JP2004018927A - Aluminum foil for container, manufacturing method therefor, and container formed from aluminum foil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil superior in alkali resistance for a container, which is not corroded even when contacting with alkaline components for a long time, and to provide a manufacturing method therefor and the container superior in corrosion resistance formed from the aluminum foil, which is suitable for preserving foods containing an alkaline juice. <P>SOLUTION: The aluminum foil for the container has an anodic oxide film with a thickness of 20 nm or more but 700 nm or less formed on the surface of a foil substrate consisting of aluminum or an aluminum alloy, wherein the anodic oxide film has a porosity of 20% or less, and is formed by direct-current electrolysis in an alkaline aqueous solution with a pH of 8 or higher. <P>COPYRIGHT: (C)2004,JPO

Description

【００２７】
【発明の効果】
以上、詳細に説明したように、本発明に係る容器用アルミ箔は、アルミニウム又はアルミニウム合金からなる箔基材の表面に、膜厚２０ｎｍ以上７００ｎｍ以下の陽極酸化皮膜が形成されており、前記陽極酸化皮膜の有孔率が２０％以下とされ、また、陽極酸化皮膜が、ｐＨ８以上のアルカリ性水溶液中で直流電解処理して形成されたものであることで、耐アルカリ性に優れるアルミ箔成形容器を構成することができるアルミ箔とされている。
【００２８】
また、陽極酸化皮膜の膜厚を３０〜３００ｎｍとし、有孔率を５％以下とするならば、しわ付き容器のように強度に加工された容器を構成する場合にも、優れた耐食性を得ることができる。
【００２９】
本発明に係るアルミ箔成形容器は、上記本発明のアルミ箔により構成されるので、耐アルカリ性に優れ、特に、アルカリ性の汁を含む食品の保存に用いる容器として好適である。
【図面の簡単な説明】
【図１】図１は、本発明に係るアルミ箔成形容器の一実施の形態であるしわ付き容器の斜視構成図である。
【図２】図２は、本発明に係るアルミ箔形成容器の一実施の形態であるしわ無し容器の斜視構成図である。
【符号の説明】
１０　しわ付き容器（アルミ箔成形容器）
１５　しわ無し容器（アルミ箔成形容器）
１１　底壁
１２　周壁
１３　フランジ部
１４　しわ[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an aluminum foil for a container, a method for producing the same, and an aluminum foil molded container.
[0002]
[Prior art]
Conventionally, aluminum foil molded containers are widely used for serving portable containers and foodstuffs, and include liquid foods (for example, curry, stew, ramen, gratin, boiled dishes, soups, etc.) and thin-walled foods (for example, pizza, Ham, cheese, etc.).
[0003]
[Problems to be solved by the invention]
In recent years, a form in which food is housed in such an aluminum foil molded container, distributed in a refrigerated or frozen state, and the aluminum foil molded container is heated by a stove or oven to cook the stored food is known. I have. Such foods often produce acidic or alkaline juice when cooked. Particularly, aluminum is more easily corroded by alkali than by acid, so that the container may be discolored by alkali corrosion during cooking. Further, when severe corrosion is caused, a hole may be formed in a side wall portion which is severely processed.
[0004]
Further, as an aluminum foil molded container used for the above-mentioned applications, there is a wrinkled aluminum foil molded container having increased strength by forming a wrinkle on a container side wall. This wrinkled container is used as a food container with a larger capacity because of its excellent strength, and after punching out aluminum foil, it is drawn into a wrinkled container and then pressed into a die without extending the wrinkles. After the uniform wrinkles are generated in the above, the wrapping is performed.
In such a container with wrinkles, food is put in, heat-sterilized, frozen and stored in many cases, but in this case, it is kept in contact with juice containing salt such as gratin or stew for a long time. Therefore, it may be corroded by salt, especially in a container with wrinkles, the alkaline component contained in the juice or juice enters the narrow gap of the wrinkle, causing crevice corrosion and perforation, and the juice of the food inside the There was a risk of leakage.
