EP0012905B1 - Process for producing metal objects by forming - Google Patents

Abstract

This relates to the hydrophilization of metal surfaces and/or metal oxide surfaces. In the forming of sheet metal by drawing and wall ironing methods, in the past it has been necessary to provide lubricants so as to not only protect the metal, but also to hold down friction noises. The lubricants are difficult to remove and require expensive washing processes after the forming operation. It has been found that an hydroxide of the metal involved may be readily generated on the surface so that the surface is easily wetted by water, for example, and thereby conventional lubricants are eliminated.

Description

The present invention relates to a method for producing metal objects by shaping, such as deep-drawing and / or stretching, sheets provided with a conversion layer, which are provided with a conversion coating before the forming.

It is known that the surfaces of metals, with the exception of the noble metals, undergo a chemical surface conversion from the pure metal to an oxygen-containing compound due to the influence of the atmosphere. With most metals, with the exception of the noble metals, this surface layer consists of an oxide layer and / or a mixed oxide layer and / or an oxide hydrate layer and / or an oxide hydroxide layer and / or an oxide hydroxide hydrate layer and / or an oxygen-containing metal complex compound layer.

From aluminum it is known that its surface consists of a few molecular layers thick, hard, coherent, transparent oxide layer, which z. B. on freshly scratched aluminum in the air and in water in just a few seconds.

This protective layer is initially only a few nanometers thick; it increases to 450 to 900 nanometers (= nm) in the course of a month and then remains almost unchanged.

The surface of iron consists of mixed iron oxides, namely trivalent iron in equivalents of oxygen, hydrogen and iron that cannot be clearly defined.

The surface of iron can - as practical tests show - in contrast to the surface of aluminum, tin and chrome mechanically with a relatively soft friction partner, such as. B. paper, do not separate layers. Layer separation is to be understood as the oxidic layer that can be mechanically transferred to the friction partner.

The surface of tinned iron sheet consists of the following layers: mixture of tin (IV) oxide layer and tin (II) oxide layer, tin layer, tin-iron alloy layer and finally the bottom iron layer. These tinned iron sheets are known as tin sheets, which are usually passivated and greased on the surface. The passivation layer (e.g. chrome layer) can be applied both chemically and electrochemically.

The amount of tin is standardized z. B. according to Euronorm 77-65 with E1 to E4 or according to ASTM A624 from Designation No. 10 to No. 135/25. Information about the type of chemical surface treatments used and the amount of e.g. B. Chromium in the passivation layer is also contained in ASTM A 624. According to this, the amount of chromium in chemical passivation (Cromic-Acid-Treated Tin Plate) is not more than 250 mg chromium / 0.09 m ² surface, while in electro-chemical passivation (Cathodic-Sodium Dichromate-Treated Tin Plate) is about 500 pg chromium / 0.09 m ² .

Furthermore, the tinplate is usually greased. Common greasing agents are e.g. B. dioctyl sebacate (DOS), cottonseed oil and butyl stearate (ATBC).

The surface of electrolytically chrome-plated iron sheets (ultra-fine sheet) consists of a chrome (III) oxide layer and a metallic chrome layer. According to ASTM A 657, the metallic chrome layer is between 3 and 13 mg chrome / 0.09 m2 surface and the overlying chrome oxide layer contains 0.3 to 0.4 mg chrome / 0.09 m ² surface. The surface of the electrolytically chrome-plated thin sheet is also greased, as is the case with the tinplate mentioned above.

It has now surprisingly been found that it is possible to subject sheet metal, in particular aluminum sheet, tin-plated iron sheet, chromium-plated iron sheet and iron sheet itself, to mechanical deformation processes, in particular deep drawing or stripping, without using the lubricants previously regarded as absolutely necessary if the sheet metal is used before the forming, is provided with a hydrophilic hydroxide-containing conversion coating onto which a preserving coating made of a chemical compound which is both water-soluble and soluble in organic solvents and / or from gelatin, gelatin-like substances, gum arabic, isoparaffins and / or polyparaffins is applied.

According to a preferred embodiment of the present invention, a hydroxide of the lowest valence level of the metal is produced on the surfaces.

