JP2658453B2 - Method of forming corrosion resistant film on aluminum can and aluminum can having corrosion resistant film - Google Patents

Description

The present invention relates to a method for forming a thin film having excellent corrosion resistance on an aluminum can and an aluminum can having a corrosion-resistant coating layer.

"Conventional technology" The manufacturing process of an aluminum can is shown below.

Cupping Deep squeezing process Degreasing Water washing Chemical conversion Water washing Drying Approx. 200 ° C, Approx. 1 minute Outer coating Baking Approx. 200 ° C, Approx. 1 minute External printing Baking Inner surface coating Baking Approx. 200 ° C, Approx. 1 minute When applying an external coating to the surface of an aluminum can, a pretreatment is performed as a base treatment in order to impart corrosion resistance to the aluminum can and to improve the adhesion of the coating film to the base. In the pretreatment for forming the base, a chemical conversion treatment is performed on the surface of the aluminum can to form a protective film such as a chromate phosphate film or a zirconium phosphate film.

"Problems to be Solved by the Invention" However, in the aluminum can produced by the above-described aluminum can production process, since the coating is not performed on the bottom of the outer surface of the can, aluminum is filled with the contents, and the can lid is tightened. The following problems may occur due to the sterilization treatment performed after the cans are formed.

When the content to be filled into the aluminum can is carbonated drinking water or drinking water such as coffee, after filling the content, the aluminum can is pasteurized (hot water sterilization, for example, at 80 ° C. for 15 minutes) or retorted ( After heating in warm water, high-temperature steam sterilization, for example, at 120 ° C 30
However, at this time, brown discoloration or black discoloration occurs during pasteurizer treatment and white discoloration occurs during retort treatment at the bottom of the outer surface of the aluminum can can body, which is an unpainted portion.

Black discoloration or white discoloration of the aluminum at the bottom of the unpainted aluminum can can body significantly impairs the appearance of the aluminum can body, and there is a problem that the aluminum can body cannot be sold as a product.

The discoloration of the bottom of the aluminum can, which is the unpainted part of the aluminum can, was investigated using the latest analytical equipment such as X-ray microanalyzer, Auger analysis or X-ray photoelectron spectroscopy. The present inventors have found that this is caused by a phenomenon.

As described above, in the manufacturing process of the aluminum can, a drying process (about 200 ° C., about 1 minute) is performed after the chemical conversion treatment, and a baking process (about 200 ° C.,
About 1 minute). In these heat treatment steps, the chemical conversion coating formed on the aluminum can, i.e., the chromate phosphate coating or the zirconium salt coating causes a dehydration phenomenon and causes a contraction of the coating. A thermal expansion difference causes a thermal crack in the chemical conversion film.

As shown in FIG. 1, the coating is not applied on the bottom 1 of the aluminum can, so that the clutch portion 3 of the chemical conversion film 2 has a structure in which the aluminum alloy 4 of the base material is directly exposed on the outer surface. In the crack part 3, there is no protective layer.

Aluminum cans with conversion coating defects on the bottom of the body of unpainted aluminum cans The contents of aluminum cans are filled into cans and then sterilized.After pasteurization, Ca, Si, etc., which are contained as impurities in warm water Is adsorbed or deposited on a portion where the aluminum alloy 4 of the base material, which is a chemical conversion film defect at the bottom of the can, is directly exposed, causing brown discoloration or black discoloration.

In the retort treatment, the aluminum of the base material directly exposed from the conversion film defect (crack 3) on the bottom 1 of the aluminum can reacts with water vapor to form a white acicular aluminum hydrated oxide, which increases the pasteurizer time treatment. At the same time, needle-like aluminum hydrated oxide grows, and the bottom of the can, which is an unpainted portion, turns white.

In addition, inside the aluminum can, the contents gradually penetrate into the coating film during storage, react with the aluminum base material at cracks in the chemical conversion film, and form hydrated aluminum oxides. To raise the adhesion of the coating on the inner surface of the can, and when an external impact is applied to the aluminum can in such a state, the coating can be easily peeled off, which may cause a problem in long-term storage of the aluminum can. there were.

