JP2002302560A - Polyester film for container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a container, suitable for a two-piece metal can for a food, having excellent properties for lamination, forming processability, taste characteristics and performance for taking out the content. SOLUTION: This polyester film for the container comprises a polyester film having at least one surface having <0.3 friction coefficient, <40 mN/m surface free energy on the surface having <0.3 friction coefficient, and 246-270 deg.C melting point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a polyester film for a container. Specifically, the present invention
Even when molded into containers, it has excellent cracking and impact resistance,
Further, the present invention relates to a polyester film for a container which exhibits excellent properties even when molded into a container after being laminated on a base material such as a metal plate, and which is further excellent in taking out contents.

[0002]

2. Description of the Related Art Conventionally, the inner and outer surfaces of a metal can are coated with a coating material in which various thermosetting resins such as epoxy or phenol are dissolved or dispersed in a solvent to prevent corrosion, and the metal surface is coated. Was widely practiced. However, such a method of coating with a thermosetting resin requires a long time to dry 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. 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 should have excellent lamination properties on metal plates. (2) Excellent adhesion to the metal plate. (3) It has excellent moldability and does not generate defects such as pinholes after molding. (4) The polyester film shall not peel, crack or pinhole due to impact on the metal can. (5) The scent component of the contents of the can adsorbs to the film,
The flavor of the contents shall not be impaired by the eluate from the film (hereinafter referred to as taste characteristics). (6) The contents do not adhere to the film on the inner surface of the can, and the contents can be easily taken out (hereinafter referred to as the contents take-out property).

[0004] Many proposals have been made to solve these demands. For example, Japanese Patent Publication No. 64-22530 discloses a polyester film having a specific density and a plane orientation coefficient.
No. 9 discloses a copolyester film having specific crystallinity. However, these proposals do not necessarily satisfy the above-mentioned various required properties comprehensively, and at the same time, achieve both excellent moldability in applications where excellent laminating properties, taste properties and contents removal properties are required. It was difficult to do.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a two-piece food metal can excellent in laminating property, molding workability and content taking-out property. An object of the present invention is to provide a suitable polyester film for a container.

[0006]

The above object of the present invention can be attained by a polyester film for a container comprising a polyester film having a friction coefficient of at least one side of less than 0.3.

The container polyester film of the present invention has the following preferred embodiments. (a) The surface free energy of the surface having a coefficient of friction of less than 0.3 is less than 40 mN / m. (b) A polyester film having a melting point of 246 ° C to 270 ° C. (c) The polyester film contains 0.3 to 2% by weight of carnauba wax. (d) The polyester film is a laminated film in which a polyester layer containing 0.3 to 2% of carnauba wax is arranged on at least one surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester constituting the polyester film for a container of the present invention is a generic term for a polymer compound having a main bond in the main chain as an ester bond, and usually comprises a dicarboxylic acid component and a glycol component. It can be obtained by a polycondensation reaction.

Here, as the dicarboxylic acid component, for example, terephthalic acid, 2,6-naphthalenedicarboxylic acid,
Aromatic dicarboxylic acids such as isophthalic acid, diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodium sulfone dicarboxylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, and maleic Examples thereof include aliphatic dicarboxylic acids such as acid and fumaric acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, and oxycarboxylic acids such as p-hydroxybenzoic acid.

As the glycol component, for example,
Aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol and neopentyl glycol; polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol and polypropylene glycol; alicyclic glycols such as cyclohexanedimethanol; bisphenol A And aromatic glycols such as bisphenol S.

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

The intrinsic viscosity of the polyester is 0.5
It is preferable that the intrinsic viscosity is 0.6 to 0.8 for applications requiring heat resistance and aging resistance.

