EP0760871B1 - Process for coating phosphatized metal substrates - Google Patents

Abstract

PCT No. PCT/EP95/01957 Sec. 371 Date Feb. 26, 1997 Sec. 102(e) Date Feb. 26, 1997 PCT Filed May 23, 1995 PCT Pub. No. WO95/33083 PCT Pub. Date Dec. 7, 1995A process for coating phosphated metal substrates with one or more organic coatings, in which after phosphating and before application of a first organic coating, the phosphated metal substrates are treated with an aqueous solution which contains 5 to 10000 ppm of dissolved titanium, vanadium, molybdenum, silver, tin, antimony and/or one or more elements of atomic numbers 57 to 83 in the form of inorganic and/or organic compounds, wherein the phosphated metal substrates are additionally connected as a cathode during the entire treatment or for part of the duration of the treatment.

Description

The invention relates to a method for coating phosphated Metal substrates with organic coatings, in particular Electrocoat coatings.

Pretreatment of metallic substrates, e.g. made of aluminium, but especially from galvanized or non-galvanized steel, for one Painting, in particular for an electrophoretically to be applied Dip painting, exists when good corrosion protection is desired and good substrate adhesion by electrophoretic deposition generated coating layer should be achieved from a phosphating and a passivating rinse. Then on this surface the electrocoat is applied and baked.

In automotive OEM painting, for example enforced that the cleaned body shells made of galvanized or non-galvanized steel first phosphated and then with a passivating rinse to be treated before cathodic deposition a so-called cathodic dip coating (KTL) is applied as a primer layer (see Glasurit manual of Lacke und Farben, pages 454 ff., 11th edition, 1984, Curt R. Vincentz Verlag Hannover). The passivation step is a necessary one Process component.

This basic process, which is still used today, is described in the past years regarding the composition of Phosphating and passivation materials as well as the KTL material have been constantly improved. For example Phosphating and passivation materials both in terms of their technological properties as well as ecological Aspects have been further developed, such as Horst Gehmecker in JOT, No. 5, 1992, pages 42 to 46.

As phosphating variants, iron phosphating, zinc phosphating, low zinc phosphating, trication phosphating, manganese-doped phosphating, nickel-free phosphating and nitrite-free phosphating have become known, as evidenced by the extensive patent literature. Phosphating solutions containing toxic nickel ions have proven to be particularly advantageous from a technological point of view. Commercial products for phosphating are sold, for example, by the Henkel company under the name Granodine ^R , for example Granodine 950 as a trication system, Granodine 1990 as a nitrite-free trication system or Granodine 2700 as a nickel-free trication system.

In the search for ecologically and health-friendly alternatives to the original and still common chromate-containing passivation solutions, success has been achieved, as demonstrated, for example, by the patent literature. Examples of this are passivation solutions based on zirconium fluoride or organic. For example, Henkel sells passivation products under the Deoxylyte ^R name, e.g. Deoxylyte 41 as a chromate system, Deoxylyte 54 NC as a zirconium fluoride system or Deoxylyte 80 as an organic-based system. Passivation solutions of this type are characterized by a complicated composition.

In polym. Mater. Sci. Eng, Volume 58, 1988 (pages 176 to 177) a process for the post-treatment of phosphate layers before application an organic coating with an aqueous solution, the tin ions contains, described. US-A-4 828 615 describes that phosphated surfaces before they are coated be treated with an aqueous solution, the pentavalente Contains vanadium compounds, DE-A-23 34 342 is based on an aqueous, Dishwasher detergent containing rare earth metals, with the under other phosphated surfaces before applying a coat of paint be treated. JP-A-58 130 282 describes the treatment of phosphated surfaces with aqueous, Fe, Zn, Ni, Mo, Co, W, Mg, Mn or Si solutions described before coating the surfaces receive. The SU-A-914652 describes the increase in wear resistance and the electrical conductivity of castings by treating a porous Phosphate coating with aqueous solutions of the formates and / or oxalates of Ag, Cu, Pb and / or Bi and then heating the treated surfaces to the Decomposition temperature of the salts.

The object of the present invention is a coating method to provide for phosphated metal substrates, which the Corrosion protection increases beyond the level reached. The Coating method should preferably be composed with simple and ecologically and health-friendly after-treatment materials be feasible. It should also allow a high one Generate level of corrosion protection if the previous one Phosphating is based on a concept for ecological reasons, which leads to only moderate corrosion protection. In particular, should the coating process allow chrome, nickel and nitrite free work.