The present invention has been made in view of the above circumstances, in the conventional conversion coating, even if the conversion coating damage due to thermal cracks when performing heat treatment such as baking after drying or painting, significantly increases the corrosion resistance of the coating. After filling the contents, for example, the aluminum can is pasteurized (sterilized with hot water, 80 ° C, 15 minutes) or retorted (preheated in hot water, followed by high-temperature steam sterilization, 120 ° C, 30 minutes). An object of the present invention is to provide a method for forming a corrosion-resistant film on an aluminum can, which can prevent blackening and whitening of an unpainted portion of the aluminum can even without wastewater treatment, and an aluminum can having a corrosion-resistant film. .

[Means for Solving the Problems] The present invention relates to a method for forming a corrosion-resistant film on an aluminum can made of an aluminum alloy, wherein the aluminum can is subjected to a chromic phosphate treatment or a zirconium salt treatment. (1) a method of forming a corrosion-resistant film on an aluminum can which forms a second corrosion-resistant film by forming a corrosion-resistant film of (1) and then performing a boehmite treatment, wherein in the above method, the boehmite treatment is a treatment performed in dry steam; A method for forming a corrosion-resistant film on an aluminum can having a steam temperature of 140 to 250 ° C. After forming the first corrosion-resistant film by this method, pure water having a specific resistance of 1 × 10 ⁵ Ω · cm or more The resistance is 1 × 10 ⁵ Ω
After applying an aqueous solution of a total of 0.01 to 3% by weight of a compound selected from ammonia, amine, alcoholamine and amide to pure water of at least cm, a boehmite treatment is subsequently performed to form a second corrosion-resistant film. A method for forming a corrosion-resistant film on an aluminum can to be formed, wherein the boehmite treatment is a treatment performed in saturated steam, and a method for forming a corrosion-resistant film on an aluminum can having a temperature of the steam of 100 to 130 ° C .; 0.01% to 3% added resistance 1 × 10 ⁵ Ω · cm or more in pure water or the resistivity of ammonia in pure water at least 1 × 10 ⁵ Ω · cm, amine, a compound selected from alcohol amines and amides in total Temperature
In a method for forming a corrosion-resistant film on an aluminum can, which is a treatment carried out in an aqueous solution at 90 ° C or higher, a method for forming a corrosion-resistant film on an aluminum can made of an aluminum alloy, wherein the aluminum can is treated with a chromic phosphate or zirconium. A first corrosion-resistant film is formed by performing a salt-based treatment, then a coating is performed, and the coated film is baked to form a second corrosion-resistant film. Further, a boehmite treatment is performed on an unpainted portion of the aluminum can. Forming a third corrosion-resistant film on the aluminum can by subjecting the aluminum can to a process in which the boehmite treatment is performed in dry steam, wherein the temperature of the steam is 140 to 200 ° C. The method of forming a corrosion-resistant coating on aluminum cans made of aluminum alloy has a phosphoric acid phosphate coating or An aluminum can having a corrosion-resistant coating, characterized by comprising an admixture layer of any one of a conium salt-based coating and a boehmite coating. In the above aluminum can, a corrosion-resistant coating characterized by being coated on a part of the can surface Aluminum cans, and aluminum cans made of aluminum alloy, in which a part of the surface of the can is coated with a chromic phosphate-based coating layer or zirconium salt under the coating film in the coating part An aluminum can having an anticorrosion coating having any one of a chromium phosphate-based coating or a zirconium salt-based coating and a boehmite coating on the surface of the raw material in the unpainted portion. Thus, the above-mentioned problem is solved.

"Action" In the case of a conventional composite coating of a chemical conversion coating and a boehmite coating formed on the surface of an aluminum can by the above method, before or during the formation of the composite composite coating
The thermal history of about 200 ° C. has already been received, and the crack portion of the chemical conversion film generated by the thermal shock is covered with the boehmite film in the base material exposed from the crack portion by the subsequent boehmite treatment. Therefore, the repaired admixture composite coating has excellent heat resistance in the boehmite coating itself, and at the same time, has thermal stability imparted to conventional conversion coatings. No new clutch is generated and it is stable.

