CS196209B2 - Acid aqueous solution for forming chemical reverse surface on aluminium and aluminium alloys - Google Patents

Abstract

An acidic aqueous coating solution for forming on an aluminum surface a coating which is corrosion resistant and to which overlying coatings adhere excellently i s disclosed. The coating solution contains compounds of zirconium and/or titanium, fluoride and phosphate in dissolved form, and optionally, polyhydroxy compounds having 6 or fewer carbon atoms. The coating solution is capable of forming on an aluminum surface a uniformly colorless and clear coating so that the coated surface has the appearance of the underlying metal surface, that is, the coating can be formed without changing the appearance of the metal surface.

Description

The invention is an acidic aqueous solution to form a chemically reverse coating on aluminum and its alloys.

The term "aluminum alloys" as used herein refers to alloys where aluminum is the predominant component, for example, aluminum alloys containing minor amounts of metals such as magnesium, manganese, copper, and silicon. However, it is envisaged that the solution according to the invention will be used to form a chemically-converting coating mainly on glossy aluminum, as is the case with aluminum strips and especially aluminum cans and cans. Probably the most common aluminum alloy used in the canning industry is aluminum alloy 3004, containing in addition to unavoidable impurities 1.2% manganese and 1% magnesium.

Acidic aqueous solutions are already known for the purpose of forming chemically conversion coatings on the aluminum surface; these coatings are corrosion resistant and thereby protect the surface from degradation caused by corrosion attack. The purpose of these chemically conversion coatings is also to assist the drying coatings applied thereto, whether decorative or functional (such as paints, varnishes and the like), to adhere tightly and firmly to the aluminum surface.

One of the important purposes of applying coatings to aluminum, precisely to which the invention relates, is the coating of aluminum cans. Chemical conversion coatings applied to aluminum cans must not only be corrosion-resistant and firmly adhered to, but also uniformly clear and colorless, so that the cans, although coated, retain the original bright shiny natural appearance of the aluminum substrate, as is normally the case desired from the final product, although some parts of the can may be coated with paint or varnish.

In addition to the aforementioned properties, which are desirable for almost all coatings on aluminum, the highly desirable property of coated coated cans is their ability to resist staining under the influence of moderately hot water, for example in the range of 60 to about 77 ° C. In some applications, aluminum is treated in this way, which is called 'canned pasteurisation' in the canning industry; but this treatment sometimes results in blackening or other coloring of the aluminum, whether or not coated, which makes the can look unattractive.

Acidic aqueous solutions are now known to form a chemically conversion coating on aluminum and its alloys, these coatings being uniformly clear and colorless and meeting all of the above requirements. Unfortunately, · the best of them contain chromic acid, phosphoric acid and · hydrofluoric acid, and their use is associated with the problem of waste water treatment containing hexavalent chromium compounds, which is a very toxic substance.

Thus, there appears to be a need for aqueous solutions to form chemically conversion coatings on aluminum and its alloys, which solutions would not contain hexavalent chromium and would be capable of forming tightly adhering, corrosion-resistant conversion coatings not subject to pasteurization coloring but clear and colorless and good base for drying coatings on aluminum surface.

It is clear from the prior art that until now it has been possible to prepare colorless coatings using hexavalent chromium-containing aqueous coating solutions and / or those resulting in coatings requiring further treatment with hexavalent chromium after water rinsing; furthermore, when using a coating solution and a rinse solution that does not contain hexavalent chromium, the coatings formed will be colored. Incidentally, many of the earlier discussions do not recommend the use of phosphate ions.

An aqueous acidic solution has now been found to coat on aluminum and its alloys, not requiring the use of hexavalent chromium or similar toxic substances, but nevertheless providing clear and colorless coatings on the aluminum surface, resisting blackening or other discoloration under the effect of boiling water.

The subject of the invention is an acidic aqueous solution for forming a chemically conversion coating on aluminum and its alloys containing phosphate, fluoride and zirconium and / or titanium, and comprising the amount of zirconium and / or titanium in an amount of from 10 ppm to to an amount corresponding to · their solubility in solution, 10 ppm to 1000 ppm of phosphate, and fluoride · in an amount of at least 13 ppm and sufficient to produce a concentration of up to 500 ppm of a fluorine-capable reaction in solution, the solution having a pH of 1.5 to 4 Moreover, the solution according to the invention is virtually free of solids which tend to precipitate and is able to form uniformly clear and colorless coatings on the aluminum surface so that these coatings do not start blackening by boiling water for 2 minutes.

Such solutions can be used to treat a bright shiny aluminum surface in such a way that the bright shiny appearance of the surface does not change but a colorless corrosion-resistant surface coating is formed to which the drying coatings applied perfectly adhere. In addition, the resulting coating is capable of resisting blackening or other discolouration when exposed to boiling water not only for the minimum period indicated, i.e. for at least about 2 minutes, but - as will be seen from the examples below - when the solutions are formulated in order to achieve optimum resistance to blackening or other coloring, the coatings are capable of withstanding exposure to boiling tap water even for 15 minutes or up to about 30 minutes.

