JPH0784533B2 - Polyester film for laminating metal plates - Google Patents

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 for 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 on the metal plate, which is a material for a metal can, or a film of a film. When a metal can is manufactured by drawing or ironing a laminated metal plate, the polyester film is required to have the following characteristics.

(1) Excellent adhesion to a metal plate. (2) It has excellent moldability. (3) The polyester film should not be peeled off, nor should cracks or pinholes be generated by the impact on the metal can. (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 in order 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 it cannot be said that they are at a sufficiently satisfactory level particularly for impact resistance and taste characteristics.

[0006]

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 copolyester film for laminating metal plates, which has excellent taste characteristics and is suitable for a metal can produced by molding.

[0007]

The above-mentioned object of the present invention is characterized in that the melting point is from 150 to 250 ° C., the diethylene glycol component is contained from 0.01 to 1% by weight, and the acetaldehyde content is 50 ppm or less. Polyester film for metal plate laminating or melting point 1
Polyester A of 50 to 230 ° C and melting point of 220 ° C to 2
A laminated polyester film obtained by laminating polyester B at 50 ° C., containing 0.01 to 1% by weight of a diethylene glycol component, and having an acetaldehyde content of 50 ppm or less. Can be achieved by

The polyester in the present invention is a polymer composed of a dicarboxylic acid component and a glycol component, and examples of the dicarboxylic acid component include terephthalic acid, ishiphthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, Aromatic dicarboxylic acids such as diphenoxyethanedicarboxylic 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, Examples thereof include alicyclic dicarboxylic acids such as cyclohexyne dicarboxylic 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,
Butanediol, Pentanediol, Hexanediol
And aliphatic glycols such as neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, and aromatic glycols such as bisphenol A and bisphenol S. Among these glycol components, ethylene glycol is preferable from the viewpoint of impact resistance and taste characteristics. Two or more 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 effect of the present invention is not impaired.

The polyester used in the present invention has a heat resistance of 150 to 250 ° C. as a melting point,
It is necessary in terms of sufficient adhesiveness with the metal plate. Preferred examples include polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate and copolyesters thereof, and when these polyesters are copolymerized with the above acid component or glycol component, all acid components constituting the polyester are preferable. and/
Alternatively, copolymerization of 1 to 40 mol% with respect to all glycol components is preferable from the viewpoint of adhesiveness to a metal plate, further 5 to 30 mol%, and particularly 8 to 20 mol% is preferable. When 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 because the crystallization of the film is promoted in the manufacturing process of the metal can. On the other hand, if it exceeds 40 mol%, the melting point becomes low and the impact resistance becomes poor. Examples of preferred copolymerization components include isophthalic acid and butanediol, with isophthalic acid being particularly preferred. Further, when a non-uniform polymer such as a blend is used as the polyester of the present invention, the impact resistance is lowered. Therefore, the polyester to be supplied to the extruder is preferably one kind, or 80% by weight or more is a uniform polyester. It is desirable to do.

In order to improve the impact resistance in the present invention, it is necessary to contain the diethylene glycol component in an amount of 0.01 to 1% by weight, preferably 0.01 to 1% by weight.
It is 0.8% by weight, more preferably 0.01 to 0.6% by weight, and particularly preferably 0.01 to 0.5% 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 reduce the amount to 1% by weight or less, the polymerization time is shortened, or an antimony compound used as a polymerization catalyst,
Examples include a method of limiting the amount of a germanium compound and a method of combining liquid phase polymerization and solid phase polymerization, but the method is not particularly limited.

