JPH11254624A - Polyester film for metal plate laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a metal plate laminate suitable for a metal can which can be subjected to a severe forming process when a can or the like is formed and in which improved abrasion resistances, taste properties, and particularly excellent bond properties after retorting can be provided. SOLUTION: In the biaxially oriented laminated polyester film comprising two or more layers, the difference (TmA-TmB) between the fusion peak point TmA of a polyester constituting a nonmetallic plate side layer and the fusion peak point TmB of a polyester constituting a metallic plate side layer is in the range of 0.5-5 deg.C, and the ratio (tA/tB) between the thickness tA of the nonmetallic plate side layer and the thickness tB of the metallic plate side layer is 3 or more and the carboxyl end group weight of a polyester constituting the metallic plate side layer is 35 equivalent weight/ton or more.

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 comprising a biaxially stretched film suitable for a container. More specifically, it has excellent laminating properties to metal plates, abrasion resistance during molding, adhesiveness after retorting, and long-term stability of the upper part of a molding can. The present invention relates to a polyester film for metal plate lamination that can exhibit excellent adhesion even afterwards.

[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 a thermosetting resin requires a long time to dry the paint, and thus has disadvantageous problems such as a decrease in productivity and environmental pollution due to a large amount of an organic solvent.

As a method of solving these problems, there is a method of laminating a film on a steel plate, an aluminum plate, or a metal plate obtained by performing various surface treatments such as plating on the metal plate as a material of a metal can. When a metal can is manufactured by drawing or ironing a laminated metal plate of a film, the film is required to have the following characteristics. (1) It has excellent laminating properties on a metal plate. (2) Excellent adhesion to a metal plate. (3) It has excellent moldability and does not cause defects such as pinholes after molding. (4) The polyester film does not peel, crack, or pinhole due to impact on the metal can. (5) The scent component of the contents of the can adsorbs to the film,
The flavor of the contents is not degraded by the eluate from the film (hereinafter referred to as taste characteristics).

Many proposals have been made to satisfy these requirements. For example, Japanese Patent Application Laid-Open No. 2-57339 discloses a copolymerized polyester film having specific crystallinity. However, in recent years, with the increase in can-making speed, the ratio of can-making from a laminated metal plate has been increasing, and further improvement in lamination properties, moldability, and adhesion between a film and a metal plate has been desired. I have. In addition, due to the increase in the molding ratio, the adhesion between the film and the metal plate, particularly after retorting after can molding, has become more important,
Long-term stability after retort is also strictly required.
The above proposals have not been able to comprehensively satisfy these required characteristics.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to satisfy recent more stringent required characteristics together with excellent abrasion resistance and taste characteristics, especially after retorting. Another object of the present invention is to provide a polyester film for metal plate lamination that can exhibit excellent adhesiveness and is suitable for use in a metal can.

[0006]

In order to solve the above-mentioned problems, a polyester film for laminating a metal plate according to the present invention is a biaxially stretched laminated polyester film having two or more layers, wherein a non-metal plate side layer is formed. (TmA-TmB) between the melting peak temperature TmA of the polyester to be formed and the melting peak temperature TmB of the polyester constituting the metal plate side layer is in the range of 0.5 to 5 ° C., and the thickness t _{A of the} nonmetallic plate side layer. the ratio between the thickness t _B of the metal plate side layer (t _a / t _B) is 3 or more, and a carboxyl end group amount of the polyester constituting the metal plate side layer is 35 equivalents / ton or more and It consists of the features.

