JP5413734B2 - Aluminum alloy foil - Google Patents

Description

  The present invention is a food package suitable for cooking by an electromagnetic cooker, an aluminum alloy foil-molded container used as a container for the food package, and a material for the container. The present invention relates to an aluminum alloy foil having an electrical resistivity value and a method for producing the aluminum alloy foil.

A food package that contains food such as noodles and pots in an aluminum foil molded container is convenient because it can be cooked and cooked as it is without being transferred to a separate container, and the container can be disposable after eating. It is widely used by being sold at convenience stores.
Conventionally, it has been common to heat these food packages by heating them directly on a gas stove, etc., but in recent years, electromagnetic cookers have rapidly become popular due to fire safety. Therefore, there is a demand for a food package that can be cooked by an electromagnetic cooker.

The principle of heating of such an electromagnetic cooker is roughly as follows.
When an alternating current is passed through a coil built in an electromagnetic cooker and a metal container is placed on it, electromagnetic induction occurs due to changes in the magnetic field lines, and eddy currents are generated on the bottom of the container in a direction that prevents the magnetic field lines from changing. .
When this eddy current flows through the container, Joule heat is generated by the electrical resistance of the metal that is the container material, and the food stored in the container is heated.

However, when an aluminum foil molded container of a food package for heating with a conventional gas stove or the like is used in an electromagnetic cooker, heating efficiency may be deteriorated.
In addition, the standard for determining whether or not an electromagnetic cooker can be operated, which is known to general consumers as a “pan check lamp”, etc., varies depending on the manufacturer. A foil-molded container could not be used.

In order to solve these problems, it is necessary to increase the electric resistance value of the aluminum foil molded container to improve the heat generation performance or to operate regardless of the type of the electromagnetic cooker.
The simplest method for increasing the electrical resistance value is to reduce the thickness of the aluminum foil. However, if the thickness is too thin, the strength of the aluminum foil molded container is lowered, and the food may not be held or may be deformed.
Other methods to increase the electrical resistance value include the addition of impurities, but the food stored in the container often contains salt, and if the corrosion resistance of the aluminum foil molded container is inferior due to the addition of the impurity, the container is discolored. Or the contents may leak from the corrosion holes.
Thus, there is a limit to reducing the thickness of the foil or increasing the amount of impurities added.

Therefore, as described below, various aluminum foil molded containers have been devised that are improved so as to be suitable for cooking by an electromagnetic cooker.
For example, Patent Document 1 discloses an aluminum foil molded container in which two or more aluminum foils are laminated and a heat insulating layer is provided on the outer surface thereof.
Patent Document 2 discloses a container formed by superposing iron foil and aluminum foil.
Patent Document 3 discloses an aluminum foil molded container in which at least the bottom surface is formed in a planar shape and the thickness thereof is formed to 12 μm to 96 μm.
In Patent Document 4, 0.15 to 0.35 wt% Si, 2.2 to 2.8 wt% Mg, and 0.10 to 0.35 wt% Cr are 1.5 in total. An aluminum foil molded container is disclosed in which trace elements of less than or equal to weight percent and the balance of 100 weight percent being made of Al are disclosed.
Moreover, 0.15-0.35 weight% Si, 1.0-1.8 weight% Mn, 0.8-1.8 weight% Mg, and 1.5 weight% or less in total A trace element and an aluminum foil molded container whose balance is made of Al in 100% by weight are disclosed.
Patent Document 5 discloses an aluminum foil molded container in which at least a bottom wall is formed by laminating two or more aluminum foils, and the laminated foils are partially in contact with each other.
Patent Document 6 discloses an aluminum alloy core material containing 0.1 to 2.0% by mass of Mg and 0.03 to 0.5% by mass of Cr, with the balance being 100% by mass of Al and inevitable impurities. An aluminum alloy skin material containing 0.01 to 0.05% by mass of Cr and 0.05 to 0.5% by mass of Ti on the one or both sides, and the balance of 100% by mass of Al and inevitable impurities A molded container made of a composite aluminum foil coated with is disclosed.

