EP0012905A1 - 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

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. In 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.

It is known from aluminum that its surface consists of a hard, coherent, transparent oxide layer a few molecular layers thick, e.g. on freshly scratched aluminum in the air and in water in just a few seconds.

This protective layer is initially only a few angstroms thick; it increases to 45 to 90 angstroms over 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, e.g. 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 lowest iron layer. These tin-plated iron sheets are known as tinplate, which is normally found on 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 eg according to Euronorm 77-65 with E1 to E4 or according to ASTM A624 from Desig nation No. 10 to No. 135/25. Information on the type of chemical surface treatments used and the amount of, for example, chromium in the passivation layer are also contained in ASTM A 624. According to this, the amount of chromium in chemical passivation (Chromc Acid-Treated Tin-Plate) is not more than 250 µg chromium / ft ² surface, while in electro-chemical passivation (Cathodic-Sodium Dichromate-Treated Tin Plate) it is about 500 µg Chromium / ft ² .

Furthermore, the tinplate is usually greased. Common greasing agents are e.g. Dioctyl sebacate (DOS), cottonseed oil and butyl stearate (ATBC). Normally the circulation is approx. 0.10 g / base box to 0.40 g / base box according to ASTM A 624.

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

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 drawing, without using the lubricants previously considered essential if the surface is used the sheets are hydrophilized, ie makes hydrophilic.

According to a preferred embodiment of the invention, this hydrophilization is achieved by producing a hydroxide of the metal in question or a hydroxide-containing compound of the metal on these metal surfaces and / or metal oxide surfaces. According to a preferred embodiment of the present invention, a hydroxide of the lowest valence level of the metal is produced on the surfaces.

The metal surfaces thus hydrophilized in accordance with the invention have technologically highly interesting unexpected properties, in particular it is possible, besides the mechanical processes molding processes such as deep drawing or drawing without using the lubricants previously considered indispensable to achieve a much more effective and at the same time leaps and bounds more economical painting.

In the following, the hydrophilization of surfaces of the following metal sheets is described 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:senk- rechtstehendem Aluminiumblech unter Bildung kleiner und kleinster Perlen abläuft, bzw. hydrophob reagiert indem diese Oberfläche konventionelle Offsetdruckfarbe annimmt.

An aluminum sheet with dimensions DIN A4, 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, remainder aluminum (% by weight) is hydrophilized by moving a paper fleece, to which an average pressure of ¹ kg / cm ^{2 is} applied, back and forth 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 (blackish ver coloring 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 smallest beads, or reacts hydrophobically by this surface using conventional offset printing ink assumes.

The aluminum sheet which has been made hydrophilic as described above can be recognized as hydrophilic in that even when the sheet is positioned vertically in relation to our site, water poured on completely wets 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 accepted.

This offset ink example is also used for this show that the surface reactions, which lead to the contrary properties such as hydrophilic hydrophobic, have not yet been sufficiently scientifically researched. The metal hydroxide level of the lowest valency disclosed according to the invention is somewhat clearer by the offset printing ink example: if a hydroxide of the known valence level were present, this could be rinsed off or, if not dissociated, it could be removed from the surface by rubbing with the moist 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. the surface remains hydrophilic - as tests have shown - for 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 thereby hydrophilized chemically by immersing it in an sodium hydroxide solution for 30 minutes; the temperature of the caustic soda is 60 to 80 ° C. Then the aluminum sheet is pulled out of the caustic soda bath and rinsed with distilled water until no more alkalinity can be found 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 which consists of a 0.5% sodium hydroxide solution at room temperature (25 ° C.).

An anodic current of 70 Amp / 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 a 200 ⁰ 0 heated electric furnace 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 amounts to for 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 after. After this time, its hydrophilicity slowly lost.

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 one. Second as anode, then one second as cathode, then another second as an anode, then another second as cathode. The current density was again 70 amp / 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 A 4 format was treated mechanically with a pressure of 5 kg / cm ² 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 hydro Philation 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 8

The surface of the chromed iron sheet of the DIN A4 format is treated chemically by rubbing a mixture of 10% gelatin and 2% glycerine and 88% water on the surface by means of dilute sulfuric acid or the sheet immersed in 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 described in detail above, it is washed off until the washing water is neutral.

The same hydrophilicity test as described above was carried out, with the result that the chromium-plated iron sheet thus chemically treated had a hydrophilicity period of 100 hours pointed.

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 format DIN A 4 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 amp / m2 Sheet. 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.

It has also been found and is an essential part of the present invention that the - as described above - hydrophilized metal surfaces or metal oxide surfaces can be temporarily preserved in the hydrophilized state.

This preservation is achieved by applying a coating of a chemical compound on the surface as soon as possible after the hydrophilization process has ended is both water soluble and soluble in organic solvents; 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 C1-C6 with a molecular weight of more than 1,000, dibutyl sebacate, acetyltributyl citrate, acetyl-tri-2-ethylhexyl citrate, diphenyl-2-ethyl-adipyl-1,4-phosphate with 1,4-ethylhexylphosphate acidic esters of phosphoric acid with monohydric saturated aliphatic alcohols of 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 conservation is over sufficient to ensure the further processing stages of the hydrophilized surfaces while maintaining the hydrophilic character.

