JP3189551B2 - Polyester film for metal plate lamination - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for laminating a metal plate. More specifically, the present invention relates to a polyester film for metal plate lamination which is excellent in adhesiveness, moldability, impact resistance and taste characteristics and is suitable for metal cans produced by molding.

[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 polyester 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 polyester film is required to have the following characteristics.

(1) The adhesiveness to a metal plate is excellent.

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

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

(4) The scent component of the contents of the can is not adsorbed on the polyester film, and the flavor of the contents is not impaired by the smell of the polyester film (hereinafter referred to as taste characteristics).

Many proposals have been made to solve these demands. For example, Japanese Patent Application Laid-Open No. Sho 64-22530 discloses a polyester film having a specific density and a plane orientation coefficient, and Japanese Patent Application Laid-Open No. 2-57339 discloses a film. Discloses a copolymerized polyester film having specific crystallinity. However, these proposals do not comprehensively satisfy the above-mentioned various required properties, and in particular, do not produce defects such as pinholes after molding, and have sufficient impact resistance and taste characteristics. He was not at a satisfactory level.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and is excellent in adhesiveness, moldability, heat resistance, impact resistance, taste characteristics, and especially impact resistance. Another object of the present invention is to provide a copolyester and a film for laminating a metal plate which are excellent in taste characteristics and suitable for a metal can produced by molding.

[0010]

The 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.
A layer obtained by mixing the polyester (II) mainly composed of butylene terephthalate in a weight ratio of 50:50 to 95: 5, and B 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 a metal plate, which is formed by laminating layers and having a plane orientation coefficient of 0.05 or less.

In the present invention, in order to enable many moldings such as ironing molding and squeezing molding, the plane orientation coefficient is 0.05
It is necessary that: When the plane orientation coefficient exceeds 0.05, severe formability such as ironing is deteriorated, and impact resistance and taste characteristics are greatly deteriorated. An unstretched film having a surface orientation coefficient of preferably 0.03 or less, more preferably substantially zero, is desirable. Here, the plane orientation coefficient fn is a plane orientation coefficient fn obtained from the refractive indexes (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 needs 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 mol%.
0 mol% or more. As the dicarboxylic acid component to be copolymerized, for example, aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, and phthalic acid; Acids, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acids such as fumaric acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, and oxycarboxylic acids such as p-oxybenzoic acid. be able to. Among these dicarboxylic acid components, isophthalic acid and naphthalenedicarboxylic acid are preferred from the viewpoint of impact resistance and taste characteristics. On the other hand, examples of glycol components to be copolymerized include aliphatic glycols such as propanediol, pentanediol, hexanediol and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as bisphenol A and bisphenol S; Is mentioned. In addition, 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, polyfunctional compounds such as trimellitic acid, trimesic acid, and trimethylolpropane may be copolymerized with the copolymerized polyester.

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

The polyester (II) mainly comprising butylene terephthalate in the present invention needs to have a melting point of 120 to 225 ° C. in terms of heat resistance and adhesion to metals. The polyester preferably has at least 50 mol% of butylene terephthalate units.
0 mol% or more. The dicarboxylic acid component to be copolymerized is the same as that of the above-mentioned polyester (I), and the glycol component is, for example, an aliphatic glycol such as propanediol, pentanediol, hexanediol and neopentyl glycol, and an alicyclic group such as cyclohexanedimethanol. And aromatic glycols such as glycol, bisphenol A and bisphenol S. In addition, two or more 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, polybutylene terephthalate copolymerized with isophthalic acid, polybutylene terephthalate copolymerized with dodecandionic acid, and polybutylene terephthalate copolymerized with sebacic acid. It is not limited to these.

