JP3067310B2 - Method for degreasing aluminum can body and management device used in the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing aluminum cans used as containers for soft drinks and beer using an acidic degreasing liquid.
The present invention relates to a method of grease and a control device used in the degreasing method, and more particularly to an improvement for enhancing corrosion resistance of a chemical conversion film formed on an outer surface of a can body.

[0002]

2. Description of the Related Art In general, an aluminum can comprises a bottomed cylindrical can body and a circular can lid fitted into an upper end opening of the can body. The body and the can lid are both called a can body.

[0003] The above-mentioned can body is formed by deep drawing of an aluminum plate, and then removing a lubricating oil and dirt adhering during the forming in a degreasing step, and performing a chemical conversion treatment on the surface to form a chemical conversion film for improving corrosion resistance and paintability. It is manufactured by forming and painting the inner and outer surfaces. The can lid is manufactured by subjecting a chemical conversion treatment and coating to an aluminum plate in advance, and then punching and forming the aluminum plate.

Conventionally, aluminum alloys such as JISA3004 and JISA5182 have been mainly used as materials for these can bodies. These alloys have a main composition of Al and additionally Mg, Mn, and Cu.
Is about 0.2 to 0.25 wt%.

The main acidic degreasing solution conventionally used is an aqueous solution containing sulfuric acid and iron ions, sulfuric acid and hydrofluoric acid or phosphoric acid and sulfuric acid as a main composition.
No. 1147 discloses a degreasing solution containing phosphoric acid and sulfuric acid as a main composition and appropriately adding a surfactant.

On the other hand, the chemical conversion treatment is usually carried out using a phosphate solution of chromium or zirconium, whereby a chromium phosphate (Cr content: 8 to 50 mg / m ²⁾ having a thickness of several tens to several hundreds of angstroms is provided. ) Or a zirconium phosphate-based (Zr content of 5 to 20 mg / m ² ) chemical conversion film is formed on the surface of the can body.

[0007]

By the way, in the conventional aluminum can, the corrosion resistance of the chemical conversion film is not so high as expected, and when the filled contents are sterilized with heated water,
Problems such as black spot-like corrosion on the outer surface of the can bottom have been pointed out. For this reason, chemical analysis of aluminum cans has been performed using various analytical methods, but the cause was not clear.

[0008] To investigate the cause, the present inventors
Conventionally, XPS analysis (X-ray photoelectron spectroscopy), which is rarely used in this type of research, was employed to examine the depth distribution of the constituent elements of the chemical conversion coating on aluminum cans. It has been discovered that Cu of unknown origin is contained in the surface layer at a relatively high concentration, and that this Cu may inhibit the corrosion resistance of the chemical conversion film.

For example, when a chemical conversion film of a normal aluminum can is analyzed by XPS, the photoelectron count of Cu on the clean surface of the material is 800 to 2000 cps, whereas that of the surface layer of the chemical conversion film is 3 to 4 cps. The count number of Cu which reached twice was detected.

Therefore, the present inventors reexamined the entire process from the molding of the can body to the chemical conversion treatment, and found that Cu
The origin of the process was investigated in detail.
As a result, in the degreasing step before the chemical conversion treatment, a very small amount (8 to 35 ppm) considered to have eluted and accumulated from the can body
Cu ions are detected in the acidic degreasing solution, and the Cu ions precipitate again on the surface of the can body, revealing a new fact that a chemical conversion film is formed in a form incorporating the Cu during the chemical conversion treatment. became. Due to such mixing of Cu, the denseness of the chemical conversion film is hindered, and the A
The formation of the internal battery by l and Cu caused the corrosion resistance to decrease.

Therefore, the present inventors have further studied the C content in the degreasing solution.
An experiment was conducted to reduce the Cu concentration in the chemical conversion film by reducing the u ions, and it was found that when the Cu ion concentration in the acidic degreasing solution was reduced to 3 ppm or less, the amount of precipitated Cu was significantly reduced. .

