JP2621406B2 - Polyester film for metal can interior and metal can - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a polyester film for metal can interiors having excellent heat resistance and excellent fragrance retention (flavor resistance), and is particularly encountered during a metal can production process. The present invention relates to a polyester film for metal can interiors which is stable to various environments and rarely causes defects such as peeling and cracks on the inner surface of a product can and a metal can having the film interior.

[Prior Art] With the progress of can making technology and material technology for cans, the production of metal cans for food, especially for beverages, has shown a dramatic increase.
As a material of such a metal can, Al, Fe and a bimetal material, which is a composite material of both, are used, and a can body is manufactured by making full use of punching, drawing, and ironing. . An interior material is provided on the inner surface of the metal can thus obtained so as not to impair the flavor and flavor of the contents and to prevent corrosion of the can material.

First, the metal can interior material is required to be non-toxic, capable of withstanding heat sterilization, and having a small amount of eluted substances, and has good adhesion and workability with metal cans. In the past, polyvinyl chloride resin was used as the interior material of such metal cans, and a method of applying this to the inner surface of the metal can by spray coating has been adopted. Have been.

However, the polyvinyl chloride resin has a problem that chlorine gas is generated at the time of incineration, has a poor barrier performance, and has a problem in hygiene. On the other hand, the spray coating method itself is disadvantageous in that the operation is complicated in view of the process and the production cost is high. For these reasons, a technique for spray coating a polyvinyl chloride resin has not always been obtained, and a technique for replacing the technique has been demanded.

[Problems to be Solved by the Invention] Under these circumstances, the present inventors have conducted various studies on a technique for replacing the spray coating, and as a result, have established a policy of laminating a plastic film on the inner surface of a metal can. I saw However, for the laminating film, it is required to satisfy all of the above properties required for metal can interior materials, so its selection is difficult,
It can be said that the success or failure of the above policy depends on the choice. The present inventors have satisfied these conditions, particularly without impairing the flavor and flavor of food, and as a result of intensive studies to provide an inexpensive film for metal can interiors, the present inventors have completed the present invention. .

[Means for Solving the Problems] That is, in the present invention, the acid component is composed of 50 to 95 mol% of terephthalic acid: 50 to 5 mol% of isophthalic acid and / or orthophthalic acid, and the glycol component is ethylene glycol: MicroRa made of 100% polyester material and heat-treated at 210 ° C for 2 minutes
An object of the present invention is to provide a polyester film for the interior of a metal can having a specific gravity of 1.350 or less according to the man method, and a metal can having the film inside.

[Function] In the case of the spray coating method, since the inner surface of the can after the can-making is spray-coated with a polyvinyl chloride resin or the like, a spray operation must be performed for each metal can to improve productivity. Has limitations. On the other hand, when laminating a film on the inner surface of a metal can, a method of laminating the film on a metal plate before forming into a can shape and then entering the can manufacturing process can be adopted, so the operation is greatly simplified It was hoped that productivity could be improved and that interior materials could be economically attached to the inner surface of a metal can. As for the technology of laminating a film on a metal plate, it is possible to freely laminate the film in the process of manufacturing the metal plate or to laminate the film in another process after the metal plate is manufactured.

However, the film laminated in this way was subjected to severe deformation during the can making process together with the metal plate,
Further, it receives heat generated by plastic deformation of the metal plate or high heat at the time of printing on the outer surface of the metal can and at the time of food sterilization. Therefore, it is required that the properties of the film do not deteriorate even after passing through these steps. In other words, it is important to have sufficient flavor resistance, adhesion to the inner surface of the can, protection against corrosion, etc. even after passing through various processes such as can manufacturing, printing, and sterilization.

From this point of view, we examined the stability of each property of various plastic films, but many general-purpose materials such as polyolefins and polyamides are insufficient in heat resistance and fragrance retention, and polyester films are optimal. It was confirmed.

By the way, in laminating a polyester film on a metal plate, when an adhesive is used, toxicity and heat resistance of the adhesive become problems, and a situation such as peeling of the laminated film due to a decrease in adhesive force with time is conceivable. Also, the use of the adhesive naturally increases the lamination cost. Therefore, in the present invention, a polyester film is selected without using an adhesive, that is, based on a lamination film that can be fused to the inner surface of a metal can. When various polyester films were fused to a metal plate, it was confirmed that many polyester films could be laminated (fused) to a metal plate at a temperature close to the melting point, and among them, amorphous Was found to be preferable from various viewpoints.

That is, in the case of crystalline polyester, when laminated, the crystallinity is lost and becomes amorphous, but when heat is applied in processes such as can making, printing, and heat sterilization, crystallization proceeds, and the laminated film is It was found that it was brittle and peeled off and cracks were generated. Therefore, in the present invention, as a result of further research for an amorphous polyester or a polyester having low crystallinity that does not have a problem of crystallization so that the film characteristics are not deteriorated by the heat history after the can manufacturing process, Has been completed.

Hereinafter, the present invention will be described in more detail with experimental descriptions. First of all, it is important for the film to have excellent performance in retaining the flavor and flavor of food as a basic property,
In order to find a polyester film having this, the fragrance retention of various polyesters was examined. The results shown in Table 1 were obtained.

These experimental results show that the polyester film in which the acid component is TPA or a mixture of TPA and IPA and the glycol component is EG has particularly excellent flavor resistance. On the other hand, it was found that polyester having an acid component of sebacic acid and polyester film having a glycol component of 1,6-HD should be excluded from the viewpoint of flavor resistance.

