JP2567588B2 - Laminated body and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laminate having excellent cold formability. The laminate of the present invention is useful as a container material, particularly as a container material for retort foods such as curry, meat sauce and salt.

Conventional technology and its problems Conventionally, a laminate in which a polypropylene film layer of about 50 μm and a heat resistant resin coating layer of about 2 μm are formed on both sides of an aluminum foil of about 90 to 120 μm (hereinafter referred to as “Al foil”) is a curry. It is used as a container material for retort foods, such as meat sauce and salt. The molded container obtained from such a laminated body is strongly affected by the dead-hold property of the Al foil, so that the containers filled with the contents may collide with each other during transportation, or may be dented by external force during handling. It is easy to cause such deformation. In addition, since it has almost no restorability, it has a drawback that once it is deformed, it does not return to its original shape and remains deformed. Further, in terms of economic efficiency, the Al foil is thick, so that there is a problem that the cost is high.

It has been proposed to laminate the plastic material on both sides of the Al foil in order to reduce the influence of the Al foil's dead-hold property and to utilize the elasticity of the plastic material, but it gives good elasticity recovery to the molding container. In order to
The plastic material layers on both sides of the foil must have a sufficient thickness, which makes it extremely difficult to cold form the laminate.

Means for Solving Problems The present inventor has conducted various experiments and studies in view of the problems of the conventional medical techniques as described above, and as a result, uses an unstretched or weakly stretched resin film or sheet having specific properties. It has been found that the problems of the prior art can be greatly reduced in the case of doing so. That is, the present invention provides the following laminate and a method for producing the same.

A laminate comprising at least one metal foil and at least one resin layer, wherein at least one of the resin layers comprises an unstretched or weakly stretched thermoplastic film or sheet, and the film or sheet is a stress-strain diagram. A laminate having a yield point on the top and showing elongation in the cold, and satisfying the relation of yield point stress ≦ breaking strength.

After heat-treating an unstretched or weakly stretched thermoplastic resin film or sheet at a temperature equal to or higher than the softening point so as to satisfy the relationship of yield point stress ≤ breaking strength, and then laminating the film or sheet with a metal foil. A method for manufacturing a laminate, comprising:

The cold formability of the laminate of the present invention is mainly influenced by the stress-strain characteristics of the unstretched or weakly stretched thermoplastic resin sheet or film used as the resin layer. Generally, the stress-strain characteristics at normal temperature of an unstretched or weakly stretched sheet or film of a thermoplastic resin are classified as shown in FIGS. 1 to 4.

First, the behavior shown in FIG. 1 is a polypropylene sheet or film which is rapidly cooled from a molten state and contains almost no spherulite. Although this type of material has excellent flexibility, it has a low elongation and a high breaking strength (T.
Since S.) is low, it breaks when cold forming.

The material that behaves as shown in Fig. 2 is a partially spherulized polypropylene sheet or film, which has a considerably high breaking strength (TS) but lower than the yield stress (YS) and sufficient elongation. Since it is hard to say, there is a case where damage is caused especially at the corners when cold forming.

The behavior shown in Fig. 3 is that of some kind such as partially spherulized polypropylene sheet or film, which has large elongation and breaking strength (TS) more than yield stress (YS). Since it is expensive, it has excellent cold formability. This material having good cold formability is obtained by heating a material having the characteristics shown in FIGS. 1 and 2 under appropriate temperature and time conditions, for example, at about 120 to 190 ° C. for about 15 seconds to 3 minutes. It can also be obtained.

The behavior shown in FIG. 4 is a completely spherulized polypropylene sheet or film, a very hard polystyrene sheet, etc., which are very hard and have a small elongation, so that they break during molding.

The deformation behaviors of the materials when the materials exhibit the stress-strain characteristics shown in FIGS. 1 to 4 and are subjected to cold press forming, pressure forming, etc. are as follows. First, the yield stress (Y.
By applying the force above S.), the molding process starts and the molding proceeds. As the molding progresses, the material stretches rapidly, and particularly at the corners and the like, a large stretch occurs. If the material has the characteristics shown in FIG. 3, it is difficult for the material to be damaged even if a large amount of elongation occurs at the corners, etc., but the material having the characteristics shown in FIG. 1, FIG. 2 and FIG. In the case of, the breakage occurs especially in a portion having a large elongation such as a corner portion. For this reason, in the present invention, at least one of the resin layers is a non-stretched or weakly stretched thermoplastic resin film or sheet having the characteristics shown in FIG.

The laminated body of the present invention has a resin layer to be the inner layer of the container and a metal foil to be the outer layer as essential components.

The resin layer to be the inner layer of the container needs to have a heat-sealing property with the lid member, and therefore needs to be a non-stretched or weakly stretched film or sheet of a thermoplastic resin.
Examples of the thermoplastic resin include polyethylene, polypropylene, polyamide, polyvinyl chloride, ethylene-polypyrene copolymer and the like. These films or sheets may contain additives such as antioxidants, antistatic agents, plasticizers and pigments. Then, as described above, the film or sheet is required to exhibit cold elongation (about 20 to 500%), have a yield point on the stress-strain diagram, and satisfy the relationship of yield point stress ≦ breaking strength. There is. Further, the film or sheet is provided in order to impart a characteristic that the molding container is not easily deformed and is easily restored when deformed,
The thickness is preferably about 100 to 300 μm.

