JPH10130405A - Biaxially oriented polyester film for molding container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester film excellent in moldability, heat resistance and taste retention and desirable for producing metallic cans excellent in taste retention after retorting by selecting a biaxially oriented film comprising a composition comprising a specified composition and a crosslinking agent. SOLUTION: This film is made from a polyester composition comprising a polyester comprising at least 95wt.% ethylene terephthalate structural units and/or ethylene naphthalate structural units and 0.01-5wt.% crosslinking agent. It is desirable that the polyester comprises 70-97wt.% ethylene terephthalate units and 3-30wt.% ethylene naphthalate structural units. It is desirable that the crosslinking agent is polyfunctional and is especially a trifunctional one. This film may be used in the form of a single-layer or laminate film. It is desirable that in the laminate film, the amount of the crosslinking agent contained in the laminating layer is below 5wt.% and is smaller than that contained in the layer to be laminated.

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 is not adsorbed on the film, or the flavor of the contents is not impaired 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.
Japanese Patent No. 192442 discloses a polyester film or the like containing a specific amount of a polycarboxylic acid and / or a polyhydric alcohol component. However, these proposals do not comprehensively satisfy the above-described various required characteristics, and can be sufficiently satisfied particularly in applications where both high moldability and excellent taste characteristics after retort treatment are required. I could not say it was on the 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 The object of the present invention is that at least 95% by weight of the structural units of the polyester are ethylene terephthalate units and / or ethylene naphthalate units, and the amount of the crosslinking agent A is 0.1%. 01-5
This is achieved by a biaxially stretched polyester film for forming a container, which is composed of the polyester composition A having a content of 10% by weight.

As a result of intensive studies, the present invention contains not only excellent lamination properties but also high formability during high-speed molding by containing a certain amount of crosslinking agent and controlling the film structure to a high degree. It has been found that a film having excellent taste characteristics can be obtained even after retort.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A film comprising a polyester composition A containing a crosslinking agent A according to the present invention (hereinafter referred to as layer A) is characterized in that, as a constitutional unit of polyester, the taste characteristics after retorting are good. It is preferable to use ethylene terephthalate and / or ethylene naphthalate as a main component in view of improving moldability in a can-making process.

The polyester containing ethylene terephthalate and / or ethylene naphthalate as a main constituent is a polyester containing 95% by weight or more of the polyester containing ethylene terephthalate and / or ethylene naphthalate as a constituent.

In the present invention, in particular, in order to improve the moldability and the taste characteristics, the ethylene terephthalate unit should be 70 to 100% by weight and the ethylene naphthalate unit should be 0 to 30% by weight in the polyester. Is preferred.
In particular, 70 to 97% by weight of ethylene terephthalate unit,
If the ethylene naphthalate unit is 3 to 30% by weight, the moldability, particularly the workability of the upper part of the beverage can called the necking, is improved, which is preferable. Further, when the ethylene naphthalate unit is used in an amount of 1 to 15% by weight and a crosslinking agent is used in combination, processability,
It is preferred because it makes the taste characteristics particularly good.

The cross-linking agent A contained in the layer A includes 0.1.
It must be contained in an amount of from 0.01 to 5% by weight, and 0.01 to 2% by weight in view of polymerization reactivity, film forming stability, moldability and the like.
Is more preferable. Further, it is preferably polyfunctional from the viewpoint of moldability, and more preferably a trifunctional crosslinking agent from the viewpoint of polymerization reactivity, thermal stability and the like.

