Patent Application
20180066365
The present invention relates to a multi-stage method for the anti-corrosive pretreatment of components fabricated from metallic materials, in which a conditioning wet-chemical treatment using an aqueous composition (A) comprising a salt of a quaternary amine is followed by a further wet-chemical treatment based on water-soluble compounds of the elements Zr, Ti and/or Si, during the course of which a corresponding conversion of the surfaces of the metallic materials takes place, which imparts an anti-corrosive primer for additionally applied organic coatings.
The conversion treatment of metallic surface for providing a coating, which offers protection against corrosion, based on aqueous compositions comprising water-soluble compounds of the elements Zr, Ti and/or Si is a technical field that has been extensively described in the patent literature. A wide variety of variants of such a metal pretreatment process are known for improving the properties profile of such conversion treatments as they relate to corrosion protection and imparting sufficient paint adhesion, which are either directed at the composition of the agents bringing about the conversion or draw on further wet-chemical treatment steps in the direct context of the conversion treatment.
EP 1 455 002 A1 for example, describes that it is advantageous for conversion treatment by way of above-described compositions, which additionally comprise fluoride ions as a complexing agent etching the metal surfaces, when an aqueous rinse comprising alkaline reacting compounds directly follows the actual wet-chemical treatment, or when a downstream drying step follows, so as to reduce the fluoride fraction in the conversion layer. Alternatively, adding certain cations selected from calcium, magnesium, zinc, copper or silicon-containing compounds to the composition that brings about the conversion of the surface is used to reduce the fluoride content in the conversion layer.
With respect to further adaptations of the procedure when using fluoride ions and water-soluble compounds of the agents comprising the elements Zr and/or Ti for conversion treatment, WO 2011012443 A1 teaches a downstream aqueous rinse comprising organic compounds that include aromatic heterocyclic compounds comprising at least one nitrogen heteroatom.
Compared to this prior art, the object was to render the anti-corrosive properties of conversion layers more consistent on various metal substrates, obtainable by way of pretreatment with compositions of water-soluble compounds of the elements Zr, Ti and/or Si, and, in particular, to improve these on steel surfaces. In particular, the average creep values in the corrosive delamination after the paint coat structure has been created is to be improved. In a further sub-aspect, the pretreatment is to take place substantially without the presence of fluorides for environmental hygiene reasons. So as to be able to implement this sub-aspect, a pretreatment method according to the present invention must therefore bring about a homogeneous and complete conversion of the so-called “free metal surface,” which is to say the degreased, cleaned metal surface comprising only the natural oxide layer, even in the presence of fluorides. Furthermore, under identical conditions, the variance in the conversion layer should be low, which is to say that, in terms of process engineering, it should be possible to reliably achieve a particular conversion. With respect to the use on various metal substrates, in particular, optimal anti-corrosive action by way of an appropriate wet-chemical pretreatment is desirable for composite structures that, in addition to surfaces made of the material iron and/or steel, also comprise surfaces made of at least one of the materials zinc, galvanized steel and/or aluminum.
This object is achieved by a multi-stage method for the anti-corrosive pretreatment of components fabricated at least partially of metallic materials, wherein initially
The components treated according to the present invention can be any arbitrarily shaped and configured three-dimensional structures, which are created in a fabrication process, in particular also semi-finished products such as ribbons, sheets, rods, tubes and the like, and composite structures joined from the aforementioned semi-finished products.
According to the invention, in the first step i) of the method according to the invention, a conditioning treatment is carried out with the aqueous composition (A) comprising the dissolved and/or dispersed salt of a quaternary organic amine (“conditioning”). As a result of this conditioning, a sufficient and homogeneous layer coating is achieved with respect to the elements Zr, Ti and/or Si in the course of the wet-chemical treatment with an aqueous composition (B), so that a conversion of the metal surfaces of the component takes place effectively, providing a potentially good paint primer. In particular, on steel surfaces, a reproducible layer coating with respect to the elements Zr, Ti and/or Si is achieved in the course of the method according to the invention, this layer coating representing the basis for effectively suppressing corrosive creep on defects in an additionally applied paint coating.
