JPH09302113A - Biaxially oriented polyester film for container molding - Google Patents

Abstract

(57) [Summary] [Structure] Biaxially stretched polyester for container molding characterized by having a melting point of 240 to 300 ° C., a carboxyl terminal group of 10 to 50 equivalents / ton, and substantially not containing an isophthalic acid component as an acid component. the film. [Effect] 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 containers manufactured by processing, especially for metal cans.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biaxially stretched polyester film for molding a container. More specifically, the present invention relates to a biaxially stretched polyester film for molding a container which has excellent moldability, impact resistance and taste characteristics and is suitable for a container manufactured by a molding process, particularly a metal can.

[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 which has been subjected to various surface treatments such as plating on the metal plate, which is a material for the 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) Excellent adhesion to a metal plate.

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

(3) The impact of the metal can does not cause the polyester film to peel off, crack, or pinhole.

(4) The scent component of the contents of the can is not adsorbed on the film, and 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, Japanese Patent Application Laid-Open No. 64-22530 discloses a polyester film having a specific density and surface orientation coefficient, and Japanese Patent Application Laid-Open No. 2-57339. Discloses a copolyester film having a specific crystallinity. However, these proposals are not capable of comprehensively satisfying the various required characteristics as described above, and are particularly satisfactory in applications in which both high moldability and excellent taste characteristics after retort treatment are required. I couldn't say I was on level.

[0009]

The object of the present invention is to eliminate 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. Another object of the present invention is to provide a biaxially stretched polyester film for container molding suitable for a metal can.

[0010]

The above-mentioned object of the present invention is to have a melting point of 240 to 300 ° C. and a carboxylic end group of 10
It can be achieved by a biaxially stretched polyester film for container molding, which is characterized by containing ˜50 equivalents / ton and substantially no isophthalic acid component as an acid component.

As a result of extensive studies, the present invention not only excels in laminating property and moldability by controlling the film structure to a high degree without substantially containing an isophthalic acid component, but also has a taste property even after retort. It was found that a good film can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester of the present invention is DSC.
It is necessary for the melting point (melting peak temperature) to be 240 to 300 ° C. in order to improve the laminate properties and the taste characteristics during retort, but the melting point is preferably 245 to 245.
It is desirable that the melting point is 300 ° C, particularly preferably 246 to 300 ° C.

Further, in the present invention, it is necessary that the amount of the carboxyl terminal group of the polyester is 10 to 50 equivalents / ton in order to improve the adhesion to metal and the taste characteristics after retort. Further, the amount of carboxyl end groups of the polyester is 15 to 48 equivalents / ton, particularly preferably 15 to 4
It is preferable that the amount is 5 equivalents / ton because the long-term storage property as a beverage can is excellent.

The polyester in the present invention is required to contain substantially no isophthalic acid component as an acid component, but it has good taste characteristics after retort and suppresses generation of abrasion powder in the can making process. Therefore, it is preferable to use ethylene terephthalate and / or ethylene naphthalate as a main constituent component.

The polyester containing ethylene terephthalate and / or ethylene naphthalate as a main constituent is a polyester containing ethylene terephthalate and / or ethylene naphthalate in an amount of 95% by weight or more. 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. On the other hand, other dicarboxylic acid components may be copolymerized within a range that does not impair the taste characteristics, and as the dicarboxylic acid component, for example, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, aromatic dicarboxylic acids such as phthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, aliphatic dicarboxylic acids such as maleic acid and fumaric acid, and cyclohexyne dicarboxylic acid Examples thereof include alicyclic dicarboxylic acids and oxycarboxylic acids such as p-oxybenzoic acid. On the other hand, as the glycol component, for example, propanediol, butanediol, pentanediol, etc.
And aliphatic glycols such as hexanediol and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as bisphenol A and bisphenol S; diethylene glycol; and polyethylene glycol. . Incidentally, two or more of these dicarboxylic acid components and glycol components may be used in combination.

