JP6989646B2 - A method for passivating the surface of a black plate or tinplate and an electrolytic system for carrying out the method. - Google Patents

Description

The present invention is a method for passivating the surface of a black plate (original plate) or tin plate by electrolysis of a chromium oxide-containing passivation layer, and a chromium and chromium oxide-containing passivation on the surface of the black plate or tin plate. It relates to an electrolytic system for electrodepositing a layer.

Steel sheets electrolytically coated with a passivation layer of chromium and chromium oxide / chromium hydroxide are known from the prior art in the manufacture of packaging materials. This steel sheet is called tin-free steel (TFS) or electrolytic chromium coated steel (ECCS) and is an alternative to tinplate. Such tin-free steel sheets are characterized by particularly good adhesion to paints or organic coatings (eg, polymer coatings of PP or PET). Despite the limited passivation layer thickness of chromium and chromium oxide / chromium hydroxide, generally less than 20 nm, these chromium-coated steel sheets have good corrosion resistance and the deformation used in the manufacture of packaging materials. It shows good workability in processing, for example, deep drawing and ironing.

The tin plate is generally provided with a passivation layer after electrolytic tin plating in order to suppress oxidation of the tin surface in an oxygen atmosphere. The chromium-containing layer has been shown to be suitable as a passivation layer, which can be electrolyzed from the chromium (VI) -containing electrolyte on the tin surface of tinplate. Such a chromium-containing passivation layer is composed of metallic chromium and chromium oxide. Chromium oxide is understood to mean all compounds of chromium and oxygen, including chromium hydroxide.

Electrolytic coating methods for producing chrome-plated steel sheets (ECCS) and for passivating tinplate surfaces are known from the prior art. Using this method, the passivation layer containing chromium metal and chromium oxide / chromium hydroxide was subjected to a plate-like substrate (uncoated steel plate) using a chromium (VI) -containing electrolytic solution at the strip coating line. Or it is provided in tinplate). However, these coating methods have serious drawbacks due to the environmentally harmful and health-threatening properties of chromium (VI) -containing electrolytes used in the electrolytic process, and the use of chromium (VI) -containing substances is not possible. It will be banned in the near future and will need to be replaced by alternative coating methods in the not too distant future.

For this reason, prior art has already developed an electrolytic coating method that eliminates the need for the use of chromium (VI) -containing electrolytic solutions. For example, Patent Document 1 and Patent Document 2 disclose a method for electrolytically passivating a strip-shaped steel sheet, particularly a black plate or a tin plate, using a metallic chromium / chromium oxide (Cr-CrOx) layer. In this method, the steel plate of the strip coating line is connected as a cathode and contains a trivalent chromium compound (Cr (III)), a complexing agent and a salt that improves conductivity, and buffers such as chlorides and boric acid. It passes through a single agent-free electrolyte at a high sheet speed of over 100 m / min.

Organic substances, especially formate, preferably sodium formate or potassium formate, are used as complexing agents. The electrolytic solution can contain sulfuric acid for adjusting to a preferable pH value in the range of 2.5 to 3.5. The immobilized layer of metallic chromium or chromium oxide can be deposited in the layer by a continuous electrolytic cell or strip coating system arranged in sequence, and each electrolytic cell is filled with the same electrolytic cell.

It has been observed that the electrodeposited passivation layer may also contain chromium sulfate and chromium carbide in addition to the metallic chromium and chromium oxide / chromium hydroxide components, and these components in the total coating weight of the passivation layer. It was observed that the proportion of was highly dependent on the current density used in the electrolytic bath. It has been established that the three regions (Regime I, Regime II and Regime III) are formed as a current density function, in the first region where the current density is low up to the first current density threshold (Regime I). In the second region where chromium-containing precipitation does not occur on the steel substrate and the current density is medium (Regime II), there is a linear relationship between the current density and the coating weight of the deposited immobilized layer, and it is formed. Since the partial decomposition of the demobilized layer occurs at a current density above the second current threshold (Regime III), the chrome coating weight of the immobilized layer in this regime increases the current density. As it decreases first, it reaches equilibrium at higher current densities. In the medium current density region (Regime II), essentially metallic chromium is deposited on the steel substrate at a weight ratio of up to 80% (relative to the total weight of the passivation layer) and a second current density. Above the threshold (Regime III), a higher proportion of chromium oxide is contained, which accounts for 1/4 to 1/3 of the total coating weight of the passivation layer in the region of higher current densities. The current density thresholds that separate the regions (Regime I-Regime III) from each other depend on the sheet speed at which the steel sheet passes through the electrolyte.