The acidic aqueous solutions according to the invention need not contain any components other than those mentioned above, as well as their cations; however, they are capable of effectively forming the aforementioned types of coatings on an aluminum surface without the presence of toxic substances and other materials which cause problems in wastewater disposal. In particular, the solutions according to the invention are free of, for example, hexavalent chromium and elements such as manganese, iron, cobalt, nickel, molybdenum and tungsten, as well as other difficult substances such as ferricyanides and ferrocyanides. Thus, the solutions according to the invention are devoid of all kinds of chemicals, the presence of which necessitates special treatment of the solutions used before they can be discharged into watercourses or even to a waste water treatment plant.

It is surprising that such excellent results can be achieved using the solutions of the invention, especially since it has previously been believed that the addition of phosphoric acid or phosphates to acidic aqueous solutions containing titanium or zirconium has an adverse effect on these solutions. Moreover, the view was quite understandable, since both zirconium phosphate and titanium phosphate are very insoluble in aqueous environments - moreover, the well-known analytical test for determining the amount of zirconium or titanium in an aqueous solution consists in adding phosphate to the solution, thereby eliminating zirconium or titanium phosphate. Existing efforts to formulate acidic aqueous solutions containing not only zirconium and fluorides, but also phosphate and to use them to coat the aluminum as described in the invention have resulted in the precipitation of zirconium phosphate. it is highly undesirable to apply the coating on an industrial scale, as will be explained further below. The invention, however, successfully makes it possible to prepare an acidic aqueous solution to form a coating, which solution practically does not contain solid portions of zirconium phosphate or titanium phosphate tending to precipitate.

The acidic aqueous solution according to the invention must contain zirconium and / or titanium, since coatings with satisfactory properties can only be formed if they contain zirconium and / or titanium bonded directly or indirectly to the aluminum surface. Compliant coatings can be formed by applying solutions containing even only 10 ppm of either zirconium or titanium or a mixture of zirconium and titanium, but larger amounts may be required depending on other parameters of the coating process. of these components. '

Zirconium and / or titanium may be used in concentrations up to their solubility. in an acidic aqueous solution, but this depends on other parameters, including in particular the acidity of the solution and the concentration of both fluoride and phosphate. These concentrations need to be controlled so as to avoid precipitation of zirconium and titanium phosphates, which is undesirable for several reasons. The precipitation not only reduces the amount of components in the solution, but adversely affects the coating process, both on the aluminum surface and elsewhere, for example, any type of precipitate may clog the spray nozzles. If the amount of zirconium and / or titanium were to exceed the respective solubility limits and if precipitation would occur, the amount of phosphate would have to be reduced and / or the pH of the solution had to be reduced and / or the amount of fluoride had to be increased.

The phosphate must be present in the acidic aqueous solutions of the invention for several reasons. On the one hand, the presence of the phosphate in the solution allows a simple test confirming the formation of the coating. This is of great importance on an industrial scale, where, for example, a large amount of aluminum is processed in a relatively short time to form a coating that is not visible to the naked eye on aluminum. Without a suitable test, the operating parameters of the solution could easily change without being observed, for example, incorrect replenishment of the components of the solution either by failure of the dosing mechanisms or by an error of the operator, which would render the solution ineffective.

In order to ascertain whether the acidic aqueous coating solutions according to the invention actually fulfill their task. · A chemical conversion coating is formed on aluminum, it is only necessary to take random samples · coated aluminum, expose them to relatively high effects for a relatively short period of time, · temperatures, for example · 538 ° C for 5 minutes, · This so-called "muffle test". Coloring or discoloration to a slightly golden brown tone or even darker shades of brown or purple indicates the presence of zirconium and phosphorus in the coating. If no zirconium and phosphorus are deposited, then the aluminum surface is grayish after the muffle test / The presence of both zirconium and phosphorus can also be detected by electron surface analysis with a suitably coated coating according to the invention.

A further reason for the necessary presence of phosphates in the solution according to the invention is that they greatly contribute to the corrosion resistance as well as to the adhesion of the resulting coatings to the substrate, especially coatings formed from solutions with pH values below 3.5.

It has now been found that in order to obtain coatings with satisfactory properties and to discolour in the above muffle test, the coating solution must contain at least 10 ppm of phosphates; higher amounts may be required to achieve the best results, which will depend on other parameters of the coating process, as will be explained below. On the other hand, excessive phosphate concentration may reduce the corrosion resistance of the coating formed; therefore, the phosphate concentration in the solution should not exceed 1000 ppm. Consequently, the phosphate concentration should be selected in the light of the above-mentioned circumstances concerning the phosphate effort to be eliminated with zirconium and titanium.

The fluorides must be in solution at a concentration that is at least sufficient to bind all of the zirconium and / or titanium to a soluble complex, such as flaorozirconate or fluorotitanate, as this reduces or even prevents precipitation of zirconium and / or titanium phosphate. Thus, the minimum amount of fluoride is dependent upon the amount of zirconium and / or titanium in the solution. In general, if the solution contains 10 ppm zirconium, the minimum amount of fluoride is 13 ppm, and if the solution is 10 ppm of titanium, the minimum amount of fluoride is 25 ppm.

