JPH05186613A - Metallic plate-laminating polyester film - Google Patents

Abstract

PURPOSE:To provide a polyester film excellent in can-making processability such as drawing through laminating with a metallic plate, and useful for producing metallic cans of outstanding heat resistance and aroma retentivity. CONSTITUTION:The objective polyester film composed of (A) 99-60wt.% of a copolyester 210-245 deg.C in melting point consisting mainly of polyethylene terephthalate and (B) 1-40wt.% of polybutylene terephthalate or a second copolyester 180-223 deg.C in melting point consisting mainly of polybutylene terephthalate, containing (C) a lubricant <=2.5mum in mean particle diameter. In addition, this film has the following characteristics: (1) refractive index in the width direction: 1.505-1.545; (2) refractive index in the planar direction: 1.61-1.66 for the overall direction; and (3) sub-peak temperature determined by DSC technique: 150-205 deg.C.

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 metal plates, and more specifically, it shows excellent moldability and heat resistance when it is laminated with a metal plate for can manufacturing such as drawing. Also, the present invention relates to a polyester film for laminating a metal plate capable of producing a metal can having excellent aroma retaining property such as a beverage can, a food can and the like.

[0002]

2. Description of the Related Art Metal cans are generally painted to prevent corrosion on the inside and outside, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention without the use of organic solvents The development of a method for obtaining the property has been advanced, and as one of them, coating with a thermoplastic resin film has been attempted. That is,
Studies have been conducted on a method of forming a can by laminating a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, or aluminum, and then drawing it. Polyolefin films and polyamide films have been tried as the thermoplastic resin film, but they do not satisfy all of the molding processability, heat resistance, and aroma retention.

On the other hand, a polyester film, particularly a polyethylene terephthalate film, has been noted as having balanced properties, and several proposals based on this have been made. That is, (A) biaxially oriented polyethylene terephthalate film is laminated on a metal via an adhesive layer of low melting point polyester and used as a can-making material (Japanese Patent Laid-Open No. 56-10451).
No. 1/192546). (B) An amorphous or extremely low crystalline aromatic polyester film is laminated on a metal plate and used as a can-making material (JP-A-1-192545 and JP-A-2-573).
39). (C) A low orientation, heat-set, biaxially oriented polyethylene terephthalate film which is heat-fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530). (D) A copolymerized polyester film having a specific plane orientation coefficient, heat shrinkage ratio, and density is laminated on a metal plate and used as a can-making material (JP-A-3-86729).

[0004]

However, as a result of the study by the present inventors, it has been clarified that neither of the sufficient characteristics is obtained, and the following problems are involved.

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and aroma retention,
Molding processability is insufficient, and whitening of the film (generation of microcracks) and breakage occur in a can-making process that involves large deformation.

Regarding (B), since it is an amorphous or extremely low crystalline aromatic polyester film, it has good moldability, but it has poor aroma retention, and printing after can making and retort sterilization treatment. After treatment such as the above, and further storage for a long period of time, the film is liable to become brittle, and there is a possibility that the film may deteriorate due to an impact from the outside of the can.

Regarding (C), although it is intended to exert its effect in the intermediate region between the above (A) and (B), it has not yet reached the low orientation applicable to can manufacturing, and Since the isotropy of the film surface is not guaranteed, the molding workability may be insufficient in a specific direction of the film when deformation is performed in all directions such as can manufacturing (deep drawing).

With regard to (D), particularly when used in a can to which internal pressure is applied, the film is likely to be broken by an impact from the outside of the can, so that a can of excellent quality may not be obtained.

[0009]

The inventors of the present invention have arrived at the present invention as a result of earnest research to develop a polyester film for can manufacturing which does not have these problems.

That is, according to the present invention, 99-60% by weight of copolymerized polyester having polyethylene terephthalate as a main component and a melting point of 210 to 245 ° C. and polybutylene terephthalate or polybutylene terephthalate as a main component having a melting point of 180 to 223 ° C. Copolyester 1-40
And a lubricant having an average particle size of 2.5 μm or less and having a refractive index in the thickness direction of the film of 1.505 to
Polyester film for laminating metal sheets, which has a refractive index of 1.545 in all directions, a refractive index of 1.61 to 1.66 in all directions, and a DSC sub-peak of 150 to 205 ° C. Is.