[0012] The present invention has been made based on this finding, aluminum which can increase the corrosion resistance of the chemical conversion coating
Method for degreasing cans made of rubber and pipes used in this method
It is an object to provide a processing device .

[0013]

Means for Solving the Problems] Hereinafter, A according to the present invention
Method for degreasing a can made of aluminum and used in the degreasing method
The management device to be used will be specifically described. FIG. 1 is a schematic diagram showing an example of the management device of the present invention. In the drawing, reference numeral 1 denotes a counterflow water tank (electrolysis tank), in which a degreasing liquid inlet 2 is formed at one end in the longitudinal direction and an inlet 3 is formed at the other end, respectively. The acidic degreasing solution is continuously or intermittently circulated with a degreasing solution circulation path (not shown) in the body degreasing step.

Partition plates 4A and 4B are alternately and vertically fixed at equal intervals inside the counter flow water tank 1, and the upper end of the partition plate 4A is lower than the set liquid level.
There is a gap between the lower end and the bottom. Thus, the degreasing liquid flows from the inlet 2 to the outlet 3 meandering up and down.

The opposite surfaces of the partition plates 4A and 4B are arranged so that different poles face each other.
Are fixed, all the anode plates 6 are connected to the anode of the power source, and all the cathode plates 5 are connected to the cathode of the power source.

The material of the anode plate 6 is made of an insoluble conductor such as carbon or platinum. The cathode plate 5 is made of a similar insoluble conductor, graphite, stainless steel, or the like. The electrolysis conditions vary depending on the conductivity of the degreasing solution and the like, but it is desirable that the anode current density be about 1 to 50 A / m ² . Below this range, the effect of removing Cu ions is small, and above this range, adverse effects such as generation of gas from the electrodes and decomposition of the degreasing solution may occur.
In addition, the total area of each electrode and the circulation flow rate of the degreasing solution are determined so that the Cu ion concentration in the degreasing solution discharged from the water tank 1 is 3 p.
pm or less.

According to this apparatus, by continuously or intermittently electrolyzing the degreasing solution circulated during the degreasing step, C eluted from the aluminum can into the acidic degreasing solution is obtained.
It is possible to deposit u ions on the cathode plate 5 and maintain the Cu ion concentration of the acidic degreasing solution at 3 ppm or less.

As a result, in the degreasing step, the precipitation of Cu ions on the surface of the aluminum can is significantly reduced, and the amount of Cu incorporated into the chemical conversion film formed after degreasing is reduced. The corrosion resistance, and thus the corrosion resistance of the aluminum can, is significantly improved over that of aluminum cans treated with conventional degreasing solutions.

Therefore, after filling the contents in the degreased aluminum can, a heating water sterilization step (pastelizer)
In this case, black spot-like corrosion, which has conventionally occurred on the unpainted can bottom (bottom portion), can be effectively prevented. In addition,
The management device of the present invention is not limited to the device of FIG.
For example, a modified example as shown in FIG. 2 or FIG. 3 is also possible.

The apparatus shown in FIG.
1 and the anode 12 are spaced apart from each other, and the space between these electrodes is divided into two chambers by the cation exchange membrane 13.
The cathode chamber on one side is filled with catholyte (electrolyte solution for cathode), and on the anode 12 side, an acidic degreasing solution is circulated and supplied from a degreasing step via a circulating means such as a chemical pump.

As the catholyte, H ₂ SO ₄ solution, H ₃
A PO ₄ solution or the like is suitable, and its concentration is from 1 g / l to 50 g / l.
It is about 0 g / l. In this case, the electrolysis conditions may be the same as those in the apparatus shown in FIG.

According to this apparatus, Cu ions in the degreasing solution move to the cathode chamber through the cation exchange membrane 13 and are not only removed from the degreasing solution but also Al ^{3+ and the} like eluted from the aluminum can. Other metal ions, which are lower than Cu, also move to the cathode compartment side through the cation exchange membrane and are removed from the acidic degreasing solution. Thereby, it is possible to extend the life of the degreasing liquid as compared with the apparatus of FIG.