That is, in the present invention, the difference in the melting peak temperature between the non-metal plate side layer and the metal plate side layer of the biaxially stretched laminated polyester film is controlled within a specific small range,
In addition, by setting the thickness ratio (t _A / t _B ) to 3 or more and setting the carboxyl terminal group amount of the polyester constituting the metal plate side layer to 35 equivalents / ton or more, especially after lamination with the metal plate. It is intended to maintain excellent adhesiveness, in particular, to exhibit excellent adhesiveness after retorting, and to obtain good long-term stability after retorting even with a can having a high molding ratio. Further, the thickness ratio (t _A / t _B ) is increased so that the moldability at the neck portion (can neck portion) and the long-term stability of the portion can be obtained particularly at the time of can molding.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with preferred embodiments. The polyester in the present invention is a general term for a high molecular weight substance constituted by an ester bond, and examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, and diphenoxyethane. Aromatic dicarboxylic acids such as dicarboxylic 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; cyclohexyne dicarboxylic acid And oxycarboxylic acids such as p-oxybenzoic acid. On the other hand, examples of the glycol component include aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; and aromatic compounds such as bisphenol A and bisphenol S. Glycol, diethylene glycol and the like can be used. In addition, two or more of these dicarboxylic acid components and glycol components may be used in combination.

The polyester of the present invention preferably has an ethylene terephthalate or ethylene naphthalate unit content of at least 80 mol%, more preferably at least 85 mol%, as a polyester which is a main component, from the viewpoint of imparting heat resistance. % Or more, more preferably 90 mol% or more.

In the present invention, two or more kinds of the above polymers may be blended and used. 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 melting peak temperature of the polyester of the present invention is from 215 to 215 from the viewpoint of improving moldability and adhesiveness after retort.
It is preferably in the range of 265 ° C., more preferably 220 to 260 ° C., even more preferably 246 to 2 ° C.
60 ° C. In particular, it is preferable that the main melting peak temperature of the film (the melting peak temperature that appears as first RUN in the measurement of the melting peak temperature) is 246 ° C. or more. The content of the ethylene terephthalate unit is preferably at least 87 mol%, more preferably at least 90 mol%.
If the melting peak temperature of the polyester is less than 215 ° C., the heat resistance decreases, and when the retort or the contents after can molding are filled and stored at a high temperature, outflow of the film contents, softening of the film itself, and thermal deterioration occur. Such problems occur, which is not preferable. On the other hand, if the melting peak exceeds 265 ° C., the moldability deteriorates, which is not preferable.

In the present invention, it is necessary to convert polyester into a biaxially stretched film from the viewpoint of heat resistance and thermal dimensional stability. The method of biaxial stretching may be either simultaneous biaxial stretching or sequential biaxial stretching.

In the present invention, in order to exhibit excellent laminating properties to a metal plate and excellent adhesiveness after retorting, the melting peak temperature TmA of polyester constituting the non-metal plate side layer and the metal plate side layer are determined. The difference (TmA-TmB) from the melting peak temperature TmB of the constituting polyester is 0.5.
To 5 ° C., preferably 1 to 5.
3 ° C. By controlling to such a specific small melting peak temperature difference, even though it is a laminated film, it is possible to suppress the occurrence of undesired distortions and the like due to differences in the properties of each layer during heat lamination, and to provide an excellent laminate to a metal plate. Characteristics, that is, excellent adhesion to the metal plate can be obtained. As a result of excellent adhesion, excellent adhesion can be exhibited even after retort. As a result, the laminated film can exhibit excellent durability and abrasion resistance.

Further, in the present invention, ironing of cans and the like,
Alternatively, in order to exhibit excellent followability during drawing, and particularly to exhibit excellent durability and stability over a long period of time at the neck of a can or the like, the thickness t of the non-metallic plate side layer is
The ratio of the thickness t _B of _A and the metal plate side layer (t _A / t _B) is 3 or more. Preferably it is 3 or more and 10 or less, more preferably 4 or more and 8 or less. That is, by increasing the thickness of the non-metal plate side layer to a specific multiple or more compared to the thickness of the metal plate side layer, the molding stress applied to the non-metal plate side layer during can molding can be smoothly absorbed, and And make sure that no large distortion or residual stress remains after molding.
Long-term stability of the neck and other parts is ensured.

In the present invention, in order to improve the adhesion between the film and the metal plate, the polyester constituting the metal plate side layer must have a carboxyl terminal group content of 35 equivalents / ton or more, and is preferably. It is in the range of 35-50 equivalents / ton, more preferably in the range of 37-47 equivalents / ton.

