JPH11277701A - Polyester film for lamination-molding metallic plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for lamination-molding a metallic plate which shows superb molding workability, outstanding flavor and aroma retaining properties, especially after retorting, and besides, high impact resistance, especially at a low temperature. SOLUTION: This polyester film is a laminated film comprising a layer (A) of a copolymer PET (III) at 210-245 deg.C melt point and a layer (B) of a composition consisting of 80-45 wt.% copolymer PET (I) at 210-245 deg.C melt point and 20-55 wt.% copolymer PET (II) at 160-223 deg.C melt point, laminated in that order. In addition, the glass transition temperature(Tg) of the polymer (III) of the layer (A) by DSC measurement and the highest temperature peak temperature(Te) at a loss modules of the laminated film satisfy formulae Tg>=78 and Te-Tg<=30 respectively. In the formulae, Tg is the glass transition temperature ( deg.C) by DSC measurement after heat fusion at 290 deg.C-quenching; and Te is the highest temperature peak temperature ( deg.C) at the loss modules of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for laminating and forming a metal plate, and more particularly, it shows excellent formability when laminating to a metal plate and performing can forming such as drawing. The present invention relates to a polyester film for metal plate lamination processing capable of producing metal cans, such as beverage cans and food cans, which are excellent in properties, retort resistance, flavor preserving property, impact resistance and the like.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion on the inner and outer surfaces, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention is performed without using an organic solvent. Development of a method for obtaining the property has been advanced, and as one of the methods, coating with a thermoplastic film has been attempted.

[0003] That is, a method of laminating a thermoplastic resin film on a metal plate of tin, tin-free steel, aluminum or the like, followed by drawing or the like is being studied.

As the thermoplastic resin film, it is gradually becoming clear that a copolymerized polyester film is suitable in terms of moldability, heat resistance, impact resistance, and taste and fragrance retention. However, this polyester film does not necessarily show sufficient flavor retention and aroma when the beverage contains extremely important tastes such as green tea and mineral water which is required to be tasteless and odorless. Is sensed.

On the other hand, Japanese Patent Application Laid-Open No. Hei 6-116376 proposes a polyester film for forming a metal sheet having an improved flavor, comprising a copolymerized polyester containing a specific amount of an alkali metal element and a germanium element. I have. However, when this film is used, it shows excellent flavor and fragrance retention in the process where heat is not applied at the stage of filling contents such as a cold pack system, but at the stage of filling contents such as retort treatment. In the step in which the heat treatment is performed, sufficient flavor and fragrance retention cannot always be obtained.

Further, the polyester film for laminating a metal plate made of a copolymerized polyester generally has insufficient impact resistance, especially at a low temperature of 15 ° C. or less, and the metal film laminated with this film is not suitable. If the can is dropped at a low temperature to give an impact to the film, the film is likely to crack. This is a serious problem in a case where the can is handled in a cooled state such as a metal can for juice or soft drink.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems of the prior art and to maintain the excellent moldability, heat resistance and retort resistance of a copolymerized polyester film. Polyester film for laminating metal plate with improved flavor retention, especially after retort treatment, improved impact resistance, and improved impact resistance, especially resistant to cracking at low temperatures Is to provide.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, among the copolymerized polyesters, copolymerized polyesters having ethylene terephthalate as a main repeating unit and having a specific melting point. By using a specific glass transition temperature, a film having dynamic viscoelasticity, the flavor retention, especially after retort treatment is significantly improved, and ethylene terephthalate as a main repeating unit Impact resistance, especially at low temperatures, by using a two-layer structure in which a layer of a composition in which a copolymerized polyester and a copolymerized polyester having butylene terephthalate as a main repeating unit are blended in a specific ratio is provided. The present inventors have found that the properties are significantly improved, and have reached the present invention.

