HK1185385A - Method for coating moulded bodies and coated moulded body - Google Patents

Description

The present invention relates to a method for coating molded bodies and, in particular, to the coated molded bodies obtained by the method according to the invention.

Molded bodies made of metal or plastic are nowadays used in a wide variety of shapes, sizes and appearances. Metallic molded bodies should generally not only be characterized by their inherent form stability, but also maintain a valuable appearance over a longer period of use. For example, metallic components are regularly required to have sufficient luster and/or a pronounced corrosion resistance. To solve these problems, various approaches have been proposed.

For example, according to EP 1 870 489, a corrosion-resistant, glossy metal substrate is obtained by applying at least one metallic composite protective layer with a thickness ranging from 20 nm to 1 µm, containing as the first metal aluminum, lead, vanadium, manganese, magnesium, iron, cobalt, nickel, copper, titanium or zinc or as the first metal alloy brass, bronze, stainless steel or a magnesium, titanium or aluminum alloy, and containing at least one oxide, double oxide, oxide-hydrate or oxihalide of a second metal selected from the group consisting of zirconium, titanium and hafnium, onto a metallic substrate surface. Initially, the metal layer made of the first metal or the first metal alloy is applied onto the coating-receptive surface of the substrate by means of PVD coating, evaporation using an electron beam evaporator, evaporation using a resistance evaporator, induction evaporation, arc evaporation and/or cathode sputtering. Then, at least one oxide, double oxide, oxide-hydrate or oxihalide of the second metal is introduced into the metal layer by treating the metal layer with an aqueous system containing at least one acid, an oxide, double oxide, oxide-hydrate, oxihalide and/or salt of the second metal. In this case, the metal layer is subjected to the aqueous system under pressure, and after application of the metal layer and before treatment with the aqueous system, the substrate is subjected to a rinsing step with VE water.

From DE 10 2005 059 314 A1 a method for corrosion protection treatment of bare metal surfaces is known, in which these metal surfaces are contacted with an acidic aqueous solution of a fluorine complex of at least one element M selected from the group consisting of B, Si, Ti, Zr and As, rinsed with water, and then coated with a cathodically depositable electrophoretic coating. It should be ensured that the aqueous solution contains no more than 1 mg/l organic polymer containing allylamine or vinylamine monomers. The aqueous solution additionally contains at least one further component selected from nitrates, copper ions, silver ions, vanadium or vanadate ions, bismuth ions, magnesium ions, zinc ions, manganese ions, cobalt ions, nickel ions, tin ions, buffer systems for the pH range of 2.5 to 5.5, aromatic carboxylic acids having at least two groups containing donor atoms, or derivatives thereof, and silica particles with an average particle size below 1 µm. Moreover, the metal surface must not be dried after contact with the aqueous solution of the fluorine complex and before coating with the cathodically depositable electrophoretic coating, if corrosion-protected bare metal surfaces are to be obtained.

The DE 43 30 104 A1 relates to a method for treating surfaces made of steel, galvanized or alloy-galvanized steel, and aluminized or alloy-aluminized steel, preferably electrolytically galvanized steel. In this process, aqueous acidic phosphate solutions are used, which contain zinc, manganese, and phosphate ions as well as hydroxylamine or a hydroxylamine compound as an accelerator, each within predetermined concentration ranges. This phosphate solution must be free from nickel, cobalt, copper, nitrite, and oxo-anions of halogens.

