JP3293261B2 - 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 laminating a metal plate which is excellent in adhesiveness, moldability, impact resistance and taste characteristics and is suitable for a metal can produced by molding.

[0002]

2. Description of the Related Art Conventionally, the inner and outer surfaces of a metal can are coated with various thermosetting resins, such as epoxy and phenol, dissolved or dispersed in a solvent to prevent 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.

[0003] As a method of solving these problems, a polyester film is laminated on a steel plate, an aluminum plate, or a metal plate which has been subjected to various surface treatments such as plating, which is a material for a metal can. When a metal can is manufactured by drawing or ironing a plate, 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.

(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 or 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, JP-A-64-22530 discloses a polyester film having a specific density and plane orientation coefficient, and JP-A-2-57339 discloses a polyester film having a specific density. Discloses a copolymerized polyester film having specific crystallinity. However, these proposals cannot comprehensively satisfy the above-mentioned various required characteristics, and cannot be said to be at a sufficiently satisfactory level especially in impact resistance. Furthermore, when laminating to a metal plate at a high speed of 100 m / min or more, a portion where the adhesion between the film and the metal plate is not sufficient may occur, and the impact resistance may be greatly deteriorated.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an impact resistance,
Excellent taste property is to provide a suitable metal plate laminating copolymer polyester Ruff Irumu the metal can be produced by molding.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to provide a polyester having a melting point of from 120 to 230.degree.
A layer as a component and a poly (melting point: 231 to 260 ° C)
Laminating the B layer ester as a main component, the wetting tension of a diethylcarbamoyl <br/> glycol component contains 0.01 to 1 wt%, less <br/> Kutomo A layer side surface is 45 dyne / cm or more.

The polyester in the present invention is a polymer comprising a dicarboxylic acid component and a glycol component. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxy acid. Aromatic dicarboxylic acids such as ethanedicarboxylic acid, 5-sodium sulfoisophthalic acid and phthalic acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid and fumaric acid, and cyclohexanedicarboxylic acid And oxycarboxylic acids such as p-oxybenzoic acid. Among these dicarboxylic acid components, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid are preferable from the viewpoint of impact resistance and taste characteristics. On the other hand, as the glycol component, for example, ethylene glycol, propanediol,
Examples thereof include aliphatic glycols such as butanediol, pentanediol, hexanediol, and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; and aromatic glycols such as bisphenol A and bisphenol S. Among them, ethylene glycol is preferred among these glycol components from the viewpoint of impact resistance and taste characteristics. 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, a polyfunctional compound such as trimellitic acid, trimesic acid or trimethylolpropane may be copolymerized with the copolymerized polyester.

The polyester used in the present invention has a heat resistance of 120 to 260 ° C. as a melting point,
It is necessary in terms of sufficient adhesion to a metal plate. Preferably, polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, and copolymerized polyesters thereof, and the like.In addition, when these acid components or glycol components are copolymerized with these polyesters, all the acid components constituting the polyester are used. From the viewpoint of adhesiveness to the metal plate, it is preferable that the copolymerization with the metal plate is 1 to 40 mol% with respect to all glycol components, and more preferably 5 to 30 mol%, particularly preferably 8 to 20 mol%. If the copolymerization amount is less than 1 mol%, the adhesion to the metal plate is poor, and the film is peeled off or the impact resistance is poor, for example, the crystallization of the film is promoted in the production process of the metal can. Preferred copolymerization components include isophthalic acid, butanediol, etc., with isophthalic acid being particularly preferred.

In order to improve the impact resistance in the present invention, it is necessary that the diethylene glycol component is contained in an amount of 0.01 to 1% by weight, preferably 0.01 to 1% by weight.
0.8% by weight, more preferably 0.01 to 0.6% by weight, particularly preferably 0.01 to 0.5% by weight. If the content of diethylene glycol is less than 0.01 % by weight, the polymerization process becomes complicated and the cost is unfavorable. If it exceeds 1% by weight, the polyester deteriorates due to heat history in the can-making process, and the film has an impact resistance. Is greatly deteriorated, which is not preferable. Diethylene glycol is by-produced during the production of polyester. To reduce the amount to 1% by weight or less, a method of shortening the polymerization time or limiting the amount of an antimony compound, a germanium compound, etc. used as a polymerization catalyst, a liquid phase polymerization, And a method of combining solid phase polymerization and the method, but the method is not particularly limited.