[0005]
The present invention has been made to solve the above problems, and provides an aluminum foil for a container which does not corrode even when contacted with an alkali component for a long time and has excellent alkali resistance, and a method for producing the same. It is intended to be.
Another object of the present invention is to provide an aluminum foil molded container having excellent corrosion resistance suitable for long-term storage of food containing alkaline juice.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the aluminum foil for a container according to the present invention has an anodized film having a thickness of 20 nm or more and 700 nm or less formed on the surface of a foil substrate made of aluminum or an aluminum alloy,
The anodic oxide film has a porosity of 20% or less, and is formed by a direct current electrolytic treatment in an alkaline aqueous solution having a pH of 8 or more.
According to the above configuration, it is possible to provide an aluminum foil for a container which has excellent resistance to alkali corrosion and does not cause discoloration or perforation even when used for a container for preserving food containing alkaline juice for a long period of time. Hereinafter, the components of the aluminum foil for a container according to the present invention will be described.
[0007]
Film thickness (20 to 700 nm): If the film thickness is less than 20 nm, the corrosion resistance of the anodic oxide film is insufficient and discoloration may occur due to alkaline juice. The film thickness is preferably 50 nm or more from the viewpoint of resistance to discoloration and perforation.
On the other hand, if the film thickness exceeds 700 nm, cracks tend to occur in the anodic oxide film at the time of forming into a container, and holes may be formed due to the cracks. In addition, the processing time of the electrolysis process is lengthened and the cost is increased.
[0008]
Porosity (20% or less): In the aluminum foil for a container according to the present invention, a substantially nonporous anodic oxide film having a porosity of 20% or less is used. The nonporous anodic oxide film refers to a dense, nonporous anodic oxide film in which local dissolution by an electrolytic solution does not occur during film growth. The aluminum foil for a container according to the present invention can effectively prevent alkali corrosion by utilizing the excellent corrosion resistance due to the denseness of the nonporous anodic oxide film. Therefore, the porosity of the anodic oxide film according to the present invention is preferably as low as possible.
The porosity of the coating can be derived by dividing the total area of the micropores in a predetermined visual field by electron microscope observation by the area of the coating.
[0009]
Further, by providing an anodic oxide film formed by a direct current electrolytic treatment in an alkaline aqueous solution having a pH of 8 or more, the aluminum foil for a container is excellent in corrosion resistance to alkali.
[0010]
Next, in the aluminum foil for a container according to the present invention, it is preferable that the porosity of the anodized film is 5% or less, and the thickness of the anodized film is 30 nm or more and 300 nm or less. Anodized film with a film thickness of more than 300 nm, when applied to a wrinkled aluminum foil molded container, may cause puncturing at the wrinkled part with a large working degree. When applied to a container to be coated, the thickness of the anodic oxide film is preferably 300 nm or less.
In addition, since a strongly processed portion has a more severe corrosive environment than other portions, it is preferable to improve the corrosion resistance of the anodic oxide film by setting the porosity to 5% or less.
[0011]
Next, the method for producing an aluminum foil for a container according to the present invention is directed to a method for producing an aluminum foil for a container in which an anodized film having a thickness of 20 nm or more and 700 nm or less is formed on the surface of a foil substrate made of aluminum or an aluminum alloy. In forming the anodic oxide film on the surface of the foil substrate, a direct current electrolytic treatment is performed in an alkaline aqueous solution having a pH of 8 or more.
According to the above manufacturing method, the alkali resistance of the film can be improved by incorporating the alkali component into the anodic oxide film formed by the electrolytic treatment. When the pH of the electrolytic solution is less than 8, the alkali component taken into the film is small, and the effect of improving the alkali resistance cannot be obtained. Further, when the pH of the electrolytic solution is close to 14, the efficiency of forming the anodic oxide film decreases, the processing time for obtaining a desired film thickness increases, and the production efficiency decreases. From the above, the pH is more preferably in the range of 9 to 12 in order to efficiently form an anodic oxide film having excellent alkali resistance.