For oxidation in oxygen-containing environments, for good passivation of black plates and tinplate surfaces, and for organic coatings such as paints or thermoplastics, especially PET, PP, PE plastic films or mixtures thereof. It has been shown that the chromium-containing passivation layer should contain as high a proportion of chromium oxide as possible in order to form a good adhesive base to the laminate.

WO2015 / 177314A1 WO2015 / 177315A1

Therefore, an object of the present invention is to passivate the surface of a black plate or tin plate by using a passivation layer containing chromium oxide / chromium hydroxide based on an electrolytic solution using a trivalent chromium compound. It consists of providing an electrolysis method that is environmentally safe and not harmful to health at all and is capable of being the most effective and cost effective. In either case, the use of chromium (VI) -containing substances should be avoided, even as an intermediate in the electrolytic process, in order to fully meet the legal provisions regarding the prohibition of chromium (VI) -containing substances. In addition, black plates or tins coated by this method have the highest possible resistance to oxidation in oxygen-containing environments, especially in oxygen atmospheres, and are also such as organic paints and especially PET, PE or PP polymer films. A good adhesive base should be formed for organic coatings such as polymer layers.

This problem is solved by a method having the characteristics of claim 1, an electrolytic system having the characteristics of claim 16, and a black plate or tin according to claim 18. Preferred embodiments of the method and electrolysis system are apparent from the dependent claims.

In the method according to the invention, the chromium oxide-containing immobilization layer comprises a trivalent chromium compound, at least one salt for improving conductivity, and at least one acid or base for adjusting to a desired pH value. From the containing electrolyte, it is provided by electrodeposition on an uncoated steel plate or tin-plated steel plate (black plate or tin-plated sheet), and the electrolyte is a trivalent chromium compound and at least one salt or at least one. It does not contain any additional components other than the acid or base of the above, in particular it does not contain an organic complexing agent, and in particular it does not contain a buffer. And, even as an intermediate, no chromium (VI) -containing material is used, so that the method is completely free of chromium (VI) -containing material, and therefore, during the implementation of the method, the method is environmental. It is safe and not harmful to health at all.

Surprisingly, it has been shown that it is possible to electrolyze a chromium oxide-containing layer onto the surface of a black plate or tin plate without the use of organic complexing agents such as formate as a component of the electrolyte. In this case, during the use of the electrolytic solution containing no organic complexing agent, the precipitation layer is composed of at least essentially chromium oxide.

It has also been shown that a layer of pure chromium oxide / chromium hydroxide that forms the surface of the passivation layer is advantageous in terms of oxidation resistance and the adhesive effect of organic coatings such as paints or polymer layers. Therefore, the method according to the invention provides for the exclusion of (organic) complexing agents, especially formate such as sodium formate or potassium formate, from the electrolyte. The passivation layer electrolyzed on the surface of the black plate or tin using such an electrolyte consists of at least essentially pure chromium oxide and / or chromium hydroxide.

Chromium oxide means the oxide form (CrOx) of all chromium, including chromium hydroxide, in particular chromium (III) hydroxide and chromium (III) oxide hydrates, and mixtures thereof. A compound of chromium and oxygen in which chromium is present in a trivalent form, particularly as dichromium trioxide (Cr ₂ O _{3), is preferred.} Therefore, the coating preferably contains only trivalent chromium compounds (in addition to metallic chromium), in particular trivalent chromium oxide and / or chromium hydroxide.

The electrodeposited passivation layer preferably has the highest possible weight percentage of chromium oxide, including chromium hydroxide. The weight ratio of chromium oxide and / or chromium hydroxide is preferably more than 90%, particularly preferably more than 95%. This ensures, on the one hand, good passivation of the surface of the black plate or tin plate against oxidation, and on the other hand, good for paints or organic coatings such as polymer layers of thermoplastics such as PET or PP. It is possible to provide a good adhesive base having an adhesive ability.

