EP2106299A1

EP2106299A1 - Composition and process for coating metal surfaces

Info

Publication number: EP2106299A1
Application number: EP07822746A
Authority: EP
Inventors: Karsten Hackbarth; Wolfgang Lorenz; Eva Wilke; Marcel Roth; Reiner Wark; Stephan Müller; Guadalupe Sanchis Otero; Manuela GÖSKE-KRAJNC; Andreas Kunz
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2006-12-28
Filing date: 2007-11-20
Publication date: 2009-10-07
Also published as: RU2009128735A; KR20090122195A; US20090324983A1; CN101573187A; AU2007341515A1; WO2008080700A1; JP2010514866A; BRPI0720642A2; DE102006062500A1

Abstract

A composition for coating metal surfaces based on crosslinking polyester resins as an organic constituent, which, based on its total mass, contains from 4 to 20% by weight of aluminum flakes and not more than 0.1% by weight of compounds containing isocyanate groups. The composition preferably comprises, as an organic binder, at least one hydroxylated polyester resin, preferably having a mean molar mass in the range from 2000 to 15 000, and a crosslinking component for the hydroxylated polyester resin and an acidic crosslinking catalyst. A process for applying the composition to metal ribbons in a belt process is likewise claimed. The layer application is adjusted within the range from 3 to 30 μm according to the end use, for which double coating may be advantageous. For example, the composition may serve as a “galvanization replacement”.

Description

"Means and Method for Coating Metal Surfaces"

The present invention relates to anticorrosion compositions for coating metal surfaces and to a process for coating metal surfaces with aluminum-containing organic coatings.

In the metalworking industry, the metallic components of the products must be protected against corrosion. For example, in vehicle and household appliance construction, for reasons of process simplification, there is a desire to reduce the cost of chemical corrosion protection treatment. This can be done by using raw material in the form of metal sheets or metal strips which already carry a corrosion protection layer.

The coating of steel sheets with organic coatings which are weldable and which are applied directly in the rolling mill by the so-called coil coating process is known in principle.

For example, DE-C-3412234 describes a conductive and weldable corrosion protection primer for electrolytically thin-galvanized, phosphated or chromated and deformable sheet steel. This anticorrosive primer consists of a mixture of more than 60% zinc, aluminum, graphite and / or molybdenum disulfide and another anticorrosive pigment and 33 to 35% of an organic binder and about 2% of a dispersing agent or catalyst. As organic binder polyester resins and / or epoxy resins and their derivatives are proposed. WO 99/24515 discloses a conductive and weldable anticorrosion composition for coating metal surfaces, characterized in that it comprises a) from 10 to 40% by weight of an organic binder containing aa) at least one epoxy resin) at least one hardener selected from guanidine, substituted guanidines, substituted ureas, cyclic tertiary amines and mixtures thereof ac) at least one blocked polyurethane resin b) 0 to 15% by weight of a silicate-based anticorrosion pigment c) 40 to 70% by weight of powdered zinc, aluminum, graphite and / or molybdenum sulfide , Carbon black, iron phosphide d) 0 to 30 wt .-% of a solvent.

WO 01/85860 describes a conductive and weldable anti-corrosion composition for coating metal surfaces, characterized in that, based on the total composition, a) from 5 to 40 wt .-% of an organic binder containing aa) at least one epoxy resin ab) at least one Hardener selected from cyanoguanidine,

Benzoguanamine and plasticized urea resin ac) at least one amine adduct selected from

B) 0 to 15% by weight of an anticorrosive pigment c) 40 to 70% by weight of conductive pigment selected from pulverulent zinc, aluminum, graphite, molybdenum sulfide, carbon black and iron phosphide d) 0 to 45% by weight a Lösungsmitttels and, if desired, up to 50 wt .-% further active ingredients or auxiliaries, wherein the proportions of the components add up to 100 wt .-%. Thus, a number of coating compositions for metals containing particles of metallic aluminum are known. The aluminum is here especially as Conducting pigment used so that the coatings thus obtained can be electrically welded and optionally electrocoated. These coatings serve as a basis for subsequent painting and are not intended to be either the only organic coating or, if desired, coated with a clearcoat.

