JPH07205383A - Polyester film for metal panel laminate - Google Patents

Abstract

PURPOSE:To provide a polyester film excellent in adhesiveness, impact resistance and taste characteristics and having excellent impact resistance even after heat treatment, especially, such as dry baking or retorting and suitably adapted to a metal can be produced by molding processing. CONSTITUTION:A polyester film is obtained by laminating a B-layer composed of polyester (III) based on polybutylene terephthalate with an m.p. of 231-260 deg.C to an A-layer composed of a mixture consisting of polyester (I) based on polyethylene terephthalate with an m.p. of 150-230 deg.C and polyester (II) based on polybutylene terephthalate with an m.p. of 120-225 deg.C on a wt. basis of 50:50-95:5 and has the coefficient of surface orientation of 0.05 or less.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film for laminating metal plates. More specifically, the present invention relates to a polyester film for laminating metal plates, which has excellent adhesiveness, moldability, impact resistance, and taste characteristics and is suitable for metal cans produced by molding.

[0002]

2. Description of the Related Art Conventionally, for the purpose of preventing corrosion, the inner and outer surfaces of a metal can have been coated with various thermosetting resins such as epoxy type and phenol type which are dissolved or dispersed in a solvent to form a metal surface. Has been widely practiced. However, such a coating method of a thermosetting resin has a problem that it takes a long time to dry the coating material, productivity is lowered, and environmental pollution is caused by a large amount of organic solvent.

As a method of solving these problems, there is a method of laminating a polyester 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 the film, the polyester film is required to have the following characteristics.

(1) Excellent adhesion to a metal plate.

(2) It has excellent 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 adsorbed on the polyester film, and the odor of the polyester film does not impair the flavor of the contents (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 able to comprehensively satisfy the various required characteristics as described above, and in particular, do not cause defects such as pinholes after molding, impact resistance, and taste characteristics. I couldn't say it was at a satisfactory level.

[0009]

The object of the present invention is to eliminate the above-mentioned problems of the prior art, and is excellent in adhesiveness, moldability, heat resistance, impact resistance, taste characteristics, and particularly impact resistance. Another object of the present invention is to provide a copolymerized polyester and a film for laminating a metal plate, which has excellent taste characteristics and is suitable for a metal can produced by molding.

[0010]

The above-mentioned object of the present invention is to provide a polyester (I) mainly composed of ethylene terephthalate having a melting point of 150 to 230 ° C. and a melting point of 120 to 225 ° C.
Polyester (II) mainly composed of butylene terephthalate is mixed in a weight ratio of 50:50 to 95: 5, and layer A is composed of polyester (III) mainly composed of ethylene terephthalate having a melting point of 231 to 260 ° C. This can be achieved by a polyester film for laminating metal plates, which is formed by laminating layers and has a plane orientation coefficient of 0.05 or less.

In the present invention, the surface orientation coefficient is 0.05 in order to enable many moldings such as ironing and pressing.
It is necessary that: If the surface orientation coefficient exceeds 0.05, severe formability such as ironing will be deteriorated, and impact resistance and taste characteristics will be greatly deteriorated. An unstretched film having a surface orientation coefficient of substantially 0 or less, preferably 0.03 or less, is desirable. Here, the plane orientation coefficient fn is obtained from the refractive indices (Nx, Ny, Nz) in the longitudinal direction, the width direction, and the thickness direction.
(Nx + Ny) / 2-Nz.

The polyester (I) mainly composed of ethylene terephthalate in the present invention is required to have a melting point of 150 to 230 ° C. from the viewpoint of heat resistance and adhesion to metal. It is desirable that 50 mol% or more of the polyester is an ethylene terephthalate unit, preferably 6
It is 0 mol% or more. Examples of the dicarboxylic acid component to be copolymerized include aromatic dicarboxylic acids such as isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodium sulfoisophthalic acid and phthalic acid, shu Acids, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids, and p-oxybenzoic acid and other oxycarboxylic acids be able to. Among these dicarboxylic acid components, isophthalic acid and naphthalenedicarboxylic acid are preferable in terms of impact resistance and taste characteristics. On the other hand, examples of the glycol component to be copolymerized include aliphatic glycols such as propanediol, pentanediol, hexanediol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, and aromatic glycols such as bisphenol A and bisphenol S. Is mentioned. Two or more kinds of these dicarboxylic acid components and glycol components may be used in combination.