• (1) US-A-3231376
• (2) US-A-2 801 604
• (3) Chemical Abstracts, Band 83, Nr. 10,1975, Nr. 83 811c, S. 301
• (4) DE-A-2 506 665
• (5) EP-A-0 001 198

The following references should be mentioned regarding the state of the art:

• (1) US-A-3231376
• (2) US-A-2 801 604
• (3) Chemical Abstracts, Volume 83, No. 10.1975, No. 83 811c, p. 301
• (4) DE-A-2 506 665
• (5) EP-A-0 001 198

Process for hydrophilizing metal surfaces by producing hydroxides or hydroxide-containing compounds, in particular hydroxides or hydroxide-containing compounds in the lowest valence level of the metal in question are known per se from reference (1), namely US Pat. No. 3,231,376. It describes the production of aluminum hydroxide and zinc hydroxide layers on aluminum and zinc parts by treatment with strong inorganic bases.

Literature (2), namely US Pat. No. 2,801,604, discloses the production of a layer on tin-plated iron sheet by anodic oxidation.

Literature (3) Chemical Abstracts Volume 83, page 301 describes the production of an aluminum hydroxide film by treating aluminum surfaces with sodium hydroxide solution.

Literature (4), namely DE-A-2 506 665, discloses the creation of coating layers on aluminum containing alkaline earth metal compounds by treatment with a basic alkaline solution containing alkaline earth metal compounds.

Finally, reference (5), namely EP-A-0001 198, describes the production of hydroxide-containing layers on magnesium and aluminum by anodic or chemical treatment.

The solution to the technical problem of creating a new method, based on the inventive step, for producing metal objects by shaping, such as deep drawing and / or stripping, metal sheets provided with a conversion layer, which are provided with a conversion coating before being deformed, is described in the above Literature cited to the prior art is not solved and should not be solved by this.

• Hydrophilierungsbeispiele

The hydrophilization of surfaces of metal sheets is now described in the following using some exemplary embodiments:

• Examples of hydrophilization

example 1

• Vor der mechanischen Hydrophilierung ist die Aluminiumoberfläche, die in vollständig entfettetem Zustand vorliegt, hydrophob, was sich leicht dadurch feststellen läßt, daß aufgegossenes Wasser bei senkrechtstehendem Aluminiumblech unter Bildung kleiner und kleinster Perlen abläuft, bzw. hydrophob reagiert, indem diese Oberfläche konventionelle Offsetdruckfarbe animmt.

An aluminum sheet with dimensions DINA4, a thickness of 0.3 mm and the following composition: silicon 0.30, iron 0.70, copper 0.25, manganese 1.0 to 1.5, magnesium 0.3 to 1.3, Zinc 0.25, balance aluminum (% by weight), is made hydrophilic by moving a paper fleece to which an average pressure of one kg / cm ² (0.098 MPa) is applied to and fro five times. In general, the rule applies that this rubbing movement is carried out until a slight residue of the aluminum surface is visible on the friction partner paper fleece (black discolouration of the paper fleece). The proof that this treatment made the previously hydrophobic aluminum surface hydrophilic is carried out as follows:

• Before the mechanical hydrophilization, the aluminum surface, which is in a completely degreased state, is hydrophobic, which can easily be determined by the fact that poured water runs off with vertical aluminum sheet with the formation of small and very small beads, or reacts hydrophobically by this surface assuming conventional offset printing ink.

The aluminum sheet made hydrophobic as described above can be recognized as hydrophilic in that even when the sheet is placed vertically to the base, water poured on causes a complete wetting of the mechanically treated aluminum surface as described above and shows a dwell time of 60 seconds, after which time one of Evaporation of the water progresses from top to bottom or no offset color is now accepted.

This offset printing ink example also serves to show that the surface reactions which lead to the contrary properties such as hydrophilic - hydrophobic have not yet been sufficiently researched scientifically. The described metal hydroxide level of the lowest value is made somewhat clearer by the offset printing ink example: If a hydroxide of the known value level was present, this could be rinsed off or, if not dissociated, it could be removed from the surface by rubbing with the damp printing ink. This is particularly interesting when noble (copper) as well as base metal (Cr, Fe, Al, Su) are treated as it were in the examples described. Copper always takes on color, as do the oxides of base metals, which have a hydrophobic effect; the hydroxides of the base metals are hydrophilic until they become hydrophobic again through gradual oxidation.

Newly added water is again accepted from the surface, i.e. H. the surface remains hydrophilic and, as tests have shown, about 24 hours. After 24 hours, the metal surface gradually becomes hydrophobic again.