It has been shown that this object can be achieved by a method for coating phosphated metal substrates with one or more organic coatings, which is characterized in that the phosphated metal substrates are free of nickel after phosphating in a phosphating solution and before application of the first organic coating can be treated with an aqueous solution which contains 5 to 10,000 ppm of dissolved bismuth in the form of inorganic and / or organic compounds, and deposits the element in a total amount of 5 to 100 mg / m ² .

The phosphated metal substrates are preferred throughout or part of the Treatment time switched additionally as cathode.

Conventional metal parts can be used as metallic substrates, as they are common in the automotive industry, for example. Examples are components made of aluminum, magnesium or their alloys, iron and especially steel, e.g. non-galvanized or with pure zinc, zinc-nickel alloy or zinc-iron alloy galvanized. The different Substrates can coexist on a workpiece (Mixed construction).

The metallic substrates are phosphated in the usual way, i.e. using phosphating solutions known per se. It can for example, such as those used by Horst Gehmecker in JOT, No. 5, 1992 pages 42 to 46. It is e.g. around Contains zinc, manganese, iron and / or nickel Phosphating materials. In the state of the art industrial practice containing phosphating solutions Nickel ions proved to be particularly advantageous with regard to Generation of a high level of corrosion protection. Within the scope of the invention However, it has been shown that the use of toxic nickel in Phosphating solutions can be avoided as there is no over the top Use of a bismuth according to the invention containing aqueous solution brings additional benefits. At Application of the method according to the invention can therefore be the foregoing Phosphating treatment with less effective, but also less toxic phosphating solutions. The Phosphating layers can be sprayed or immersed be applied. The solutions become on the surface of the Metal substrate deposited a thin layer of phosphate crystals. This should be as dense and fine-grained as possible. After phosphating the metal substrate is rinsed and optionally dried before it according to the invention before application of the organic coating with a aqueous solution containing 5 to 10,000 ppm of bismuth dissolved in Contains form of inorganic and / or organic compounds treated becomes.

The treatment with the aqueous solution can, for example, in Dipping method with an exposure time of, for example, between 1 and 120 seconds. In the case of more complex shapes Metal substrates, e.g. Automobile bodies, is the immersion process prefers.

The dipping process is particularly preferably carried out in such a way that aqueous solutions which contain 5 to 10,000 ppm of dissolved bismuth in the form of inorganic and / or organic compounds are used, the phosphated metal substrate being additionally connected as a cathode in a DC circuit during the treatment. For example, the treatment vessel can serve as an anode, and a counter electrode can be inserted. This procedure also leads to the removal of interfering anions from the phosphate layer. A DC voltage in the range from 3 to 100 V, preferably 5 to 50 V, is preferably used, current densities of 0.1 to 10 A / m ^{2 being} used, the current flow being able to exist during the entire immersion period or the current only flows during part of the immersion period. The current strength can be kept constant during the current flow or the current strength is varied.

Serve as aqueous solutions that can be used in the process according to the invention those containing 5 to 10,000 ppm, preferably above 10 and below 6000 ppm, dissolved bismuth in the form of inorganic and / or organic compounds included, calculated as an element.

The inorganic and / or organic compounds of the above Elements bismuth mentioned are readily water-soluble or they have one sufficient water solubility to maintain as a source a concentration of 5 to 10,000 ppm of the above Elements bismuth can be used in the aqueous solutions. In in this case, those used in the aqueous solutions Compounds as a finely divided colloidal solution or dispersion and have a depot effect for the element bismuth.

Inorganic or organic compounds are inorganic or organic complex compounds of bismuth. An example of a chelating ligand is acetylacetone called. However, there are other complexing agents with one or several complex-forming groups possible. Preferred inorganic or however, organic compounds are the corresponding salts inorganic or preferably organic acids. Examples of salts inorganic acids are chlorides, sulfates and nitrates. As organic Acids serve, for example, mono- or polycarboxylic acids, e.g. aromatic, araliphatic and aliphatic mono- or dicarboxylic acids The salts of monocarboxylic acids, such as, for example, are preferred Benzoates, formates, acetates, propionates, octoates, neodecanoates. As The salts of hydroxycarboxylic acids and including that of aliphatic hydroxycarboxylic acids. Examples for this are the salicylates, 4-hydroxybenzoates, lactates, Dimethylol propionate.

In the context of the present invention, aqueous media which are 5 to 10000 ppm, preferably between 10 and 6000 ppm, of dissolved bismuth included, most preferred. Bismuth is preferred in form a salt of a mono- or polycarboxylic acid. examples for suitable organic carboxylic acids, of which in the invention Bismuth salts that can be used are aromatic, araliphatic and aliphatic mono- or dicarboxylic acids. Prefers are the bismuth salts of organic monocarboxylic acids, especially with more than two carbon atoms, such as bismuth benzoate, propionate, -octoate, -neodecanoate. The bismuth salts of are particularly preferred "Hydroxycarboxylic acids. Examples are bismuth salicylate, -4-hydroxybenzoate, lactate, dimethylol propionate.