A salt of a quaternary organic amine dissolved or dispersed in water within the meaning of the invention has an average particle diameter of less than 1 μm in the aqueous phase. The average particle diameter can be determined in accordance with ISO 13320:2009 by way of laser diffraction from cumulative particle size distributions in the form of what is known as the D50 value directly in the aqueous composition (A) at 20° C.
The presence of quaternary organic amines in an aqueous composition (A) in step i) increases the suitability of the conversion coating applied in step ii) to serve as a good paint primer. In the context of the present invention, a quaternary organic amine comprises at least one nitrogen atom, which exclusively has covalent bonds with carbon atoms, and thus has a permanent positive charge.
In the context of the present compound, it is preferred that the quaternary organic amines have a weight average molecular weight Mw of less than 5,000 g/mol.
Furthermore, it has been shown that, in particular, heterocyclic compounds comprising at least one nitrogen heteroatom, which exclusively has covalent bonds with carbon atoms, represent suitable quaternary organic amines, so that these are a preferred component of the aqueous composition (A) in a method according to the invention.
In a preferred embodiment, a quaternary organic amine present in the aqueous composition (A) is a heterocyclic compound comprising at least one nitrogen heteroatom of the following chemical formula (I):
comprising the functional groups R1, R2 and R3, which are each selected from hydrogen, branched or unbranched aliphatic compounds having no more than 6 carbon atoms or the functional group —(CR4R4)x—[Z(R4)(p-1)—(CR4R4)y]n—Z(R4)p, where Z is selected from oxygen or nitrogen, p, in the case in which Z is nitrogen, takes on the value 2 and otherwise is equal to 1, x and y are each natural numbers from 1 to 4, n likewise is a natural number from 0 to 4, and R4 is selected from hydrogen or branched or unbranched aliphatic compounds having no more than 6 carbon atoms, with the proviso that at least one of the functional groups R2 or R3 is not selected from hydrogen; comprising Y as a ring-constituting divalent functional group, which comprises no more than 5 bridge atoms, wherein no more than one heterobridge atom different from carbon atoms selected from oxygen, nitrogen or sulfur can be a bridge atom, and the carbon atoms again, independently of one another, are present substituted with functional groups R1 or with functional groups via which an annulation of aromatic homocyclic compounds having no more than 6 carbon atoms is achieved.
In general, it has been found to be advantageous that the quaternary organic amine is represented by heterocyclic compounds that comprise the skeleton of imidazole, imidazoline, pyrimidine, purine and/or quinazoline. In the present context, it is thus preferred that the heterocyclic compound according to chemical formula (I) comprises, as the ring-constituting divalent functional group Y, substituents selected from ethylene, ethenediyl, 1,3-propanediyl, 1,3-propenediyl, 1,4-butanediyl, 1,4-butenediyl, 1,4-butadienediyl, —CH═N—, —CH2—NH—, (N, N-dimethylene)amine, (N-methylene-N-methylylidene)amine, particularly preferably from ethenediyl, 1,4-butadienediyl, —C═N— or (N-methylene-N-methylylidene)amine, especially particularly preferably from ethenediyl or —C═N—, and especially preferably from ethenediyl, wherein in each case hydrogen covalently bound to carbon atoms can be substituted by the remaining representatives of the functional group R1 according to the general chemical formula (I).
Quaternary organic amines that have been found to be particularly advantageous are those selected from 1,2,3-trimethylimidazolium, 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-isopropyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-(n-butyl)-3-methylimidazolium, 1-(isobutyl)-3-methylimidazolium, 1-methoxy-3-methylimidazolium, 1-ethoxy-3-methylimidazolium, 1-propoxy-3-methylimidazolium, and particularly preferably from 1,2,3-trimethylimidazolium.
It is generally advantageous according to the invention when the proportion of the quaternary organic amine in the aqueous composition (A) is at least 0.05 g/kg, preferably at least 0.2 g/kg, and particularly preferably at least 0.4 g/kg, but preferably no more than 5 g/kg, and particularly preferably no more than 10 g/kg.
Above 10 g/kg, no further suppression of the corrosive delamination after the paint structure was created is observed, even when a rinsing step follows the conditioning in step i), so that any amount of the quaternary organic amine that goes beyond this level would be used uneconomically in the method according to the invention.
