US20140127520A1

US20140127520A1 - Mixtures for coating metallic surfaces

Info

Publication number: US20140127520A1
Application number: US14/072,921
Authority: US
Inventors: Christian Schade; Tobias Urban
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2012-11-07
Filing date: 2013-11-06
Publication date: 2014-05-08

Abstract

A method for coating a metallic surface by contacting it with an aqueous copolymer dispersion, wherein the aqueous copolymer dispersion comprises an effective amount of magnesium ions and phosphate or phosphonate ions, the copolymers present in the dispersion being constructed from the following components: (A) from 20 to 95 weight % of monoethylenically unsaturated hydrocarbons and/or hydrocarbons having two conjugated double bonds, (B) from 5 to 80 weight % of monoethylenically unsaturated monomers which contain acid groups, and/or anhydrides or salts thereof. Further provided are metallic surfaces coated with such copolymers, and the use of such aqueous copolymer dispersions to coat metallic surfaces.

Description

The present invention relates to methods for coating metallic surfaces by bringing the metallic surface into contact with aqueous copolymer dispersions. The invention further relates to copolymer-coated metallic surfaces and also to the use of aqueous copolymer dispersions to coat metallic surfaces.
Further embodiments of the present invention can be found in the claims, description, and examples. It will be appreciated that the features of the subject matter of the invention that have been identified above, and those still to be elucidated below, can be used not only in the respective combination specifically indicated but also in other combinations as well without departing from the scope of the invention. Preferred and especially preferred embodiments of the present invention, respectively, are more particular those embodiments in which all of the features of the subject matter of the invention have the preferred and especially preferred definitions, respectively.
The coating of surfaces by aqueous copolymer dispersions is known.
WO 2004/108601 A1 describes the use of aqueous dispersions comprising at least one at least partly neutralized ethylene copolymer wax, selected from those ethylene copolymer waxes which comprise as comonomers in copolymerized form (A) 26.1 to 39 weight % of at least one ethylenically unsaturated carboxylic acid and (B) 61 to 73.9 weight % of ethylene, and those ethylene copolymer waxes which comprise in copolymerized form (A′) 20.5 to 38.9 weight % of least one ethylenically unsaturated carboxylic acid, (B′) 60 to 79.4 weight % of ethylene, and (C′) 0.1 to 15 weight % of at least one ethylenically unsaturated carboxylic ester, as auxiliaries for wastewater treatment. The partly neutralized ethylene copolymer waxes are at least partially neutralized with a basic substance, preferably an amine. The basic substance may also be a carbonate and/or hydrogencarbonate of an alkali metal.
WO 2008/092853 A1 describes a method for coating surfaces by treating them with a substantially paraffin-free formulation which comprises a copolymer at least partly neutralized with an alkali metal and made from ethylene and 25.5-35 weight % of an ethylenically unsaturated carboxylic acid. The formulation further comprises at least one nonionic or anionic surfactant, at least one defoamer, and optionally further components. The basic component may also be a carbonate and/or hydrogencarbonate of an alkali metal.
WO 2007/137963 A1 describes a method for coating plastics or metallic surfaces with an aqueous dispersion of ethylene copolymers having a molar mass in the range of 2000-20 000 g/mol, comprising in copolymerized form 15.5-19.9 weight % of an ethylenically unsaturated carboxylic acid, and comprising at least one base, the coated surfaces being provided with at least one further coat. Examples of the selected base are alkali metal salts and more preferably amines.
WO 2006/066824 A1 describes a method for coating metallic surfaces with a copolymer of olefins and/or dienes, acidic monomers, and also, optionally, further monomers, the metal surfaces being contaminated with oil and/or grease and the contamination not being removed prior to coating. The polymers used are neutralized by a base; preferred metal cations designated include Mg²⁺ions. The use of phosphates, and especially of magnesium phosphate, is not mentioned, however.
WO 98/10023 describes the use of aqueous polymer dispersions comprising a polymer made from an olefin and from an acidic comonomer, at least one colorant and/or a corrosion inhibitor to protect metallic surfaces against corrosion. The corrosion inhibitors used are preferably pigments which are insoluble in the aqueous phase and which limit the transparency and surface properties of the films.
The above-described dispersions are still deserving of improvement in relation to corrosion control of metallic surfaces, especially with regard to the passivation of surfaces comprising steel and/or zinc or zinc-containing alloys.
It was an object of the invention to provide an improved method for treating metallic surfaces that can be employed with particular advantage in the passivation of surfaces comprising steel and/or zinc or zinc-containing alloys.
As is evident from the disclosure content of the present invention, these and other objects are achieved by means of the various embodiments of the preparations of the invention.
One subject of the invention is therefore a method for coating metallic surfaces by bringing the metallic surface into contact with an aqueous copolymer dispersion, wherein the aqueous copolymer dispersion comprises an effective amount of magnesium ions and phosphate or phosphonate ions or mixtures of phosphate and phosphonate ions, the copolymers present in the dispersion being constructed from the following components:

- (A) from 20 to 95 weight % of monoethylenically unsaturated hydrocarbons and/or hydrocarbons having two conjugated double bonds,
- (B) from 5 to 80 weight % of monoethylenically unsaturated monomers which contain acid groups, and/or anhydrides or salts thereof.

Here, the amount of components (A) and (B) is based on the total amount of components (A) and (B). The total amount of components (A) and (B) here is 100 weight %. The components (A) are present preferably in the range from 20 to 95 weight % and (B) in the range from 5 to 50 weight %.
Surprisingly it has been found that metal surfaces treated with the method of the invention are significantly more resistant to corrosion than those in accordance with the prior art.
An aqueous copolymer dispersion for the purposes of the present invention is a mixture comprising water and copolymers. The water here is present in an aqueous solvent mixture, with the aqueous solvent mixture being composed substantially, more preferably completely, of water. The copolymer may be present in dispersion, in emulsion or else as a molecular solution in the aqueous solvent mixture.
The aqueous solvent mixture contains preferably from 75 weight % to 100 weight % of water. Besides water, the aqueous solvent mixture may optionally comprise organic solvents as well. The organic solvents preferably comprise compounds selected from the group consisting of alcohols, ethers, esters, ketones, and amides. Organic solvents of this kind are frequently used as an ingredient of paints, and are known to the skilled person from the prior art. Examples of such solvents are alcohols such as methanol, ethanol, propanol, butanol, phenoxypropanol, or ethylene glycol, ketones such as acetone, methyl ethyl ketone, cyclohexanone, oligomeric and optionally partially etherified alkylene glycol ethers such as, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, butyl glycol, butyl diglycol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, dimerized butyl glycol, dipropylene glycol n-butyl ether, dipropylene glycol dimethyl ether, esters such as the dimethyl esters of adipic acid, succinic acid, and glutaric acid, and mixtures thereof, 2-ethylhexyl lactate, butyl phthalate, dibutyl phthalate, amides such as dimethylacetoacetamide, N-methylpyrrolidone, or N,N-dimethyllactamide. In small amounts it is also possible to use water-immiscible solvents, examples being hydrocarbons. The small amounts in this case are selected such that no visible additional phase is formed; the small amount is typically less than 5 weight % based on the overall mixture.
The copolymers in the aqueous solvent mixture are present preferably in largely molecularly disperse form or in the form of a very fine dispersion having an average particle size of below 100 nm, determined by dynamic light scattering in accordance with DIN ISO 13321. This means that they do not lead to significant changes in the transparency of the aqueous solvent, let alone to the formation of a sediment.
The copolymers preferably have molecular weights M_w(weight average) of above 20 000 g/mol, very preferably of above 50 000 g/mol. More particularly the molecular weights of the copolymers are in the range from 20 000 g/mol to 200 000 g/mol, very preferably from 50 000 g/mol to 200 000 g/mol.
In one preferred embodiment of the method of the invention, the copolymers present in the dispersion comprise as a further component:

- (C) from 0 to 30 weight % of ethylenically unsaturated monomers different from (A) and (B).