Further, in the manufacturing method according to the present invention, the anodic oxide film is formed by direct current electrolytic treatment. This is because it is difficult for the film formed by the AC electrolytic treatment to increase the film thickness, and the tendency is particularly remarkable in the electrolytic treatment in an alkaline aqueous solution. Further, the formed film is likely to become porous, and a film defect which is strongly dissolved in alkali easily occurs in a part of the film, which is not preferable.
Furthermore, since the anodic oxidation and dissolution of the substrate surface occur alternately due to the characteristics of the alternating current, a dense film is difficult to form, and discoloration and perforation are apt to occur due to insufficient corrosion resistance.
[0012]
Next, an aluminum foil molded container according to the present invention is characterized in that the container aluminum foil described in any of the above is molded into a container shape.
Next, in the wrinkled aluminum foil molded container according to the present invention, a bottom wall and a peripheral wall rising from a peripheral edge of the bottom wall are formed by molding the aluminum foil for a container described above, and wrinkles are formed on the peripheral wall. It is characterized by having been given.
According to the aluminum foil molded container according to the present invention, a food container excellent in alkali resistance can be provided. In particular, it is suitable as a food container for long-term storage of food containing alkaline juice.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for manufacturing an aluminum foil for a container according to the present invention will be described, but the present invention is not limited to the following embodiment.
First, a foil substrate made of aluminum or an aluminum alloy is prepared. The foil substrate applied to the aluminum foil for a container according to the present invention is not particularly limited, and a 3000 series aluminum alloy such as 3004 conventionally used as an aluminum foil for a container can be used without any problem. Further, the thickness of the substrate may be about 30 to 150 μm which is usually used, or may be more than that.
[0014]
In forming the nonporous anodized film on the substrate, it is preferable to perform a pretreatment on the surface of the substrate. The pre-treatment is not particularly limited, and it is essential that the pre-treatment remove oils and fats adhering to the surface of the material and remove a heterogeneous oxide film on the surface of the material. For example, after performing a degreasing treatment with a weak alkaline degreasing solution, after performing alkali etching with an aqueous sodium hydroxide solution, a method of performing a desmut treatment in a nitric acid aqueous solution or a method of performing acid cleaning after the degreasing treatment is appropriately selected. Used.
[0015]
Next, an anodic oxide film is formed on the surface of the foil substrate by electrolytic treatment. In the production method according to the present invention, an anodic oxide film having a porosity of 20% or less is formed on the surface of the foil base material by using an alkaline aqueous solution having a pH of 8 or more as an electrolytic solution and performing a DC electrolytic treatment. As the electrolyte, it is difficult to dissolve the anodic oxide film to be generated, and carbonate, an alkali metal hydroxide, silicate, boric acid, borate, which is an electrolyte that generates a nonporous anodic oxide film, An aqueous solution in which one or more selected from the group of phosphate, adipate, phthalate, benzoate, tartrate, citrate and the like are used. Among these electrolytes, carbonates, silicates and phosphates are preferred in view of the properties of the oxide film, cost and the like. The pH of the electrolyte can be easily adjusted by, for example, adding an appropriate amount of NaOH to the electrolyte. The thickness of the anodic oxide film can be adjusted by the electrolysis time.
The concentration of the electrolyte in the electrolyte is selected from the range of 2% by weight to the saturation concentration of the electrolyte. The bath temperature of the electrolytic bath is sufficient in the range of 15 to 50 ° C, and it is not necessary to set the bath temperature to a high temperature exceeding 50 ° C.
In the DC electrolytic treatment, the foil base material is used as an anode, and a conductive material insoluble in an electrolytic solution is used as a cathode. For example, a carbon electrode is used as a cathode.
Then, the aluminum foil for a container according to the present invention can be obtained by washing the surface of the foil substrate after the electrolytic treatment with water.
