JPH0623419B2 - Aluminum foil for packaging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used for confectionery, dairy products, luxury items, frozen products, cooked foods (retort foods), detergents, cosmetics, pharmaceuticals, photographic products, and other packaging. The present invention relates to an aluminum foil for packaging, which is useful as a material, particularly as a packaging material that requires water-tightness for filling a liquid.

[Prior Art] Laminated products of synthetic resin and aluminum foil are inexpensive raw materials, lightweight, easy to package in an automatic packaging machine and have high productivity, good light transmission resistance, and packaging. It is widely used as a packaging material in various fields because it has excellent properties such as beauty. In addition, the application field is expanded by changing the thickness of the aluminum foil and the material of the synthetic resin layer (film) when changing the application.

However, particularly when the object to be packaged is a liquid, the adhesive strength between the aluminum foil and the synthetic resin film becomes a problem, and a laminated product having a high adhesive strength has been demanded.

On the other hand, magnesium in aluminum material reduces the adhesiveness with synthetic resin in the presence of water.
vies, JA Treverton: Summary of the 62nd Annual Meeting of the Japan Institute of Light Metals 161. , Toyose, Fukui, Hatanaka, Outline of the 67th Annual Meeting of the Japan Institute of Light Metals 17. , K. Wefers: Aluminum 57.198
It is reported in 1.722.

In addition, when an aluminum material containing magnesium is heated to a high temperature, remarkable diffusion of magnesium into the aluminum surface layer is observed, and it is recognized that the adhesiveness is reduced (Uchiyama, Isoyama, Takenaka, Kawai: Abstracts of the 68th Spring Meeting of the Japan Institute of Light Metals 229).

Considering the behavior of magnesium as described above, in order to obtain a laminated product with good adhesion between synthetic resin and aluminum foil, it is desirable to develop an aluminum material with less diffusion of magnesimu into the surface layer even when heated at high temperature. Was there.

The magnesium content in aluminum materials conventionally used as raw materials for aluminum foil is generally 100 ppm.
There were many before and after, and especially when the molten metal treatment with chlorine etc. was carried out to reduce magnesium consciously, it was only up to around 30 ppm. Therefore, in order to reduce the concentration of magnesium on the surface of the aluminum foil, there was no method other than means for reducing the surface concentration of magnesium by etching-cleaning the surface layer enriched with magnesium after annealing, but at a high cost. It was not generally applicable.

[Problems to be Solved by the Invention] In the aluminum foil annealing step, even if the annealing temperature is increased, the concentration due to the diffusion of magnesium to the surface is extremely small, and a synthetic resin having excellent adhesiveness with the synthetic resin is laminated. The purpose is to develop aluminum foil for packaging and its manufacturing method.

[Means for Solving the Problems] In the present invention, the packaging aluminum foil laminated with a synthetic resin has a magnesium content of 10 ppm or less.
N30 and 1100 series pure aluminum; 3000 series Al-Mn alloy with no Mg content standard;
Alternatively, the present invention relates to a packaging aluminum foil, which is an aluminum foil of an Al-Fe-based aluminum alloy such as 8079.

As mentioned above, the presence of magnesium on the surface of the aluminum foil was known to inhibit the adhesion with the synthetic resin in the presence of water, but most of the aluminum foil for packaging requires annealing. However, due to the annealing, the magnesium in the foil diffused to the foil surface and concentration was unavoidable. Therefore, it was thought that reducing the magnesium in the aluminum foil used as the foil raw material would not be very effective. It has not been studied so much, and the direction of preventing the diffusion of magnesium by lowering the annealing temperature was adopted.

As a result, long annealing is inevitably required to enhance the annealing effect.

In the present invention, the behavior of the magnesium in the aluminum material during the annealing step is observed, and the magnesium concentration has a great influence on the diffusion of the aluminum foil.When the magnesium concentration is a certain concentration or less, magnesium diffusion occurs regardless of the heat treatment temperature. I found it difficult.

Further, in the usual aluminum foil for packaging, when looking at the magnesium content and the heat seal strength of the synthetic resin, there is no clear difference with the magnesium content in the aluminum foil, and the adhesive strength in academic literature is The control of the amount of magnesium does not appear to be very strict as it behaves differently.

However, even with these aluminum foils for packaging, a long-term immersion test in water (corresponding to the case when used in a packaging container for packaging liquids) showed that the difference was not clear in the dry state. It became clear that the lower the concentration of magnesium, the greater the adhesive strength.

That is, the magnesium concentration in the aluminum material is 10
It was found that when the content is less than or equal to ppm, the diffusion concentration of magnesium on the surface of the aluminum foil is extremely small regardless of the heat treatment temperature, and therefore the adhesive strength with the synthetic resin is not lowered.

Aluminum foil is generally manufactured in the order of melt-cast hot-rolling cold-rolling intermediate-annealing foil-rolling separator final-annealing slitter aluminum foil, but the magnesium content of the aluminum material in the melting-casting step may be 10 ppm or less. is necessary.