For the passivation of the passivation layer, a black plate or tin plate is connected as a cathode so that it is in contact with the electrolytic solution in at least one electrolytic cell for a predetermined electrolytic time. The electrolysis time is preferably in the range of 0.3 to 5.0 seconds, and particularly preferably in the range of 0.6 to 1.5 seconds. For this purpose, the black plate or tin sheet is continuously passed through at least one electrolytic cell or a plurality of electrolytic cells arranged in the front-rear direction in the sheet moving direction at a predetermined sheet speed, in which case the sheet. The speed is preferably at least 100 m / min, especially 200 m / min to 750 m / min. The high seat speed ensures high efficiency of this process.

The thickness and coating weight of the passivation layer of chromium oxide can be adjusted by the electrolysis time and thus the sheet speed. Electrolysis time, precipitated chromium oxide of at least 3 mg / ^{m 2,} preferably preferably to have a coating weight of ^7mg / ^{m 2 ~10mg} / m 2 is selected. To obtain sufficient oxidation resistance and corrosion resistance for packaging applications, at least 5 mg / m ^2, preferably from 7 mg / m ² greater than the coating weight of chromium oxide passivation layer is preferred. Such coating weight of chromium oxide ensures sufficient resistance to oxidation and corrosion of the surface of the black plate or tinplate and also provides a good adhesive base for organic coatings such as paints or thermoplastic films.

After electrodeposition of the immobilized layer, it adheres well to the chromium oxide layer of the immobilized layer in order to improve corrosion resistance and form a barrier against sulfur-containing substances, especially the polyethylene or sulfite-containing contents of the packaging. Coating of organic materials, especially paints or thermoplastics, especially PET, PE, PP polymer films or mixtures thereof, by coating the surface of the demobilized layer with organic paint, or PET, PE and By providing a plastic layer of a thermoplastic such as / or PP, it can be easily formed without any problem.

To ensure a process that is completely free of chromium (VI) -containing substances, during the electrodeposition of the passivation layer, a suitable anode was conveniently selected and placed in the electrolytic cell to place the trivalent chromium in the electrolyte. Prevents the oxidation of the compound chromium (III) to chromium (VI). Anodes made of metal oxides, especially iridium oxide, or mixed metal oxides, especially iridium-tantalum oxide, with an outer surface or passivation layer are particularly suitable for this purpose. Has been proven. The anode preferably contains neither stainless steel nor platinum. By using such an anode, a coating containing only trivalent chromium oxide and / or chromium hydroxide, in particular Cr ₂ O ₃ and / or Cr (OH) ₃ , can be deposited on a black plate or tin plate. can.

As with any galvanic process, at least one anodic oxidation is present simultaneously in addition to cathode reduction during galvanic chrome plating from the chromium (III) electrolyte. During galvanic chromium plating from a chromium (III) electrolyte, anodic oxidation consists, on the one hand, the oxidation of chromium (III) to chromium (VI) and, on the other hand, the oxidation of water to oxygen. Both potentials are very close in the electrochemical series.
(1) Chromium (Cr) Cr ⁶⁺ + 3e ⁻ ⇔ ^{Cr 3+} + 1.33V
(2) Oxygen (O) O ₂ + 4H ⁺ + 4e ⁻ ⇔ 2H ₂ O + 1.23V

The potential is measured with the associated Daniell cell. The redox potential depends on the anode material used. Therefore, the choice of anode material is clearly determined by whether reaction (1) is suppressed and only reaction (2) occurs. ^{In order to prevent the formation of Cr 6+} by the method according to the present invention, metal oxide-based, especially iridium oxide-based, or mixed metal oxide-based, for example, mainly from a multilayer of tantalum oxide and iridium oxide. A mixed metal oxide-based anode can be used to suppress reaction (1). The anode can have an outer surface or outer passivation layer of the mixed metal oxide. Anodes with a titanium core and an outer passivation layer of tantalum oxide-iridium oxide have been found to be particularly suitable. Using such an anode, it was possible to demonstrate that Cr (VI) is not formed by polarographic measurements (dropped mercury electrodes).

When an anode made of stainless steel is used, (reaction 1) from Cr (III) to Cr (VI) is not (sufficiently) suppressed. Comparative measurements using stainless steel anodes show clearly detectable Cr (VI) concentrations after only a few seconds of electrolysis time. Therefore, when stainless steel is used as the anode material, the oxidation of Cr (III) to Cr (VI) is not suppressed at least completely. This leads to the enrichment of Cr (VI) in the Cr (III) electrolyte, thus resulting in a different precipitation mechanism. Therefore, it is preferred that the stainless steel-free anode be used in the method according to the invention. This ensures that Cr (VI) is not formed as an intermediate during electrolysis and that the precipitated passivation layer contains only Cr (III) compounds and metallic chromium. Further, this allows the final treatment with, for example, thiosulfate to be omitted, otherwise the precipitated Cr (VI) is converted to Cr (III) when a stainless steel anode is used. Final treatment may be required for reduction.