Further, the boehmite formation temperature was limited to the above range, in the method using dry steam, the formation speed of the boehmite film is slow at 140 ° C or less, and the drying speed of the aluminum can is slow, and the temperature is 250 ° C or more. This is because the tempering effect provided for toughening the aluminum alloy (A3004) of the base material is lost.

Further, in the method using saturated steam, the temperature is set to the above-mentioned temperature, the formation rate of the boehmite film is slow at 100 ° C or lower, and the vapor pressure increases at 130 ° C or higher, which leads to an increase in the size of the apparatus, which is not preferable. That's why.

In a treatment with pure water having a specific resistance of 1 × 10 ⁵ Ω · cm or more or an aqueous solution obtained by adding a compound selected from ammonia, amine, alcoholamine and amide to pure water under these conditions, boehmite is not used at 90 ° C. or less. This is because the formation speed is low.

As shown in FIG. 2, the conventional composite coating film 6 composed of the chemical conversion coating film 2 and the boehmite coating film 5 formed by the above-described method has denseness and continuity by complementing each other. 1, there is no portion where the aluminum alloy 4 as the base material is directly exposed to the outer surface, as in the surface of the conventional aluminum can bottom 1 having only the chemical conversion coating 2 shown in FIG. 1, and oxygen, water, contents, etc. Has good corrosion resistance. Therefore, after filling the contents such as drinking water into an aluminum can, it is subjected to a pasteurizer treatment (hot water sterilization, 80 ° C, 15 minutes) or a retort treatment (high temperature steam sterilization, 120 ° C, 30 minutes). Even so, the aluminum alloy 4 of the base material is protected without breaking the mild composite film, and the aluminum alloy does not turn black or white.

In addition, when the contents are filled into aluminum cans and stored for a long period of time, even if the contents gradually penetrate into the coating film during storage, the admixture composite film has no defect and shows good corrosion resistance. The deterioration of the secondary adhesion of the film is also extremely small, and even if the compound composite film is directly exposed to the outer surface at the pinhole-shaped defect, the corrosion resistance of the compound composite film is excellent, so that the base material is sufficiently protected. And the elution of Al is extremely small, and it can withstand long-term storage.

In the above method, when the boehmite film is formed by the boehmite forming method using dry steam and the chemical conversion film is repaired, the aluminum can can also be used for conventional chemical conversion treatment and drying after washing with water.

Furthermore, in the restoration of the chemical conversion film by boehmite treatment, harmful substances such as chromium ions are not used or generated, so cleaning after boehmite treatment is unnecessary, and since there is no need to perform wastewater treatment, There is no need to install new wastewater treatment facilities.

"Example" Hereinafter, a method for forming a corrosion-resistant film on an aluminum can of the present invention will be described with reference to the drawings and Table 1.

First, a first corrosion-resistant coating is applied to the surface of an aluminum can body made by forming an aluminum alloy (A3004) sheet material by deep squeezing.

As a method of forming the first corrosion-resistant film, the surface of the aluminum can body is subjected to a chemical conversion treatment of a chromate phosphate or zirconium salt by a spray method.

The conditions for forming the first corrosion-resistant film are shown in Table 1.

Next, the aluminum can body on which the first corrosion-resistant film is formed is washed with pure water and immediately or after drying, a boehmite film is formed as a second corrosion-resistant film.

As a method for forming the boehmite film, there is a method in which the boehmite treatment is carried out in a boehmite treatment liquid, in dry steam, or in saturated steam.

A method for forming a boehmite film in the above boehmite treatment solution is to add a compound selected from ammonia, amine, alcoholamine and amide to pure water having a specific resistance of 1 × 10 ⁵ Ω · cm or more or pure water under these conditions. The resulting aqueous solution is heated to a temperature of 90 ° C. or higher to obtain a boehmite treatment solution, and the aluminum can is immersed in the boehmite treatment solution.

Hereinafter, a method of forming a boehmite film in dry steam or saturated steam will be described with reference to the drawings. FIG. 3 is a schematic configuration diagram of a boehmite forming apparatus using dry steam or saturated steam.