The polyester in the present invention preferably has a diethylene glycol content of 0.01 to 3.5% by weight, more preferably 0.01 to 2.5% by weight, and particularly preferably 0.01 to 2.0% by weight. Is desirable in order to maintain excellent taste characteristics even after receiving many histories such as heat treatment in a can making process and retort treatment after can making. This is considered to be due to the improvement in resistance to oxidative decomposition at 200 ° C. or higher.
A known antioxidant may be added in an amount of 0.0001 to 1% by weight. In addition, diethylene glycol may be added at the time of polyester production as long as taste characteristics are not impaired.

In the polyester used in the present invention, the amount of carboxy terminal groups in the polyester is preferably 20 to 55 mmol / kg, more preferably 25 to 50 mmol / kg, from the viewpoint of improving the compatibility with the particles.
g, particularly preferably 30 to 45 mmol / kg.

In order to improve taste characteristics, the content of acetaldehyde in the film is preferably 25 ppm.
Below, it is more desirable to make it 20 ppm or less. When the content of acetaldehyde exceeds 25 ppm, the taste characteristics tend to be inferior.

The method for reducing the acetaldehyde content in such a film to 25 ppm or less is not particularly limited. For example, in order to remove acetaldehyde generated by thermal decomposition in producing a polyester by a polycondensation reaction or the like, a polyester is used. A heat treatment at a temperature not higher than the melting point under reduced pressure or in an inert gas atmosphere.
A method of solid-phase polymerization at a temperature of 5 ° C. or more and a melting point or less, a method of melt-extrusion using a vented extruder, and a method of melt-extruding polyester by setting the extrusion temperature within the melting point + 30 ° C., preferably within the melting point + 25 ° C. For example, a method of extruding within an hour, preferably within one hour of the average residence time can be used.

In producing the polyester used in 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 and zinc compounds. , A lead compound, a manganese compound, a cobalt compound, an aluminum compound, an antimony compound, a titanium compound, a germanium compound, and the like, and a coloring compound such as a phosphorus compound can be used, but are not particularly limited thereto. It is preferable to use an alkali metal compound and / or an alkaline earth metal compound for the reaction catalyst from the viewpoint of the content removal property.

In general, it is preferable to add an antimony compound, a germanium compound and / or a titanium compound as a polymerization catalyst at any stage before the production of the polyester is 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 No. 54-22234, glycol A method of dissolving and adding a germanium compound to the components can be used.

Examples of such germanium compounds include germanium dioxide, germanium hydroxide hydrate or germanium alkoxide compounds such as germanium tetramethoxide and germanium ethyleneglycoxide, germanium phenoxide compounds, germanium phosphate, and germanium phosphite. A phosphoric acid-containing germanium compound, germanium acetate, or the like can be used. Among them, germanium dioxide is preferably used, and amorphous germanium dioxide is particularly preferably used.

The antimony compound is not particularly restricted but includes, for example, oxides such as antimony trioxide,
Antimony acetate or the like is used. The titanium compound is not particularly limited, but titanium tetraalkoxide such as titanium tetraethoxide and titanium tetrabutoxide is preferably used.

As described above, the polyester used in the present invention is produced. Here, a more specific example will be described. For example, when producing polyethylene terephthalate, when germanium dioxide is added as a catalyst, a terephthalic acid component and an ethylene glycol component are subjected to a transesterification or esterification reaction, and then germanium dioxide and a phosphorus compound are added. A method in which polycondensation is performed under reduced pressure until the content of diethylene glycol becomes constant to obtain a germanium element-containing polymer is preferably employed. As a more preferred method, 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 acetaldehyde, and obtain a predetermined intrinsic viscosity and a carboxy terminal group. A method or the like is used.

The polyester film for a container of the present invention comprises:
From the viewpoint of moldability and content take-out, it is necessary that at least one surface has a friction coefficient of less than 0.3. The coefficient of friction is more preferably from 0.28 to 0.1, and when the range of the coefficient of friction is from 0.26 to 0.15, even if the degree of molding (decrease in film thickness before and after molding) exceeds 40%. It is even more preferable because molding becomes possible. If the coefficient of friction is less than 0.1, winding deviation may occur in the last winding of the film.