Furthermore, those which can be used in the process according to the invention can be used aqueous solutions contain customary auxiliaries, e.g. Surfactants.

During the treatment of the phosphated metal substrates with the aqueous solution, the latter is depleted of the corresponding element by incorporating an appropriate amount of the same on the surface of the phosphated metal substrate. This does not result in galvanic deposition of the corresponding element or elements on the phosphate layer in the form of a closed coating, but rather the method according to the invention is carried out in such a way that the element is present in a total amount of 5 to 100 mg / m ² on the surface of the phosphated one Deposit metal substrate. The phosphate layer is doped with the element. EDX (energy-dispersive X-ray analysis), for example, can preferably be used as the detection method for such low amounts of the element.

The composition of the aqueous solution is preferably continuous monitored analytically, for example using appropriate ion selective electrodes. According to the measured consumption Element in the aqueous solution must be replenished, for example by adding an appropriate aqueous concentrate. If you work with salt solutions of the element, see above the counter anion accumulates as a free acid in the consumption of Elements corresponding way. By dragging out when diving However, the substrates from the solution will accumulate free acid withdrawn from the system in sufficient quantities and it sets in Balance one. This dragging effect occurs in particular Wear when the phosphated metal substrates are concerned three-dimensional and thus creating objects. The immersion bath with the aqueous solution can also with a Electrodialysis circuit to be coupled, which serves the purpose to remove enriching free acid from the immersion bath.

After treatment of the phosphated metal substrates with the aqueous If desired, the substrates can be rinsed with solution, e.g. with deionized water, and dried before using according to the invention can be provided with an organic coating. The Organic coatings can be made from aqueous or non-aqueous Coating agents, preferably stoving coating agents, are applied, for example by spraying, dipping or rolling. To be favoured the organic coatings by electrocoating (ETL), especially preferably applied by cataphoretic dip painting (KTL).

As electrodeposition paints in the process according to the invention per se known electrodeposition lacquers which can be deposited on the anode or are preferred cathodic electrodeposition coatings can be used. she are not subject to any limitation. You can use the usual additives and Contain catalysts.

Examples of those which can be used in the process according to the invention Electrocoating paints are aqueous coating compositions with a solids content of for example 10-20% by weight. The solids content consists of usual binders that are ionic or in ionic groups transferable substituents and those capable of chemical crosslinking Wear groups, and optionally pigments and / or fillers and other additives. The ionic groups can be anionic or in groups convertible to anionic groups, e.g. -COOH groups or cationic or convertible basic groups, e.g. Amino, ammonium, e.g. quaternary ammonium, phosphonium and / or Be sulfonium groups. Binders with basic are preferred Groups. Nitrogen-containing basic groups are particularly preferred. These groups can be quaternized or they can be combined with a usual neutralizing agents, e.g. an organic monocarboxylic acid, such as. Lactic acid, formic acid, acetic acid, as the expert common, converted into ionic groups.

Examples of anionic groups containing anodic electrodeposition paint binders and paints (ATL) are described in DE-A-28 24 418. These are, for example, binders based on polyesters, epoxy resin esters, (meth) acrylic copolymers, maleate oils or polybutadiene oils with a weight average molecular weight of, for example, 300-10000 and an acid number of 35-300 mg KOH / g. The binders carry -COOH, -SO ₃ H and / or -PO ₃ H ₂ groups. After neutralization of at least some of the acidic groups, the resins can be converted into the water phase. The lacquers can also contain customary crosslinking agents, for example triazine resins, crosslinking agents which contain groups capable of transesterification and / or transamidation, or blocked polyisocyanates.

However, cathodic electrocoat materials (KTL) based are preferred cationic or basic binders. Such basic resins are for example primary, secondary and / or tertiary amino groups resins containing, the amine numbers e.g. at 20 to 250 mg KOH / g lie. The weight average molecular weight (Mw) of the base resins is preferably from 300 to 10,000. Examples of such base resins are Amino (meth) acrylic copolymer resins, amino epoxy resins, amino epoxy resins with terminal double bonds, amino epoxy resins with primary OH groups, Aminopolyurethane resins, amino group-containing polybutadiene resins or modified epoxy resin-carbon dioxide-amine reaction products. This Base resins can be self-crosslinking or they are known Crosslinkers used in the mixture. Examples of such crosslinkers are Aminoplast resins, blocked polyisocyanates, crosslinkers with terminal Double bonds, polyepoxide compounds or crosslinkers contain groups capable of transesterification and / or transamidation.