Next, in the apparatus shown in FIG. 3, in addition to the structure shown in FIG. 2, the cation exchange membrane 13 and the anode 12 are separated by an anion exchange membrane 14, and anolyte (anode electrolyte solution) is provided on the anode 12 side. Is satisfied, and the acidic degreasing solution is circulated in a portion partitioned by the cation exchange membrane 13 and the anion exchange membrane 14.

As the anolyte, an acid which is a component of the acidic degreasing solution is preferable, and sulfuric acid and the like can be used. By the electrolysis, the acid in the degreasing solution moves through the anion exchange membrane 14 into the anode chamber and is concentrated. Since the transferred acid is purified in this process, it can be reused as a degreasing solution after concentration adjustment. Further, in this configuration, since no electrode is present in the degreasing solution, it is possible to prevent the surfactant from being deteriorated by electrolysis.

When the apparatus shown in FIG. 2 or FIG. 3 is used, the catholyte on the cathode 11 side is difficult to react with Cu ions such as sulfides or oxysulfur compounds having an oxidation number of S of +2 to +4. A substance that produces a soluble compound may be dissolved. In this case, C
Since u ions are precipitated and removed as a sparingly soluble salt, the management and maintenance of the electrode can be omitted, and the management of the catholyte becomes easy.

Further, the degreasing method and the management device of the present invention
It is also applicable to an acidic degreasing solution of any composition that is conventionally used. The following are some examples of the general composition of the acidic degreasing solution. Sulfuric acid: 0.5-2 wt% Phosphoric acid: 0.5-1 wt% Surfactant: 0.01-0.2 wt%

Low temperature type (treatment liquid temperature 50 ° C.) SO ₄ ^2- : 6000 ppm F: 100 ppm Surfactant: 1200 ppm Inhibitor (Cr ⁶⁺ ): 100 ppm

Medium temperature type (treatment liquid temperature 70 ° C.) SO ₄ ^2- : 16000 ppm NO ₃ ⁻ : 1000 ppm Fe: 1200 ppm Surfactant: 2000 ppm

Medium temperature type (treatment liquid temperature 70 ° C.) SO ₄ ^2- : 6500 ppm PO ₄ ^3- : 6500 ppm Fe: 200 ppm Surfactant: 1500 ppm

High temperature type (treatment liquid temperature: 80 ° C.) SO ₄ ^2- : 3700 ppm NH ₄ ⁺ : 800 ppm Surfactant: 100 ppm Inhibitor (Cr ⁶⁺ ): 80 ppm

The processing temperature conditions in the management device are as follows:
Can be performed in parallel with degreasing of aluminum cans
The degreasing conditions may be the same. For example, the degreasing conditions for the sulfuric acid-phosphoric acid-based degreasing solution described above are as follows:
90 ° C, preferably 65-75 ° C. In addition, the above degreasing solution may be treated at the described temperature.

Further, the material of the can body to be degreased may be any conventionally used material, and for example, the above-mentioned JISA3004 and JISA5182 are suitable.
For example, JISA3004 has the following composition. Al: 95.5 to 98.2 wt% Mg: 0.8 to 1.3 wt% Mn: 1.0 to 1.5 wt% Cu: 0.25 wt% or less

As the chemical conversion film formed on the can body after degreasing, a chromium phosphate or zirconium phosphate film is suitable, as in the prior art, and the amount of the film is 10
It is desirable that the coating amount is 3 to ²⁰ mg / m ² as Cr or Zr according to a measurement value of 0 to 500 Å and X-ray fluorescence.

According to the method for degreasing an aluminum can of the present invention ,
Since the deterioration of corrosion resistance due to the action of the electrode part formed between the base material aluminum and the reprecipitated copper is removed, and the chemical conversion film is densified and the corrosion resistance is improved, the conventional degreasing method is used. When used, at least 250 angstroms (=
12 mg / m ² )
m ² or less.