Examples of the type of the crosslinking agent A include an epoxy crosslinking agent, an isocyanate crosslinking agent, a melamine crosslinking agent, an oxazoline crosslinking agent, a silane coupling agent, trimellitic acid, trimesic acid, and hemi-meritic acid. Acid, pyromellitic acid, prenit acid, dihydroxyterephthalic acid, dihydroxyisophthalic acid, trimethylolethane, trimethylolpropane, trimethylolbutane, trimethylolbenzene, triethylolbenzene, tributyrolbenzene, hexanetriol, tetramethylolcyclohexanol, Pentaerythritol, glycerol and the like are preferable, and among them, trimellitic acid, trimesic acid,
Trimethylolpropane is particularly preferred. These compounds may be used alone or in combination of two or more. On the other hand, other dicarboxylic acid components and glycol components may be copolymerized as long as the taste characteristics are not impaired.Examples of the dicarboxylic acid components include diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodium sulfoisophthalic acid, aromatic dicarboxylic acids such as phthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acids such as fumaric acid, cyclohexyne dicarboxylic acid, etc. Examples thereof include alicyclic dicarboxylic acids and oxycarboxylic acids such as p-oxybenzoic acid. 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 polyester composition A for the layer A
Examples of components contained in small amounts include diethylene glycol, polyethylene glycol, cyclohexane dimethanol, sebacic acid, dimer acid, and the like. For applications with strict taste characteristics, diethylene glycol, polyethylene glycol, and the like are exemplified.

The melting point of the polyester in the layer A is preferably from 246 to 280 ° C. from the viewpoint of moldability and impact resistance, and more preferably from 250 to 280 ° C. from the viewpoint of taste characteristics after retort. It is preferred that

A film comprising a polyester composition B containing a crosslinking agent B in the present invention (hereinafter referred to as layer B)
As a constitutional unit of polyester, ethylene terephthalate and / or ethylene naphthalate may be used as a main component in that taste characteristics after retort are good and moldability in a can making process is good. preferable.

The polyester containing ethylene terephthalate and / or ethylene naphthalate as a main component is a polyester containing 96% by weight or more of the polyester containing ethylene terephthalate and / or ethylene naphthalate as a main component. More preferably 97
When the content is not less than% by weight, the taste characteristics are good even when the beverage is filled into the metal can for a long period of time.

The content of the cross-linking agent B contained in the layer B is preferably less than 5% by weight, and is preferably less than 2% by weight in view of polymerization reactivity, film forming stability, moldability and the like. More preferred. Further, it is preferable that the content relationship with the cross-linking agent A satisfies the following formula in terms of moldability, taste characteristics, and the like.

Content of crosslinker A in layer A (% by weight)> B
Content of cross-linking agent B in layer (% by weight) Examples of the type of cross-linking agent B include those similar to cross-linking agent A. As such a crosslinking agent B, only one kind may be used, or two or more kinds may be used in combination. Further, a crosslinking agent A,
B may use the same crosslinking agent or different crosslinking agents.

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 and phthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid and fumaric acid; cyclohexyne dicarboxylic acid Examples thereof include alicyclic dicarboxylic acids such as acids, and oxycarboxylic acids such as p-oxybenzoic acid. On the other hand, as the glycol component, for example, propanediol,
Butanediol, pentanediol, hexanediol-
And aliphatic glycols such as neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, 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 polyester composition B for the layer B is used.
Examples of components contained in small amounts include diethylene glycol, polyethylene glycol, cyclohexane dimethanol, sebacic acid, dimer acid, and the like. For applications with strict taste characteristics, diethylene glycol, polyethylene glycol, and the like are exemplified.

In the present invention, isophthalic acid may be copolymerized as long as the properties are not significantly impaired. However, from the viewpoints of impact resistance over time and deterioration of taste characteristics, polyesters containing no isophthalic acid may be used. preferable.

Further, various particles may be added as long as the effects of the present invention are not impaired.

Specifically, the inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate,
Examples thereof include barium sulfate, alumina, mica, kaolin, and clay, and among them, aluminum silicate, calcium carbonate, and the like are preferable from the viewpoints of moldability, winding characteristics, and affinity with polyester.

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.

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, the 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.

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.

