JP2002362528A - Metallic can and metallic plate with polyester film laminated thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metallic can formed of a metallic plate with a polyester film for metallic plate lamination, which is excellent in heat lamination properties with the metallic plate, machinability such as moldability of the can, drawing and wipe-molding or the like in particular and suitable as a laminate metallic can. SOLUTION: The metallic can is molded of a metallic plate with a polyester film laminated by thermocompression bonding. The polyester film comprises 40 to 80 mass % of a polybutylene terephthalate with a melting point of 200 to 223 deg.C or a polyester (A) mainly containing it and 60 to 20 mass % of a polyethylene terephthalate with a melting point of 230 to 256 deg.C (except 230 to 245 deg.C) or a polyester (B) mainly containing it. A temperature-raised crystallization peak temperature from an amorphous state ranges within 60 to 100 deg.C, and a specific heat capacity at 60 to 100 deg.C is 0 J/g deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate in which a metal can body and a polyester film are laminated, and more particularly, to a metal plate obtained by laminating a polyester resin on a metal plate, and particularly to drawing and forming. The present invention relates to a metal can body obtained by performing a process such as ironing, and a metal plate on which a polyester film is laminated, which is useful as a material used for the metal can body.

[0002]

2. Description of the Related Art Conventionally, to prevent corrosion of the inner and outer surfaces of a metal can,
A solvent-type paint mainly composed of a thermosetting resin has been applied. However, solvent-type paints require heating at a high temperature to form a coating film, and a large amount of solvent is generated at that time, and thus there is a problem in terms of work safety and the environment. Therefore, metal coating with a thermoplastic resin has recently been proposed as a corrosion prevention method that does not use a solvent. Among the thermoplastic resins, polyesters are particularly excellent in workability and heat resistance. The development of film for use is underway.

[0003] As a method of coating a film on a metal plate, there are a method of melting a thermoplastic resin and extruding it directly onto a metal, and a method of thermocompression bonding a thermoplastic resin film directly or through an adhesive. Above all, a method using a thermoplastic resin film is considered to be an effective method because the handling of the resin is easy, the workability is excellent, and the uniformity of the resin film thickness is also excellent. In addition, since the method using an adhesive has environmental and cost problems, a method of directly thermocompression-bonding a film has attracted attention.

[0004] A metal can coated with a thermoplastic resin film is formed by laminating a thermoplastic resin film on a metal plate such as a steel plate or an aluminum plate (including a plate subjected to a surface treatment such as plating) to form a laminated metal plate. Manufactured.

[0005] The thermoplastic resin film used for such an application has good heat laminating properties with a metal plate and excellent moldability of a can. Various properties such as no pinholes, no embrittlement during printing after can molding, retort sterilization and long-term storage, and excellent content and flavor retention of the contents are required at the same time. You.

As such a polyester film for laminating a metal plate, there has been proposed a method in which other components are mixed or copolymerized for the purpose of imparting heat lamination properties and improving the moldability of a can. .

For example, (a) PET obtained by copolymerizing other components is disclosed in JP-B-8-19245 and JP-B-8-1.
No. 9246, Japanese Patent No. 2528204, and the like. In addition, (b) a copolymer obtained by blending PBT or a copolymer thereof with copolymerized PET (Japanese Patent No. 2851468).
JP, JP-A-5-186612, JP-A-5-1
86613), (c) a film for a can lid in which PBT or a copolymer thereof is blended with PET or a copolymer thereof and the crystal characteristics thereof are limited (JP-A-5-331302, JP-A-7-145252) ) Is disclosed.

However, in (a), although the thermal lamination property and moldability are improved by copolymerizing PET and lowering the melting point and lowering the crystallization, the PET becomes brittle during the heat treatment after the can molding and the retort sterilization treatment. There is a problem that impact resistance is reduced. In (b), a PBT-based resin is blended to improve the heat laminating property and the embrittlement and impact resistance, which are the drawbacks of (a) above, in a well-balanced manner. Laminating properties and adhesive properties were not sufficient, and particularly high workability such as drawing or ironing was not sufficient. In (c), whitening and white spots after heat treatment at a relatively low temperature such as retort sterilization treatment are improved by limiting the crystallinity, but formability under severe conditions such as drawing and ironing (high processing) ) Was not considered, and sufficient moldability was not provided.