In FIG. 3, reference numeral 11 denotes an apparatus. This device
Numeral 11 denotes a processing chamber 12, a steam supply chamber 13, and a heating and keeping tube 14.

The processing chamber 12 is communicated with the steam supply chamber 13 by a heating and keeping tube 14, and saturated steam 15a or dry unsaturated steam 15b is sent from the steam supply chamber 13 through the heating and keeping tube 14. The processing chamber 12 is provided with an exhaust port 16.

A heater 17 is mounted in the steam supply chamber 13 so that pure water 18 can be charged.

A portion indicated by a dotted line in the figure is a heating and heating heater 19 for heating the entire apparatus to maintain a predetermined temperature.

Further, a valve 20 is provided in the heating and insulated tube 14,
By opening this valve 20, the air in the apparatus can be exhausted.After closing the valve 20, the valve 23 is opened, and by operating the pressure adjusting valve 24 provided in the processing chamber 12, the pressure in the apparatus can be reduced. Can be adjusted.

In order to form boehmite on the aluminum can body 21 having the first corrosion-resistant film formed thereon using the apparatus having the above-described structure, the following method is used.

Pure water 18 is charged into the steam supply chamber 13 of the apparatus 11 shown in FIG. 3, and is heated by the heater 17 to generate steam 22. Then, the generated steam 22 is heated by the heating / insulating heater 19 to heat the entire apparatus.
In the case of the saturated steam treatment, the temperature is heated to 100 to 130 ° C., and in the case of the unsaturated steam treatment, the temperature is kept at 140 to 250 ° C. to keep the temperature. When sufficient steam is generated and the steam supply chamber 13 is sufficiently filled with steam, an aluminum can body 21 having a first corrosion-resistant film formed therein is put into the treatment chamber 12, then the valve 20 is closed, and the valve 23 is closed. Opening, the steam is led to the processing chamber 12. By operating the pressure control valve 24 provided in the processing chamber 12,
While maintaining the pressure in the apparatus at a predetermined value of 1 to 10 atm, the steam 22 generated in the steam supply chamber 13 is
It is continuously supplied into the processing chamber 12 as 15a or dry unsaturated steam 15b. Note that the inside of the processing chamber 12 is preheated before introducing steam.

Then, the supplied saturated steam 15a of 100 to 130 ° C.
Alternatively, the second corrosion resistance made of boehmite in the thermal crack portion of the first corrosion resistant film of the aluminum can body 21 formed with the first corrosion resistant film in the processing chamber 12 by the dry unsaturated steam 15b at 140 to 250 ° C. A film is formed, and an admixture composite film is obtained on the surface of the aluminum can body 21.

Next, the inner and outer surfaces of the aluminum can are coated with the same method as in the prior art, and the coating is baked.

In the above description, the boehmite film is formed as the second corrosion-resistant film immediately or after the aluminum can body on which the first corrosion-resistant film is formed is rinsed with pure water or dried. The order is not limited to this, and the boehmite treatment may be performed after painting and baking of this painting.

Further, in the case of performing boehmite treatment with dry steam, it can also serve as drying for washing with water after forming the first corrosion-resistant film, and can also serve as baking after painting.

"Experimental example 1" Aluminum alloy A3004H19 sheet material (thickness 0.35mm) was formed by deep squeezing and the aluminum can body (can diameter 66)
mm, can height 170 mm). A first corrosion-resistant film was formed on the aluminum can body. As the first corrosion resistant film, a chromate phosphate film (Cr amount 15 mg / m ² )
(Samples 1 and 2) and zirconium salt-based coating (Zr content 15mg /
m ² )... (Samples 3 and 4) were performed. Further, this aluminum can was treated with pure water having a specific resistance of 10 ⁶ Ω · cm or more, and a second corrosion-resistant film was immediately formed on the aluminum can body in dry steam under the following conditions.

The boehmite treatment in the dry steam at this time could also serve to dry the aluminum can wet by the pure water treatment.

Conditions for forming boehmite Temperature: 200 ° C. Steam pressure: 1 atm (sample 1), (sample 3) 5 atm (sample 2), (sample 4) Processing time: 2 minutes After forming only the corrosion-resistant film, it was dried (200 ° C., 1 minute) to produce a film.