As long as the effects of the present invention are not impaired, trimellitic acid, trimesic acid, polyester
A polyfunctional compound such as trimethylolpropane may be copolymerized.

In the present invention, the components contained in the polyester in a small amount include diethylene glycol, polyethylene glycol, cyclohexanedimethanol, sebacic acid,
Although there are dimer acids and the like, diethylene glycol, polyethylene glycol and the like can be mentioned for applications with severe taste characteristics.

In the present invention, it is necessary to biaxially stretch the polyester in terms of heat resistance and taste characteristics.
The method of biaxial stretching may be any of simultaneous biaxial stretching and sequential biaxial stretching, but the stretching conditions and heat treatment conditions are specified, and the refractive index in the thickness direction of the film is 1.50 or more. Is preferable in terms of improving laminating properties and draw-forming properties. Furthermore, the thickness direction refractive index is 1.51 or more,
In particular, when it is 1.52 or more, it is possible to control the plane orientation coefficient in a specific range in order to achieve both moldability and impact resistance even when there is some temperature variation during lamination.

The biaxially stretched polyester film according to the present invention has a thickness of 200 to 230 after drawing in the can making process.
The relaxation time of the carbonyl portion in the structural analysis by solid-state high resolution NMR is preferably 270 msec or more from the viewpoint of improving the workability when the neck portion is processed after being subjected to a thermal history of about ° C. More preferably, 280 msec
More preferably, it is 300 msec or more.

Further, in the present invention, the thermal crystallization parameter ΔTcg (temperature rising thermal crystallization temperature-glass transition temperature) of the polyester is 60 from the viewpoint of improving workability when processing the neck portion.
℃ or more and 150 ℃ or less is preferable, particularly preferably 70 ℃
It is above 150 ° C. The method of imparting such thermal crystallinity can be achieved by controlling the catalyst, the molecular weight, and the content of diethylene glycol.

In the present invention, the intrinsic viscosity of the polyester is preferably 0.5 to 1.5, more preferably 0.6 to 1.3, and particularly preferably 0 in terms of moldability, impact resistance and taste characteristics. 7 to 1.2.

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 germanium dioxide and a phosphorus compound are added. 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 an amount of diethylene glycol component 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.

Further, in order to improve the taste characteristics, the content of acetaldehyde in the film is preferably 27 ppm.
The following is more preferable, 23 ppm or less is preferable, and 18 ppm or less is particularly preferable. 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 of the present invention may be either a single layer or a laminated layer. The thickness of the biaxially stretched film of the present invention is preferably from 3 to 50 μm, more preferably from 8 to 50 μm, in terms of moldability after lamination on metal, coatability to metal, impact resistance and taste characteristics. 30 μm.
When used in a laminate, a thermoplastic polymer, a polymer such as a thermosetting polymer may be laminated, polyester, for example, high molecular weight polyethylene terephthalate, isophthalic acid copolymerized polyethylene terephthalate, butanediol, isophthalic acid residue skeleton. Having copolymerized polyethylene terephthalate, further added diethylene glycol,
Copolymerized polyester or the like may be laminated, but in terms of taste characteristics, thermosetting polymer, diethylene glycol is added, and copolymerized polyethylene terephthalate and / or
Alternatively, polyethylene naphthalate may be used.

The method for producing the biaxially stretched film in the present invention is not particularly limited, but for example, polyester is dried if necessary and then fed to a known melt extruder,
It is extruded into a sheet form from a slit die, adhered to a casting drum by a method such as electrostatic application, cooled and solidified to obtain an unstretched sheet. The unstretched sheet is stretched in the longitudinal and width directions 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.
Further, the film is subjected to a heat treatment after biaxial stretching, and 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 may be arbitrary, but is preferably 0.1 to 60 seconds, more preferably 1 to 20 seconds. The heat treatment may be performed while relaxing the film in its longitudinal direction and / or width direction. Furthermore, re-stretching may be performed once or more in each direction, and then heat treatment may be performed.