The electrolytic solution preferably has a temperature in the range of 20 ° C to 65 ° C, more preferably in the range of 30 ° C to 55 ° C, and particularly in the range of 35 ° C to 45 ° C. The electrodeposition of the chromium oxide-containing passivation layer is very effective at these temperatures. When referring to the temperature of the electrolytic cell or the temperature in the electrolytic cell, the average temperature means an average value over the entire volume of the electrolytic cell. Generally, the electrolytic cell has a temperature gradient in which the temperature rises from the upper part to the lower part.

In addition to the trivalent chromium compound, the electrolyte contains at least one salt to improve conductivity and at least one acid or base to adjust to an appropriate pH value, the electrolyte is preferably chloride. It does not contain compound ions, does not contain a buffer, and does not contain a borate buffer in particular.

The trivalent chromium compound in the electrolytic solution is preferably basic sulfate Cr (III) (Cr ₂ (SO ₄ ) ₃ ), nitrate Cr (III) (Cr (NO ₃ ) ₃ ), oxalate Cr (III) ( It is selected from the group containing CrC ₂ O ₄ ), Cr (III) acetate (C ₁₂ H ₃₆ ClCr ₃ O ₂₂ ), Cr (III) formate (Cr (OOCH) _{3) or a mixture thereof.} The concentration of the trivalent chromium compound in the electrolytic solution is preferably at least 10 g / L, particularly more than 15 g / L, and particularly more than 20 g / L.

In order to improve conductivity, the electrolyte comprises at least one salt, preferably an alkali metal sulfate, in particular potassium sulfate or sodium sulfate.

Very effective chromium oxide content when the pH value of the electrolyte (measured at a temperature of 20 ° C.) is in the range of 2.3 to 5.0, preferably between 2.5 and 2.9. Precipitation of the passivation layer is achieved. A desired pH value can be obtained by adding an acid or a base to the electrolytic solution. When basic sulfuric acid Cr (III) is used as a trivalent chromium compound, sulfuric acid or an acid mixture containing sulfuric acid is particularly suitable for adjusting the desired pH value.

Particularly preferable composition of the electrolytic solution is Cr (III) sulfate (Cr ₂ (SO ₄ ) ₃ ), which is basic as a trivalent chromium compound, sodium sulfate as a salt for improving conductivity, and 2.3 to 5.0. Contains sulfuric acid to adjust to a preferred pH value in the range of.

The electrolyte contains no additional components other than a trivalent chromium-containing substance, at least one salt for improving conductivity, and at least one acid or base for adjusting the pH value. This ensures the production of a simple and cost-effective electrolyte.

To produce the electrolyte, water is added with a trivalent chromium compound from which most of the organic residues are initially removed, at least one salt, and at least one acid or base to adjust to the desired pH value. Dissolves in. Since the electrolyte is free of complexing agents, the resulting solution should be allowed to stand for convenience for complexing for at least 5 days, preferably at least 7 days (in an oxygen atmosphere). Then, by adding an acid or a base, the pH value can be finely adjusted to a desired value.

A black plate or tin with a chromium oxide-containing passivation layer can be produced using the method according to the invention, where the passivation layer is at least essentially chromium oxide and / or chromium hydroxide only, preferably trivalent. It consists only of chromium oxide and / or chromium hydroxide, and preferably has a weight ratio of chromium oxide and / or chromium hydroxide of more than 90%, particularly preferably more than 95%. Such black plates or tinplates according to the invention are characterized by high corrosion resistance and good adhesion to organic coatings such as paints or polymer layers. The passivation layer preferably contains at least essentially only compounds of chromium and oxygen, where chromium is present in trivalent form, in particular as Cr ₂ O ₃ and / or Cr (OH) ₃ .

In addition to chromium oxide and / or chromium hydroxide, residual components of chromium sulfate (as the initial chromium compound of the electrodeposition process) can be included in the passivation layer in addition to the unavoidable impurities.