Example 2

An aluminum sheet of the type mentioned in Example 1 is hydrophilized chemically by immersing it in a 1N sodium hydroxide solution for 30 minutes; the temperature of the sodium hydroxide solution is 60 to 80 ° C. Then the aluminum sheet from the caustic soda bath pulled out and rinsed with distilled water until there is no alkalinity in the rinsing water. Then, as described in Example 1, the hydrophilization test is carried out by observing the running speed in the vertical position of the sheet. The experiments show that the hydrophilization in the chemical manner described in this example has the same degree as the mechanical hydrophilization described in Example 1.

Example 3

An aluminum sheet of the type mentioned in Example 1 is immersed in an electrolyte consisting of a 0.5% sodium hydroxide solution at room temperature (25 ° C).

An anodic current of 70 A / m ^{2 is} applied (based on the surface of the aluminum). After only 2 seconds, the entire aluminum sheet is of the same hydrophilic nature as the sheet treated according to Examples 1 and 2. The sheet is also cleaned here by rinsing with distilled water until the drained distilled water is alkali-free. The method of determining the hydrophilicity is also the same as in the aforementioned examples.

Example 4

The aluminum sheet of the type mentioned in Example 1 is placed in an electric furnace heated to 200 ° C. and left there for 6 minutes. The sheet is then removed from the electric furnace and allowed to cool to room temperature in a normal laboratory atmosphere. The test for the hydrophilicity achieved, which is shown in detail in Example 1, was then carried out; Here, too, the experiment showed that the sheet thermally treated in this way had the same degree of hydrophilicity as the sheets shown in Examples 1 to 3. In the present case, an even longer lasting hydrophilicity is achieved; it is at least 36 hours.

Example 5

A tinplate of the DIN A4 format is subjected to the hydrophilization process shown in Examples 1 to 4.

In the case of mechanical hydrophilization in the analogous application of Example 1, it was found that the tinplate remained hydrophilic for 100 hours and slowly lost its hydrophilicity after this time.

The treatment with sodium hydroxide solution is completely analogous to Example 2. The hydrophilization result is the same as in the previous example.

Example 6

A A4 tinplate is immersed in the NaOH electrolyte as above and then first switched as an anode for a second, then as a cathode for a second, then as an anode for a second, and then again as a cathode for one second. The current density was again 70 A / m ² tinplate.

After the end of this electrochemical treatment, the tinplate was removed from the bath and rinsed with distilled water until the rinsed water was no longer alkaline. The hydrophilicity achieved was then measured by carrying out the hydrophilicity test already described in detail above in the vertical position of the sheet.

It was found that the hydrophilicity of the electrochemically treated tinplate continued for another 100 hours and then slowly decreased.

Example 7

A chrome-plated iron sheet of the DIN A4 format was treated mechanically with a pressure of 5 kg / cm ² (0.49 MPa) by means of a fine polishing disc (based on plastic fabric) by moving the fine polishing disc up and down 5 times.

It was found that this mechanical treatment led to the hydrophilization of the previously hydrophobic chrome-plated iron sheet surface. The hydrophilization was again determined using the standard test shown above; it was found that the hydrophilization was maintained for a period of 5 hours and then slowly decreased.

example

The surface of the chrome-plated iron sheet of the DIN A4 format is treated chemically by rubbing the mixture of 10% gelatin and 2% glycerine and 88% water on the surface using dilute sulfuric acid or rubbing the sheet into immerse the solution just described for 5 seconds. Instead of immersing, the surface of the chromed iron sheet can be subjected to 5 rubbing movements using a chemically inert fleece.

Then; as detailed above, washed off until the wash water is neutral.

It has the same hydrophilicity _t est as described above carried out with the result that the thus chemically treated chrome-plated iron plate having a Hydrophilitätsdauer of 100 hours.

Example 9

A chromed iron sheet of the DIN A4 format is thermally treated for 6 minutes in an electric furnace with an internal temperature of 200 ° C. and then removed from this furnace. After cooling to room temperature, the chrome-plated iron sheet thus thermally treated had a hydrophilicity for a period of 100 hours.

Example 10

An iron sheet of the DIN A4 format and a thickness of 0.3 mm (bare) iron sheet, so-called ultra-fine sheet of the composition: C 0.6%, Si 0.01%, Mn 0.25%, P 0.010%, S 0.020% The rest of iron is placed in an electrolyte bath which was filled with an electrolyte consisting of 0.25 normal sodium hydroxide solution. The black plate was then operated first as a cathode for one second, then as an anode for a second and finally as a cathode for a second. The current density was again 70 A / m ^{2 of} sheet metal. It was then removed from the electrolyte bath and washed with distilled water until the wash water was free of alkali. The hydrophilicity test was then carried out as described above; it was found that the black plate treated in this way electrolytically had a hydrophilicity of one hour.