Further, a polyfunctional compound such as trimellitic acid, trimesic acid and trimethylolpropane may be copolymerized with the copolyester as long as the effects of the present invention are not impaired.

As the polyester (I) preferably used in the present invention, isophthalic acid copolymerized polyethylene terephthalate is preferable from the viewpoint of taste characteristics.

The polyester (II) containing butylene terephthalate as a main component in the present invention is required to have a melting point of 120 to 225 ° C. from the viewpoint of heat resistance and adhesion to metal. It is desirable that 50 mol% or more of the polyester is a butylene terephthalate unit, preferably 6
It is 0 mol% or more. The dicarboxylic acid component to be copolymerized is the same as the above polyester (I), and the glycol component is, for example, an aliphatic glycol such as propanediol, pentanediol, hexanediol or neopentyl glycol, or an alicyclic compound such as cyclohexanedimethanol. Aromatic glycols such as glycol, bisphenol A, bisphenol S and the like can be mentioned. Two or more kinds of these dicarboxylic acid components and glycol components may be used in combination.

Examples of the polyester (II) preferably used in the present invention include polybutylene terephthalate, isophthalic acid copolymerized polybutylene terephthalate, dodecanedioic acid copolymerized polybutylene terephthalate, sebacic acid copolymerized polybutylene terephthalate and the like. It is not limited to these.

In the present invention, the A layer is formed of polyester (I) and polyester (II), but the weight ratio of polyester (I) to polyester (II) is 50 in terms of the balance of impact resistance and taste characteristics. : 50 to 95: 5. More preferably, it is 60:40 to 90:10.

On the other hand, in consideration of scratch resistance in contact between the inner surface of the can and the holder during baking coating in the can making process and non-adsorption of the perfume component of the can contents, the melting point of the film is 231 to 260. It is necessary to laminate the B layer of polyester (III) mainly composed of ethylene terephthalate at ℃. Here, the polyester mainly composed of ethylene terephthalate is 50 mol% or more, preferably 70 mol%
The above is a polyester which is an ethylene terephthalate unit.

In the present invention, it is preferable that the film contains 0.01 to 1% by weight of a diethylene glycol component in order to improve impact resistance after being subjected to various heat histories in the can making process. More preferably 0.01
˜0.8% by weight, particularly preferably 0.01 to 0.6% by weight. When the content of the diethylene glycol component is less than 0.01, the polymerization process becomes complicated and it is not preferable in terms of cost. When it exceeds 1% by weight, the polyester is deteriorated due to the heat history in the can making process, and the impact resistance of the film is increased. It is not preferable because it gets worse. Diethylene glycol is by-produced during the production of polyester, but in order to make it 1% by weight or less,
Methods such as shortening the polymerization time or limiting the amount of an antimony compound or germanium compound used as a polymerization catalyst, a method of combining liquid phase polymerization and solid phase polymerization, a method of containing an alkali metal component, etc. are mentioned. Is not particularly limited.

Further, the polyester film of the present invention is
The intrinsic viscosity [η] is preferably 0.7 or more, and more preferably the intrinsic viscosity [η] is 0.75 or more, since impact resistance and taste characteristics can be greatly improved.

In order to improve the taste characteristics, the content of acetaldehyde in the film is preferably 50 ppm.
The following is more preferable, 30 ppm or less is more preferable, and 20 ppm or less is particularly preferable. If the acetaldehyde content exceeds 50 ppm, the taste characteristics are poor. The method for adjusting the content of acetaldehyde in the film to 50 pm or less is not particularly limited, but for example, in order to remove acetaldehyde generated by thermal decomposition when the polyester is produced by a polycondensation reaction or the like, the polyester is used under reduced pressure or Heat treatment at a temperature below the melting point of polyester in an inert gas atmosphere, preferably at 150 ° C. under reduced pressure or in an inert gas atmosphere
As mentioned above, the method of solid-phase polymerization at a temperature below the melting point, the method of melt film formation using a vent type extruder, the extrusion temperature when melt-extruding polyester is within the melting point +35 ℃, preferably within the melting point +30 ℃, Examples thereof include a method of extruding in a short time.