First Corrosion Resistant Coating (Comparative Example A): Chromic Phosphate-Based Coating (Comparative Example B): Zirconium Salt-Based Coating Next, for samples 1, 2, 3, 4 and Comparative Examples A and B, Can body outer surface coating (epoxy amino resin, coating thickness 5μm)
→ baking (210 ° C, 2 minutes) → inner coating of the can body (thermosetting vinyl resin, coating thickness 5 μm) → baking (200 ° C, 2 minutes) → flange and necking.

Further, aluminum can lids (material A5182H38) were prepared for Samples 1, 2, 3, and 4 by performing the same first corrosion-resistant coating treatment, second corrosion-resistant coating treatment, and painting and baking.

Similarly, for Comparative Examples A and B, an aluminum can body was prepared by performing a first corrosion-resistant coating, drying, painting, and baking.

Samples 1, 2, 3, and 4 prepared as above and Comparative Example
The following evaluation tests were performed on the aluminum cans A and B. In addition, the test number was implemented about 5 cans each.

50% 3% NaCl solution in each aluminum can body
After injecting 0 ml, the solution was stored for one month at room temperature under the atmosphere, and the amount of Al eluted into the NaCl solution in each can was measured. Table 2 shows the results.

As shown in Table 2, the aluminum can (samples 1, 2, 3, and 4) obtained by applying a boehmite film as a second corrosion-resistant film on the first corrosion-resistant film to form a composite has the first corrosion resistance. It showed better corrosion resistance than aluminum cans with only a coating (Comparative Examples A and B).

Next, the unpainted portions of the aluminum bottoms of the aluminum cans of Samples 1, 2, 3, 4 and Comparative Examples A, B and Samples 5, 6, 7, 8 and Comparative Examples C, D, which were subjected to the coating and baking processes For the target, simulating pasteurizer treatment as a heat sterilization test, immersed in city water of 80 ° C. for 30 minutes, visually determine the discoloration state of the can bottom outer surface,
The results are shown in Table 3.

Further, as a steam sterilization test, simulating retort treatment, in 125 ° C saturated steam, samples 5, 6, 7, 8 and Comparative Example C,
The aluminum can of D was exposed for 20 minutes, and the discolored state of the outer surface of the can bottom, which was an unpainted portion, was visually judged. The results are shown in Table 3.

As can be seen from Table 3, the unpainted portions of the aluminum cans of Samples 5, 6, 7, and 8 in which the boehmite film was further combined with the first corrosion-resistant film were subjected to the heat sterilization test and the steam sterilization test. No discoloration occurred. On the other hand, the unpainted portions of the aluminum cans of Comparative Examples C and D having only the first corrosion-resistant coating were discolored.

Next, aluminum can bodies corresponding to Samples 1, 2, 3, 4 and Comparative Examples A and B were filled with lager beer or orange juice, and the aluminum can lids that had been treated according to the treatment of each can body were used. It was tightened to give a canned body. ...
(Samples 9, 10, 11, 12), ... (Comparative Examples E, F) In the contents of the cans of Samples 9, 10, 11, 12 and Comparative Examples E, F obtained as described above. The elution amount of Al and the adhesion of the coating film on the inner surface of the can body were measured by a T-type coating film peeling test method, and the results are shown in Table 4.

As can be seen from Table 4, the aluminum cans of Samples 9, 10, 11, and 12 in which the second corrosion-resistant coating was further composited on the first corrosion-resistant coating were all the same as Comparative Examples E and F. In comparison, the corrosion resistance to the contents and the secondary adhesion of the coating film were excellent.

"Experimental example 2" A zirconium salt-based first corrosion-resistant film (Zr content 10 mg / m ² ) was formed on an aluminum can body according to the steps shown in Table 1, and purified with 11 × 10 ⁶ Ω · cm pure water. Immediately after washing with water,
A boehmite treatment was performed under the following conditions to form a second corrosion resistant film.
A sample was prepared by performing heat treatment for one minute.

