JP2001179880A - Polyester resin film coated metal panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin film coated metal panel excellent in processing adhesion and molding processability. SOLUTION: In a polyester resin film coated metal panel, the film formed on a metal panel has a three-layered structure wherein an upper layer comprises an oriented polyester resin with a double refractive index of 0.020-0.100, a lower layer comprises a polyester resin with a double refractive index of 0.015 or less and an intermediate layer comprises an obliquely oriented polyester resin and the thickness of the lower layer is above 3.0 μm but a film thickness ratio is below 40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal sheet coated with a polyester resin film for a can container which is excellent in processing adhesion and molding workability.

[0002]

2. Description of the Related Art In the can manufacturing industry, application of a resin film-coated metal plate obtained by laminating a thermoplastic resin film on a metal plate has been studied instead of painting in recent years. In particular,
From the viewpoints of corrosion resistance, safety, and heat resistance, polyester resin films have attracted attention as having balanced properties, and proposals based on these have been made.

[0003] Representative proposals are shown below. (1) A polyester film laminated on a metal plate without using an adhesive (Japanese Patent Publication No. 60-471)
03, JP-A-10-138389, JP-A-10-138390). (2) A polyester film laminated on a metal plate using an adhesive (JP-B-63-13829,
Japanese Patent Publication No. 4-74176).

[0004] The proposal of JP-B-60-47103 shown in (1) requires that a polyester film be heat-sealed to a metal plate at a temperature higher than the melting point of the film.
An amorphous polyester layer is formed near the interface of the metal plate,
The feature is that this resin layer improves the adhesion to the metal plate. However, in such a film having a two-layer structure, there is a problem that the moldability is inferior, so that the cylinder is broken and the film is peeled off when the can is formed.

Further, Japanese Patent Laid-Open No. 10-138389,
In JP-A-10-138390, the resin film layer in the vicinity of the interface of the metal plate is set to a low orientation state having a birefringence of 0.010 or less, and the thickness ratio is regulated to 40% to 90%, whereby the processing is performed. The feature is that the post-adhesion is improved. However, the thickness ratio of this low orientation layer is 40% to 90%.
And the thickness ratio of the upper biaxially stretched resin layer is small,
Since the effect is small, the corrosion resistance and impact resistance are also reduced.

On the other hand, the proposal of (2) is a method in which a biaxially stretched polyester resin is coated on a metal plate with an adhesive,
The feature is that excellent adhesion is obtained. However, since the biaxially stretched polyester resin film has tight oriented crystals and the free movement of molecules is restricted by the oriented crystal region, the biaxially stretched polyester There is a problem that cracks are easily formed in the resin and the workability is limited. In addition, the process of applying the adhesive to the film is complicated, and the cost is greatly increased, which is not a preferable method.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal sheet coated with a polyester resin film having excellent workability and moldability in view of the above problems.

[0008]

According to the present invention, there is provided a film formed on a metal plate, wherein an upper layer is an oriented polyester resin having a birefringence of 0.020 to 0.100, and a lower layer is Polyester characterized by a polyester resin having a birefringence of 0.015 or less, an intermediate layer having a three-layer structure of an inclined polyester resin, and a lower layer having a thickness of more than 3.0 μm and less than 40% of a film thickness ratio. It is a metal plate coated with a resin film.

Since the metal plate is excellent in processing adhesion and molding workability, it can be widely applied as a body material of food cans or beverage cans subjected to severe deep drawing.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the contents of the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view of a metal plate coated with a polyester resin film according to an embodiment of the present invention. The metal plate has a birefringence of 0.02 on a metal plate 5.
0-0.100 oriented polyester resin layer 1, intermediate layer:
Tilt-oriented polyester resin layer 2, lower layer: birefringence 0.0
A resin film layer 4 having a three-layer structure composed of 15 or less polyester resin layers 3 is covered.

Here, the birefringent index of the upper biaxially oriented polyester resin layer 1 needs to be 0.020 to 0.100. If the birefringence is less than 0.020, the impact resistance and corrosion resistance are remarkably reduced. If the birefringence is more than 0.100, there is a danger that molding workability is deteriorated and can-making defects are caused.

The lower polyester resin layer 3 must have a birefringence of 0.015 or less, a thickness of more than 3.0 μm and less than 40% of the film thickness ratio.

By setting the birefringence to 0.015 or less,
Since strong adhesion is ensured and the processability of the resin layer itself is also improved, excellent moldability is obtained. Further, by setting the film thickness to more than 3.0 μm, the film does not peel even in severe deep drawing, and can follow the processing deformation, thereby maintaining excellent coverage. When the film thickness is 5.0 μm or more, this effect becomes more clear because it is more desirable.

When the thickness of the lower film is 40% or more of the total thickness of the film, the thickness ratio of the upper biaxially stretched layer is reduced, so that deterioration of impact resistance and corrosion resistance becomes a problem. When the film thickness is 3.0 μm or less, the adhesiveness is ensured, but the effect of improving the moldability on the whole film is poor, so that it is insufficient.