Further, in the present invention, it is necessary that the wetting tension of at least one surface of the film is 45 dyne / cm or more in order to greatly improve the impact resistance of a can obtained by making a can after high-speed lamination. Preferably, the wetting tension of the film surface bonded to the metal plate is 48 dyne / cm.
More preferably, it is more preferably 50 dyne / cm or more.

The wetting tension of at least one side of the film is 4
As a method for controlling the dive rate to 5 dyne / cm or more, a known method such as a discharge treatment, a chemical treatment, and a flame treatment can be used. Among them, a method of performing corona discharge treatment on the surface is preferable as a method of improving impact resistance. Corona discharge treatment means that when a strong electric field is localized, such as when a high voltage is applied to an electric wire, a local discharge limited to that region occurs.This is called corona discharge treatment, Surface treatment is performed by interposing a film under the discharge. Further, the corona discharge treatment may be performed in air, under nitrogen or carbon dioxide gas.
A corona discharge treatment as disclosed in JP-A-20236 and JP-B-57-30854 can be preferably used. The strength at the time of the corona discharge treatment is expressed as an E value.
E value = W / (D · V), where W is the processing intensity (W), D is the processing width (m), and V is the film speed (m /
Minute). This E value is preferably 10 to 60, more preferably 15 from the viewpoint of improving the wetting tension and the surface defect.
In the range of ~ 35. When the treatment is performed at a temperature lower than the glass transition point of the polymer, the surface wetting tension can be effectively increased. The surface treatment is preferably performed on the side of the film to be bonded to the metal.

A layer mainly composed of polyester having a melting point of 120 to 230 ° C. and a melting point of 231 to 260 ° C.
The laminated film formed by laminating the layer B containing polyester as a main component not only improves the adhesiveness between the layer A and the metal plate, but also provides a retainer for baking the can after baking. It is preferable to provide a layer B so as not to damage the inner surface. Further, the composition, catalyst, amount of diethylene glycol, and amount of carboxyl terminal group in each layer may be different. When collecting the edge of the film, it is preferable that the film be contained in the polyester A layer from the viewpoint of taste characteristics.

Preferably, the intrinsic viscosity [η] of the film is 0.7 or more, and more preferably, the intrinsic viscosity [η] is 0.7.
If it is 5 or more, it is considered that the entanglement density of the polymer is increased, and the impact resistance and taste characteristics can be further improved.

Furthermore, in the present invention, the intrinsic viscosity [η] is 0.1.
7 or more laminated cast films can be suitably used,
In this case, the average surface roughness Ra of the layer B, which is the non-adhesive surface, is set to 0.
A thickness of 001 to 1 μm, preferably 0.01 to 0.5 μm, and particularly preferably 0.01 to 0.3 μm is preferable in terms of blocking resistance and defect resistance.

In order to improve taste characteristics, the content of acetaldehyde in the polyester is preferably 50 ppm or less, preferably 40 ppm or less, more preferably 30 ppm or less, and particularly preferably 20 pp or less.
m or less is desirable. Acetaldehyde content is 50p
If it exceeds pm, the taste characteristics are inferior. The method for reducing the content of acetaldehyde in the film to 50 ppm or less is not particularly limited. A method in which heat treatment is performed at a temperature not higher than the melting point of the polyester under an inert gas atmosphere, preferably a method in which the polyester is subjected to solid-state polymerization at a temperature not lower than the melting point and a temperature of 150 ° C. or higher under reduced pressure or an inert gas atmosphere, Melt extrusion using polyester, when the polyester is melt-extruded, the extrusion temperature should be within the melting point + 40 ° C., preferably the melting point +3.
A method of extruding at 0 ° C or less in a short time can be mentioned.

The polyester of the present invention preferably contains germanium element in an amount of 1 to 500 ppm, more preferably 5 to 300 ppm, and particularly preferably 10 to 100 ppm, from the viewpoint of taste characteristics. When the amount of germanium element is less than 1 ppm, the effect of improving taste characteristics is not sufficient,
If it exceeds 500 ppm, foreign matter is generated in the polyester, so that impact resistance is deteriorated and taste characteristics are deteriorated.
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 for incorporating the germanium element into the polyester is not particularly limited, but it is usually preferable to add a germanium compound as a polymerization catalyst at any stage before the production of the polyester is completed. As such a method, for example, a method of directly adding a powder of a germanium compound, or as described in Japanese Patent Publication No. 54-22234, dissolves a germanium compound in a glycol component which is a starting material of a polyester. And the like. As the germanium compound, for example, germanium dioxide, germanium hydroxide containing crystal water, or germanium alkoxide compounds such as germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium ethylene glycolide, germanium phenolate, germanium β-
Examples thereof include germanium phenoxide compounds such as naphtholate, phosphorus-containing germanium compounds such as germanium phosphate and germanium phosphite, and germanium acetate. Among them, germanium dioxide is preferable.