Further, in the present invention, the amount of carboxyl terminal groups of the polyester constituting the non-metal plate side layer is less than 35 equivalents / ton from the viewpoint of suppressing the amount of eluate from the film and improving the taste characteristics. And particularly preferably less than 30 equivalents / ton.

Further, in the present invention, in order to further improve the abrasion resistance and abrasion resistance of the non-metallic plate side layer at the time of forming a can, and to facilitate the molding, the non-metallic plate side layer is formed. It is preferable that the polyester contains particles having a shape degree (ratio of the maximum length D to the minimum length d of the particles) of 1.1 or more in the film defined by the following formula (1). Shape degree = D / d (1)

As described above, the film layer on the non-metallic plate side is required to have abrasion resistance and abrasion resistance because stress is particularly applied to the surface thereof during drawing, such as when making cans, etc. By containing particles having a relatively large particle size in this layer, it is possible to improve abrasion resistance and abrasion resistance while giving the surface good sliding properties. By giving good slipperiness, occurrence of troubles during the manufacturing process of the film itself can be suppressed, and the manufacturing is facilitated.

The shape of the particles in the present invention is:
It is expressed by the ratio of the maximum length to the minimum length of the particles observed in the film as defined by the equation (1), and is determined by the method defined later. Here, the maximum length of a particle is defined as a single particle that is formed at an interval smaller than an individual particle or a primary particle diameter, and is a distance between parallel lines at the longest interval in contact with its contour, and the minimum length is It is the distance between the shortest-spaced parallel lines that touch the contour.

From the viewpoint of further improving the abrasion resistance during molding, the degree of aggregation of the particles contained in the polyester of the non-metallic plate side layer is preferably from 5 to 100, more preferably from 8 to 80. It is.

In the present invention, it is preferable that the amount of free aromatic dicarboxylic acid monomethyl ester contained in the film of the metal plate side layer is more than 2 ppm from the viewpoint of adhesiveness. More preferably, it is 3 ppm or more and 50 ppm or less. The method for containing the dicarboxylic acid monomethyl ester in such an amount or more is not particularly limited, and examples thereof include a method for obtaining a polyester by transesterification with a glycol component using a dicarboxylic acid ester as a dicarboxylic acid component when producing a polyester. Can be.

By increasing the amount of free aromatic dicarboxylic acid monomethyl ester contained in the film of the metal plate side layer to more than 2 ppm, not only the lamination property with the metal plate but also the adhesiveness with the metal plate after retorting are improved. Can be improved. In addition, the film layer of such a metal plate side layer made by the above-described manufacturing method can have a high affinity for the particles, and has a small particle content and a high abrasion resistance. And the laminating property with the metal plate and the adhesiveness after retort can be further improved.

On the other hand, the free aromatic dicarboxylic acid monomethyl ester contained in the non-metal plate side layer film is 2
It is preferably set to ppm or less. By setting the content to 2 ppm or less, low dissolution can be achieved when the beverage is filled as a metal can, and excellent taste characteristics can be obtained. The method for reducing the amount of dicarboxylic acid monomethyl ester to the amount or less is not particularly limited, and examples thereof include a method of obtaining a polyester by an esterification reaction between a dicarboxylic acid component and a glycol component when producing a polyester. Can be. Further, a naphthalenedicarboxylic acid component is preferable as the copolymerization component.

Further, it is preferable to further improve the adhesiveness by subjecting the film surface to a surface treatment such as a corona discharge treatment from the viewpoint of improving the characteristics. At this time, the E value is 5 to 50, preferably 10 to 45. Here, the E value is the intensity of the corona discharge treatment, and the applied voltage (V
p), applied current (Ip), processing speed (S), processing width (W
t) and is expressed as E = Vp × Ip / S × Wt.

The thickness of the biaxially stretched laminated film of the present invention is
In terms of moldability after lamination to metal, coatability to metal, impact resistance, taste characteristics, it is preferably 3 to 50 μm, more preferably 5 to 35 μm, and particularly preferably 10 to 30 μm. .