Examples of cathodic dip lacquer (KTL) baths Base resins and crosslinking agents which can be used according to the invention, are in EP-A-0 082 291, EP-A-0 234 395, EP-A-0 209 857, EP-A-0 227 975, EP-A-0 178 531, EP-A-0 333 327, EP-A-0 310 971, EP-A-0 456 270, US 3,922,253, EP-A-0 261 385, EP-A-0 245 786, DE-33 24 211, EP-A-0 414 199, EP-A-0 476 514. These resins can be used alone or in Mixture can be used.

In addition to the base resins and any crosslinking agents present Can the electrocoat (ETL) coating agent pigments, fillers and / or conventional paint additives. They come as pigments usual inorganic and / or organic pigments in question. Examples are carbon black, titanium dioxide, iron oxide, kaolin, talc or Silicon dioxide. It is also possible to use common anti-corrosion pigments to use. Examples include zinc phosphate, lead silicate or organic corrosion inhibitors. The type and amount of pigments depends on the intended use of the coating agent. Should be clear Coatings are obtained, so no or only transparent Pigments such as micronized titanium dioxide or silicon dioxide used. If opaque coatings are to be applied, so are preferably contain coloring pigments in the electrocoating bath.

The pigments can be dispersed into pigment pastes, e.g. under Use of known paste resins. Such resins are known to the person skilled in the art common. Examples of paste resins that can be used in KTL baths are in EP-A-0 183 025 and EP-A-0 469 497.

The usual additives for ETL coating agents are possible as additives. Examples include wetting agents, neutralizing agents, leveling agents, Catalysts, anti-foaming agents and conventional ones in coating agents solvents used.

After coating with electrocoat, the coating is applied Branding networked. If it is a primer, you can Subsequent layers are applied.

A coating is obtained with the process according to the invention excellent adhesion to the substrate and excellent Corrosion protection, which is the level of previously known coatings from phosphating, usual passivation and organic coating, exceed. The method according to the invention avoids the use of Nickel, chrome and nitrite. The phosphating agent can work free of environmental and metal compounds that are hazardous to health. The invention The method allows the after-treatment of the phosphate layer with simple to carry out aqueous solutions.

example 1 (Production of an organic bismuth salt)

2154 parts of deionized water and 938 parts (7 mol) of dimethylolpropionic acid are introduced and heated to 70 ° C. 466 parts (1 mol) of commercial bismuth oxide (Bi ₂ O ₃ ) are added in portions with stirring. After stirring for a further 6 hours at 70 ° C., the batch is cooled to approx. 20 ° C. and left for 12 hours without stirring. Finally, the precipitate is filtered off, washed with a little water and ethanol and dried at a temperature of 40 to 60 ° C.

Example 2 Production of a KTL dispersion)

a) 832 parts of the monocarbonate of an epoxy resin based on bisphenol A (commercial product Epicote 828) are mixed with 830 parts of a commercially available polycaprolactone polyol (commercial product CAPA 205) and 712 parts of diglycol dimethyl ether and at 70 to 140 ° C. with about 0.3% BF ₃ etherate reacted until an epoxide number of 0 is reached. 307 parts of a reaction product of 174 parts of tolylene diisocyanate (2 equivalents of NCO) with 137 parts of 2-ethylhexanol are added to this product (solids 70%, 2 equivalents of carbonate) at 40 to 80 ° C. in the presence of 0.3% of Zn-acetylacetonate as catalyst added with the addition of 0.3% benzyltrimethylammonium hydroxide (Triton B) with an NCO content of about 12.8%. It is reacted up to an NCO value of approximately 0 and then adjusted to approximately 70% solids with diglycol dimethyl ether.

b) To 1759 parts of a biscarbonate of an epoxy resin based on bisphenol A (commercial product Epicote 1001 ^(R) 618 parts of a reaction product from 348 parts of tolylene diisocyanate (80% 2,4-isomer; 20% 2, 6-isomer) with 274 parts of 2-ethylhexanol with addition of 0.3% benzyltrimethylammonium hydroxide as catalyst with a residual NCO content of 12.8% slowly added with catalysis of 0.3% of a non-ionic emulsifier (Triton B ^{( R).} the reaction is continued to an NCO value of about 0 continued. the product has a solids content of 70%. to 860 parts of bishexamethylene triamine in 2315 parts of methoxypropanol are dissolved at a temperature of 20 to 40 ° C, 622 parts of the reaction product added from 137 parts of 2-ethylhexanol with 174 parts of tolylene diisocyanate with benzyltrimethylammonium hydroxide catalysis (0.3%) (NCO content approx. 12.8%) and reacted to an NCO content of approximately 0. Then 4737 parts of the reaction product ktes b) and 3246 parts of the reaction product a) (each 70% in diglycol dimethyl ether) are added and the reaction is carried out at 60 to 90 ° C. The reaction is terminated at an amine number of about 32 mg KOH / g. The resulting product is distilled off in vacuo to a solid of approximately 85%. It is neutralized with 30 mmol of formic acid per 100 g of resin and converted into a dispersion with a solids content of 40% by weight with deionized water.