Incidentally, such a chemical conversion film is an extremely thin film of several tens to several hundreds of angstroms, and its constituent elements and impurity contents can be quantified by X-ray photoelectron spectroscopy (XPS). The method for obtaining the amount of Cu in the chemical conversion film by XPS will be described below.

The photoelectron intensity is a value proportional to the density of atoms. The present inventors have investigated the distribution of constituent elements in the depth direction by measuring the photoelectron intensity while etching a sample with Ar ions at a constant rate using MgKα as an X-ray source.

The abundance of Cu in the chemical conversion film depends on the maximum value of the photoelectron intensity (unit: cps) of Cu and the bulk value at this time.
It is represented by the ratio of the photoelectron intensity of Al of (the material itself of the can body).
Expressed in this way, Cu atoms show the maximum photoelectron intensity, that is, the maximum abundance at a certain depth of the chemical conversion film, but the depth is the degreasing condition, the chemical conversion condition, the surface analysis method and the measurement condition,
This is because it varies depending on the sample area and the like. According to the experiments of the present inventors, Cu /
It has been found that the maximum value of the Al photoelectron intensity ratio is 0.3 or less, preferably 0.2 or less.

[0038]

EXAMPLES Next, the effects of the present invention will be described with reference to examples. (Comparative Example 1) A can body molded using JIS A3004 material was immersed and degreased at 70 ° C for 60 seconds using four types of degreasers having the compositions shown in Table 1.

[0039]

[Table 1]

Next, using an XPS analyzer, the outer surface of the bottom of the can body was etched with Ar ions, and Cu, Al,
The photoelectron intensities of O and C were measured under the conditions shown in Table 2.

[0041]

[Table 2]

No. 1 in Table 1. FIG. 4 shows the results when the degreasing solution of No. 4 was used. As is clear from this figure, the photoelectron intensity of Cu reached a maximum value several minutes after the start of etching with Ar ions, and the photoelectron intensity ratio of Cu / Al reached 0.9.

Comparative Example 2 A can body subjected to the same degreasing treatment as in Comparative Example 1 was treated with a Zr chemical conversion treatment solution shown in Table 3 at 35 ° C. for 30 minutes.
Immersion for 2 seconds, the Zr phosphate chemical conversion film was Zr amount 15mg / m
It was formed with a thickness of ² .

[0044]

[Table 3]

Then, using an XPS analyzer, Cu and A were etched while the outer surface of the bottom of the can body was etched with Ar ions.
The photoelectron intensities of 1, Zr, F, and P were measured under the conditions shown in Table 2. No. 1 in Table 1. FIG. 5 shows the results obtained with the degreasing solution of No. 4.
As is clear from this figure, the photoelectron intensity of Cu is Ar ⁺
It takes a maximum value several minutes after the start of etching by ions, and C
The photoelectron intensity ratio of u / Al reached 0.9.

Next, the bottom portion of the aluminum can body treated as described above was immersed in heated water at 75 ° C. for 30 minutes, and the occurrence of black spot-like corrosion was examined. Table 4 shows the results
Shown in Under conditions where the Cu ion concentration in the degreasing solution exceeded 10 ppm, a marked decrease in corrosion resistance was clearly observed.

[0047]

[Table 4]

(Comparative Example 3) A can body subjected to the same degreasing treatment as in Comparative Example 1 was treated with a Cr phosphate conversion treatment solution shown in Table 5 at 35 ° C.
For 30 seconds with Cr phosphate conversion coating as Cr
It was formed in a thickness of 5 mg / m ² .

[0049]

[Table 5]

Next, using an XPS analyzer, Cu and A were etched while the outer surface of the bottom of the can body was etched with Ar ions.
The photoelectron intensities of 1, Cr, F, and P were measured under the conditions shown in Table 2. The bottom part of the aluminum can body that has been subjected to the above processing,
It was immersed in heated water at 75 ° C. for 30 minutes, and the state of occurrence of black spot-like corrosion was examined. Table 6 shows the results. Under conditions where the Cu ion concentration in the degreasing solution exceeded 10 ppm, a marked decrease in corrosion resistance was clearly observed.