Further, it is preferred that the carboxyl terminal group of the polyester film of the present invention be 45 equivalents / ton or less in view of impact resistance and taste characteristics of the film. In particular, it is preferable that the carboxyl terminal group is 40 equivalents / ton or less in view of impact resistance and taste characteristics of the film.

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.

The copolyester of the present invention contains 0.001 to 10 μm of inorganic and / or organic particles having an average particle size of 0.1 to 10 μm in order to improve the handleability of the film and the moldability of the metal can. 10% by weight, more preferably 0.1 to 8 μm in average particle size.
m of inorganic particles and / or organic particles of 0.001 to 3
% By weight. 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.

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 handling. The relationship D / d between the thickness d (μm) of the layer B and the average particle diameter D (μm) is preferably 0.05 to 5
0, more preferably 0.1 to 10.

On the other hand, particles may be added to the layer A as long as the characteristics are not impaired in terms of recovery and 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.

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 film made of the copolymerized polyester in the present invention may be an unstretched sheet or a stretched film stretched uniaxially or biaxially.

In a molding method in which the formability of the film is important, such as ironing, an unstretched sheet or
Refractive index (Nx, Ny, N
plane orientation coefficient fn obtained from z) = (Nx + Ny) / 2
A stretched film having a value of -Nz of 0 to 0.12. Among them, an unstretched film is preferable for improving the adhesiveness and the impact resistance.

The thickness of the polyester film of the present invention is not particularly limited, but is preferably 5 to 50 μm, more preferably 8 to 40 μm, particularly preferably 8 to 40 μm, in consideration of the moldability, impact resistance and taste characteristics of the metal can. 10-35 μm
It is.

Further, the laminated film preferably has a ratio of the thickness of the layer A to the thickness of the layer B of 20: 1 to 1: 1 (A: B) in view 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 particular, when the thickness of the layer B is preferably 7 μm or less, and more preferably 5 μm or less, the impact resistance becomes good, which is desirable.

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 polyester A, isophthalic acid 17.
5 mol% copolymerized polyethylene terephthalate (germanium content 40 ppm, [η] = 0.85, diethylene glycol 0.92 wt%, melting point 213 ° C., acetaldehyde content 12 ppm, carboxyl end group 21 equivalents / ton) and polyester B as isophthalic acid 5 mol% copolymerized polyethylene terephthalate (germanium element amount 4
2 ppm, [η] = 0.90, diethylene glycol 0.89% by weight, melting point 240 ° C., acetaldehyde amount 1
0 ppm, 20 equivalents / ton of carboxyl end groups) in a separate twin screw vented extruder (extruder temperature is melting point + 25 ° C)
And then melted, and then laminated in two layers by a feed block, discharged from a normal die, and cooled and solidified by a cooling drum to obtain a cast film. The two-layer laminated film thus obtained was subjected to the corona discharge treatment described above by E.
The layer A is processed and wound up at a value of about 15 to 25 W · min / m ² .

Further, a method of biaxially stretching the above-mentioned 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 according to the orientation degree, strength, elastic modulus and the like of the target film, but is preferably 2.5 to 500 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, 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. Further, 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 or on a heated roll. The heat treatment temperature can be any temperature from the crystallization temperature of the polyester to the softening point, but is preferably from 120 to 240 ° C. Although the heat treatment time can be arbitrarily set, 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. Thereafter, a corona discharge treatment is performed.

The metal plate of the present invention is not particularly limited, but a metal plate made of iron, aluminum, or the like is preferable from the viewpoint of formability. Furthermore, in the case of a metal plate made of iron, an inorganic oxide coating layer that improves adhesion and corrosion resistance on the surface thereof,
For example, a chemical conversion coating layer represented by chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, chromium chromate treatment, or the like may be provided. Particularly, in terms of chromium metal, 6.5 to 15 as chromium.
0 mg / m ² chromium hydrated oxide is preferred,
A malleable 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 surface and outer surface 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.