In another preferred embodiment of the method of the invention, the total amount of magnesium ions, phosphate ions, and phosphonate ions is in the range from 0.1 to 5 weight %, based on the amount of the copolymers, preferably in the range from 0.2 to 3.5 weight %, more preferably in the range from 0.4 to 2 weight %, very preferably from 0.6 to 1.6 weight %.
For the purposes of the method of the invention, the magnesium ions and phosphate or phosphonate ions are preferably added in the form of a salt containing magnesium phosphate or magnesium phosphonate to the aqueous copolymer dispersion. Preferred salts in this context are magnesium phosphate, magnesium phosphonate, magnesium phosphate octahydrate, or other hydrates of these salts. The compounds may also be in partly protonated form, for example as hydrogenphosphates or dihydrogenphosphates, and the corresponding phosphonates. It is also possible to use mixed salts of magnesium phosphate or magnesium phosphonate with other salts, as for example with ammonium compounds, alkali metal compounds, or alkaline earth metal compounds. Examples of such compounds are ammonium magnesium phosphate or sodium magnesium phosphate.
In one preferred embodiment of the method of the invention, component (A) is at least one alkene selected from the group consisting of ethene, propene, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.
In another preferred embodiment of the method of the invention, the acidic group in (B) is at least one group selected from the group consisting of carboxyl groups, sulfonic acid groups, and phosphonic acid groups.
More preferably component (A) is ethene and component (B) is (meth)acrylic acid.
In one preferred embodiment of the method of the invention, 0.5 to 50 mol % of the acid groups present in the copolymer are present in the form of neutralized groups. This neutralization is accomplished preferably by dispersing the polymer in the solvent with addition of the base at an elevated temperature.
Bases used are typically one or more substances having a basic action, examples being hydroxides and/or carbonates and/or hydrogencarbonates of alkali metals, or, preferably, amines such as ammonia, for example, and organic amines such as alkylamines, N-alkylethanolamines, alkanolamines, and polyamines, for example.
Examples of alkylamines include the following: triethylamine, diethylamine, ethylamine, trimethylamine, dimethylamine, methylamine. Preferred amines are monoalkanolamines, N,N-dialkylalkanolamines, N-alkylalkanolamines, dialkanolamines, N-alkylalkanolamines and trialkanolamines having in each case 2 to 18 C atoms in the hydroxyalkyl radical and optionally in each case 1 to 6 C atoms in the alkyl radical, preferably 2 to 6 C atoms in the alkanol radical and optionally 1 or 2 C atoms in the alkyl radical. Especially preferred are ethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, n-butyldiethanolamine, N,N-dimethylethanolamine, and 2-amino-2-methylpropan-1-ol. Especially preferred are ammonia and N,N-dimethylethanolamine. Examples of polyamines that may be mentioned include the following: ethylenediamine, tetramethylethylenediamine (TMEDA), diethylenetriamine, and triethylenetetramine.
The copolymers are prepared by methods known to the skilled person. For example, the copolymers are prepared in accordance with the methods described in WO 2004/108601 A1.
The mixtures of copolymer and aqueous solvent mixture are prepared by methods known to the skilled person. For example, the copolymer is dispersed in the solvent mixture produced by mixing beforehand.
In the context of the method of the invention it is preferred to use the copolymer in the form of a formulation with water or with an aqueous solvent mixture comprising least 75 weight % water. It is particularly preferred in this case for the copolymer to be formulated only in water as solvent, and for the concentration of the copolymer to be 0.5 to 50 weight %, relative to the sum of all the components of the formulation.
The aqueous copolymer dispersions in the method of the invention are applied preferably by means of injecting, spraying, dipping, spread-coating, or electrophoretic painting.
The method of the invention can be used to coat a multiplicity of metallic surfaces. The metallic surface preferably comprises a metal selected from the group consisting of Mg, Al, steel, Zn, and steel coated with Zn, Al, Ni, Sn, Cr, or alloys thereof; more preferably the metallic surface comprises the metal Zn.
In another embodiment of the method of the invention, the aqueous copolymer dispersion is contacted with an intermediate coat, the intermediate coat being in contact with the metallic surface. The intermediate coat is preferably a conversion coat which serves to passivate the metal surface. Examples of such coats are Cr conversion coats, phosphation coats, polymer-based aftertreatments, passivating coats comprising Ti compounds or Zr compounds, metal oxide coats, layer-by-layer coats, silane-crosslinked coats or oils, especially anticorrosion oils. The intermediate coat is preferably a Cr conversion coat. These conversion coats are generated, as the skilled person is aware, from acidic (pH 0.5 to 5) Cr(III)- or Cr(VI)-containing solutions which include an oxidizing agent (such as NO₃—). The Zn surface here is minimally dissolved, and the consequent pH increase at the surface is accompanied by the formation of a Cr- and Zn-containing oxidic/hydroxidic network which, according to application parameters (temperature, solution pH, application time) has a coat thickness of 20 nm to 2 μm. The chromating, chromiting or passivating coats, as they are called, are known from the prior art (US19810265487, DE19638176A). It is also possible to remove some or all of the intermediate coat prior to treatment with the aqueous copolymer dispersion, such removal taking place for example in an alkaline cleaning bath. Oiled substrates which have not been degreased or have been only partly degreased may be treated directly with the copolymer dispersion by the method of the invention.
In a further embodiment of the method of the invention, copolymer dispersions comprise, as a further component, film formers, crosslinking components, wetting agents, or other corrosion inhibitors different from the copolymers.
The copolymer dispersions may additionally, as described above, be admixed with film-forming assistants. The latter may be solvents or solvent mixtures, especially those having an evaporation number according to DIN 53170 in the 50-20 000 range, examples being butyl glycol or butyl diglycol. It is also possible, however, to add non-evaporating compounds, especially alcohols which have been reacted with alkylene oxides, more particularly ethylene oxide and/or propylene oxide. These alcohols may be monohydric or polyhydric. These compounds may result in better spreading of the solution on the metal surface. Use may also be made of alkoxylates of oligomeric or polymeric alcohols, such as of silicone derivatives, for example.
The addition of further components is possible as described above—examples are crosslinking components such as various silicon compounds, nanoparticles, components with epoxy and/or isocyanate groups, and also corrosion inhibitors differing from the copolymers. Examples of suitable silicon compounds are silyl ethers and silanols of the formula Y,X—SiOR)_3—x, where X and Y are any desired organic radicals, R is H or alkyl, and x is 0 or 1. These compounds may also be nanoparticulate dispersions or oligomeric compounds that have already undergone preliminary condensation.
Wetting agents as well may—as described above—be added to the copolymer dispersions. Examples of suitable wetting agents are nonionic, anionic, or cationic surfactants, more particularly ethoxylation and/or propoxylation products of fatty alcohols, or propylene oxide-ethylene oxide block copolymers, ethoxylated or propoxylated fatty alcohols or oxo-process alcohols, and also ethoxylates of oleic acid or alkylphenols, alkylphenol ether sulfates, alkylpolyglycosides, alkylphosphonates, alkylphenylphosphonates, alkyl phosphates, or alkylphenyl phosphates. Further examples are, in particular, polyethoxylated C₁₀-C₃₀fatty alcohols or polyethoxylated C₁₁-C₃₁oxo-process alcohols.
Preference is given to using low-foam wetting agents, examples being endgroup-capped ethoxylation and/or propoxylation products of fatty alcohols, where the alcoholic end group has been reacted to give an ether, a methyl ether or ethyl ether, for example.
Particularly preferred wetting agents are alkoxylated fatty alcohols of the formula (I)
R¹—(OCH₂CHR²)_x(OCH₂CHR³)_y—OR⁴ (I)
where

