JPH10324754A - Biaxially oriented polyester film for container molding - Google Patents

Abstract

(57) [Summary] [Constitution] The melting point of ethylene terephthalate and / or polyethylene naphthalate as a main component is 2
The mixing ratio of polyester A having a temperature of 46 ° C. or higher and polyester B having a melting point of 245 ° C. or lower is 99: 1 to 70:30 by weight.
A biaxially stretched polyester film for forming a container. [Effect] The biaxially stretched polyester film for container molding of the present invention not only has excellent moldability and impact resistance when molded into a can or the like, but also has excellent taste characteristics, particularly, excellent characteristics after retort. A container having, and manufactured by molding,
In particular, it can be suitably used for metal cans.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biaxially oriented polyester film for forming a container. More specifically, the present invention relates to a biaxially stretched polyester film having excellent moldability, impact resistance, and taste characteristics, which is excellent in moldability, and is particularly suitable for metal cans.

[0002]

2. Description of the Related Art Conventionally, the inner and outer surfaces of metal cans are coated with various thermosetting resins, such as epoxy and phenol, dissolved or dispersed in a solvent for the purpose of preventing corrosion. Has been widely practiced. However, such a method of coating the thermosetting resin requires a long time for drying the paint, and has unfavorable problems such as a decrease in productivity and environmental pollution due to a large amount of an organic solvent.

As a method of solving these problems, there is a method of laminating a film on a steel plate, an aluminum plate, or a metal plate obtained by subjecting the metal plate to various surface treatments such as plating, which is a material of a metal can. When a metal can is manufactured by drawing or ironing a laminated metal plate of a film, the film is required to have the following characteristics.

(1) It has excellent adhesion to a metal plate.

(2) It is excellent in moldability and does not cause defects such as pinholes after molding.

(3) The polyester film does not peel off, crack or pinhole due to impact on the metal can. (4) The scent component of the contents of the can adsorbs to the film,
The flavor of the contents is not degraded by the eluate from the film (hereinafter referred to as taste characteristics).

Many proposals have been made to solve these requirements. For example, JP-A-64-22530 discloses a polyester film having a specific density and plane orientation coefficient, and JP-A-2-57339 discloses a polyester film having a specific density. Is a copolyester film having a specific crystallinity;
JP-A-895-895, JP-A-6-107815 and the like disclose polyester films containing specific particles.
JP-A-156356 discloses a film obtained by laminating layers obtained by blending polyesters having different melting points on a copolymerized polyester film. However, these proposals do not comprehensively satisfy the above-described various required characteristics, and particularly require not only high moldability and impact resistance, but also excellent taste characteristics after retort treatment. In some applications, it was not at a satisfactory level.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and is excellent in moldability, heat resistance and taste characteristics, and particularly excellent in taste characteristics produced by molding. To provide a biaxially oriented polyester film for forming a container suitable for a metal can.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyethylene terephthalate and / or polyethylene naphthalate having a melting point of 24%.
This is achieved by a biaxially stretched polyester film for container molding, in which polyester A having a temperature of 6 ° C. or more and polyester B having a melting point of 245 ° C. or less are mixed at a weight ratio of 99: 1 to 70:30.

[0010] The present invention has been made under the scrutiny of a specific structure,
It has been found that by blending a polyester having a melting point with a polyester having a low melting point, a film having not only excellent moldability and impact resistance but also excellent taste characteristics can be obtained, especially after retorting.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, ethylene terephthalate and / or ethylene naphthalate are used as main components in terms of improving taste characteristics after retort and improving moldability in a can-making process. It is necessary to use polyester A. Polyester A has a melting point of 24
It is necessary that the temperature be 6 ° C. or higher from the viewpoint of taste characteristics and impact resistance, and preferably the melting point is 248 to 280 ° C., more preferably 250 to 275 ° C. Further, from the viewpoint of impact resistance and taste characteristics, the ethylene terephthalate: ethylene naphthalate ratio is preferably from 50:50 to 100: 0 by weight.