[0039]

[Methods for measuring and evaluating characteristics] The characteristics of the polyester film were measured and evaluated by the following methods.

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

(2) Wetting tension (γ) on the film surface This was carried out according to JIS K-6768. The following three series of standard solutions were used according to the magnitude of the surface tension.

30 dyne / cm ≦ γ <56 dyne /
cm: JIS K-6768 standard solution 56 dyne / cm ≦ γ <72 dyne / cm: ammonia water 72 dyne / cm ≦ γ: aqueous sodium hydroxide solution

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

(4) Melting Point of Polyester A polyester chip was crystallized and subjected to 10 ° C./C with a differential scanning calorimeter (DSC-2, manufactured by Perkin-Elmer Co.).
The measurement was performed at a heating rate of min.

(5) Acetaldehyde content in polyester or film 2 g of fine powder of polyester 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) Carboxyl terminal group (equivalent / ton) The polyester was dissolved in o-cresol / chloroform (weight ratio: 7/3) under the conditions of 90 to 100 ° C for 20 minutes, and potentiometric titration was performed with alkali.

(7) Oligomer content 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 oligomer amount.

(8) Plane Orientation Coefficient Measured using an Abbe refractometer using sodium D line (wavelength 589 nm) as a light source. The plane orientation coefficient fn = (Nx + Ny) / 2-Nz obtained from the refractive indexes (Nx, Ny, Nz) in the longitudinal direction, the width direction, and the thickness direction was calculated and obtained.

(9) Impact Resistance The adhesive surface of the polyester film and the Sn-plated tin metal plate were pressure-bonded at a temperature of 180 to 230 ° C. at a speed of 200 m / min, and an ironing machine (forming ratio (maximum thickness) / Minimum thickness) = 3.0), bottom molding
An Ironing can was obtained. In addition, this can
Dry baking was performed at 10 ° C. for 10 minutes, and after baking, the mixture was filled with carbonated water and bubbled with carbon dioxide at 0 ° C. for 24 hours. Then, after applying impact to each of the five places with a punch from the outside of the bottom of the can, the contents are removed and the inside of the can is masked with a wax, and 1% saline solution is put in the cup, and the electrode and the metal can in the saline solution are added. 6V
And a current value was read.

Class A: less than 0.5 mA Class B: 0.5 mA or more and less than 1 mA Class C: 1 mA or more and less than 3 mA Class D: 3 mA or more

(10) Taste characteristics The can (9) (diameter 6 cm, height 12 cm) was filled with a perfume aqueous solution (d-limonene 10 ppm aqueous solution) at 20 ° C. for 5 days, and then the can was heated at 80 ° C. for 30 days. The components removed by heating in a nitrogen stream for one minute were quantified by gas chromatography to determine the amount of d-limonene adsorbed per gram of the film, and the taste characteristics of the film were evaluated.

The perfume aqueous solution was placed in a metal can, left for one month after sealing, and then opened and subjected to a sensory test.
The change in odor was evaluated according to the following criteria.

Class A: no change in odor is observed Class B: little change in odor is observed Class C: change is observed in odor

[0054]

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

Example 1 17.5 mol% of isophthalic acid was used as the polyester for the layer A.
Copolymerized polyethylene terephthalate (germanium content 40 ppm, [η] = 0.85, diethylene glycol 0.92 wt%, melting point 213 ° C., acetaldehyde content 8 ppm, carboxyl end group 21 equivalents / ton), isophthalic acid 5 as polyester in layer B Mol% copolymerized polyethylene terephthalate (germanium element amount 42 pp
m, 0.2% by weight of silicon oxide particles having an average particle diameter of 4 μm,
[Η] = 0.90, 0.89% by weight of diethylene glycol, melting point 240 ° C., acetaldehyde amount 6 ppm, carboxyl end group 20 equivalents / ton) and a separate twin-screw extruder (the temperature of the extruder is melting point + 25 ° C.) (A layer side is set to a melting point + 25 ° C. with respect to the high melting point polyester, average residence time is about 20 minutes) and melted. Then, two layers (polyester A layer / polyester B) are fed by a feed block.
Layer = 9/1), discharged from an ordinary die, cooled and solidified by a cooling drum to obtain a 30 μm cast film. The resulting film had diethylene glycol 0.9.
1% by weight, acetaldehyde 12 ppm, [η] = 0.
80, and 0.60% by weight of the oligomer. Further, before winding up the film, the layer A was subjected to a corona discharge treatment at an E value of 25 W · min / m ² in air at 30 ° C. to obtain 52 dyne / cm.