There are other factors influencing the appropriate fluoride concentration. The solution of the invention dissolves aluminum during application, and therefore the concentration of dissolved aluminum in the solution increases whenever the aluminum comes into contact with the solution during immersion, spraying or flow if the excess solution used or unreacted solution is recycled. Dissolved aluminum has an adverse effect. effect on coating if there is not enough fluoride in the solution to bind the aluminum to the complex. The amount of fluoride in the solution therefore also depends on the extent to which aluminum accumulates in the solution, which in turn is dependent on factors such as the shape of the aluminum surface to which the coating is applied and the way in which the treated surface is brought into contact. solution.

From a practical point of view, when operating on an industrial scale, of course, the solution should contain an excess of fluoride, an amount higher than the amount complexly bound with aluminum (and also with any other metal in the solution capable of forming a fluoride complex), referred to as "reaction-capable fluoride" for simplicity, and includes fluorides present in both hydrogen fluoride and fluoride ions.

The concentration of 'reaction-capable fluoride' can be measured as follows: First, a constant ionic strength buffer containing 40.8 g of sodium acetate, 28.5 ml of glacial acetic acid and 58.0 g of deionized sodium chloride is prepared, and the pH is adjusted by adding a solution of sodium hydroxide to a range of 5.0 to 5.3. A sample of the solution, diluted with this constant strength buffer, is then tested with a pH-meter with a specific fluorld electrode. Subtraction directly

198209 detects the concentration of the reaction-capable fluoride in solution.

Generally speaking, the problem is: how to avoid too little fluoride-capable reaction rather than too much, but it is necessary to avoid such a high concentration of fluoride-capable reaction that causes unwanted etching of the aluminum surface that would cause unwanted appearance of the aluminum surface, and could adversely affect the corrosion resistance and adhesion of the coating. It is difficult to indicate the exact concentration limits of the reaction-capable fluoride that would lead to these problems, since these limits vary depending on - other parameters of the loading process, for example the pH of the solution as well as the contact time of the aluminum product with the solution. its temperature. According to experience, however, these problems can be avoided in that the concentration of the reaction-capable fluoride is at most 500 ppm. ·

The pH of the solution must be in the range of 1.5 to 4.0, since at higher pH values, phosphate excretion problems may occur. Preferably, a solution having a pH in the range of 2.6 to 3.1 is used.

The pH of the solution - can be adjusted by adding any acid or base, if its use does not interfere with the coating; for example, perchloric acid or sulfuric acid may be used, although when using sulfuric acid it is recommended that the pH of the solution does not fall below 2, since below this value sulfuric acid adversely affects the coating process. Preferred pH adjusters are nitric acid and ammonium hydroxide.

The acidic aqueous solution of the invention for coating on aluminum and its alloys can be prepared from a variety of readily available zirconium and / or titanium containing materials, fluorides and phosphates when dissolved in the solution. Generally speaking, it is preferable to use zirconium in the form of a soluble fluoro-zirconate and / or fluorotitanate, such as fluoro-zirconium acid and its ammonium and alkali salts; and likewise, it is preferred to use titanium in the form of soluble fluorotitanium compounds, such as fluorotitanic acid, and salts thereof, such as the ammonium salt and alkali metal salts. However, the solution can also be prepared using zirconium fluoride and / or titanium or titanium fluoride, and can additionally be prepared from a mixture of soluble compounds, one containing zirconium or titanium and the other containing fluoride such as nitrate or zirconium sulfate. and titanium sulfate on the one hand and hydrofluoric acid and its water-soluble salts on the other, such as the ammonium salt or the alkali metal salts. Zirconium carbonate and the corresponding ammonium or alkali metal double salts can also be used.

Similarly, the acidic aqueous solution of the invention can be prepared from a number of readily available phosphate sources. Generally speaking, it is preferred to use orthophosphoric acids, but ammonium and alkali metal salts may also be used; it is also possible to use other forms of phosphoric acid, for example metaphosphoric, pyrophosphoric, tripolyphosphoric, hypophosphoric acid, as well as the corresponding salts.

In general, the same applies to fluorides: any fluoride source that is capable of complexly binding aluminum can be used if it is soluble in solution and does not contain any other component that would adversely affect the deposition of the coating. However, if fluoride is added as a complex fluoride of titanium or zirconium, then the amount of reaction-capable fluoride that is released by hydrolysis of such complex fluoride may not be sufficient to bind aluminum to the complex, but hydrolysis may. - to the extent that zirconium or titanium, - not bound in the complex, reacts with phosphates to form undesirable precipitates. To avoid this, the solution should also contain an additional fluoride source capable of complexly binding aluminum, which accumulates in solution during operation. Examples of fluoride-capable aluminum-binding sources include hydrofluoric acid, its salts, ammonium hydrofluoride and alkali metal hydrofluorides, with hydrofluoric acid being a particularly suitable source of fluoride ions since it easily releases sufficient fluoride ions for complex aluminum bonding, but is not a source of other cations that could interfere with the coating.

Obviously - when problems arise - with disposal - of wastewater and when aluminum products are to be used in the food or beverage industry after coating, - the coatings are obviously free of - chromium and other toxic substances such as -. are iron cyanides. It is equally important - although - for quite different reasons - that the solutions according to the invention are free of the components from which also the substances which are precipitated from the solution are formed.

