JPH10279708A - Biaxially oriented polyester film for forming container and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject film comprising ester units having terephthalic acid residues and ester units having naphthalene dicarboxylic acid residues, having a specific refractive index in the thickness direction, excellent in moldability, impact resistance and taste characteristics, and suitable for metal cans. SOLUTION: This film is obtained by separately producing polyethylene terephthalate and polyethylene naphthalene, respectively, mixing and kneading the produced polyesters, and subsequently processing the mixture of the polyethylene terephthalate with the polyethylene naphythalate into the film. The obtained film comprises ester units whose 50-99 wt.% have terephthalic acid residues and ester units whose 1-50 wt.% have naphthalene dicarboxylic acid residues, and has a refractive index of 1.5-1.6 in the film thickness direction.

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 has excellent moldability and does not cause defects such as pinholes after molding. (3) The polyester film is peeled off by impact on a 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).

[0005] Many proposals have been made to solve these requirements. For example, Japanese Patent Application Laid-Open No. 64-22530 discloses a polyester film having a specific density and a plane orientation coefficient. 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-331255 discloses a polyester composition and the like obtained by melting and mixing specific amounts of polyethylene terephthalate and polyethylene naphthalate. However, these proposals do not comprehensively satisfy the above-described various required properties, and are particularly required for applications requiring both high moldability, excellent taste characteristics after retort treatment, and particularly low dissolution. It was not at a satisfactory level.

[0006]

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.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is that 50 to 99% by weight of a polyester constituting unit has an ester unit having a terephthalic acid residue, and 1 to 50% by weight has a naphthalenedicarboxylic acid residue. It is an ester unit, and the refractive index in the thickness direction of the film is 1.5 to 1.
6 is achieved by a biaxially stretched polyester film for forming a container.

As a result of intensive studies, the present invention provides not only excellent lamination properties but also excellent moldability during high-speed molding by copolymerizing or blending a specific polymer and highly controlling the film structure. Is also excellent,
In particular, they have found that a film having good taste characteristics can be obtained even after retort.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the polyester composition of a film comprising a polyester containing ethylene terephthalate and ethylene naphthalate as a main component (hereinafter referred to as A layer) has a good taste characteristic after retort. From the viewpoint of improving moldability in the can-making process, 50 to 99% by weight of the polyester component is an ester unit having a terephthalic acid residue, and 1 to 50% by weight is an ester unit having a naphthalenedicarboxylic acid residue. It is necessary to be a certain polyester, and further, from the viewpoint of moldability, the ester unit having a naphthalenedicarboxylic acid residue is 5 to 30% by weight, and the ester unit having a terephthalic acid residue is 70 to 95% by weight. Is preferred. As a method for producing a polyester containing ethylene terephthalate and ethylene naphthalate as main components, even when copolymerized, polyethylene terephthalate and polyethylene naphthalate are each polymerized,
This may be chip-blended with a kneader or the like,
A method of chip blending with a kneader is preferred from the viewpoint of handling properties, thermal characteristics, and the like of the obtained polymer.

Specifically, from the viewpoint of thermal characteristics, the kneading temperature is preferably set to a melting point + 30 ° C. or lower, more preferably a melting point + 25 ° C. or lower. Particularly, kneading in a high vacuum state suppresses thermal decomposition. Is preferred. The kneading time is preferably within one hour 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.

As for the thermal properties of such a polymer, it is preferable that the polymer has one crystal melting peak from the viewpoints of moldability, laminability and impact resistance.

Further, other dicarboxylic acid components and glycol components may be copolymerized as long as taste characteristics are not impaired. Examples of the dicarboxylic acid component include diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxyethane and the like. Aromatic dicarboxylic acids such as dicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid and isophthalic acid;
Oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acids such as fumaric acid,
Alicyclic dicarboxylic acids such as cyclohexine dicarboxylic acid,
Oxycarboxylic acids such as p-oxybenzoic acid and the like can be mentioned. On the other hand, examples of the glycol component include aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentyl glycol, and alicyclic glycols such as cyclohexanedimethanol. And aromatic glycols such as bisphenol A and bisphenol S, diethylene glycol, polyethylene glycol and the like. Incidentally, two or more of these dicarboxylic acid components and glycol components may be used in combination.