When the film of the present invention is used for beverages and food cans, the polyester (III) preferably contains 1 to 500 ppm of a germanium element in terms of taste characteristics, more preferably 5 to 300 ppm, especially It is preferably 10 to 100 ppm. The amount of germanium element is 1
If it is less than ppm, the effect of improving the taste characteristics is not sufficient, and if it exceeds 500 ppm, foreign matter is generated in the polyester to deteriorate the impact resistance and the taste characteristics. The polyester of the present invention can have improved taste characteristics by containing the above-mentioned specific amount of germanium element in the polyester. The method of incorporating the germanium element into the polyester may be any conventionally known method and is not particularly limited, but usually, at any stage before the completion of the production of the polyester, a germanium compound may be added as a polymerization catalyst. preferable. As such a method, for example, a method of directly adding a powder of a germanium compound, or Japanese Patent Publication No. 54-222
As described in Japanese Patent Laid-Open No. 34-34, a method of dissolving a germanium compound in a glycol component which is a starting material of polyester and adding it can be mentioned. Examples of the germanium compound include germanium dioxide,
Crystal water-containing germanium hydroxide, or germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium alkoxide compounds such as germanium ethyleneglycoxide, germanium phenolate, germanium phenoxide compounds such as germanium β-naphtholate, germanium phosphate, Examples thereof include phosphorus-containing germanium compounds such as germanium phosphite and germanium acetate. Of these, germanium dioxide is preferable.

The polyester of the present invention has a content of the oligomer in the polyester of 0.8% by weight from the viewpoint of taste characteristics.
The amount is preferably below, more preferably 0.7% by weight or less, and particularly preferably 0.6% by weight or less. Content of oligomer in copolymerized polyester is 0.8% by weight
If it exceeds, the taste characteristics are deteriorated, which is not preferable. The method for adjusting the content of the oligomer in the polyester to 0.8% by weight or less is not particularly limited, but the same method as the method for reducing the acetaldehyde content in the above-mentioned copolymerized polyester should be adopted. Can be achieved with.

The polyester of the present invention can be produced by any conventionally known method and is not particularly limited. For example, a case will be described where polyethylene terephthalate is copolymerized with an isophthalic acid component and germanium dioxide is added as a germanium compound. A terephthalic acid component, an isophthalic acid component and ethylene glycol are transesterified or esterified, and then germanium dioxide is added, followed by polycondensation reaction at a high temperature and reduced pressure until a constant diethylene glycol content is obtained, and a germanium element-containing polymer To get Then, the obtained polymer is subjected to a solid-state polymerization reaction at a temperature below its melting point under reduced pressure or in an inert gas atmosphere to reduce the content of acetadeldide to obtain a predetermined intrinsic viscosity [η] and a carboxyl end group. Etc. can be mentioned.

In producing the polyester of the present invention,
Conventionally known reaction catalysts and anti-coloring agents can be used, and examples of the reaction catalysts include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium. Examples of the anti-coloring agents such as compounds include phosphorus compounds.

In the present invention, polyester (I) and polyester (III) are a catalyst, an amount of diethylene glycol,
The amount of carboxyl end groups may be different. When the edges of the film are collected, it is preferable to collect them in the polyester A layer from the viewpoint of taste characteristics.

Further, the laminated film preferably has a ratio of the thickness of the A layer to the thickness of the B layer of 20: 1 to 1: 1 (A: B) from the viewpoint of taste characteristics and impact resistance, and particularly 1
It is preferably 5: 1 to 4: 1 (A: B) from the viewpoint of impact resistance.