Table 1 shows the physical properties of the two-layer laminated cast film thus obtained. As can be seen from the table, both impact resistance and taste characteristics were good.

[0057] 3.2 times in the longitudinal direction at 90 ° C. The key catcher strike film produced in the same manner as in Example 1, and then in the width direction at 105 ° C. 3.3
It was stretched twice. Furthermore, this biaxially stretched film is
Heat treatment at 0 ° C., E value = 20 W · min / m ² for layer A
Was subjected to a corona discharge treatment in air at a temperature of 30 ° C. to obtain a polyester film having a thickness of 53 dyne / cm and a thickness of 25 μm. The resulting film is
Diethylene glycol was 0.90% by weight, acetaldehyde was 9 ppm, [η] was 0.79, and oligomer was 0.49% by weight.

Table 1 shows the physical properties of the film thus obtained. As can be seen from the table, the adhesiveness, moldability, impact resistance and taste characteristics were all good.

[0059] Example 3, a corona discharge treatment conditions of Example 4 Example 1, added particles conditions and poly
By changing the ester conditions , a polyester cast film was obtained in the same manner as in Example 1. Tables 1 and 2 show the results.

In the third embodiment, the E value for the layer A = 15 W
· Minutes per minute / m ² corona discharge treatment, N ₂ / CO ₂ = 8
When performed in an atmosphere of 5/15 (volume ratio) and 80 ° C., it was 59 dyne / cm. Table 1 shows the results.

In the fourth embodiment, the E value = 15 W for the A layer
A minute / m ² corona discharge treatment at 50 ° C. in an N ₂ atmosphere resulted in 52 dyne / cm. Table 2 shows the results . [Η] of the obtained film is slightly lower and impact resistance
Slightly reduced.

Comparative Example 1 As layer A, 17.5 mol% of copolymerized polyethylene terephthalate isophthalic acid (a germanium element content of 40 ppm,
[Η] = 0.72, diethylene glycol 1.50% by weight, melting point 209 ° C., acetaldehyde amount 18 ppm, carboxyl end group 32 equivalents / ton), isophthalic acid 5 mol% copolymerized polyethylene terephthalate (germanium element amount 42 ppm, Polyester of silicon oxide particles having an average particle diameter of 4 μm, 0.2% by weight, [η] = 0.72, diethylene glycol 2.0% by weight, melting point 236 ° C., acetaldehyde amount 26 ppm, carboxyl terminal group 37 equivalents / ton) is polymerized. , The extrusion temperature of both is 280
° C, and a corona discharge treatment of E value = 20 W · min / m ² was performed on the layer A in air at 25 ° C, except that
A film having a wetting tension of 52 dyne / cm was obtained in the same manner as in Example 1. Table 2 shows the results.

As a result, the polyester film
The content of diethylene glycol was large, and the impact resistance of the film was poor.

Comparative Example 2 A film was obtained in the same manner as in Comparative Example 1 except that the content of diethylene glycol in the polyester of the layer A in Comparative Example 1 was 0.9% by weight and the surface corona discharge treatment was not performed. As shown in FIG. 2, the impact resistance of the film was poor.

[0065]

[Table 1]

[Table 2]

[0066]

The polyester film for laminating a metal plate of the present invention has excellent adhesiveness, moldability, impact resistance and taste characteristics, and can be suitably used for metal cans produced by molding.

Continuation of the front page (56) References JP-A-5-186612 (JP, A) JP-A-5-148349 (JP, A) JP-B-57-30854 (JP, B1) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B32B 15/08 B29C 55/02-55/20 B32B 27/36 C08J 5/18

Claims (2)

(57) [Claims] An A layer mainly composed of polyester having a melting point of 120 to 230 ° C, a melting point of 231 ° C to 2
A layer B mainly composed of polyester at 60 ° C. is laminated, and the diethylene glycol component is contained in an amount of 0.01 to 1% by weight.
Containing at least 45 dyn of wetting tension on the A layer side surface
e / cm or more, a polyester film for laminating a metal plate. 2. The polyester film for laminating a metal plate according to claim 1, wherein the intrinsic viscosity [η] of the film is 0.7 or more.