On the other hand, the present inventors have previously proposed a biaxially stretched film composed of polyethylene terephthalate or a polyester based on the same, and polybutylene terephthalate or a polyester based on the same. JP-A-9-194604, JP-A-10-194
No. 110046). Even if the film has a high degree of crystallinity, it can be thermocompression-bonded at a relatively low temperature, and the resulting laminated metal plate has excellent workability. In addition, it does not become brittle during retort sterilization treatment and long-term storage, and has excellent impact resistance.However, in high processing such as drawing and ironing, the film whitens or micro cracks in severe processing parts. May occur.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a metal sheet which is excellent in heat laminating property with a metal plate and moldability of a can, particularly high workability such as drawing and ironing. An object of the present invention is to provide a metal plate obtained by laminating a polyester film for plate lamination, and a metal can formed from the metal plate.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that two or more kinds of substantially incompatible polyesters having different crystallinities, that is, mainly polybutylene terephthalate. It consists of a polyester and a film obtained by melt-mixing a polyester mainly composed of polyethylene terephthalate at a specific ratio, and by adjusting the crystallization characteristics of this film to a specific performance, the moldability of the can,
In particular, they have found that high workability such as drawing and ironing is improved, and have reached the present invention.

That is, the gist of the present invention is as follows. (1) A metal can body formed by processing a metal plate obtained by laminating a polyester film by thermocompression bonding, wherein the polyester film is a polybutylene terephthalate having a melting point of 200 to 223 ° C. or a polyester (A) mainly containing the same. 40-80% by mass, melting point 230-256 ° C (2
(Excluding 30 to 245 ° C.) polyethylene terephthalate, or a polyester (B) containing the same as a main component.
20% by mass, wherein the temperature-rise crystallization peak temperature from the amorphous state is in the range of 60 to 100 ° C, and the specific heat capacity at 60 to 100 ° C is 0 J / g · ° C or more. A metal can body characterized in that:

(2) The polyester film has a thickness of 200 to
223 ° C and 230-256 ° C (230-2
The metal can according to the above (1), which has one or more melting points in a temperature range of (excluding 45 ° C.).

(3) The metal can according to the above (1) or (2), wherein the polyester film has an elongation at break at a rising temperature of crystallization peak temperature of 100% or more. (4) A metal plate obtained by laminating a polyester film by thermocompression bonding, wherein the polyester film has a melting point of 20
40 to 80% by mass of polybutylene terephthalate at 0 to 223 ° C or polyester (A) containing the same as a main component
And melting point 230-256 ° C (excluding 230-245 ° C)
A polyethylene terephthalate or a polyester (B) containing the same as a main component, which has a crystallization peak temperature in the range of 60 to 100 ° C. A metal sheet laminated with a polyester film, having a specific heat capacity at 0 to 100 ° C. of 0 J / g · ° C. or more.

(5) The polyester film has a thickness of 200 to
223 ° C and 230-256 ° C (230-2
(4) Except for 45 degreeC), The metal plate which laminated | stacked the polyester film of said (4) characterized by having each one or more melting points.

(6) A metal sheet laminated with the polyester film as described in (4) or (5) above, wherein the polyester film has a breaking elongation at the temperature of crystallization peak temperature at an elevated temperature of 100% or more.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, polybutylene terephthalate (P
BT) The polyester (A) mainly composed of PBT and a copolymer obtained by copolymerizing other components with PBT.
The temperature must be between 00 and 223 ° C, and the melting point is 200
If the temperature is lower than ℃, the heat resistance decreases.

The copolymerization ratio may be such that the melting point is within the above range, and 1,4-butanediol is preferably at least 80 mol%, particularly preferably at least 90 mol%, based on all alcohol components. If the amount of 1,4-butanediol is less than 80 mol%, the crystallinity, particularly the crystallization speed, is reduced, and the impact resistance after the retort treatment is reduced.

The copolymerization component is not particularly limited. Examples of the acid component include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, and the like.
Azelaic acid, dodecane diacid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, dicarboxylic acids such as cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, lactic acid, and the like. No.