- R¹is C₆-C₂₄alkyl, linear or branched,
- R²and R³are H or C₁-C₁₆alkyl, linear or branched,
- R⁴is H or C₁-C₈alkyl, linear or branched,
- x is an integer from the range from 1 to 200, and
- y is an integer from the range from 0 to 80.

The alkylene oxide units in formula (I) may be arranged in one or more blocks or randomly.
The present invention further provides a copolymer-coated metallic surface obtainable according to any embodiment of the method of the invention.
Generally speaking, the thickness of the copolymer-containing layer on the metallic surface is from 0.1 to 30 μm, preferably from 0.2 to 30 μm, more preferably from 0.5 to 10 μm, very preferably from 1 to 6 μm.
In one embodiment of the coated metallic surface of the invention there are also one or more paint layers, applied one above another, present on the copolymer-containing layer.
In general the coated metallic surfaces may take on any desired form. The metallic surfaces are preferably surfaces of shaped or sheetlike bodies, more preferably the surface of coils, wires, tubes, panels, workpieces, shaped parts, joined parts and/or connected parts.
The copolymer dispersions may be applied to sheetlike or shaped metal surfaces, as for example to coils, wires, and tubes, or to other shaped or sheetlike bodies.
When shaped bodies are used, the copolymer dispersions are applied preferably by dipping or spraying methods. After drying in this case, the applied films have a preferred average coat thickness in the range from 0.2 to 30 μm, more particularly from 0.5 to 10 μm, very preferably from 1 to 6 μm.
Drying may take place by various methods. In many cases, conventional drying at slightly elevated temperature is sufficient. The workpieces (shaped or sheetlike bodies) are preferably stored in an oven at 80° C. for 5 to 20 minutes. As and when necessary, however, higher temperatures and longer or shorter times may be arranged.
A further subject of the present invention is the use of aqueous copolymer dispersions comprising an effective amount of magnesium ions and phosphate or phosphonate ions, or mixtures of phosphate and phosphonate ions, the copolymers present in the dispersion being constructed from the following components:

- (A) from 20 to 95 weight % of monoethylenically unsaturated hydrocarbons and/or hydrocarbons having two conjugated double bonds,
- (B) from 5 to 80 weight % of monoethylenically unsaturated monomers which contain acid groups, and/or anhydrides or salts thereof
  to coat metallic surfaces.

Here, the amount of components (A) and (B) is based on the total amount of components (A) and (B). The total amount of components (A) and (B) here is 100 weight %. The components (A) are present preferably in the range from 20 to 95 weight % and (B) in the range from 5 to 50 weight %.
In one preferred embodiment of the use in accordance with the invention, the copolymers present in the dispersion comprise as a further component:

The total amount of magnesium ions, phosphate ions, and phosphonate ions here is in the range from 0.1 to 5 weight %, based on the amount of copolymers, preferably in the range from 0.2 to 3.5%, more preferably in the range from 0.4 to 2 weight %, very preferably from 0.6 to 1.6 weight %.
In the context of use in accordance with the invention, the aqueous copolymer dispersions are preferably contacted with an intermediate coat, the intermediate coat being in contact with the metallic surface.
In a further embodiment of the method of the invention, the aqueous copolymer dispersions comprise further additives as an additional component. Preferred further additives used are dispersants, dispersing assistants and/or wetting agents.
Examples of dispersants are polyacrylic acids or polyacrylic acid copolymers. These polyacrylic acids or polyacrylic acid copolymers are preferably in the form of their sodium salts. Further preferred are dispersants having a molecular weight Mw (weight average) of 1000 to 30 000 g/mol, more particularly of 2000 g/mol to 10 000 g/mol. The total amount of dispersant is from 0.01 to 1 weight %, based on the amount of copolymers in the aqueous copolymer dispersion. Preferably from 0.01 to 0.2 weight % is used.
The use of dispersants in the aqueous copolymer dispersion leads to a surprising improvement in the storage stability.
Examples of dispersing assistants are surfactants. The total amount of dispersing assistant is from 0.01 to 0.1 weight %, based on the amount of copolymers in the aqueous copolymer dispersion.
Examples of wetting agents are nonionic surfactants. The total amount of wetting agent is from 0.01 to 0.1 weight %, based on the amount of copolymers in the aqueous copolymer dispersion.
With particular preference in the context of the use in accordance with the invention, the coatings are used as what are called sealers, with a Cr conversion coat acting as an intermediate coat. The sealer in this case leads to a distinct improvement in the corrosion control properties of the Cr conversion coat.
The present invention provides improved methods for the treatment of metallic surfaces, which can be employed with particular advantage in the passivation of surfaces comprising steel and/or zinc or zinc-containing alloys.
The invention is illustrated by the examples, without the examples restricting the subject matter of the invention.

EXAMPLES

Polymer A:
An aqueous solution of 21 weight % (based on the amount of water) of a copolymer of ethylene and acrylic acid in a 70:30 weight ratio, having a molecular weight of approximately 30 000 D, and 3.5 weight % of the base dimethylethanolamine (based on the amount of water).
Polymer B:
An aqueous solution of 21 weight % (based on the amount of water) of a copolymer of ethylene and methacrylic acid in a 73:27 weight ratio, having a molecular weight of approximately 90 000 D, and 3.5 weight % of the base dimethylethanolamine (based on the amount of water).