In general, all anions may be used as the counterion to the quaternary organic amine, in particular sulfates, nitrates, chlorides, carbonates and organic anions such as alkyl sulfates, alkyl sulfonates, alkyl phosphates and/or alkyl phosphonates.
Surprisingly, the presence of anions (K) selected from monoalkyl sulfates, monoalkyl sulfonates, dialkyl phosphates and/or dialkyl phosphonates having preferably no more than 5 carbon atoms, preferably from monoalkyl sulfates and/or monoalkyl sulfonates having preferably no more than 5 carbon atoms, and particularly preferably from methyl sulfate, has been found to be advantageous for a uniform conversion layer formation in step ii) of the method according to the invention, so that the additional presence of these is accordingly preferred.
As a result, the anions (K) are preferably also the anionogenic component of the salt of the quaternary organic amine, so that the corresponding salt thus serves both as a source for the quaternary amine and as a source for the anion (K), and the ion load in the aqueous composition (A) can thus be minimized. In addition to the salts of the alkali metals and/or alkaline earth metals and the corresponding ammonium salts, suitable sources for the anions (K) are thus, in particular, the corresponding salts of the above-described quaternary organic amines.
According to the invention, the proportion of anions (K) in the aqueous composition (A) is preferably at least 0.05 g/kg, particularly preferably at least 0.2 g/kg, and especially preferably at least 0.4 g/kg, however the proportion is preferably no more than 5 g/kg, and particularly preferably no more than 3 g/kg, each calculated as an equivalent amount of SO4 based on the aqueous composition (A). Above 5 g/kg, the conversion layer formation in step ii) is not further increased or made more consistent, even when a rinsing step follows the conditioning in step i), so that any amount of the conditioner that goes beyond this level would be used uneconomically in the method according to the invention.
The pH value of the aqueous composition (A) in step i) can be selected substantially freely and is usually in the range of 2 to 14, preferably above 3.0, particularly preferably above 4.0, and especially preferably above 5.0, but preferably below 12.0, particularly preferably below 10.0, and especially preferably below 8.0.
Moreover, it may be advantageous for the treatment of components that comprise surfaces made of the materials zinc and/or galvanized steel that the aqueous composition (A) additionally contains an amount of iron ions, which, upon contact with the zinc surfaces, results in a thin iron coat structure there, and thus additionally contributes to making the corrosion protection more consistent, which is made available by the method according to the invention in particular for surfaces made of iron material. This kind of ironizing can take place according to the teaching of WO 2008135478 A1 in an acid environment, preferably in the presence of a reducing agent, or according to the teaching of WO 2011098322 A1 in an alkaline environment, preferably in the presence of complexing agents and phosphate ions.
According to the invention, the aqueous composition (A) can comprise further components. In addition to the pH-regulating substances, this may also include surface-active substances, the use of which is preferred in an aqueous composition (A) having cleaning action.
In a preferred embodiment, the aqueous composition (A), however, comprises less than 0.05 g/kg, preferably less than 0.01 g/kg, and particularly preferably less than 0.001 g/kg surface-active compounds which are not composed of quaternary organic amines, so that the interaction of the surface-active compounds with the surfaces of the metallic material of the component does not compete with that of the quaternary organic amine, and thereby counteracts the respective desired technical effect.
Surface-active compounds within the meaning of the present invention have an HLB (Hydrophilic-Lipophilic Balance) value of less than 5 or more than 10. The HLB value is calculated according to the following formula and, on the arbitrary scale, can take on values from zero to 20:
HLB=20·(1−Ml/M).
where MI: molecular weight of the lyophilic group of the non-ionic surfactant; M: molecular weight of the non-ionic surfactant
Furthermore, it is preferred when the aqueous composition (A) in step i) of the method according to the invention comprises, in total, less than 0.5 g/kg, particularly preferably less than 0.1 g/kg, and especially preferably less than 0.05 g/kg dissolved and/or dispersed organic polymers which do not represent quaternary organic amines. As described above with respect to the presence of surface-active compounds, it is thus ensured that the interaction of such polymers with the surfaces of the metallic materials of the component does not compete with that of the conditioner, or the quaternary organic amines additionally present in a preferred embodiment of the present invention, and thereby counteracts the respective desired technical effect. A dissolved or dispersed organic polymer in the present context of the invention has a weight average molecular weight Mw of at least 5,000 g/mol and takes on an average particle diameter of less than 1 μm in the aqueous phase. The average particle diameter can be determined in accordance with ISO 13320:2009 by way of laser diffraction from cumulative particle size distributions in the form of what is known as the D50 value directly in an aqueous composition (A) at 20° C.