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

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

In the present invention, in order to improve the impact resistance after receiving various heat histories in the can making process, the film preferably contains 0.01 to 1% by weight of a diethylene glycol component in the film, More preferably 0.01
To 0.8% by weight, particularly preferably 0.01 to 0.6% by weight. If the diethylene glycol component is less than 0.01, the polymerization process becomes complicated, which is not preferable in terms of cost. If it exceeds 1% by weight, the polyester deteriorates due to the heat history in the can making process, and the impact resistance of the film increases. It is not preferable because it deteriorates Diethylene glycol is a by-product of polyester production.
Methods that shorten the polymerization time, limit the amount of an antimony compound used as a polymerization catalyst, the amount of a germanium compound, etc., a method that combines liquid-phase polymerization and a solid-phase polymerization, and a method that contains an alkali metal component, are examples of the method. Is not particularly limited.

Further, the polyester film of the present invention comprises:
Preferably, the intrinsic viscosity [η] is 0.7 or more, and more preferably, the intrinsic viscosity [η] is 0.75 or more, because 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 content is more preferably 30 ppm or less, particularly preferably 20 ppm or less. When the content of acetaldehyde exceeds 50 ppm, the taste characteristics are inferior. The method for reducing the content of acetaldehyde in the film to 50 pm or less is not particularly limited. For example, in order to remove acetaldehyde generated by thermal decomposition during production of the polyester by a polycondensation reaction or the like, the polyester is reduced under reduced pressure or In an inert gas atmosphere, a method in which heat treatment is performed at a temperature equal to or lower than the melting point of the polyester, preferably at 150 ° C.
Above, a method of solid-phase polymerization at a temperature below the melting point, a method of melt-forming a film using a vented extruder, and when extruding polyester, the extrusion temperature should be within the melting point + 35 ° C, preferably within the melting point + 30 ° C. A method of extruding in a short time can be mentioned.

When the film of the present invention is used for drinks and food cans, the polyester (III) preferably contains germanium element in an amount of 1 to 500 ppm, more preferably 5 to 300 ppm, particularly preferably 5 to 300 ppm in terms of taste characteristics. Preferably it is 10-100 ppm. Germanium element content 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 substances are generated in the polyester to deteriorate the impact resistance or the taste characteristics. The polyester of the present invention can improve taste characteristics by including the above-mentioned specific amount of the germanium element in the polyester. The method of causing the germanium element to be contained in the polyester can be a conventionally known arbitrary method, and is not particularly limited.However, it is usually possible to add a germanium compound as a polymerization catalyst at an arbitrary stage before the completion of the production of the polyester. preferable. As such a method, for example, a method of adding a powder of a germanium compound as it is, or a method of Japanese Patent Publication No. 54-222
As described in JP-A-34-34, there can be mentioned a method in which a germanium compound is dissolved and added to a glycol component which is a starting material of a polyester. As the germanium compound, for example, germanium dioxide,
Germanium hydroxide containing crystal water, 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 include phosphorus-containing germanium compounds such as germanium phosphite, and germanium acetate. Among them, germanium dioxide is preferable.

The polyester of the present invention has an oligomer content of 0.8% by weight in view of taste characteristics.
It is preferably at most 0.7% by weight, more preferably at most 0.6% by weight. 0.8% by weight of oligomer in copolymerized polyester
If it exceeds, taste characteristics are inferior and it is not preferable. The method for reducing the content of the oligomer in the polyester to 0.8% by weight or less is not particularly limited, but a method similar to the above-described method for reducing the acetaldehyde content in the copolymerized polyester may be employed. Can be achieved.

For the production of the polyester of the present invention, any conventionally known method can be employed and is not particularly limited. For example, a case will be described in which an isophthalic acid component is copolymerized with polyethylene terephthalate and germanium dioxide is added as a germanium compound. The terephthalic acid component, isophthalic acid component and ethylene glycol are subjected to transesterification or esterification reaction, and then germanium dioxide is added.Then, the polycondensation reaction is continued under high temperature and reduced pressure until a constant diethylene glycol content is reached. Get. Then, the obtained polymer is subjected to a solid-phase polymerization reaction under reduced pressure or an inert gas atmosphere at a temperature not higher than its melting point to reduce the content of acetoadheride to obtain a predetermined intrinsic viscosity [η] and a carboxyl end group. And the like.

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.