Example 3 (Manufacture of pigment paste)

To 223 parts of the paste resin according to EP-A-0 469 497 Al Example 1 (55%) 15 parts of acetic acid (50%) are 30 parts of a commercial wetting agent (50%) and 374 parts given deionized water.

5 parts of carbon black, 5 parts of fumed silica, 25 parts Dibutyltin oxide powder, 38 parts lead silicate and 560 parts titanium dioxide given. With deionized water it becomes about 50% solid adjusted and ground on a pearl mill. A stable one is created Pigment paste.

Example 4 (Production of a lead and tin containing KTL)

4.5 parts are added to 815.5 parts of the dispersion from Example 2 Formic acid (50%) and 1760 parts of deionized water. Under 420 parts of pigment paste according to Example 3 are added with thorough stirring.

Manufacture of multi-layer coatings Example 5a

A non-galvanized steel sheet (ST 1405) Bonder ^R 26/60 / 0C (for testing purposes, a so-called "Bonder" sheet sold by Chemetall with a pretreatment of nickel-containing trication phosphating and chromic acid passivation) is coated with the KTL from Example 4 in a 20 µm dry layer thickness and Baked for 10 min at 175 ° C (object temperature). A commercially available filler is then sprayed on in a 35 µm dry layer and baked for 15 minutes at 165 ° C (object temperature). Then a single-coat topcoat suitable for automotive serial painting is applied by spraying in a thickness of 40 µm and baked for 30 minutes at 130 ° C (object temperature).

Example 5b

Example 5a is repeated, however, using a steel sheet (ST 1405) Bonder ^R 2640 / W / OC ("bonder" sheet sold for experimental purposes by Chemetall with a pretreatment consisting of nickel-free trication phosphating without passivation).

Example 5c (example according to the invention)

Example 5b is repeated with the difference that before the KTL is applied, the sheet is immersed for 10 seconds at room temperature in an aqueous solution of the bismuth salt from Example 1 with a bismuth content of 1000 ppm and then rinsed with deionized water and dried. During the immersion, the sheet is switched as a cathode at a voltage of 10 volts and a current density of 1.5 A / m ² .

The corrosion protection was tested according to VDA guideline 621-415, test duration 10 cycles. Indication of the infiltration as a range from 5 tests according to DIN 53 167 in mm. The results obtained are shown in Table 1. example Corrosion protection test 5a comparative experiment 1.2 - 1.8 mm 5b comparative experiment 3.7 - 4.5 mm 5c according to the invention 1.1 - 1.4 mm

It turns out that with the procedure according to the invention Infiltration of a KTL cover even a comparison with one previously phosphating using nickel-containing Substrate subjected to phosphating solutions withstands and even is reduced.

Claims (7)

1. Process for coating metal substrates with one or more organic coatings, wherein the metal substrates are phosphatized in a phosphatizing solution which is free from nickel and the metal substrates phosphatized in this way, after phosphatizing and before applying the first organic coating, are treated with an aqueous solution, characterised in that treatment is carried out with an aqueous solution containing 5 to 10000 ppm of dissolved bismuth in the form of inorganic and/or organic compounds and the element is deposited in a total quantity of 5 to 100 mg/m².
2. Process according to claim 1, characterised in that the phosphatized metal substrates are additionally connected as cathodes during the entire treatment or during part of the period of treatment.
3. Process according to claim 1 or 2, characterised in that the aqueous solution contains one or more salts of organic and/or inorganic acids of bismuth.
4. Process according to claim 3, characterised in that mono- or polycarboxylic acids are used as organic acids.
5. Process according to one of the above claims, characterised in that the aqueous solution contains bismuth salts of hydroxycarboxylic acids.
6. Process according to one of the above claims, characterised in that the organic coatings are applied using a stoving coating composition.
7. Process according to one of the above claims, characterised in that an electrophoretic lacquer is applied as the organic coating by electrophoretic lacquering.