It has been found that the addition of fluoroboric acid to the inventive solutions improves the gloss or hardness of the color coatings which are then applied to the aluminum surfaces of the inventive coatings; the addition of this acid also helps to stabilize the solution of the invention when prepared from hard water. Calcium - and - magnesium ions in hard water have an affinity to fluorides, and if they would drain fluoride ions from zirconium and / or titanium complexes with fluoride ions, the released zirconium and / or titanium would tend to react with the phosphates to form undesirable precipitates, insoluble zirconium - and / or titanium phosphates. It is believed that when fluoroboric acid is used, it acts as a buffer, providing fluoride ions for calcium or magnesium ions in hard water. However, too much fluoroboric acid can reduce the corrosion resistance of the coating. In general, therefore, it is preferred to use solutions containing fluoroboric acid in a concentration ranging from 8 to 200 ppm.

It has also been found to be advantageous to add some polyhydro compounds to the solution according to the invention, whereby the coating formed is then characterized by better adhesion for the subsequently applied paints or lacquers, more precisely any organic compound soluble in the solution according to the invention. dissolution in the solution provides at least 40 ppm of polyhydroxy compounds containing no more than 6 carbon atoms and which, of course, does not have a beneficial effect on the coating of the solution, and the desirable curd resistance and satisfactory adhesion to paints. Examples of such polyhydroxy compounds include gluconic acid and its salts, sorbitol, mannitol, D-glucose, ethylene glycol and glycerol.

Particularly preferred polyhydroxy compounds include gluconic acid and its ammonium salt and alkali metal salts, as well as the compounds soluble in the solution of the invention to form salts of gluconic acid and / or gluconic acid, such as stable gluconic acid lactones, e.g., χ-lactone and β-lactone.

Although higher amounts can be used, it is recommended to use the polyhydroxy compound in an amount of at most about 1000 ppm, preferably in the range of 40 to 400 ppm.

The solution of the invention typically contains up to 125 ppm zirconium or an equivalent amount of titanium, up to 1000 ppm phosphates, and up to 500 ppm reaction of hydrophobic fluoride.

Particularly preferred solutions according to the invention are those in which the pH is in the range of 2.6 to 3.1 and which contains a component of an approximate concentration in ppm

Zr 45 to 125

PO4 50-200 reaction-capable fluoride 10-200

A preferred source of zirconium in the above solution is ammonium fluorosilicate, and a preferred source of phosphate ions is orthophosphoric acid. Hydrofluoric acid is preferably used as a source of reaction capable of fluoride, and nitric acid is used to adjust the pH. For the above reasons, it is preferred to add 8 to 200 ppm of a polyhydroxy compound, preferably D-gluconic acid.

Although it is now preferred to use zirconium-containing solutions, titanium-containing solutions may also be used, preferably containing up to _: 65 ppm Ti, up to 200 ppm. PO 1, up to 200 ppm of fluoride-capable reaction.

A preferred source of titanium is fluorotitanic acid. The other preferred components, and the amounts thereof, are the same as those described above with respect to the zirconium-containing solution.

There are still some general factors to consider in order to achieve the best results. When working at relatively high pH values, relatively small amounts of zirconium or titanium are preferred. and / or phosphates to avoid elimination. If the solution is contacted with the aluminum surface for a relatively short time, relatively large amounts of zirconium or titanium and phosphates should be used. Similarly, if the temperature at contact of the solution with the aluminum surface is relatively low, relatively high amounts of components should be used. In general, the lower the amount of phosphates used in the solution, the higher the amount of zirconium and / or titanium can be used.

The invention also discloses a method of applying uniformly clear and colorless but firmly adhering chemical conversion coatings, forming a good basis for subsequent deposition drying coatings on an aluminum surface, wherein the aluminum surface is contacted with an acidic, aqueous coating to form a chemically conversion coating as has been described above.

Of course, the aluminum surface to be contacted with the solution according to the invention should be clean. Any commercially available cleaning agent, such as both alkaline and acidic cleaning solutions, can be used to clean the aluminum surface using conventional procedures. As already mentioned, this method is commonly used in cleaning aluminum cans with a bright shiny surface. The aluminum surface may be contacted with the solution by any suitable method, for example, by spraying, dipping, by rollers, by flow coating or by mist formation. For many purposes, the solution can be sprayed most economically. The coating may be applied either to individual finished products, such as cans, or may be formed on unfinished semi-finished products, such as aluminum strips, from which the finished products are then made.

The deposition temperature must naturally be such that the reactive components of the solution bind to the aluminum surface, but otherwise are not of critical importance, for example deposition can also be carried out at room temperature. However, it is preferable to bring the solution into contact with the aluminum surface at a temperature of at least 27 ° C, but on the other hand, to avoid too high a temperature, since it produces a matt and speckled appearance of the aluminum surface. This occurs at temperatures dependent on the various coating parameters, including

19-64223-9 including, for example, contact time a. the reactivity of the solution, which in turn depends on the pH and the concentration of the components in the solution. It is recommended that the maximum permissible temperature be about 66 ° C; preferably, the solution is contacted with the aluminum surface at a temperature in the range of 27 to 43 ° C.

The satisfactory coatings are formed by contacting the solution with the aluminum surface for at least 5 seconds, preferably for at least 15 seconds. The lower the solution temperature, the longer the contact time of the working solution with the aluminum surface; on the contrary, the higher the temperature of the solution, the more the contact time must be shortened. It is usually not necessary to allow the solution to contact the aluminum surface. was longer than 1 minute.