In order to improve the handleability and processability of the film of the present invention, any of known external particles having an average particle diameter of 0.01 to 5 μm, external particles such as inorganic particles and / or organic particles can be used. The particles selected for 0.01 to
It is preferably contained in an amount of 10% by weight. In particular, it is preferable that the film used on the inner surface of the can contains 0.01 to 3% by weight of internal particles, inorganic particles and / or organic particles having an average particle diameter of 0.1 to 5 μm. A known technique can be adopted as a method for depositing the internal particles. For example, JP-A-48-61556 and JP-A-51-1286 can be used.
0, JP-A-53-41355, JP-A-54
The techniques described in Japanese Patent Publication No. 90397 and the like are mentioned. Further, JP-A-55-20496 and JP-A-59-20
It can also be used in combination with other particles such as 4617. The use of particles having an average particle size of more than 5 μm is not preferable because defects in the film are likely to occur.
Examples of the inorganic particles and / or organic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay and the like, and styrene, silico-. Examples thereof include organic particles and the like, which include silane, acrylic acid, and the like as constituent components. Among these, wet and dry silica, colloidal silica, inorganic particles such as aluminum silicate, and organic particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components can be mentioned. These internal particles, inorganic particles and / or organic particles may be used in combination of two or more kinds.

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.

Further, it is preferable to improve the adhesiveness by subjecting the film to a surface treatment such as 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 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. For tin plating 0.5-15 / m ^2, it is preferable to have a plating amount when nickel or aluminum 1.8~20g / 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.

[0033]

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) Content of diethylene glycol component in polyester It was measured by NMR (13C-NMR spectrum).

(2) Intrinsic viscosity of polyester Dissolve polyester in orthochlorophenol and prepare 25
Measured in ° C.

(3) 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 potentiometric titration was carried out with an alkali.

(4) Refractive index in the thickness direction of film The measurement was carried out using an Abbe refractometer with sodium D line (wavelength 589 nm) as a light source.

(5) Melting Point of Polyester, Thermal Crystallization Parameter Polyester was dried, melted, and then rapidly cooled, and was measured with a differential scanning calorimeter (DSC-2 type manufactured by Perkin Elmer Co.) to 16
It was measured at a temperature rising rate of ° C / min.

(6) Content of acetaldehyde in the film 2 g of the fine powder of the film was sampled and charged into a pressure resistant container together with ion-exchanged water, extracted with water at 120 ° C. for 60 minutes, and then quantified by high sensitivity gas chromatography.

(7) Average particle size of particles The resin is removed from the film by a plasma low temperature ashing method to expose the particles. The processing conditions are selected so that the resin is incinerated but the particles are not damaged. The number of the particles was observed at 5,000 to 10,000 using a scanning electron microscope, and the particle image was obtained from the equivalent circle diameter by an image processing apparatus.

When the particles are internal particles, a polymer cross section is cut to prepare an ultrathin section having a thickness of about 0.1 to 1 μm, and a photograph (10 sheets: 10: (25 cm × 25 cm) was photographed, and the average dispersion diameter of internal particles was calculated from the equivalent circle diameter.

(8) Surface Roughness of Film (Centerline Average Roughness Ra, Maximum Roughness Rt) The surface roughness was measured using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 20 measurements was taken as the value.

-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 / Evaluation Method "(General Technology Center, 1983)
Is shown.

(9) Relaxation time T1ρ by solid-state high-resolution NMR A solid-state NMR measuring apparatus is a spectrometer JNM-GX270 manufactured by JEOL Ltd., a solid-state amplifier made by JEOL Ltd., MAS controller NM-GSH27MU, probe NM-GSH27T VT produced by JEOL Ltd. ． W) was used. Measurement is ¹³ C
A T1ρ (longitudinal relaxation in rotational coordinates) measurement of the nucleus was performed.