To improve corrosion resistance, steel is often hot dipped or electrolytically galvanized or alloy galvanized. These zinc or zinc alloy coatings give the steel a distinctive silvery-metallic appearance. Galvanized surfaces in the hot dipping process have a characteristic, ice-like appearance due to the crystallization of the solidifying zinc melt. Depending on the purpose of use, this can be regarded as desirable for decorative reasons, but also as disturbing. On the other hand, the electrodeposited zinc or zinc alloy layers are uniform and homogeneous to the human eye.

This zinc coated ("galvanized") steel may be overcoated, however, the adhesion of the paint to the zinc layer may be problematic and may require special pre-treatment, but often the zinc coated steel is used unpainted or, if necessary, clear coated because of the silver appearance Due to the cathodic protective effect of the zinc layer, which can also be passivated by environmental influences, the underlying steel does not rust as long as the zinc layer is still closed It can take decades for galvanized steel to show red rust.

The galvanizing of steel is therefore a classic and widespread measure for corrosion protection. However, galvanizing is energy consuming and increases the thickness of the material and thus the total material consumption. Therefore, there is a need for a process which gives a similar appearance and corrosion protection to galvanized steel as galvanizing. The The present invention provides such a method and a means to be employed therewith.

The first aspect of the present invention relates to an agent for coating metal surfaces based on crosslinking polyester resins as an organic binder, characterized in that the agent, based on its total mass, 4 to 20 wt .-% aluminum flakes and not more than 0.1 wt. Containing% isocyanate group-containing compounds.

The crosslinking polyester resins are particularly suitable for permanently entrapping the aluminum flakes and fixing them on the metal surface, resulting in a coating with good anti-corrosive properties. In order to obtain an isocyanate- or polyurethane-free coating as far as possible, the composition according to the invention contains not more than 0.1% by weight, preferably not more than 0.01% by weight and particularly preferably no detectable isocyanate groups at all. containing compounds. Due to the absence of isocyanate or polyurethanes, the coating is particularly insensitive to environmental influences and in particular to sunlight.

A content of 4 to 20 wt .-% aluminum flakes causes the cured coating at a desired thickness between about 3 and about 30 microns optically completely covers the underlying metal surface. The metal surface then visually looks as if it had been electrolytically galvanized. Due to the anti-corrosive effect of the coating, red rust formation in the case of steel coated in this way is suppressed in the long term. The agent thus gives the steel coated herewith similar optical and corrosion protection properties as galvanized steel. However, the energy required to apply the coating is less than that for galvanizing. In addition, the layer obtained with the agent according to the invention is lighter than a galvanizing layer, so that material is saved compared to a galvanizing. Suitable aluminum flakes are commercially available. They may, for example, have a mean surface diameter in the range of 20 to 60 μm, preferably 30 to 50 μm, and a thickness in the range of 0.3 to 1 μm, preferably in the range of 0.4 to 0.6 μm. Preferably, the agent contains, based on its total mass, 5 to 12 wt .-% aluminum flakes.

The anticorrosive effect of the agent according to the invention can be improved if it is added to it, based on its total mass, from about 2 to about 10% by weight, in particular from about 3 to about 7% by weight, of corrosion inhibitors and / or anticorrosion pigment. Anticorrosion pigments can be selected, for example, from calcium or zinc phosphates, magnesium oxide, in particular in nanoscale form, fine-grained or very fine-grained barium sulfate and anticorrosive pigments based on calcium silicate. The latter are preferred because of their particularly good effectiveness.

Usually, the inventive composition, based on its total mass, 20 to 50 wt .-% and in particular 30 to 40 wt .-% organic binder and 30 to 70 wt .-%, in particular 50 to 60 wt .-% solvent, wherein the Sum of the proportions of solvent and organic binder due to the presence of other ingredients such as at least the aluminum flakes not greater than 96 wt .-%, preferably not greater than 90 wt .-% and in particular not greater than 70 wt .-%.