The melting point of polyester B is required to be 245 ° C. or less from the viewpoint of moldability, and preferably 200
C. to 245C, more preferably 200C to 243C. As polyester B having a melting point of 245 ° C. or less,
There is no particular limitation. For example, polyethylene terephthalate, polypropylene terephthalate, polyethylene isophthalate, polycyclohexylene dimethylene terephthalate, polyethylene naphthalate, polyethylene-1,2-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, etc. are used as main components. Specifically, it is preferable in terms of moldability that 70% by weight or more of the constituent components of the polyester B is the above component. Among them, it is preferable to use polyethylene terephthalate and polyethylene naphthalate as main components from the viewpoint of impact resistance and taste characteristics. Further, from the viewpoint of impact resistance, the glass transition temperature of the polyester B is preferably 50 ° C. or lower, more preferably 40 ° C. or lower. Further, it is preferable not to contain butanediol as a glycol component from the viewpoint of improving taste characteristics.

Polyester B includes diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-
Sodium sulfoisophthalic acid, isophthalic acid, phthalic acid, aromatic dicarboxylic acids such as 4,4-diphenyldicarboxylic acid and ester-forming derivatives thereof, oxalic acid,
Aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid and fumaric acid; alicyclic dicarboxylic acids such as cyclohexyne dicarboxylic acid; oxycarboxylic acids such as p-oxybenzoic acid; be able to. On the other hand, examples of the glycol component include aliphatic glycols such as propanediol, pentanediol, hexanediol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, bisphenol A, and the like. Bisphenol S, aromatic glycols such as resorcinol, polyethylene glycol, diethylene glycol,
Dioxy compounds such as hexamethylene glycol and polypropylene glycol, oxycarboxylic acids such as p- (β-oxyethoxy) benzoic acid, and ester-forming derivatives thereof can be copolymerized. Among them, dimer acid is preferred from the viewpoint of moldability and impact resistance.

When the polyester B is amorphous, the melting point may be determined by the Vicat softening temperature (ASTM D1525).

Further, it is preferable that the heat of crystal fusion of the polyester B is not more than 20 J / g because not only the adhesion to the steel sheet is excellent but also the moldability is good. It is more preferably 0 to 10 J / g, particularly preferably 0 to 5 J / g. As a method therefor, a method of copolymerizing 10 mol% or more and a method of reducing the metal component as much as possible are used.

In the present invention, in order to achieve both impact resistance and taste characteristics, it is necessary that the mixing ratio of polyester A and polyester B is 99: 1 to 70:30 by weight. Further, it is preferably from 94: 6 to 70:30.

Further, from the viewpoint of taste characteristics and adhesion to a steel sheet, the amount of carboxylic acid end groups in the film is preferably from 32 to 48 equivalents / ton, more preferably from 32 to 46 equivalents / ton, especially from 35 to 44 equivalents / ton. It is preferably equivalent / ton.
Preferably, a method of controlling the temperature and time during melt polymerization or reducing the residence time during extrusion is used.

As a blending method, specifically, from the viewpoint of taste characteristics, the kneading temperature is preferably set to a melting point of polyester A + 30 ° C. or lower, and more preferably to a melting point + 25 ° C. or lower.
In particular, kneading in a high vacuum state is preferred from the viewpoint of suppressing thermal decomposition. The kneading time is preferably within 20 minutes from the viewpoint of suppressing thermal decomposition. The kneading device may be either a twin screw or a single screw, but it is preferable to use a twin screw kneader from the viewpoint of uniformity of the polymer.

In terms of long-term stability, one of the films
The oxygen permeability in terms of 00 μm is 17 ml · mm / (m ² ·
d · MPa) or less. More preferably, the oxygen permeability is 15 ml · mm / (m ² · d · MPa)
It is as follows. Such a low oxygen permeability is preferable because not only the corrosion resistance is improved, but also the long-term stability of the taste of the beverage is improved.

The refractive index in the thickness direction of such a film composed of polyester A and polyester B is preferably 1.5 to 1.6 from the viewpoint of moldability and laminability, and more preferably 1.51 to 1.6. ~ 1.6, especially 1.52
It is preferably from 1.6 to 1.6. As the method, a method of lowering the stretching ratio, increasing the stretching temperature, or decreasing the heat treatment temperature is employed.

The heat of crystal fusion of the entire film is 25 J / g
It is preferable if it is above because the heat resistance becomes good and the corrosion resistance after aging becomes particularly good. Further, it is particularly preferable that the content be 30 J / g or less. Preferably, means for suppressing the transesterification reaction between the polyester A and the polyester B is preferably used, and shortening of the melt extrusion time, reduction of the carboxylic acid terminal group, and the like are employed.