The measurement is carried out at a temperature of 24.5 ° C. and a humidity of 50 RH.
%, ¹ H, ¹³ C under static magnetic field strength of 6.34 T (Tesla)
Have resonance frequencies of 270.2 MHz and 67.94, respectively.
MHz. The MAS (Magic Angle Rotation) method was adopted to eliminate the influence of chemical shift anisotropy. The rotation speed was 3.5 to 3.7 kHz. The conditions of the pulse series were 90 ° with respect to ¹ H, a pulse width of 4 μsec, and a locking magnetic field strength of 62.5 kHz. ¹ H polarization to ¹³ C
The contact time of CP (cross-polarization) to be transferred to is 1.5 msec. The holding time τ is 0.00
1, 0.5, 0.7, 1, 3, 7, 7, 20, 30, 40, 50ms
I used ec. Free induction decay (FID) of ¹³ C magnetization vector after retention time τ was measured ( ¹ H during FID measurement)
High-power decoupling was performed to eliminate the effect of dipole interaction due to. Note that 512 times of integration were performed to improve the S / N ratio). The pulse repetition time was set between 5 seconds and 15 seconds. In the measurement data, carbonyl carbon (164 ppm,
The following analysis was performed on the internal standard silicone rubber (1.56 ppm).

The T1ρ value can be usually described by I (t) = Σ (Ai) exp (−t / T1ρi) (Ai: ratio of components to T1ρi), and the peak observed for each retention time. The intensity can be obtained from the slope of the logarithmic plot. Here, the two-component system (T1ρ1
: Amorphous component, T1ρ2: Crystal component), and the value was obtained by the least squares fitting using the following formula.

I (t) = fa1.exp (-t / T1.rho.1) + fa2.e
xp (-t / T1ρ2) fa1: Ratio of components to T1ρ1 fa2: Ratio of components to T1ρ2 fa1 + fa2 = 1

(10) Formability a. Before heat treatment After laminating a film on a TFS steel plate (thickness 0.25 mm) heated to a melting point of -20 ° C to a melting point + 50 ° C at 60 m / min, it is cooled with warm water of 60 ° C and then two-stage molding is performed with a drawing machine. (Final forming ratio (maximum thickness / minimum thickness) = 2.0, 8
A molded can was obtained at a temperature range of 0 to 100 ° C.). A 1% saline solution was placed in the obtained can, and a voltage of 6 v was applied to the electrode in the saline solution and a metal can to read a current value after 3 seconds and obtain an average value after 10 cans were measured.

Class A: less than 0.001 mA Class B: 0.001 mA or more and less than 0.01 mA Class C: 0.01 mA or more and less than 0.05 mA Class D: 0.05 mA or more

B. After heat treatment After the above-mentioned lamination, after heat treatment at 210 ° C for 30 seconds, 7
After the steel plate is bulged from the non-laminated surface with a sphere of 0 ° C and a radius of 2 cm (the height of the bulged portion is 5 mm), retort treatment (120 ° C, treatment with pressurized steam for 30 minutes) is performed, and the laminated steel plate is in the following state. It was judged as follows.

Class A: Almost no change. Class B: Whitening, but no problem. Class C: A small darkened part is seen. Class D: The film was broken.

(11) Impact resistance A can that was actually made was heat-treated at 200 ° C. for 30 seconds, and then 350 g of water was filled and the lid was closed. 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.

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

(12) Taste characteristics A can (diameter 6 cm, height 12 cm) was filled with water, and 120
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. Almost no change is seen in the B-grade liquid. A slight change can be seen in the C-class liquid. A change is seen in the D-class liquid.