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

Further, as the laminated film, the ratio of the thickness of the layer A to the thickness of the layer B is preferably from 20: 1 to 1: 1 (A: B) from the viewpoint of taste characteristics and impact resistance.
A ratio of 5: 1 to 4: 1 (A: B) is preferable 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 layer A or the layer B contains 0 to 10 μm of inorganic particles and / or organic particles having an average particle diameter of 0.1 to 10 μm. .01 to 10% by weight
The inorganic particles and / or organic particles having an average particle diameter of 0.1 to 5 μm are preferably contained in an amount of 0.01 to 3% by weight. 1
It is not preferable to use particles having an average particle diameter of more than 0 μm because defects in the film are likely to occur. Especially 3
Since it is not preferable to contain particles of 0 μm or more,
It is preferable to use a filter capable of drastically reducing foreign substances of 30 μm or more as a filter at the time of film formation. Inorganic and / or organic particles include, for example, wet and dry silica, colloidal silica, titanium oxide, calcium carbonate,
Calcium phosphate, barium sulfate, alumina, mica,
Examples include inorganic particles such as kaolin and clay, and organic particles containing 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 containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituents can be exemplified. Two or more of these inorganic particles and / or organic particles may be used in combination.

Although the particles may be added to either the A layer or the B layer, it is preferable to add the particles to the B layer for handling. On the other hand, particles may be added to the layer A as long as the properties are not impaired in terms of recovery or the like. When particles are not contained, when the polymer is melt-extruded and solidified with a casting drum, a method is adopted in which the layer B is turned into a drum surface on a roughened drum, the film is pressed with air, and the film is rapidly cooled and solidified. May be.

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

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

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

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

As the polyester (I), isophthalic acid 1
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, 0.89% by weight of diethylene glycol, melting point 240
° C) is supplied to a twin-screw vent type extruder (the temperature of the extruder is set to a melting point + 25 ° C (the melting point of the layer A is + 30 ° C with respect to the polyester (I)) and melted. After discharging from a normal die after laminating in two layers,
The whole or a part of the film is pressed with air and cooled and solidified by a cooling drum roughened so that the layer B becomes a drum surface to obtain a cast film. The two-layer laminated film thus obtained is subjected to heat aging or surface activation treatment if necessary, and then wound up. Further, it is preferable to apply a dustproof treatment to the film, since defects of the film hardly occur.

Further, the above-mentioned method of biaxially stretching the polyester cast film simultaneously or sequentially may be performed. In the case of sequential biaxial stretching, stretching in the longitudinal direction or the width direction can be performed twice or more. The stretching ratio in the longitudinal direction and the width direction of the film can be arbitrarily set in accordance with the degree of orientation, strength, elastic modulus and the like of the target film.
It is 5.0 times. 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 temperature may be any temperature as long as it is in the range from the glass transition temperature of the polyester to the crystallization temperature, but it is usually preferably from 80 to 150 ° C. After the biaxial stretching, the film can be subjected to a heat treatment. This heat treatment can be performed by any conventionally known method, such as in an oven, on a heated roll, or the like, but heat treatment is performed so that the plane orientation coefficient becomes 0.05 or less. The heat treatment temperature can be any temperature equal to or higher than the crystallization temperature of the polyester, but is preferably 150 to 260 ° C. The heat treatment time can be arbitrarily set, but it is usually preferable to perform the heat treatment for 1 to 60 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction.

The metal plate of the present invention is not particularly limited.
From the viewpoint of formability, a metal plate made of iron, aluminum, or the like is preferable. Further, in the case of a metal plate made of iron, an inorganic oxide coating layer on the surface thereof for improving adhesion and corrosion resistance, for example, chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment A chemical conversion treatment coating layer represented by, for example, a chromate treatment or a chromium chromate treatment may be provided. In particular, in terms of chromium metal, 6.5 to chrome
A chromium hydrated oxide of 150 mg / m ² is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gunmetal, brass, etc. may be provided. It is preferable that tin plating has a plating amount of 0.5 to 15 mg / m ² , and nickel or aluminum has a plating amount of 1.8 to 20 g / m ² .