In the present invention, the components contained in the polyester in small amounts include diethylene glycol, polyethylene glycol, cyclohexanedimethanol, sebacic acid,
Although there are dimer acids and the like, diethylene glycol, polyethylene glycol and the like are used in applications where taste characteristics are severe.

In particular, it is preferable that a diethylene glycol component is contained in an amount of 1 to 5% by weight from the viewpoint of laminating property, moldability and impact resistance. More preferably, it contains 1.5 to 3% by weight of a diethylene glycol component.

Further, the carboxyl terminal group is preferably 25 to 42 equivalents / ton from the viewpoint of improving taste characteristics and adhesion to a steel sheet after lamination and improving formability. More preferably, it is 30 to 40 equivalents / ton.

The refractive index of the layer A in the thickness direction is required to be 1.5 to 1.6 from the viewpoint of moldability and laminability, and more preferably 1.52 to 1.6. It is preferred that

Further, from the viewpoint of moldability, the thickness is preferably set to 20% or less, particularly preferably 15% or less, and more preferably 10% or less.

In terms of thermal characteristics, one of the DSC peaks (at the time of film formation,
In particular, the endothermic peak related to the temperature during heat treatment) is 220 ° C.
Or less, and more preferably 200 ° C. or less.

The lubricant particles in the present invention are not particularly limited in terms of composition regardless of whether they are organic or inorganic. However, the shape of the protrusions when formed into a film, the abrasion resistance, the adhesion after lamination, and the The volume average particle diameter is preferably from 0.01 to 5.0 μm, particularly preferably from 0.05 to 3.0 μm, from the viewpoints of properties and taste characteristics. Further, from the viewpoints of the shape of the projections when formed into a film, abrasion resistance, and the like, the relative standard deviation shown below is preferably 0.3 or less, and more preferably 0.3 or less.

[0020]

(Equation 2) In order to sufficiently exhibit these effects, the particles are preferably contained in an amount of 0.01 to 5% by weight, and more preferably 0.05 to 3% 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, and clay. Preferred are wet silica, aluminum silicate, calcium carbonate, and the like from the viewpoints of properties, winding characteristics, affinity with polyester, and the like.

Among such inorganic particles, those which react with a polyester and a functional group on the particle surface to form a metal carboxylate are particularly preferred, and specifically, 10 ^-5 mol or more per 1 g of the particles. Is preferred in terms of affinity with polyester, abrasion resistance and the like.
It is preferably at least 10 ^-5 mol.

As the organic particles, various organic polymer particles can be used, and the type of the organic particles is not particularly limited as long as at least a part of the particles is 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.

The main melting peak of the film comprising the polyester A layer is preferably 246 ° C. or higher from the viewpoint of heat resistance, taste characteristics and impact resistance. Further, the temperature is preferably from 250 to 280C from the viewpoint of taste characteristics after retort.

In order to improve the taste characteristics after retorting and to improve the moldability in the can-making process, the polyester A contains at least 80% by weight of an ester unit having a terephthalic acid residue, and the naphthalenedicarboxylic acid residue. It is preferable to laminate a polyester B layer containing 0.1 to 20% by weight of an ester unit having the following formula:

Further, it is preferable that the degree of deformation of the particles contained in the polyester B layer is 1.1 or more from the viewpoint of abrasion resistance during can making.

Here, the degree of deformation of the particles refers to a value obtained by observing at least 100 or more particles with a transmission electron microscope after cutting a cross section in the longitudinal direction of the film into ultra-thin pieces, Aggregates (aggregates) formed at small intervals are regarded as one particle,
The maximum length and the minimum length of each particle present in the film were determined, the ratio was calculated, and the arithmetic average was defined as the degree of deformation.

The main melting peak of polyester B is preferably at least 246 ° C. from the viewpoint of heat resistance, taste characteristics and impact resistance, and more preferably from 250 to 280 from the viewpoint of taste characteristics after retort. C. is preferred.

It is preferable that 90% by weight or more of the constituent components of the polyester B be ethylene terephthalate, and more preferably 97% by weight or more because the taste characteristics are good even when a metal can is filled with a drink for a long time. .