Boehmite treatment conditions Pressure; 1 atm (dry steam) Steam temperature; 140 ° C ・ ・ ・ Sample 13 180 ° C ・ ・ ・ Sample 14 200 ° C ・ ・ ・ Sample 15 220 ° C ・ ・ ・ Sample 16 250 ° C ・ ・ ・ Sample 17 Processing time ; 120 seconds Also, as a comparative example, under the above conditions,
A boehmite treatment at a temperature of ° C was performed. ... (Comparative Example G) Further, a film composed of only the first corrosion-resistant film was produced. ... (Comparative Example H) Heat sterilization test (City Water, 80) on the aluminum cans of Samples 13, 14, 15, 16, 17 and Comparative Examples G and H under the same conditions as Experimental Example 1
℃, 30 minutes) and steam sterilization test (saturated steam, 125 ℃, 20
Min).

 Table 5 shows the results.

As can be seen from Table 5, none of the aluminum cans of Samples 13, 14, 15, 16 and 17 showed any change with respect to the heat sterilization test and the steam sterilization test. On the other hand, discoloration was observed in the aluminum can of Comparative Example G in which the boehmite treatment temperature was 120 ° C. and Comparative Example H in which only the first corrosion-resistant coating was applied.

In compliance with the steps shown in Table 1 in "Experimental Example 3" aluminum can body, after the formation of the first corrosion-resistant coating of zirconium salt (Zr weight 10 mg / m ^2), processes the aluminum can with treated water in the following did.

Treatment aqueous solution (The following chemicals are added to pure water with a specific resistance of 10 ⁶ Ω · cm) Additive concentration: Ammonia 0.5% ・ ・ ・ Sample 18 Monoethylamine ・ ・ ・ Sample 19 Triethanolamine ・ ・ ・ Sample 20 No addition (Pure water) Sample 21 These aluminum cans were immediately subjected to boehmite treatment under the following conditions.

Boehmite treatment conditions Pressure; 1 atm (dry steam) Steam temperature; 180 ° C Treatment time: 20 seconds, 40 seconds, 60 seconds, 80 seconds, 100 seconds, 120 seconds After the formation of the first corrosion resistant film, city water (10 ² Ω ・ cm)
, And immediately subjected to boehmite treatment. ··· (Comparative Example I) Heat sterilization test under the same conditions as in Example 1 (city water, 80 ° C, 30 minutes) was performed on the samples 18, 19, 20, 21 and the aluminum cans of Comparative Example I produced as described above. ).

As a result, in Samples 18, 19 and 20, more than 40 seconds, in Sample 21, 60
Discoloration did not occur when the boehmite treatment was performed for more than a second.

On the other hand, in Comparative Example I, even after the boehmite treatment for 80 seconds, discoloration occurred in the above heat sterilization test.

"Experimental example 4" A zirconium salt-based first corrosion-resistant film (Zr content 10 mg / m ² ) was formed on an aluminum can body according to the steps shown in Table 1, and then purified water having a specific resistance of 10 ⁶ Ω · cm. , And then dried (200 ° C., 1 minute). Next, the aluminum can body was suspended in steam in the steam supply chamber 13 of the apparatus 11 shown in FIG. 3, and subjected to boehmite treatment in saturated steam under the following conditions.

Boehmite treatment conditions Steam temperature; 110 ° C ··· Sample 22 130 ° C ··· Sample 23 150 ° C ··· Sample 24 Treatment time; 2 minutes Under the above boehmite conditions, the steam temperature was 90 ° C and the boehmite treatment was performed. This was produced.
... (Comparative Example J) A steam sterilization test (saturated steam, 125 ° C, 20 minutes) was performed on the aluminum cans of Samples 22, 23, and 24 and Comparative Example J as described above under the same conditions as in Experimental Example 1. Carried out.

As a result, none of Samples 22, 23, and 24 caused discoloration. On the other hand, in Comparative Example J, partial white discoloration occurred.