On the other hand, among the polyester films having good flavor resistance, a polyester film having an acid component of 100% TPA and containing no IPA or the like as a copolymer component has high crystallinity, and crystallization proceeds due to a thermal environment after lamination. , Peeling and cracking easily occur. Therefore, in consideration of thermal degradation after lamination, it is not possible to use a polyester film in which the acid component is TPA alone. Further, since the polyester film according to the present invention needs to be fused to a metal plate, it must be stable at a fusion temperature (generally 200 to 240 ° C.) without decomposition. However, if melting is not performed to some extent, fusion itself becomes impossible or unstable, so the melting point is preferably 240 ° C. or less.

As a result of repeated studies on a polyester film satisfying these requirements, as shown in the above constitution, the acid component was terephthalic acid: 50 to 95 mol%, isophthalic acid and / or
Or, a polyester film consisting of orthophthalic acid: 50 to 5 mol% and all glycol components being ethylene glycol was found to be able to meet the above requirements. However, simply satisfying the above requirements may cause the crystallinity to become too high in a thermal environment after the canning process depending on the combination and composition of the acid component and the glycol component. Must be appropriately adjusted within the above-mentioned range.
The scale of the adjustment of the compounding ratio is the specific gravity (Mi) when the polyester film is treated under the following heat treatment conditions.
cro Raman method).

Heat treatment conditions 210 ° C. × 2 minutes That is, the heat treatment conditions are determined by assuming the heat treatment conditions that the polyester film undergoes after lamination to a metal plate and can production when using the polyester film for metal can interior according to the present invention. Under such heat treatment conditions, crystallization does not excessively proceed even under the heat treatment conditions, and as a physical property such as not causing peeling or cracking, in the present invention, the specific gravity measured by the micro-Raman method after the heat treatment is 1.350 or less. Stipulated. In other words, the heat treatment conditions were set as conditions for confirming the state of crystallization of the film of the present invention by heat treatment, and thus the specific gravity after heat treatment,
This is an essential requirement for specifying the specific gravity. In the present invention, it is indispensable that the specific gravity is 1.350 or less. If the specific gravity exceeds 1.350, crystallization proceeds excessively in a thermal environment after the can making step, and causes deterioration of the material.

Although the basic constitution of the present invention is as described above, a lubricant such as calcium carbonate or thyroid is added for the purpose of improving workability in a film production process and a laminating process on a metal plate, and a metal plate is added as necessary. One surface of the film may be subjected to a surface treatment such as a corona discharge treatment or a chemical treatment for the purpose of improving the adhesion to the film. Further, it is permissible to add additives such as a polyester modifier. In the case of ordinary polyester film, retort treatment (130 ° C
(30 minutes) will cause problems such as whitening, but adding copolyester as a countermeasure solves the whitening problem.

Further, the polyester film according to the present invention is preferably stretched in a uniaxial direction or even in a biaxial direction, and by reducing the film damage during can making by matching the stretching direction with the film deformation direction during can making. Can be done. Further, the thickness of the film is desirably from 9 to 50 μm, most preferably from 20 to 25 μm. If the thickness is less than 9 μm, the film thickness is too small, so that breakage or the like is liable to occur at the time of can making. On the other hand, exceeding 50 μm is excessive quality and uneconomical.

Examples of the material of the metal can to which the polyester film of the present invention is attached include the above-described Al and Fe and their bimetallic materials, and the like. An inventive metal can can be obtained. In addition, it is recommended to apply Sn plating or the like on the side corresponding to the outer surface of the metal can material in order to improve workability in drawing or the like.

[Examples] (i) Homopolymer: TPA / EG = 100/100 (parts by weight) (ii) Copolymer: TPA / IPA / EG = 78/22/100 (parts by weight) (iii) TPA / IPA / EG = Biaxially stretched film composed of a copolymer of 78/22/100 (parts by weight) The specific gravity (SG) of the polymer (i) to (ii) or the film (iii) was measured by the Micro Raman method. The result shown in FIG.

Next, the specific gravities of the polyester films having various compositions and the films obtained by heat-treating the films under the following conditions were measured in the same manner, and the results shown in Table 3 were obtained.

Heat treatment conditions: 210 ° C. × 2 minutes The crack resistance of each of the above films was evaluated by the following method, and the results are shown in Table 3.

(Crack resistance evaluation method) Each film was pressure-bonded to a metal plate (tin-free steel) heated to 190 ° C with a roll, heated to 210 ° C and cooled. Of the deep drawn container was visually observed, and the ratio of the container in which cracks occurred was evaluated.

[Effects of the Invention] The present invention is configured as described above, can be fused to a metal plate, and can follow deformation without being damaged even during drawing in a can making process. It is possible to provide a polyester film excellent in flavor resistance, which does not cause peeling or cracking due to a thermal environment after the can process, and a metal can having the film inside. Thus, it became possible to commercialize the metal can interior technology by film lamination instead of the conventional spray coating, and it was possible to reduce the production cost of the metal can.

Claims (2)

(57) [Claims] 1. An acid component comprising terephthalic acid: 50 to 95 mol%.
And isophthalic acid and / or orthophthalic acid: 50 to 5 mol%, and the glycol component is constituted by a polyester raw material consisting of ethylene glycol: 100 mol%, and heat-treated at 210 ° C. for 2 minutes. A polyester film for metal can interiors with excellent scent retention, having a specific gravity of 1.350 or less according to a micro-Raman method. 2. A metal can containing the polyester film according to claim 1.