On the other hand, other dicarboxylic acid components and glycol components may be copolymerized as long as taste characteristics are not impaired. Examples of the dicarboxylic acid component include diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxyethane and the like. Aromatic dicarboxylic acids such as dicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid and isophthalic acid;
Oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acids such as fumaric acid,
Alicyclic dicarboxylic acids such as cyclohexine dicarboxylic acid,
Oxycarboxylic acids such as p-oxybenzoic acid and the like can be mentioned. On the other hand, examples of the glycol component include aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentyl glycol, and alicyclic glycols such as cyclohexanedimethanol. And aromatic glycols such as bisphenol A and bisphenol S, diethylene glycol, polyethylene glycol and the like. Incidentally, two or more of these dicarboxylic acid components and glycol components may be used in combination.

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.

In order to improve taste characteristics, the content of acetaldehyde in the film is preferably 27 ppm.
Below, more preferably 23 ppm or less, particularly preferably 18 ppm or less is desirable. The method for lowering the content of acetaldehyde in the film is not particularly limited.For example, in order to remove acetaldehyde generated by thermal decomposition when producing a polyester by a polycondensation reaction or the like, the polyester is reduced in pressure or inert. In a gas atmosphere, a method of heat-treating at a temperature not higher than the melting point of the polyester, preferably a method of subjecting the polyester to solid-state polymerization at a temperature of 150 ° C. or higher and a melting point or lower under reduced pressure or an inert gas atmosphere, using a vented extruder And melt extrusion of the polymer, the extrusion temperature should be within the melting point of the high melting polymer side + 30 ° C., preferably the melting point +2 when the polymer is melt extruded.
A method of extruding at 5 ° C. within a short time, preferably within an average residence time of 1 hour or the like can be mentioned.

In the present invention, the method for producing a polyester containing polyethylene terephthalate and polyethylene naphthalate as main components may be copolymerization or chip blending using a kneader or the like.
From the viewpoints of handling properties, thermal characteristics, and the like, a chip blend is preferred.

As a specific method of chip blending,
Although not limited thereto, for example, polyethylene terephthalate and polyethylene naphthalate were each vacuum-dried at 180 ° C. for 4 hours, and then 93 parts by weight of polyethylene terephthalate and 7 parts by weight of polyethylene naphthalate were uniformly mixed to obtain. A method in which the mixed chips are melt-extruded into a film by a single screw extrusion type melt film forming machine at 280 ° C. and a polymer residence time of 30 minutes, for example, may be mentioned. In addition, in the method of mixing chips, a method of simultaneous feeding using a feeder, a kneading method includes a method of using a twin-screw extrusion type melt film forming machine, a method of manufacturing mixed chips by a kneading machine, and then manufacturing a melt. Examples of the method include a method of forming a film.

The biaxially stretched film in the present invention has a single layer,
Any of the laminations can be used. When laminating, A /
B, A / B / A, or B / A / B may be employed, and particularly preferably A / B, and it is desirable to laminate the A layer on a metal plate. Note that a polyester other than the layer A and the layer B may be laminated.

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, the polyester 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 can 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, particularly preferably the glass transition temperature + 30 ° 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 ℃ or more and 250 ℃
The temperature can be any of the following, preferably 1
50-240 ° 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 30, preferably 10
When it is up to 20, 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. At this time, the E value is 5 to 60, preferably 10 to 50.

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 oriented 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 manufactured 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.

[0042]

The present invention will be described in detail with reference to the following examples. The characteristics were measured and evaluated by the following methods. In addition, the amount of diethylene glycol and the amount of carboxyl terminal groups were determined by a conventional method.

(1) Melting Point of Polyester The polyester was dried, melted, quenched, and measured by a differential scanning calorimeter (DSC-2, manufactured by Perkin Elmer).
The measurement was performed at a heating rate of ° C./min.

(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) Intrinsic viscosity of polyester Polyester is dissolved in orthochlorophenol and
Measured in ° C.

(4) DSC peak (sub-endothermic peak),
Measurement of Crystal Melting Peak The polyester film was measured at a heating rate of 16 ° C./min using a differential scanning calorimeter (DSC-2, manufactured by Perkin Elmer) without any pretreatment.

The crystal melting peak was determined, and when a plurality of peaks were observed, the main melting peak was determined as the peak having the largest heat of fusion.

(5) Measurement of Film Thickness Unevenness A film having a length of 2 m was measured at 10 points at intervals of 20 cm, and calculated by the following equation.