However, the container described in Patent Document 1 is not suitable for freezing storage, and when the heat insulating layer is paper or the like, there is a risk of burning when it is blown.
Further, the container described in Patent Document 2 has a problem that the manufacturing process is complicated and the weight is increased.
Since the containers described in Patent Documents 3 and 4 have not reached a sufficient resistance value, there has been a problem that some of the electromagnetic cookers cannot be cooked by heating.
The container described in Patent Document 5 has a different resistance value if the contact area of the laminated aluminum foil on the container bottom wall is different. For example, the resistance value is increased if the bottom surface is deformed and the contact area is increased when filling the contents. The required resistance value cannot be obtained.
Since the container described in Patent Document 6 has different processability if the composition of the core material and the skin material are different, the shape of the container obtained as a laminated foil is limited, and this is in response to market demands for containers with high design properties. In addition, there is a problem that it is expensive as a disposable aluminum foil container because it cannot be met and the man-hours are increased.

In addition, in Japanese Patent Application No. 2007-57474, which is an earlier application by the present applicant, in 100% by mass, 93% by mass or more of Al, 2-5% by mass of Mg, and 0.2-1.0%. % By mass of Cr, 0.01-3.0% by mass of Mn, 0.005-0.6% by mass of Ti, 0.005% by mass or less of Cu, and 0.1% by mass or less of Si And 0.2% by mass or less of Fe, and an aluminum foil molded container using an aluminum alloy having an electrical resistivity of 5 to 10 μΩcm is described. Because Cr-Mn hard and coarse intermetallic compounds crystallize, there is a possibility that defects such as pinholes may occur when molding containers from aluminum foil, and there is room for improvement in pinhole resistance. Was left.

As described above, both have problems or room for improvement. However, the above-described problem is formed by an aluminum alloy foil having a specific electric resistance value of a certain level or more, and has excellent formability and corrosion resistance. If an aluminum alloy foil molded container suitable for cooking by a vessel can be devised, all can be solved.
Japanese Utility Model Publication No. 61-194293 JP-A-7-33133 JP 2002-51906 A JP 2003-153802 A JP 2004-379 A JP 2002-19835 A

  Accordingly, the present invention provides an aluminum alloy foil molding container, etc., which is formed of an aluminum alloy foil having a specific electric resistance value of a certain value or more and is excellent in moldability and corrosion resistance and suitable for cooking with an electromagnetic cooker. Is the subject.

As a result of intensive studies, the present inventors have found that an aluminum alloy foil having a specific thickness and specific electrical resistance value has excellent properties by a specific manufacturing method, and has completed the present invention. .
Specifically, the aluminum alloy foil according to the present invention is cast into a thickness of 10 mm or less at a cooling rate of 100 ° C./second or higher, and then cold-rolled to a thickness of 50 to 300 μm, and then 300 Annealing was performed so that the heating and holding time at a temperature of 10 ° C. or higher was within 10 minutes, and the thickness was 50 to 200 μm and the electrical resistivity value was 6.0 μΩcm or higher.

  The aluminum alloy foil as described above is excellent in formability (particularly pinhole resistance) and corrosion resistance, and when the electrical resistivity value is molded from the alloy foil, the electrical resistance is suitable for cooking with an electromagnetic cooker. It is suitable.

In addition, an aluminum alloy foil molding container according to the invention, which has at least a bottom wall and a peripheral wall rising from the bottom wall, is formed from this aluminum alloy foil.
Furthermore, the food packaging body according to the invention is formed by storing food in this aluminum alloy foil molded container.
Here, it is preferable that the annealing time of the aluminum alloy foil is set to be within 1 minute at 350 ° C. or higher.
The average crystal grain size of the aluminum alloy foil is more preferably 1 to 30 μm.

  The composition of this aluminum alloy foil is as follows: Mn of 0.5 ≦ Mn ≦ 3.0 mass%, Cr of 0.0001 ≦ Cr <0.20 mass%, and 0.2 ≦ Mg ≦ 1.8 mass%. Mg, 0.0001 ≦ Ti ≦ 0.6 mass% Ti, 0 <Cu ≦ 0.005 mass% Cu, 0 <Si ≦ 0.1 mass% Si, and 0 <Fe ≦ 0. More preferably, it contains 2% by mass of Fe, with the balance being aluminum and inevitable impurities.

  Considering this method from a method viewpoint, a step of casting a molten aluminum alloy to a thickness of 10 mm or less at a cooling rate of 100 ° C./second or more, a step of cold rolling to a thickness of 50 to 300 μm, and a step of 300 It is understood that it is a manufacturing method of the aluminum alloy foil including the step of performing the annealing in which the heating and holding time at a temperature of not less than 10 ° C. is within 10 minutes.