The components of the organic binder are usually commercially available as a solution or dispersion in organic solvent. Due to the use of such raw materials, the coating composition according to the invention is also solvent-containing. The presence of solvent has a favorable effect on the viscosity of the agent. This should in particular be adjusted so that the agent can be applied by conventional methods of coil coating on a running metal strip. The viscosity at the temperature at which the agent is applied to the metal strip can be adjusted by varying the amount of solvent to the desired range. It may therefore be advantageous if the inventive agent except the solvent content of the raw materials additionally contains solvent. Depending on the raw material used, the solvent may be, for example, so-called "solvent naphtha", diethylene glycol monobutyl ether acetate, propylene glycol methyl ether, cyclohexanone, diacetone alcohol, diethylene glycol, propylene glycol n-butyl ether, methoxypropyl acetate, methoxypropanol, butanol, in particular isobutanol, xylene or more commonly used in the field of paints and paints solvents.

As an organic binder, the coating composition of the invention preferably contains at least one hydroxylated polyester resin and a crosslinking component therefor. The hydroxylated polyester resin preferably has an average molecular weight in the range of 2,000 to 15,000, more preferably in the range of about 3,000 to about 10,000. As the method of determining the molecular weight, gel permeation chromotography can be selected. In general, however, molecular weights are given in the technical product data sheets of the manufacturers, which can be used for the purpose of the present invention.

Preference is given to using those hydroxylated polyester resins which, in the solvent-free state, have an acid number of less than 5, in particular not more than 3 mg KOH / g and an OH number in the range from 10 to 50, in particular in the range from 15 to 40 mg KOH / g.

As the crosslinking component for the hydroxylated polyester resin, a melamine-formaldehyde crosslinking agent is preferably used. For example, a methoxymethylmelamine can be used, which is usually present as a secondary amine and is alkoxylated on the nitrogen. Such crosslinking agents are commercially available and often contain solvents.

The crosslinking reaction upon curing of the organic binder can be improved and accelerated if the agent additionally contains at least one acidic crosslinking catalyst, preferably a weakly acidic crosslinking catalyst. This is preferably in blocked form, so that the crosslinking reaction starts only at a temperature which is above the storage and application temperature of the agent. For example, a nonionic blocked acidic cross-linking catalyst is suitable, which is activated at a temperature of above 110 ^0C. Such catalysts for melamine formaldehyde-based stoving lacquers are commercially available and are usually present as a solution in an organic solvent (eg xylene).

Preferably, such an agent is used, which, based on the total mass of the composition, 15 to 40 wt .-%, preferably 20 to 35 wt .-% hydroxylated polyester resin, 2 to 10 wt .-%, preferably 3 to 8 wt .-% crosslinking component for the hydroxylated polyester resin, 0.05 to 1 wt .-%, preferably 0.1 to 0.5 wt .-% acidic crosslinking catalyst.

In addition to these components, the composition according to the invention may contain further additives which are customary in the field of organic coating compositions. For example, these may be fillers, anti-settling agents, defoamers or leveling agents. For example, the agent according to the invention may contain inorganic fillers, for example based on mica, quartz and / or chlorite. The average particle size should be compatible with the desired coating thicknesses and preferably not above 5 μm. The filler should preferably contain no more than 1% by weight of particles larger than 15 μm. The agent preferably contains from about 2 to about 20% by weight, in particular from about 4 to about 10% by weight, based on its total weight of fillers.

A second aspect of the present invention resides in a process for coating metal strip, particularly non-galvanized steel strip by strip, characterized by i) purifying the strip if necessary, ii) contacting the strip with an acidic treating solution which is on the steel surface produces a conversion layer containing not more than 1 mg of chromium per m ² and then with or without intermediate rinsing with water, iii) coated with an agent as described above having such a wet film thickness to give a layer coverage in the range of 3 to 30 microns after curing, and iv) the applied in step iii) wet layer by IR radiation or by heating the tape a substrate temperature in the range of 120 to 280 ⁰ C, preferably in the range of 230 to 250 ⁰ C hardens.