The biaxially stretched film in the present invention has a single layer,
Any of the laminations can be used. Also, when performing lamination, A
Layer, polyester other than layer B may be laminated,
From the viewpoint of moldability, when laminating to a metal, it is preferable to laminate the layer A on one of the outermost layers to form a laminate surface. From the viewpoint of moldability, taste characteristics after retort, and impact resistance, the other is preferred. It is preferable to laminate the B layer on the outermost layer.

The elongation at break of the biaxially stretched film in the present invention is preferably 130% or more as an average value of elongation at break as shown in the following formula from the viewpoints of moldability, impact resistance after retort, and the like. preferable.

Average value of elongation at break = ( _SMD + _STD ) / 2 where _SMD : elongation at break in longitudinal direction (%) _STD : elongation at break in width direction (%)

The thickness unevenness of the biaxially stretched film in the present invention is preferably less than 30% from the viewpoint of moldability and impact resistance.

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 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 the can, the center line average roughness Ra is preferably 0.003 to 0.05 μm,
More preferably, it is 0.005 to 0.03 μm. Further, when the ratio Rt / Ra to the maximum roughness Rt is 4 to 50, preferably 6 to 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. At this time, the E value is 5 to 60, preferably 10 to 50.

The refractive index in the thickness direction of such a film is preferably 1.50 or more from the viewpoint of laminating properties and moldability.

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.

[0043]

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 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) 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.

(5) Measurement of average value of elongation at break of film A sample having a length of 150 mm and a width of 10 mm was cut out from a biaxially stretched film, and the sample was stretched with an initial length of 50 mm using a tensile tester manufactured by Orientec. Speed 300m
It was pulled under the condition of m / min, and the breaking elongation in each direction was determined from the obtained load-strain curve.

From the obtained elongation at break, the average value of the elongation at break was determined using the following equation.

Average value of elongation at break = ( _SMD + _STD ) / 2 where _SMD : elongation at break in longitudinal direction (%) _STD : elongation at break in width direction (%)

(6) 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 (μm) for the number of measurements n = number of measurements (10 times) T = thickness unevenness (%) | Xn−X _AVE | _MAX = maximum absolute value of difference from average value (μm)

(7) Surface Roughness of Film (Center Line Average Roughness Ra, Maximum Roughness Rt) This was measured using a high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory. The conditions were as follows, and the value was an average value of 20 measurements.

・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measurement length: 1 mm ・ Cutoff value: 0.08 mm Note that Ra and Rt are defined, for example, by Jiro Nara, “Surface roughness measurement”. Measurement and evaluation method ”(General Technology Center, 1983)
Is shown.

(8) Formability After laminating a film on a TFS steel sheet (thickness 0.25 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., and then drawn. Two-stage high-speed molding with a molding machine (final molding ratio (maximum thickness / minimum thickness) = 1.
5, Molding in the moldable temperature range at 80 to 100 ° C)
did. Thereafter, the molded can was rapidly cooled at a melting point of polyester (in the case of a laminated film, the steel plate surface polyester) at −20 ° C., and then water-cooled 10 seconds after, followed by neck-in-flange 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: There is 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.

(9) Impact Resistance After the can actually manufactured was heat-treated at 200 ° C. for 30 seconds, 350 g of water was filled and the can was covered. 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 A can (diameter 6 cm, height 12 cm) is filled with water,
A pressurized steam treatment was performed at 30 ° C. for 30 minutes, and a change in the liquid was visually evaluated after one month at 40 ° C. according to the following criteria.

No change is observed in the Class A liquid. There is almost no change in the Class B liquid. A slight change is seen in the Class C liquid. A change is seen in the class D liquid.

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 at room temperature for 2 hours with a dissolver 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 at room temperature for 0.5 hour with a dissolver to obtain a slurry (B) of calcium carbonate particles.