The passivation layer preferably comprises a first layer facing the surface of the black plate or tin and a second layer forming the surface of the passivated black plate or tin. It contains metallic chromium and the second layer consists of pure chromium oxide and / or chromium hydroxide in addition to the residual components of chromium sulfate and unavoidable impurities described above.

Passivation layer is at least 3 mg / ^{m 2,} preferably from ^{5 mg} / m 2 to 15 mg / ^m when having a total coating weight of chromium oxide and / or chromium hydroxide of ^2, particularly good black plate or tin according to the present invention It is possible to achieve excellent corrosion resistance.

The invention will be described in more detail with reference to the accompanying drawings and on the basis of the following examples, but the aforementioned examples never limit the scope of protection defined by the appended claims. , It is intended to illustrate the invention merely by way of example. The drawings show:

It is a schematic diagram of the strip coating line for carrying out the method by this invention. FIG. 3 is a schematic cross-sectional view of a black plate or tin coated with the strip coating line of FIG. 1 in the method according to the invention. It is a glow discharge emission analysis method (GDOES) spectrum of a layer electrodeposited using an electrolytic solution of a trivalent chromium substance (basic sulfate Cr (III)) and an organic complexing agent (sodium formate) on a steel plate. The layer contains metallic chromium, chromium oxide and chromium carbide. It is a glow discharge emission analysis method (GDOES) spectrum of a layer electrodeposited on a steel plate using an electrolytic solution containing a trivalent chromium substance (basic sulfate Cr (III)) without containing an organic complexing agent. The layer consists essentially of pure chromium oxide.

FIG. 1 schematically shows a strip coating line for carrying out the method according to the invention. The strip coating line includes three electrolytic cells 1a, 1b, and 1c arranged continuously in the front-rear direction, and each electrolytic cell is filled with the electrolytic cell E. The first uncoated black plate sheet or tin sheet (hereinafter referred to as sheet B) continuously passes through the electrolytic cells 1a to 1c. For this purpose, the sheet B is pulled by a transport device (not shown) in the sheet moving direction v so as to pass through the electrolytic cells 1a to 1c at a predetermined sheet speed. The current roll S is arranged above the electrolytic cells 1a to 1c, and the sheet B is connected as a cathode by the current roll S. The deflection roll U is also disposed in each electrolytic cell, and the sheet B is guided around the deflection roll U, thereby moving it in and out of the corresponding electrolytic cell.

At least one anode pair AP is arranged in each electrolytic cell 1a to 1c below the liquid level of the electrolytic cell E. In the illustrated embodiment, two anode pairs AP arranged in the front-rear direction in the sheet moving direction are provided in each electrolytic cell 1a to 1c. Sheet B is guided between the opposite anodes of the anode vs. AP. In the embodiment of FIG. 1, therefore, two anode pairs AP are arranged in each electrolytic cell 1a, 1b, 1c, so that the sheet B is guided to continuously pass through these anode pairs AP. To. The last anode vs. APc of the last electrolytic cell 1c present downstream in the sheet moving direction v has a shorter length than the other anode vs. AP. Therefore, higher current densities can be generated for this last anode pair APc when the same amount of current is applied.

To prepare for the electrolysis process, the sheet B is first degreased, washed, pickled and rewashed, and the sheet B is continuously passed through the electrolytic cells 1a-1c in this pretreated form and is a current roll. By supplying a current through S, it is connected as a cathode. The sheet speed at which the sheet B passes through the electrolytic cells 1a to 1c is at least 100 m / min, and can be up to 900 m / min.

The electrolytic cells 1a to 1c arranged in the front-rear direction in the sheet moving direction are each filled with the same electrolytic solution E. The electrolytic solution E contains a trivalent chromium compound, preferably basic sulfate Cr (III) (Cr ₂ (SO ₄ ) ₃ ). In order to increase the conductivity, the electrolytic solution E also contains salts, in particular alkali metal sulfates such as potassium sulfate or sodium sulfate, and acids or bases for adjusting to an appropriate pH value. The pH value of the first electrolytic solution E is adjusted to a preferable value of 2.0 to 5.0 by adding an acid or a base. When the basic sulfuric acid Cr (III) is used as a trivalent chromium compound, sulfuric acid has been shown to be a suitable acid for pH adjustment. The concentration of the trivalent chromium compound in the electrolytic solution E is preferably at least 10 g / L, particularly preferably 20 g / L or more.