The biaxially stretched film of the present invention preferably has a plane orientation coefficient of from 0.08 to 0.130, more preferably from 0.100 to 0.1, mainly from the viewpoint of laminating properties and moldability. 120.

In the present invention, in order to improve the adhesion between the film and the metal plate, and particularly to reduce the influence of peeling due to the shrinkage stress of the film during retort, the heat shrinkage stress in the longitudinal direction of the film at 125 ° C. 0.1-1.0MPa
And more preferably 0.2 to 0.8
MPa.

In the present invention, the coefficient of linear thermal expansion in the longitudinal direction of the film at 125 ° C. is −140 × 10 ⁻⁶ to −5 × 10 ⁻⁶ K ⁻¹ , mainly from the viewpoint of improving the adhesion between the film and the metal plate. And more preferably −130 × 10 ^{−6.
−−40} × 10 ⁻⁶ K ⁻¹ . When the coefficient of linear thermal expansion is out of this range, residual stress is generated due to the difference in thermal expansion behavior with the metal plate during lamination, so that cracks and peeling from the metal plate occur in the film during subsequent molding or retort There is.

In the present invention, in order to improve the adhesion between the film and the metal plate, particularly to increase the adhesion area and the thickness of the polymer portion at the adhesion interface between the film and the metal plate, at least 1 μm from one surface. The ratio of the particle concentration R ₁ to the particle concentration R ₂ at 0.1 μm from the surface, R ₁ /
R ₂ is preferably from ₂ to 200, more preferably from 3 to 150.

In the present invention, in order to further improve the adhesiveness and taste characteristics, the intrinsic viscosity of the polyester is 0.6 dl /
g or more, more preferably 0.62 dl / g or more, and particularly preferably 0.65 or more. When the intrinsic viscosity is less than 0.6 dl / g, the taste characteristics are deteriorated due to elution of the oligomer and the like, which is not preferable.

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. Preferably, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at any stage before the production of the polyester is usually completed. As such a method, for example, when a germanium compound is taken as an example, a method of adding a germanium compound powder as it is, or as described in JP-B-54-22234, a glycol component which is a starting material of a polyester, A method in which a germanium compound is dissolved and added therein can be used. 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 glycoloxide, germanium phenolate, germanium β-naphtholate, etc. And phosphorus-containing germanium compounds such as germanium phenoxide compound, germanium phosphate and germanium phosphite, and germanium acetate. Among them, germanium dioxide is preferable. Examples of the antimony compound include, but are not particularly limited to, antimony oxides such as antimony trioxide, and antimony acetate. The titanium compound is not particularly limited, but an alkyl titanate compound such as tetraethyl titanate and tetrabutyl titanate is preferably used.

For example, a case where germanium dioxide is added as a germanium compound when producing polyethylene terephthalate will be described. The terephthalic acid component and ethylene glycol are subjected to a transesterification or esterification reaction, and then germanium dioxide and a phosphorus compound are added.Then, the polycondensation reaction is continued under a high temperature and a reduced pressure until a constant diethylene glycol content is obtained, and a germanium element-containing polymer is obtained. obtain. Further, preferably, the obtained polymer is subjected to a solid-phase polymerization reaction under reduced pressure or an inert gas atmosphere at a temperature equal to or lower than its melting point to reduce the content of acetoadheride to obtain a predetermined intrinsic viscosity and a carboxyl end group. And the like.

The polyester in the present invention preferably has a diethylene glycol content of 0.01 to 3.5% by weight, more preferably 0.01 to 2.5% by weight, and particularly preferably 0.01 to 2.0% by weight. Is desirable in order to maintain excellent taste characteristics even when subjected to many heat histories such as heat treatment in a can making process and retort treatment after can making. This is considered to improve oxidative decomposition resistance at 200 ° C. or higher.
You may add 1 weight%. Further, diethylene glycol may be added during the production of the polymer as long as the properties are not impaired.