After transesterification by adding magnesium acetate as a catalyst to dimethyl terephthalate, ethylene glycol, and trimethyl trimellitate, the reaction product was subjected to the previously prepared slurry (A), germanium dioxide as a catalyst, Phosphoric acid was added as a stabilizer and a polycondensation reaction was performed to obtain a polyester composition A for layer A.
The polymer properties of the polyester composition A were as follows: intrinsic viscosity 0.78, diethylene glycol 1.0% by weight, melting point 2
56 ° C.

The polyethylene terephthalate composition obtained as described above was vacuum dried at 170 ° C. for 4 hours.
After being supplied to a single screw extruder and discharged from a normal die, it was cooled and solidified by a mirror-surface cooling drum while applying static electricity 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 115 ° C, and then relaxed at 200 ° C for 3% for 5 seconds. Heat treated.

Example 2 A transesterification reaction was carried out by adding magnesium acetate as a catalyst to dimethyl terephthalate, ethylene glycol and trimethyl trimellitate, and then the reaction product was adjusted to the slurry (B) previously prepared, and to the catalyst germanium dioxide ,
In addition, phosphoric acid was added as a heat stabilizer, and a polycondensation reaction was performed to obtain a polyester composition A for layer A. The polymer physical properties of the polyester composition B were an intrinsic viscosity of 0.78, diethylene glycol 0.9% by weight, and a melting point of 257 ° C. A biaxially stretched film was obtained in the same manner as in Example 1 except that the film thickness was changed to 15 μm. As a result, the refractive index in the thickness direction was slightly low at 1.4899, and the thickness unevenness was large. Therefore, a slight decrease in the characteristics was observed, and in particular, the degree of the moldability was slightly larger than the other characteristics. Was.

Example 3 Except that trimethylolpropane was used as a crosslinking agent,
A biaxially stretched film was obtained in exactly the same manner as in Example 2. As a result, the elongation was reduced and the moldability was reduced, but the film was almost good.

Example 4 Biaxial stretching using isophthalic acid copolymerized PET (isophthalic acid copolymerized amount: 3% by weight) as a polyester species and stretching conditions at a stretching temperature of 95 ° C. and a stretching ratio of 3.0 in both the longitudinal and width directions. A film was obtained. As a result, as shown in Table 1, there was a slight decrease in the characteristics, and the degree of the taste characteristic was much lower than the other characteristics.

Example 5 As a polyester species, polyethylene naphthalate (PE)
A film was obtained in the same manner as in Example 1 except that the stretching conditions were changed to 140 ° C. and the stretching ratio to 2.8 in both the longitudinal and width directions using N). As a result, the moldability was greatly improved, and the taste characteristics were slightly improved.

Example 6 Polymerization was carried out in the same manner as in Example 2 except that no particles were added.
A polyester composition A for a layer was obtained.

Polymerization was carried out in the same manner as in Example 1 except that no crosslinking agent was added to obtain a polyester composition B for layer B.

A biaxially stretched film was obtained in the same manner as in Example 1 except that the polyester composition A was laminated on the polyester composition B, and the stretching was performed at a stretching temperature of 110 ° C. As a result, both moldability, impact resistance, and taste characteristics are improved.
The moldability was greatly improved.

Example 7 A polymer was polymerized so that the amount of ethylene terephthalate units was 88% by weight and the amount of ethylene naphthalate units was 12% by weight. The obtained polymer is subjected to a longitudinal stretching temperature of 120 ° C.
A film was obtained in the same manner as in Example 1 except that the transverse stretching temperature was 123 ° C and the heat treatment temperature was 180 ° C. The resulting film was particularly excellent in moldability, and particularly excellent in neck workability.

Example 8 Polymerization was carried out in the same manner as in Example 1 except that the amount of trimethyl trimellitate added and no particles were added, to obtain a polyester composition B for the B layer.

A film was obtained in the same manner as in Example 1 except that the polyester composition A for layer A obtained in Example 1 was laminated on the polyester composition B and stretched at a stretching temperature of 110 ° C. As a result, the moldability was slightly reduced,
It was a good film.