DE 103 20 765 A1 describes a method for producing a layer on a metallic surface to protect against corrosion. In this method, a coating composition is used which must contain a sol based on silicon compounds, at least one aminoalkyl-functional alkoxysilane and/or at least one reaction product of the two aforementioned components. Furthermore, it must be ensured that the total content of aminoalkyl-functional silane component in the sum lies within the range of 0.01 to 15 wt.-%. From DE 10 2008 007 977 A1, a method for producing zinc-coated non-ferrous metal parts is known, wherein the coating is applied by a zinc diffusion process using a zinc powder mixture at a temperature ranging from 300 to 600 °C, resulting in the formation of a zinc diffusion layer.A particularly smooth cathodic electrodeposition coating can be obtained according to DE 10 2008 012 085 A1 by using such an electrodeposition paint which contains at least one water-dispersible, cationic group-containing organic binder and 0.005 to 0.5 weight-%, based on the solids content of the cathodic electrodeposition paint, of an organic, four-valent titanium, zirconium or hafnium complex having one or more oxygen-containing ligands. A corrosion-protected chromated metal surface, which is characterized by a very good adhesion of the metal coating to the metal substrate, can be obtained according to DE 38 33 119 C2 by applying the electrodeposition paint directly onto the chromate layer immediately after chromating without intermediate drying. Electrodeposition coatings with improved corrosion protection are available according to DE 39 32 744 A1 via such aqueous coating materials,in addition to conventional water-soluble or water-dispersible electrophoretically depositable binders and optionally crosslinking agents, solvents, pigments, and other usual additives, it contains one or more zirconates. US 2004/137239 describes a method for producing a substrate provided with a multi-layer protective coating, in which first a silicate layer and then a cathodically depositable layer are applied thereon. Common corrosion protection coatings for metal substrates still have disadvantages and leave much to be desired. Often, only solutions for very specific substrate components are proposed. Therefore, the present invention was based on the task of making available a method for coating metallic molded parts that is no longer burdened with the disadvantages of the systems known from the prior art and in particular ensures improved corrosion protection properties under aggressive conditions over a longer period of time.

Accordingly, a method for coating molding bodies has been found, comprising the steps of: a) providing a molding body containing or consisting of copper or at least one copper alloy, or a molding body having at least one coating containing or consisting of copper or at least one copper alloy, b) phosphating, in particular iron and/or zinc phosphating, of the molding body, d) treating the molding body with at least one aqueous basic system, in particular at least one aqueous basic solution, and/or with at least one aqueous acidic system, in particular an aqueous acidic solution, h) treating the molding body with at least one aqueous system, in particular at least one aqueous solution, of at least one fluorine complex of at least one element selected from the group consisting of B, Si, Ti, Zr and Hf and/or with at least one acidic aqueous system, in particular an acidic aqueous solution, containing at least one fluoride of an element selected from the group consisting of B, Si, Ti, Zr and Hf, m) treating the molding body with at least one cathodically depositable electrophoretic lacquer (KTL coating step), and p) curing the coating obtained in step m), in particular tempering the molding body.

The method according to the invention can optionally be supplemented by one or more of the following steps: c) rinsing the mold body with at least one aqueous system and/or draining, in particular drying, of the mold body and/or e) rinsing the mold body with at least one aqueous system and/or draining, in particular drying, of the mold body and/or f) rinsing the mold body with at least one aqueous system, in particular comprising VE water, and/or g) draining, in particular drying, of the mold body and/or i) rinsing the mold body with at least one aqueous system and/or j) draining, in particular drying, of the mold body and/or k) rinsing the mold body with at least one aqueous system, in particular comprising VE water, and/or l) draining, in particular drying, of the mold body and/or n) rinsing the mold body with at least one aqueous system and/or o) draining, in particular drying, of the mold body.

The alphabetical designation of the individual process steps previously selected is intentionally used within the scope of the present invention to enable a clear assignment of each step to the inventive sequence of the mandatory process steps a), d), h), m), and p). Thus, process step b) must follow process step a), process step e) must follow process step d), process step g) must precede process step h), and process step j) must precede process step k), and so on. Of course, additional process steps can be inserted between adjacent process steps (e.g., between a) and b)).

In a particularly preferred embodiment, the inventive method comprises, in this order, the steps a), b), c), d), f), g), h), k), l), m), and p).

Preferred shapes or coatings based on a copper alloy include or consist of brass, for example, brass casting.