In addition, in order to improve the taste characteristics, the content of acetaldehyde in the polyester needs to be 50 ppm or less, preferably 40 ppm or less, more preferably 30 ppm or less, and particularly preferably 20 ppm or less. If the content of acetaldehyde exceeds 50 ppm, the taste characteristics are poor. The method for adjusting the acetaldehyde content 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 reduced in pressure or A method of heat-treating at a temperature not higher than the melting point of polyester in an inert gas atmosphere, preferably a method of solid-phase polymerizing polyester at a temperature not lower than 150 ° C. and not higher than the melting point under reduced pressure or in an inert gas atmosphere, vent-type extruder And a method of performing extrusion in a short time at a melting point of + 40 ° C. or less, preferably a melting point of + 30 ° C. or less when melt-extruding polyester.

The intrinsic viscosity [η] is preferably 0.7.
As described above, it is more preferable that the intrinsic viscosity [η] is 0.75 or more, because impact resistance and taste characteristics can be further improved.

From the viewpoint of taste characteristics, the polyester of the present invention preferably contains 1 to 500 ppm of a germanium element, more preferably 5 to 300 ppm, and particularly preferably 10 to 100 ppm. If the amount of germanium element is less than 1 ppm, the effect of improving the taste is not sufficient, and if it exceeds 500 ppm, foreign matter is generated in the polyester, and the impact resistance is deteriorated or the taste characteristics are deteriorated. The polyester of the present invention can have improved taste characteristics by containing the above-mentioned specific amount of germanium element in the polyester. A method of incorporating a germanium element into a polyester can be adopted and is not particularly limited, but it is usually preferable to add a germanium compound as a polymerization catalyst at an arbitrary stage before the production of the polyester is completed. As such a method, for example, a method of adding powder of germanium compound as it is, or, as described in JP-B-54-22234, glyco-a starting material for polyester is used.
Examples of the method include adding a germanium compound by dissolving it in an aluminum component. Examples of the germanium compound include germanium dioxide, germanium hydroxide containing water of crystallization, germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium alkoxide compounds such as germanium ethylene glycoloxide, germanium phenol-
And germanium phenoxide compounds such as germanium β-naphthoate, phosphorus-containing germanium compounds such as germanium phosphate and germanium phosphite, and germanium acetate. Of these, germanium dioxide is preferable.

Further, when the carboxyl terminal group of the polyester film of the present invention is 45 equivalents / ton or less, it is preferable in terms of impact resistance and taste characteristics of the film. In particular, it is preferable to set the carboxyl terminal group to 40 equivalents / ton or less from the viewpoint of film recoverability and impact resistance.

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 range, the taste characteristics are inferior, 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 where an isophthalic acid component is copolymerized with polyethylene terephthalate and germanium dioxide is added as a germanium compound will be described. The terephthalic acid component, isophthalic acid component and ethylene glycol are transesterified or esterified, 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 is contained. A polymer is obtained. 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.

The polyester of the present invention contains 0.001 to 10 inorganic particles and / or organic particles having an average particle diameter of 0.01 to 8 μm in order to improve the handling property of the film and the processability of the metal can. It is preferable that the content of inorganic particles and / or organic particles having an average particle diameter of 0.1 to 5 μm is 0.005 to 3% by weight. Inorganic particles and / or organic particles include, for example, wet and dry silica,
Inorganic particles such as colloidal silica, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin and clay, and styrene, silicon
Examples thereof include organic particles and the like, which include silane, 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.

Further, in producing the polyester film of the present invention, additives such as an antioxidant, a plasticizer, an antistatic agent, a weathering agent and a terminal blocking agent can be appropriately used if necessary. 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 polyester film of the present invention may be an unstretched sheet or a uniaxially or biaxially stretched film.

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

Further, the polyester film in the present invention may be a laminated film composed of the same kind or two or more kinds of polyesters, and particularly has a melting point of 150 to 2
A laminated film having a configuration in which polyester A having a temperature of 30 ° C. and polyester B having a melting point of 220 ° C. to 250 ° C. are laminated and polyester A is laminated on a metal plate is preferable for improving adhesiveness and impact resistance. In any case, when the polyester film for metal plate lamination of the present invention is a laminated film, it is necessary to have at least one melting point peak determined by the method described below within the range of 150 to 250 ° C. The composition, catalyst, amount of diethylene glycol, and amount of carboxyl end groups in each layer may be different. When the edge of the film is collected, it is preferable to collect it in the polyester A layer from the viewpoint of taste characteristics.