Comparative Example 1 The stretching temperature was adjusted to 95 without adding trimethyl trimellitate.
A biaxially-stretched film was obtained in the same manner as in Example 1 except that the temperature was set at 3.3 ° C. and the stretching ratio was 3.3 times. As a result, as shown in Table 5, the moldability was greatly reduced.

Comparative Example 2 Polymerization was carried out in the same manner as in Example 1 except that the addition amount of trimethyl trimellitate was 6% by weight. As a result, the polymer gelled violently and the polymer could not be discharged.

COMPARATIVE EXAMPLE 3 16% by weight of a polyester type copolymerized with isophthalic acid PET
And a biaxially stretched film was obtained in the same manner as in Example 1 except that the stretching conditions were changed to a stretching temperature of 90 ° C. and a stretching ratio of 3.3 in both the longitudinal and width directions without adding trimethyl trimellitate. Was. As a result, as shown in Table 6, the moldability, impact resistance, and taste characteristics were all reduced.

[0078]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

The symbols in the table are as follows.

DEG: diethylene glycol PET: polyethylene terephthalate PET / N: naphthalenedicarboxylic acid copolymerized PET TMTM: trimethyl trimellitate TMP: trimethylolpropane

[0081]

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

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Claims (12)

[Claims] (1) at least 95% by weight of the constituent units of the polyester are ethylene terephthalate units and / or ethylene naphthalate units, and 0.01% of the crosslinking agent A is used.
A biaxially stretched polyester film for forming a container, comprising a polyester composition A containing up to 5% by weight. 2. An ethylene terephthalate unit comprising 70 to 97.
The biaxially stretched polyester film for forming a container according to claim 1, wherein the content of ethylene naphthalate is 3 to 30% by weight. 3. The polyester film according to claim 1, wherein 95% by weight or more of the constituent units of the polyester are ethylene terephthalate units and / or ethylene naphthalate units, and the content of the crosslinking agent B is 5%.
A biaxially stretched polyester film for forming a container which is less than 10% by weight and is laminated on a film made of a polyester composition B satisfying the following formula, wherein the content of the crosslinking agents A and B satisfies the following formula Content of crosslinking agent A in polyester composition A (% by weight)
> Content of crosslinker B in polyester composition B (% by weight) 4. The melting point of each of the polyester compositions A and B is 2
The biaxially stretched polyester film for forming a container according to any one of claims 1 to 3, wherein the temperature is 46 to 280 ° C. 5. The polyester compositions A and B having a melting point of 2
The biaxially stretched polyester film for forming a container according to any one of claims 1 to 3, wherein the temperature is 50 to 280 ° C. 6. The biaxially stretched polyester film for forming a container according to claim 1, wherein the crosslinking agent A and / or B is a polyfunctional crosslinking agent. 7. The biaxially stretched polyester film for forming a container according to claim 1, wherein the crosslinking agent A and / or B is a trifunctional crosslinking agent. 8. A center line average roughness Ra of 0.003 to 0.5.
The biaxially stretched polyester film for forming a container according to any one of claims 1 to 7, wherein the ratio Rt / Ra with respect to the maximum roughness Rt is 4 to 50 µm. 9. The film according to claim 1, wherein the average value of the elongation at break of the film represented by the following formula is 130% or more.
The biaxially stretched polyester film for forming a container according to any one of items 1 to 8. Average value of elongation at break = ( _SMD + _STD ) / 2 where _SMD : elongation at break in longitudinal direction (%) _STD : elongation at break in width direction (%) 10. The biaxially stretched polyester film for forming a container according to claim 1, wherein the thickness unevenness is less than 30%. 11. The biaxially oriented polyester film for forming a container according to claim 1, wherein the refractive index in the thickness direction is 1.5 or more. 12. The biaxially stretched polyester film for forming a container according to claim 1, which is formed after heat lamination on a metal plate.