Even after this hour has elapsed, the surface of the black plate does not begin to change into a hydrophobic one, since slowly the formation of clearly colored iron oxide begins, which in turn is water-friendly.

Preservation is achieved by applying a coating of a chemical compound that is both water-soluble and soluble in organic solvents as soon as possible after the hydrophilization process has ended. preferred coating formers are the glycols, amines, alkanolamines, as well as gelatin and gelatin-like substances.

Gum arabic, iso-paraffins or polyparaffins in solution and / or in emulsion are suitable as further coating agents.

These coating agents desirably effect the exclusion or prevention of the access of atmospheric oxygen and / or atmospheric moisture to the hydrophilic metal surface or metal oxide surface.

An exemplary embodiment of the preservation of a hydrophilized metal surface is described below:

Example 11

The aluminum sheet made hydrophilic according to Example 1 is preserved immediately after the end of the hydrophilization treatment by applying tetraethylene glycol to the surface, for example by spraying; alternatively, the preservation can also be effected by passing the hydrophilized metal sheet through a bath of tetraethylene glycol immediately after the hydrophilization.

Other preservatives include esters of montanic acid with ethanediol and / or 1,3-butanediol, glycerol monoacetate, polyethylene glycol, copolymer of esters of acrylic acid with monohydric aliphatic alcohols C ₁ - C _4, mixture of alkylphenol polyglycol ether with 20 ethylene oxide groups, alkylphenol polyglycol ether-Formaldehydacetat and C ₁₂ -C ₁₈ Fatty alcohol-polyethylene glycol-polypropylene glycol ether, polyvinyl acetate from aliphatic saturated aldehydes C ₁ -C ₆ with a molecular weight of over 1000, dibutyl sebacate, acetyltributyl citrate, acetyl-tri-2-ethylhexyl citrate, Diphenyl-2-ethylhexyl phosphate, adipic acid polyester with 1,3- and 1,4-butanediol, acid esters of phosphoric acid with monohydric saturated aliphatic alcohols with chain length C ₂ -C ₄ .

The duration of the preservation depends on the intensity and time of the preservation treatment; at least the duration of the preservation is sufficient to ensure the further processing stages of the hydrophilized surfaces, the hydrophilic character having to be retained.

The entire surprising behavior of the metal surfaces made hydrophilic according to the invention can only be explained in the current state of knowledge in this way that the hydrophilization produced at least hydroxyl-containing compounds of the lowest valence level of the metal in question, it being irrelevant in the context of this invention how many valences of the concerned Metals are saturated with hydroxyl groups.

From the four previously described hydrophilization procedures, namely the mechanical, the chemical, the electrochemical and the thermal method, the person skilled in the art can see that the naturally grown oxides are removed on the surface and compounds containing hydroxyl groups are reproduced or released from internal areas in the thermal hydrophilization process.

The declaration of the invention is also supported in the following table of the formation energy of metal oxides or metal hydroxides · from the respective metallic state:

From this table z. B. it can be seen that the formation energy of the oxide of divalent iron is substantially lower than the formation energy of the hydroxide of divalent iron; on the other hand, the energy of formation of the hydroxide of trivalent iron is considerably greater than that of the hydroxide of divalent iron. After all, the formation energy of the ferro-ferric oxide is greatest.

It can be seen from the table that the stability, in particular of the hydroxide of trivalent iron, is not far from the stability of the most stable body, namely Fe ₃ 0 ₄ .

It can also be seen from the table that the formation energy gap between the hydroxide of the divalent tin and the oxide of the tetravalent tin is very small; it is only 2 kcal / mol. This explains the high stability and long duration of the hydrophilized tin in tinplate.

With aluminum sheet, too, the distance between the formation energy of the hydroxide of trivalent aluminum and oxide of trivalent aluminum is relatively small. It is 304 to 390 kcal / mol, but with 86 kcal / mol the residual energy is so great that the hydroxide stability is lower relative to that of tin, iron and chromium.