Example 1 As a polyester, ethylene glycol slurry containing aluminum silicate particles having an average particle size of 0.2 μm was added after completion of the esterification reaction, and polycondensation reaction was carried out to contain polyethylene terephthalate (germanium) containing a predetermined amount of the particles. Chips having a system catalyst, an intrinsic viscosity of 0.75, diethylene glycol 1.5% by weight, a melting point of 250 ° C., a carboxyl group: 25 equivalents / ton, ΔTcg = 79 ° C.) were produced. The polyester was vacuum dried at 170 ° C. for 4 hours, supplied to a single-screw extruder, discharged from an ordinary die, and then cooled and solidified by a mirror cooling drum while applying static electricity to obtain an unstretched film. This unstretched film was 2.8 at a temperature of 110 ° C. in the longitudinal direction.
Double stretching, cooling to 40 ° C., and then a temperature of 115 ° C. in the width direction.2.
After being stretched 8 times, it was heat-treated at 180 ° C. for 3 seconds to relax for 3%. The obtained film characteristics and can characteristics are as shown in Table 1, and the refractive index in the thickness direction was 1.518,
It was possible to obtain excellent moldability, impact resistance, and taste characteristics.

Examples 2 to 9 and Comparative Examples 1 to 3 Films were obtained in the same manner as in Example 1 except that the production of polyester, the film forming method, the lamination ratio, the kind of polyester, etc. were changed. The results are shown in Tables 1 to 4.

In Example 2, the particles had an average particle size of 1.1 μm.
Polyethylene glycol terephthalate containing 2 wt% of particles by adding poly (ethylene glycol) slurry containing the particles after completion of the esterification reaction to obtain wet silica particles (antimony-based catalyst, intrinsic viscosity 0.68,
A chip (particle master) having 0.7% by weight of diethylene glycol, a melting point of 256 ° C., and a carboxyl group of 35 equivalent / ton was produced. Then, polyethylene terephthalate without added particles (germanium-based catalyst, intrinsic viscosity 0.78, diethylene glycol 1.5% by weight, melting point 2
49 ° C., carboxyl group: 21 equivalent / ton, ΔTcg =
81 ° C.) The chips and the particle master chips are mixed so as to have a predetermined amount of particles, and the temperature is 113 ° C. in the longitudinal direction of 2.7.
Double stretching and cooling to 40 ° C., then at a temperature of 120 ° C. in the width direction 2.
After being stretched 7 times, it was heat-treated at 185 ° C. for 2 seconds for 2 seconds to relax. The obtained film characteristics and can characteristics are as shown in Table 1, and excellent moldability, impact resistance, and taste characteristics could be obtained.

In Example 3, an ethylene glycol slurry containing colloidal silica particles having different average particle diameters as polyester was heat-treated at 190 ° C. for 2 hours, and after the transesterification reaction was completed, the slurry was added to carry out a polycondensation reaction. A polyethylene terephthalate (antimony-based catalyst, intrinsic viscosity 0.55) chip containing a predetermined amount of particles was produced. The polyester was solid-phase polymerized to obtain a polymer having an intrinsic viscosity of 0.79, a carboxyl terminal group of 13 equivalents / ton, diethylene glycol of 0.5% by weight and a melting point of 251 ° C. Then, it was vacuum-dried, supplied to a twin-screw extruder of a vacuum vent system, measured by a gear pump, discharged from a normal die, cooled and solidified by a mirror-surface cooling drum by electrostatic application to obtain an unstretched film. This unstretched film was stretched 3.1 times in the longitudinal direction at a temperature of 105 ° C. and cooled to 35 ° C.
The film was stretched 3.0 times in the width direction at 0 ° C. and then heat-treated at 190 ° C. for 3 seconds to relax for 3%. The obtained film properties and can properties are as shown in Table 1, showing good moldability,
The taste characteristics could be obtained.

In Example 4, diethylene glycol 6% by weight copolymerized polyethylene terephthalate was used, the draw ratio was 3.5 times, and the heat treatment temperature was 230 ° C. for 7 seconds. As shown in Table 2, the refractive index in the thickness direction was as shown in Table 2. It became higher and the characteristics deteriorated.

