DE4017187A1 - METHOD FOR REFILLING CONVERSION LAYERS - Google Patents

Description

The invention relates to a method for rinsing on Surfaces of aluminum or aluminum alloys with Solutions based on titanium, zirconium and / or hafnium ions generated conversion layers and its application as Pretreatment for a subsequent painting, Foil coating or adhesive coating.

The generation of conversion layers on aluminum or Aluminum alloy surfaces, especially as Pretreatment before the order of an organic Coating is done industrially on a large scale. Such conversion layers prevent or complicate the appearance of corrosion phenomena and serve in the Case of an organic coating improved Adhesion of the applied coating. Although the fulfill widespread chromate coating these requirements in usually sufficient; because of Workplace hygiene, environmental protection or because that treated material for special purposes, eg. B. as Food packaging, however, will be used increasingly the production is chromium free Conversion layers preferred. The used for it Treatment solutions are generally acidic pH adjusted and contain z. Titanium, fluoride, Phosphate and tannin (US Pat. No. 4,017,334) or zirconium, Fluoride and boron (US-PS 39 64 936). A treatment solution containing hafnium and fluoride is in FR-PS 24 17 537 described.

The properties of the generated conversion layers can be further improved if subsequently a passivating rinsing takes place. For the reasons mentioned  become chrome-free even during the final rinse Treatment solutions are preferred, which are usually organic Contain active ingredients. Such a rinse aid on the Basis of polyvinylphenol is described in US-A 43 76 000. However, it causes pollution of the sewage in particular, due to the high oxygen demand, the degradation the organic component is required.

The object of the invention is to provide a method for passivating rinsing of chromium-free Conversion layers on aluminum or To provide aluminum alloy surfaces that the Disadvantage of rinsing solutions with organic components in terms of wastewater treatment does not have, but the Corrosion protection and paint adhesion in at least the same Way improved.

The problem is solved by the procedure of the beginning mentioned type according to the invention in such a way is configured that one with the conversion layers aqueous solutions containing aluminum, Zirconium and fluoride and to a pH <5 are set.

The inventive method is suitable for passivating rinsing of conversion coatings on Aluminum or aluminum alloy surfaces produced were made, the materials of solid aluminum or solid aluminum alloy or hereby z. In the Hot dip process plated objects can exist. For example, the material made of steel, in the Hot dip method with an aluminum or Aluminum alloy surface has been provided. Suitable alloying partners of aluminum are in particular Silicon, manganese, magnesium, zinc and copper.  

On such surfaces with solutions based on Ti, Zr and / or Hf generated conversion layers are outstanding characterized in that the layer thickness is well below 1μm, the layers are at least partially amorphous and that they are do not contain chromium. The treatment solutions by means of which The conversion layers generated are included next to Titanium, zirconium and / or hafnium ions further coating-forming and / or pickling components, such. B. Fluorides, phosphates, compounds of boron, and if necessary. Passivating ingredients such. Tannins. suitable Treatment solutions are in the aforementioned Patents described.

Conveniently, the surface is after generation of the Conversion layer rinsed with water.

The application of the rinse solution can, for. B. by diving, Flooding, spraying or rolling done.

A preferred embodiment of the invention is to rinse with a solution containing aluminum, zirconium and Fluoride in a total concentration Al + Zr + F between 0.1 and 8 g / l, preferably between 0.2 and 5 g / l. The molar ratios Al: Zr: F should advantageously on (0.15 to 8): 1: (5 to 52), in particular (0.15 to 2.0): 1: (5 to 16). In a particularly preferred embodiment of the method the Al: Zr: F ratio in the rinse solution (0.15 to 0.67): 1: (5 to 7). The pH is corresponding to one further advantageous embodiment of the invention to 2 bis 5 set.  

The coming in the inventive method used Rinsing solutions contain u. a. acid Aluminum fluorozirconate and an excess of aluminum additionally other salts of aluminum (eg fluorides, Tetrafluoroborates, nitrates). Their production can z. For example take place that first metallic zirconium or Zirconium carbonate is dissolved in aqueous hydrofluoric acid, wherein forms complex fluorozirconic acid. Than it will be metallic aluminum or aluminum hydroxide or a Aluminum salt, e.g. As nitrate, fluoride, tetrafluoroborate, Formate, acetate, preferably in dissolved form and possibly dissolved. A possible slight clouding of the Solution does not affect the effectiveness. Although the described manufacturing route is preferred, can be the Preparing solutions in a different way.

The pH of the solution is adjusted preferably with cations of volatile bases. Which includes in particular ammonium, ethanolammonium and di- and Tri-ethanol ammonium. In particular, the setting of higher pH values in the specified pH range and at higher Concentrations in the specified range of Total Concentration Al + Zr + F may cause haze Solution that does not affect the effectiveness of the process has negative influence.

According to a further advantageous embodiment of the Invention flushes those with a conversion coating provided surfaces with an aqueous solution, the additionally at least one of the anions benzoate, caprylate, Ethylhexoate, salicylate in a total concentration of preferably 0.05 to 0.5 g / l. This will especially the blank corrosion protection further increased. The Incorporation of the anions may be via the appropriate acids or their salts take place.  

The duration of the application of the rinse solution is according to a further advantageous embodiment of the invention between about 1 and 120 seconds, especially between 1 and 30 seconds. The application temperature can be between 20 ° C and about 80 ° C lie. Temperatures between 20 and 50 ° C are preferred.

For the approach of Nachspülbades is preferably demineralized or low-salt water used. Water with high salt content is less suitable for bath preparation.