With the KTL treatment step m), a colored coating or a transparent coating can be produced. In one embodiment, an epoxy resin, particularly a cationic epoxy resin, is used in the KTL treatment step m). The electrophoretic coating may further contain alcohols, ethers, ketones and/or alkoxylated alcohols and/or ether compounds. Examples include 1-methoxy-2-propanol, 2-butoxy-ethanol, butyl glycol, polyethanol, methyl isobutyl ketone, 1-phenoxypropan-2-ol, 2-methoxy-1-propanol, N-hexyl glycol, propylene glycol monomethyl ether, bis 2-(butoxyethoxy)-ethoxymethane and 3-butoxy-2-propanol. These alcohol and ether compounds can be added to the electrophoretic coating composition in amounts of 1 to 15, preferably 3 to 10 weight percent. In another embodiment, the dip coating composition contains alkyltin or alkyltin oxide compounds such as dioctyltin oxide.

The electro-tinning composition can further be adjusted to a suitable pH value using acids, such as amidosulfonic acid, sulfamic acid and/or acetic acid.

In one embodiment, the electrocoating composition may be based on an epoxy resin compound, for example in amounts of 1 to 30 weight-%, preferably in amounts of 4 to 20 weight-%, an acid, for example acetic acid, for adjusting the pH value, preferably to a range of 4 to <7, particularly in the range of 5 to 6, and at least one binder.

The electro-deposition bath composition, in a suitable embodiment, contains 20 to 60 weight-% water, in particular deionized water, 20 to 60 weight-% of a binder, and 1 to 20 weight-% of a pigment paste.

The KTL treatment step is applied, for example, for a duration of 30 seconds to 5 minutes, preferably for a duration of 1 to 4 minutes.

It has proven to be advantageous to agitate the electrocoating composition over a longer period, for example from 24 to 90 hours, preferably from 36 to 80 hours, before its actual use. In a preferred embodiment, the bath temperature is below 35 °C.

In the KTL treatment step, a voltage in the range of 150 to 400 V, preferably in the range of 180 to 360 V, can be applied.

In a preferred embodiment, the duration of the electrophoretic coating step, i.e., the dwell time of the molded part in the electrophoretic paint bath composition under electrophoretic coating conditions, is approximately 1 to 3 minutes.

One refers to VE-water in the sense of the present invention particularly when the conductivity is less than 25 µS/cm and the number of bacterial colonies is less than 1000/ml.

In a preferred embodiment, the coated mold part is rinsed with an aqueous system containing water, particularly VE water, as well as optionally also phenoxypropanol, methoxypropanol, and/or hexylene glycol, after the KTL treatment step.

Step p) of the curing process preferably takes place thermally, i.e., as a tempering step. Alternatively, the curing step can also be chemically activated using catalysts, which may allow the curing step to take place even at room temperature. In the context of the present invention, the curing or tempering step p) is intended to dry or cure the CTL coating obtained via method step m). Consequently, this tempering step can also represent a drying step or an accelerated drying step. In the context of the present invention, tempering is preferably carried out at temperatures above room temperature.

The curing or tempering step p) is carried out in one embodiment at temperatures ranging from 150 to 200 °C, preferably from 160 to 190 °C. The duration of the curing or tempering step is usually between 2 and 30 minutes, preferably between 5 and 20 minutes. For example, in one embodiment, the temperature during the curing or tempering step can be maintained for a period of 10 minutes within the range of 170°C to 180°C, e.g., at 175°C. It is also possible to heat the coated component, for example, for a period of 10 to 60 minutes at a temperature ranging from 200 to 250°C.for example, in the range of 205 to 230 °C, to temper. Particularly preferred is a tempering temperature in the range of 130 to 230 °C, preferably in the range of 140 to 225 °C. It has proven advantageous if higher temperatures, for example in the range of 160 to 265 °C, are selected in a first temperature phase. This first temperature phase can, for example, last up to 10 or 15 minutes. In a subsequent, following temperature phase, a suitable tempering temperature lies in the range of 140 to 190 °C, preferably in the range of 140 to 185 °C. The transition from the higher to the lower tempering temperature can take place continuously.For example, over a period of 5 to 30 minutes, preferably 10 to 25 minutes.

The coating thicknesses obtainable by the inventive method can be varied over a wide range and, according to one embodiment, are conveniently in the range of 5 to 50 µm. With the inventive method, for example, coatings with a layer thickness of 10 to 35 µm can easily be obtained. For example, very satisfactory results can already be achieved with layer thicknesses in the range of 15 to 30 µm.