Examples 1-11

Additive A:
Additive 1: magnesium phosphate octahydrate
Additive 2: magnesium methanesulfonate
Additive 3: magnesium acetate
Additive 4: di-sodium hydrogenphosphate
The corresponding additives 1 to 4 were added to the solution of the polymers, and the solutions were then stirred for at least 3 hours.
The amount of the selected additive in weight % is based on the amount of copolymer used.
The aqueous preparations were adjusted to a copolymer concentration of 20 weight %, based on the total amount of the preparation, by addition of the corresponding amount of water.
Oiled galvanized metal panels (dimensions about 220 mm*10 mm*0.5 mm, Zn add-on 100 g/m²) were immersed in ethyl acetate for around 1 minute and then rubbed down with a paper towel.
They were then placed for 30 seconds at 60° C. in a bath of an alkaline cleaning solution (SurTec® 133 from Surtec Oberflächentechnik, Zwingenberg, Germany, 4% strength).
After that they were immersed 2 to 3 times into a bath containing mains water at 60° C., and then into a bath containing fully demineralized water, then allowed to drip dry, and blown off with compressed air.
The dry metal panels were coated by doctor-blade application of the polymer solutions. The doctor blades in this case were selected so as to produce a wet film thickness of 12 μm. The metal panels were subsequently dried in a forced-air drying oven (about 12 seconds, PMT (peak metal temperature) 50° C.), and then stored in a drying oven at 80° C. for 10 minutes.
After 48 hours of storage in the laboratory, the metal panels were subjected to a neutral salt spray mist test in accordance with DIN EN ISO 9227. The degree of corrosion control RI24, according to EN ISO 10289:2001, was ascertained after 24 hours. The results are summarized in Table 1.

TABLE 1

			Amount of additive
Example	Polymer	Additive A	A (weight %)	RI24

Comparative	A			3
example 1
1	A	1	0.8	10
2	A	1	1.2	10
3	A	2	4	2
4	A	3	4	0
5	A	4	1.6	9
Comparative	B			2
example 2
5	B	1	0.8	6
6	B	1	1.2	8
7	B	1	1.7	10
8	B	1	3	6
9	B	2	4	5
10	B	3	4	2
11	B	4	1.7	3

The examples show the advantageous corrosion control produced by adding magnesium phosphate. The amount of additive A is based on the amount of copolymer.
The corrosion control provided by the preparations can in many cases also be enhanced by magnesium ions or phosphates which originate from other compounds of these ions. Nevertheless, the increase in corrosion resistance often turns out to be somewhat lower than when using magnesium phosphate (octahydrate).

Examples 12-16

The copolymers specified above can also be applied by means of immersion methods. In that case the substrates used were hot-dip galvanized and electrolytically galvanized metal test panels. The galvanized metal panels were pretreated as described above and then immersed in copolymer emulsions at different concentrations, with different immersion times and multiple immersion being investigated.
Polymer B was diluted with water to a copolymer concentration of 12 weight %, and immersed twice. The drip-dry time between the immersion steps was 1 minute.
Results (substrates):

- a) application to electrolytically galvanized substrates:
- b) application to electrolytically galvanized and Cr(III) passivated/chromited substrates:

Results after neutral salt spray mist test in accordance with DIN EN ISO 9227 (Table 2).

TABLE 2

		Addi-	Amount of
	Poly-	tive	additive A
Example	mer	A	(weight %)	Substrate	CA(24)	C(28 d)

Comparative	B			a)	100
example 3
12	B	1	1.6	a)	15
Comparative	B	—	—	b)		7
example 4
13	B	1	1.6	b)		<3

CA(24): corroded area in % of exposed metal panel area after 24 hours
C(28 d): corroded area in % of exposed metal panel area after 28 days
The amount of additive A is based on the amount of copolymer.

A very great advantage is the fact that the copolymers can be formulated with a nonionic surfactant (e.g., Plurafac LF 300—alkoxylated fatty alcohol) without severe detriment to the corrosion control. Additionally, as a result, the visual appearance (very uniform without edges) and the mechanical properties (thinner polymer coat about 3 g/m²with wetting agent versus about 6 g/m²without wetting agent) of sealing, in the case of immersion application, are massively improved.
Polymer B was admixed with the wetting agent Plurafac LF 300 (alkoxylated fatty alcohol) and also, optionally, with 1.6 weight % (based on the amount of copolymer) of additive 1. The results are summarized in Table 3.