The coefficient of friction of the polyester film is 0.3
The method for making the polyester particles less than 0.1 is not particularly limited, but as long as other characteristics are not deteriorated, the polyester may contain inorganic or organic particles having an average particle diameter of 1 to 3 μm in an amount of 0.1 to 0.1 μm.
A method of adding about 5% by weight or a method of adding a wax or a silicone compound is preferable, and it is particularly preferable to add a wax. Here, examples of the wax include carnauba wax, candelilla wax, stearate stearate and the like, and among them, carnauba wax is preferably used.

The polyester film for a container of the present invention comprises:
It is preferable that the surface free energy of the surface having a friction coefficient of less than 0.3 is less than 40 mN / m from the viewpoint of the content taking-out property. The surface free energy is more preferably 2
0 to 38 mN / m.

The method of reducing the surface free energy to less than 40 mN / m is not particularly limited, but it is preferable to add a wax or a silicone compound as long as other characteristics are not deteriorated. Is preferred. Particularly, carnauba wax is preferably used. The addition amount is preferably 0.3 to 2% by weight,
More preferably, the content is 0.4 to 1.2% by weight and 0.5 to 1% by weight. As a method of adding carnauba wax, a method of adding during the polymerization of polyester or a method of mixing by kneading in a twin-screw melt extruder are preferably used.

The polyester film for a container of the present invention comprises:
The melting point is preferably from 246 to 270 ° C. from the viewpoint of taste characteristics, heat resistance, and laminating properties. 246 melting point
If the temperature is lower than ℃, taste characteristics and heat resistance may be deteriorated, and if it is higher than 270 ° C, the laminating property may be deteriorated. Further, a more preferable melting point is 250 to 260 ° C. from the viewpoint of taste characteristics and laminating properties.

In the polyester film for a container according to the present invention, known internal particles, inorganic particles and / or organic particles having an average particle diameter of 0.01 to 10 μm are used in order to improve the handleability, processability and content take-out property. 0.0
It is preferable to contain 1 to 3% by weight. More preferably, the particle concentration is from 0.05 to 3% by weight.
More preferably 1 to 3% by weight, 0.3 to 3% by weight
Is more preferable. As a method for precipitating the internal particles, known techniques can be used. For example, JP-A-48-61556, JP-A-51-12860, JP-A-53-41355, and 54
The technology described in JP-A-90397 can be employed. Further, other particles described in JP-B-55-20496 and JP-A-59-204617 can be used in combination. When particles having an average particle diameter of more than 10 μm are used, the film may have defects.

Examples of such inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, aluminum oxide, mica, kaolin, clay, and the like.
As the organic particles, particles containing styrene, silicone, acrylic acids, methacrylic acids, polyesters, divinyl compounds, and the like as constituent components can be used. Among them, it is preferable to use inorganic particles such as wet and dry silica and alumina and particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components. Furthermore, two or more of these internal particles, inorganic particles and organic particles may be used in combination.

The thickness of the polyester film for a container of the present invention is preferably from 10 to 30 μm, and more preferably from 10 to 20 μm, from the viewpoints of laminability to a metal plate, moldability and impact resistance.

The polyester film for a container of the present invention comprises:
As a film configuration, even if it is a single layer, two layers of A / B,
It may have a three-layer structure of A / B / A or A / B / C, or may have a multilayer structure of more than three layers. Among the laminations, two layers of A / B are preferable, and a preferable lamination ratio at that time is 1: 1 to 1: 9. Here, the coefficient of friction of the surface of layer A, which is the surface that comes into contact with the contents when molded into a container, is 0.3
When the content is less than the above, excellent content take-out property can be exhibited. As a method for obtaining a laminated film, a co-extrusion method is used in which the polyester used for the layer A and the polyester used for the layer B are supplied to separate extruders and laminated in a feed block placed above the die to obtain sheets at a time. Or A
A method of forming a film consisting of only the layer or the layer B and extruding and laminating the polyester used for the layer remaining thereon can be preferably used. From the viewpoint of productivity, the co-extrusion method is preferable, and the layer on the side not in contact with the cooling drum when extruded from the die is preferably a low surface free energy layer to which wax or the like is added. This is because the cooling drum is usually a mirror-finished metal drum.
This is because wax penetrates into the polyester and it becomes necessary to add a larger amount of wax to obtain a target low energy surface.