In Example 5, polyethylene naphthalate containing particles (germanium catalyst, intrinsic viscosity 0.6) was used.
1, diethylene glycol 0.9% by weight, melting point 266
C, carboxyl end group: 25 equivalents / ton, ΔTcg =
A film was obtained in the same manner as in Example 1 except that the polyethylene terephthalate of Example 1 was laminated at 99 ° C.) and stretched at a stretching temperature of 140 ° C. Film characteristics obtained, PE
The can characteristics obtained by laminating T and a steel plate are as shown in Table 2, and the taste characteristics were particularly good.

In Example 6, when a film was formed so that the relaxation time of the carbonyl portion was 250 msec in Example 2, as shown in Table 2, the impact resistance and the workability after heat treatment deteriorated.

In Example 7, Example 1 was repeated except that the polyethylene naphthalate of Example 5 was mixed with the polyethylene terephthalate of Example 1 and stretched at a stretching temperature of 140 ° C.
A film was obtained in the same manner as described above. The resulting film properties,
The can characteristics obtained by laminating PET and a steel plate are as shown in Table 3, and the taste characteristics were particularly good.

In Example 8, when a film was formed so that the relaxation time of the carbonyl portion was 370 msec in Example 2, as shown in Table 3, impact resistance and workability after heat treatment were significantly improved.

In Example 9, the polyester of Example 1 was added to the antioxidant IRGANOX1 manufactured by Nippon Ciba-Geigy Co., Ltd.
010 <pentaerythrityl-tetrakis [3- (3,
5-di-t-butyl-4-hydroxyphenyl) propionate]> in 0.05% by weight of diethylene glycol copolymerized polyethylene terephthalate (germanium-based catalyst, intrinsic viscosity 0.80, diethylene glycol 3.0% by weight, melting point 248) ° C, carboxyl end group:
12 equivalents / ton) was formed in the same manner as in Example 8. Obtained film characteristics, copolymerized PET
The can properties obtained by laminating the steel sheet and the steel plate are as shown in Table 3, and excellent moldability, impact resistance, and taste properties could be obtained.

In Comparative Example 1, diethylene glycol copolymerized PET (melting point 235 ° C.) was used, and the draw ratio was 3.6.
Double the heat treatment temperature at 200 ° C., the characteristics deteriorated as shown in Table 4.

In Comparative Example 2, when 5 mol% isophthalic acid copolymerized PET (melting point 242 ° C.) was used, the taste characteristics were significantly deteriorated.

In Comparative Example 3, when a film having a carboxyl end group of 52 equivalents / ton was used, impact resistance and taste characteristics were deteriorated.

[0069]

[Table 1]

[Table 2]

[Table 3]

[Table 4] The abbreviations in the table are as follows.

PET: Polyethylene terephthalate PET / I: Isophthalic acid copolymerized polyethylene terephthalate (numbers are copolymerized mol%) PET / DEG: Diethylene glycol copolymerized polyethylene terephthalate (numbers are copolymerized mol%) DEG: Diethylene glycol

[0071]

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.

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Claims (5)

[Claims] 1. A biaxially stretched polyester film for container molding, which has a melting point of 240 to 300 ° C., a carboxyl terminal group of 10 to 50 equivalents / ton, and does not substantially contain an isophthalic acid component as an acid component. 2. The biaxially stretched polyester film for container molding according to claim 1, which has a refractive index in the thickness direction of 1.50 or more. 3. The twin-screw for molding a container according to claim 1, wherein 95% by weight or more of the constitutional unit of the polyester is an ethylene terephthalate unit and / or an ethylene naphthalate unit. Stretched polyester film. 4. The biaxially stretched polyester film for container molding according to claim 1, wherein the relaxation time of the carbonyl portion in the structural analysis by solid-state high resolution NMR is 270 msec or more. 5. The biaxially stretched polyester film for forming a container according to claim 1, wherein the biaxially stretched polyester film is formed after heat lamination on a metal plate.