If metal strips are coated which have been coated immediately before with a metal coating, for example with zinc or zinc alloys, electrolytically or by hot dipping, it is not necessary to clean the metal surfaces before carrying out the conversion treatment (ii). If the metal strips have already been stored and in particular provided with corrosion protection oils, a purification step is necessary before carrying out step (ii).

The conversion solution to be used in step (ii) may be a layer-forming or non-layer-forming phosphating solution known in the art. Alternatively, it is possible to use an acidic treatment solution which contains, as a layer-forming component, complex fluorides of silicon and in particular of titanium and / or zirconium. Furthermore, the conversion solution may contain organic polymers such as, for example, polyacrylates or amino-substituted polyvinylphenol derivatives. Addition of nanoscale silica or nanoscale alumina to the conversion solution in step (ii) may result in further improved corrosion protection and adhesion properties. In this case, "nanoscale" means particles which on average have a particle diameter of less than 1000 nm, in particular of less than 500 nm.

In this case, at least steps (ii) and (iii) are carried out as a strip treatment process, wherein the liquid treatment agent is applied in step (iii) in such an amount that after hardening the desired layer thickness in the range of 3 to 30 microns. The coating composition may vary according to various methods are applied, which are familiar in the art. For example, applicator rolls can be used to directly adjust the desired wet film thickness. Alternatively, one may immerse the metal strip in the coating agent or spray it with the coating agent, after which the desired wet film thickness is adjusted by means of squeeze rolls.

After applying the liquid treatment agent in step (iii), the coated sheet is heated to the required drying or crosslinking temperature for the organic coating. The heating of the coated substrate to the required substrate temperature ("peak-metal-temperature" = TMP) in the range from 120 to 280 ^° C., preferably in the range from 230 to 250 ^° C., can be carried out in a heated continuous furnace, but the treatment agent can also be brought by infrared radiation to the appropriate drying or crosslinking temperature.

Depending on the later intended use of the metal substrate coated according to the invention, different ranges for the layer thickness are preferred. If it is desired to have a layer thickness of more than about 10 μm and in particular more than about 15 μm, it may be advisable to carry out the coating in two stages, with the agent applied in each stage being cured in each case. This process sequence is thus characterized in that the two steps iii) and iv) are carried out in duplicate and in the first step pair iii) + iv) a layer support in the range of 3 to 15 .mu.m and then in the second step pair iii) + iv) another layer support in the range of 10 to 27 microns applies.

For example, in the first step pair, a layer thickness in the range of 5 μm and in the second step pair a layer thickness in the range of 20 μm can be applied. Further conceivable combinations are: about 10 μm in the first coating step and about 15 μm in the second coating step or about 12 μm in the first coating step and likewise about 12 μm in the second coating step. Furthermore, the present invention comprises a band or a sheet or component produced therefrom, which is obtainable by the method according to the invention. Depending on the intended use, the coating thickness may vary and the coating may or may not be overcoated.

In one embodiment, the layer support produced in steps iii) and iv) is in the range of 3 to 10 .mu.m, whereupon at least one further lacquer layer is applied which does not represent a clearcoat. In this embodiment, the coating according to the invention therefore acts as a primer for a subsequent coating. Although the optical effect of similarity to a galvanized layer explained above is lost, the corrosion protection effect of the coating applied according to the invention is exploited. Such opaque painted sheets can be used or produced for example in vehicle construction or in the manufacture of household appliances or metal furniture. You can then each form the outside of the products mentioned. The overpainting may be, for example, a cathodic dip paint or a powder paint.

In a further embodiment, the coating applied according to the invention is present after curing in step iv) with a layer thickness in the range from about 3 to about 15 μm and in particular in the range from about 8 to about 14 μm. It then provides sufficient corrosion protection to serve as a so-called "backside coating" without further overcoating, so it covers the interior surfaces of, for example, vehicles, furniture or household appliances, which are not very corrosive enough, so that no further overpainting is required ,

If the coating according to the invention is to lie on the outside of the articles produced from the coated substrate and if it is not or should be overcoated with a clearcoat, it is preferred to produce a total of one coat in the range of about 20 to 30 .mu.m. Preferably this is produced according to the above-described two-stage process in which steps iii) and iv) are carried out twice in succession.