Further, as a laminated film, the ratio of the thickness of polyester A to the thickness of polyester B is 20: 1.
It is preferably from 1: 1 (A: B) in terms of taste characteristics and impact resistance, and particularly preferably from 15: 1 to 4: 1 (A: B) in terms of impact resistance.

The polyester film (including a single-layer film and a laminated film) of the present invention may be laminated with a metal plate by itself, but may be laminated as a composite film by laminating other layers. May be.

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 present invention is not limited thereto.

Isophthalic acid as polyester A 17.
5 mol% copolymerized polyethylene terephthalate (germanium element amount 40 ppm, [η] = 0.85, diethylene glycol 0.92 wt%, melting point 213 ° C., acetaldehyde amount 12 ppm, carboxyl terminal group 21 equivalent / ton), isophthalic acid as polyester B 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
0ppm, carboxyl end group 20 equivalents / ton) twin screw vent type separate extruder (extruder temperature is melting point + 25 ° C)
(1) is melted, and after that, two layers are laminated by a feed block, discharged from an ordinary die and cooled and solidified by a cooling drum to obtain a cast film. The two-layer laminated film thus obtained is subjected to heat aging or surface activation treatment if necessary and wound up. This heat treatment and surface activation treatment are effective steps for preventing the gas dissolved in the film, for example, a gas such as tetrahydrofuran, from being scattered or from selectively adsorbing the perfume of the contents. As the method, for example, the volatile component is reduced to 5 μg / g or less and the adsorbed amount of d-limonene is 20 μg /
It is possible to set g.

The polyester cast film may be biaxially stretched simultaneously or sequentially. 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 width direction of the film can be arbitrarily set according to the degree of orientation, strength, elastic modulus, etc. of the target film, but is preferably 2.5 to 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 as long as it is in the range of the glass transition temperature of the polyester or more and the crystallization temperature or less, but it is usually 80 to 150.
C is preferred. Further, the film can be heat-treated after the biaxial stretching. This heat treatment can be performed by any conventionally known method such as heating in an oven or on a heated roll. The heat treatment temperature can be any temperature above the crystallization temperature of the polyester and below the softening point, but it is preferably 120 to 240 ° 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
A hydrated chromium oxide of 150 mg / m ² 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 plate laminating film of the present invention comprises
It 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 as the colorant, white type, red type, etc. are preferably used, and titanium oxide, zinc white, lithophone,
5 to 50 colorants selected from inorganic or organic pigments
It is desirable to add it 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.

[0031]

The present invention will be described in detail below with reference to examples. The characteristics of the polyester film were measured and evaluated by the following methods.

(1) Content of diethylene glycol component in polyester It was measured by NMR (13 C-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 of polyester Dissolve the polyester in orthochlorophenol and prepare 25
It was measured at ° C.

(4) Melting Point of Polyester A polyester chip was crystallized, and it was heated at 10 ° C. by a differential scanning calorimeter (DSC-2 type manufactured by Perkin Elmer Co.).
It was measured at a temperature rising rate of min.

(5) Content of Acetaldehyde in Polyester or Film 2 g of fine powder of polyester film was sampled and put in a pressure resistant container 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) at 90 to 100 ° C. for 20 minutes, and potentiometric titration was carried out with an alkali.

(7) Content of Oligomers 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.

(8) Adhesiveness Between the metal roll heated to 180 to 230 ° C. and the silicone rubber roll, the polyester film surface of the present invention and Sn
The plate was joined with a plated tin plate, pressure-bonded at a pressure of 20 kg / cm, and cooled in air after bonding. The adhesive strength of the laminate was determined by a peel test at an angle of 180 °,
Those having an adhesive strength of 250 g / cm or more were accepted.

