JP2982263B2 - Aluminum can and manufacturing method thereof - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an aluminum can used as a container for soft drinks, beer and the like, and particularly to enhance the corrosion resistance of a chemical conversion film formed on the outer surface of the can body. For improvement.

"Prior art" This type of aluminum can is generally composed of a bottomed cylindrical can body and a circular can lid fitted into an upper end opening of the can body. The can body and the can lid are collectively referred to as a can body.

After deep-drawing the aluminum plate, the can body removes lubricating oil and dirt adhering at the time of molding in a degreasing process and performs a chemical conversion treatment to form a chemical conversion film on the surface to enhance corrosion resistance and coating film adhesion. In addition, it is manufactured by painting the inner and outer surfaces. Also, the can lid is manufactured by applying a chemical conversion film and coating to an aluminum plate in advance, and then punching and forming the aluminum plate.

Conventionally, as the material of these cans, JISA300
4. Aluminum alloy such as JISA5182 is used.
These alloys contain Al as a main composition, and additionally contain Mg, Mn, and Cu, and have a Cu content of about 0.2 to 0.25 wt%.

As the degreasing solution, sulfuric acid or an acidic type having phosphoric acid and sulfuric acid as a main composition is generally used,
For example, Japanese Patent Publication No. 50-21147 discloses an acidic degreasing solution containing phosphoric acid and sulfuric acid as a main composition and appropriately adding a surfactant.

Further, the chemical conversion treatment is usually performed using a phosphate-based solution of chromium or zirconium, and the
A chromium phosphate-based or zirconium phosphate-based chemical conversion film of about 10 to several hundred degrees is formed on the surface of the can body.

[Problems to be Solved by the Invention] By the way, in the conventional aluminum can, the corrosion resistance of the chemical conversion film is not so high as expected, and the outer surface of the can bottom which is an unpainted portion of the can body in the sterilization process after filling the contents. In some cases, discoloration due to corrosion occurs in portions where the aluminum is directly exposed, which has been a problem. For this reason, chemical analysis of aluminum cans has been performed using various analytical methods, but the cause was not clear.

The present inventors employed XPS analysis (X-ray photoelectron spectroscopy), which has been rarely used in this type of research, to increase the depth distribution of the constituent elements of the aluminum can in order to investigate the cause. The accuracy was checked.

As a result, it was found that Cu of unknown origin was contained in the surface layer portion of the chemical conversion film at a relatively high concentration, and that the corrosion resistance of the chemical conversion film might be inhibited by the Cu.

For example, when a chemical conversion coating on a normal aluminum can is analyzed by XPS analysis, the material on the clean surface after polishing is
While the photoelectron count of Cu is 800-2000 cps,
In the surface layer of the chemical conversion film, counts of Cu reaching 3 to 8 times that of the chemical conversion film were detected.

Then, the present inventors reexamined all the processes from the molding of the aluminum can to the chemical conversion treatment, and examined in detail which process Cu originated from this chemical conversion film. As a result, in the degreasing step before the chemical conversion treatment, it was considered that Cu ²⁺ was eluted and accumulated from the aluminum can in the acidic degreasing solution.
Was detected in an extremely small amount of 8 to 35 ppm, and the new fact that Cu ²⁺ was deposited again on the surface of the aluminum can and a chemical conversion film was formed in a form incorporating the Cu during the chemical conversion treatment was found.

Such mixing of Cu impairs the denseness of the chemical conversion film and causes the deterioration of corrosion resistance because Cu and Al of the can form an internal battery.

The present invention has been made based on this finding, and it is an object of the present invention to provide an aluminum can having improved corrosion resistance of a chemical conversion film.

"Means for Solving the Problems" The aluminum can according to the present invention has a chemical conversion film formed on at least one surface of a can body and a can lid constituting a can body, and contains Cu in the chemical conversion film. Is not more than twice the maximum value of the density of Cu in the material itself of the aluminum can, more preferably, the maximum value of the number of photoelectron counts of Cu by X-ray photoelectron spectroscopy in the chemical conversion coating 3,000 cp at less than twice the count number in the material itself of this aluminum can
s or less.

An inner surface coating and / or an outer surface coating may be partially or entirely applied to the can body and the can lid. Further, the shape, dimensions, and thickness of the aluminum can are not limited, and the case of the can body or the can lid alone is also included in the claims of the present invention.

The material of the can body and the can lid may be any material conventionally used for this purpose, for example, the above-mentioned JISA3004 or
JISA5182 is preferred. Incidentally, 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 conversion coating, a chromium phosphate coating or a zirconium phosphate coating is suitable as in the past. is there. Each of the preferred conversion coating weight was represented by Cr or Zr ^{content, Cr: 4~20mg / m 2,} Zr: a 5 to 25 mg / m ² or so.

From the viewpoint of corrosion resistance, the amount of the conversion coating in the conventional product required at least 8 mg / m ² as Cr for the chromium phosphate coating and at least 10 mg / m ² as Zr for the zirconium phosphate coating.
However, in the present invention product, respectively ^{Cr: 4mg / m 2, Zr} : it can be reduced to 5 mg / m ^2.