The temperature of the electrolytic cell E is equal for convenience in the electrolytic cells 1a, 1b, and 1c, and is preferably between 25 and 70 ° C. However, the temperature of the electrolytic solution can be set to a different temperature in each of the electrolytic cells 1a, 1b, and 1c. For example, the temperature of the electrolytic cell in the central electrolytic cell 1b can be made lower than the temperature of the electrolytic cell in the front electrolytic cell 1a located upstream of the temperature of the electrolytic cell. The temperature of the electrolytic cell in the central electrolytic cell 1b is, for example, between 25 ° C. and 37 ° C., particularly 35 ° C., and the temperature of the electrolytic cell E in the front electrolytic cell 1a is between 40 ° C. and 75 ° C., particularly 55 ° C. ℃.

The electrolytic solution E does not contain an organic component and does not particularly contain a complexing agent. The electrolytic solution E does not contain a buffer such as a halogen compound and boric acid.

Anodes arranged in the electrolytic cells 1a to 1c so that a sufficiently high current density exists in the electrolytic cells 1a, 1b, and 1c in order to electrolyze the chromium-containing (particularly Cr (III) -containing) layer. A direct current is applied to the AP. The minimum current density required for this purpose depends on the seat speed and is about 15-20 A / dm ² at a (minimum) seat speed of 100 m / min. At higher velocities, the minimum current density required for electrodeposition of the chromium-containing layer increases.

Depending on the sheet speed, the sheet B connected as a cathode and passing through the electrolytic cells 1a to 1c is effective with the electrolytic solution E during the electrolytic cells t1, t2 and t3 in the electrolytic cells 1a, 1b and 1c, respectively. Electrolytically contact with. At a sheet speed of 100 to 700 m / min, the electrolysis times t1, t2, and t3 in each electrolytic cell 1a, 1b, and 1c are 0.5 to 2.0 seconds. A high sheet speed is preferably set so that the electrolysis time in each of the electrolytic cells 1a, 1b and 1c is less than 2 seconds, particularly 0.6 seconds to 1.8 seconds. The total electrolytic time tG = t1 + t2 + t3 in which the sheet B is electrolytically contacted with the electrolytic solution E over all the electrolytic cells 1a to 1c is therefore 1.8 to 5.4 seconds. The electrolysis time in the individual electrolytic cells 1a, 1b, 1c can be adjusted by the sheet speed on the one hand, and can be adjusted by the dimensions of the electrolytic cells 1a to 1c on the other hand.

When a current density larger than the minimum current density is adjusted in the corresponding electrolytic cells 1a to 1c, it is composed of at least essentially chromium oxide and / or chromium hydroxide, and when the sulfate-containing electrolytic solution E is used. An optional layer containing chromium sulfate is deposited on at least one side of the sheet B in each of the electrolytic cells 1a, 1b and 1c. When the same electrolytic cell E is contained in the electrolytic cells 1a to 1c and the same electrolytic parameters, particularly the same current density and temperature are used, the layers B1, B2 and B3, each having at least essentially the same composition, are electrolyzed. It is generated in each of the tanks 1a, 1b and 1c.

The weight ratio of chromium oxide / chromium hydroxide to the coating weight of the layers B1, B2 and B3 and the total coating weight of the coating consisting of these layers B1, B2 and B3 is at least 90%, preferably more than 95% for convenience.

A cross-sectional view of the sheet B electrolytically coated using the method according to the present invention is schematically shown in FIG. The passivation layer P composed of the individual layers B1, B2 and B3 is formed on one side of the sheet B. Each individual layer B1, B2, B3 is formed on the surface in each electrolytic cell 1a, 1b, 1c.

The layer structure of the layers B1, B2 and B3 deposited on the sheet is shown by the GDOES spectrum (glow discharge emission spectrometry).

In the comparative experiment, according to the present invention, a metal chromium layer having a thickness of 10 to 15 nm was formed in the electrolytic cells 1a, 1b, 1c without using a known prior art electrolyte solution containing an organic complexing agent such as formate. , It is shown that it is possible to precipitate on the sheet B as a function of the electrolysis time. The surface of these layers is oxidized after precipitation and is mostly present as chromium oxide in the form of _{Cr 2} O ₃ or as a mixed oxide-hydroxide in the form of _{Cr 2} O ₂ (OH) _2. This oxide layer is several nanometers thick. Further, chromium carbide and chromium sulfate compounds formed by reducing the sulfate of the organic complexing agent and the electrolytic solution are formed and uniformly incorporated in the entire finished layer. Typical GDOES spectra of layers B1, B2, B3 precipitated in each electrolytic cell show a strong increase in oxygen signal at the first few nanometers of the layer, which is why the oxide layer corresponds to the corresponding layer (FIG. 3). ) Can be concluded to be concentrated on the surface.