In order to improve the handleability and processability of the polyester film of the present invention, at least either the A layer or the B layer is free of inorganic particles and / or organic particles having an average particle diameter of 0.1 to 10 μm. 0.01 to 10% by weight
It is preferably contained, and further preferably, 0.01 to 3% by weight of inorganic particles and / or organic particles having an average particle diameter of 0.1 to 5 μm is contained. 1
The use of particles having an average particle size of more than 0 μm is not preferable because defects in the film are likely to occur. Especially 3
Since it is not preferable to include particles of 0 μm or more,
It is preferable to use a filter capable of drastically reducing foreign matters of 30 μm or more as a film forming filter. Examples of the inorganic particles and / or organic particles include wet and dry silica, colloidal silica, titanium oxide, calcium carbonate,
Calcium phosphate, barium sulfate, alumina, mica,
Examples thereof include inorganic particles such as kaolin and clay, and organic particles including styrene, silicone, acrylic acid and the like as constituent components. Among them, inorganic particles such as wet and dry colloidal silica and alumina, and organic particles having styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components can be mentioned. Two or more kinds of these inorganic particles and / or organic particles may be used in combination.

The particles may be added to either the A layer or the B layer, but it is preferable to add the particles to the B layer for ease of handling. On the other hand, particles may be added to the layer A as long as the characteristics are not impaired in terms of recovery. In addition, when particles are not contained, when the polymer is melt extruded and solidified by a casting drum, a method in which the layer B is on the drum surface is roughened and the film is pressed with air to solidify rapidly is adopted. May be.

The thickness of the polyester film of the present invention is not particularly limited, but considering the moldability, impact resistance and taste characteristics of the metal can, it is preferably 5 to 50 μm, more preferably 8 to 45 μm, and particularly preferably. 10-40 μm
Is.

Further, in producing the polyester film of the present invention, if necessary, additives such as an antioxidant, a plasticizer, an antistatic agent, a weatherproofing agent and a terminal blocking agent can be appropriately used. In particular, the combined use of an antioxidant is preferable because it prevents deterioration of the polyester due to heat history during the can making process.
The amount is 0.001-1 with respect to the total film weight.
About wt% is preferable.

Further, it is preferable to improve the adhesiveness by applying a surface treatment such as corona discharge treatment in order to further improve the characteristics. At that time, the E value is 5 to 4
It is 0, preferably 10 to 25.

The polyester film of the present invention can be formed into a film by any conventionally known method. next,
The method for producing the film of the present invention will be described, but the invention is not limited thereto.

Isophthalic acid 1 as polyester (I)
7.5 mol% copolymerized polyethylene terephthalate ([η] = 0.84, diethylene glycol 0.7% by weight, melting point 215 ° C.) and polybutylene terephthalate as polyester (II) (melting point 221 ° C., [η] = 1.
0), 5 mol% of isophthalic acid as polyester (III)
Copolymerized polyethylene terephthalate ([η] = 0.9
0, diethylene glycol 0.89% by weight, melting point 240
C.) to separate twin-screw vent type extruders (the temperature of the extruder is set to the melting point + 25.degree. C. (the layer A side is set to the melting point + 30.degree. C. for polyester (I)) to melt, and then the feed block After stacking in 2 layers and discharging from the normal die,
A cast film is obtained by pressing the whole or a part of the film with air and cooling and solidifying with a cooling drum roughened so that the layer B becomes the drum surface. The two-layer laminated film thus obtained is optionally heat-aged or surface-activated and wound up. Further, it is preferable to subject the film to dust-proof treatment because defects in the film are less likely to occur.