Experimental Example 5 A zirconium salt-based first corrosion-resistant film (Zr content: 10 mg / m ² ) was formed on an aluminum can body according to the steps shown in Table 1. Then, the substrate was washed with pure water having a specific resistance of 10 ⁶ Ω · cm, dried (200 ° C., 1 minute), and immersed in boehmite-treated water shown below to form a boehmite film as a second corrosion-resistant film. . Furthermore, these aluminum can bodies were subjected to heat treatment (200 ° C, 5 minutes) to simulate painting and baking.

Boehmite treatment conditions treated water; (ratio of pure water to chemicals added resistor 10 ⁶ Ω · cm) Ammonia ... Sample 25 (0.4%) monoethyl amine (0.7%) ... sample 26 triethanolamine ... sample 27 (0.6%) No addition (pure water) ・ ・ ・ Sample 28 Processing temperature; 100 ° C Processing time; 60 seconds, 80 seconds, 100 seconds, 120 seconds, 140 seconds Samples 25, 26, 27 prepared as above And 28 aluminum can bodies were subjected to a heat sterilization test under the same conditions as in Experimental Example 1 (City Water, 8
(0 ° C., 30 minutes).

As a result, for the samples 25, 26, and 27 to which the above-mentioned chemicals were added, the treatment time was 80 seconds or more, and no discoloration occurred in the heat sterilization test.

The sample 28 which was subjected to boehmite treatment with pure water was 10
The treatment for 0 seconds or longer did not cause discoloration in the heat sterilization test.

To form a first corrosion-resistant coating of zirconium salt according Table 1 step in "Experimental Example 6" aluminum can body (Zr weight 10mg / m ^2). Then dry in this aluminum can (200 ℃, 1 minute)
→ Can body exterior coating (epoxy amino resin, coating thickness 5 μm)
→ Baking (210 ° C, 2 minutes) → Inner body inner coating (thermosetting vinyl resin, coating thickness 5 μm) → Baking (200 ° C, 2 minutes). Further, the outer surface of the can bottom, which is the unpainted part of the aluminum can body, is placed in dry steam (200 ° C, 1 atm) against the image
Then, boehmite treatment was performed for 180 seconds to form a boehmite coating layer. ... Sample 29 A sample subjected to the same treatment as Sample 29 except that the above-mentioned boehmite treatment was not applied to the outer surface of the can bottom was used as a comparative example. ... Comparative Example K The heat sterilization test (city water, 80 ° C, 30 minutes) and the steam sterilization test (saturated steam, 125 ° C) under the same conditions as in Experimental Example 1 were applied to Sample 29 and Comparative Example K prepared as described above. , 20 minutes).

As a result, the outer surface of the aluminum can bottom of the aluminum can of Sample 29 did not discolor in any of the heat sterilization test and the steam sterilization test.

On the other hand, the entire outer surface of the aluminum can bottom of the aluminum can of Comparative Example K turned brown in the heat sterilization test and turned white in the steam sterilization test.

[Effects of the Invention] As described above, according to the method for forming a corrosion-resistant film on an aluminum can of the present invention, an aluminum can provided with a conventional chemical conversion film, that is, a phosphate chromate-based film or a zirconium salt-based film, High temperature heat treatment (for example, 200 ° C., 1 minute) such as drying or baking of the coating causes thermal cracks in the chemical conversion coating layer and lowers corrosion resistance. However, boehmite treatment is performed simultaneously with or after drying after chemical conversion treatment. By forming the boehmite film on the surface of the aluminum alloy on the base material exposed at the thermal crack portion of the chemical conversion film, it is possible to repair the chemically damaged chemical film.

Further, in the corrosion-resistant film formed by the method of the present invention, the chemical conversion film as the first corrosion-resistant film and the boehmite film as the second chemical conversion film are complementary to each other,
These admixture composite coating layers have continuity, protect the base aluminum alloy, and impart good corrosion resistance and thermal stability to the aluminum can surface. Therefore, in an aluminum can provided with a corrosion-resistant coating by the method of the present invention, after filling the contents such as drinking water into the aluminum can, a pasteurizer treatment (heated water, for example, 80 ° C.) which is a heat sterilization treatment is performed. , 30 minutes) or retort treatment (after preheating in warm water, then in saturated steam, for example at 120 ° C, 30 minutes)
Even if it is subjected to (min), the unpainted portion on the outer surface of the aluminum bottom of the aluminum can does not discolor to brown or white.