By treatment with an acidic aqueous solution, a very thin and very light coating can be formed. The weight of the coating will be. they vary depending on the concentration of the individual components of the solution, as well as on the temperature and duration of the solution. For use, such as described above, is. the coating weight is preferably in the range of about 21.5 to 215 mg / m 2, especially in the range of about 53.8 to about 107.6 mg / m 2. Coatings of these weights can be produced by deposition under the above conditions. Higher weight coatings can cause industrial scale coating problems on aluminum cans, because the machinery that applies the base paint or the ink on the coated aluminum cans has precise tolerances for the placement of the very thin cans and the cans. a relatively thick coating could damage the machinery.

According to the invention, coatings can be formed which are very uniform, which allows uniform application of the base paints or inks in the desired coverage on the coated aluminum surface. In the industrial manufacture of aluminum cans, the base inks and printing inks are applied to aluminum cans coated with an automatic machine and a coating roll, where the base or printing ink is applied to the roller and with it onto the coated can surface as the roller rolls over the coated can surface. . If the coating is uneven, then the primer or ink applied thereto would not have to cover the respective portions of the can surface.

After working. solution to the aluminum surface, the treated surface is to be rinsed with water, finally with deionized water. Rinsing with water containing a small amount of dissolved solids may result in a coating having poor adhesion properties to the subsequent paint layer. It is not necessary to rinse the aluminum surface coated according to the invention with any aqueous solution. containing chromium, for example. a solution containing hexavalent chromium, as is. this is common in many other chemical deposition processes. conversion coatings.

After rinsing the coated surface. with water as described above, the coating is to be dried. It. can be carried out by any suitable drying, for example in an oven, or by hot air in forced circulation.

After application of a chemical conversion coating and usually after rinsing with water and drying. se. a protective or decorative layer may be applied to the coated surface, for example. drying out. layer. Sometimes the protective layer is applied after rinsing with water, and then the two coatings applied, i.e. the chemically-conversion coating and the protective layer, are dried simultaneously.

If aluminum cans are intended to be filled with beer, they should first be treated with the solution according to the invention before the protective and / or decorative layer is to be applied. Only then cans are filled with beer and pasteurized after filling.

Acid aqueous. the solution according to the invention is most conveniently prepared by diluting the aqueous concentrate of the ingredients with an appropriate amount of water.

Therefore, another variation of the invention is a concentrate such that when the solution according to the invention contains 0.5 to 10% by weight. % of the concentrate are the amounts of the individual components in the solution. this:

zircon. and / or titanium in an amount of from 10 ppm to an amount corresponding to their solubility in solution, ppm to 1000 ppm of phosphate, and fluoride in an amount of at least 13 ppm and sufficient to form a concentration of up to 500 ppm. a fluorine-capable reaction in solution, the solution having a pH in the range

1.5 to 4.0.

Advantageous. the concentrates are such that when the solution of the invention contains 0.5 to 10% by weight of the concentrate, the solution of the invention contains about 45 to 125 ppm of zirconium added in the form of a fluorosirconate, for example sodium or potassium, but most preferably ammonium, about 50 to 200 ppm in the form of orthophosphoric acid, about 8 to 200 ppm of fluoroboric acid, about 10. up to 50 ppm hydrogen fluoride and nitric acid in an amount such that the pH of the solution is in the range of 2.6 to 3.1.

Such concentrates may also contain a polyhydroxy compound, preferably gluconic acid, in an amount such that the solution contains 40 to 400 ppm of the compound.

Of course, in continuous coating, it is important to adequately replenish the solution to maintain it. the coating efficiency. It has been found that the content of some of the ingredients of the solution decreases during coating. Zirconium and / or phosphorus are deposited in the coating, the fluoride-capable reaction being consumed to form a complex with. dissolved aluminum and hydrogen is consumed during oxidation of the aluminum surface. The amount of components in the solution is also reduced by their retention on the aluminum surface. In addition, the rate of reduction of the constituents by retention on the aluminum surface is dependent on the shape of the surface to be coated and the manner in which the solution is brought into contact with the aluminum surface, for example .

Refilling of working solution. may be carried out either by individually monitoring the amount of the individual components of the solution and replenishing them as much as they are lost, or by adding an aqueous concentrate of the components in approximately the correct proportions to keep the individual components in solution in working effective amounts. .

Whenever possible, that. If aluminum has accumulated in the solution, it is recommended that the additional amount of concentrate contains a relatively high proportion of reaction-reactive fluoride for complex binding of the dissolved aluminum. Preferred sources of reaction. capable of fluoride ion are hydrogen fluoride or. ammonium hydrofluoride or mixtures thereof.

The following is a composition of a suitable concentrate for use in replenishing the ingredients of the solution of the invention:

about 5. up to 10 g / liter of zirconium or about 2.5 to 5 g / liter of titanium, about 5 to 10 g / liter of phosphate anions (considered as PO i), and.

a substance which is a source of about 5 to 20 g / liter of reaction-capable fluoride, preferably hydrogen fluoride or ammonium hydrofluoride, or a mixture thereof.

If polyhydroxy compounds are used, they should be included in the make-up. concentrate · in an amount of 5 to 20 g / liter.

When fluoroboric acid is used, it should be present in the make-up concentrate in an amount of from about 1 to about 5 g / liter.