The polyester cast film may be biaxially stretched simultaneously or successively. In the case of sequential biaxial stretching, it is also possible to perform stretching in the longitudinal direction or the width direction twice or more. The stretching ratio in the longitudinal direction and the width direction of the film can be arbitrarily set according to the degree of orientation, strength, elastic modulus, etc. of the target film, but preferably 2.5 to 2.5 in each direction.
It is 5.0 times. Either the stretching ratio in the longitudinal direction or the stretching ratio in the width direction may be increased or may be the same. The stretching temperature may be any temperature in the range of not less than the glass transition temperature of polyester and not more than the crystallization temperature, but it is usually preferably 80 to 150 ° C. Further, the film can be heat-treated after the biaxial stretching. This heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll, but the heat treatment is performed so that the plane orientation coefficient is 0.05 or less. The heat treatment temperature can be any temperature above the crystallization temperature of the polyester, but is preferably 150 to 260 ° C. The heat treatment time may be arbitrary, but it is usually preferably 1 to 60 seconds. The heat treatment may be performed while relaxing the film in its longitudinal direction and / or width direction.

The metal plate of the present invention is not particularly limited,
A metal plate made of iron, aluminum or the like is preferable in terms of formability. Furthermore, in the case of a metal plate made of iron, an inorganic oxide coating layer that improves the adhesion and corrosion resistance on the surface of the metal plate, 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, chromate treatment or chromium chromate treatment may be provided. Particularly, in terms of metallic chromium, 6.5 to 6.5 as chromium
150 mg / m ² of hydrated chromium oxide is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gun metal or brass may be further 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 metal laminating film of the present invention can be suitably used for coating the inner and outer surfaces of a two-piece metal can produced by drawing or ironing. Also, good metal adhesion for covering the lid part of a two-piece can, or the body, lid, and bottom of a three-piece can,
Since it has moldability, it can be preferably used. In particular, the colored film of the present invention can be used for coating the outer surface. Therefore, a colorant can be blended in the polyester layer, and a white colorant, a red colorant or the like is preferably used as the colorant, and a colorant selected from titanium oxide, zinc white, an inorganic or organic pigment, etc. It is desirable to add 50% by weight, preferably 15-40% by weight. If the addition amount is less than 5% by weight, the color tone and the whiteness are inferior, which is not preferable. You may use together a pinking agent, a bluing agent, etc. as needed.

[0038]

[Characteristics Evaluation Method] 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) Content of Germanium Element in Polyester The content of germanium element in the polyester composition and the peak intensity were quantified by fluorescent X-ray measurement.

(3) Intrinsic viscosity ([η]) of polyester Dissolve the polyester in orthochlorophenol,
It was measured at ° C.

(4) Melting point Polyester is crystallized, and it is subjected to a differential scanning calorimeter (DSC-2 type manufactured by Perkin Elmer Co., Ltd.) at 10 ° C./min.
The heating rate was measured.

(5) 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.

(6) Content of Oligomer in Polyester Film 100 mg of polyester film was dissolved in 1 ml of orthochlorophenol to prepare a liquid chromatograph (Varia).
The cyclic trimer was measured with a model 8500 manufactured by N. Co. to obtain the amount of oligomer.

(7) Adhesiveness Between the metal roll heated to 180 to 230 ° C. and the silicon rubber roll, the polyester film A side of the present invention and the S side are coated.
Aligned with n-plated tin plate, pressure 40kg / cm
After pressure bonding, the mixture was cooled in air after bonding. The adhesive strength of the laminated plate was determined by a peeling test at an angle of 180 °, and the adhesive strength of 250 g / cm or more was regarded as acceptable.

(8) Impact resistance The adhesive surface of the polyester film and the tin-plated tin metal plate are heated and pressure-laminated at a temperature of 180 to 230 ° C., and then subjected to an ironing molding machine (molding ratio (maximum thickness / minimum thickness)).
= 2.8), bottom molding, etc.
I got a necking can.

(Impact resistance in carbonated drinks) 220 after can making
℃, 10 minutes heat treatment, filled with carbonated water, 0 ℃, 24
Carbonated bubbling for an hour. Then, after punching each 5 points from the outside of the can bottom with a punch, the contents were removed and the inside of the can was masked with wax, and 1% saline was put into the cup,
A voltage of 6 V was applied to the electrode in the saline solution and the metal can to read the current value. The average value of 5 cans was measured and evaluated as follows.