[0016]
(Aluminum foil container)
1 and 2 are perspective structural views of an aluminum foil molded container which can be produced by forming an aluminum foil for a container according to the present invention. The aluminum foil molded container 10 shown in FIG. 1 has a relatively shallow bottom wall. 11, a peripheral wall 12 rising from the peripheral edge thereof, and a flange 13 extending from the upper end of the peripheral wall 12 to the outer peripheral side. The peripheral wall 12 has a large number of wrinkles 14 formed in its standing direction. ing. Such an aluminum foil molded container can be manufactured by forming the peripheral wall 12 while forming a wrinkle 14 by drawing after forming the bottom wall 11, forming a flange portion 13 thereafter, and curling the outer periphery thereof. .
The aluminum foil molded container 15 shown in FIG. 2 is a container with no wrinkles formed on the peripheral wall 12.
[0017]
The aluminum foil molded container 10 shown in FIGS. 1 and 2 is made of the aluminum foil for a container of the present invention having excellent alkali resistance. It is an aluminum foil molded container suitable for cooking and preserving alkaline food without discoloration. In particular, in the container with wrinkles shown in FIG. 1, there has been a problem of perforation due to crevice corrosion occurring in the gaps of wrinkles, but by using an aluminum foil excellent in alkali resistance according to the present invention, An excellent food container without discoloration or perforation is realized.
[0018]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples do not limit the technical scope of the present invention.
In this example, an aluminum foil for a container was produced by the production method of the above embodiment, and the obtained aluminum foil was formed to produce a wrinkled container shown in FIG. 1 and a wrinkle-free container shown in FIG. The discoloration resistance and perforation of the foil molded container were verified.
[0019]
First, an A3004 O-material foil base material having a thickness of 80 μm is prepared, etched with 10% NaOH at 50 ° C. for 10 seconds, washed with water for 10 seconds, and then neutralized with 25% 10% nitric acid for 10 seconds. And washed with water for 10 seconds. All of the above processes were performed by a spray process.
Next, various electrolytic solutions having the constitutions shown in Table 1 were prepared, and an electrolytic treatment was performed using the foil substrate after the above treatment as an anode and a carbon plate as a cathode to form an anodic oxide film on the surface of the foil substrate. did. The pH of the electrolytic solution shown in Table 1 was adjusted by appropriately adding NaOH. After the foil substrate after the electrolytic treatment was washed with water for 10 seconds, it was dried at 120 ° C. for 20 seconds to obtain an aluminum foil. In addition, about the comparative example 3, the alternating current electrolytic treatment was performed at the time of formation of the anodic oxide film.
Next, the obtained aluminum foil was subjected to blanking, drawing, wipe-down, and curling forming steps to produce a wrinkled container with an edge shown in FIG. 1 and a wrinkle-free container shown in FIG.
[0020]
(Evaluation)
About each aluminum foil container obtained above, the discoloration property, evaluation of perforation, and measurement of film thickness and porosity were performed. These evaluation and measurement results are also shown in Table 1. The evaluation method and the measurement method are shown below.
[0021]
<Discoloration> A stew of pH 9 was placed in each aluminum foil container, and after boiling for 3 minutes, the contents were taken out, the container was washed with water and dried, and the presence or absence of discoloration and the degree of discoloration were visually observed. The evaluation criteria were x when clear discoloration was observed in the aluminum foil container, and ○ when no discoloration was observed at all.
[0022]
<Perforability> Each aluminum foil container was charged with soy sauce at a pH of 8 diluted to 10%, kept at 40 ° C. for 7 days, and the perforated state of the container was visually observed. In particular, wrinkles where holes easily occur were also observed in detail. The evaluation criterion was evaluated as ○ when no perforation occurred, as Δ when corrosion did not occur but perforation occurred, and x when perforation occurred.