Aluminum ingots have a magnesium content of 1 because variations in magnesium content cannot be avoided from lot to lot.
It is preferable to use a lot of 0 ppm or less as the aluminum foil raw material for packaging used in the liquid storage container which is the subject of the present invention. As such an aluminum material, 1N30, 1100 series pure aluminum series, 3000 series A
An alloy of 1-Mn-based alloy with no standard content of Mg, such as 3003, 3102, 3203, 3303,
Alternatively, it is an Al-Fe alloy such as 8079. From the viewpoint of magnesium, of course, there are 1085 series, 1080 series, etc., but this is not preferable because not only the cost increases but also the strength becomes insufficient.

Further, in the conventional final annealing step, in order to avoid the diffusion of magnesium to the surface of the aluminum foil, the direction in which the temperature is kept as low as possible for a long time is fixed.

If it is cold, it is carried out at 250 to 310 ° C. However, since it is not necessary to consider diffusion of magnesium in the final annealing step of the aluminum foil of the present invention, it is possible to use the conventional 250.
Although it is possible to use a low temperature such as ℃, considering the high temperature such as 400 ℃, heat treatment time, and heat treatment effect, it is 300 to 4
It is possible to perform heat treatment at a high temperature such as 00 ° C., and as a result, it is possible to obtain an aluminum foil for packaging having excellent adhesive strength with a synthetic resin even in the presence of a liquid.

The target synthetic resin, vinyl chloride, polyethylene, polypropylene, ethylene-vinyl acetate copolymer,
It is a well-known synthetic resin such as polyacrylic acid ester, styrene-butadiene rubber, nitrile rubber, chloroprene rubber, and ionomer.

These synthetic resins are available in various cases such as emulsion, a method of applying a solution dissolved in an organic solvent, a method of once forming a film and adhering as dry lamination, or extrusion coating. Is.

Further, the aluminum foil may be an aluminum foil in the as-annealed state, or may be treated with a corona discharge treatment, a silane coupling agent, a coupling agent such as a titanium coupling agent, or the like.

Thus, when the aluminum foil having a magnesium content of 10 ppm or less is used as the aluminum foil raw material for packaging, the final annealing temperature can be increased, and therefore the productivity can be improved by shortening the annealing time. .

[Example] (Reference Example) 1N30 was used as a test material, and aluminum foil was prepared with magnesium contents of 6 ppm and 26 ppm adjusted in the melting and casting steps.

A fluorescent X-ray analyzer was used to measure the magnesium content on the surface of the aluminum foil, and the analysis condition was 30 mmφ.
The area and samples of magnesium and aluminum at 40 KV, 70 mA, 100 seconds were counted, and the evaluation was determined as Mg / Al. The holding time for annealing was 13 hours. The results are shown in FIG.

As can be seen from Fig. 1, there is a large difference in the magnesium content of the aluminum materials used as samples, but the reason is unknown, but there is no difference in the magnesium concentration on the foil surface made from these, and in the case of unannealed The difference is not remarkable in. However, it is clear that the amount of diffusion of magnesium markedly increases on the foil surface as the temperature increases due to the annealing, and the magnesium is concentrated on the surface.

(Example) 1N30 was used as an aluminum material, various magnesium foils were manufactured by adjusting the magnesium content in a melting / casting process, and a water resistance test was conducted.

For the water resistance test (peel strength), 5 g / m ^{2 of a} vinyl chloride paint was applied to an aluminum foil and dried at 150 ° C. for 20 seconds.

Then heat seal under the condition of 200 ° C x 1 sec, and
After soaking in warm water of 0 ° C. for 3 days, the peel strength of the heat-sealed portion was tested. The results are shown in Table 1.

As can be seen from Table 1, the adhesive strength between the aluminum foil and the synthetic resin having different magnesium contents may be the same as long as the initial peeling strength is observed. Therefore, although it is sufficient as an aluminum foil for packaging that does not come into contact with liquid, a water resistance test reveals a difference depending on the magnesium content, and it has been clarified that the influence cannot be overcome even by the final annealing step under mild conditions.

[Effect of the Invention] When the magnesium content of the aluminum foil used for the packaging aluminum foil is 10 ppm or less, the concentration of magnesium on the surface of the aluminum foil due to diffusion hardly occurs even in the final annealing step.

Therefore, according to the present invention, it is possible to manufacture an aluminum foil for packaging having a high adhesive strength of the coating film even if the annealing temperature is increased.

Since the annealing temperature can be raised, the annealing time can be shortened,
Highly productive manufacturing has become possible.

A low surface magnesium content on the surface eliminates the need for a foil surface cleaning step.

Since the magnesium surface concentration is low, the adhesive strength between the aluminum foil and the coating film is high, and an aluminum foil for packaging suitable for a liquid container can be obtained.

There are many effects.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the annealing temperature of an aluminum foil and the amount of surface magnesium.

Claims (1)

[Claims] 1. An aluminum foil for packaging which is laminated with a synthetic resin, wherein the aluminum foil has a magnesium content of 10 ppm or less.