The aqueous alkaline solution according to process step d) preferably comprises an alkali hydroxide solution, for example a potassium hydroxide solution, or is such a solution. The aqueous alkaline solution may further contain silicates and/or complexing agents. The pH value of this aqueous alkaline solution is advantageously at a value of 9 or higher, particularly at a value of 10 or higher.

The aqueous acidic solution according to process step h) contains, in a preferred variant, hexafluorozirconic acid, preferably in an amount ranging from 0.5 to 10 weight-%.

The object underlying the invention is further achieved by coated shaped bodies obtainable according to the aforementioned inventive method. Among the coated shaped bodies obtainable by this method, those are preferred which comprise a shaped body substrate containing or consisting of copper or containing at least one or consisting of at least one copper alloy, in particular brass, or comprising at least one coating containing or consisting of copper or containing at least one or consisting of at least one copper alloy, in particular brass, and having at least one KTL coating present on this shaped body substrate. Preferred shaped bodies according to the invention are based on at least one copper alloy, in particular brass. The KTL coating of these coated shaped bodies according to the invention can be transparent or colored. Particularly preferred are those coated shaped bodies in which the shaped body or the shaped body substrate has been subjected to at least one phosphating step, in particular an iron and/or zinc phosphating, prior to applying the KTL coating.

With the present invention comes the surprising insight that metallic shaped parts made of copper or copper alloys, or containing coatings of copper or copper alloys, do not show significant corrosion even under aggressive conditions, and in particular are not prone to stress corrosion cracking.

Examples:

1) The coated copper tube according to the invention was obtained as follows: The copper tube was treated with a potassium hydroxide solution at a pH of 10 for a duration of 10 minutes at a temperature of 60°C (dipping bath). After rinsing with deionized water by successively immersing in two separate dipping tanks, the copper tube was exposed for about 2 minutes at approximately 30°C to an acidic aqueous hexafluoro zirconic acid solution (dipping bath). The resulting copper tube was rinsed with deionized water and subjected to the KTL coating step in the presence of a cationic epoxy electrocoating lacquer. The coated copper tube was rinsed with water, dried, and then subjected to the previously described test. 2) In a similar manner, essentially identical copper tubes were subjected to the following non-inventive coating processes.A bent copper tube with a diameter of 18 mm, which corresponded in its dimensions to the copper tube according to Example 1), was coated with titanium hydride in a vacuum in a manner known to experts.3) A bent copper tube with a diameter of 18 mm, which corresponded in its dimensions to the copper tube according to Example 1), was coated with titanium oxide in a vacuum in a manner known to experts.4) A bent copper tube with a diameter of 18 mm, which corresponded in its dimensions to the copper tube according to Example 1), was coated with silicon oxide in a vacuum in a manner known to experts.5) The resulting coated copper tubes were subjected to the stress corrosion cracking chamber test according to DIN 50916-2 as described below.

The bent, coated copper tube with a flared end was subjected to a stress corrosion cracking test after the coating had been applied. For this purpose, the coated copper tube was fixed to a vertical threaded connection using a locknut with a force of 40 Nm. This means that the copper tubes were tightened in a defined manner. The setup is shown in Figure 1. The copper tube was subjected only to bending stress, not to torsional stress resulting from the screwed connection. Subsequently, the coated tubes were exposed for a period of 30 days, as shown in Fig. 1, to gaseous ammonia from the outside according to the spray chamber test specified in DIN 50916-2 (Solution B). During this exposure, the tube was continuously displaced up and down by 7 mm over a length of 150 mm by means of a piston mechanism.