In a preferred method according to the invention, no conversion layer is generated on the surfaces of the metallic components in step i). Accordingly, the aqueous composition (A) does not comprise any components in an amount that would allow a conversion layer to form on a surface of a metallic material of the component during the time period provided for the conditioning in step i). A conversion layer during the course of conditioning in step i) of the method according to the invention exists when, on the respective surface of the metallic material, a cover layer is produced, by way of a wet-chemical process, which comprises the phosphates, oxides and/or hydroxides of elements of the titanium group, vanadium group and/or chromium group, or phosphates of the elements calcium, iron and/or zinc in a coat structure of at least 5 mg/m2, based on the respective transition metal, or of at least 50 mg/m2, based on the element phosphorus. The corresponding transition metals can be quantitatively determined by way of X-ray fluorescence (XRF) analysis, while the coat structure, with respect to the element phosphorus, can be quantitatively determined by acid cleaning the surfaces of the metallic materials in aqueous 5 wt. % CrO3 and subsequent atomic emission spectroscopy (ICP-AES).
To prevent the formation of a conversion layer on the surfaces of the metallic materials of the component, a method according to the invention is preferably wherein the aqueous composition (A) in step i) comprises less than 0.005 g/kg, and particularly preferably less than 0.001 g/kg water-soluble compounds of the elements Zr, Ti and/or Si, based on the respective element, preferably less than 1 g/kg water-soluble compounds of the elements Zn, Mn and Ca, based on the respective element, and/or preferably less than 0.05 g/kg, and particularly preferably less than 0.01 g/kg free fluoride, determined by way of a fluoride-sensitive electrode at 20° C. In a further preferred embodiment, the total proportion of fluorides in the aqueous composition (A) is less than 0.05 g/kg, particularly preferably less than 0.02 g/kg, and especially preferably less than 0.01 g/kg. The total proportion of fluorides (total fluoride) is determined in a TISAB buffered aliquot of the aqueous composition (A) by way of a fluoride-sensitive electrode at 20° C. (TISAB: total ionic strength adjustment buffer), wherein the volume-based mixing ratio of buffer to the aliquot of the aqueous composition (A) is 1:1. The TISAB is produced by dissolving 58 g NaCl, 1 g sodium citrate and 50 ml glacial acetic acid in 500 ml deionized water (κ<1 μScm−1) and setting a pH of 5.3 by way of 5 N NaOH, and adding, again, deionized water (κ<1 μScm-1) until a total volume of 1000 ml is reached.
In method step ii), an amount of active components sufficient for forming a conversion layer should be present in the acid aqueous composition (B). In this regard, it is advantageous when the aqueous composition (B) in step ii) preferably comprises at least 0.01 g/kg, particularly preferably at least 0.05 g/kg, and especially preferably at least 0.1 g/kg water-soluble compounds of the elements Zr, Ti or Si, based on the respective element Zr, Ti or Si. In this context, it should be noted that such compounds according to the present invention are considered to be water-soluble if the solubility thereof in deionized water (κ<1 μScm−1) is at least 1 g/L at 20° C.
For economic considerations, it is furthermore advantageous when the total proportion of these compounds, based on the elements Zr, Ti and Si, is preferably no more than 0.5 g/kg, since higher contents usually do not further improve the anti-corrosive properties of the conversion layer, but make it more difficult to control the coat structure with respect to these elements due to higher deposition kinetics.
Due to the conditioning in step i) of the method according to the invention, fluorine-free water-soluble compounds of the elements Zr, Ti or Si are also suitable in the aqueous composition (B) for bringing about sufficient conversion of the surfaces of the metallic materials of the component, and are therefore preferred. (NH4)2Zr(OH)2(CO3)2, ZrO(NO3)2 or TiO(SO4) or silanes comprising at least one covalent Si—C bond are particularly preferred representatives.