The GDOES spectrum of the sheet B passivated by the method according to the present invention using the electrolytic solution E containing no organic complexing agent such as formate is shown in FIG. It has been shown that a layer (passivation layer) consisting of at least essentially chromium oxide / chromium hydroxide and optionally a limited proportion of chromium sulfate is deposited on Sheet B.

The composition of the passivation layer can be determined by the EURO standard DIN EN 10202 (Cr oxide metering: (European standard) Step 1: 40 mL NaOH (330 g / L), react at 90 ° C. for 10 minutes, 10 mL 6% oxidation by H ₂ O _2, photometry at 370 nm).

After the passivation of the passivation layer, the sheet B provided with the passivation layer can be washed, dried and oiled (eg, using DOS). An organic coating can be provided on the sheet B electrolytically coated with the passivation layer. The organic coating is provided by a known method, eg, by painting on the surface of the passivation layer, i.e. on the upper layer B3 of chromium oxide, or by laminating a plastic film. The chromium oxide surface of layer B3 provides a good adhesive base for organic materials by coating. The organic coating can be, for example, an organic paint or a polymer film of a thermoplastic polymer such as PET, PE, PP or a mixture thereof. The organic coating can be provided, for example, by a strip coating process or a plate process, in which the coated sheet is first divided into plates and then painted with an organic paint or coated with a polymer film.

In order to obtain sufficient oxidation resistance and corrosion resistance for packaging applications, the passivation layer provided by the method according to the invention is of at least 3 mg / m ² , preferably at least 5 mg / m ² of chromium oxide / chromium hydroxide. It is preferable to have a total coating weight. A coating weight of up to 15 mg / m ² of chromium oxide / chromium hydroxide provides good adhesion of the organic paint or thermoplastic polymer material to the surface of the passivation layer P. Therefore, the preferred range of chromium oxide / chromium hydroxide coating weight in the passivation layer is 3 to 15 mg / m ² , particularly preferably 5 to 15 mg / m ² .

The thickness and coating weight of each layer B1, B2, B3 can be adjusted by the electrolytic time t1, t2, t3 and the current density in the electrolytic cell in the embodiment shown by the method according to the present invention. As soon as a sufficiently high current density is selected for the electrolytic cell, the thickness and coating weight of the precipitation layers B1, B2, B3 will be the current in the electrolytic cell where the sheet B is in effective electrolytic contact with the electrolytic cell E. It is a linear function of density and electrolysis time t1, t2, t3 (at the equivalent temperature of the electrolytic solution).

Therefore, the coating weight of the passivation layer can be adjusted by the electrolysis time and / or the current density, and the sheet B is effectively in contact with the electrolytic solution E during the electrolysis time. The electrolysis time t depends on the dimensions of the electrolytic cell and the sheet speed.

Claims (15)