The method for producing the polyester film for a container in the present invention is not particularly limited. For example, after drying the polyester as required,
It is supplied to a known melt extruder, melted and extruded into a sheet from a slit-shaped die, and is not particularly limited. For example, a method of applying static electricity using a wire-shaped electrode or a tape-shaped electrode, a casting drum and a polymer extruded Casting method in which a water film is provided between sheets, and the temperature of the casting drum is changed from the glass transition point of polyester to (glass transition point-
(20 ° C.) to adhere the extruded polymer, or a method in which a plurality of these methods are combined to bring the sheet-shaped polymer into close contact with a casting drum and cool and solidify to obtain an unstretched film. Among these casting methods, a method of applying static electricity is preferably used from the viewpoint of productivity and flatness, and a method using a tape electrode is particularly preferably used. After stretching in the longitudinal direction using such an unstretched film, stretching in the width direction, or stretching in the width direction, and then stretching in the longitudinal direction, a sequential biaxial stretching method, stretching in the longitudinal direction and the width direction of the film almost simultaneously. Stretching is performed by a simultaneous biaxial stretching method.

In such a stretching method, the stretching ratio employed is preferably 1.6 to 4.2 in each direction.
And more preferably 1.7 to 4.0 times. Also,
The stretching speed is preferably from 1,000 to 200,000% / min, and the stretching temperature is from the glass transition point of the polyester to
Any temperature within a temperature range of (glass transition point + 100 ° C.) can be used, but preferably 80 to 170
° C, particularly preferably a stretching temperature in the longitudinal direction of 90 to 150 ° C.
C. and the stretching temperature in the width direction are preferably 80 to 150C. The stretching may be performed a plurality of times in each direction.

After the biaxial stretching, the film is subjected to heat treatment. This heat treatment can be carried out by any conventionally known method such as in an oven or on a heated roll. The heat treatment temperature can be any temperature from 120 ° C. to the melting point of the polyester, but is preferably from 120 to 230 ° C. from the viewpoint of moldability and impact resistance. If the temperature is lower than this temperature, the impact resistance may be deteriorated, and if the temperature is high, the moldability may be deteriorated. From the viewpoint of impact resistance after molding, the temperature is more preferably from 150 to 220 ° C, and even more preferably from 170 to 210 ° C. The heat treatment time can be arbitrarily set as long as other characteristics are not deteriorated, but it is usually preferable to perform the heat treatment for 1 to 60 seconds. Further, the heat treatment may be performed by relaxing the film in the longitudinal direction and / or the width direction.

The polyester film for a container of the present invention comprises:
It is used for container applications, and the application is not particularly limited as long as it is a container application, and examples thereof include aluminum vapor deposition applications, metal oxide vapor deposition applications, polyester sealant applications, containers made of polyester laminates, and the like. Among them, it is preferable to be used for forming into containers by forming processes such as bending, drawing, and ironing,
Further, it is preferably used for forming after lamination with a substrate.

As described above, the container surface can be formed by using the polyester film for a container of the present invention on at least a part of the surface of the container base material.