The alcohol component includes ethylene glycol, diethylene glycol, 1,3-propanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene. Glycol, ethylene oxide adducts of bisphenol A and bisphenol S, and the like.

Further, trimellitic acid, trimesic acid,
Trifunctional compounds such as pyromellitic acid, trimethylolpropane, glycerin and pentaerythritol may be used in small amounts. Two or more of these copolymer components may be used in combination.

In the present invention, the polyester (B) mainly composed of polyethylene terephthalate (PET) includes PE
T and PET copolymerized with other components can be mentioned, and the melting point needs to be in the range of 230 to 256 ° C. However, the range of 230 to 245 ° C is excluded. When the melting point is less than 230 ° C., the crystallinity is reduced, whitening or white spots are generated after the retort treatment, and the impact resistance after the retort treatment is poor.

The component that can be copolymerized with PET is not particularly limited, and examples thereof include compounds similar to polyester (A). The limiting viscosity of the polyester used for producing the polyester film for the metal can and the metal plate of the present invention is 0.6% for the polyester (A).
And 1.6 and polyester (B) are preferably 0.5 to 0.9, and the intrinsic viscosity after melt mixing is preferably 0.6 to 1.0. When the intrinsic viscosity is less than the above range, the practical performance of the film is insufficient, and when it exceeds the above range, the productivity is poor and the heat laminating property of the film on a metal plate is impaired.

The method for polymerizing the raw material polyester is not particularly limited. For example, it can be polymerized by a transesterification method, a direct polymerization method or the like. Examples of the transesterification catalyst include oxides and acetates of Mg, Mn, Zn, Ca, Li, and Ti. As the polycondensation catalyst, S
Compounds such as b, Ti, Ge oxide, acetate and the like can be mentioned.

Since the polyester after polymerization contains monomers and oligomers, by-products such as acetaldehyde and tetrahydrofuran, it is preferable to carry out solid-phase polymerization at a temperature of 200 ° C. or more under reduced pressure or an inert gas flow.

In the polymerization of polyester, if necessary, additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber,
An antistatic agent or the like can be added. As antioxidants, for example, hindered phenol compounds, hindered amine compounds, etc., as heat stabilizers, for example, phosphorus compounds, etc., as ultraviolet absorbers, for example, benzophenone compounds, benzotriazole compounds, etc. Can be mentioned.

In the present invention, the polyesters (A) and (B) are melt-mixed at a specific mixing ratio, and the mixing ratio is (A) /
(B) = 40 to 80/60 to 20 (% by mass), preferably (A) / (B) = 50 to 70/50 to 30 (% by mass)
It is necessary that

When the content of the polyester (A) exceeds 80% by mass, the properties of the polyester (A) having high crystallinity are remarkably exhibited, and not only are the moldability inferior, but also the impact resistance deteriorates. When the content of the polyester (A) is less than 40% by mass,
The crystallization rate decreases, and the physical properties after the retort treatment decrease. In the present invention, it is particularly important to incorporate the polyester (A) in an amount of 40% by mass or more in order not to lose the properties relating to the crystallization speed of the polyester (A).

In the above polyester film, the characteristics of the film in an amorphous state are limited. This is because the moldability of the can is greatly affected by the crystallinity in the amorphous state. In other words, forming a can involves deforming or drawing a metal plate on which a polyester film is laminated into a cylindrical shape or its special shape, and ironing it.At this time, the bonding side of the polyester film with the metal plate is in an amorphous state. Or, it is often in a state close to it. In particular, when thermocompression bonding is performed without using an adhesive, the ratio of the amorphous state increases. Further, in order to improve drawing and ironing workability, a method of amorphizing a part or all of the resin is used. As described above, conventionally, it has been difficult to achieve both good formability that can withstand severe drawing and ironing, and the quality of a can such as impact resistance and retort resistance. By focusing on the state, we succeeded in achieving both of the above qualities.

That is, it is necessary that the above-mentioned film has a temperature rising crystallization peak temperature (Tc) from an amorphous state in the range of 60 to 100 ° C., preferably 60 to 90 ° C.

When Tc exceeds 100 ° C., not only embrittlement occurs during the retort sterilization treatment, but also white spots may occur to deteriorate the appearance of the film. On the other hand, when Tc is lower than 60 ° C., the moldability may be poor when the molding temperature is high, and the content may have poor flavor and aroma.