In terms of thermal characteristics, one of the DSC subpeaks derived from the heat treatment temperature of the film is preferably 220 ° C. or less from the viewpoints of moldability and laminability.
Further, the temperature is preferably 200 ° C. or lower.

The lubricant particles in the present invention are not particularly limited in terms of composition regardless of whether they are organic or inorganic. However, when formed into a film, the shape of projections, abrasion resistance, workability,
From the viewpoint of taste characteristics, etc., the volume average particle size is 0.01 to 5.0 μm.
It is particularly preferable that the thickness be 0.05 to 3.0 μm. In addition, from the viewpoint of the shape of the protrusions when formed into a film, abrasion resistance, and the like, the ratio of the major axis to the minor axis is preferably from 1.0 to 1.2, and particularly preferably from 1.0 to 1.2.
It is preferably 1.15.

In order to sufficiently exhibit these effects, the particles are preferably contained in an amount of 0.01 to 40% by weight, more preferably 0.05 to 30% by weight.

Specifically, examples of the inorganic particles include wet and dry silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay and the like. Preferred are wet silica, aluminum silicate, titanium oxide and the like from the viewpoints of properties, winding properties, affinity with polyester and the like.

As the organic particles, various organic polymer particles can be used, and any kind of particles may be used as long as the particles are at least partially insoluble in the polyester. Further, as a material of such particles, polyimide, polyamide imide,
Various materials such as polymethyl methacrylate, formaldehyde resin, phenol resin, cross-linked polystyrene, and silicone resin can be used, but vinyl-based cross-linked polymer particles having high heat resistance and easy to obtain uniform particle size distribution particles Is particularly preferred.

In producing the polyester of the present invention,
Conventionally known reaction catalysts and coloring inhibitors can be used. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, and titanium. Examples of the coloring inhibitor such as a compound include a phosphorus compound. Preferably, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at any stage before the production of the polyester is usually completed. As such a method, for example, when a germanium compound is taken as an example, a method of adding a germanium compound powder as it is, or, as described in JP-B-54-22234, glyco- And a method in which a germanium compound is dissolved and added to the toluene component. As the germanium compound, for example, germanium dioxide, germanium hydroxide containing crystal water, or germanium alkoxide compounds such as germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium ethylene glycoloxide, germanium phenolate, germanium β- Examples include germanium phenoxide compounds such as naphtholate, phosphorus-containing germanium compounds such as germanium phosphate and germanium phosphite, and germanium acetate. Among them, germanium dioxide is preferable. Examples of the antimony compound include, but are not particularly limited to, antimony oxides such as antimony trioxide, and antimony acetate. The titanium compound is not particularly limited, but an alkyl titanate compound such as tetraethyl titanate and tetrabutyl titanate is preferably used.

For example, a case where germanium dioxide is added as a germanium compound when producing polyethylene terephthalate will be described. The terephthalic acid component and the ethylene glycol are subjected to a transesterification or esterification reaction, and then a germanium dioxide and a phosphorus compound are added, followed by a polycondensation reaction under a high temperature and a reduced pressure until a constant diethylene glycol content is obtained. Get united. Further, preferably, the obtained polymer is subjected to a solid-phase polymerization reaction under reduced pressure or an inert gas atmosphere at a temperature equal to or lower than its melting point to reduce the content of acetoadheride to obtain a predetermined intrinsic viscosity and a carboxyl end group. And the like.

The polyester in the present invention preferably has a diethylene glycol content of 0.01 to 5% by weight,
More preferably, the content is 0.01 to 3% by weight, particularly preferably 0.01 to 2% by weight,
It is desirable to maintain good impact resistance even when subjected to many heat histories such as retort treatment after can making. This means that
It is considered that the oxidative decomposition resistance at 00 ° C. or higher is improved, and a known antioxidant is added in an amount of 0.0001 to 1% by weight.
It may be added. Further, diethylene glycol may be added during the production of the polymer as long as the properties are not impaired.