The laminate substrate is desirably a substrate selected from metal, paper or plastic, and an adhesive or the like is used at the interface with metal, paper or plastic as long as the properties are not significantly impaired. However, it is preferable to directly bond the polyester film by heat without using an adhesive. Food containers formed from metal-polyester film, paper-polyester film and plastic-polyester film,
It is preferable in terms of taste characteristics because the polyester film does not directly contact the base material and the contents that cause the taste change. In this case, it is particularly preferable that the laminate substrate is made of a metal in terms of barrier properties and sufficient heating, and the protection of the contents is further improved.
The metal plate is not particularly limited, but is preferably a metal plate made of iron, aluminum, or the like in terms of molding. Furthermore, in the case of a metal plate made of iron, an inorganic oxide coating layer on the surface of the metal plate to improve adhesion and corrosion resistance, for example, chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment A chemical conversion coating layer represented by a chromate treatment or a chromium chromate treatment may be provided. In particular,
6.5 to 150 mg / as chromium in terms of chromium metal
A hydrated chromium oxide of m ² is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gunmetal or brass may be provided. For tinned 0.5-15 / m ^2, in the case of nickel or aluminum preferably has a plating weight of 1.8~20mg / m ^2.

The polyester film for a container of the present invention comprises:
It can be suitably used for the inner surface coating of a two-piece metal can manufactured by drawing or ironing.
In addition, it can be preferably used as a lid for a two-piece can or for coating a body, a lid, and a bottom of a three-piece can because it has good metal adhesion and moldability. In particular,
Particularly preferably used for food metal cans, since the contents can be easily taken out without sticking to the can wall and can bottom for coating the inner surface of food metal cans that store the contents that are cured by heat and the like. can do.

[0038]

The present invention will be described below in detail with reference to examples. In addition, each characteristic was measured and evaluated by the following methods.

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

(2) Melting Point of Film About 10 mg of the film was measured with a differential scanning calorimeter (DSC220CU, manufactured by Seiko Instruments Inc.) at a heating rate of 20 ° C./min. To determine the melting point. In addition, indium, tin, and lead were used for calibration of the apparatus.

(3) Surface free energy As a measuring solution, water, ethylene glycol, formamide
And diiodomethane using a contact angle meter
Using CA-D type (manufactured by WA Interface Science Co., Ltd.)
The static contact angle on the lum surface was determined. Each liquid
Was measured 5 times, and the average contact angle (θ) and the measurement solution
Substituting each component of the surface tension of (j) into the following equation,
Is a system of equations^L, Γ⁺, Γ^-About
Was. (Γ^Lγ_j ^L)^1/2+2 (γ⁺γ_j ^-)^1/2+2 (γ_j ⁺γ^-)^1/2
= (1 + cos θ) [γ_j ^L+2 (γ_j ⁺γ_j ^-)^1/2] / 2 where γ = γ^L+2 (γ⁺γ^-)^1/2 γ_j= Γ_j ^L+2 (γ_j ⁺γ_j ^-)^1/2 Where γ, γ^L, Γ⁺, Γ^-Is the film surface
Free energy, long-range force term, Lewis acid parameter
Parameters, Lewis base parameters, and γ _j,
γ_j ^L, Γ_j ⁺, Γ_j ^-Indicates the surface freedom of the measurement solution used.
Energy, long range force term, Lewis acid parameter,
The chair base parameters are shown. In addition, each liquid used here
The surface tension of the body is Oss ("fundamentals of Adhesio
n ", L. H. Lee (Ed.), p153, Plenum ess, New York (19
The values in Table 1 proposed by 91).) Were used.

[0042]

[Table 1] (4) Coefficient of friction The slit film obtained by slitting the film into a tape having a width of 12.7 mm is run on a stainless steel guide pin (surface roughness: 100 nm by Ra) using a tape running tester (running speed: 250 m / Minute, wrap angle 60 °,
Outgoing side tension 90g, number of running times 1). At this time, the friction coefficient was calculated using the following equation, with the entry-side tension being Ti. Coefficient of friction = 2.20 log (90 / Ti) (5) Wax concentration The wax concentration contained in the film was determined by Fourier transform infrared absorption spectroscopy-total reflection method. The measurement uses FTS-60A / 896 (FTIR made by GIGILAB) as a spectroscope, uses ZnSE as IRE,
It was measured by single reflection at an incident angle of 60 °. At that time, the resolution was 4 cm ^-1 and the number of integration was 256 times. In the determination, the CH stretching vibration band 2850c derived from wax was used.
It was determined from the intensity ratio between the peak near m ^{-1 and} the peak near 3050 cm ^-1 derived from the benzene ring in the polyester. The quantification was performed by preparing a calibration curve in advance.

