ° C for 4 minutes with the conversion agent according to example 1a and alternatively treated with the conversion agent 1b. After that The coated sheet is rinsed with distilled water and with Nitrogen is blown dry.

The coated sheets and the reference samples mentioned below cut with a tin snips to free edges on all sheets to obtain.

When Reference for the example of the invention 2a becomes Gardobond 958W (Chemetall GmbH: sheet steel with phosphating and rinsing with zirconium hexafouride solution) also for the example of the invention 2b Gardobond 958 54 (Fa.Chemetall GmbH: galvanized sheet steel with phosphating and rinsing with zirconium hexafouride solution) used.

Example 3: Rapid corrosion test with 3% aqueous sodium chloride solution according to example 2 coated substrates

It becomes a solution of 3% sodium chloride in demineralized water. As substrates can Here steel, galvanized steel or zinc alloys can be used. For aluminum and its alloys, the sodium chloride solution is additionally mixed with acetic acid set a pH = 3. The samples (3 x 3 cm) are placed in 170 ml of these solution immersed in a desiccator at almost 100% humidity stored. The humid atmosphere is made by grease-free compressed air generated by two wash bottles with demineralized water is passed and then flows through the desiccator. This structure is a constant humidity and a constant Ensures carbon dioxide content, the temperature being kept at 25 ° C becomes. The samples are dipped on an analytical balance before immersion weighed. Non-treated reference plates (steel, galvanized steel) be for Purified for 5 minutes in ethanol in an ultrasonic bath. After 24 hours Storage, the sheets are removed from the solution and with a Disposable pipette over The beaker is rinsed with the loaded 3% sodium chloride solution (about 10 ml of sodium chloride solution each Sample side). The sheet is then dry with nitrogen blown and for 15 minutes at 50 ° C dried and weighed. The sheet is then again in a fresh Sodium chloride solution the same concentration. The used sodium chloride solution becomes with 1 ml of a 32% hydrochloric acid offset to solve any precipitation. The resulting clear solution is using ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry) measured on the content of substrate metal (Zn, Fe, Al, Mg).

The The procedure described above is repeated after 24h, 72h, 96h and 168h. The measurement is verified by a double determination.

Evaluation of the corrosion test:

a) ICP-OES data of the immersion solution

The ICP-OES data will be on the surface standardized to the samples. These data give a linear progression. Because of the linearity the corrosion kinetics, can the different coatings through the slopes of the graph be compared. The ICP-OES data gives the resolution of the Substrates per area and time again and are thus a direct measure of the corrosion rate at a respective coating possible is.

b) Weighing the samples

The weighings also give information about the possibilities in how far the coating makes a passivation of the surface possible or not. For this purpose, the weight loss is converted into molarities and normalized to the area of the samples. To compare the corrosion kinetics is the respective substrate, which was only cleaned alkaline. The slopes from the ICP-OES data are then compared to the zero reference (pure substrate) and other references. Table 1: Results of the corrosion test substratum Weight loss (10 ^-4 · mol / l · h · cm ² ) according to ICP-OES Sheet steel (uncoated) 4,098 Steel sheet with conversion agent 1a 1,728 Steel sheet with conversion agent 1b 1,621 Gardobond 958W (reference) 3,410 Galvanized steel sheet (uncoated) 8,136 Galvanized steel sheet with conversion agent 1a 3,487 Gardobond 958 54 (reference) 6,171

The Results of the corrosion tests clearly show the superiority the coating compositions of the invention across from a conventional one Phosphating.

Claims (10)

Aqueous corrosion inhibitor for metallic substrates having a pH of between 1 and 5, characterized in that it contains a. at least one compound with a lanthanide metal as cation and / or a d-element metal with the exception of chromium as cation and / or a d-element metalate with the exception of chromium-containing metalates as anion and b. contains at least one acid capable of oxidation with the exception of phosphorus-containing and / or chromium-containing acids. Anti-corrosion agent according to claim 1, characterized that the Lanthanide metal and / or d-element cations containing compound (A) has at least one component which is selected from the group of anions of oxidizing acids of the elements of VI., VII. And VIII. Subgroup, the elements of the V. and VI. main group of the Periodic Table of the Elements, with the exception of anions of phosphorus and / or chromium-containing acids, the halides except fluoride and the potentially anionic complexing mono- and / or polydentate ligands. Anti-corrosion agent according to claim 2, characterized that at least an anionic component of the compound (A) is selected from the group chloride and bromide as well as the anions of nitric acid, the nitrous acid, sulfuric acid and / or the sulphurous acid. Corrosion inhibitor according to claim 2 or 3, characterized characterized in that at least a component of the compound (A) is selected from the group of potentially anionic inputs and / or polydentate Ligands phytic acid and their derivatives, thioureas and their derivatives, amines, polyamines, Imines, organosulfur compounds, organoboron compounds, polyalcohols, polyacids Carbenes, acetylacetonates, acetylenes and / or carboxylic acids. Corrosion protection agent according to one of claims 1 to 4, characterized in that the Acid (B) is selected from the group of nitric acid, the nitrous acid, sulfuric acid and / or the sulphurous acid. Corrosion protection agent according to one of claims 1 to 5, characterized in that the cationic metals of the compound (A) are selected from the group molybdenum, manganese, Tungsten, vanadium, bismuth, cerium, lanthanum, scandium and / or yttrium. Corrosion protection agent according to one of claims 1 to 6, characterized in that the compound (A) is present in a concentration of 10 ^-4 to 10 ^-4 mol / l. Single-stage process for corrosion protection equipment metallic Substrates, characterized in that the substrate is immersed in a bath of the Corrosion inhibitor according to a the claims 1 to 7 is immersed. Method according to claim 8, characterized in that that this Substrate for a duration of 1 second to 10 minutes in the bath of the corrosion inhibitor is immersed. Process according to Claim 9, characterized in that the substrate contains at least 20% by weight of egg contains metal selected from the group Fe, Al and / or Zn.