In this embodiment, a metal strip or a sheet or component produced therefrom is obtained, in which the coating applied according to the invention is either not coated on the surface of the component or at best coated with a clearcoat. In this embodiment, the galvanizing-like appearance of the coating according to the invention is visible, which may be desirable for aesthetic reasons. In this embodiment, the coating according to the invention serves, so to speak, as a "galvanizing substitute." Both the visual impression and the anticorrosive effect of a galvanized steel surface are produced in a cost-effective manner, without having to resort to galvanizing, which is more energy consuming and more expensive.

In this embodiment, in which the coating according to the invention remains visible, the strip or a sheet metal or component produced therefrom is preferably used for the production of household appliances or architectural parts, in particular for building walls or roofs or for the outer covering of building walls or roofs. The coated in this embodiment sheets can therefore be used for all applications for which one currently uses not painted or possibly provided with a clear coat galvanized steel. In addition to the examples already mentioned, these can also be rain gutters on buildings or ducts of air conditioning systems or for supply or exhaust air ducts, for example. Furthermore, so coated material for railing or for posts, for example, used as a carrier for traffic lights or traffic signs. Fences, gates, guardrails, containers such as garbage containers are other uses for the material coated according to the invention as a "galvanizing substitute".

From the above explanations on the effect as a "galvanizing substitute" it follows that the preferred substrate is non-galvanized steel, in particular cold-rolled steel. However, common metals such as zinc or aluminum or their alloys in each case can also be coated with the agent or process according to the invention. This also applies to galvanized or alloy-galvanized steel. In the last-mentioned cases, it is less the optical effect of the "galvanizing set" that plays a role, but rather the anticorrosive effect, for example, an agent according to the invention can be composed as follows (quantities in% by weight, based on the total mass):

Where: component 1

1 branched saturated polyester, SZ <3, OH number 45, molecular weight: 3000, 65% in SN 150 / BG

2 linear saturated polyester, SZ <3, OH number 15, molecular weight: 7,000, 60% in SN150 / DBE

3 linear saturated polyester, SZ <3, OH number 35, molecular weight: 3,000, 60% in SN150 / BG

4 methylbutyl melamine resin, 82% in butanol

5 linear saturated polyester, SZ <3, OH number 5-10, molecular weight: 15,000, granules

6 OH-containing polycarbonate polyester, equivalent weight 1000, 100%

7 linear saturated polyester, SZ <3, OH number 20, molecular weight: 5,000, 55% in SN150, methoxypropyl acetate, methoxypropanol

8 linear saturated polyester, SZ <3, OH number 25-35, molecular weight: 5,000, 60% in SN150, methoxypropyl acetate, methoxypropanol

9 methylated melamine-formaldehyde cross-linking agent ^

10 Corrosion protection pigment based on calcium silicate

11 Anti-corrosive pigment based on oxiaminophosphate, magnesium salt

12 Anti-corrosive pigment based on a modified Sr / Al polyphosphate

13 Anti-corrosion pigment based on oxiaminophosphate, magnesium salt

14 anticorrosion pigment based on Zn / Al polyphosphate silicate

15 Zn / Al polyphosphate based anti-corrosive pigment

16 talc-based inorganic filler

17 inorganic filler based on mica, Quarz.Chlorit

18 inorganic filler based on barium sulfate

19 inorganic filler based on mica

20 inorganic filler based on kaolin

21 silicone-free leveling agent

22 nonionic blocked acidic crosslinking catalyst

23 aluminum powder type 1

24 aluminum powder type 1

25 aluminum powder type 2

26 aluminum powder type 3

27 aluminum powder type 4

28 aluminum powder type 1

29 Solvent naphtha

30 solvent naphtha

31 Solvent naphtha

32 propylene glycol methyl ester

33 diethylene glycol monobutyl ether acetate

Claims

claims

1. An agent for coating metal surfaces based on crosslinking polyester resins as an organic binder, characterized in that the agent based on its total mass, 4 to 20 wt .-% aluminum flakes and not more than 0.1 wt .-% isocyanate-containing compounds ,

2. Composition according to claim 1, characterized in that the aluminum flakes have a mean surface diameter in the range of 20 to 60 microns and a thickness in the range of 0.3 to 1 micron.