[0051]

[Table 6]

(Comparative Example 4) A can body formed using JIS A3004 material was prepared by using a degreasing solution having the composition shown in Table 7
Degreasing was performed at 0 ° C. for 60 seconds.

[0053]

[Table 7]

Next, 3 parts of the Zr chemical conversion treatment solution shown in Table 3 were added.
Immersion at 5 ° C for 30 seconds, Zr phosphate conversion coating
It was formed to a thickness of 5 mg / m ² . Further, using an XPS analyzer, the photoelectron intensity of Cu, Al, O, Zr, F, and P was measured under the conditions shown in Table 2 while etching the outer surface of the bottom portion of the can body with Ar ions.

The bottom portion of the aluminum can body treated as described above was immersed in heated water at 75 ° C. for 30 minutes, and the state of occurrence of black spot-like corrosion was examined. Table 8 shows the results. Under conditions where the Cu ion concentration in the degreasing solution exceeded 10 ppm, markedly degraded corrosion resistance was clearly observed.

[0056]

[Table 8]

(Example) Using the same acidic degreasing solution as in Comparative Example 1, the aluminum can body was degreased by the method described below while using the management device shown in FIG. Note that Ti-Pt mesh was used as the anode, and SUS mesh was used as the cathode.

While continuously supplying the degreasing solution to the counter flow water tank, the electrolytic current was set to 10 A / m ² and electrolysis was carried out to reduce the Cu ion concentration to the concentration shown in Table 9, and then, in the degreasing tank. The can body was degreased.

The bottom portion of the aluminum can body subjected to the above treatment is immersed in heated water at 75 ° C. for 30 minutes.
The state of occurrence of black spot-like corrosion was examined. Table 9 also shows the results. By removing Cu ions from the degreasing solution by electrolysis, the corrosion resistance of the aluminum can was improved.

Next, the degreasing-treated can body was immersed in a Zr chemical conversion treatment solution shown in Table 3 at 35 ° C. for 30 seconds to form a Zr phosphate chemical conversion coating. Then, the photoelectron intensity of Cu, Al, Zr, F, and P was measured under the conditions shown in Table 2 using an XPS analyzer while etching the outer surface of the bottom portion of the can body with Ar ions. Table 9 shows the results.

[0061]

[Table 9]

[0062]

As described above, according to the present invention, A according to the present invention
Method for degreasing a can made of aluminum and used in the degreasing method
According to the management device , Al from the surface of the can body during degreasing
Cu ions eluted from the material of the can with the elution of are deposited on the anode and removed as metallic copper.
It is possible to reduce the amount of u deposition. Thereby, in the chemical conversion treatment step after degreasing, physical property deterioration of the chemical conversion film due to mixing of Cu atoms into the chemical conversion film is prevented, and the corrosion resistance of the finally obtained aluminum can is greatly improved.
Can be

In addition, since the chemical resistance of the chemical conversion film is enhanced, the chemical conversion film may be made thinner than the conventional product, so that the production cost of the aluminum can can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first example of an apparatus for managing a degreasing liquid for aluminum cans according to the present invention.

FIG. 2 is a schematic view showing a second example of the apparatus for managing a degreasing liquid for aluminum cans according to the present invention.

FIG. 3 is a schematic view showing a third example of the apparatus for managing a degreasing liquid for aluminum cans according to the present invention.

FIG. 4 is a graph for explaining the effect of the present invention.