Further, the specific heat capacity (Cp) of the above film at 60 to 100 ° C. must be 0 J / g · ° C. or more. When Cp is less than 0 J / g · ° C., the crystallization speed near the crystallization start temperature becomes too fast, the formability is deteriorated, and whitening occurs during high workability such as drawing or ironing. And pinholes and cracks are easily generated. here,
The temperature of 60 to 100 ° C. is a temperature range in which can molding is usually performed, and it is important that Cp in the molding temperature range is 0 J / g · ° C. or more.

The conditions for melt-mixing the polyesters (A) and (B) are not particularly limited, and a method in which the blended raw material chips are melt-mixed in the same extruder, or mixed after being melted in separate extruders. Method and the like. In the case of mixing for a long time at a high melting temperature or under a high shear as a melt mixing condition, a transesterification reaction or a decomposition reaction proceeds, and the characteristics of the mixture are greatly changed. In particular, when the transesterification proceeds too much, the melting point and the glass transition temperature decrease, and the specific heat capacity also becomes 0 J / g · ° C. or less. As a result, the excellent properties of the film made of the polyesters (A) and (B) disappear, and the heat resistance and the moldability decrease.
The melting and mixing conditions are as follows: at a temperature not higher than the melting point of (B) + 20 ° C,
The residence time is preferably 15 minutes or less.

Further, the above-mentioned film has a temperature of 200 to 223 ° C.
And at least one melting point in the temperature range of 230 to 256 ° C. (excluding 230 to 245 ° C.). That is, the film is in a state where it is preferable to have independent melting points derived from the polyester (A) and the polyester (B).

In particular, when the melting point derived from the polyester (A) is lower than 200 ° C., the heat resistance of the film decreases, and the moldability and impact resistance are poor. Further, it is preferable that the film has a breaking elongation of 100% or more at the temperature-rise crystallization peak temperature. If the elongation is less than 100%, the moldability of the can may be poor.

The above film is usually used as a biaxially stretched film. For example, dry-blended polyesters (A) and (B) are supplied to an extruder equipped with a T die,
After being melt-mixed at a temperature of 250 to 280 ° C. for 3 to 15 minutes, the mixture is extruded into a sheet, and the extruded sheet is cooled by closely contacting it with a cooling drum adjusted to a temperature of room temperature or lower. Depending on the vertical direction (MD)
Pre-stretch about 1.2 times, then 5
The film is biaxially stretched at a temperature of 0 to 150 ° C. in the MD and transverse direction (TD) so as to have a draw ratio of about 2 to 4 times each. It can be manufactured by performing a heat treatment for seconds.
As the biaxial stretching method, a sequential or simultaneous biaxial stretching method can be used.

Heat treatment after stretching is a necessary step for imparting dimensional stability to the film. Examples of the method include a method of blowing hot air, a method of irradiating infrared rays, and a method of irradiating microwaves. A known method can be used. Among them, the method of blowing hot air is optimal because heating can be performed uniformly and accurately.

In order to improve the processability during film production and can production, it is desirable to add a small amount of an inorganic lubricant such as silica, alumina, kaolin or the like to form a film to impart slip properties to the film surface. Furthermore, in order to improve the appearance and printability of the film, for example, the film may contain a silicone compound or the like. Also, in order to improve laminating properties with metal and further increase strength,
An optional coating layer such as an adhesive layer may be formed by in-line coating during film production or post-coating after film production.

The polyester film is heat-laminated on a metal plate such as a steel plate or aluminum. The metal plate to be laminated is formed by a chemical treatment such as a chromic acid treatment, a phosphoric acid treatment, an electrolytic chromic acid treatment, a chromate treatment, or the like. , Tin,
Zinc, aluminum, gunmetal, brass, and other various types of plated steel plates can be used.

[0040]

Next, the present invention will be described specifically with reference to examples. The raw materials of the films and the methods for measuring the characteristic values in the examples and comparative examples are as follows.

(1) Raw Materials In Table 1, polyesters (A) and (B) represent PBT and PET, respectively, when there is no copolymer component, and the intrinsic viscosity (IV) and melting point (Tm) are as shown in Table 1. As shown in FIG.