The film for metal lamination of the present invention can be suitably used for coating the inner and outer surfaces of a two-piece metal can manufactured by drawing or ironing. In addition, good metal adhesion for covering the lid 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. For this reason, a coloring agent can be blended in the polyester layer. As the coloring agent, a white coloring agent, a red coloring agent, or the like is preferably used, and a coloring agent selected from titanium oxide, zinc white, an inorganic or organic pigment, and the like is used. It is desirable to add 50% by weight, preferably 15 to 40% by weight. If the addition amount is less than 5% by weight, the color tone, whiteness and the like are inferior and are not preferred. If necessary, a pinking agent, a bluing agent and the like may be used in combination.

[0038]

[Evaluation method of characteristics] The characteristics were measured and evaluated by the following methods.

(1) Content of diethylene glycol component in polyester Measured by NMR (13C-NMR spectrum).

(2) Content of Germanium Element in Polyester The content of the germanium element in the polyester composition and the peak intensity were quantified by X-ray fluorescence measurement.

(3) Intrinsic Viscosity of Polyester ([η])
Measured in ° C.

(4) Melting point The polyester was crystallized and subjected to differential scanning calorimetry (DSC-2, manufactured by Perkin Elmer) at 10 ° C./min.
The temperature was measured at a rate of temperature rise.

(5) Acetaldehyde content in the film 2 g of a fine powder of the film was collected and charged in a pressure vessel together with ion-exchanged water, extracted with water at 120 ° C. for 60 minutes, and 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, and the solution was subjected to liquid chromatography (Varia).
The cyclic trimer was measured using Model 8500 (manufactured by N Co., Ltd.) and defined as the amount of oligomer.

(7) Adhesive property The surface of the polyester film A of the present invention is placed between the metal roll and the silicone rubber roll heated to 180 to 230 ° C.
Combined with n-plated tin plate, pressure 40kg / cm
, And cooled in air after bonding. The adhesive strength of the laminate was determined by a peel test at an angle of 180 °, and a laminate having an adhesive strength of 250 g / cm or more was judged to be acceptable.

(8) Impact resistance The adhesive surface of the polyester film and the tin-plated tin metal plate are laminated by heating and pressurizing to a temperature of 180 to 230 ° C., and the ironing machine (forming ratio (maximum thickness / minimum thickness))
= 2.8), bottom molding, etc.
A ning can was obtained.

(Impact resistance in carbonated beverage)
Heat treatment at 0 ° C for 10 minutes.
Carbonated bubbling for hours. Then, after applying impact to each of the 5 places with a punch from the outer surface of the can bottom, the contents are removed and the inner surface of the can side is masked with a wax, and 1% saline solution is put in the cup,
A voltage of 6 V was applied to the electrode and the metal can in the saline solution, and the current value was read. The average value of five 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)
Perform baking at 20 ° C for 10 minutes.
Perform a retort treatment for 30 minutes, fill with commercially available oolong tea, leave at 20 ° C. for 24 hours, apply an impact to each of the five places with a punch from the outer surface of the can bottom, then remove the contents and mask the inner surface of the can with a wax. Then, a 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, and the current value was read. The average value of five 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 (9) Taste characteristics Layer B side of polyester film Only after contacting with a fragrance aqueous solution (d-limonene 20 ppm aqueous solution) (contact area: 314 cm ² ) for 7 days, the film was washed with 80
The components that are heated and expelled in a nitrogen stream at
According to gas chromatography, d / g of film
-The amount of limonene adsorbed was quantified to evaluate the taste characteristics of the film.

In addition, a perfume aqueous solution (d-
Limonene (20 ppm aqueous solution) was added, left for one month after sealing, then opened, and the change in odor was evaluated by a sensory test according to the following criteria.