3. Composition according to one or both of claims 1 and 2, characterized in that it additionally contains, based on its total mass, 2 to 10 wt .-% corrosion inhibitors or anticorrosion pigment.

4. Composition according to one or more of claims 1 to 3, characterized in that it, based on its total mass,

From 20 to 50% by weight of organic binder,

Contains 30 to 70 wt .-% solvent, wherein the sum of the proportions of solvent and organic

Binder is not greater than 96 wt .-%, preferably not greater than

90% by weight.

5. Composition according to one or more of claims 1 to 4, characterized in that it contains as organic binder at least one hydroxylated polyester resin, preferably having an average molecular weight in the range of 2000 to 15000, as well as a crosslinking component for the hxdroxylierte polyester resin.

6. Composition according to claim 5, characterized in that it contains as crosslinking component at least one melamine-formaldehyde crosslinking reagent.

7. Composition according to claim 6, characterized in that additionally contains at least one acidic crosslinking catalyst, preferably in blocked form.

8. Composition according to claims 5 to 7, characterized in that it, based on the total mass of the composition,

15 to 40% by weight, preferably 20 to 35% by weight hydroxylated polyester resin,

2 to 10 wt .-%, preferably 3 to 8 wt .-% crosslinking component for the hydroxylated polyester resin,

0.05 to 1 wt .-%, preferably 0.1 to 0.5 wt .-% acidic crosslinking catalyst.

9. A method of coating metal strip in the strip process, characterized by i) cleaning the strip if necessary, ii) bringing the strip into contact with an acidic treatment solution which produces on the steel surface a conversion layer containing not more than 1 mg of chromium per m ² contains, and then with or without intermediate rinsing with water, iii) coated with an agent according to one or more of claims 1 to 5 with such a wet film thickness that is obtained after curing a layer support in the range of 3 to 30 microns, and iv) the wet layer applied in step iii) is cured by IR radiation or by heating the strip to a substrate temperature in the range from 120 to 280 ^° C., preferably in the range from 230 to 250 ^° C.

10.A method according to claim 9, characterized in that the two steps iii) and iv) is carried out twice and in the first step pair iii) + iv) a layer support in the range of 3 to 15 microns and then in the second step pair iii) + iv) a another layer of coating in the range of 10 to 27 microns applies.

11. Tape or sheet metal or component produced therefrom, which is obtainable by a method according to claim 9 or claim 10.

12. strip or sheet metal produced therefrom or component according to claim 11, characterized in that the layer support produced in steps iii) and iv) is in the range of 3 to 10 microns and then at least one further lacquer layer is applied, which is not a clearcoat.

13. strip or sheet metal produced therefrom or component according to claim 11, characterized in that the layer support produced in steps iii) and iv) is in the range of 3 to 15 microns and in that no further lacquer layer is applied thereto.

14 strip or sheet metal or component produced therefrom according to claim 11, characterized in that in the steps iii) and iv) total layer thickness produced in the range of 20 to 30 microns and that thereon no further lacquer layer or only a clear coat is applied.

15. strip or sheet metal or component produced therefrom according to claim 14, characterized in that the steps iii) and iv) were carried out in duplicate according to claim 10.

16. Use of a strip or a sheet or component produced therefrom according to any one of claims 12 and 13 for the production of vehicles, furniture or household appliances.

17. Use of a strip or a sheet metal or component produced therefrom according to any one of claims 14 and 15 for the production of household appliances or architectural parts, in particular for building walls or roofs or for the outer lining of building walls o of roofs.