As described above, the upper layer has a birefringence of 0.020.
When a polyester resin layer 1 having an orientation of ~ 0.100 and a polyester resin layer 3 having a birefringence of 0.015 or less are formed as a lower layer, the heat shrinkage behavior of the two is different. Stress is generated, and the resin is easily damaged. In the present invention, the presence of the inclined oriented polyester resin layer 2 as the intermediate layer can reduce stress generated at the interface and suppress film damage.

The birefringence of the intermediate polyester resin layer 2 is in the range of (lower layer birefringence) to (upper layer birefringence), and as shown in FIG. It is desirable that the birefringence has a structure in which the birefringence decreases continuously. Further, the thickness is desirably 1.0 μm or more. If the thickness is less than 1.0 μm, the above-mentioned stress relaxation effect cannot be sufficiently exerted.

As the birefringence of such a polyester resin, a value determined by the following measuring method is employed.

Using a polarizing microscope, the retardation in the cross-sectional direction of the resin-coated film 4 after removing the metal plate 5 of the resin-coated metal plate is measured, and the birefringence in the cross-sectional direction of the resin film is determined. The linearly polarized light incident on the film layer 4 is decomposed into two linearly polarized light beams in the principal refractive index directions. At this time, the vibration of light in the high refractive index direction becomes slower than in the low refractive index direction,
For this reason, a phase difference is generated at the time when the light exits the film layer 4.
This phase difference is called a retardation R, and the relationship with the birefringence △ n is defined by Expression (1). Δn = R / d (1) where d is the thickness of the film layer 4

Next, a method of measuring retardation will be described. The monochromatic light is passed through a polarizing plate to become linearly polarized light, and this light is incident on a sample (film layer 4). Since the incident light causes retardation as described above, the light becomes elliptically polarized light after passing through the film layer. This elliptically polarized light becomes linearly polarized light having an angle of θ with respect to the vibration direction of the first linearly polarized light by passing through the Senarmont-type compensator. This θ is measured by rotating the polarizing plate. The relationship between retardation R and θ is defined by equation (2). R = λ · θ / 180 (2) where λ is the wavelength of monochromatic light, and the birefringence Δn is defined by Expression (3) derived from Expressions (1) and (2). Δn = (θ · λ / 180) / d (3)

The polyester resin film used in the present invention is preferably an aromatic polyester resin film, and is preferably a film copolymerized with a resin such as polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphthalene carboxylate. You. More preferably, it is a polyethylene terephthalate copolymer film in which 25 mol% or less of the acid component is isophthalic acid.

Such a copolymer resin film is formed by forming a film by a known extruder, stretching the film in two directions in the vertical and horizontal directions, and then performing a heat fixing process.

The thickness (total film thickness) of the polyester resin film is not particularly limited, but is preferably in the range of 5 to 50 μm. When the thickness is less than 5 μm, laminating workability is remarkably reduced, and sufficient processing corrosion resistance is not obtained. On the other hand, when the thickness is more than 50 μm, it is economical as compared with epoxy-based coatings widely used in the field of cans. Not a target.

Further, coloring agents such as pigments and dyes for improving aesthetics, inorganic lubricants for imparting lubrication,
Further, an antistatic agent or the like may be added and blended in the polyester film.

Further, the metal plate used in the present invention includes:
Various surface-treated steel sheets, and light metal sheets such as aluminum, copper, and alloys thereof are exemplified. As the surface-treated steel sheet, cold-rolled steel sheet is annealed and then subjected to secondary cold rolling, zinc-based plating, tin plating, nickel plating, chromium plating, tin / chrome double-layer plating, electrolytic chromic acid treatment, chromic acid treatment, phosphorus One or more surface treatments such as an acid treatment can be used. Pure aluminum plate,
An aluminum alloy plate, a copper alloy, or the like can be used.

The method of thermocompression-coating the surface of the metal plate with a resin film is not particularly limited as long as the polyester resin film structure shown in the present invention can be formed.

In general, a metal band 12 heated in a heating zone 11 is sandwiched between a pair of laminating rolls 14 using a heat fusion type laminating apparatus shown in FIG. Then, the resin film 13 is continuously laminated on one side or both sides of the metal strip 12.

Here, the lamination temperature (the temperature of the metal band during lamination) is desirably in the range of the crystal melting temperature of the polyester resin film ± 40 ° C. If the temperature exceeds the crystal melting temperature + 40 ° C., the polyester resin film is thermally degraded, and the barrier property against corrosion factors is lost. When the crystal melting temperature is lower than −40 ° C., it is difficult to reduce the birefringence of the lower layer 3 shown in FIG. 1 to 0.015 or less, and the working adhesion between the polyester resin film and the metal plate is reduced. Here, the crystal melting temperature is a temperature indicating a maximum peak depth of an endothermic peak when the temperature is raised at a rate of 10 ° C./min by a differential scanning calorimeter.