On the other hand, if the amount of the chemical conversion film is larger than Cr: 20 mg / m ² and Zr: 25 mg / m ² , the adhesion of the coating film is reduced or the production cost is increased, and it is useless.

The photoelectron count is a value proportional to the existing density of Cu atoms.Here, MgKα rays are used as an X-ray source, and the surface of the chemical conversion film is etched at a constant rate with argon ions, and the depth direction of the chemical conversion film is determined. The distribution of the photoelectron count number (unit: cps) of Cu is obtained over the entire region, and the maximum value is defined as the value of the photoelectron count number of Cu.

The reason for this definition is that the density distribution of Cu atoms has a peak at a certain depth position on the surface side of the chemical conversion film, and the depth varies depending on the degreasing conditions, the formation conditions of the chemical conversion film, and the like.

If the photoelectron count of Cu in the chemical conversion film is larger than twice the photoelectron count of the material of the can body, the corrosion resistance of the chemical conversion film is reduced and the conventional problem cannot be solved. More specifically, the photoelectron count of Cu made of aluminum is
1500 cps or less and conversion film photoelectron count is 3000 c
ps or less.

To manufacture such an aluminum can, the can body or / and the can lid are exposed with their metal surfaces exposed.
When degreased by immersing in sulfuric acid or an acidic degreasing solution containing phosphoric acid and sulfuric acid as a main composition, it is possible to maintain Cu ²⁺ concentration in the acidic degreasing solution at 3 ppm or less. The present inventors have found.

Furthermore, they have also found that the following means are possible.

A method in which a substance which selectively reacts with or binds to Cu ²⁺ is mixed in an acidic degreasing solution in advance.

In circulation process acidic degreasing solution, an acidic degreasing solution Cu ²⁺
Contacting with a substance that selectively reacts with or binds to

Specific examples of the above include nitrilotriacetic acid (NTA),
A complexing agent such as glycine is added to the acidic degreasing solution to add Cu ²⁺
Is converted to complex ions to make precipitation impossible, or soluble sulfide or oxysulfur compound (S oxidation number is 2 to 4) is appropriately added to the acidic degreasing solution to convert Cu ²⁺ to a hardly soluble salt such as CuS. To remove the precipitate.

Examples of the above specific examples include a method in which H ₂ S gas is blown into the degreasing solution, and a method in which CuS is precipitated by adding Na ₂ S ₂ O ₄ .

"Examples" Next, the effects of the present invention will be demonstrated with examples.

(Example 1) A can body molded using A3004 was prepared by using the following composition 70
It was degreased by immersing it in an acidic degreasing solution at 60 ° C for 60 seconds.

Main composition: phosphoric acid: 8000 ppm Sulfuric acid: 8000 ppm Surfactant: 1000 ppm Complexing agent (NTA): 30 ppm Total copper ions (including complexed ions): 15 ppm Then, using an XPS apparatus, the outer peripheral surface of the can body was Ar ⁺ , The photoelectron counts of Cu, Al, O, and C were measured. Table 1 shows the measurement conditions.

The results are shown in FIG. As is clear from this graph, the maximum photoelectron count of Cu on the outer surface of the can body is 2 times the Cu photoelectron count of the bulk (can body before degreasing).
It was twice.

Comparative Example 1 An experiment was performed under the same conditions as in Experimental Example 1 except that the complexing agent was not included in the degreasing solution. The results are shown in FIG. As can be seen from this graph, the maximum photoelectron count of Cu on the outer surface of the can body reached more than four times the same count in bulk.

As is clear from FIGS. 1 and 2, by adding the complexing agent, the maximum value of the Cu photoelectron count on the surface of the aluminum can after degreasing was reduced in Comparative Example 1 in which no complexing agent was used. In contrast to 6000 cps or more, in Experimental Example 1 using the complexing agent, the value was reduced to about 3000 cps. As compared with the can before degreasing, the number decreased from about 4 times to about 2 times.
That is, by the complexation of Cu ^2+, the precipitation of Cu on the surface of the aluminum can during the degreasing treatment could be suppressed.

(Example 2) The same can body that had been subjected to the same degreasing treatment as in Example 1 was immersed in a chemical conversion treatment solution having the following composition at 35 ° C for 30 seconds, and a zirconium phosphate-based chemical conversion film was formed as Zr at 15 mg / m ^2. The thickness was formed.

Main composition: phosphoric acid: 60 ppm, hydrofluoric acid: 100 ppm, zirconium salt: 40 ppm, nitric acid: 200 ppm Next, while the surface of the chemical conversion film was etched with Ar ⁺ by XPS, the photoelectron counts of Cu, Zr, P, and F were respectively measured. It was measured. The results are shown in FIG.

(Comparative Example 2) The same chemical conversion treatment and XPS analysis as in Example 2 were performed on the can body that had been subjected to the same degreasing treatment as in Comparative Example 1. The results are shown in FIG.

As is clear from FIGS. 3 and 4, Cu concentrated on the surface of the can body by degreasing was present at almost the same level as immediately after degreasing even after the chemical conversion treatment.