That is, a layer (A) composed of copolymerized polyester (III) having ethylene-terephthalate as a main repeating unit and having a melting point of 210 to 245 ° C., and a melting point of ethylene-terephthalate as a main repeating unit of 210
A layer comprising a composition containing 80 to 45% by weight of the copolymerized polyester (I) at a temperature of from 245 to 245 ° C and 20 to 55% by weight of a copolymerized polyester (II) having a melting point of 160 to 223 ° C and having butylene terephthalate as a main repeating unit. (B) is a laminated film, wherein the DSC of the copolymerized polyester (III) constituting the layer (A)
A polyester film for metal plate laminating processing, wherein the glass transition temperature (Tg) and the maximum peak temperature (Te) of the loss elastic modulus of the laminated film in the measurement satisfy the following formulas (1) and (2). It is.

[0010]

Tg ≧ 78 (1) Te−Tg ≦ 30 (2) (where, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heating-quenching, and Te is the loss elasticity of the film. Rate is the highest peak temperature (° C).)

The copolymerized polyesters (I) and (II)
The copolymer component of I) is preferably 2,6-naphthalenedicarboxylic acid, and the copolymer polyester (II) is preferably a copolymerized polybutylene terephthalate obtained by copolymerizing adipic acid at 5 to 40 mol%. Further, it is preferable that the amount of extraction when the laminated film is subjected to extraction treatment with ion-exchanged water at 121 ° C. for 2 hours is 0.5 mg / inch ² or less.

In the present invention, the copolymerized polyester (III) used in the layer (A) may have excellent moldability, heat resistance and retort resistance while maintaining the flavor and fragrance retention, particularly after retort treatment. The copolymer polyester having ethylene terephthalate as a main repeating unit, that is, a copolymerized polyethylene terephthalate, is used because it is possible to improve the flavor retention and fragrance retention of polyethylene terephthalate.

In the present invention, the copolymerized polyester (II
The copolymer component of I) may be a dicarboxylic acid component or a diol component.

The dicarboxylic acid component includes aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be exemplified.
Examples thereof include aliphatic diols such as -butanediol, 1,6-hexanediol, and diethylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol; and aromatic diols such as bisphenol A. These can be used alone or in combination of two or more.

The proportion of the copolymerization component depends on the kind thereof, but the proportion is such that the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 240 ° C. If the melting point is lower than 210 ° C., the heat resistance will be poor. On the other hand, when the melting point exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolyester (III) was measured by Du Pont Instruments.
A method in which a melting peak is obtained at a heating rate of 20 ° C./min using 910 DSC. The sample amount is 20 mg.

The intrinsic viscosity of the copolymerized polyester (III) used in the present invention (orthochlorophenol, 35
C) is preferably from 0.52 to 1.50, more preferably from 0.57 to 1.00, and particularly preferably from 0.
60 to 0.80. If the intrinsic viscosity is less than 0.52, the impact resistance may be insufficient, which is not preferable.
On the other hand, when the intrinsic viscosity exceeds 1.50, the moldability may be impaired.

The laminated film of the present invention has the following glass transition temperature (Tg) and maximum temperature peak temperature (Te) of the loss modulus of the laminated film in the DSC measurement of the copolymerized polyester (III) constituting the layer (A). Equations (1) and (2) must be satisfied.

[0019]

Tg ≧ 78 (1) Te−Tg ≦ 30 (2) (where Tg is the glass transition temperature (° C.) in DSC measurement after heating and melting and quenching at 290 ° C., and Te is the loss elasticity of the film. Rate is the highest peak temperature (° C).)

If the Tg of the film is less than 78 ° C., the heat resistance becomes poor, and the flavor and odor retention after retorting deteriorates. For this reason, as the copolymerization component of the copolymerized polyester (III), it is preferable to use, as at least one component, a component whose glass transition temperature does not change or increases when the proportion of the copolymerization component is increased. preferable. Preferred examples of the component that increases the glass transition temperature when the proportion of the copolymer component is increased are 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component, and 1,4-cyclohexanedimethanol as the diol component. it can.

Here, the Tg of the polyester was measured by placing a 20 mg film sample in a pan for DSC measurement,
After heating and melting for 5 minutes on a heating stage, the sample pan was quickly cooled and solidified on an aluminum foil spread on ice,
A method of determining a glass transition point at a heating rate of 20 ° C./min using on Instruments 910 DSC.