The present invention is further based on the surprising finding that the hydrophilization of the metal surfaces or the metal oxide surfaces is achieved by creating hydroxyl-containing compounds on the surface.

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 measure that the naturally grown oxides are removed on the surface and compounds containing hydroxyl groups were reproduced or released from internal areas in the thermal hydrophilization process.

The declaration of 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 is e.g. 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 in turn significantly 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 removed from the stability of the most stable body, namely the Fe304.

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.

Even with aluminum sheet, the distance between the formation energy of the hydroxide is trivalent Aluminum and oxides of trivalent aluminum are relatively low. 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 about 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 is the fact that condensation with hydroxyl-containing organic substances such as e.g. Salicylic aldehyde takes place.

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

One of the surprising ways in which the hydrophilized sheets are stripped 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 well-preserved bowls are fed to the ironing press, with particular attention being paid to rapid processing.

Surprisingly, it was found that these bowls can be formed into cans without any coolant - that is, dry - as well as 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 was extended 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 application is still far from being suitable for commercial production, since it is first of all necessary to prove that the hydrophilized metal surface does not release any oxides during mechanical shaping, as is the case with conventional ones This is the case with hydrophobic surfaces, which, in the absence of lubricants, significantly rubs the surface of the can after two wells and thus also causes the squeaking noise.

A person skilled in the art can measure that the working heat must be dissipated by means of deep-frozen external or internal media, if water is to be consumed, in order to ensure continuous production. The increase in the length of the can clearly indicates the cooling of the stamp, since the reduced distances between the ring and the 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 produced 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, that is the hydrophillized surface has been kept upright or, based on the end surface, has reproduced by 50% 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 can areas and, unlike the can produced as standard, no longer needs to be made hydrophilic in an alkaline cleaning bath.

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

The person skilled in the art can measure that the hydrophilization can be made simpler and more controllable in terms of process technology if it is carried out on a belt, that is to say before forming, instead of 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 mechanical forming the tensile and sliding forces detach those parts from the surface which - as described above - were detached during 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 tension 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 = p1-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, according to the current state of the art it was considered absolutely necessary to apply conventional lubricants to the surface of both the molded parts 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.

pH 6 to pH 9 for 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, clear noises, raised surfaces and tears were detected by the tool. 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 which were previously considered essential, the drawing without cracking, without squeaking, i.e. can be carried out without the typical rubbing noises.

• Die Absteckung 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 staking out of the sheets which have been hydrophilized according to the invention leads to such stretched 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 better affinity and adhesion to the paint than the surface of non-hydrophilized sheets that have been ironed in the conventional manner. This is also due to an abruptly progressive effect. It can be seen that once on The lubricant film 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 in view of their painting is that by omitting the lubricants and thus the elimination of the lubrication removal operation necessary before painting, both substances that 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-based cleaners.

Another method is to use aqueous alkalis to remove the lubricants due to saponification.

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 hydrophilized sheets according to the invention for ironing.

It was shown above that the metal surfaces hydrophilized according to the invention can optionally be stabilized by substances which are soluble in water as well as in organic solvents, for example glycols.

When metal surfaces stabilized in this way are used for stripping and subsequent painting, it can be found that a large part of the glycol evaporates during stripping, but this proportion is very small compared to the organic substances which previously required lubricant removal. Ver 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 glycose and the amines themselves components of the paint.

Claims (10)

1. A method for hydrophilizing metal surfaces and / or metal oxide surfaces, characterized in that at least one hydroxide of the metal in question is generated on these surfaces. 2. A method for hydrophilizing metal surfaces and / or metal oxide surfaces, characterized in that at least one hydroxide of the lowest valence level of the metal in question is produced on these surfaces. 3. A method for hydrophilizing metal surfaces and / or metal oxide surfaces, characterized in that at least one hydroxide-containing compound of the metal in question is produced on these surfaces. 4. A process for hydrophilizing metal surfaces and / or metal oxide surfaces, characterized in that at least one hydroxide-containing compound of the relevant in question on the surfaces Metal that corresponds to the lowest severity level of the last. 5. A method for hydrophilizing metal surfaces according to claims 1 to 4, characterized in that a coating of a chemical compound is applied to the metal surface after the actual hydrophilization process, which is both water-soluble and soluble in organic solvents. 6. The method according to claim 5, characterized in that immediately after completion of the actual hydrophilization process on the metal surface a lacquer-metal crosslinking coating of glycol, amines, acanolamines, gelatin, gelatin-like substances, from gum arabic and from iso- Attaches paraffins or polyparaffins. 7. Application of the process products of claims 1 to 6 as substrates for forming or deep-drawing or ironing processes. 8. Application of the process products according to claims 1 to 6 as substrates for surface coating. 9. Application of the process products according to claims 1 to 6 as substrates of a crosslinking between the inorganic metal and an organic compound. 10. Application of the process products according to claims 1 to 6 as substrates for an addition.