The copolymer component was composed of 8 mol% and 12 mol% of SEA of PBT, and the copolymer component was composed of IPBT.
All polyesters except A12 mol% PET were subjected to solid phase polymerization.

The polyester resin is filled with 0.1 wt% of silica having an average particle diameter of 1.1 μm. In Table 1, "IPA" represents isophthalic acid and "S
EA "represents sebacic acid.

(2) Measurement method Intrinsic Viscosity (IV) Using an equal weight mixed solvent of phenol / ethane tetrachloride,
It was determined from the solution viscosity measured at a temperature of 20 ° C.

B. Melting point (Tm) and elevated temperature crystallization peak temperature (Tc) Using Perkin Elmer DSC, 10 ° C. /
In minutes, the melting point and the crystallization peak temperature at the time of temperature rise were measured. The measurement sample is 100 ° C after melting the stretched film.
/ Min was rapidly cooled at a speed of not less than / min to be in an amorphous state.

C. Specific heat capacity (Cp) JISK using Perkin Elmer DSC
It was measured according to 7123-1987. Sapphire was used as a standard. As a measurement sample, a stretched film was melted and then rapidly cooled at a rate of 100 ° C./min or more to be in an amorphous state.

D. Tensile elongation (%) Using a film sample (n = 5) having a width of 10 mm and a length of 10 cm, the tensile elongation at a temperature-rise crystallization peak temperature (Tc) according to the measurement method specified in ASTM D882. The degree was measured. In addition, data was shown by the minimum value of MD and TD.

E. Heat laminating property Between heated metal roll and silicon rubber roll,
A sample film and a tin-free steel plate having a thickness of 0.21 mm are supplied in a superimposed manner, and heated and bonded at a speed of 20 m / min at a linear pressure of 50 kgf / cm. I got

From the obtained laminate, eleven strip-shaped test pieces having a width of 18 mm (ends were not laminated, and the laminated portion was secured to the MD by 8 cm or more) were cut out into TDs. Next, on the film surface of this test piece,
Adhesive tape specified in JIS Z-1522 was applied, and 10 mm / min using an autograph manufactured by Shimadzu Corporation.
A 180-degree peel test was performed at a speed of and the peel strength was measured to evaluate the adhesiveness according to the following criteria.

A: Peel strength of 10 or more test pieces is 30
The film was broken at 0 gf or more, or at 300 gf or more. ：: The peel strength of 5 to 9 test pieces was 300 gf or more, or the film was broken at 300 gf or more. Δ: 7 or more test pieces having a peel strength of less than 300 gf.

F. Formability Using the film side of the laminated metal plate obtained in E above as the inner surface of the can body, the state when deep drawing was performed on two-piece cans equivalent to 350 ml and 500 ml was observed. The evaluation was XX for peeling, rupture or whitening that was visually observed, but was not visually observed, but X where corrosion of the metal was observed by immersing in copper sulfate aqueous solution,腐 食 indicates that no corrosion was observed.

G. Retort resistance The laminated metal plate obtained in the above E was treated at 125 ° C. for 30 minutes.
The state of the film after the min retort treatment was observed. The evaluation was evaluated as x with obvious whitening or white spots,
Although it is not clear, whitening that can be visually discerned was recognized as Δ, and that no change was visually observed was evaluated as ○.

H. Impact resistance The laminated metal plate obtained in the above E was treated at 125 ° C. for 30 minutes.
After the min retort treatment, at 5 ° C, a 1 kg weight from the height of 50 cm (the tip is a spherical surface with a diameter of 1/2 inch)
Was dropped from the film side, and the state of the film was observed. The evaluation was XX if peeling or breakage was visually observed, but not visually observed, but × if metal corrosion was observed by immersing in copper sulfate aqueous solution, and metal corrosion was observed even if immersed in copper sulfate aqueous solution. A sample in which no was observed was evaluated as ○.

Example 1 Polyester (A) having the properties shown in Table 1 was added to 50
Parts by weight and 50 parts by weight of (B) were dry-blended and melt-extruded into a sheet at 275 ° C. (residence time: 8 minutes) using an extruder equipped with a T-die. The sheet was cooled in close contact with a cooling drum to obtain an unstretched sheet having a thickness of 240 µm.