Further, when the value of Te-Tg exceeds 30, the molecular orientation and the crystallinity of the film become too high, so that the moldability is remarkably reduced. Although the value of Te depends on the copolymerization component and the copolymerization amount, a method of adjusting the film forming conditions, particularly the biaxial stretching ratio, the stretching temperature, and the heat setting temperature, is preferably mentioned.

Here, Te is determined using a dynamic viscoelasticity measuring device at a measurement frequency of 10 Hz and a dynamic displacement of ± 25 × 10 ⁻⁴ cm.

In the present invention, the copolymer polyester (I) constituting the layer (B) is a copolymer polyester having ethylene terephthalate as a main repeating unit.

In the present invention, the copolymer component of the copolymerized polyester (I) may be a dicarboxylic acid component or a diol component.

Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be exemplified.
Examples thereof include aliphatic diols such as -butanediol, 1,6-hexanediol, neopentyl glycol, and diethylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol; and aromatic diols such as bisphenol A. These can be used alone or in combination of two or more. Among these, 2,6-naphthalenedicarboxylic acid is preferably used for the same reason as the above-mentioned copolymerized polyester (III).

The proportion of the copolymer component depends on the type thereof, but is a proportion that results in a polymer melting point of 210 to 245 ° C., preferably 215 to 240 ° C. If the melting point is lower than 210 ° C., the heat resistance will be poor. On the other hand, when the melting point exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolymerized polyester (I) is measured by the same method as the above-mentioned method for measuring the melting point of the copolymerized polyester (III).

The intrinsic viscosity of the copolyester (I) used in the present invention (orthochlorophenol, 35 ° C.)
Is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to 0.70.
０．６0.65.

In the present invention, the polyester (II) constituting the layer (B) is a polyester containing butylene terephthalate as a main repeating unit. The polyester having butylene terephthalate as a main repeating unit may be a polybutylene terephthalate homopolymer or a copolymer of an acid component and / or an alcohol component. Examples of the acid component that can be copolymerized include aliphatic dicarboxylic acids such as aliphatic dicarboxylic acids represented by H00C— (CH ₂ ) _n —COOH (where n = 4 to 8) and decane dicarboxylic acid, isophthalic acid, and phthalic acid. Acids, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, etc. can be exemplified. On the other hand, as copolymerizable alcohol components, aliphatic diols such as ethylene glycol, hexanediol, neopentyl glycol and the like, and oils such as cyclohexanedimethanol, etc. Examples thereof include a cyclic diol. These can be used alone or in combination of two or more. Among these, an aliphatic dicarboxylic acid represented by H00C- (CH ₂ ) _n -COOH (where n = 4), that is, adipic acid is preferred.

The proportion of the copolymer component is such that the melting point of the polymer is 1
The ratio is in the range of 60 to 223 ° C, preferably 170 to 220 ° C, and more preferably 180 to 215 ° C. If the melting point of the polymer is less than 160 ° C., the heat resistance of the laminated film is poor, which is not preferable. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

A particularly preferred embodiment from the viewpoint of the impact resistance of the laminated film of the present invention is a film obtained by copolymerizing adipic acid as an acid component in an amount of 5 to 40 mol%.

The measurement of the melting point of the copolyester (II) is carried out in the same manner as the measurement of the melting point of the copolyester (III).

The intrinsic viscosity of the copolyester (II) is preferably 0.70 to 2.00, more preferably 0.80 to 1.70, and particularly preferably 0.85.
１．５1.50.

In the laminated film of the present invention, the layer (B)
Is a copolymer polyester (I) containing ethylene terephthalate having a melting point of 210 to 245 ° C. as a main repeating unit.
80 to 45% by weight, preferably 70 to 45% by weight, more preferably 59 to 50% by weight, and a melting point of 160 to 22%.
20 to 55% by weight, preferably 30 to 55% by weight, more preferably 41 to 50% by weight of polyester (II) containing butylene terephthalate as a main repeating unit at 3C.
Is formed from.

If the content of the polyester (II) containing butylene terephthalate as a main repeating unit is less than 20% by weight and the content of the copolymerized polyester (I) containing ethylene terephthalate as a main repeating unit exceeds 80% by weight, the temperature of the laminated film under low temperatures may increase. Is not preferred because the impact resistance cannot be improved. When the content of the polyester (II) containing butylene terephthalate as a main repeating unit exceeds 55% by weight and the content of the copolymerized polyester (I) containing ethylene terephthalate as a main repeating unit is less than 45% by weight, the heat resistance of the laminated film is low. It is not preferable because the resistance is lowered and the impact resistance becomes insufficient.