In order to improve the taste characteristics, the content of acetaldehyde in the film is preferably 25 ppm.
Below, more preferably 20 ppm or less is desirable. When the content of acetaldehyde exceeds 25 ppm, the taste characteristics are inferior. When the content of acetaldehyde in the film is 25
pm or less is not particularly limited,
For example, in order to remove acetaldehyde generated by thermal decomposition when producing a polyester by a polycondensation reaction or the like, a method of heat-treating the polyester under reduced pressure or an inert gas atmosphere at a temperature equal to or lower than the melting point of the polyester,
Preferably, a method of solid-state polymerization of polyester at a temperature of 155 ° C. or more and a melting point or less under reduced pressure or an inert gas atmosphere, a method of melt-extrusion using a vented extruder, and an extrusion temperature when melt-extruding a polymer. Extruded within the melting point of the high melting polymer side + 30 ° C., preferably within the melting point + 25 ° C., for a short time, preferably within an average residence time of 1 hour.

The method for producing the biaxially stretched laminated film in the present invention is not particularly limited. For example, after drying each polyester as necessary, it is supplied to each of the known melt extruders, and for example, at a polymer stage, a predetermined Laminate,
The sheet is extruded into a sheet form from a slit-shaped die, brought into close contact with a casting drum by a method such as electrostatic application, and cooled and solidified to obtain an unstretched sheet. As the stretching method, simultaneous biaxial,
Although any of biaxial stretching may be performed successively, the unstretched sheet is stretched in the longitudinal direction and width direction of the film and heat-treated to obtain a film having a desired degree of plane orientation. Preferably, a tenter method is preferable in terms of film quality.After stretching in the longitudinal direction, a sequential biaxial stretching method in which the film is stretched in the width direction, a simultaneous biaxial stretching method in which the film is stretched almost simultaneously in the longitudinal direction and the width direction. Is desirable. The stretching ratio is 1.6 to 4.2 times, preferably 1.7 to 4.0 times in each direction. 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 speed is 1000
% / Minute to 200,000% / minute, and the stretching temperature can be any temperature as long as it is equal to or higher than the glass transition temperature of the polyester and equal to or lower than the glass transition temperature + 100 ° C., but is usually preferably 80 to 170 ° C. . After the biaxial stretching, the film is subjected to a heat treatment.
It can be carried out by any method known in the art, such as on a heated roll or on a heated roll. Heat treatment temperature is 120 ° C or higher and 24
Any temperature of 5 ° C. or less can be used, but preferably 120 to 240 ° 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. Furthermore, re-stretching may be performed once or more in each direction, and then heat treatment may be performed.

As the additive particles in the present invention, particles arbitrarily selected from known internal particles having an average particle diameter of 0.01 to 10 μm and external particles such as inorganic particles and / or organic particles can be contained. . In particular, it is preferable that the film used for the inner surface of the can contain the specific amount of particles having an average particle diameter of 0.1 to 5 μm as described above.
It is not preferable to use particles having an average particle diameter of more than 10 μm because defects in the film are likely to occur. Examples of the particles include inorganic particles such as wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, and clay, and styrene, silicone,
Organic particles containing acrylic acid or the like as a constituent component can be exemplified. 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 internal particles, inorganic particles and / or organic particles may be used in combination as long as the properties are not impaired.

In the present invention, the degree of shape in the film is 1.
Examples of the one or more particles include dry silica, wet silica, and the like. In particular, aggregated inorganic particles are preferable, but not limited thereto.

Further, when used on the inner surface of the can, the center line average roughness Ra is preferably 0.005 to 0.07 μm,
More preferably, it is 0.008 to 0.05 μm. Further, when the ratio Rt / Ra to the maximum roughness Rt is 4 to 50, preferably 6 to 40, high-speed can-making properties are improved. Also,
In particular, the center line average roughness Ra on the beverage side is preferably 0.0
02 to 0.04 μm, more preferably 0.003 to
A thickness of 0.03 μm is preferable because taste characteristics are improved.

Various coatings may be applied on the film of the present invention.
There is no particular limitation as long as the effects of the present invention are not impaired.