Regarding the copolyester mainly composed of polyethylene terephthalate used in the present invention, the copolymerization component may be an acid component or an alcohol component. Examples of the acid component include aromatic dibasic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and alicyclic compounds such as cyclohexanedicarboxylic acid. Examples thereof include group dicarboxylic acids, and examples of alcohol components include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more.

The proportion of the copolymerization component depends on the kind thereof, but as a result, the polymer melting point is 210 to 245 ° C., preferably 215 to 240 ° C., more preferably 220 to 235 ° C.
It is the ratio to be in the range of. When the melting point of the polymer is less than 210 ° C., the heat resistance is poor, so that it cannot withstand the heating during printing after can making. On the other hand, when the melting point of the polymer exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

On the other hand, in the copolymerized polyester mainly composed of polybutylene terephthalate used in the present invention, the copolymerized component may be an acid component or an alcohol component. As the acid component, isophthalic acid, phthalic acid,
Aromatic dibasic acids such as naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, etc., alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, etc. can be exemplified, and alcohol component Examples thereof include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more.

The proportion of the copolymerization component depends on the kind thereof, but as a result, the melting point of the polymer is 180 to 223 ° C, preferably 200 to 223 ° C, more preferably 210 to 223 ° C.
It is the ratio to be in the range of. If the melting point of the polymer is less than 180 ° C., the heat resistance is poor, and the polymer cannot withstand heating during printing after can making. The melting point of polybutylene terephthalate homopolymer is 223 ° C., and it is difficult to obtain a copolyester having a melting point higher than this.

The melting point of polyester is measured by Du P
Ont Instruments 910 DSC, heating rate 20
According to the method of obtaining the melting peak at ° C / min. The sample amount is about 20 mg.

The polyethylene terephthalate-based copolymerized polyester and the polybutylene terephthalate or polybutylene terephthalate-based copolymerized polyester used in the present invention are not limited by the production method thereof. For example, in the case of a copolyester mainly composed of polyethylene terephthalate,
Terephthalic acid, ethylene glycol and a copolymerization component are subjected to an esterification reaction, then the resulting reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester, or dimethyl terephthalate, ethylene glycol and a copolymerization component are transesterified, Then, the obtained reaction product is subjected to a polycondensation reaction to form a copolyester,
Is preferably used. In the production of each copolyester and polybutylene terephthalate, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent may be added, if necessary.

The polyester film of the present invention is mainly composed of polyethylene terephthalate and has a melting point of 210 to 24.
It is necessary to comprise 99 to 60% by weight of a copolyester at 5 ° C. and 1 to 40% by weight of a copolyester mainly composed of polybutylene terephthalate or polybutylene terephthalate and having a melting point of 180 to 223 ° C. Films containing less than 1% by weight of polybutylene terephthalate or polybutylene terephthalate-based copolyesters and more than 99% by weight of polyethylene terephthalate-based copolyesters, especially when used in cans with internal pressure It is easily cracked by external impact, and cans of excellent quality cannot be obtained. When the polybutylene terephthalate or the copolymerized polyester mainly composed of polybutylene terephthalate exceeds 40% by weight and the copolymerized polyester mainly composed of polyethylene terephthalate is less than 60% by weight, the heat resistance of the film is lowered and The impact resistance is also insufficient.

The polyester in the present invention contains a lubricant having an average particle size of 2.5 μm or less. This lubricant may be inorganic or organic, but is preferably inorganic. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate, and the like, and examples of the organic lubricant include crosslinked polystyrene particles and silicone particles. Both require that the average particle size is 2.5 μm or less. If the average particle size of the lubricant exceeds 2.5 μm,
Coarse lubricant particles (for example, particles having a particle size of 10 μm or more) in a portion deformed by processing such as deep-drawing can are used as a starting point, and pinholes are generated or, in some cases, broken, which is not preferable.