(6) Workability The film was laminated at 65 m / min on a TFS steel plate (0.22 mm thick) heated to the melting point of the film + 28 ° C., and then rapidly cooled in a 45 ° C. water bath. The reduction rate of the laminated steel sheet was 4
It was molded at 0% to obtain a can. The state after the obtained can was subjected to a pressurized steam treatment at 130 ° C. for 20 minutes was observed and judged as follows. Class A: No rust was generated, and no crack was observed in the film. Class B: No rust was generated, but slight cracks were observed in the film. Class C: Rust occurred.

(7) Taste characteristics A can made in the same manner as described above was subjected to a pressurized steam treatment at 110 ° C. for 30 minutes, filled with water, sealed, allowed to stand at 37 ° C. for 2 weeks, and then opened. Turbidity measurement based on components eluted from the film using a turbidity meter (Yasui Kikai's high-sensitivity turbidity / colorimeter
TUB801), and evaluated according to the following criteria. In the measurement of turbidity, a calibration curve was prepared in advance using a turbidity standard solution for water quality test (manufactured by Wako Pure Chemical Industries, Ltd.). Class A: less than 0.10 Class B: 0.15 to 0.10 Class C: above 0.15.

(8) Content take-out property Ground beef and whole eggs were mixed at a weight ratio of 3: 2 using a mixer and added to a beaker (capacity: 1 dm3). There slide glass (length 76mm, width 26mm, thickness 1.2m)
m), a film was wound around and a sample fixed with a polyester tape was pierced. This was subjected to a pressurized steam treatment at 120 ° C. for 30 minutes to solidify the mixture of ground meat and eggs. After cooling to room temperature, the degree of adhesion of the mixture to the film surface when the film was separated from the mixture together with the slide glass was evaluated according to the following criteria. Class A: No adhesion of the mixture is observed on the entire surface of the film. Class B: Adhesion of the mixture was observed on a part of the film surface. Class C: Adhesion of the mixture was observed on the entire surface of the film.

Examples 1 to 4 In Example 1, polyethylene terephthalate (hereinafter referred to as polyethylene terephthalate) containing 0.08% by weight of aggregated silica having an average primary particle size of 0.6 μm and 0.6% by weight of carnauba wax was added. , PET). The PET was vacuum-dried at 180 ° C. for 3 hours, supplied to a single screw extruder, discharged from a normal die, cooled and solidified with a mirror-surface cooling drum while applying static electricity to obtain an unstretched film. The unstretched film is stretched 3.1 times in the longitudinal direction at a temperature of 110 ° C., and then stretched in the width direction at 115 ° C.
After stretching 3 times, relax at 200 ° C 5% 10%
Heat treatment was performed for 2 seconds to obtain a biaxially stretched biaxially stretched film having a thickness of 15 μm. As shown in Table 2, this biaxially stretched film exhibited excellent characteristics.

In Example 2, PET containing 0.2% by weight of aggregated silica having an average primary particle size of 1.2 μm was used. The PET was vacuum-dried at 180 ° C. for 3 hours, supplied to a single screw extruder, discharged from a normal die, cooled and solidified with a mirror-surface cooling drum while applying static electricity to obtain an unstretched film. The unstretched film is stretched 3.2 times in the longitudinal direction at 107 ° C., then stretched 3.0 times in the width direction at 120 ° C., and then heat-treated at 230 ° C. for 3 seconds at 3% relaxation. A stretched biaxially stretched film having a thickness of 20 μm was obtained. This biaxially stretched film is shown in Table 2,
It showed excellent properties.