Class A: less than 0.2 mA Class B: 0.2 mA or more and less than 0.4 mA Class C: 0.4 mA or more and less than 0.6 mA Class D: 0.6 mA or more

(Impact resistance in retort beverages) 2 after canning
Bake at 20 ℃ for 10 minutes, and after baking at 20 ℃
After retort treatment for 30 minutes, fill it with commercially available oolong tea, leave it at 20 ° C for 24 hours, and apply 5 punches from the outside of the can bottom with punches, then remove the contents and mask the inside of the can with wax. Then, 1% saline solution was put into the cup, and a voltage of 6 V was applied to the electrode and the metal can in the saline solution to read the current value. The average value of 5 cans was measured and evaluated as follows.

A class: less than 0.2 mA B class: 0.2 mA or more and less than 0.4 mA C class: 0.4 mA or more and less than 0.6 mA D class: 0.6 mA or more (9) Taste characteristics B layer side of polyester film After leaving it alone for 7 days so as to come into contact with the fragrance aqueous solution (20 ppm aqueous solution of d-limonene) (contact area: 314 cm ² ), the film was exposed to 80
The components that are heated and expelled in a nitrogen stream for 30 minutes at
D per 1 g of film by gas chromatography
-The amount of limonene adsorbed was quantified to evaluate the taste characteristics of the film.

Further, a perfume aqueous solution (d-
Limonene (20 ppm aqueous solution) was put therein, and after sealing, the mixture was left for 1 month, then opened and the sensory test evaluated the change of odor according to the following criteria.

Class A: No change in odor is observed Class B: Almost no change in odor C Class: Change in odor is observed

[0053]

The present invention will be described in detail below with reference to examples.

Example 1 17.5 mol% of isophthalic acid as polyester (I)
Copolyethylene terephthalate ([η] = 0.8
4, 0.7% by weight of diethylene glycol, melting point 215
C., 150.degree. C. for 5 hours under vacuum drying) and polybutylene terephthalate (melting point 221.degree. C., [.eta.] = 1.0, 140.degree. C. for 5 hours under vacuum drying) were chip-blended to a weight ratio of 70:30, and polyester ( III) as isophthalic acid 5
Mol% copolymerized polyethylene terephthalate ([η] =
0.90, diethylene glycol 0.89% by weight, melting point 240 ° C., silicon oxide particles 0.2% by weight having an average particle diameter of 3 μm, vacuum dried at 175 ° C. for 3 hours. Melting point + 25 ° C. (A layer side is set to melting point + 30 ° C. with respect to polyester (I)) to melt, and then two layers (polyester A layer / polyester B layer = 9/1) in a feed block After stacking and discharging from a normal spinneret, the entire film is pressed by air and cooled and solidified by a cooling drum (surface roughness 8 s) roughened so that the layer B becomes the drum surface to obtain a cast film. Further, the A layer was subjected to corona discharge treatment in the atmosphere at 25 ° C. so that the E value was 20. The thus obtained two-layer laminated film had a polyester film [η] of 0.79. Table 1 shows the physical properties and the results of forming a can by laminating the layer A on a metal plate. As can be seen from the table, the film of the present invention was excellent not only in adhesiveness but also in impact resistance and taste characteristics.

Examples 2 to 6 Films were obtained in the same manner as in Example 1, except that the type of polyester, the lamination ratio, the conditions for film formation were changed. The results are shown in Tables 1 and 2.

In Example 2, 13 mol% of dodecanedioic acid copolymerized polybutylene terephthalate as polyester (I) and polyester (II) (melting point 190 ° C., [η] =
A film was obtained in the same manner as in Example 1 except that the weight ratio of (0.90) was 75:25.

In Example 3, as polyester (I) and polyester (II), isophthalic acid 35 mol% copolymerized polybutylene terephthalate (melting point 140 ° C., [η] =
0.90) was changed to 80:20 in the weight ratio, and Example 1 was changed.
A film was obtained in the same manner as. In each case, good characteristics were obtained as shown in Table 1.

In Example 4, the stacking ratio was 1: 2 (A: B).
A film was obtained in the same manner as in Example 1 except that B
The impact resistance was slightly reduced due to the large layer stacking ratio.