After passivating rinsing, the surface may be e.g. dried in the air or in the oven, if necessary with before rinsed with demineralised water. An advantageous Embodiment of the invention provides for the surface after accelerates the passivating rinse, z. B. by Hot air or infrared radiation to dry.

The inventive method is used primarily the Pretreatment of the aluminum or Aluminum alloy surfaces before painting, Foil coating or the application of adhesives. When For example, organic coating agents are used Polyester, silicone-modified polyester, Polyvinylidene fluorides, acrylates, epoxides, Epoxy-phenolic resins, plastisols or organosols (e.g. PVC or acrylates) for use.

The advantage of the method lies in particular in increasing the liability of the organic Films on the metallic underground, as for example by correspondingly good results in the T-bend test (ISO 1519-1973) or in the feathering test (lacquer adhesion when opening of can closures). Likewise, the Durability of organic films  Corrosion stress, z. In one Condensed water constant climate test (DIN 50017 KK) or one Sterilization test increased. It also improves that Process according to the invention the corrosion resistance of not organically coated surface, as z. In the Test for well water blackened (no blackening at Cooking in water).

Based on the following example, the inventive Method exemplified and explained in more detail.  

example

Cleaned and degreased aluminum sheets became the Generation of a conversion coating 10 seconds into one Dipped solution whose temperature was 50 ° C and the had the following composition:

Ti 0.17 g / l F 1.24 g / l P₂O₅ 0.09 g / l NH₄ 0.91 g / l tannin 0.11 g / l N / A 0.003 g / l biocide 0.10 g / l

The sheets were then rinsed with water and passively rinsed. For this purpose, the sheets were 5 Submerged in the rinse solution for seconds and then from Excess solution freed by squeezing. After a Drying time of 0.5 min in a convection oven at 60 ° C. the sheets are painted with a 2-coat food-grade lacquer, whose first layer is an epoxy-phenolic resin and its second layer is an organosol. The layer thickness of the Total paint was between 10 and 15μm.

Subsequently, from the treated, about 0.25 mm thick Sheet metal punched circular blanks with 60 mm diameter and punched Cups with a diameter of 26 mm and a height of 25 mm deep drawn.

These wells were subjected to a sterilization test, by exposing for 40 minutes in a pressure vessel an aqueous solution of 3% saline, 1% citric acid and 0.5% lactic acid at 121 ° C were exposed. The after defects detected in the wells (lacquer removal, blisters)  were on a scale of 1 (paint throughout Sheath area of the cup detached = unusable) to 15 (no paint defects = excellent) rated.

The used rinse solution was through Dilute 1.6 g / l (rinse solution A) or 3.2 g / l (Rinsing solution B) of an aqueous concentrate with 0.855 Wt% Al and 8.62 wt% Zr and 10.7 wt% F under Use made of demineralized water. The pH was about 3.6 in both solutions with ammonia been discontinued.

For comparison, a polyvinylphenol solution was used with 0.6 g / l and a pH of approx. 5 (rinsing solution C) rinsed.

The composition of the invention within the Used rinsing solutions was:

Test results of the sterilization test (Rating scale: 1 = unusable to 15 = excellent) after-rinse rating A (invention) 11 B (invention) 10 C (comparison) 6

A comparison of the table values shows that the inventive method provides significantly better values as the comparative example with a rinsing solution Polyvinylphenolbasis.

Claims (11)

1. A process for the rinsing of conversion surfaces produced on surfaces of aluminum or aluminum alloys with solutions based on titanium, zirconium and / or hafnium ions, characterized in that the conversion layers are rinsed with aqueous solutions which have a content of aluminum, zirconium and fluoride and adjusted to a pH of 5. 2. The method according to claim 1, characterized in that rinsing the conversion layers with solutions whose Total concentration of Al + Zr + F between 0.1 and 8.0 g / l, preferably between 0.2 and 5.0 g / l. 3. The method according to claim 1 or 2, characterized that the conversion layers are rinsed with solutions, in the molar ratios Al: Zr: F on (0.15 to 8.0) : 1: (5 to 52), preferably (0.15 to 2.0): 1: (5 to 6), are set. 4. The method according to claim 1, 2 or 3, characterized characterized in that the conversion layers with Wash solutions in which the molar ratios Al: Zr: F are set to (0.15 to 0.67): 1: (5 to 7). 5. The method according to one or more of claims 1 to 4, characterized in that the conversion layers rinses with solutions whose pH is adjusted to 2 to 5 is.   6. The method according to one or more of claims 1 to 5, characterized in that the conversion layers rinses with solutions whose pH is more volatile with cations Bases, preferably ammonium, ethanolammonium, di- or Tri-ethanolammonium, is set. 7. The method according to one or more of claims 1 to 6, characterized in that the conversion layers with solutions that additionally contains at least one of Anions benzoate, caprylate, ethylhexoate, salicylate in a total concentration of 0.05 to 0.5 g / l. 8. The method according to one or more of claims 1 to 7, characterized in that the conversion layers 1 to 120 seconds, preferably 1 to 30 seconds, flushes. 9. The method according to one or more of claims 1 to 8, characterized in that the conversion layers with solutions that has a temperature of 20 to 80 ° C, preferably 20 to 50 ° C, have. 10. The method according to one or more of claims 1 to 9, characterized in that the surface after the final rinse dries. 11. Application of the method according to one or more of Claims 1 to 10 as a pretreatment for a subsequent painting, foil coating or Adhesive coating.