Examples of the metal foil to be the outer layer of the container include Al foil, steel foil, copper foil and the like. When using Al foil,
The thickness is preferably about 20 to 120 μm. 120 μm
If it is more than 20 .mu.m, the container's resilience is lowered due to the dead-holding property of the Al foil, while if it is less than 20 .mu.m, the laminate is likely to break during molding.

The unstretched or reverse-stretched plastic resin film or sheet and the metal are bonded to each other by an adhesive according to a conventional method. Examples of such adhesives include urethane-based, polypropylene-based, polyester-based, epoxy-based and acrylic-based adhesives.

In the present invention, by further forming a second resin layer on the other surface of the metal foil, it is possible to further improve the deformation resistance of the molded container, the resilience from the deformed state, the strength and the like. . The second resin layer is a biaxially stretched film such as polyamide, polyethylene or polypropylene, a non-stretched film such as polyethylene, polypropylene or polyamide, an epoxy resin, a urethane resin, an acrylic resin,
It is formed of a coating layer of heat resistant resin such as polyester resin. Films may be attached by an ordinary method using the same adhesive as above, and the coating layer of the heat resistant resin may be formed by an ordinary method.
The second resin layer has a thickness of about 10 to 50 μm when a film is used and a coating layer when the film is used so as not to impair the cold formability of the laminate and to improve container properties. It is about 1 to 10 μm.

In the laminated body of the present invention, a second metal foil can be attached on the second resin layer. As the second metal foil,
Al foil, steel foil, Cu foil or the like having a thickness of about 20 to 50 μm is used, and adhesives such as polyethylene-based, polypropylene-based, modified polyolefin-based, ethylene ionomer, and urethane-based adhesives are used for bonding. By using the second metal foil, the barrier property against light, oxygen, odor, etc. is improved, and the shape stability as a molding container is further improved.

Effect of the Invention The laminated material of the present invention has excellent cold formability,
Further, when it is used as a container, it is excellent in deformation resistance and restoration from a deformed state. Further, the laminated material of the present invention is low in material cost.

Examples The following examples will be given to further clarify the features of the present invention.

Example 1 An unstretched polypropylene sheet having a thickness of 240 μm and a softening point of 119 ° C. was heat-treated at 120 ° C., 140 ° C., 160 ° C. and 180 ° C. for 1 minute, and then subjected to a tensile test at normal temperature (pulling speed: 200 mm / mi).
n) was performed, and the stress at yield point, the breaking strength and the elongation were measured.

Then, the heat-treated polypropylene sheet is bonded to the Al foil of the bonding material of the biaxially stretched polypropylene film (20 μm) and the Al foil (50 μm) bonded with the urethane adhesive with the urethane adhesive to form a three-layer structure. A laminate of the present invention having a structure was obtained.

The thus-obtained laminate was air-pressure molded at an air pressure of 7 kg / cm ² to make a 9 cm × 9 cm × 2 cm (depth) container, and its cold formability was evaluated.

Table 1 shows the results of the yield stress, the breaking strength and the elongation, and the cold formability as Nos. 2 to 5. In addition, Table 1 also shows the tensile test results of the unstretched polypropylene sheet not subjected to the heat treatment and the cold formability of the comparative laminate using the same as No. 1.

As is clear from the results shown in Table 1, No. 1 has a large elongation, but the breaking strength is smaller than the yield point stress, so that the cold formability is poor (corresponding to FIG. 2). In contrast,
Nos. 2 to 5 have a large elongation and a breaking strength larger than the yield point stress, and therefore have excellent cold formability (corresponding to FIG. 3).

[Brief description of drawings]

1 to 4 are graphs showing classified stress-strain characteristics at room temperature of an unstretched or weakly stretched sheet or film of a thermoplastic resin. YS ... Yield point stress, TS ... Breaking stress.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Eiichi Takeuchi 1 at 4-25 Minamikyutaro-cho, Higashi-ku, Osaka City Toyo Aluminum Co., Ltd. (72) Inventor Shoichi Makimoto 1 at 4-25-4 Minamikyutaro-cho, Higashi-ku, Osaka Toyo Aluminum Co., Ltd. (56) Reference JP-A-57-133056 (JP, A) JP-A-53-111380 (JP, A) Actual development Shou- 60-32024 (JP, U) JP-B-60-44121 ( JP, B2)

Claims (2)

(57) [Claims] 1. A laminate comprising at least one metal foil and at least one resin layer, wherein at least one layer of the resin layer comprises an unstretched or weakly stretched thermoplastic film or sheet, and the film or sheet comprises It has a yield point on the stress-strain diagram and shows cold extension, and the yield point stress ≤
A laminate characterized by satisfying the relationship of breaking strength. 2. An unstretched or weakly stretched thermoplastic resin film or sheet is heat-treated at a temperature equal to or higher than the softening point so as to satisfy the relationship of stress at yield point ≦ breaking strength, and then the film or sheet and the metal foil. And a method for manufacturing a laminate, which comprises laminating and.