The biaxially stretched film in the present invention has a single layer,
Any of the laminations can be used. A layer containing polyester A and polyester B (hereinafter referred to as (I) layer) is added to another layer (hereinafter referred to as (I
When the (I) layer) is laminated, in the (I) layer / (II) layer / metal plate, the polyester of the (II) layer is not particularly limited, but may contain polyester A and / or polyester B, The melting point is preferably from 200 to 260 ° C.

Particularly in applications where the taste characteristics and moldability are severe, it is preferable that the melting point is lower than that of polyester A and the melting point exceeds 245 ° C. It is more preferably at least 246 ° C, particularly preferably at least 248 ° C.

From the viewpoint of moldability, it is particularly preferable that the melting point is lower by 1 to 40 ° C. than the melting point of polyester A.

In the (II) layer / (I) layer / metal plate, the (II) layer preferably contains ethylene terephthalate and / or ethylene naphthalate as a main component, and 95% by weight or more of ethylene terephthalate and And / or ethylene naphthalate units. The stacking ratio of the (I) layer / (II) layer is 1/3
It is preferably 0 to 30/1, particularly preferably 1 to 30.
/ 20 to 20/1. Also, three layers such as (I) layer / (II) layer / (I) layer and (II) layer / (I) layer / (II) layer may be laminated. When the (II) layer is laminated on at least one of the outermost layers, the (II) layer is preferably made of polyethylene terephthalate from the viewpoint of moldability and taste characteristics, and from the viewpoint of taste characteristics and impact resistance. Preference is given to polyethylene naphthalate.

The thickness of the biaxially stretched film of the present invention is preferably 3 to 50 μm, more preferably 3 to 50 μm, in view of moldability after lamination on metal, coatability to metal, impact resistance and taste characteristics. Is 8 to 30 μm.

The method for producing a biaxially stretched film in the present invention is not particularly limited. For example, after drying polyester as required, it is supplied to a known melt extruder.
The sheet is extruded into a sheet form from a slit-shaped die, brought into close contact with a casting drum by a method such as electrostatic application, and cooled and solidified to obtain an unstretched sheet. The unstretched sheet is stretched in the longitudinal direction and width direction of the film and heat-treated to obtain a film having a desired refractive index in the thickness direction. Preferably, a tenter method is preferable in terms of film quality.After stretching in the longitudinal direction, a sequential biaxial stretching method in which the film is stretched in the width direction, a simultaneous biaxial stretching method in which the film is stretched almost simultaneously in the longitudinal direction and the width direction. Is desirable. The stretching ratio is 1.5 to 4.0 times, preferably 1.8 to 3.5 times in each direction. Either the stretching ratio in the longitudinal direction or the stretching ratio in the width direction may be increased, and may be the same. The stretching speed is 100
0% / min to 200000% / min is desirable,
The stretching temperature may be any temperature as long as it is equal to or higher than the glass transition temperature of the polyester and equal to or lower than the glass transition temperature + 80 ° C, but is preferably the glass transition temperature + 20 ° C to 60 ° C.
After the biaxial stretching, the film is subjected to a heat treatment. This heat treatment can be carried out by any conventionally known method, such as in an oven or on a heated roll. Heat treatment temperature is 120
The temperature can be set to an arbitrary temperature of not lower than 250 ° C. and preferably 150 to 240 ° C. The heat treatment time can be arbitrarily set, but is preferably 0.1 to 60 seconds, and more preferably 1 to 20 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction. Further, re-stretching may be performed once or more in each direction, and then heat treatment may be performed.

Further, when used on the inner surface of a can, the center line average roughness R of the surface of the polyester film inside the can is
a is preferably 0.003 to 0.05 μm, more preferably 0.005 to 0.03 μm. Further, the ratio Rt / Ra to the maximum roughness Rt is 4 to 50, preferably 6 to 50.
When it is 40, high-speed can-making properties are improved.

It is preferable to improve the adhesiveness by subjecting the film to a surface treatment such as a corona discharge treatment in order to further improve the characteristics.

Although the metal plate of the present invention is not particularly limited,
From the viewpoint of formability, a metal plate made of iron, aluminum, or the like is preferable. Further, in the case of a metal plate made of iron, an inorganic oxide coating layer on the surface thereof for improving adhesion and corrosion resistance, for example, chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment A chemical conversion treatment coating layer represented by, for example, a chromate treatment or a chromium chromate treatment may be provided. In particular, in terms of chromium metal, 6.5 to chrome
A chromium hydrated oxide of 150 mg / m ² is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gunmetal, brass, etc. may be provided. It is preferable that tin plating has a plating amount of 0.5 to 15 mg / m ² , and nickel or aluminum has a plating amount of 1.8 to 20 g / m ² .