Grade A: no change in odor B class: little change in odor C class: change in odor

[0053]

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

Example 1 17.5 mol% of isophthalic acid as polyester (I)
Copolymerized polyethylene terephthalate ([η] = 0.8
4, 0.7% by weight of diethylene glycol, melting point 215
C., 150 ° C. for 5 hours under vacuum) and polybutylene terephthalate (melting point: 221 ° C., [η] = 1.0, vacuum drying at 140 ° C. for 5 hours) are chip-blended to a weight ratio of 70:30, and polyester ( III) as isophthalic acid 5
Mol% copolymerized polyethylene terephthalate ([η] =
0.90, 0.89% by weight of diethylene glycol, melting point 240 ° C., 0.2% by weight of silicon oxide particles having an average particle diameter of 3 μm, and vacuum drying at 175 ° C. for 3 hours. Melting point + 25 ° C (A layer side is set to + 30 ° C for polyester (I)) and melted, then two layers (Polyester A layer / Polyester B layer = 9/1) by feed block After laminating and discharging from a normal die, the entire film is pressed with air and cooled and solidified by a cooling drum (surface roughness 8 s) roughened so that the layer B becomes a drum surface to obtain a cast film. Further, the layer A was subjected to a corona discharge treatment in an air atmosphere at 25 ° C. so that the E value = 20. [Η] of the polyester film of the two-layer laminated film thus obtained was 0.79. Table 1 shows the physical properties and the results of laminating the layer A on a metal plate to make a can. 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 types, lamination ratios, film forming conditions, etc. of the respective polyesters were changed to obtain films. The results are shown in Tables 1 and 2.

In Example 2, 13 mol% of dodecandionic acid copolymerized polybutylene terephthalate (melting point 190 ° C., [η] =
A film was obtained in the same manner as in Example 1 except that the amount of 0.90) was changed to 75:25 by weight.

In Example 3, 35 mol% of isophthalic acid copolymerized polybutylene terephthalate (melting point 140 ° C., [η] = 100%) was used as polyester (I) and polyester (II).
0.90) was changed to a weight ratio of 80:20 in Example 1.
A film was obtained in the same manner as described above. In each case, good characteristics were obtained as shown in Table 1.

In Example 4, the lamination 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 lamination ratio of the layers.

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 (III) is a copolymerized polyethylene terephthalate of 3 mol% isophthalic acid ([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 μm of silicon oxide particles having a thickness of 0.2 μm and vacuum drying at 175 ° C. for 3 hours were used. The obtained film had [η] = 0.69, and the impact resistance and taste characteristics were slightly reduced.

In Example 6, a film was obtained in the same manner as in Example 1 except that the part after the casting was changed as follows. That is, the cast is electrostatically applied to a mirror drum at 25 ° C. so that the layer A is on the drum surface, and the unstretched film is 3.3 times in the longitudinal direction at 95 ° C., and then 3.times. In the width direction at 105 ° C. 3
It was stretched twice. Further, the biaxially stretched film is placed under
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. The impact resistance of the carbonated beverage was slightly reduced, but had good taste characteristics.

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

This polyester film was not blended with polybutylene terephthalate and had a low intrinsic viscosity, so that its properties were deteriorated.

Comparative Example 2 In Example 6, the stretching conditions were 95 ° C. and 3.7 in the longitudinal direction.
And then stretched 3.6 times in the width direction at 105 ° C. Further, the biaxially stretched film was heat-treated at a constant length of 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.

Table 3 shows the properties of the film thus obtained. As can be seen from the table, the surface orientation coefficient was large and the moldability was deteriorated, so that the impact resistance and taste characteristics were greatly reduced.

[0065]

[Table 1]

[Table 2]

[Table 3]

[0066]

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

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (2)

(57) [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.
Layer A, which is a mixture of polyester (II) mainly composed of butylene terephthalate and a weight ratio of 50:50 to 95: 5 at 225 ° C. to 225 ° C., polyester (III) mainly composed of ethylene terephthalate having a melting point of 231 ° C. to 260 ° C. A polyester film for laminating a metal plate, characterized in that a layer B made of the following is laminated and the plane orientation coefficient is 0.05 or less. 2. The polyester film for laminating a metal plate according to claim 1, wherein the intrinsic viscosity [η] is 0.7 or more.