  By forming the aluminum alloy foil having the above-described thickness and electrical resistivity through the above-described steps, the aluminum alloy foil is formed as a single body and is excellent in moldability and corrosion resistance, and suitable for cooking with an electromagnetic cooker. An aluminum alloy foil molded container or the like can be obtained.

Perspective view of aluminum alloy foil molding container (A) of aluminum alloy foil molding container is a plan view, (b) is a cross-sectional view taken along arrow II-II in (a).

Explanation of symbols

10 Aluminum Alloy Foil Molding Container 11 Bottom Wall 12 Perimeter Wall 13 Flange

The aluminum alloy foil forming container 10 of the embodiment shown in FIGS. 1 and 2 is a single piece of aluminum alloy foil formed by a known method, and spreads from the rounded square bottom wall 11 and the bottom wall 11 periphery. It consists of a peripheral wall 12 that rises and a flange 13 that projects horizontally from the upper edge of the peripheral wall 12.
As shown in the figure, a lot of embosses are formed on the bottom wall 11, a number of vertical ribs are formed on the peripheral wall 12, and edge windings are provided on the outer periphery of the flange 13.
This aluminum alloy foil molding container 10 is mainly used for cooking by an electromagnetic cooker in a state in which food such as noodles and pots is stored.
Here, the projected area of the bottom wall 11 is preferably about 70 to 255 cm ² . If it is less than 70 cm ² , heating by an electromagnetic cooker cannot be performed (the temperature does not increase), and if it exceeds 255 cm ² , the strength as a container becomes insufficient.
Needless to say, the container 10 can be used for cooking by a direct fire such as a gas stove.

The thickness of the aluminum alloy foil is preferably 50 to 200 μm, and more preferably 60 to 100 μm.
If the thickness is less than 50 μm, the strength of the aluminum alloy foil molded container 10 may be reduced, and food may not be held or may be deformed. If the thickness exceeds 200 μm, it may be difficult to process the molded container.
If the thickness is less than 50 μm, defects such as pinholes may occur starting from a hard and coarse intermetallic compound when molded into a container, and if it exceeds 200 μm, it becomes difficult to obtain a desired electrical resistance value. It is.

The electrical specific resistance value of the aluminum alloy foil of the aluminum alloy foil forming container 10 is 6.0 μΩcm or more, preferably 6 to 10 μΩcm, more preferably 6.5 to 10 μΩcm.
If the electrical specific resistance value is less than 6.0 μΩcm, the aluminum alloy foil must be made thin in order to obtain a resistance value necessary for use of the electromagnetic cooker, and the strength of the molded container 10 is reduced. This is because the object may not be held or may be deformed.
The upper limit of the electrical specific resistance value is not particularly limited, but is generally about 10 μΩcm.
The electrical resistivity can be increased by introducing a solid solution of an alloy element having a large specific resistance contribution ratio or processing strain. However, if the electrical resistivity exceeds 10 μΩcm, it may be difficult to process the molded container. Because there is.

  An aluminum alloy foil having a desired electrical resistivity value is prepared by preparing a molten metal having a predetermined composition, and then cold rolling the aluminum alloy cast to a thickness of 10 mm or less at a cooling rate of 100 ° C./second or more. It can be obtained by rolling to a thickness of 50 to 300 μm, annealing at a temperature of 300 ° C. or higher for 10 minutes or less, and then cold rolling if necessary to obtain a thickness of 50 to 200 μm. it can.

The reason why the cooling rate during casting is set to 100 ° C./second or more is to suppress crystallization of the added alloy element to promote solid solution and to increase the electrical resistivity to 6 μΩcm or more.
The reason why the casting thickness is 10 mm or less is that the cooling rate at the time of casting the central portion of the plate thickness is 100 ° C./second or more.
As such a casting method, various continuous casting and rolling methods, for example, (1) a belt type that pours into a mold formed between a parallel steel belt and blocks on both sides, and (2) instead of the belt Examples include a connection block type using a connection block, and (3) a twin-roll type in which pouring is performed with a ceramic nozzle between a pair of rollers.
The reason for setting the foil thickness after cold rolling to 50 to 300 μm is to control the average grain size by imparting sufficient working strain until annealing.