The biaxially stretched polyester film for forming a container of the present invention can be suitably used for coating the inner surface of a two-piece metal can produced by drawing or ironing. Further, it can be preferably used for covering the lid portion of a can because it has good metal adhesion and moldability.

[0040]

The present invention will be described in detail with reference to the following examples. The characteristics were measured and evaluated by the following methods.

(1) Melting point of polyester, heat of crystal fusion Polyester or film was dried, melted and quenched, and then subjected to differential scanning calorimetry (DSC-2 manufactured by Perkin Elmer).
(Type) at a heating rate of 16 ° C./min.

When the polyester B is amorphous, the melting point may be determined by the Vicat softening temperature (ASTM D1525).

(2) Refractive index in the thickness direction of the film: Measured with an Abbe refractometer using sodium D line (wavelength: 589 nm) as a light source.

(3) Measurement and calculation of particle diameter ratio, volume average particle diameter, primary particle diameter, and long diameter / short diameter ratio After blending the particles with polyester and cutting them into ultra-thin pieces having a thickness of 0.2 μm, transmission electron With a microscope, at least 5
Observation and measurement were performed on 00 particles.

(4) Amount of carboxyl terminal group of polyester The polyester was dissolved in o-cresol / chloroform (weight ratio: 7/3) at 90 to 100 ° C for 20 minutes and subjected to potentiometric titration with alkali.

(5) Oxygen Permeability The oxygen permeability was measured with an oxygen permeability meter at 25 ° C. and 0% RH, and was converted per 100 μm thickness.

(6) Formability After laminating a film on a TFS steel sheet (thickness 0.20 mm) heated at a melting point of −20 ° C. to a melting point of + 50 ° C. at a rate of 60 m / min, cooled with hot water at 60 ° C. Two-stage molding with a molding machine (final molding ratio (maximum thickness / minimum thickness) = 1.4, 8)
At a moldable temperature range of 0 to 130 ° C).
Thereafter, the can was heat-treated at an optimum temperature of 200 to 250 ° C. for 30 seconds, and subjected to neck-in processing according to a conventional method. The obtained can was subjected to a retort treatment (treatment with pressurized steam at 120 ° C. for 30 minutes), and a neck portion (see FIG. 1) was observed.
It was determined as follows.

Class A: Almost no change. Class B: A small whitened portion can be seen, but there is no problem. Class C: Whitens, but no problem. Class D: A small darkened portion is observed. Class E: The film was broken.

(7) Impact Resistance A can actually manufactured was filled with 350 g of water and the lid was wound. After that, the container was left at 5 ° C. for 48 hours. When the bottom of the container dropped, the container was dropped from a height of 40 cm at 45 ° with respect to the concrete ground to give an impact. Mask the inner surface with wax and put 1 in the cup
% Saline solution, left for one day, apply a voltage of 6 V to the electrode and the metal can in the saline solution, and read the current value 3 seconds later.
The average value after can measurement was determined.

Class A: less than 0.1 mA Class B: 0.1 mA or more and less than 0.3 mA Class C: 0.3 mA or more and 0.5 mA or less Class D: 0.5 mA or more

(8) Taste Characteristics A can (diameter 6 cm, height 12 cm) is filled with water,
℃ × 30 minutes pressurized steam treatment, cooled to 20 ℃,
After standing for 24 hours, the change in turbidity of the solution was visually evaluated according to the following criteria.

The Class A liquid is not turbid at all. Class B liquid is almost turbid. Class C liquid is slightly cloudy. Class D liquid is cloudy.

Example 1 10 parts by weight of aluminum silicate particles having a volume average particle diameter of 0.2 μm and 90 parts by weight of ethylene glycol were mixed, and the mixture was stirred at room temperature for 2 hours with a dissolver to obtain an ethylene glycol slurry of aluminum silicate particles. I got

After transesterification by adding magnesium acetate and lithium acetate as catalysts to dimethyl terephthalate and ethylene glycol, the reaction product was adjusted to the above-prepared slurry, germanium dioxide as a polymerization catalyst, and phosphoric acid as a heat stabilizer. Was added to carry out a polycondensation reaction to obtain a polyester A.