Examples .

The following examples illustrate the invention. Comparative examples are also given.

Unless otherwise specified, aluminum surfaces with coatings applied using the solutions of the examples are drawn or pressed aluminum cans that are first degreased, if necessary, in an acidic aqueous cleaning solution containing sulfuric acid and detergent. Unless otherwise specified, the solution is sprayed for about 25 seconds at about 43 ° C. After treatment with the solutions given in the examples, the aluminum surface is rinsed with deionized water and dried in an oven at 205 ° C for 2 minutes.

Then the aluminum surface is tested for corrosion resistance by a pasteurization test. The test consists in immersing the aluminum surface in water at the temperature and for the times given in the examples. Completely clean, only aluminum · surface · turns pasteurized in a few minutes. It will be apparent from the examples below that treatment of the aluminum surface with a working solution of the invention results in a surface with a coating that is neither blackened nor discolored in any way. .

The test results are evaluated as follows: 5 perfect surface · no blackening, 3x acceptable surface, 0 perfect failure, considerable blackening during the test. ·. *

Aluminum surfaces treated using the solutions described in the examples are also tested for paint adhesion. Once the coated surface has dried as described above, a white base paint is applied to a portion of the surface, and. for the remainder of the surface inner vinyl lacquer. After the ink has cured, the surface is immersed either in a boiling aqueous detergent solution or in an aqueous sodium chloride solution. After being removed from water or from the solution, the coated surface is rinsed with water and the excess water is wiped off the surface. The surface with the colored layer is then · laterally scratched with a sharp metal object, exposing the aluminum in the form of lines alternating with the paint or varnish, · followed by color adhesion testing. It consists of sticking cellophane tape to the scratched area; which is then detached by a rapid movement in the opposite direction. Results, tests are evaluated as follows:

perfect adhesion if · tape · does not eject any paint · from surface, acceptable adhesion, complete failure.

The different compositions of the solutions in the first six examples and the first seven comparative examples are shown in Table I, and include the compositions within the scope of the invention as well as the comparative compositions. Table II shows the results of pasteurisation and paint adhesion tests. The solutions in Table I are adjusted to pH · 2.7 by addition of concentrated nitric acid or ammonium hydroxide. The surfaces are then exposed to either boiling tap water for 15 minutes or hot water (70 ° C tap water for 45 minutes, as shown in Table II).

In some cases, several aluminum surface samples are treated in the same manner. In such cases, the following tables show a greater number of evaluations.

198209

Example # 15 Dec TABLE I Components of solutions and their amounts in g / liter (NHiJzZrFe HBFá HřSiFe HzTiFe 1B HF H3PO1 1 0.240 _ - · 0.164 0.050 0.294 2 -  - - ' 0.164 0.050 0.294 3 - 0.264 -. . . 0.164 0.050 0.294 4 0.240 0.264 - 0.164 0.050 0.294 5 0.240 0.264 - - . - - 0.294 6 0.240 0.264 - 0.164 - 0.294 C-1 + 0 0 0 0 0 0 02 / 0.240 - - - 0.050 - 03 / 0.240 0.264 - - 0.050 - C-4 - 0.264 - - 0.050 0.294 C-5 0.240 - 0,442,. - 0.050 - C 6 - - 0.442 - 0.050 0.294  C-7 0.240 - - 0.164 0.050 - ⁺ ) only cleaned, without any adjustments TABLE II Example pasteurization t est < adhesion barev y ^{+ +} C. 100 ° C for 15 min. 70 ° C 45 min. white basic color internal vinyl lacquer 1 3+ 4— 10, 94-, 94 · , 9 10, 10, 10, 10 2  3 3 10-, 9-, 94- , 9 10, 10, 10, 10 3 2 3— 9, 9, 9, 8 10, 10, 10, 10 4 3 3+ 9+, 84-, 8 , 8 10, 10, 10, 10 5 • 44- 4+ 10, 10, 94- . 9 10, 10, 10, 10 6 44- 4+ 10, 10, 10 10 10, 10, 10, 10 C-1 + 0 0 0, 0, 0, 0 10, 10, 94-8 C-2 0 0 9, 84, 8, 6 10, 10, 10, 10 C-3 0 0 6, 5, 5, 0 10, 10, 10, 10 C-4 0 0 0, 0, 0, 0 10, 10, · 10, 94- C-5 0 0 0, 0, 0, 0 10, 94-, 94- C-6 0 0 0, 0, 0, 0 10, 10, 10 C-7 0 0 7, 6, 5 10, 10, 10, 94-

⁺ } only cleaned, without any modification ^{+ +} j detergent 0.7%, 100 ° C; Fifteen minutes

The examples given in Table III illustrate the effect of different phosphate concentrations in fluoro-zirconate solutions. The pH of the solutions in these examples is 2.5, except for Example C-9 (pH 3.25). The pasteurization test depends on immersion of the unpainted aluminum can in hot water (70 ° C) from the tap for 45 minutes. The adhesion of both the white base paint and the inner vinyl varnish is tested by immersing the paint-coated cans in a boiling 1% detergent solution for 15 minutes followed by standardized scratching and tearing off the adhesive tape.