X _AVE = X _TOTAL / n T (%) = | Xn−X _AVE | _MAX / X _AVE × 100 where X _AVE = average thickness (μm) X _TOTAL = total thickness for the number of measurements (μm) n = number of measurements (10 times) T = thickness irregularity _{(%) │Xn-X AVE │} MAX = maximum value of the absolute value of the difference between the average value ([mu] m)

(6) Calculation of volume average particle diameter, number average particle diameter, relative standard deviation σ, degree of particle deformation After cutting the cross section in the longitudinal direction of the film into ultra-thin pieces,
At least 100 or more particles were observed and measured with a transmission electron microscope. The volume average particle diameter and the number average particle diameter were determined by an ordinary method. The formulas for calculating the relative standard deviation σ and the number average particle diameter are as follows.

[0051]

(Equation 3) As for the degree of deformation of the particles, the maximum length of each particle present in the film, assuming that individual particles or aggregates (aggregates) formed at intervals smaller than the primary particle diameter are regarded as one particle,
The minimum length was determined, the ratio was calculated, and the arithmetic mean was defined as the degree of deformation.

(7) Measurement of Metal Carboxylate 100 g of a polymer containing 1% by weight of particles is dissolved in 1 liter of orthochlorophenol (OCP) at 100 ° C. Next, the polymer solution is centrifuged to separate particles. Further, the polymer adhering to the separated particles is dissolved in 100 ml of orthochlorophenol at 100 ° C. and centrifuged. After such an operation is repeated three times, the remaining particles are sufficiently washed with acetone. The thus obtained particles are subjected to Bio-Rad Digila.
FT-IR using FTS60A / 896 manufactured by Company b
Analysis was performed.

(8) Formability After laminating a film on a TFS steel sheet (0.25 mm thick) heated at a melting point of 60 m / min.
After cooling with hot water of 0 ° C, three-stage molding (8
At a moldable temperature range of 0 to 100 ° C).
Thereafter, the formed can was subjected to neck processing according to a conventional method.
The obtained can was subjected to a retort treatment (a treatment with pressurized steam at 120 ° C. for 30 minutes), and a neck portion (see FIG. 1) was observed.

Class A: Almost no change Class B: Small whitened part can be seen but no problem Class C: Whitened but no problem Class D: Small darkened part can be seen Class E: Film is broken Oops

(9) Impact Resistance The cans actually manufactured were heat-treated at 200 ° C. for 30 seconds, and then filled with 350 g of water and capped. After that, the container was left at 35 ° C. for 72 hours. When the bottom of the container dropped, the container was dropped from a height of 30 cm at 45 ° to the concrete ground to give an impact. Mask the inner surface with a wax, put 1% saline in the cup, leave it for one day, apply a voltage of 6V to the electrode and the metal can in the saline, read the current value 3 seconds later, and measure the current after 10 can measurements The average was determined.

Class A: less than 0.3 mA Class B: 0.3 mA or more and less than 0.5 mA Class C: 0.5 mA or more and 1.0 mA or less Class D: 1.0 mA or more

(10) Taste characteristics Fill a can (diameter 6 cm, height 12 cm) with water and
℃ × 30 minutes pressurized steam treatment, cooled to 20 ℃,
After standing for one day, the change in turbidity of the liquid was visually evaluated according to the following criteria.

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

Example 1 A mixture of 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 was stirred with a dissolver at room temperature for 2 hours to obtain an ethylene glycol slurry of aluminum silicate particles. (A) was obtained.

10 parts by weight of calcium carbonate particles having a volume average particle diameter of 0.6 μm and 90 parts by weight of ethylene glycol were stirred with a dissolver at room temperature for 0.5 hour to obtain a slurry (B) of calcium carbonate particles.

After transesterification by adding magnesium acetate and lithium acetate as catalysts to dimethyl terephthalate and ethylene glycol, the slurry (A) previously prepared for the reaction product, germanium dioxide as a polymerization catalyst, and a heat-resistant stabilizer And a polycondensation reaction was performed to obtain polyethylene terephthalate.

On the other hand, in the same manner, polyethylene naphthalate was obtained according to a conventional method.