[0023]
<Measurement of film thickness> The film thickness was determined by cutting each sample shown in Table 1, observing the cross section with a transmission electron microscope, and calculating the average value of the film thickness at arbitrary 10 points in the microscope image.
[0024]
<Measurement of porosity> The porosity is measured by observing the surface of the anodic oxide film formed on the surface of the foil base material with a 100,000-magnification electron microscope, and measuring the area ratio of the hole to the total observation area at any 10 locations. Determined by However, sites where the film quality was uneven around the metal compound existing in the sample were excluded.
[0025]
As shown in Table 1, the aluminum foil molded containers of Examples 1 to 8 produced using the aluminum foil satisfying the requirements of the present invention, when boiled in an alkaline stew, have a surface regardless of the presence or absence of wrinkles. It was confirmed that the container was excellent in corrosion resistance without discoloration.
Regarding the piercing property, among the containers without wrinkles (Examples 1 to 3) and the containers with wrinkles, those having a thickness of the anodic oxide film of 30 to 300 nm and a porosity of 5% or less (implementation) In Examples 4 to 6, no perforation occurred at all. In the wrinkled container having a relatively thick anodic oxide film (Example 7) and one having a relatively large porosity (Example 8), corrosion that did not result in perforation was observed.
In contrast, in Comparative Examples 1 to 5, which did not satisfy the requirements of the present invention, discoloration occurred on the container surface and perforations were observed.
[0026]
[Table 1]

[0027]
【The invention's effect】
As described above in detail, the aluminum foil for a container according to the present invention has an anodic oxide film having a thickness of 20 nm or more and 700 nm or less formed on the surface of a foil substrate made of aluminum or an aluminum alloy. The porosity of the oxide film is not more than 20%, and the anodic oxide film is formed by direct current electrolysis in an alkaline aqueous solution having a pH of 8 or more. It is an aluminum foil that can be configured.
[0028]
Further, if the thickness of the anodic oxide film is 30 to 300 nm and the porosity is 5% or less, excellent corrosion resistance is obtained even when a container processed to be strong like a container with wrinkles is formed. be able to.
[0029]
Since the aluminum foil molded container according to the present invention is constituted by the aluminum foil of the present invention, it has excellent alkali resistance, and is particularly suitable as a container used for storing food containing alkaline juice.
[Brief description of the drawings]
FIG. 1 is a perspective view of a wrinkled container as an embodiment of an aluminum foil molded container according to the present invention.
FIG. 2 is a perspective view of a wrinkle-free container, which is an embodiment of the aluminum foil forming container according to the present invention.
[Explanation of symbols]
10 Wrinkled container (aluminum foil molded container)
15 Wrinkle-free container (aluminum foil molded container)
11 bottom wall 12 peripheral wall 13 flange 14 wrinkle

Claims (5)

An anodic oxide film having a film thickness of not less than 20 nm and not more than 700 nm is formed on the surface of the foil substrate made of aluminum or an aluminum alloy,
An aluminum foil for a container, wherein the anodic oxide film has a porosity of 20% or less and is formed by a direct current electrolytic treatment in an alkaline aqueous solution having a pH of 8 or more. The aluminum foil for containers according to claim 1, wherein the porosity of the anodic oxide film is 5% or less, and the thickness of the anodic oxide film is 30 nm or more and 300 nm or less. A method for producing an aluminum foil for a container in which an anodized film having a film thickness of not less than 20 nm and not more than 700 nm is formed on a surface of a foil substrate made of aluminum or an aluminum alloy,
A method for producing an aluminum foil for a container, comprising: performing a DC electrolytic treatment in an alkaline aqueous solution having a pH of 8 or more when forming an anodic oxide film on the surface of the foil base material. An aluminum foil molded container obtained by molding the container aluminum foil according to claim 1 or 2 into a container shape. A bottom wall and a peripheral wall rising from a peripheral edge of the bottom wall are formed by molding the aluminum foil for a container according to claim 2, and wrinkles are applied to the peripheral wall. container.

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