TABLE 3

			Wetting
		Additive 1	agent			Add-on
Example	Substrate	(weight %)	(weight %)	KF(24)	KF(28 d)	(g/m²)

Comparative	a)		1.0	10		4.0
example 5
14	a)	1.6	1.0	7		2.9
Comparative	b)	—	1.0		25	4.1
example 6
15	b)	1	1.0		13	3.1
16	b)	1	0.1		10	3.1

CA(24): corroded area in % of exposed metal panel area after 24 hours
C(28 d): corroded area in % of exposed metal panel area after 28 days
The amount of additive 1 is based on the amount of copolymer.
The amount of wetting agent is based on the amount of polymer B.

In the presence of the wetting agents, the films obtained with the composition of the invention were thinner relative to the comparative system, exhibiting a higher corrosion control in the neutral salt spray mist test in accordance with DIN EN ISO 9227.

Example 17

Using the solution from example 7, experiments were conducted on the storage stability of the aqueous copolymer solutions. The experiments were conducted over a period of 3 months each at temperatures of 10, 20, or 60° C. The stability of the solutions was evaluated by means of visual inspection. An unstable solution was apparent through gel formation at the surface of the solution.

TABLE 4

Results of stability test

		Time of
Dispersant	Temperature [° C.]	gel formation

	10	—
	20	after one month
	60	after one week
Polyacrylic acid	10	—
Polyacrylic acid	20	—
Polyacrylic acid	60	—

The polyacrylic acid employed was the sodium salt of a low molecular mass polyacrylic acid with a weight average of 4000 g/mol (Sokalan® CP 10 from BASF SE). The concentration of the polyacrylic acid was 0.05 weight %, based on the copolymers of example 7.
Using a dispersant reliably prevents gel formation even at elevated temperatures.

Claims

1. A method for coating a metallic surface, the method comprising:

bringing the metallic surface into contact with an aqueous copolymer dispersion, wherein the aqueous copolymer dispersion comprises an aqueous copolymer, a magnesium ion and a phosphate or phosphonate ion,

wherein the aqueous copolymer comprises:

(A) from 20 to 95 weight % of a monoethylenically unsaturated hydrocarbon and/or a hydrocarbon having two conjugated double bonds,

(B) from 5 to 80 weight % of a monoethylenically unsaturated monomer comprising an acid group, and/or an anhydride or a salt thereof.

2. The method according to claim 1, wherein the aqueous copolymer further comprises:

(C) from 0 to 30 weight % of an ethylenically unsaturated monomer different from components (A) and (B).

3. The method according to claim 1, wherein a total amount of the magnesium ion, a phosphate ion, and a phosphonate ion is from 0.1 to 5 weight %, based on an amount of the aqueous copolymer.

4. The method according to claim 1, wherein component (A) is at least one alkene selected from the group consisting of ethene, propene, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.

5. The method according to claim 1, wherein the acid group is at least one group selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic acid group.

6. The method according to claim 1, wherein 0.5 to 50 mol % of an acid group in the aqueous copolymer is neutralized.

7. The method according to claim 1, further comprising:

applying the aqueous copolymer by spraying, injecting, dipping, spread-coating or electrophoretic painting.

8. The method according to claim 1, wherein a metal in the metallic surface is one selected from the group consisting of Mg, Al, steel, Zn, and a steel coated with Zn, Al, Ni, Sn, Cr, or an alloy thereof.

9. The method according to claim 1, further comprising:

contacting the aqueous copolymer dispersion with an intermediate coat,

wherein the intermediate coat is in contact with the metallic surface.

10. The method according to claim 9, wherein the intermediate coat is a Cr conversion coat.

11. The method according to claim 1, wherein the aqueous copolymer dispersion further comprises a film-former, a crosslinking component, a wetting agent, or a corrosion inhibitor different from the aqueous copolymer.

12. A copolymer-coated metallic surface obtainable by the method according to claim 1.

13. The coated metallic surface according to claim 12, comprising:

one or more paint coats applied one over another located on a copolymer-containing coat.

14. An aqueous copolymer dispersion comprising:

an aqueous copolymer, a magnesium ion and a phosphate or phosphonate ion,

wherein the aqueous copolymer comprises:

15. The aqueous copolymer dispersion according to claim 13,

wherein the aqueous copolymer dispersion is brought into contact with an intermediate coat, and

the intermediate coat is in contact with the metallic surface.