TABLE III

Solution components and their amounts in g / liter

Example # H3PO4 (NHijzZrFe HF Pasteurization test Color adhesion test white base color inner vinyl varnish C-8 0 0.24 0.05 0 8, 7, 0, 0. 10, 10, 10 7 0.05 0.24 0.05 3 9+, 9+, 9, 9 10, 10, 10, 10 8 0.10 0.24 0.05 4— 9+, 8+, 8,5 10, 10, 10, 10 9 0.49 0.24 0.05 4— . 9+, 9+, 9, 9 10, 10, 10, 10 10 0.98 0.24 0.05 3+ 9+, 9+, 9+, 9+ 10, 10, 10, 10 C-9 0.98 0 0.05 0 0, 0 10, 7

Y1

199209

Example 11

This example describes the use of a make-up solution and a make-up concentrate in the continuous coating of cans in which 400 cans are coated. The make-up concentrate contains

4.8 g / liter ammonium fluorosilicate, 3 g / liter phosphoric acid, 0.44 g / liter hydrofluoric acid, 2.64 g / liter fluoroboric acid, 11.4 g / liter nitric acid and 1.92 g / / liter of sodium gluconic acid salt. This make-up concentrate is then diluted to a concentration of 2.5% in aqueous solution; the pH is then 2.70. The make-up solution is prepared from 24 g / liter of ammonium fluorosirconate. 9.4 g / liter phosphoric acid,

11.7 g / liter of hydrofluoric acid, 0.68 g / liter of fluoroboric acid, 21.4 g / liter of nitric acid and 0.4 g / liter of sodium gluconic acid salt.

As coating is continued on the aluminum cans, a make-up solution is added as necessary to maintain the pH of the bath in the range of 2.70 ± 0.02. The pH is checked after each coating on 10 cans. The pasteurization test depends on immersion for 15 minutes in boiling tap water. The paint adhesion test is carried out by immersion in boiling water containing 0.7% detergent for 15 minutes, followed by lateral scratching and tearing off of the adhesive tape provided. The test results are shown in the following table

Color adhesion test

Number of cans Pasteurization test white base color Inner vinyl lacquer coated

1 3 10, 10 10, 10 50 4+ 10, 10 10, 10 51 44- 10, 10 10, 10 100 ALIGN! 4+ 10, 8+ 10, 10 101 3 84-, 7 10, 10 150 4+ 94-, 8 10, 10 151 44- 94-, 9 10, 10 200 4+ 10, δ-Ι- 10, 10 201 .44- 10, 8+ 10, 10 250 4+ 10, 9 10, 10 251 4+ 94-, 9+ 10, 10 300 44- 9, 9 10, 10 301 4 10, 10 10, 10 350 44- 10, 94- 10, 10 351 4+ 10, 10 10, 10 400 4 10, 10 10, 10

Table IV shows the results of the pasteurization test and the results of the ink adhesion test. When coating, the cans No. 3, 80, 160, 240, 320 and 399 were exposed to a temperature of 540 ° C for about 5 minutes. The entire surface of the cans thus becomes evenly brown.

It should be noted that the solution remains clear during coating of the first 100 cans. Thereafter, the solution becomes slightly cloudy and is still cloudy when coating No. 400 cans is applied. After slurrying, neither the sludge nor the precipitate is isolated by centrifugation.

The concentration of zirconium, a reaction capable of fluoride and phosphates is monitored throughout the procedure. The zirconium concentration increases during deposition from the original 46 ppm to 111 ppm, the phosphate concentration from 70 ppm to 110 ppm, and the reaction-capable fluoride concentration from 85 ppm to about 95 ppm, which then drops to 87 ppm.

Examples 12 to 26, shown in Tables V and VI, illustrate the improved ink adhesion achieved by using the polyhydroxy compounds in the solution of the invention. More specifically, the results in Table V relate to the use of a sodium salt of gluconic acid of varying concentrations in a working solution comprising ammonium fluorosilicate and / or fluorotitanic acid, phosphoric acid and hydrofluoric acid. Table VI shows the results obtained using polyhydroxy compounds other than the sodium salt of gluconic acid. In these examples, the working solutions are sprayed for 15 seconds at 32 ° C and a white polyester polyester paint is applied to the coated cans. Before the ink cures, another alkydamine topcoat is applied to the wet ink coating. Curing is carried out for 6 minutes at 190 ° C.

TABLE V

The pH of all solutions was adjusted to pH 2.7 by the addition of nitric acid

Example (NHzZrFe H2TiF6 H3PO4 HF Sodium salt Pasteurization Adhesion 1% g / 1 g / 1 g / 1 g / l acid test 15 min.