FIG. 5 is a graph for explaining the effect of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Counter flow water tank (electrode tank) 2 Degreasing liquid inlet 3 Degreasing liquid outlet 4A Partition plate 4B Partition plate 5 Cathode plate 6 Anode plate 10 Electrolysis tank 11 Cathode 12 Anode 13 Cation exchange membrane 14 Anion exchange membrane

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshio Kikuchi 1500 Suganuma, Koyama-cho, Sunto-gun, Shizuoka Prefecture Mitsubishi Materials Corporation Aluminum Can Development Center (56) References JP-A-51-68430 (JP, A) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) C23G 1/12 C23C 22/78

Claims (7)

(57) [Claims] 1. An aluminum can is prepared by using an acidic degreasing solution.
A method of degreasing by removing Cu ions from the acidic degreasing solution
The concentration is kept at 3 ppm or less at all times. For this purpose, the anode and the cathode are brought into contact with the acidic degreasing solution , and a current is supplied between the anode and the cathode to remove Cu ions in the acidic degreasing solution from the metal. Be deposited on the cathode as copper .
And a method for degreasing an aluminum can body. 2. An aluminum can body is prepared by using an acidic degreasing solution.
A method of degreasing by removing Cu ions from the acidic degreasing solution.
In order to always keep the ion concentration at 3 ppm or less, while using an electrode tank partitioned into an anode chamber and a cathode chamber by a cation exchange membrane, while circulating the acidic degreasing solution in the anode chamber, Fill the cathode chamber with a cathode electrolyte solution,
An electric current is supplied between the anode immersed in the acidic degreasing solution and the cathode immersed in the electrolyte solution for the cathode, and the cations in the acidic degreasing solution are moved to a cathode chamber.
Method for degreasing aluminum cans. 3. An aluminum can body is prepared by using an acidic degreasing solution.
A method of degreasing by removing Cu ions from the acidic degreasing solution.
The concentration of the ion is always kept at 3 ppm or less. For this purpose, the inside of the electrolytic cell is partitioned into three chambers by a cation exchange membrane and an anion exchange membrane, and the cathode chamber is partitioned into the cation exchange membrane. Filling the electrolyte solution and circulating the acidic degreasing solution in the intermediate chamber defined by the cation exchange membrane and the anion exchange membrane, and supplying the acidic degreasing solution to the anode chamber defined by the anion exchange membrane The acidic degreasing solution is filled with an anode-containing electrolyte solution containing the contained anions, a cathode is immersed in the cathode electrolyte solution, and an anode is immersed in the anode electrolyte solution, and a current is passed between the cathode and the anode. Move the cations inside to the cathode compartment
Of aluminum cans, characterized in that
Fat method. 4. The aluminum can according to claim 1, wherein the acidic degreasing solution is a phosphoric acid-based degreasing solution containing phosphoric acid, sulfuric acid, and Fe ^3+.
How to degrease the body. Wherein said acidic degreasing solution is as claimed in claim 1, 2, 3 or 4, wherein in that it contains a surfactant
Method for degreasing cans made of minium. 6. An acidic degreasing liquid C for aluminum cans
Management device to keep u ion concentration below 3ppm
An electrolytic cell, a cation exchange membrane that partitions the interior of the electrolytic cell into a cathode chamber and an anode chamber, a cathode disposed in the cathode chamber and an anode disposed in the anode chamber, and the cathode chamber a cathode electrolyte solution filled in the anode chamber and acidic
A circulating means for circulating the acidic degreasing solution between the degreasing solution and a circulation path of the degreasing solution .
Management device used in the degreasing method. 7. An acidic degreasing liquid C for an aluminum can body
Management device to keep u ion concentration below 3ppm
An electrolytic cell, a cation exchange membrane and an anion exchange membrane that partition the interior of the electrolytic cell into three chambers, and a cathode electrolyte solution filled in a cathode chamber partitioned by the cation exchange membrane, A circulating means for circulating the acidic degreasing solution between the intermediate chamber defined by the cation exchange membrane and the anion exchange membrane and the circulation path of the acidic degreasing solution; and an anode chamber defined by the anion exchange membrane. An aluminum can comprising: an anode electrolytic chamber solution containing an anion contained in the prepared acidic degreasing solution; an anode disposed in the anode chamber; and a cathode disposed in the cathode chamber.
Management device used in the body degreasing method.