In the present invention, the copolymer polyester (III) used for the layer (A), the copolymer polyester mainly containing ethylene terephthalate used for the copolymer polyester (I) of the layer (B), and the layer ( The polyester having butylene terephthalate as a main repeating unit used in the copolymerized polyester (II) of B) is not limited by the production method.
For example, a method of subjecting terephthalic acid, ethylene glycol and a copolymer component to an esterification reaction and then subjecting the resulting reaction product to a polycondensation reaction to obtain a copolymerized polyester, or a transesterification reaction of dimethyl terephthalate, ethylene glycol and a copolymer component. And then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester.

In the production of polyester, other additives such as a fluorescent whitening agent, an antioxidant, an antistatic agent and the like can be added as required.

In the present invention, the ester conversion of the polyester composition can be represented by the melting point of the polyester composition forming the layer (B). That is, when the melting point of the polyester composition is low, the transesterification reaction proceeds, and when the melting point is high, the transesterification reaction does not proceed. The melting point of such a polyester composition is preferably from 220 to 240 ° C.

The melting point of the polyester composition is measured in the same manner as in the above-mentioned measurement of the melting point of the copolyester (III).

The laminated film of the present invention has a structure in which a layer (A) and a layer (B) are laminated, and the film having such a laminated structure includes, for example, a copolymer polyester (III) and a polyester composition constituting each layer. The materials are separately melted, co-extruded, laminated and fused before solidification, then biaxially stretched, heat-fixed, the copolyesters constituting each layer are separately melted and extruded. It can be produced by a method of producing a film, in an unstretched state or after stretching, laminating both.

In this case, the refractive index in the thickness direction of the layer (A) is preferably 1.500 to 1.540,
More preferably, it is 1.505 to 1.530.
If the refractive index is less than 1.500, the moldability may be insufficient. On the other hand, if it exceeds 1.540, the structure may be nearly amorphous, and the heat resistance may be reduced.

Here, the refractive index in the thickness direction is measured with a monochromatic NaD line by attaching a polarizing plate analyzer to the eyepiece side of the Abbe refractometer. The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C.

The laminated film of the present invention preferably has a thickness of 6 to 75 μm. 10 to 75 μm, especially 15
It is preferably from 50 μm to 50 μm. If the thickness is less than 6 μm, breakage or the like tends to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

[0045] The ratio of the thickness T _B of the thickness T _A and the layer of the layer (A) (B) (T A / T B) is 0.02 to 1.5, further from 0.04 to 0.67, Particularly, 0.04 to 0.25 is preferable. Specifically, for example, in the case of a laminated film having a thickness of 20 μm, the thickness of the layer (A) is set to 0.5 to 15 μm, preferably 1 to 10 μm, and more preferably 1 to 4 μm.

Since the polyester film of the present invention is used particularly for food cans or beverage cans, it is better that the amount of the substances eluted or scattered from the film is smaller, but it is substantially impossible to eliminate such substances at all. It is possible. Therefore, for use in food cans or beverage cans, for example, the extraction amount per square inch of a film when extracted with ion-exchanged water at 121 ° C. for 2 hours is 0.5 mg.
Or less, more preferably 0.1 mg or less.

To reduce the amount of extraction, the glass transition temperature of the film may be increased. The glass transition temperature of the film is determined by the glass transition temperature and the degree of orientation of the polymer constituting the film. However, when the degree of orientation is increased, moldability deteriorates. Therefore, it is preferable to increase the glass transition temperature of the polymer as much as possible.

As a metal plate to which the laminated film of the present invention is bonded, in particular, a metal plate for can making, a plate of tin, tin-free steel, aluminum or the like is suitable. Lamination of the polyester film on the metal plate, for example,
Can be performed in the following manner. The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is laminated, and then cooled. The surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. An adhesive layer is primer-coated on the film in advance, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

When the laminated film of the present invention is bonded to a metal plate, the layer (B) side is bonded to the metal plate. Furthermore, in the laminated film of the present invention, if necessary, another additional layer may be laminated between the layer (A) and the layer (B).