(9) Formability 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 a press molding machine (manufactured by Semba Iron Works, VAS-33P) is used.
Cold forming at a pressure of 100 kg / cm ^{2 with} a mold and a drawing ratio (h / h) of 100 mm in diameter D and 130 mm in depth h.
D) A cup of 1.3 was obtained. Put 1% saline in this cup, heat the whole to 80 ° C and let stand for 24 hours.
The formability was judged based on the condition of rust generated in the can.

Class A: No rust was generated. Class B: Rusts of 1 mm or less occur within 3 pieces. Class C: A lot of rust has occurred.

(10) Impact resistance After the can making in the above (9), heat treatment was performed at 200 ° C. for 10 minutes, and impact was applied to each of 5 points by punches from the side surface of the can and the outer surface of the bottom of the can in the same manner as in (9). After leaving it in the heated saline solution for 24 hours, observe the formation of rust on the part impacted by the punch, (9)
The same evaluation as was done.

(11) Taste characteristics A polyester film cut into a size of 15 cm × 15 cm was added to an aroma solution (20 ppm aqueous solution of d-limonene) to give 5 parts.
The film was soaked for a day, and then the film was heated at 80 ° C. for 30 minutes in a nitrogen stream to remove the components, and the adsorbed amount of d-limonene per 1 g of the film was quantified by gas chromatography to evaluate the taste characteristics of the film.

Further, an aqueous fragrance 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.

Grade A: No change in odor was observed. Class B: Almost no change in odor. Class C: Change in odor is seen.

Example 1 As Polyester A, 17.5 mol% of isophthalic acid copolymerized polyethylene terephthalate (amount of germanium of 4
0 ppm, [η] = 0.85, diethylene glycol 0.92% by weight, melting point 213 ° C., acetaldehyde amount 8
ppm, carboxyl end group 21 equivalent / ton), as polyester B 5 mol% of isophthalic acid copolymerized polyethylene terephthalate (germanium element amount 42 ppm, 0.2% by weight of silicon oxide particles having an average particle diameter of 4 μm, [η] =
0.90, diethylene glycol 0.89% by weight, melting point 240 ° C., acetaldehyde amount 6 ppm, carboxyl end group 20 equivalents / ton, separate twin-screw vent type extruders (extruder temperature is set to melting point + 25 ° C., average) It is supplied for a residence time of about 20 minutes) and melted, after which two layers (polyester A layer / polyester B layer = 9 /
After being laminated on 1) and discharged from an ordinary die, it was cooled and solidified by a cooling drum to obtain a cast film of 30 μm. The obtained film was 0.91% by weight of diethylene glycol, 12 ppm of acetaldehyde, [η] = 0.76,
The carboxyl end group was 28 equivalents / ton and the oligomer was 0.6% by weight.

The physical properties of the two-layer laminated cast film thus obtained are shown in Table 1. The layer A of the obtained film was laminated on a metal plate. As can be seen from the table, the adhesiveness, moldability, impact resistance and taste characteristics were good.

Example 2 As polyester, 132 parts by weight of dimethyl terephthalate, 18 parts by weight of dimethyl isophthalate (12 mol% based on the total acid component of polyester), 96 parts by weight of ethylene glycol, and 0.05 part by weight of manganese acetate were used. The mixture was placed in a flask equipped with a rectification column and a distillation condenser and heated to 150 to 235 ° C. with stirring to distill methanol to carry out a transesterification reaction. After about the theoretical amount of methanol was distilled, 0.03 part by weight of trimethyl phosphate and 0.04 part by weight of germanium dioxide were added, and the reaction product was transferred to a reactor equipped with a distillation condenser. Then, while stirring, the pressure inside the reactor was gradually reduced by 0.5 mmHg and the temperature was raised to 290 ° C. to carry out a polycondensation reaction to obtain a copolyester having an intrinsic viscosity [η] of 0.61. Then, the copolyester was subjected to a solid phase polymerization reaction at 190 ° C. under N ₂ flow according to a conventional method to obtain an intrinsic viscosity [η] of 0.68, a melting point of 228 ° C., a diethylene glycol component amount of 0.90% by weight, and a germanium element amount. A copolyester having a content of 51 ppm, an acetaldehyde content of 3 ppm and an oligomer content of 0.55% was obtained.