Particularly preferred from the viewpoint of pinhole resistance is a monodispersed lubricant having an average particle size of 2.5 μm or less and a particle size ratio (major axis / minor axis) of 1.0 to 1.2. is there. Examples of such a lubricant include true spherical silica, true spherical titanium oxide, true spherical zirconium, true spherical silicone particles and the like.

Here, the average particle diameter and particle diameter ratio of the spherical monodispersed lubricant are as follows. First, a metal is vapor-deposited on the surface of the particle and then the image is magnified 10,000 to 30,000 times with an electron microscope. It is calculated by obtaining the minor axis and the area equivalent circle diameter, and then applying these to the following equation.

Average particle size = sum of area circle equivalent diameters of measured particles / number of measured particles Particle size ratio = average major axis of particles / average minor axis of the particles

The spherical lubricant particles preferably have a sharp particle size distribution, and the relative standard deviation representing the steepness of the distribution is preferably 0.5 or less, more preferably 0.3 or less.

This relative standard deviation is expressed by the following equation.

[0024]

[Equation 1]

The amount of the lubricant in the polyester may be determined by the windability in the film manufacturing process. Generally, it is preferable to add a small amount of particles having a large particle size and a large amount of particles having a small particle size. For example, it is preferable to add about 0.05% by weight in the case of monodisperse silica having an average particle size of 2.0 μm, and about 0.3% by weight in the case of titanium dioxide having an average particle size of 0.3 μm. The film can also be made opaque by intentionally adjusting the content of the lubricant. For example, titanium dioxide 5
A white film can be obtained by adding -20% by weight, preferably 10-15% by weight.

The polyester film of the present invention comprises the above-mentioned copolymerized polyester mainly composed of polyethylene terephthalate, and polybutylene terephthalate or a copolymerized polyester mainly composed of polybutylene terephthalate in predetermined amounts, and melt-extruded to obtain a film. It can be manufactured by molding into a shape, biaxial stretching and heat setting. At this time, the above-mentioned lubricant, for example, a spherical monodispersed lubricant, is contained in either or both of a copolymerized polyester mainly composed of polyethylene terephthalate and polybutylene terephthalate or a copolymerized polyester mainly composed of polybutylene terephthalate, at the time of polymerization. Alternatively, they may be added or mixed at the time of melt extrusion.

The polyester film of the present invention is obtained by melting the above-mentioned lubricant-containing polyester, discharging it from a die to form a film, biaxially stretching and heat-setting.
And this film needs to satisfy the following requirements (1), (2) and (3).

(1) The refractive index in the thickness direction of the film is 1.
It is 505 or more and 1.545 or less, preferably more than 1.510 and 1.540 or less, and more preferably more than 1.510 and 1.530 or less. If the refractive index is less than 1.505, the moldability becomes insufficient, while if it exceeds 1.545 (that is, if the orientation is excessively low), the structure is close to amorphous, resulting in heat resistance. Will be insufficient.

(2) The refractive index in the film surface direction is 1.61 or more and 1.66 or less in all directions, preferably 1.61.
It is within the range of 5 or more and 1.655 or less. In deep drawing and drawing-ironing, which are often used in can making, the deformation must be uniform in all directions, and any part of the film must be able to follow this deformation. In the direction where the film surface refractive index is less than 1.61, the moldability is good, but the heat resistance is poor, while the refractive index is 1.
In the direction exceeding 66, the whiteness and breakage of the film occur during deep drawing due to poor moldability. In addition,
The refractive indices in the film thickness direction and the surface direction are measured as follows.

A polarizing plate analyzer is attached to the eyepiece side of the Abbe refractometer, and the refractive index of each is measured with a monochromatic NaD ray. Methylene iodide was used as the mount solution, and the measurement temperature was 25 ° C.

For the measurement of the refractive index in the thickness direction and the refractive index in the plane direction, the total width of the film when the film is opened after the heat setting is set to 1, and the film is set to the center of the stretching by 0.8 times the width. This is done for the end part when cut out symmetrically.