The metal plate in the present invention is not particularly limited, but 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 adhesion and corrosion resistance on the surface thereof, for example, chromic acid treatment, phosphoric acid treatment, chromic acid /
A chemical conversion coating layer represented by phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, chromium chromate treatment, or the like may be provided. In particular, as chromium in terms of metal chromium 6.
5 to 150 mg / m ² chromium hydrated oxide is preferred,
In addition, a spreadable metal plating layer, such as nickel, tin,
Zinc, aluminum, gunmetal, brass and the like 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 biaxially stretched laminated polyester film for a container of the present invention can be suitably used for coating the inner surface of a two-piece metal can manufactured by drawing or ironing after being laminated on a metal plate or the like. Further, it can be preferably used for covering a lid portion of a two-piece can or a body, a lid, and a bottom of a three-piece can because it has good metal adhesion and moldability.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. In addition, each characteristic was measured and evaluated by the following methods. (1) Intrinsic viscosity (IV) of polyester, carboxyl terminal group Measured according to a conventional method.

(2) Melting Peak Temperature of Polyester The polyester was crystallized and measured at a heating rate of 10 ° C./min with a differential scanning calorimeter (DSC2, manufactured by Perkin-Elmer). did.

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

(4) Shape of Particles A cross section in the longitudinal direction of the film was observed with a transmission electron microscope, and individual particles or ones in which aggregates were formed at intervals smaller than the primary particle diameter were determined. Two particles were considered, the maximum length of each particle present in the film was determined as the minimum length, and the ratio was calculated. Further, values were obtained for at least 100 or more particles, and the arithmetic mean thereof was defined as the shape. Here, the maximum length of a particle is defined as a single particle that is formed at an interval smaller than an individual particle or a primary particle diameter, and is a distance between parallel lines at the longest interval in contact with its contour, and the minimum length is It is the distance between the shortest-spaced parallel lines that touch the contour.

(5) Average Particle Diameter The thermoplastic resin is removed from the surface of the film by plasma low-temperature ashing to expose the particles. Processing conditions are selected such that the thermoplastic resin is ashed but the particles are not damaged. This is observed with a scanning electron microscope (SEM), and the image of the particles is processed with an image analyzer. The following numerical processing is performed on the number of particles of 5,000 or more by changing the observation position, and the number average diameter D obtained thereby is defined as the average particle diameter. D = ΣD _i / N Here, Di is the equivalent circle diameter of the particles, and N is the number of particles. For the internal particles, the section of the section of the film may be observed by a transmission microscope.

(6) Monomethyl ester of dicarboxylic acid (MMT) content 500 mg is scraped off from the film and dissolved in hexafluoroisopropanol. Methanol was added thereto, and the filtrate was filtered and subjected to liquid chromatography to determine the amount of dicarboxylic acid monomethyl ester in the film.

(7) Laminability A tin-free steel metal plate having a thickness of 0.2 mm
C. (at a temperature in the range of the melting point of the film to the melting point + 30 ° C., the average value of the plane orientation coefficient fn of the non-metal plate side surface is 0.0%).
2 to 0.03), the film is stuck at 100 m / min, quenched, and the plane orientation coefficient of the film after being laminated on a metal plate is measured. This is 10
For each sample, the lamination property was evaluated according to the following criteria based on the difference between the maximum value and the minimum value of the plane orientation coefficient therein. Class A: less than 0.005 Class A: 0.005 or more and less than 0.01 Class B: 0.01 or more and less than 0.02 Class C: 0.02 or more

(8) Adhesion (Adhesive force after retort) The laminated steel sheet obtained in the section (7) was cut into a width of 30 mm, a part of the steel sheet was cut while leaving a film, and 100 g of the cut portion was cut. The weight was suspended, the temperature was rapidly raised to 125 ° C., and a retort treatment was performed for 25 minutes. The evaluation was performed based on the peel length of the film from the steel sheet after the retort. Class A: less than 5 mm Class A: less than 10 mm 5 mm or more Class B: less than 15 mm 10 mm or more Class C: 15 mm or more