Therefore, by adding the complexing agent of Cu ^{2+ to} the degreasing solution, reprecipitation of Cu can be suppressed, and as a result, the Cu content in the outermost surface of the can body after the chemical conversion treatment, that is, the chemical conversion film can be reduced. Was.

(Example 3) Can body 10 subjected to the same degreasing and chemical conversion treatment as in Example 2
The individual pieces were subjected to a heating water test at 75 ° C. for 30 minutes to evaluate the degree of black discoloration.

(Comparative Example 3) On the other hand, the same test was performed on 10 can bodies that had been subjected to the same degreasing and chemical conversion treatment as in Comparative Example 2.

 Table 2 shows the results.

As is clear from this table, the corrosion resistance of the can was improved by suppressing the precipitation of Cu on the surface of the Al can.

(Example 4) Degreasing liquids having the following compositions (1) to (4) were prepared by changing only the Cu ²⁺ concentration, and the can bodies were subjected to these degreasing liquids at the described temperatures in the same manner as in Example 1. It was degreased by immersion for 60 seconds.

Next, these can bodies were subjected to the same chemical conversion treatment as in Example 2 except that only the processing time was changed to 20 seconds to form a zirconium phosphate chemical conversion coating. The thickness of the film was 8 mg / m ² as Zr.

The 10 can bodies thus obtained were subjected to a heating water test at 75 ° C. for 30 minutes to evaluate the degree of black discoloration. Table 3 ~
It is shown in Table 6.

As is clear from these tables, the Cu ²⁺ concentration of the degreasing solution
If it exceeds 3 ppm, a significant decrease in corrosion resistance was observed.

(1) Phosphoric acid-sulfuric acid degreasing solution Phosphoric acid: 9000 ppm Sulfuric acid: 9000 ppm Surfactant: 1000 ppm Degreasing temperature: 70 ° C (2) Sulfuric acid-iron degreasing solution Sulfuric acid: 20000 ppm Nitric acid: 1500 ppm Total Fe: 1500 ppm Surfactant: 3000 ppm Degreasing temperature: 70 ° C (3) Sulfuric acid degreasing solution Sulfuric acid: 5000 ppm NH ₄ ⁺ : 1000 ppm Surfactant: 200 ppm Degreasing temperature: 80 ° C (4) Sulfuric acid-hydrofluoric acid type degreasing solution Sulfuric acid: 8000 ppm Hydrofluoric acid: 200 ppm Surfactant : 1500ppm Degreasing temperature: 50 ℃ (Example 5) To each of the degreasing solutions containing Cu ²⁺ at each concentration shown in Example 4, 300 mg / Na ₂ S ₂ O ₅ was added, and the Cu ²⁺ concentration in the acidic degreasing solution was determined. 0.1 ppm or less.

These degreasing solutions were subjected to the same degreasing treatment as in Example 4, washed with water, and further subjected to the same zirconium phosphate chemical conversion treatment as in Example 4.

The same heating water test as in Example 4 was performed on the can body thus produced. As a result, there was no discoloration of the can body by any of the treatments.

From these results, it can be seen that by removing Cu ²⁺ in the degreasing solution, the corrosion resistance of the aluminum can body after the degreasing and chemical conversion treatment is improved.

[Effect of the Invention] As described above, according to the aluminum can according to the present invention, deterioration of the physical properties of the chemical conversion film due to the incorporation of Cu atoms can be prevented, and the corrosion resistance of the aluminum can can be significantly improved. In addition, by increasing the corrosion resistance of the chemical conversion coating, there is a possibility that the chemical conversion coating can be made thinner than conventional products, and the production cost of aluminum cans can be reduced.

[Brief description of the drawings]

1 to 4 are graphs for explaining the effect of the present invention.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshio Kikuchi 1500 Suganuma, Koyama-cho, Sunto-gun, Shizuoka Prefecture Inside the Aluminum Can Development Center Mitsubishi Metal Corporation (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 23 / 227 B65D 1/12 B65D 25/34

Claims (4)

(57) [Claims] 1. An aluminum can having a conversion coating formed on at least a part of the outer surface of a can body, wherein the density of Cu in the conversion coating is not more than twice the maximum value of the density of Cu in the material of the aluminum can itself. An aluminum can, characterized in that: 2. In an aluminum can having a conversion coating formed on at least a part of the outer surface of a can body, the maximum value of the number of photoelectrons of Cu by X-ray photoelectron spectroscopy in the conversion coating is determined by the material of the aluminum can itself. Wherein the count is not more than twice the count number and not more than 3000 cps. 3. The aluminum can according to claim 1, wherein the material of the aluminum can is JISA3004 or JISA5182. 4. A method for producing an aluminum can having a conversion coating formed on at least a part of the outer surface of a can body, wherein the aluminum surface is exposed to an acidic degreasing solution while the metal surface is exposed, and degreasing is performed. At that time, the acid degreasing solution
A method for producing an aluminum can, characterized in that a Cu ²⁺ concentration is maintained at 3 ppm or less and a chemical conversion film is formed after the degreasing.