As described above, the use of complex fluorides, and also of free fluorides, in step ii) for bringing about the conversion of the surfaces of the metallic materials of the components can be dispensed with in the present method according to the invention due to the conditioning in step i). Accordingly, methods that are preferred according to the invention are those in which the proportion of free fluoride in the aqueous composition (B), with increasing preference, is less than 0.05 g/kg, 0.01 g/kg, 0.001 g/kg and 0.0001 g/kg, and especially particularly preferably no free fluoride is present. Furthermore, in a preferred embodiment of the method according to the invention, the total proportion of fluorides (total fluoride) in the aqueous composition (B), with increasing preference, is less than 0.05 g/kg, 0.02 g/kg, 0.01 g/kg, 0.001 g/kg and 0.0001 g/kg, and especially particularly preferably no fluoride is present. The proportion of free fluoride and the total proportion of fluorides can be ascertained analogously to the procedure that is used to determine the same parameters in the aqueous composition (A).
In combination with the conditioning in step i), the best results with respect to corrosion protection are achieved when copper ions are present in the aqueous composition (B) in step ii). In a particularly preferred embodiment of the method according to the invention, the aqueous composition (B) thus additionally comprises water-soluble compounds that represent a source for copper ions, preferably in the form of water-soluble salts, such as copper sulfate, copper nitrate and copper acetate. In this context, it should be noted that such compounds according to the present invention are considered to be water-soluble if the solubility thereof in deionized water (κ<1 μScm−1) is at least 1 g/L at 20° C.
The content of copper from water-soluble compounds in the aqueous composition (B) is preferably at least 0.001 g/kg, and particularly preferably at least 0.005 g/kg. The content of copper ions, however, preferably does not exceed 0.1 g/kg, and particularly preferably does not exceed 0.05 g/kg, since otherwise the deposition of elemental copper begins to dominate in relation to the conversion layer formation.
The pH value of the aqueous composition (B) is preferably in the acid range, particularly preferably in the range of 2.0 to 5.0, and especially preferably in the range of 2.5 to 3.5.
It is furthermore preferred when the aqueous composition (B) comprises nitrate ions as an accelerator for the conversion layer formation, wherein the proportion of nitrate ions is preferably at least 0.5 g/kg, but for economic reasons preferably does not exceed 4 g/kg.
Surprisingly, the success according to the invention occurs substantially independently of the execution of a rinsing and/or drying step directly after conditioning in step i). Differences in the performance of the method, caused by a rinsing step in between, can be regularly compensated for by moderately increasing the concentration of quaternary organic amine present in the aqueous composition (A) and of the anions (K). In any case, the general suitability of the method for achieving the object of the invention is not affected by the execution of a rinsing and/or drying step between method steps i) and ii). From a process engineering point of view, however, it is preferred that a rinsing step directly follows step i) in a method according to the invention so as to separate the active components in the individual treatment steps, wherein preferably no drying step takes place prior to step ii).
According to the invention, a rinsing step is always used to remove water-soluble residues, chemical compounds that do not firmly adhere, and loose solid particles from the component to be treated, which are dragged out of a preceding wet-chemical treatment step together with the wet film adhering to the component, by way of a water-based liquid medium. The water-based liquid medium does not comprise any chemical components that cause the surfaces of the components fabricated from metallic materials to become significantly covered with transition metals, metalloids or polymeric organic compounds. Such a significant surface coverage, however, exists when the liquid medium of the rinse becomes depleted by at least 10 milligrams per square meter of the rinsed surfaces, and preferably by at least 1 milligram per square meter of the rinsed surfaces, on these components, based on the respective element or the respective polymeric organic compound, without consideration of amounts gained as a result of carry-over and amounts lost due to drag-out by wet films adhering to the component.
According to the invention, a drying step is any method step during which drying of the aqueous liquid film adhering to the surface of the component is intended as a result of the provision and use of technical means, in particular by supplying thermal energy or applying an air current.