The obtained cold rolled foil is annealed at 300 to 600 ° C. in order to facilitate processing into a molded container.
At this time, the reason why the holding time at 300 ° C. or higher is set to be within 10 minutes is to suppress precipitation of the added alloy element to promote solid solution and to increase the electrical resistivity to 6 μΩcm or higher.
More preferably, the holding time at 350 ° C. or higher is 1 minute or less, and the lower limit of the holding time is about 1 second.
Such an annealing method includes a continuous annealing line (CAL).

The average crystal grain size of the aluminum alloy foil is not limited, but is preferably 1 to 30 μm, more preferably 5 to 20 μm, and even more preferably 5 to 10 μm.
This is because if it exceeds 30 μm, it may be difficult to process into a molded container, and the average crystal grain size is preferably smaller, but is usually about 1 μm.
Such an aluminum alloy foil can be obtained by cold rolling and annealing an aluminum alloy cast to a thickness of 10 mm or less at a cooling rate of 100 ° C./second or more to 50 to 300 μm.
In addition, the crystal grain diameter as used in the field of this invention means the maximum width | variety of the crystal grain of a perpendicular | vertical direction with respect to a cold rolling direction.

  The composition of the aluminum alloy foil is not particularly limited, but Al includes 0.5 ≦ Mn ≦ 3.0 mass% Mn, 0.0001 ≦ Cr <0.20 mass% Cr, and 0.2 ≦ Mg ≦ 1.8% by mass of Mg, 0.0001 ≦ Ti ≦ 0.6% by mass of Ti, 0 <Cu ≦ 0.005% by mass of Cu, 0 <Si ≦ 0.1% by mass of Si, It is more preferable to contain 0 <Fe ≦ 0.2% by mass of Fe.

  If the Mn is less than 0.5% by mass, the electrical resistivity required for the electromagnetic cooking molded container 10 cannot be obtained. On the other hand, if it exceeds 3.0% by mass, the strength becomes too high. Molding may be difficult.

  If Cr is less than 0.0001% by mass, the electrical resistivity required for the electromagnetic cooking molded container 10 cannot be obtained, and if it is 0.20% by mass or more, it is a hard and coarse metal together with other additive elements. Since the intermetallic compound is crystallized, defects such as pinholes may occur when the container is molded from the aluminum alloy foil.

  If the Mg content is less than 0.2% by mass, the strength required for the electromagnetic cooking molded container 10 cannot be obtained. If the Mg content exceeds 1.8% by mass, the strength becomes too high and the molding of the container 10 becomes difficult. There is a risk.

When Ti is less than 0.0001% by mass, the electrical resistivity required for the electromagnetic cooking molded container 10 cannot be obtained, and the average crystal grain size of the aluminum alloy foil becomes large, making it difficult to mold the container 10. There is a fear.
Moreover, when it exceeds 0.6 mass%, intensity | strength will become large too much and there exists a possibility that shaping | molding of the container 10 may become difficult.

When Cu exceeds 0.005 mass%, the aluminum alloy foil may be discolored or a corrosion hole may be formed depending on the food stored in the molded container 10.
The lower limit of the Cu content is not particularly limited, but is generally about 0.0005% by mass.

When Si exceeds 0.1% by mass, the aluminum alloy foil may be discolored or a corrosion hole may be formed depending on the food stored in the molded container 10.
Although the minimum of Si content rate is not specifically limited, Generally, it is about 0.0005 mass%.

When Fe exceeds 0.2% by mass, the aluminum alloy foil may be discolored or a corrosion hole may be formed depending on the food stored in the molded container 10.
The lower limit of the Fe content is not particularly limited, but is generally about 0.0005% by mass.

Al, which is the main composition of the aluminum alloy, is widely used as a raw material for disposable containers because of its excellent heat transfer, light weight, low cost, and easy processing.
Here, in general, elements such as Fe, Si, Cu, Ti, V, and Ga are mixed as impurity elements during the smelting, refining, and melting processes of aluminum. The content of these elements can be adjusted.
The aluminum alloy in the present invention is produced by adding and blending certain elements as significant elements after adjusting the impurity elements in this way.

Examples and comparative examples are shown below to further clarify the features of the invention. However, the scope of the present invention is not limited to these examples.
In the examples and comparative examples, aluminum alloys having the compositions shown in Table 1 were used. The composition analysis of the foil was performed using an ICP emission spectroscopic analyzer.