12 0.120 0 0,098 0.010 0 5, 5 0, 0 13 0.120 0 0,098 0.010 0.04 4+ 8, 8 14 0.120 0 0,098 0.010 0.08 4+ 8, 94- 15 Dec 0.120 0 0,098 0.010 0.195 44-, 44- 9, 94- 16 0.120 0 0,098 0.010 0.40 4 94-, 94- 17 0.120 0,041 0,098 0,098 0.010 0 4, 4 5, 9 18 0.120 0,041 0.010 0.195 4, 4 9, 94- 19 Dec 0.120 0,082 0,098 0.010 0 4-, 34- 7, 9 álU η Ί nn n ЛЙО 0,098 0.010 0.195 3+, 3+ 9+, 9+

TABLE VI

The pH of all solutions was adjusted to pH 2.7 by the addition of nitric acid

Example # (NH 4) 2 ZrFe g / 1 ' H5PO4 g / l HF -. g / 1 Ingredient 0.1 g / l. · Pasteurization 15 min; 100 ^e C Adheze 1% Reagent, 100 ° C, 15 min. 21 0.120 0,098 0.010 - 44-, 4+. 0, 5 22nd 0.120 0,098. 0.010 sorbltol 44-, 44- ' 0, 94- 23: 0.120 0,098. 0.010 mannitol 44-, 44- 9, 94- 24. ... 0.120 0,098 0.010 D-glucose .44-, 44- 5, 9 25 0,120 ’ 0,098 0.010 ethylene glycol 44-, 44- 7, 9 26 0.120 0,098 0.010 glycerol 4+, 44-. 0, 6

The other two groups of examples describe the use of the previous working solutions of the invention containing phosphate, fluoride and either zirconium or titanium. The examples show the undesirable results obtained by using these solutions to coat the aluminum. Examples C-ΙΌ, C-11, C-12 and C-13 describe the use of the solutions prepared in Examples 7, 9, 14 and 15 of U.S. Patent No. 3109,757 to coat on aluminum cans.

For use in Examples C-10, C-11; C-12 and C-13, a concentrate of the following composition is prepared:

Weight%

The above concentrate is diluted with water to a content of 4% by volume with the addition of 0.25 w / v%. % sodium hydroxide solution. Glycerophosphate and complex metal fluoride are added to the diluted solution in the amounts shown in Table VII. The solutions were heated to about 62 ° C and sprayed ^one on aluminum cans for 30 seconds. In Example C-12, copper nitrate hexahydrate is added to a concentration of 0.005% copper ions. '-

Table VII shows the properties of the working solutions and coatings thus produced.

zinc oxide 8.0 phosphoric acid, 75% 39.5 nitrate hexahydrate nickel 6.75 nitric acid (38 ° Bé) 2.87 water 42.88

100.00

Pasteurization Test Assay, 15 min., Paint adhesion • 100 · ° C 1% Joy Reagent, 15 min <, 100 ° C

19В209 .TABLE VII

Example Glycero- (NH3JZZFFe H2T1F6) Appearance phechocompound phosphate weight% weight% age with coating weight% layer before pasteurization

Appearance of working solution

c-10 0.1 0.05 0 slightly gray white precipitate 1 9+ c-11 0.4 0.05 0 slightly gray white precipitate 1 9+ C-12 0.2 0 0,033 dark gray white precipitate 0 9 C-13 0.2 0 0.33 dark gray white precipitate 0 9+

Example C-14

This example describes the use of a working solution of the type described in Example 8 of U.S. Pat. No. 2,813,814. A concentrate containing the following components is prepared:

g 'manganese carbonate183,4 phosphoric acid, 75 ° / on555,3 nitric acid, 70% n22,5 ammonium nitrate77,3 sodium hydrofluoride6,0 potassium fluorotitanate ´15, 8 water 573,5 total 1433,8

In this preparation, manganese carbonate reacts with phosphoric acid to form manganese dihydrophosphate. 840 g of the above concentrate are added to 4 liters of water, then 44.8 g of manganese carbonate and 9.2 g of sodium hydrofluoride are added, and the solution is heated to 93 ° C.

The solution is then sprayed onto aluminum cans for 30 seconds. The working solution contains a considerable amount of precipitate and a gray coating forms on the cans. It tests corrosion resistance by immersing the can in water at 100 ° C for 15 minutes. The color of the can becomes very dark: graded 0. The adhesion of the white base paint is tested by dipping the can for 15 minutes in a one percent Joy reagent at 100 ° C. The result of the adhesion test can be graded 9+.

These examples show that the invention provides a working solution for forming a coating on aluminum and its alloys which does not contain hexavalent chromium and is capable of forming a clear colorless coating on the aluminum surface that does not alter the appearance of the aluminum surface. The coated surface is resistant to discoloration even if it is exposed to boiling water for a long time and is characterized by excellent adhesion to the drying coatings applied thereto. The solution according to the invention can be very advantageously used in continuous coating on an industrial scale.

Claims (4)

SUBJECT OF THE INVENTION An acidic aqueous solution for forming a chemically conversion coating on aluminum and its alloys, containing phosphate, fluoride and zirconium and / or titanium, characterized in that it contains zirconium and / or titanium in an amount of from 10 ppm to an amount corresponding to their solubility in of a solution, 10 ppm to 1000 ppm of phosphate, and fluoride in an amount of at least 13 ppm and sufficient to form a concentration of up to 500 ppm of reactable fluorine in the solution, the solution having a pH in the range of 1.5 to 4. 2. The acidic aqueous solution of claim 1, further comprising fluoroboric acid in a concentration of 8 ppm to 200 ppm. 3. An acidic aqueous solution as claimed in claim 1, further comprising an organic polyhydroxy compound having at most 6 carbon atoms at a concentration of 40 ppm to 1000 ppm. An acidic aqueous solution according to claims 1 to 3, characterized in that it contains 40 ppm to 400 ppm of gluconic acid and / or a salt thereof. Severografla, η. μ., plant 7, Most