The end of the obtained unstretched sheet was gripped by clips of a tenter-type simultaneous biaxial stretching machine, and after traveling in a preheating zone of 60 ° C., at a temperature of 80 ° C., 3.0 times MD and TD.
And the film was simultaneously biaxially stretched at 3.3 times. Thereafter, the TD was subjected to a heat treatment at a temperature of 150 ° C. for 4 seconds at a relaxation rate of 5%, then cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 25 μm.

Table 2 shows various characteristic values of the obtained film.

Examples 2 to 4 and Comparative Examples 1 to 6 Various films were obtained in the same manner as in Example 1 except that the raw material resin, the compounding ratio and the film production conditions were changed as shown in Table 1.

Table 2 shows various characteristic values of the obtained film.

[0059]

[Table 1]

[0060]

[Table 2]

The films obtained in Examples 1 to 4 were excellent in heat laminating property, moldability, impact resistance and retort resistance, but the films obtained in Comparative Examples 1 to 6 Nothing satisfying the performance of was obtained.

[0062]

According to the present invention, a metal can having excellent heat laminating properties and moldability, particularly high workability such as drawing and ironing, and also having excellent impact resistance and retort resistance after molding. And a metal plate on which a polyester film is laminated for forming the metal can.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C23C 26/00 B65D 1/00 B (72) Inventor Masanobu Hioki 31-3 Ujiinosojiri, Uji City, Kyoto Unitika Unitika Inside the Uji Plastic Factory (72) Inventor Shigemi Majima 31-3 Uji Hinojiri, Uji City, Kyoto Unitika Fuji Term Co., Ltd. Uji Plastic Factory 3E033 AA06 BA07 BA17 BA18 BB01 BB08 CA14 CA20 DD01 FA01 3E086 AD30 BA04 BA13 BA15 BB51 BB77 BB90 CA01 CA11 4F100 AB01B AB03B AK41A AK42A AL05A BA02 BA10A BA10B DA01 GB16 JA01A JA04A JA11A JJ03 JK01A JK06 JK08A JK10 JL01 YY00A 4J002 CF06X CF07W GF4 AB01 BC04 BC01 BC04

Claims (6)

[Claims] 1. A metal can body formed by molding a metal plate obtained by laminating a polyester film by thermocompression bonding, wherein the polyester film is made of polybutylene terephthalate having a melting point of 200 to 223 ° C. A) 40-80% by mass, melting point 230-25
6 ° C. (excluding 230 to 245 ° C.) polyethylene terephthalate or polyester (B) based on this
A film comprising 60 to 20% by mass, wherein the temperature-rise crystallization peak temperature from the amorphous state is in the range of 60 to 100 ° C, and the specific heat capacity at 60 to 100 ° C is 0 J / g ·
A metal can body having a temperature of at least ℃. 2. A polyester film having a thickness of 200 to 22.
A temperature range of 3 ° C and 230-256 ° C (230-245
The metal can body according to claim 1, wherein each of the metal can bodies has one or more melting points in a temperature range of (excluding ° C). 3. The metal can according to claim 1, wherein the polyester film has an elongation at break of 100% or more at an elevated temperature crystallization peak temperature. 4. A metal plate obtained by laminating a polyester film by thermocompression bonding, wherein the polyester film is
Polybutylene terephthalate having a melting point of 200 to 223 ° C.,
Or a polyester (A) 40-80 based on this.
A film comprising polyethylene terephthalate having a melting point of 230 to 256 ° C. (excluding 230 to 245 ° C.) or 60 to 20% by weight of a polyester (B) containing the same as a main component, wherein The hot crystallization peak temperature is in the range of 60-100 ° C,
A metal plate laminated with a polyester film, having a specific heat capacity at 0 ° C. of 0 J / g · ° C. or more. 5. A polyester film having a thickness of 200 to 22.
A temperature range of 3 ° C and 230-256 ° C (230-245
5. The metal sheet according to claim 4, wherein the metal sheet has one or more melting points in a temperature range of (excluding ° C). 6. The metal sheet according to claim 4, wherein the polyester film has a breaking elongation at a temperature of a crystallization peak temperature at an elevated temperature of 100% or more.