This copolymerized polyester chip was melt extruded on a casting drum using an extruder under the conditions of a melting temperature of 270 ° C. and a residence time of 20 minutes to obtain an unstretched film. This unstretched film was stretched in the longitudinal direction at 90 ° C.
The film was stretched 5 times and then 3.5 times in the width direction at 105 ° C.
Further, this biaxially stretched film was heat-treated at 190 ° C. under a constant length to obtain a polyester film having a thickness of 25 μm. The obtained film had 0.89% by weight of diethylene glycol, 10 ppm of acetaldehyde, [η] = 0.65,
Carboxyl end group 41 equivalent / ton, oligomer 0.72
It became weight%.

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

[0051]

[Table 1] Examples 3 to 6 Polyester cast films were obtained in the same manner as in Example 1, except that the amount of copolymerization components, the type of catalyst, the amount added, the polymerization conditions, the film lamination ratio, etc. were changed.

The results are shown in Tables 2 and 3.

As a result, the polyester film of the present invention had excellent adhesiveness, moldability, impact resistance and taste characteristics. However, in Example 6, since [η] was low and the film was an unstretched film, impact resistance and taste characteristics were slightly lowered.

[0054]

[Table 2]

[Table 3] Comparative Example 1 Copolyester of 1.5% by weight of diethylene glycol, 35 ppm of acetaldehyde, [η] = 0.6
A copolyester and a film were obtained in the same manner as in Example 2 except that the polyester of No. 8 was polymerized and the extrusion temperature was changed to 285 ° C. The results are shown in Table 4.

As a result, this polyester film is
Since the content of diethylene glycol and acetaldehyde was large, the impact resistance and taste characteristics of the film were inferior.

Comparative Example 2 Polyester was used as polyethylene terephthalate (intrinsic viscosity [η] 0.68, melting point 257 ° C., diethylene glycol component amount 1.2% by weight, germanium element amount 60 ppm,
A copolyester and a film were obtained in the same manner as in Example 1, except that the acetaldehyde content was 35 ppm and the oligomer content was 0.65%. Table 4 shows the evaluation results of the characteristics of the copolyester and the film. As a result, this polyester film has a melting point, DE
The amount of G and the amount of acetaldehyde are outside the scope of the present invention, and the adhesiveness,
It was inferior in moldability, impact resistance and taste characteristics.

[0057]

[Table 4]

[0058]

Industrial Applicability The polyester film for laminating metal plates 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 front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display area B29K 67:00 B29L 9:00 C08L 67:00

Claims (5)

[Claims] 1. A polyester film for laminating metal plates, which has a melting point of 150 to 250 ° C., contains 0.01 to 1% by weight of a diethylene glycol component, and has an acetaldehyde content of 50 ppm or less. 2. A laminated polyester film obtained by laminating polyester A having a melting point of 150 to 230 ° C. and polyester B having a melting point of 220 ° C. to 250 ° C., containing 0.01 to 1% by weight of a diethylene glycol component. A polyester film for laminating metal plates, which has an acetaldehyde content of 50 ppm or less. 3. The polyester film for laminating metal plates according to claim 1, which has an intrinsic viscosity [η] of 0.7 or more. 4. The polyester film for laminating a metal plate according to claim 1, which contains germanium element in an amount of 1 to 500 ppm. 5. The polyester film for laminating metal plates according to claim 1, wherein the carboxyl terminal group is 45 equivalents / ton or less.