After each of polyethylene terephthalate and polyethylene naphthalate was dried at 180 ° C. for 3 hours, it was kneaded and extruded with a vent-type biaxial kneader to obtain a polyester composition A for layer A. The polymer physical properties of the polyester composition A were an intrinsic viscosity of 0.65, diethylene glycol of 0.8% by weight, a carboxyl terminal group of 35 equivalents / ton, and a melting point of 247 ° C.

The polyester composition A obtained as described above is vacuum-dried at 170 ° C. for 4 hours, supplied to a single-screw extruder, discharged from a normal die, and applied to a mirror cooling drum while applying static electricity. After cooling and solidification, an unstretched film was obtained.
1. The unstretched film is heated in the longitudinal direction at a temperature of 110 ° C.
After stretching 8 times, cooling to 40 ° C, stretching 2.8 times in the width direction at a temperature of 115 ° C, relaxing 3% at 210 ° C, 5%
Heat treated for seconds. The resulting film had a carboxyl end group of 40 equivalents / ton. The melting point was high and the taste characteristics were particularly excellent.

Example 2 A transesterification reaction was carried out by adding dimethyl terephthalate, dimethyl naphthalenedicarboxylate, ethylene glycol, and a catalyst such as magnesium acetate and lithium acetate, and then the slurry (B) previously prepared was added to the reaction product, A polycondensation reaction is performed by adding germanium dioxide and phosphoric acid as a heat stabilizer, and the polyester composition B for the layer A is added.
I got The polymer physical properties of the polyester composition B were: intrinsic viscosity 0.69, diethylene glycol 0.9% by weight,
Melting point: 247 ° C. A biaxially stretched film was obtained in the same manner as in Example 1 except that the film thickness was changed to 20 μm.
The resulting film had a carboxyl end group of 38 equivalents / ton. In particular, it had excellent taste characteristics.

Example 3 In exactly the same manner as in Example 1, polyethylene terephthalate was obtained. A polyester composition A was obtained in exactly the same manner as in Example 1. A biaxially stretched film was obtained in the same manner as in Example 1 except that the polyethylene terephthalate was laminated on the polyester composition A. The carboxyl end groups of the obtained film were as follows: layer A: 38 equivalents / ton, layer B: 38 equivalents / ton.
Tons. When the layer A was laminated on a steel sheet, it was particularly excellent in formability, impact resistance and taste characteristics.

Example 4 The mixture ratio of polyethylene terephthalate and polyethylene naphthalate was changed, and vacuum drying was performed at 170 ° C. for 4 hours.
A biaxially-stretched film was obtained in exactly the same manner as in Example 1, except that only the single-screw extruder was supplied. Melting point peak 2
And the moldability deteriorated.

Example 5 A biaxially stretched film and a can were obtained in exactly the same manner as in Example 3 except that the mixing ratio of polyethylene terephthalate and polyethylene naphthalate was changed. The carboxyl end groups of the obtained film were as follows: layer A: 44 equivalents / ton, layer B: 38
Equivalent / ton. In particular, it was excellent in moldability, impact resistance and taste characteristics.

Example 6 A biaxially stretched film was obtained in exactly the same manner as in Example 1 except that the stretching ratio was 2.7 times in both the longitudinal and width directions and the stretching temperature in the longitudinal direction was 115 ° C. The thickness unevenness deteriorated, and the moldability decreased.

Example 7 A biaxially stretched film was obtained in exactly the same manner as in Example 5, except that the particle type was changed. The moldability and taste characteristics slightly deteriorated.

Example 8 A biaxially stretched film and a can were obtained in exactly the same manner as in Example 3 except that the mixing ratio of polyethylene terephthalate and polyethylene naphthalate was changed and the heat treatment temperature was 240 ° C. The result was inferior moldability and reduced impact resistance.

Example 9 A biaxially stretched film was obtained in the same manner as in Example 3, except that the mixing ratio between polyethylene terephthalate and polyethylene terephthalate was changed. Moldability was slightly deteriorated in terms of thickness unevenness and melting peak of the raw material.

Example 10 A film was obtained in the same manner as in Example 1 except that the carboxyl terminal group of the film was changed to 45 equivalents / ton. This resulted in slightly reduced taste characteristics.