In addition, since the corrosion resistance of the composite film of the admixture is good and the deterioration with time is small, the elution amount of aluminum into the content is small, and the secondary adhesion of the coating film is more excellent.

Further, in the boehmite formation, which is the repair treatment of the chemical conversion coating on the aluminum can of the present invention by the method for forming a corrosion-resistant coating, washing with water after the treatment is unnecessary, and harmful heavy metal ions are not contained. There is no.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a conventional aluminum can bottom part, FIG. 2 is a schematic cross-sectional view showing an admixture composite film comprising a boehmite film and a chemical conversion film formed by the method of the present invention, and FIG. It is a schematic structure figure of an apparatus for forming boehmite in a can. 2 ... first corrosion-resistant film (chemical conversion film), 4 ... aluminum alloy, 5 ... second corrosion-resistant film (boehmite film), 6 ... mixture layer (mixture composite film), 21 ... aluminum can .

Claims (10)

(57) [Claims] 1. A method for forming a corrosion-resistant film on an aluminum can made of an aluminum alloy, wherein the aluminum can is subjected to a chromate phosphate treatment or a zirconium salt treatment to form a first corrosion-resistant film. And a boehmite treatment to form a second corrosion-resistant film on the aluminum can. 2. The method for forming a corrosion-resistant film on an aluminum can according to claim 1, wherein the boehmite treatment is performed in dry steam, and the temperature of the steam is 140 to 250 ° C. 3. The method according to claim 1, wherein the boehmite treatment is performed in saturated steam, and the temperature of the steam is
A method for forming a corrosion-resistant film on an aluminum can, wherein the temperature is 100 to 130 ° C. 4. The method according to claim 1, wherein the boehmite treatment is performed by adding ammonia, pure water having a specific resistance of 1 × 10 ⁵ Ω · cm or more, or pure water having a specific resistance of 1 × 10 ⁵ Ω · cm or more to ammonia. A method for forming a corrosion-resistant film on an aluminum can, characterized in that the treatment is carried out in an aqueous solution at a temperature of 90 ° C. or more to which a compound selected from amine, alcoholamine and amide is added in a total amount of 0.01 to 3% by weight. 5. After forming the first corrosion resistant coating in the description of claim (2), the resistivity is 1 × 10 ⁵ Ω · cm or more pure water or the resistivity is 1 × 10 ⁵ Ω · cm or more After applying an aqueous solution obtained by adding a total of 0.01 to 3% of a compound selected from ammonia, amine, alcoholamine and amide to pure water, subsequently performing boehmite treatment to form a second corrosion resistant film. Characterized by the method of forming a corrosion-resistant film on an aluminum can. 6. A method for forming a corrosion-resistant film on an aluminum can made of an aluminum alloy, wherein said aluminum can is subjected to a chromate phosphate treatment or a zirconium salt treatment to form a first corrosion-resistant film. And then applying a coating, baking the coating film to form a second corrosion-resistant film, and further performing a boehmite treatment on an unpainted portion of the aluminum can to form a third corrosion-resistant film. Of forming a corrosion-resistant film on a rotating aluminum can. 7. The method for forming a corrosion-resistant film on an aluminum can according to claim 6, wherein the boehmite treatment is performed in dry steam, and the temperature of the steam is 140 to 200 ° C. 8. An aluminum can made of an aluminum alloy, wherein the surface of the material is made of a mixture of a chromate phosphate coating or a zirconium salt coating and a boehmite coating. Having aluminum cans. 9. The aluminum can according to claim 8, wherein said aluminum can has a corrosion-resistant coating formed by coating a part of the surface of the can. 10. An aluminum can made of an aluminum alloy, wherein a part of the surface of the can is painted. In the painted part, a chromic phosphate-based coating layer or a zirconium salt-based coating is provided under the coating film. An aluminum can having a corrosion-resistant coating, characterized in that the uncoated part has an admixture layer of either a chromate phosphate coating or a zirconium salt coating and a boehmite coating in the unpainted part .