[0050]

The present invention will be further described with reference to the following examples.
The properties of the film were measured by the following methods. (1) Intrinsic viscosity of copolymerized polyester Measured in orthochlorophenol at 35 ° C.

(2) Melting point of copolymerized polyester Du Pont Instruments 910 D
A method in which a melting peak is determined at a heating rate of 20 ° C./min using SC. The sample amount is 20 mg.

(3) Glass Transition Temperature (Tg) of Copolyester A 20 mg film sample was placed in a pan for DSC measurement, heated and melted on a 290 ° C. heating stage for 5 minutes, and then the sample pan was quickly spread on ice. Quenched and solidified on aluminum foil, Du Pont Instruments 910
A method in which the glass transition point is determined at a heating rate of 20 ° C./min using DSC.

(4) Maximum peak temperature of loss elastic modulus of film (Te) The loss elastic modulus was determined at a measurement frequency of 10 Hz and a dynamic displacement of ± 25 × 10 ⁻⁴ cm using a dynamic viscoelasticity measuring apparatus. The peak temperature at this time is shown.

(5) Deep drawing workability The film was heated at a temperature equal to or higher than the melting point of polyester.
Affixed to both sides of 25 mm tin-free steel, water-cooled, cut into a 150 mm diameter disk, deep-drawn in four stages using a drawing die and punch, and a 55 mm diameter side-side seamless container (hereinafter referred to as can and Abbreviated). The following observations and tests were performed on the cans, and the cans were evaluated according to the following criteria.

Deep drawing processability-1 ○: No whitening or breakage is observed in the film processed without any abnormality. Δ: Whitening is observed at the top of the film can. X: Film breakage is observed in a part of the film. Deep drawing processability-2 ○: Processed without abnormality, rust prevention test of film surface in can (1% NaCl aqueous solution was put in the can, electrodes were inserted, and a voltage of 6 V was applied using the can body as an anode. The current value at that time is measured, and is 0.2 mA or less in the ERV test. ×: There is no abnormality in the film, but the current value exceeds 0.2 mA in the ERV test, and pinhole-shaped cracks starting from the coarse lubricant of the film are observed when the energized portion is observed under magnification.

(6) Impact resistance For cans having good deep drawing, pour water completely, cool to 0 ° C., drop 10 pieces for each test from a height of 50 cm onto a PVC tile floor. As a result of the ERV test in the can, the results were as follows: ○: 0.2 mA or less for all 10 samples. Δ: Exceeded 0.2 mA for 1 to 5 pieces. X: More than 6 pieces exceeded 0.2 mA, or cracking of the film was already observed after dropping.

(7) Heat Embrittlement Resistance The can which had good deep drawing was heated and held at 200 ° C. for 5 minutes, and the above-mentioned impact resistance was evaluated. ○: 0.2 mA or less for all 10 pieces Met. Δ: Exceeded 0.2 mA for 1 to 5 pieces. ×: Exceeding 0.2 mA for 6 or more pieces, or cracking of the film was already observed after heating at 200 ° C. × 5 minutes.

(8) Retort Resistance The cans having good deep drawing properties are filled with water and subjected to a retort treatment at 120 ° C. for 1 hour in a steam sterilizer.
Stored at 50 ° C. for 30 days. After dropping 10 cans for each test from a height of 50 cm onto a PVC tile floor, an ERV test in the cans was performed. ：: 0.2 mA or less for all 10 samples. Δ: Exceeded 0.2 mA for 1 to 5 pieces. X: More than 6 pieces exceeded 0.2 mA, or cracking of the film was already observed after dropping.

(9) Flavor Retention and Flavor-1 For cans having good deep drawing, filled with ion-exchanged water and stored at room temperature (20 ° C.) for 30 days. Using the immersion liquid, a tasting test was conducted by 30 panelists, compared with ion-exchanged water for comparison, and evaluated according to the following criteria. ：: Three or less out of thirty felt changes in taste and aroma as compared with the comparative solution. 〇: Four to six out of thirty people felt a change in taste and aroma as compared with the comparative solution. Δ: 7 to 9 out of 30 persons felt a change in taste and aroma as compared with the comparative solution. ×: Ten or more of the 30 persons felt a change in taste and aroma as compared with the comparative solution.