The components treated in the method according to the invention are at least partially made of metallic materials. Preferred metallic materials, which clearly exhibit an improvement in the properties of the conversion layer as a paint primer, are iron and iron alloys, and in particular steel. Iron alloys in this context are understood to mean materials in which at least 50 at % of the respective material is formed of iron atoms. On surfaces made of iron and the alloys thereof, a significant improvement in corrosion protection occurs with respect to corrosive creep on defects, which takes place even substantially independently of whether a rinsing and/or drying step follows immediately after conditioning in step i).
In the method according to the invention, step ii) is preferably followed by the application of an organic coating, specifically a powder coating or dip coating, which, in turn, is preferably an electro dip coat. Electro dip-coating preferably takes place in a rinsing step, but particularly preferably not in a drying step.
In a preferred embodiment of the method according to the invention, the component at least partially comprises surfaces made of the materials iron and/or steel, wherein preferably at least 50%, and particularly preferably at least 80% of the surface of the component representing surfaces made of metallic materials are formed of surfaces made of the materials iron and/or steel.
In principle, however, composite structures and, in particular, components that, in addition to surfaces made of the materials iron and/or steel, also comprise surfaces made of the materials zinc and/or galvanized steel and aluminum, which, if necessary, may additionally be present in phosphated form, are treated in the method according to the invention.
Furthermore, it is generally preferred, if the component comprises surfaces made of the materials zinc and/or galvanized steel, that a thin amorphous layer containing iron is applied to these surfaces, so that effective conditioning is likewise imparted to the surfaces made of these materials in step i) of the method according to the invention, such as is usually found for the surfaces made of the materials iron and/or steel. Particularly effective ironizing of the surfaces made of zinc and/or galvanized steel in this regard is described in documents WO 2011098322 A1 and WO 2008135478 A1, in each case in the form of a wet-chemical process, which can be applied in equivalent fashion immediately prior to carrying out method step i) according to the invention. In this respect, it is preferred for methods according to the invention in which the component is made at least partially of the materials zinc and/or galvanized steel that at least 20 mg/m2, preferably, however, no more than 150 mg/m2 of the surfaces of the component fabricated from these materials is covered with iron.
Hereafter, sheets made of steel (CRS) are subjected to a multi-stage process for anti-corrosive pretreatment. The suitability of metal sheets thus pretreated and provided with a paint coat to serve as a good paint primer is examined in a test according to DIN EN ISO 4628-8 for corrosive delamination.
The general method for pretreatment and coating comprises the successive mandatory and optional individual steps (A) to (E):
Table 1 below shows the different organic compounds used in the conditioning in step (C).
Subsequent to the conversion treatment in method step (E), the respective sheet was first rinsed with deionized water (κ<1 μScm−1) at 20° C. and then coated with a cataphoretic paint and dried at 180° C. (dry layer thickness: 18 to 20 μm; CathoGuard® 800 from BASF Coatings).
It is apparent from a review of the results of Table 2 that, on steel sheets, a coat structure in the range of 0 to 20 mg/m2 zirconium cannot be reproducibly implemented in step (D) in the experiment for carrying out a conversion treatment solely based on a fluoride-free composition (No. 1). Conditioning based on a pretreatment using an aqueous solution comprising polyvinylpyrrolidone (No. 2) likewise fails since the conversion layer formation takes place neither at an increased level nor reproducibly as a whole.
Only when imidazolium salts are added is a significant conversion of the steel surfaces achieved, so that a coating weight in the range of 15 to 60 m2, which is usually sufficient for good corrosion protection and serving as a good paint primer, is achieved (Nos. 3 and 4). If methyl sulfate anions are additionally present, moreover strong acceleration of the conversion layer formation is observed (No. 5).
The corrosion results and the respective associated process sequence are provided in Table 2.
1Corrosion at the cut according to DIN EN ISO 4628-8,after aging in the V W alternating climate test according to PV 12103.
2Mean value and standard deviation across 5 sheets, wherein the averaged value from 6 individual measurements for the same sheet is used for the coat structure of each individual sheet, and the determination was made by way of an X-ray fluorescence analyzer Niton ® XL3t 900 (Thermo Fisher Scientific) using an analysis surface of 50 mm2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102015209910.5 | May 2015 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2016/061209 | May 2016 | US |
| Child | 15800520 | US |