A transesterification reaction was carried out in the same manner as in polyester A, and a dimer acid was added, followed by a polymerization reaction to obtain polyester B (melting point: 228 ° C., heat of crystal fusion: 32).
J / g).

After sufficiently drying 75% by weight of polyester A and 25% by weight of polyester B, the mixture was kneaded and extruded with a biaxial kneader to obtain a polyester composition for layer (I).

The polyester composition for layer (I) obtained as described above is vacuum-dried at 150 ° C. for 4 hours, supplied to a single screw extruder, discharged from a usual die, and charged with static electricity. It was cooled and solidified by a mirror-surface cooling drum to obtain an unstretched film. This unstretched film is stretched 2.8 times in the longitudinal direction at a temperature of 110 ° C., cooled to 40 ° C., stretched 2.8 times in a width direction at a temperature of 110 ° C., and then relaxed at 205 ° C. 3
% For 5 seconds.

The resulting film had a heat of fusion of 37 J / g.

The resulting film had an oxygen permeability of 19 m
l · mm / (m ² · d · MPa).

Example 2 Polyester A was obtained in the same manner as in Example 1.

As the polyester B, isophthalic acid, terephthalic acid, ethylene glycol, diethylene glycol, resorcinol (molar ratio: 39.4: 4.8: 6.3: 4)
8.4: 1.1, softening temperature 63 ° C, heat of crystal fusion 0 J /
g) was used.

The mixing ratio of the polyester for the layer (I) is 70% by weight of polyester A and 30% by weight of polyester B.
A biaxially stretched film was obtained in the same manner as in Example 1, except for the following.

The resulting film had a heat of crystal fusion of 36 J / g.

The resulting film had an oxygen permeability of 16 m
l · mm / (m ² · d · MPa).

In particular, the moldability was improved, and the corrosion resistance of the neck portion was improved.

Example 3 A polyester composition for layer (I) shown in the table was obtained.

On the other hand, in the same manner as in polyester A of Example 1, polyethylene terephthalate for layer (II) was obtained.

A biaxially stretched film was obtained in the same manner as in Example 1 except that the polyester composition for the layer (I) was laminated on the polyethylene terephthalate for the layer (II).

At this time, the layer (I) was a metal laminate surface. Polyester B had a heat of crystal fusion of 8 J / g, and was particularly excellent in moldability among the A class.

Example 4 A biaxially stretched film was obtained in the same manner as in Example 3 except that the lamination ratio was changed.

At this time, the layer (I) was a metal laminate surface.

Example 5 A biaxially stretched film was obtained in the same manner as in Example 3 except that the amount of the dimer acid added to polyester B and the type of particles were changed.

At this time, the layer (I) was a metal laminate surface.

Example 6 A polyester composition for the (I) layer was obtained in substantially the same manner as in Example 5 except that the mixing ratio of the polyester in the (I) layer and the type of polyester in the (II) layer were changed.

A polyester B was obtained in the same manner as in Example 5. This was used as the polyester composition for the (II) layer.

A biaxially stretched film was obtained in the same manner as in Example 5, except that the lamination ratio and the stretching temperature were changed to 105 ° C. in both the longitudinal and width directions.

At this time, the layer (II) was used as a metal laminate surface.

Example 7 Polyester C for layer (I) was obtained in the same manner as in Example 1 except that polyester A and polyester B were changed to polyethylene terephthalate copolymerized with naphthalenedicarboxylic acid.

A biaxially stretched film was obtained in the same manner as in Example 3 except that polyethylene terephthalate was used as the polyester composition for the (II) layer and the stretching temperature was 115 ° C. in both the longitudinal and width directions.

At this time, the layer (I) was used as a metal laminate surface.

Comparative Example 1 The mixing ratio of polyester A and polyester B was changed.
(II) A biaxially stretched film was obtained in the same manner as in Example 6, except that polyethylene terephthalate copolymerized with isophthalic acid was used as the polyester composition for the layer.

At this time, the layer (II) was used as a metal laminate surface.