The formation energy of the hydroxide of trivalent chromium is 245 kcal / mol, in contrast the formation energy of the oxide of trivalent chromium is 267 kcal / mol. It is therefore only slightly above that of the hydroxide, which in turn can be used to derive the great stability and duration of the hydrophilic stage in chromed sheet metal.

A chemical proof of the presence of hydroxyl-containing metal compounds on the surfaces of the hydrophilized metals consists in the fact that a condensation with hydroxyl-containing organic substances such as. B. salicylic aldehyde takes place.

The analytical proof of the presence of free OH ions was further provided by the fact that the standardized indicator neutral red clearly detected free OH ions in an aqueous medium on the surface of the hydrophilized metals.

One of the ways in which the hydrophilized sheets are used in the drawing process for the purpose of producing beverage cans will now be described.

• Bisher wurden Metallbleche ohne klare Definition der Metalloxid- bzw. Metallhydroxidstruktur eingesetzt. Es sind Fälle bekannt, bei denen absichtlich eine Oxidschicht erzeugt wurde und zwar in der Annahme, daß dabei hydrophobe Abstreckmittel besser haften.

Practical application of further processing of a hydrophilized aluminum sheet as described above in the ironing process without using a lubricant:

• So far, metal sheets have been used without a clear definition of the metal oxide or metal hydroxide structure. Cases are known in which an oxide layer was deliberately created, assuming that hydrophobic ironing agents adhere better.

The aluminum sheet, which has been hydrophilized and preserved analogously to one of the processes mentioned in the examples, is immediately immersed in an inert solution consisting of isopropanol and 0.5% triethanolamine in order to renew the preservation effect.

Such hydrophilic and post-preserved bowls are fed to the ironing press, special attention being paid to rapid processing.

Surprisingly, it was found that these cups can be formed into cans without any coolant - that is, dry - and with coolants in the form of the above preservative solution without squeaking and scratching.

Since the extremely effective coolant, water, was missing in this case, the workpiece lengthened after 8 cans in the dry state and only after 22 cans using isopropanol and triethanolamine (0.5%), so that the experiment had to be stopped. After the tools had cooled (within 45 minutes to room temperature), the experiment could be started again with the same result.

The person skilled in the art can measure that this use case is far from being for a Commercial production is suitable, since it is first of all necessary to prove that the hydrophilized metal surface does not release any oxides during mechanical forming, as is the case with conventional hydrophobic surfaces, which, in the absence of lubricants, already clear the surface of the can after two wells rubs and thus causes the squeaking noise.

A person skilled in the art can appreciate that the working heat must be removed by means of frozen external or internal media if water is to be avoided in order to ensure continuous production. The increase in can length clearly indicates stamp cooling, since the reduced distances between the ring and stamp were caused by the thermal expansion of the stamp. Cans with a wall thickness of less than 0.06 mm are not standard in order to be able to be carried out easily through the next work steps.

When the cans made in this way are viewed microscopically, slightly milky veils can be found on the outside of the can, which in no way questions the optical quality of this can.

The water hydrophilicity test is positive, i. that is, that the hydrophilized surface has been maintained or, based on the end surface, has reproduced by 500/0 analogously to the hydrophilicity examples by means of mechanical friction energy.

Compared to a can made as standard, i.e. in the presence of lubricants and hydrophobic sheet metal surfaces, the metal surface is homogeneous, hydrophilic in all areas of the can and no longer needs to be made hydrophilic in an alkaline cleaning bath, in contrast to the can produced as standard.

This is a special feature of the present can metal surface produced according to the invention.

The person skilled in the art can appreciate that the hydrophilization can be made simpler and more controllable in terms of process technology if it is carried out on a strip, that is to say prior to the forming, instead of on individual pieces which are contaminated with lubricants in the complex surface area of the can bottom contour.

When stretching without lubrication, it was found on this side that during the mechanical shaping with the tensile and sliding forces, those parts detach from the surface which, as described above, were detached in the hydrophilization test using the paper fleece. This shows that material can build up on the clearly defined working radius of the tools, which changes the working radius. As a result, the balance of forces between train and pressure is changed so that the molded body tears off in the machine. The working radius in the ironing process is the radius under which the material is tapered. The most common angles are between 10 and 6 °. At this working angle, the optimum tensile strength of the molded article which has already been drawn is then given under the formula p3 = pl-p2; with regard to the details, reference is made to the specialist literature on deep drawing. In order to prevent the tearing off, which is usually first shown or noticeable in a change in the working radius, it has been considered essential in the current state of the art to apply conventional lubricants to the surface of both the moldings and the ironing process also to apply the ironing tools. The usual lubricants include: aqueous 3-20% oil emulsions, effecting a pH correction of e.g. B. pH 6 to pH 9 for the purpose of biological protection. Rust inhibitors are also added; synthetic lubricants such as polyglycols are also used.