Examples of the method for heating the metal strip include a known hot air circulation heat transfer system, a resistance heating system, an induction heating system, and a heat roll system, and are not particularly limited.
The heat roll heat transfer method is preferable in consideration of equipment cost and simplification of equipment.

With respect to the surface temperature of the laminating roll when laminating the polyester film on the metal plate,
The temperature is desirably 60 to 130 ° C. Thereby, the birefringence of the intermediate layer 2 and the upper layer 1 shown in FIG. 1 can be set within the range of the present invention.

The material of the laminating roll is preferably a rubber roll. As for the rubber material, a silicon roll excellent in heat conductivity and heat resistance is preferable.

After pressing the polyester film, it is desirable to cool rapidly. It is preferable that the temperature be lower than the glass transition point of the film within 5 seconds.

[0032]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

With respect to the various metal plates shown in Table 1, various polyester resins also shown in Table 1 were laminated with the laminating apparatus shown in FIG. 3 under the laminating conditions (metal strip heating temperature, laminating roll temperature, polyester resin film heat). After adjusting the cooling conditions after pressure bonding, etc.), the film layer structure after lamination was controlled to produce a polyester resin-coated metal plate, and then various performances were evaluated.

(Performance Evaluation Method) Moldability After wax was applied to a polyester resin-coated metal plate, the diameter was 1 mm.
A 79 mm disk was punched out to obtain a shallow drawn can with a drawing ratio of 1.65. Next, the shallow drawn can was redrawn twice. The aperture ratios are 1.40 and 1.35, respectively.
Met. The deep drawn can thus obtained is subjected to a heat treatment at 215 ° C. × 2 minutes 30 seconds after trimming of the open end,
After cooling, neck processing was performed to prepare a 350 g two-piece can. About the obtained can, the degree of damage of the film was visually observed and evaluated according to the following criteria. ◎: No damage to film and no whitening observed ○: No damage to film, but slight whitening observed △: Film whitened ×: Film damaged

For a two-piece can prepared by the method of adhesion after processing, a sample for peel test (width 15 mm, length 1
00 mm). The resin film was peeled from the long side end of the cut sample, and the film peeled by the tensile tester was opened in the direction opposite to the metal plate from which the film was peeled (angle: 180 °), and the tensile speed was 30 mm / min.
A peel test was performed to evaluate the adhesion. The adhesion is 0.
1kg / 15mm or more passed (symbol ○), 0.1kg /
Less than 15 mm was evaluated as failed (symbol x).

The cans prepared by the method of impact resistance were filled with water, cooled to 5 ° C. or less, dropped from a height of 1 m onto a vinyl chloride resin tile floor, and allowed to age for one week. . Thereafter, the contents (water) are removed from the can, the inside of the can is masked with a wax, 0.5% saline is injected, and a voltage of 6.2 V is applied to the electrode and the can in the saline. The current value after 5 minutes was read and the average value after measuring 10 cans was determined and evaluated according to the following criteria. ：: less than 0.1 mA ×: 0.1 mA or more Table 1 shows the evaluation results.

[0037]

[Table 1]

Comparative Examples outside the scope of the present invention are inferior in at least one of the molding processability, the post-processing adhesion, and the impact resistance.

On the other hand, each steel sheet of the embodiment within the scope of the present invention is:
It has excellent moldability, adhesion after processing, and impact resistance, and is most suitable for deep-drawn metal cans, especially beverage cans and food cans.

[0040]

The metal sheet coated with a polyester resin film of the present invention is excellent in moldability, adhesiveness after processing and heating, and impact resistance, and can be used in food cans or beverages requiring heat treatment such as retort treatment. It is suitable as a lid material and a body material for cans.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a metal sheet coated with a polyester resin film according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a change in the birefringence in the thickness direction of an inclined oriented polyester resin layer provided in an intermediate layer of the polyester resin film-coated metal plate of FIG.

FIG. 3 is a view showing an example of a heat-sealing type laminating apparatus for producing a metal sheet coated with a polyester resin film according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper layer 2 Middle layer 3 Lower layer 4 Resin film layer of three-layer structure 5 Metal plate 11 Heating zone 12 Metal band 13 Resin film 14 Laminating roll

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Suzuki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masahiko Shigeno 1-2-1-2 Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Shinsuke Watanabe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan F-term (reference) 4F100 AB01A AB03A AK41B AK41C AK41D BA04 BA07 BA10A BA10D BA13 BA21B BA21D BA42C GB16 GB23 JA20B JA20C JA20D JB02 JJ03 JK06 JK10 JL01 JN18B JN18C JN18D YY00B YY00D

Claims (1)

[Claims] 1. A film formed on a metal plate, wherein the upper layer is an oriented polyester resin having a birefringence: 0.020 to 0.100, the lower layer is a polyester resin having a birefringence: 0.015 or less, and the intermediate layer is A metal sheet coated with a polyester resin film excellent in processing adhesion and molding workability, characterized in that it has a three-layer structure of an inclined oriented polyester resin, and the thickness of a lower layer is more than 3.0 μm and less than 40% of a film thickness ratio. .