Comparative Example 2 The polyester composition for the polyester A, polyester B, and (II) layers was changed to isophthalic acid copolymerized polyethylene terephthalate, the mixing ratio of polyester A and polyester B was changed, and the stretching temperature ratio was changed in the longitudinal direction. A biaxially-stretched film was obtained in the same manner as in Example 6, except that the film was heated at 90 ° C. and 3.5 times in both width directions.

At this time, the layer (I) was used as a metal laminate surface.

The heat of crystal fusion of the film was 11 J / g, and the taste characteristics and moldability after aging deteriorated.

Comparative Example 3 A biaxially stretched film was obtained in the same manner as in Example 1, except that only the polyester composition A was used, the stretching temperature was 95 ° C., and the stretching ratio was 3.4 times in both the longitudinal and width directions. .

At this time, the layer (I) was a metal laminate surface.

Comparative Example 4 In Comparative Example 2, when polyester B was used as isophthalic acid copolymerized PBT, the taste characteristics were particularly deteriorated.

[0089]

[Table 1]

[0090]

[Table 2]

[0091]

[Table 3]

[0092]

[Table 4]

[0093]

[Table 5]

[0094]

[Table 6]

[0095]

[Table 7]

[0096]

[Table 8]

[0097]

[Table 9]

[0098]

[Table 10]

[0099]

[Table 11]

The symbols in the table are as follows. PET: polyethylene terephthalate NDCM: dimethyl naphthalenedicarboxylate DMI: dimethyl isophthalate PBT: polybutylene terephthalate DA: dimer acid

[0101]

The biaxially stretched polyester film for forming a container of the present invention not only has excellent moldability when forming into a can or the like, but also has excellent taste characteristics, particularly excellent taste characteristics after retort. It can be suitably used for metal cans manufactured by molding.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a metal can.

[Explanation of symbols]

 1: Thin wall 2: Neck

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67/00 C08L 67/00 // C08G 63/183 C08G 63/183 63/189 63/189 B29K 67:00 B29L 7:00 9:00

Claims (13)

[Claims] The melting point of ethylene terephthalate and / or ethylene naphthalate as a main component is 2
A biaxially stretched polyester film for container molding, comprising a polyester A having a temperature of 46 ° C. or more and a polyester B having a melting point of 245 ° C. or less mixed at a weight ratio of 99: 1 to 70:30. 2. The biaxially stretched polyester film for forming a container according to claim 1, wherein the polyester B comprises a glycol component other than butanediol. 3. Polyester B has a heat of crystal fusion of 20 J /
g. The biaxially stretched polyester film for forming a container according to claim 1 or 2, wherein 4. An oxygen permeability of 17 ml in terms of 100 μm.
The biaxially stretched polyester film for forming a container according to any one of claims 1 to 3, wherein the thickness is not more than mm / (m ² · d · MPa). 5. The film according to claim 5, wherein the carboxylic acid terminal group is from 32 to
The biaxially stretched polyester film for container molding according to any one of claims 1 to 4, wherein the amount is 48 equivalents / ton. 6. A film having a refractive index in the thickness direction of 1.5 to 1.5.
The biaxially stretched polyester film for forming a container according to any one of claims 1 to 5, which is 1.6. 7. Particles having a volume average particle diameter of 0.01 to 5 μm and a ratio of major axis / minor axis of 1.0 to 1.2 are converted to particles of 0.01 to 4
The biaxially stretched polyester film for forming a container according to any one of claims 1 to 6, which contains 0% by weight. 8. The biaxially stretched polyester for container molding according to claim 1, wherein a polyester in which 95% by weight or more of the structural unit is ethylene terephthalate and / or ethylene naphthalate is laminated on at least one surface. the film. 9. The biaxially stretched polyester film for forming a container according to claim 1, wherein polyethylene terephthalate is laminated on at least one surface. 10. The biaxially stretched polyester film for forming a container according to claim 1, wherein polyethylene naphthalate is laminated on at least one surface. 11. Melting point of polyester A is 1 to 40 ° C.
9. The biaxially stretched polyester film for container molding according to claim 8, wherein a low polyester is laminated on at least one surface. 12. The biaxially stretched polyester film for forming a container according to claim 1, wherein the polyester film is used after being formed by heat lamination on a metal plate. 13. The biaxially stretched polyester film for forming a container according to claim 1, wherein the film has a heat of crystal fusion of 25 J / g or more.