(9) Abrasion resistance The above laminated steel sheet was formed into an 8000 m coil by an ironing machine and a drawing machine (forming ratio (maximum thickness / minimum thickness) =
2.0, molded in moldable temperature range), can (diameter 6c)
m, height 12 cm). At this time, the abrasion resistance of the film was evaluated by measuring the shaving amount of the film attached to the tool. Class A: Less than 1 mg Class B: 1-3 mg Class C: More than 3 mg

(10) Taste characteristics After the above can was subjected to pressurized steam treatment at 125 ° C. × 25 minutes,
After filling with water and sealing at 40 ° C., it was left for one month, then opened and cooled to 10 ° C., and the turbidity was evaluated according to the following criteria. Special grade A: No turbidity is observed. Class A: Almost no turbidity is observed. Class B: Some turbidity is observed. Class C: Turbidity is observed on the entire surface. Class D: The surface is quite cloudy.

Example 1 Isophthalic acid copolymerized polyethylene terephthalate containing 0.1% by weight of monodispersed spherical silica having an average particle diameter of 1.0 μm as polyester B constituting a metal plate side layer (intrinsic viscosity: 0.69 dl / g) , Melting point: 224 ° C., carboxyl terminal amount: 39 equivalents / ton), and a secondary particle diameter of 0.4 μm (primary particle diameter: 4 μm) as polyester A constituting the non-steel side layer.
Isophthalic acid copolymerized polyethylene terephthalate containing 0.05% by weight of agglomerated dry silica particles (0 nm, average particle diameter 0.4 μm) (intrinsic viscosity 0.69 dl / g, melting point 2)
26 ° C, carboxyl terminal amount 24 equivalents / ton)
After vacuum drying at 80 ° C. for 3 hours, the mixture was supplied to separate extruders, laminated with a pinol in a ratio of B / A = 1: 4, discharged from a die, and then applied with a mirror cooling drum while applying static electricity (6.7 kv). After cooling and solidification, an unstretched film was obtained. This unstretched film is stretched 3.0 times in the longitudinal direction at a temperature of 98 ° C., and a preheating temperature of 95 ° C.
(3 seconds), after stretching 3.05 times in the width direction at a stretching temperature of 110 ° C., relaxing at 180 ° C. for 5% for 5 seconds to obtain a biaxially stretched laminated polyester film having a thickness of 20 μm.
The melting peak temperature difference (TmA-TmB) between the polyester A and the polyester B is 2 ° C., and the thickness t of the non-metallic plate side layer in the obtained biaxially stretched laminated polyester film.
The ratio of the thickness t _B of _A and the metal plate side layer (t _A / t _B) was 4. Further, the shape of the agglomerated dry silica particles in the non-metal plate side layer of the obtained film is 12, the content of free aromatic dicarboxylic acid monomethyl ester in the film of the metal plate side layer is 6 ppm, The content of free aromatic dicarboxylic acid monomethyl ester in the film of the plate side layer was 0.6 ppm. The film properties and can properties were as shown in Table 1, and excellent properties could be obtained.

Example 2 In Example 1, 2,6-naphthalenedicarboxylic acid copolymerized PET was used as the polyester A constituting the non-metal plate side layer.
(Intrinsic viscosity 0.72 dl / g, melting point 226 ° C., carboxyl terminal amount 20 equivalents / ton), and the longitudinal stretching temperature is 108
A biaxially stretched laminated polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1 except that the temperature and the horizontal stretching temperature were changed to 120 ° C. The difference in melting peak temperature (TmA-TmB) between the polyester A and the polyester B is 2 ° C., and the thickness t _A of the non-metal plate side layer and the thickness t _{B of the} metal plate side layer in the obtained biaxially stretched laminated polyester film. And the ratio (t _A / t
_B ) was 5. Further, the shape of the agglomerated dry silica particles in the non-metal plate side layer of the obtained film was 11, the content of free aromatic dicarboxylic acid monomethyl ester in the film of the metal plate side layer was 6 ppm, The free aromatic dicarboxylic acid monomethyl ester content in the film of the plate side layer was 1 ppm. Film properties,
The can properties were as shown in Table 1, and excellent properties could be obtained.