(10) Flavor Retention and Flavor Retention-2 Cans having good deep drawability were filled with ion-exchanged water, retorted in a steam sterilizer at 120 ° C. for 1 hour, and then at room temperature (20 ° C.). C) Store for 30 days. Using the immersion liquid, a tasting test was conducted by 30 panelists, compared with ion-exchanged water for comparison, and evaluated according to the following criteria. ：: Three or less out of thirty felt changes in taste and aroma as compared with the comparative solution. 〇: Four to six out of thirty people felt a change in taste and aroma as compared with the comparative solution. Δ: 7 to 9 out of 30 persons felt a change in taste and aroma as compared with the comparative solution. ×: Ten or more of the 30 persons felt a change in taste and aroma as compared with the comparative solution.

Examples 1-5 and Comparative Examples 1-2 Table 1
(A), a copolymerized polyethylene terephthalate (intrinsic viscosity: 0.64) obtained by copolymerizing the copolymer components shown in
Polyester composition containing 55% by weight of copolymerized polyethylene terephthalate (melting point: 228 ° C.) copolymerized with 12 mol% of naphthalenedicarboxylic acid and 45% by weight of copolymerized polybutylene terephthalate (melting point: 195 ° C.) copolymerized with 20% by mole of adipic acid So that the thing becomes layer (B),
After drying separately, each was melted at 280 ° C., co-extruded from dies adjacent to each other, laminated and fused, and then quenched and solidified to obtain an unstretched film.

Next, after stretching this unstretched film longitudinally at the temperature and magnification shown in Table 1, it was horizontally stretched at the temperature and magnification shown in Table 1, and then heat-set at 170 ° C. to obtain a biaxially stretched laminated film. Was.

The thickness of the obtained film was 20 μm, and the thicknesses of the layers (A) and (B) were 4 μm and 16 μm, respectively. Table 2 shows the glass transition temperature (Tg), refractive index, maximum peak temperature (Te) of the loss modulus of the laminated film and the amount of ion-exchanged water extracted from the copolymerized polyester of the layer (A), and Table 3 shows the evaluation results. Shown in

[0064]

[Table 1]

[0065]

[Table 2]

[0066]

[Table 3]

As is clear from the evaluation results in Table 3, the copolyester of the layer (A) has a melting point of 210 to 245 ° C.
In the case of the present invention (Examples 1 to 5), good results were obtained, but when the melting point was less than 210 ° C. (Comparative Example 1)
Was inferior in heat resistance, poor in flavor preservation after retort treatment, and in the case of exceeding 245 ° C. (Comparative Example 2), poor in moldability.

[Examples 6 and 7 and Comparative Examples 3 and 4] In Example 2, the copolyester of the layer (A) whose copolymerization ratio was changed as shown in Table 4 was melt-extruded.
The unstretched film obtained by quenching and solidification was stretched and heat-set under the conditions shown in Table 4 to obtain a biaxially stretched laminated film.

The thickness of the obtained film was 20 μm, and the thicknesses of the layers (A) and (B) were 4 μm and 16 μm, respectively. Table 5 shows the glass transition temperature (Tg), refractive index, maximum peak temperature (Te) of the loss modulus of the laminated film and the amount of ion-exchanged water extracted from the copolymerized polyester of the layer (A), and Table 6 shows the evaluation results. Shown in

[0070]

[Table 4]

[0071]

[Table 5]

[0072]

[Table 6]

As is clear from the evaluation results in Table 6, Tg
In the case of the present invention where is not less than 78 ° C. and Te-Tg is not more than 30 ° C. (Examples 6 and 7), good results were obtained.
When g is less than 78 ° C. (Comparative Example 3), heat resistance is poor,
When the taste and aroma retention after retort were poor and Te-Tg exceeded 30 ° C. (Comparative Example 4), the moldability deteriorated.

Examples 8 to 17 and Comparative Examples 5 to 10
In Example 2, biaxially stretched films in which the polyester composition of the layer (B) was changed as shown in Table 7 were obtained.