  The aluminum alloy foil according to the example and the comparative example was prepared by preparing a molten aluminum alloy, and then casting, rolling and annealing under the conditions shown in Table 2 to obtain a sample having a thickness of 100 μm.

  The numerical value underlined in Table 2 indicates that the aluminum alloy foil according to the invention is outside the range of the cooling rate at the time of casting, the casting thickness, and the heating and holding time of annealing.

  Next, Table 3 shows the results of tests of electrical resistivity, average crystal grain size, corrosion resistance and formability of the aluminum alloy foils according to Examples and Comparative Examples.

In addition, the electrical resistivity and average crystal grain size of the samples obtained in the examples and comparative examples were measured as follows.
First, the electrical resistivity was measured by the DC four-terminal method at a temperature of 293 K, and the numerical value underlined in Table 3 indicates that it is outside the range of the electrical resistivity of the aluminum alloy foil according to the invention.
Next, the average crystal grain size is obtained by measuring the maximum width of crystal grains in the direction perpendicular to the cold rolling direction for an arbitrary 100 crystal grains from a crystal grain photograph taken with an optical microscope. Asked.
The numerical value underlined in Table 3 indicates that it is outside the range of the particularly preferable average crystal grain size of the aluminum alloy foil according to the invention.

Corrosion resistance was evaluated by placing 500 ml of soy sauce in a 10 cm × 17 cm plastic bat, dipping a 3 cm × 6 cm sample and holding at 20 ° C. for 10 days, and then visually observing the corrosion state of the surface.
In Table 3, o indicates that no discoloration is observed, and x indicates that corrosion holes are observed.

Furthermore, the moldability A was evaluated by press-molding 100 samples each having a size of 30 cm × 30 cm into the shape shown in FIGS. 1 and 2 and visually observing the appearance of each molded container.
In Table 3, o indicates that there is no molded container in which cracks are observed on the bottom wall and the peripheral wall rising from the bottom wall, and x indicates that there are one or more molded containers in which cracks are observed.
Further, the moldability B was evaluated by press-molding 100 samples each having a size of 30 cm × 30 cm into the shape shown in FIGS. 1 and 2, and checking the presence or absence of pinholes with each pinhole detector. .
In Table 3, ○ indicates that there is no molded container in which pinholes are detected, and x indicates that there is one or more molded containers in which pinholes are detected.

From Table 3, in an Example, all are excellent in a moldability and corrosion resistance, and the electrical specific resistance has shown sufficient value for the heat cooking by an electromagnetic cooker.
In particular, in the examples, as can be seen from the test of formability B, the pinhole resistance at the time of molding is very good.

  On the other hand, in Comparative Example 2, the moldability A is inferior, in Comparative Examples 1 and 2, the moldability B is inferior, in Comparative Examples 3 and 4, the corrosion resistance is inferior, and Comparative Examples 2, 3, 4 In Example 1, the electrical resistivity is small and the heat build-up is insufficient, and it can be seen that all the comparative examples are inferior to the examples.

Claims (3)

0.5 ≦ Mn ≦ 3.0 mass% Mn, 0.0001 ≦ Cr <0.20 mass% Cr, 0.2 ≦ Mg ≦ 1.8 mass% Mg, 0.0001 ≦ Ti ≦ 0.6% by mass of Ti, 0 <Cu ≦ 0.005% by mass of Cu, 0 <Si ≦ 0.1% by mass of Si, and 0 <Fe ≦ 0.2% by mass of Fe Cast a molten aluminum alloy consisting of aluminum and inevitable impurities to a thickness of 10 mm or less at a cooling rate of 100 ° C./second or more,
Then cold rolled to a thickness of 50-300 μm,
Then, annealing was performed with a heating and holding time at a temperature of 300 ° C. or higher within 10 minutes.
An aluminum alloy foil having a thickness of 50 to 200 μm, an electrical specific resistance value of 6.0 μΩcm or more, and an average crystal grain size of 1 to 20 μm. An aluminum alloy foil molding container comprising the aluminum alloy foil according to claim 1 and having at least a bottom wall and a peripheral wall rising from the bottom wall. The food packaging body which accommodates a foodstuff in the aluminum alloy foil shaping | molding container of Claim 2 .

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