In Example 3, 8 mol% of isophthalic acid copolymerized PET containing 0.1% by weight of spherical colloidal silica having an average particle diameter of 1.0 μm and 0.5% by weight of carnauba wax was used. . This copolymerized PET is
Vacuum dried at 60 ° C. for 3.5 hours and fed to a single screw extruder,
After discharging from a normal die, it was cooled and solidified with a mirror-surface cooling drum while applying static electricity to obtain an unstretched film. This unstretched film was stretched 3.2 times in the longitudinal direction at a temperature of 105 ° C., then stretched 3.1 times in the width direction at a temperature of 115 ° C., and then heat-treated at 190 ° C. without relaxation for 6 seconds.
An axially stretched biaxially stretched film having a thickness of 25 μm was obtained.
As shown in Table 2, this biaxially stretched film exhibited excellent characteristics.

In Example 4, the layer on the side of the steel sheet when laminated on the steel sheet was made of polyester having an average particle size of 1.0
using PET containing 0.1% by weight of spherical colloidal silica of 0.1 μm, a layer serving as a non-steel plate side surface containing 0.12% by weight of aggregated silica having an average primary particle size of 0.6 μm, and carnauba wax Was used with the addition of 0.8% by weight. Each of these PETs was vacuum-dried at 150 ° C. for 5 hours, then supplied to separate extruders, laminated in a feed block placed above the die, and electrostatically charged so that the wax-containing layer was on the non-drum surface side. Casting was performed while applying voltage to obtain an unstretched laminated film. This film was stretched in the same manner as in Example 1 under the conditions shown in Table 2 to obtain a biaxially stretched film. As shown in Table 2, the properties of this biaxially stretched film showed excellent properties.

(Comparative Examples 1 to 3) In Comparative Example 1, 0.1% by weight of spherical silica having an average particle diameter of 0.8 μm was contained.
ET was used, and in Comparative Example 2, the average primary particle size was 0.6 μm.
Using PET containing 0.05% by weight of spherical silica and 0.2% by weight of carnauba wax,
In Comparative Example 3, 12 mol% isophthalic acid copolymerized PET containing 0.05% by weight of agglomerated silica having an average primary particle diameter of 0.5 μm was used, and the same as in Example 1 under the stretching conditions shown in Table 2. To obtain a biaxially stretched film. The properties of the obtained biaxially stretched film were as shown in Table 2, and the properties were inferior.

[0051]

[Table 2] The abbreviations in the above table are as follows. PET: polyethylene terephthalate PET / I ^* : isophthalic acid copolymerized polyethylene terephthalate (* indicates copolymer mole%) IV: intrinsic viscosity of polyester

[0052]

According to the present invention, it is possible to obtain a polyester film for a container which has not only the moldability but also the excellent content take-out property. This polyester film for a container is particularly suitable for a two-piece metal can.

Continued on the front page F-term (reference) 3E033 AA06 BA17 BB08 CA03 EA10 FA10 3E086 AA21 AB01 BA02 BA15 BA33 BB51 BB85 BB90 4F071 AA43 AA46 AA71 AA84 AB26 AE17 AF28Y AH05 BB06 BC01 BC10 4F100 A01B10B01A02BJB EJ38 GB16 JA06 JK10 JK14 JL01 YY00B

Claims (6)

[Claims] 1. A container polyester film comprising a polyester film having a coefficient of friction of at least one side of less than 0.3. 2. The polyester film for a container according to claim 1, wherein the surface free energy of the surface having a friction coefficient of less than 0.3 is less than 40 mN / m. 3. The polyester film for a container according to claim 1, comprising a polyester film having a melting point of 246 ° C. to 270 ° C. 4. The polyester film for a container according to claim 1, wherein the polyester film contains 0.3 to 2% by weight of carnauba wax. 5. The polyester film according to claim 1, wherein the polyester film is a laminated film having a polyester layer containing 0.3 to 2% of carnauba wax disposed on at least one surface.
4. The polyester film for a container according to any one of 3. 6. A container using the polyester film for a container according to claim 1 on at least a part of the surface of a container substrate.