(3) DSC sub-peak is 150-
The temperature is 205 ° C, preferably 155 to 200 ° C, more preferably 160 to 195 ° C. This sub-peak contributes to the stability of the film quality after heat-lamination on a metal plate, and when this sub-peak is less than 150 ° C, the bottom of the can becomes brittle when the heat-lamination temperature with the metal plate is increased, while the heat-lamination temperature is increased. If it is lowered, the film will break during processing, and a good can cannot be produced by adjusting the heating laminating temperature. On the other hand, if the sub-peak exceeds 205 ° C., the film breaks during can making at any heating laminating temperature, making it impossible to make a can.

The sub-peak temperature is measured by the same method and conditions as the melting point of polyester. That is, Du P
Ont Instruments 910 DSC, heating rate 20
Determine subpeaks in ° C / min. Film sample is about 2
Set to 0 mg. The relationship between the subpeak and the melting point can be understood from FIG. 1, for example.

To obtain the film characteristics of the present invention,
In the biaxial stretching process, the longitudinal stretching ratio is 2.5 to 3.6 times and the transverse stretching ratio is 2.7 to 3.6 times in the biaxial stretching process.
Stretching heat treatment may be performed at a heat setting temperature of 150 to 230 ° C. More preferably, among these conditions, the refractive index in the thickness direction is 1.505 or more and 1.545 or less, the refractive index distribution of the film surface is 1.61 or more and 1.66 or less, and the DSC sub-peak is 150 to 150. It is advisable to carry out the biaxially stretching heat-setting treatment by finding the condition of 205 ° C. Particularly in order to control the refractive index distribution (maximum and minimum values of refractive index), JP-A-58-160122 and JP-A-59-160122
The methods described in JP-A-115812 and JP-A-59-114028 may be used, or the method described below may be used.

The polyester is melt extruded into a sheet and rapidly cooled to prepare an unstretched film, which is heated by roll heating, infrared heating or the like and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed of two or more rolls. The stretching temperature is higher than the glass transition point (Tg) of polyester, and further 20 to 40 from Tg.
It is preferable that the temperature is higher by ℃. The stretching ratio depends on the final film characteristics, but is preferably 2.5 times or more. This magnification is preferably 3.6 times or less.

The longitudinally stretched film is subsequently subjected to transverse stretching, heat setting and heat relaxation to obtain a biaxially oriented film, which is carried out while the film is running. The transverse stretching process is 2 from the glass transition point (Tg) of polyester.
Start with temperatures above 0 ° C. Then, the temperature is raised to a temperature (120 to 30) ° C. lower than the melting point (Tm) of the polyester. The stretching start temperature is preferably (Tg + 40) ° C. or lower. The maximum stretching temperature is preferably (100 to 40) ° C. lower than Tm.

The temperature rise in the transverse stretching process may be continuous or stepwise (sequential). Usually, the temperature is raised sequentially. For example, the transverse stretching zone of the stenter is divided into a plurality of zones along the film running direction, and a heating medium having a predetermined temperature is flown in each zone to raise the temperature. If the transverse stretching start temperature is too low, the film may break, which is not preferable. Also, the maximum drawing temperature is (Tm
If it is lower than -120) ° C, the heat absorption of the film will increase,
In addition, the ratio of physical property uniformity in the width direction becomes small, which is not preferable. On the other hand, if the maximum stretching temperature is higher than (Tm-30) ° C, the film becomes soft and the film is torn due to disturbance or the like, which is not preferable.

The transverse stretching ratio depends on the physical properties of the final film, but is preferably 2.7 times or more, more preferably 3.0 times or more. This magnification is preferably 3.6 times or less.

The heat-setting treatment is carried out subsequent to the transverse stretching, but it starts from the temperature at the end of the transverse stretching. Then, while stretching the film in the width direction by 2 to 20%, (Tm-20)
The temperature is raised to a temperature of ℃ or below. This extension is usually called toe-out, and is preferably 5 to 15
%. The difference between the temperature at the end of heat setting and the temperature at the start of heat setting is preferably 40 ° C or lower, more preferably 30 ° C or lower. The temperature difference may be 1 ° C in some cases,
The temperature is preferably 5 ° C or higher, more preferably 10 ° C or higher. If the extension in heat setting is less than 5%, the isotropic region in the film width direction becomes small, which is not preferable. On the other hand, if the extension is larger than 20%, not only the heat absorption in the lateral direction is significantly increased, but also the film is easily broken, which is not preferable.