In Comparative Example 10, a single-layer film (20 μm thick) having only the layer (A) without the layer (B) was provided.
It was created.

The thickness of the obtained film was 20 μm, and the thicknesses of the layers (A) and (B) were 4 μm and 16 μm, respectively. Further, the glass transition temperature (Tg), the refractive index, the maximum peak temperature (Te) of the loss modulus of the laminated film of the copolymerized polyester of the layer (A), and the extraction amount of ion-exchanged water show the same values as in Example 2, The extraction amount of the film with ion-exchanged water was 0.12 to 0.25 mg / inch ² . Table 8 shows the evaluation results of the obtained films.

[0077]

[Table 7]

[0078]

[Table 8]

The melting point of the copolymerized polyester (I) is 210
245 ° C., the compounding amount is 80-45% by weight, the melting point of the copolyester (II) is 160-223 ° C., and the compounding amount is 20-55% by weight (Examples 8-8).
17) gave good results, but when the melting point of the copolymerized polyester (I) is lower than 210 ° C. (Comparative Example 5),
When the heat resistance of the laminated film was inferior and exceeded 245 ° C. (Comparative Example 6), the moldability was poor. Also, when the melting point of the copolymerized polyester (II) was lower than 160 ° C. (Comparative Example 7), the heat resistance of the laminated film was inferior. Further, the copolymerized polyester (I) exceeds 80% by weight,
When the copolymerized polyester (II) is less than 20% by weight (Comparative Example 8), the impact resistance of the laminated film at low temperature cannot be improved, and the copolymerized polyester (I) is less than 45% by weight, When the copolymerized polyester (II) exceeds 55% by weight (Comparative Example 9), the heat resistance of the laminated film was reduced, and the impact resistance was insufficient. Moreover, the single-layer film (Comparative Example 10) consisting only of the layer (A) was inferior in impact resistance at low temperatures.

[0080]

The polyester film for laminating and forming a metal plate of the present invention has a copolyester in forming a metal can by laminating with a metal plate and then forming the metal can, for example, by deep drawing. Excellent moldability, heat resistance,
While maintaining retort resistance, it has improved flavor retention, especially after retort, and has improved impact resistance, especially at low temperatures. Very useful as a film.

Claims (5)

[Claims] 1. A layer (A) comprising a copolymerized polyester (III) having ethylene terephthalate as a main repeating unit and having a melting point of 210 to 245 ° C., and a melting point of ethylene terephthalate as a main repeating unit of 210 to 245.
80-45% by weight of copolymerized polyester (I) at 20 DEG C. and copolymerized polyester (II) 20 having butylene terephthalate as a main repeating unit and a melting point of 160-223 DEG C.
A layered film obtained by laminating a layer (B) composed of a composition containing about 55% by weight with a glass transition temperature (Tg) of the copolymerized polyester (III) constituting the layer (A) by DSC measurement. And the maximum peak temperature (Te) of the loss modulus of the laminated film is expressed by the following formulas (1) and (2).
A polyester film for laminating and forming a metal plate, characterized by satisfying the following. Tg ≧ 78 (1) Te−Tg ≦ 30 (2) (where Tg is the glass transition temperature (° C.) in DSC measurement after heating and melting and quenching at 290 ° C., and Te is the loss elasticity of the film. Rate is the highest peak temperature (° C).) 2. The polyester film according to claim 1, wherein the copolymerized component of the copolymerized polyester (III) constituting the layer (A) is 2,6-naphthalenedicarboxylic acid. 3. The polyester film according to claim 1, wherein the copolymerized component of the copolymerized polyester (I) constituting the layer (B) is 2,6-naphthalenedicarboxylic acid. 4. The polyester according to claim 1, wherein the copolymerized polyester (II) constituting the layer (B) is a copolymerized polybutylene terephthalate obtained by copolymerizing adipic acid in an amount of 5 to 40 mol%. the film. 5. A film is treated with ion-exchanged water at 121.degree.
The amount of extraction when the time extraction process is performed is 0.5 mg / inch
^The polyester film for metal plate lamination processing according to any one of claims 1 to 4, which is ² or less.