Example 11 A film was obtained in the same manner as in Example 1 except that the composition of the film was changed, the amount of DEG was 2.0% by weight, the carboxyl terminal group was 40 equivalents / ton, and the heat treatment temperature was changed. As a result, the thickness unevenness was improved and the moldability was excellent.

Example 12 A biaxially stretched film was prepared in exactly the same manner as in Example 3 except that the composition of the layer B was changed (90% by weight of PET and 10% by weight of the polyester of the layer A) and the particle formulation was changed. Obtained. The carboxyl end group of the obtained film was A layer: 3
6 equivalents / ton, layer B: 30 equivalents / ton. In particular, it was excellent in moldability, impact resistance and taste characteristics. Comparative Example 1 Polyester A was made only of polyethylene naphthalate,
A biaxially stretched film was obtained in exactly the same manner as in Example 3 except that the stretching temperature was changed to 135 ° C.

Comparative Example 2 The same procedure as in Example 1 was carried out except that 10 mol% of isophthalic acid copolymerized polyethylene terephthalate was stretched at 90 ° C., the stretching ratio was 3.5 times in the longitudinal and width directions, and the heat treatment temperature was 190 ° C. Thus, a biaxially stretched film was obtained (48 equivalents of carboxyl end groups / ton). As a result, as shown in Table 5, the moldability and taste characteristics were significantly reduced.

[0077]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7] The symbols in the table are as follows: DEG: diethylene glycol PET: polyethylene terephthalate

[0078]

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

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08G63 / 189 C08G63 / 189 C08K 7/16 C08K 7/16 C08L 67/03 C08L 67/03 // B29K 67:00 B29L 7 : 00 C08L 67:02

Claims (14)

[Claims] 1. An ester unit having a terephthalic acid residue in an amount of 50 to 99% by weight of a constituent unit of the polyester;
A biaxially stretched polyester film for container molding, wherein 0% by weight is composed of an ester unit having a naphthalenedicarboxylic acid residue, and has a refractive index in the thickness direction of the film of 1.5 to 1.6. 2. The film has a refractive index in the thickness direction of 1.52.
2. The biaxially stretched polyester film for forming a container according to claim 1, wherein the thickness is from 1.6 to 1.6. 3. The biaxially stretched polyester film for forming a container according to claim 1, wherein the carboxyl terminal group is 25 to 42 equivalents / ton. 4. The biaxially stretched polyester film for forming a container according to claim 1, which contains 1 to 5% by weight of diethylene glycol. 5. The biaxially stretched polyester film for forming a container according to claim 1, wherein one of the peaks of DSC exists at 220 ° C. or lower. 6. A lubricant containing 0.01 to 5% by weight of a lubricant particle having a volume average particle diameter of 0.01 to 5 μm and a relative standard deviation σ represented by the following formula of 0.3 or less. Item 6. The biaxially stretched polyester film for forming a container according to any one of Items 1 to 5. (Equation 1) 7. The biaxially stretched polyester film for forming a container according to claim 6, wherein the surface of the lubricant particles has a metal carboxylate salt in an amount of 10 ^-5 mol or more per 1 g of the lubricant particles. 8. The biaxially stretched polyester film for forming a container according to claim 1, wherein a main melting peak of the polyester film is 246 ° C. or higher. 9. The film according to claim 1, wherein the content of the ester unit having a terephthalic acid residue is 80% by weight or more and the content of the ester unit having a naphthalenedicarboxylic acid residue is 0.1 to 20% by weight. A biaxially stretched polyester film for forming a container obtained by laminating a polyester B layer. 10. The biaxially stretched polyester film for forming a container according to claim 9, wherein the degree of deformation of the particles contained in the polyester B layer is 1.1 or more. 11. Polyester B has a main melting peak of 24.
The biaxially stretched polyester film for container molding according to claim 9, wherein the temperature is 6 ° C. or higher. 12. The biaxially stretched polyester film for forming a container according to claim 1, which is formed after heat lamination on a metal plate. 13. A method for producing polyethylene terephthalate and polyethylene naphthalate separately, followed by kneading,
The method for producing a biaxially stretched polyester film for forming a container according to any one of claims 1 to 12, wherein a mixture of polyethylene terephthalate and polyethylene naphthalate is obtained, and a film is produced from the mixture. 14. A biaxially stretched polyester film for molding a container, wherein the mixture according to claim 13 has one crystal melting peak.