The heat-fixed film is once cooled to a temperature not higher than the glass transition point (Tg) of polyester, the film edge is slit with a predetermined width, separated, and then subjected to heat relaxation treatment if necessary. ..

The thermal relaxation treatment does not restrain the film width direction,
Moreover, under a low running tension of 4 to 10 kg / cm ² , (Tg + 3
It is performed at a temperature of 0) to (Tg + 80) ° C. for 0.3 to 20 seconds. The thickness of the film used for this heat relaxation treatment is 6 to 75.
μm, more preferably 10 to 75 μm. The width of the film is preferably 1 m or more. The heat relaxation treatment is preferably performed by using a heating levitation treatment device. A heated inert gas, particularly heated air, is preferably used as a medium for heating and floating the film. According to this heating floating process, the thermal relaxation process can be efficiently performed while maintaining stable film running.

The object of the present invention is to obtain the above-mentioned polymer composition,
It is achieved only after all five requirements of the lubricant, the refractive index in the thickness direction, the refractive index distribution, and the sub-peak temperature by DSC are satisfied. For example, in polyethylene terephthalate homopolymer, the lubricant, the refractive index in the thickness direction, and the refractive index are obtained. Even if the distribution and DSC sub-peak temperature requirements are satisfied, good can-making processability (deep drawability) is not obtained, and if the average particle size of the lubricant exceeds 2.5 μm, the other four requirements are satisfied. However, it causes pinholes and causes troubles. Moreover, the sub peak temperature by DSC is 150 to 2
If it is not within the range of 05 ° C, good can quality cannot be obtained even if the other four requirements are satisfied.

The polyester film of the present invention preferably has a thickness of 6 to 75 μm. 10-75 μm,
It is particularly preferably 15 to 50 μm. Thickness is 6μ
If it is less than m, tearing tends to occur during processing, while 75
Those exceeding μm are uneconomical because of excessive quality.

As the metal plate for can making to which the polyester film of the present invention is laminated, a plate made of tin plate, tin-free steel, aluminum or the like is suitable. The polyester film can be attached to the metal plate by the following method, for example.

The metal plate is heated to a temperature above the melting point of the film, the films are pasted together and then rapidly cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is made amorphous and adhered.

The film is preliminarily coated with an adhesive layer as a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

[0047]

EXAMPLES The present invention will be further described with reference to the following examples.

[0048]

Examples 1 to 6 and Comparative Examples 1 to 8 Average particle size 1.5 μm
0.1% by weight of spherical monodisperse silica (particle size ratio 1.07, relative standard deviation 0.1) was added and copolymerized polyester mainly composed of polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 , PET copolyester) and polybutylene terephthalate (hereinafter PB
T) or a copolymerized polyester mainly composed of polybutylene terephthalate obtained by copolymerizing the components shown in Table 1 (hereinafter abbreviated as PBT copolymerized polyester) at a ratio shown in Table 1 and mixed at 280 ° C. It was melt extruded and rapidly solidified to obtain an unstretched film.

Next, this unstretched film was longitudinally stretched and laterally stretched under the conditions shown in the table, and subsequently heat-set to a thickness of 2
A 5 μm biaxially oriented film was obtained.

[0050]

[Table 1] Table 2 shows the refractive index in the thickness direction of the film, the refractive index in the film surface direction, and the DSC sub-peaks.

[0051]

[Table 2]

[0052]

Example 7 and Comparative Example 9 The lubricants shown in Table 3 in Example 5 were used, and the other conditions were the same as in Example 5,
A biaxially oriented film was obtained.

[0053]

[Table 3]

Table 4 shows the refractive index in the thickness direction, the refractive index in the film plane direction, and the sub-peak by DSC of the obtained biaxially oriented film.