Example 3 Polyester B constituting the metal plate side layer in Example 1
5.5 mol% copolymerized isophthalic acid PET (intrinsic viscosity 0.68 dl / g, melting point 245 ° C., carboxyl terminal amount 36 equivalents / ton), and polyester A constituting the non-metal plate side layer 5 mol% isophthalic acid copolymer Polymerized PET (intrinsic viscosity 0.68 dl / g, melting point 246 ° C., carboxyl terminal amount 29 equivalents / ton), longitudinal stretching temperature was 108 ° C., transverse stretching temperature was 120 ° C., and transverse stretching ratio was 3.0 times. Except for the above, a biaxially stretched laminated polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1. The difference in melting peak temperature (TmA-TmB) between the polyester A and the polyester B is 1 ° C., and the thickness t _A of the non-metal plate side layer and the thickness t _{B of the} metal plate side layer in the obtained biaxially stretched laminated polyester film. (T _A / t _B ) was 6. The shape of the agglomerated dry silica particles in the non-metal plate side layer of the obtained film was 11, the content of free aromatic dicarboxylic acid monomethyl ester in the film of the metal plate side layer was 5 ppm, The content of free aromatic dicarboxylic acid monomethyl ester in the film of the plate side layer was 0 ppm. The film properties and can properties were as shown in Table 1, and excellent properties could be obtained.

Examples 4 to 6 and Comparative Examples 1 and 2 The conditions were changed as shown in Table 1 to obtain a biaxially stretched laminated polyester film having a thickness of 25 μm or 20 μm.
As shown in Table 1, the properties of the obtained film were as shown in Example 4.
6 were excellent, but Comparative Examples 1 and 2 were inferior.

[0056]

[Table 1]

[0057]

According to the present invention, the difference in the melting peak temperature between the non-metal plate side layer and the metal plate side layer of the polyester film for laminating a metal plate comprising a biaxially stretched laminated polyester film within a specific small range. And the thickness ratio (t _A
/ T _B ) is 3 or more and the amount of carboxyl terminal groups of the polyester constituting the metal plate side layer is a specific amount or more, whereby excellent laminating properties, abrasion resistance during can molding, and film after retorting are obtained. And a metal plate can be obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 9:00 C08L 67:02

Claims (5)

[Claims] 1. A difference between a melting peak temperature TmA of a polyester constituting a non-metal plate side layer and a melting peak temperature TmB of a polyester constituting a metal plate side layer, which is a biaxially stretched laminated polyester film having two or more layers. (TmA-Tm
B) is in the range of 0.5 to 5 ° C., and the ratio (t _A / t _B ) of the thickness t _A of the non-metal plate side layer to the thickness t _B of the metal plate side layer is 3
A polyester film for laminating a metal plate, wherein the amount of carboxyl terminal groups of the polyester constituting the metal plate side layer is 35 equivalents / ton or more. 2. The method according to claim 1, wherein the polyester of the non-metallic plate side layer has particles having a shape degree (ratio of a maximum length D to a minimum length d of the particles) of 1.1 or more in a film defined by the following formula (1). The polyester film for laminating a metal plate according to claim 1, which contains the polyester film. Shape degree = D / d (1) 3. The main melting peak temperature of the film is 24.
The polyester film for metal plate lamination according to claim 1 or 2, which is at least 6 ° C. 4. The free aromatic dicarboxylic acid monomethyl ester contained in the metal plate side layer film is 2 ppm.
The polyester film for laminating a metal plate according to any one of claims 1 to 3, wherein the amount of the polyester film is larger than that of the polyester film. 5. The free aromatic dicarboxylic acid monomethyl ester contained in the non-metallic plate side layer film is 2 pp.
The polyester film for laminating a metal plate according to any one of claims 1 to 4, which has a molecular weight of m or less.