It is a method for electrolyzing the surface of a black plate or a tin by electrolyzing a chromium oxide-containing immobilization layer on the surface, and the electrolysis of the chromium-containing immobilization layer is trivalent chromium. In a method resulting from an electrolytic solution (E) composed of a compound, at least one salt for improving conductivity, and at least one acid or base for adjusting to a desired pH value, the electrolytic solution (E). Does not contain an organic complexing agent and does not contain a buffering agent, the black plate or the tin is connected as a cathode, and the black plate or the tin is attached to the electrolytic solution (v) at a predetermined sheet speed (v). At least one electrolytic tank (1) or a plurality of electrolytic tanks (1a, 1b) filled with E) and provided with an anode (2) having an outer surface or coating of a metal oxide or a mixed metal oxide. 1c) is continuously passed through, whereby the surface of the black plate or the tin is electrolytically effectively contacted with the electrolytic solution (E) to precipitate the immobilization layer, and the immobilization layer is deposited. A method comprising a dynamic layer consisting of chromium oxide and / or chromium hydroxide having a total coating weight of ^{at least 3 mg / m 2 of chromium oxide and / or chromium hydroxide.} The method according to claim 1, wherein the passivation layer has a weight ratio of chromium oxide and / or chromium hydroxide of more than 90%. The black plate or tin plate for electrodeposition of the passivation layer is brought into contact with the electrolytic solution (E) during the electrolytic time, and the electrolytic time is in the range of 0.1 to 2.0 seconds. The method according to claim 1, wherein the method is characterized by the above-mentioned method. The method according to any one of claims 1 to 3, wherein the predetermined seat speed (v) is at least 100 m / min. The first aspect of the present invention is characterized in that the temperature of the electrolytic solution (E) is an average temperature over the entire volume of the corresponding electrolytic cell (1; 1a, 1b, 1c) and is in the range of 20 ° C to 65 ° C. The method described. The electrolytic time (t) at which the black plate or the tin is effectively electrolytically contacted with the electrolytic solution (E) is less than 1.0 second in each electrolytic cell (1, 1a to 1c), and the black. _{The total electrolysis time (t G} ) at which the plate or tin is effectively electrolytically contacted with the electrolytic solution (E) in the total electrolytic cell (1; 1a to 1c) is between 0.5 seconds and 2.0 seconds. The method according to claim 3, wherein the method is characterized by the above. The trivalent chromium compounds include basic sulfate Cr (III) (Cr ₂ (SO ₄ ) ₃ ), nitrate Cr (III) (Cr (NO ₃ ) ₃ ), and oxalate Cr (III) (CrC ₂ O _4). ), Cr (III) acetate (C ₁₂ H ₃₆ ClCr ₃ O ₂₂ ), Cr (III) formate (Cr (OOCH) ₃ ) or a mixture thereof, and the salt of the electrolytic solution is at least one kind. The method according to any one of claims 1 to 6, wherein the alkali metal sulfate is used. The electrolytic solution has a pH value in the range of 2.5 to 2.9 (measured at a temperature of 20 ° C.), and the pH value is obtained by adding at least one acid to the electrolytic solution. The method according to any one of claims 1 to 7, wherein the method is adjusted. The method according to any one of claims 1 to 8, wherein the concentration of the trivalent chromium compound in the electrolytic solution is at least 10 g / L. The anode used during the electrodeposition of the passivation layer is characterized in that it prevents the oxidation of chromium (III) of the trivalent chromium compound of the electrolyte to chromium (VI). Item 2. The method according to any one of Items 1 to 9. 10. The method of claim 10, wherein the anode is free of stainless steel and platinum. 10. The method of claim 10, wherein the anode comprises an outer surface or coating of iridium oxide, or the anode is composed of iridium oxide. The trivalent chromium compound from which organic residues have been removed to produce the electrolyte, the at least one salt, and at least one for adjusting to the desired pH value. The acid or base of the above is dissolved in water and the solution thus obtained is allowed to stand for complexing for at least 5 days, after which the fine adjustment of the pH value is carried out by the addition of the acid or base. The method according to any one of 1 to 12. An electrolytic system for electrolytically passivating the surface of a black plate or tin plate by precipitating a chromium oxide-containing passivation layer on the surface.
-Including at least one electrolytic cell (1) filled with the electrolytic cell (E) or a plurality of electrolytic cells (1a, 1b, 1c) each filled with the electrolytic cell (E) and arranged in the front-rear direction. In each electrolytic cell (1a, 1b, 1c), an anode (2) having an outer surface or coating of a metal oxide or a mixed metal oxide is arranged.
-The electrolytic solution (E) is composed of a trivalent chromium compound, at least one salt for improving conductivity, and at least one acid or base for adjusting to a desired pH value, and comprises an organic component. Does not contain and does not contain buffers
-For the electrodeposition of the immobilization layer, the black plate or tin is connected as a cathode, and the black plate or tin is connected to the black plate or tin at a predetermined sheet speed (v) in the sheet moving direction, said at least one electrolytic cell. (1) is passed or the plurality of electrolytic cells (1a, 1b, 1c) are continuously passed, whereby the surface is effectively in contact with the electrolytic solution (E) in an electrolytic manner, and at least. An electrolytic system in which a mobilized layer consisting essentially only of chromium oxide and / or chromium hydroxide is deposited on the surface. 14. The electrolytic system of claim 14, wherein the anode has an outer surface or coating of iridium oxide.

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