[0055]

[Table 4]

[0056]

Comparative Examples 10 and 11 In Example 5, the heat setting temperature was set to 1
A biaxially oriented film was obtained in the same manner as in Example 5 except that the temperatures were changed to 45 ° C. (Comparative Example 10) and 210 ° C. (Comparative Example 11).

Table 5 shows the refractive index in the thickness direction, the refractive index in the film plane direction, and the DSC subpeaks of the obtained biaxially oriented film.

[0058]

[Table 5]

A total of 18 kinds of films obtained in Examples 1 to 7 and Comparative Examples 1 to 11 were laminated on both sides of a 0.25 mm thick tin-free steel heated to 230 ° C., and water-cooled to 150 mm. It was cut into a disk shape having a diameter, and deep drawing was performed in four steps using a drawing die and a punch to prepare a side surface seamless container (hereinafter, abbreviated as a can) having a diameter of 55 mm.

The following observations and tests were carried out on this can, and each was evaluated according to the following criteria.

(1) Lamination suitability ○: Laminateable without wrinkling Δ: Significant width shrinkage during laminating ×: Wrinkling during laminating

(2) Deep drawing workability-1 ○: The inner and outer surfaces of the film were processed without any abnormalities, and no whitening or breakage was observed in the film on the inner and outer surfaces of the can. Δ: Whitening was observed on the upper part of the film on the inner and outer surfaces of the can. Permitted: Film rupture is observed in part of the film inside and outside the can.

(3) Deep drawing workability-2 ○: Both the inner and outer surfaces were processed without any abnormality, and the rust prevention test of the film surface inside the can (1% NaCl water was put in the can, the electrode was inserted, and the can body was The current value is measured when a voltage of 6 V is applied as an anode, which is 0.1 mA in the ERV test.
Shown below: There is no abnormality in the film on both the inner and outer surfaces, but the current value is 0.1 mA or more in the ERV test, and pinhole-like cracks originating from the coarse lubricant are observed in the film when the energized portion is observed under magnification.

(4) Impact cracking resistance With respect to cans with good deep drawing, water was fully poured, and 10 pieces for each test were dropped from a height of 10 cm onto the PVC tile floor surface, and then the ERV test in the cans. As a result, ◯: 0.1 mA or less for all 10 pieces Δ: 0.1 mA or more for 1 to 5 pieces ×: 0.1 mA or more for 6 or more pieces, or already after dropping Film cracks were observed

(5) Heat embrittlement resistance After the cans that had been well-formed by deep drawing were heated and held at 200 ° C. for 5 minutes, the impact crack resistance evaluation described in (4) was performed. It was 0.1 mA or less for 10 pieces. Δ: 0.1 mA or more for 1 to 5 pieces: 0.1 mA or more for 6 pieces or more, or after heating at 200 ° C for 5 minutes. Cracks were found

Table 6 shows the evaluation results of the above five types.

[0067]

[Table 6]

From the results shown in Table 6, it can be seen that the films of Examples have excellent laminating suitability, deep drawability, impact crack resistance, and heat resistance.

[0069]

EFFECT OF THE INVENTION The polyester film for laminating metal sheets of the present invention is suitable for laminating and deep drawing when forming a metal can by laminating with a metal plate and thereafter forming a can, for example, deep drawing. It has excellent impact resistance and heat resistance after can making, and is extremely useful for metal containers.

[Brief description of drawings]

FIG. 1 is a DSC measurement chart of a film, showing a sub peak and a melting point peak.

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Claims (1)

[Claims] 1. A copolymerized polyester 99, which is mainly composed of polyethylene terephthalate and has a melting point of 210 to 245 ° C.
60% by weight, and polybutylene terephthalate or a polybutylene terephthalate-based melting point of 180 to 22
Consisting of 1-40% by weight of copolyester at 3 ° C,
The film contains a lubricant having an average particle diameter of 2.5 μm or less, the film thickness direction refractive index is 1.505 to 1.545, and the film surface direction refractive index is 1.61 to 1.45 in all directions.
66 and the DSC sub-peak is 150 to 2
A polyester film for laminating metal plates, which has a temperature of 05 ° C.