While the copper tube according to the invention showed no corrosion at all, in particular no cracks were found, neither macroscopically nor by means of a microscope in the polished section, in all non-invention coated tubes the flange was cracked. In addition, the tube bend was cracked in the case of the copper tube coated with silicon dioxide. The damages found are illustrated in figures 2 to 8: Figure 2 shows, after 30-day treatment according to DIN 50916-2, a photographic reproduction of the titanium hydride coated copper tube in the area of the flange; Figure 3 shows an enlargement of the crack visible in Figure 2; Figure 4 shows, after 30-day treatment according to DIN 50916-2, a photographic reproduction of a titanium oxide coated copper tube in the area of the flange; Figure 5 shows an enlarged representation of the crack visible in Figure 4; Figure 6 shows a photographic reproduction of the silicon dioxide coated copper tube in the area of the flange after 30-day treatment according to DIN 50916-2; Figure 7 shows a photographic reproduction of the silicon dioxide coated copper tube after 30-day treatment according to DIN 50916-2 in the area of the 90° bend of the copper tube (see also arrow in Figure 1); and Figure 8 shows a polished section image of the corrosion crack according to Figure 7 in cross-sectional view.

No cracks were visible in the copper tubes according to the invention.

The features of the invention disclosed in the foregoing description, in the claims and in the drawings may be essential for the realization of the invention in its various embodiments, both individually and in any possible combination.

Claims (12)

1. A method for coating moulded bodies containing copper or copper alloys, or moulded bodies with a coating containing copper or copper alloys, comprising, in this order, the steps of:

   a) providing a moulded body containing copper or at least one copper alloy, or a moulded body with at least one coating containing copper or at least one copper alloy,

   b) phosphating, in particular iron and/or zinc phosphating, the moulded body,

   d) treating the moulded body with at least one aqueous basic system, in particular at least one aqueous basic solution, and/or at least one aqueous acidic system, in particular an aqueous acidic solution,

   h) treating the moulded body with at least one aqueous system, in particular at least one aqueous solution, of at least one fluoro complex of at least one element selected from the group consisting of B, Si, Ti, Zr and Hf and/or with at least one acidic aqueous system, in particular an acidic aqueous solution, containing at least one fluoro acid of an element selected from the group consisting of B, Si, Ti, Zr and Hf,

   m) CED treating the moulded body with at least one cathodically depositable electrophoretic paint (CED coating step) and

   p) curing the coating obtained in step m), in particular thermally treating the moulded body.
2. The method according to claim 1, further comprising the steps of

   c) rinsing the moulded body with at least one aqueous system and/or draining, in particular drying, the moulded body and/or

   e) rinsing the moulded body with at least one aqueous system and/or draining, in particular drying, the moulded body and/or

   f) rinsing the moulded body with at least one aqueous system, in particular comprising deionised water, and/or

   g) draining, in particular drying, the moulded body and/or

   i) rinsing the moulded body with at least one aqueous system and/or

   j) draining, in particular drying, the moulded body and/or

   k) rinsing the moulded body with at least one aqueous system, in particular comprising deionised water, and/or

   l) draining, in particular drying, the moulded body and/or

   n) rinsing the moulded body with at least one aqueous system and/or

   o) draining, in particular drying, the moulded body.
3. The method according to claim 1 or 2, comprising, in this order, the steps a), b), c), d), f), g), h), k), l), m) and p).
4. The method according to any one of the preceding claims, characterized in that in the CED coating step m) a coloured coating or a transparent coating is produced.
5. The method according to any one of the preceding claims, characterized in that the copper alloy comprises or constitutes brass.
6. The method according to any one of the preceding claims, characterized in that the aqueous basic solution comprises or constitutes an alkali metal hydroxide solution, in particular potassium hydroxide solution.
7. The method according to any one of the preceding claims, characterized in that the pH of the aqueous basic solution is ≥ 9, in particular ≥ 10.
8. The method according to any one of the preceding claims, characterized in that the aqueous acidic solution contains hexafluorozirconic acid as the fluoro acid.
9. The method according to claim 8, characterized in that the aqueous acidic solution contains 0.5 to 10 wt.% hexafluorozirconic acid.
10. The method according to any one of the preceding claims, characterized in that in the CED coating step at least one epoxy resin, in particular a cationic epoxy resin, is used.
11. The method according to any one of the preceding claims, characterized in that the aqueous basic solution further contains silicates and/or complexing agents.
12. A coated moulded body obtainable using a method according to any one of the preceding claims.