In experiments with tinplate, it was found that, in the absence of conventional lubricants, the can surface is roughened immediately, so that after the third can passage through the tool, clear noises, raised surfaces and tears were found. However, if such sheets are used as the starting sheets, which are hydrophilized according to the invention, it surprisingly shows that even without the use of the lubricants previously considered essential, the drawing without cracking, without squeaking, ie. H. without the typical rubbing noises.

• Die Abstreckung der erfindungsgemäß hydrophilierten Bleche führt zu solchen abgestreckten Teilen, die ohne jede weitere Vorbehandlung, insbesondere ohne jede weitere Reinigungsbehandlung einem Lackierverfahren unterworfen werden können. Zu solchen Lackierungsverfahren gehören die folgenden: Spritzlackieren, Tauchlackieren, Pulverlackieren, Walzenlackieren.

The surface of the ironed sheets shows the same smoothness and smoothness as that of the ironed sheets. By using the hydrophilized surface in accordance with the invention, a whole bundle of advantages is achieved:

• The ironing of the sheets which have been hydrophilized according to the invention leads to such ironed parts which can be subjected to a painting process without any further pretreatment, in particular without any further cleaning treatment. Such painting processes include the following: spray painting, dip painting, powder painting, roller painting.

The roller coating is to be carried out for an external coating, the spray coating and the powder coating is preferably to be used for an internal coating. Dip painting is usually carried out with simultaneous interior and exterior painting.

It has also surprisingly been found that the surface of hydrophilized ironed parts has a better affinity and better adhesion with the lacquer than the surface of non-hydrophilized sheets used in the conventional manner have been stripped of lubricants. This is also due to an abruptly progressive effect. It can be seen that a lubricant film once applied to the metal sheet surface cannot always be removed 100% in all areas, which is why the application of paint to sheet metal surfaces that were first lubricated and then cleaned is always more problematic than applying paint to metal surfaces. that have never come into contact with lubricants.

Another very significant advance in the use of the hydrophilized metal surfaces with regard to their painting is that by omitting the lubricants and thus the elimination of the lubrication removal operation necessary before painting, both substances which serve to remove the lubricants are saved to a large extent environmental risks are eliminated to a high degree.

With the conventional lubricant-using ironing processes, the lubricants had to be removed in large cleaning systems using solvent-containing cleaners. Another method is to use aqueous alkalis to remove the saponification lubricants.

All processes require a large amount of energy and lead to the generation of a large amount of toxic waste water or toxic solvent residues. All of these environmentally hazardous cleaning techniques are dispensed with when using the hydrophilic sheets for ironing according to the invention.

When using the means of a preservative coating z. B. from glycol stabilized metal surfaces for ironing and subsequent painting, it can be seen that a large part of the glycol evaporates during ironing, but this proportion is very small compared to the previously required lubricant-removing organic substances. Remaining small residues of the stabilizer glycol, which can possibly not be completely excluded, are compatible with the coating.

Normally, the stabilizing agents such. B. the glycols and the amines in turn co-constituent of the paint.

Another possible use of the formed metal objects stabilized with the preserving coating can be seen from claim 5.

Claims (5)

1. Process for the production of metal articles by the forming, such as deep-drawing and/or stretching, of metal sheets provided with a conversion layer, which are provided with conversion coating prior to the forming, characterized in that, prior to the forming, the sheets are provided with a hydrophilic hydroxide-containing conversion coating, onto which is applied a preserving coating consisting of a chemical compound which is both watersoluble and soluble in organic solvents, and/or consisting of gelatin, gelatin-like substances, gum arabic, isoparaffins and/or polyparaffins.

2. Process in accordance with claim 1, characterized in that the preserving coating is applied immediately after producing the conversion coating.

3. Process in accordance with claim 1 or 2, characterized by the use of glycol, amines, alkanolamines as compounds which are both water-soluble and soluble in organic solvents.

4. Use of the process products in accordance with claims 1 to 3 as substrates for the surface lacquering.

5. Use of the process products in accordance with claims 1 to 3 as substrates for a bond between the metal and organic compound.