In Example 5, as the polyester (I), 20 mol% of isophthalic acid copolymerized polyethylene terephthalate ([η] = 0.70, diethylene glycol 0.7% by weight, melting point 207 ° C., dried at 120 ° C. for 8 hours), polyester As (III), 3 mol% of isophthalic acid copolymerized polyethylene terephthalate ([η] = 0.70, diethylene glycol 0.89% by weight, melting point 247 ° C., average particle size 3)
A film was obtained in the same manner as in Example 1 except that 0.2% by weight of silicon oxide particles having a particle diameter of 175 and vacuum drying at 175 ° C. for 3 hours was used. The obtained film had [η] = 0.69, and the impact resistance and taste characteristics were slightly lowered.

In Example 6, a film was obtained by changing the cast and subsequent steps in Example 1 as follows. That is, the cast was electrostatically cast onto a mirror-finished drum at 25 ° C. so that the layer A would be the drum surface, and this unstretched film was stretched 3.3 times in the longitudinal direction at 95 ° C. and then in the widthwise direction at 105 ° C. Three
It was stretched twice. Furthermore, this biaxially stretched film is
Heat treatment was performed at 5 ° C. for 7 seconds to obtain a polyester film having a thickness of 30 μm. The obtained film has a plane orientation coefficient of 0.0.
It was 3. Although the impact resistance of the carbonated beverage was slightly lowered, it had good taste characteristics.

Comparative Example 1 As layer A, isophthalic acid 17.5 mol% copolymerized polyethylene terephthalate (germanium element content 50 ppm,
[Η] = 0.65, diethylene glycol 1.50% by weight, melting point 210 ° C., acetaldehyde amount 37 ppm, carboxyl terminal group 41 equivalent / ton), B layer as isophthalic acid 5 mol% copolymerized polyethylene terephthalate (germanium element amount 42 ppm, [Η] = 0.64, diethylene glycol 1.20% by weight, melting point 239 ° C., acetaldehyde amount 38 ppm, carboxyl end group 39 equivalent / ton, silicon oxide particles having an average particle size of 6 μm 0.1% by weight) At 285 ° C., a copolyester film was obtained in the same manner as in Example 1. The results are shown in Table 3.

Since the polyester film was not blended with polybutylene terephthalate and had a low intrinsic viscosity, the characteristics were deteriorated.

Comparative Example 2 The stretching conditions in Example 6 were 95 ° C. and 3.7 in the longitudinal direction.
Then, the film was stretched in the width direction at a temperature of 105 ° C. by 3.6 times. Further, this biaxially stretched film was heat-treated under a constant length at 190 ° C. for 7 seconds to obtain a polyester film having a thickness of 30 μm. The obtained film had a plane orientation coefficient of 0.10.

The characteristics of the film thus obtained are shown in Table 3. As can be seen from the table, the impact resistance and taste characteristics were greatly reduced because the surface orientation coefficient was large and the moldability was deteriorated.

[0065]

[Table 1]

[Table 2]

[Table 3]

[0066]

INDUSTRIAL APPLICABILITY The polyester film for laminating metal sheets of the present invention has excellent adhesiveness, impact resistance, and taste characteristics, and particularly has excellent impact resistance even after heat treatment such as baking and retorting. It can be suitably used for a metal can manufactured by processing.

Claims (2)

[Claims] 1. A polyester (I) mainly composed of ethylene terephthalate having a melting point of 150 to 230 ° C. and a melting point of 120.
Polyester (III) mainly composed of ethylene terephthalate having a melting point of 231 to 260 ° C. is added to an A layer formed by mixing polyester (II) mainly composed of butylene terephthalate at ˜225 ° C. in a weight ratio of 50:50 to 95: 5. A polyester film for laminating a metal plate, which is formed by laminating a B layer made of (1) and has a plane orientation coefficient of 0.05 or less. 2. The polyester film for laminating metal plates according to claim 1, which has an intrinsic viscosity [η] of 0.7 or more.